Journal of Colloid And Interface Science (v.376, #1)
Cover 1 (OFC).
Tuning properties of silver particle monolayers via controlled adsorption–desorption processes by Magdalena Oćwieja; Zbigniew Adamczyk; Katarzyna Kubiak (1-11).
Display Omitted► Formation of silver particle monolayers of desired coverage in the self-assembly process of particles. ► Controlled adsorption and desorption of silver nanoparticles. ► Efficient method of determining the equilibrium adsorption constant.Using the well-defined silver particle suspension, systematic studies of adsorption kinetics on mica modified by poly(allylamine hydrochloride) (PAH) were carried out. The coverage of adsorbed particles was directly determined by AFM and SEM imaging. The dependence of the coverage on adsorption time, bulk suspension concentration, and ionic strength was systematically studied. It was confirmed that adsorption was diffusion controlled, with the initial rate proportional to the bulk concentration of particles. On the other hand, for long adsorption times, the saturation coverage was attained, which increased systematically with the ionic strength of the particle suspension. The adsorption kinetic runs were adequately reflected for the entire range of times and bulk concentration by the random sequential adsorption (RSA) model. Additionally, particle desorption kinetics from previously formed monolayers were studied. The decrease in the surface coverage of particles as a function of time was measured, which allowed one to determine the equilibrium adsorption constant Ka . The binding energy of silver particles (energy minimum depth) derived form these measurements varied between −16.9 kT and −17.8 kT, which suggests that it is mainly controlled by electrostatic interactions. Knowing the equilibrium adsorption constant, a particle adsorption isotherm was theoretically derived using the RSA model. Experimental data obtained for various bulk concentration of particles were in agreement with these theoretical predictions. These measurements suggest that it is feasible to produce uniform silver particle monolayers of desired coverage in the self-assembly process of particles.
Keywords: Silver particle deposition; Kinetics of silver particle adsorption; Morphology of silver nanoparticles films; Stability of silver nanoparticles monolayers; Controlled desorption of nanoparticles;
Polystyrene nanoparticles doped with a luminescent europium complex by Jessie Desbiens; Benjamin Bergeron; Maxime Patry; Anna M. Ritcey (12-19).
Display Omitted► Polymer nanoparticles can be doped during miniemulsion polymerization. ► PS particles can be doped with Eu(tta)3phen at levels up to 2% by weight. ► Luminescence of the complex is unchanged by the polymer matrix. ► No self-quenching is found despite relatively high local Eu3+ concentrations.Polystyrene nanoparticles doped with a luminescent europium complex, Eu(tta)3phen, are prepared by miniemulsion polymerization. The influence of the complex on the miniemulsion polymerization is investigated by the systematic variation of the initial concentration of Eu(tta)3phen from 2 to 7 wt% relatively to styrene. A maximum doping level of about 2% by weight in the final particles can be achieved. At higher doping levels, destabilization of the miniemulsion leads to a loss of reproducibility with respect to both the degree of conversion and the final Eu content of the particles. Doped nanoparticles of varying diameter, ranging from 19 to 94 nm, are successfully prepared. Steady-state and time-resolved luminescence measurements indicate that the luminescence properties of Eu(tta)3phen in the doped latexes are unchanged from those found in THF solution. Aqueous dispersions of the doped particles exhibit characteristic red emission under UV light irradiation. The luminescence intensity increases linearly with Eu(tta)3phen content, indicating the absence of self-quenching despite the relatively high local concentrations within the particles.
Keywords: Miniemulsion; Polystyrene nanoparticles; Luminescent nanoparticles; Europium;
Synthesis of colloidal dispersions of NiAl, ZnAl, NiCr, ZnCr, NiFe, and MgFe hydrotalcite-like nanoparticles by Francesca Bellezza; Morena Nocchetti; Tamara Posati; Stefano Giovagnoli; Antonio Cipiciani (20-27).
Display Omitted► Colloidal dispersions of hydrotalcite-like compounds were prepared by microemulsions. ► Nanoparticle sizes were between 10 and 30 nm, except for ZnAl (150–200 nm). ► Colloidal stability was investigated by dynamic light scattering and zeta potential. ► High tendency to form homogeneous stacking of plate-like crystals was evidenced.Colloidal aqueous dispersions of nanometric NiAl, ZnAl, NiCr, ZnCr, NiFe, and MgFe hydrotalcite-like compounds were prepared in a water/cetyltrimethylammonium bromide/n-butanol/isooctane microemulsion. Particle sizes were analyzed with different techniques, and the results confirm dimensions between 10 and 30 nm, except for ZnAl–HTlc (150–200 nm). A good colloidal stability of HTlc–NPs aqueous dispersions, investigated with DLS and Pz measurements, was obtained without the need for any stabilizing agent. SEM images clearly showed that the obtained HTlc posses a high tendency to spontaneously form homogeneous and dense stacking of plate-like HTlc crystals directly from aqueous solution, giving rise to the developing of functional materials in optical, electrical and magnetic fields.
Keywords: Hydrotalcite-like compounds; Microemulsion; Nanoparticles; Aqueous dispersions; Colloidal stability;
Crystallization process of zeolite rho prepared by hydrothermal synthesis using 18-crown-6 ether as organic template by Sadao Araki; Yasato Kiyohara; Shunsuke Tanaka; Yoshikazu Miyake (28-33).
Display Omitted► A zeolite rho prepared by hydrothermal synthesis using 18-crown-6 ether has four synthesis steps. ► The dehydration and condensation reaction occurred in the 0–2 h period. ► The particle size of the amorphous aluminosilicate increased in the 3–20 h period. ► The crystallization and crystal growth occurred with incorporation 18C6 in the 20–48 h period. ► The zeolite rho gently grew with an increase in Na/Si ratio in the 48–96 h period.There are many viewpoints on the formation mechanisms for zeolites, but the details are not clear. An understanding of the elementary steps for their formation is important for the development of large-scale membranes and efficient manufacturing processes. In this study, the effects of silicon, aluminum, and the incorporation of 18-crown-6 (18C6) ether, on the formation of zeolite rho, using 18C6 as the structure directing agent (SDA) have been investigated by using field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray fluorescence spectrometry (EDX), nuclear magnetic resonance spectroscopy (NMR), thermo gravimetric analysis (TGA), and the pH measurement. These results suggested that a zeolite rho has four synthesis steps; (1) 0–3 h, the dehydration and condensation reaction between the silica and alumina to form amorphous aluminosilicates; (2) 3–20 h, the particle growth and aggregation process for the amorphous aluminosilicates; (3) 20–48 h, the crystallization and crystal growth of zeolite rho, with the incorporation of 18C6; and (4) 48–96 h, gentle growth with an increase in Na/Si ratio and a change in rate for the bounding state between the silica- and the alumina-based species. We consider the above to reflect the four steps for the formation of zeolite rho.
Keywords: Zeolite rho; Crystallization; 18-Crown-6; Formation mechanism; Hydrothermal synthesis;
Controlled synthesis of NaYF4 nanoparticles and upconversion properties of NaYF4:Yb, Er (Tm)/FC transparent nanocomposite thin films by Wenjuan Huang; Chunhua Lu; Chenfei Jiang; Wei Wang; Jianbin Song; Yaru Ni; Zhongzi Xu (34-39).
Display Omitted► β-NaYF4:Yb, Er (Tm) nanoparticles as excellent upconverting powder. ► The upconverting nanoparticles disperse well in FC resin. ► FC nanocomposites offer luminescence, high transparency, and stain resistance. ► β-NaYF4:Yb, Er (Tm)/FC nanocomposites show intense green (blue) luminescence.Monodisperse oleic acid stabilized pure NaYF4 nanoparticles with controlled size and shape have been successfully synthesized by changing the initial reaction temperature. Transparent nanocomposite thin films consisting of NaYF4:Yb, Er (Tm) upconverting nanoparticles (UCNPs) and fluorocarbon resin (FC) are deposited on the slide glass by dip-coating method. The results show that these nanocomposite thin films exhibit intense green and blue upconversion photoluminescence under 980 nm laser excitation and higher transparency than blank substrate. The NaYF4:Yb,Er (Tm) nanoparticles and NaYF4:Yb,Er (Tm)/FC nanocomposite thin films have been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), scanning electron microscopy (SEM), SEM/back-scattered electron (BSE), atomic force microscopy (AFM), UV–Vis spectrophotometer (UVPC), and photoluminescence (PL) spectra. These nanocomposite thin films can be potentially used in solar cells field.
Keywords: NaYF4; Upconversion luminescence; Nanocomposite; Fluorocarbon resin; Solar cell;
Ionic transport across tailored nanoporous anodic alumina membranes by V. Romero; V. Vega; J. García; V.M. Prida; B. Hernando; J. Benavente (40-46).
Display Omitted► Self-ordered nanoporous alumina membranes have well-defined pore size and porosity. ► Ionic and solute transport determined from membrane potential measurements. ► Significant influence of the membrane pore diameter on both ions and mass transport. ► Possibility of correlating diffusive and charge transport. ► Alumina membranes used for applications in microfluidic and electrochemical devices..Highly ordered Nanoporous Alumina Membranes (NPAMs) with a precise control of the pore size and different porosity but thickness around 63 μm were fabricated by the two-step anodization process using different acidic aqueous solutions, oxalic (Al-Ox), sulfuric (Al-Sf), and phosphoric (Al-Ph) acids, respectively. The pore size was controlled by properly changing the anodization voltage and the electrochemical bath conditions, obtaining the following average pores diameter values, dp , as determined by scanning electron micrographic analysis: Al-Ox (dp = 46 ± 2 nm), Al-Sf (dp = 27 ± 2 nm), and Al-Ph (dp = 240 ± 20 nm). A pore increasing of around 5% for samples Al-Ox and Al-Sf was obtained after membranes immersion in 5 wt.% phosphoric acid for a certain etching time. Electrochemical characterization of NPAMs was performed with the samples in contact with NaCl solutions at different electrolyte concentrations. Ionic transport numbers and effective membrane fixed charge were determined from membrane potential measurements, which clearly show the significant influence of the pore diameter on ions transport. Moreover, frictional and electrical effects on mass transfer parameters (salt and ions diffusion coefficients) into the pores of alumina membranes were also evaluated from these results.
Keywords: Nanoporous alumina membranes; Membrane potential; Ion transport; Salt diffusion;
Mechanism of dehydroxylation temperature decrease and high temperature phase transition of coal-bearing strata kaolinite intercalated by potassium acetate by Hongfei Cheng; Qinfu Liu; Xiaonan Cui; Qian Zhang; Zhiliang Zhang; Ray L. Frost (47-56).
Display Omitted► We have measured the thermal decomposition of kaolinite–potassium acetate intercalation complexes. ► The mechanism of dehydroxylation temperature is proposed. ► The most possible structural models of the kaolinite–potassium acetate intercalation complex have been proposed.The thermal decomposition and dehydroxylation process of coal-bearing strata kaolinite–potassium acetate intercalation complex (CSKK) has been studied using X-ray diffraction (XRD), infrared spectroscopy (IR), thermal analysis, mass spectrometric analysis and infrared emission spectroscopy. The XRD results showed that the potassium acetate (KAc) have been successfully intercalated into coal-bearing strata kaolinite with an obvious basal distance increase of the first basal peak, and the positive correlation was found between the concentration of intercalation regent KAc and the degree of intercalation. As the temperature of the system is raised, the formation of KHCO3, KCO3 and KAlSiO4, which is derived from the thermal decomposition or phase transition of CSKK, is observed in sequence. The IR results showed that new bands appeared, the position and intensities shift can also be found when the concentration of intercalation agent is raised. The thermal analysis and mass spectrometric analysis results revealed that CSKK is stable below 300 °C, and the thermal decomposition products (H2O and CO2) were further proved by the mass spectrometric analysis. A comparison of thermal analysis results of original coal-bearing strata kaolinite and its intercalation complex gives new discovery that not only a new mass loss peak is observed at 285 °C, but also the temperature of dehydroxylation and dehydration of coal bearing strata kaolinite is decreased about 100 °C. This is explained on the basis of the interlayer space of the kaolinite increased obviously after being intercalated by KAc, which led to the interlayer hydrogen bonds weakened, enables the dehydroxylation from kaolinite surface more easily. Furthermore, the possible structural model for CSKK has been proposed, with further analysis required in order to prove the most possible structures.
Keywords: Coal-bearing strata kaolinite; Potassium acetate; Intercalation complex; Dehydroxylation; Structural model;
Electrospinning preparation, characterization and magnetic properties of cobalt–nickel ferrite (Co1− x Ni x Fe2O4) nanofibers by Jun Xiang; Yanqiu Chu; Xiangqian Shen; Guangzhen Zhou; Yintao Guo (57-61).
Display Omitted► Uniform Co1− x Ni x Fe2O4 nanofibers have been prepared by electrospinning combined with sol–gel process. ► The average diameter of the obtained nanofibers is about 110 nm, and the length can reach millimeters. ► The structural characteristics and magnetic properties can be conveniently tuned by changing the Co/Ni ratio. ► The coercivity of the nanofibers is superior to that of the corresponding nanoparticle counterparts.Uniform Co1− x Ni x Fe2O4 (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) nanofibers with average diameter of 110 nm and length up to several millimeters were prepared by calcination of electrospun precursor nanofibers containing polymer and inorganic salts. The as-spun and calcined nanofibers were characterized in detail by TG–DTA, XRD, FE-SEM, TEM, SAED and VSM, respectively. The effect of composition of the nanofibers on the structure and magnetic properties were investigated. The nanofibers are formed through assembling magnetic nanoparticles with poly(vinyl pyrrolidone) as the structure-directing template. The structural characteristics and magnetic properties of the resultant nanofibers vary with chemical composition and can be tuned by adjusting the Co/Ni ratio. Both lattice parameter and particle size decrease gradually with increasing nickel concentration. The saturation magnetization and coercivity lie in the range 29.3–56.4 emu/g and 210–1255 Oe, respectively, and both show a monotonously decreasing behavior with the increase in nickel concentration. Such changes in magnetic properties can mainly be attributed to the lower magnetocrystalline anisotropy and the smaller magnetic moment of Ni2+ ions compared to Co2+ ions. Furthermore, the coercivity of Co–Ni ferrite nanofibers is found to be superior to that of the corresponding nanoparticle counterparts, presumably due to their large shape anisotropy. These novel one-dimensional Co–Ni ferrite magnetic nanofibers can potentially be used in micro-/nanoelectronic devices, microwave absorbers and sensing devices.
Keywords: Co–Ni ferrite; Nanofibers; Magnetic properties; Electrospinning; Sol–gel processing;
Precipitation of silver/palladium alloy platelets from homogeneous solutions by Brendan P. Farrell; Lu Lu; Dan V. Goia (62-66).
Display Omitted► AgPd alloy platelets were obtained by reducing the metal nitrates with ascorbic acid. ► The anisotropic growth is triggered by the structural defects in the AgPd lattice. ► The particle size and aspect ratio vary with the AgPd ratio and solution acidity.Dispersed silver/palladium (Ag/Pd) nanoplatelets were prepared by delivering in parallel solutions of mixed metal nitrates and L-ascorbic acid into a nitric acid solution containing Arabic gum. The shape and size of bimetallic nanoparticles varied with the silver/palladium weight ratio and the concentration of nitric acid. The optimum conditions for platelets formation were a palladium content of ∼2.0 wt.% and nitric acid concentrations above 1.0 mol dm−3. The data presented show that both parameters play a critical role in the nucleation and growth of AgPd particles. A mechanism explaining the formation of the bimetallic nanoplatelets is proposed.
Keywords: Silver/palladium; Nanoplatelets; L-ascorbic acid; Arabic gum; Bimetallic;
A simple approach to prepare monodisperse mesoporous silica nanospheres with adjustable sizes by Meihua Yu; Liang Zhou; Jun Zhang; Pei Yuan; Peter Thorn; Wenyi Gu; Chengzhong Yu (67-75).
A simple approach has been developed to obtain monodisperse mesoporous silica nanospheres with adjustable sizes from 50 to 110 nm in a sodium acetate solution without any other base or organic solvent.Display Omitted► A simple approach to obtain monodisperse mesoporous silica nanospheres (MMSNs). ► The particle size can be easily adjusted in the range of 50–110 nm. ► The pore volume and pore size of MMSNs can be enhanced by hydrothermal treatment. ► A spherical micelle templating mechanism proposed to interpret the formation of MMSNs.A new and facile approach has been developed to prepare monodisperse mesoporous silica nanospheres (MMSNs) with controlled particle sizes and pore structures. In our approach, MMSNs were synthesized simply in a sodium acetate solution without adding any other alkali or alcohol additives. MMSNs have a spherical shape and uniform particle sizes, which can be adjusted from 50 to 110 nm by increasing the reaction temperature from 40 to 80 °C. By performing a subsequent hydrothermal treatment (HT) under basic condition (pH = ∼11.5) at 130 °C, the mesoporous pore volume and surface area can be enhanced, while keeping the mono-dispersion characteristics and the mesopore size almost unchanged. The pore sizes of MMSNs can be adjusted from 2.8 to 4.0 nm under acidic solutions by changing the HT temperature from 100 to 130 °C. The formation process of MMSNs has been investigated by transmission electron microscopy (TEM) and attenuated total reflection Fourier transform infrared (ATR-FTIR) techniques. A spherical micelle templating mechanism is proposed to explain the formation of MMSNs in our system, which is different from that of traditional highly ordered mesoporous silica nanoparticles (MCM-41).
Keywords: Mesoporous silica; Monodisperse spheres; Self-assembly; Hydrothermal treatment; Formation mechanism;
Effect of adsorbed poly(ethylene glycol) on the gelation evolution of Laponite suspensions: Aging time-polymer concentration superposition by Weixiang Sun; Yanrui Yang; Tao Wang; Haohao Huang; Xinxing Liu; Zhen Tong (76-82).
Display Omitted► Gelation kinetics of Laponite/PEG suspensions were monitored by small amplitude oscillatory shear (SAOS) rheology. ► Time-PEG concentration-NaCl concentration superposition was observed. ► The effect of PEG on the gelation kinetics was quantitatively modeled by a model of interaction-limited coagulation.The effects of the concentration of polyethylene glycol (PEG) and NaCl on the gelation kinetics of aqueous Laponite suspensions were investigated. The PEG concentration c p was increased from 0.063 wt.% to 1.0 wt.%, and the NaCl concentration c s was increased from 3.0 mM to 5.0 mM. The gelation process was monitored with the small amplitude oscillatory shear (SAOS) rheology. At each NaCl concentration, the time curves of storage and loss moduli G′ and G″ at different PEG concentrations were shifted horizontally to construct a master curve. Master curves for different NaCl concentrations were shifted further into a main master curve. The results were understood in terms of an increase in steric repulsion with increasing c p. A model based on the theory of interaction-limited coagulation was proposed to describe the dependence of the shift factor on the PEG concentration, taking into account of the interactions between particles. The quantitative description of the observed results has been achieved with this model.
Keywords: Laponite; Polyethylene glycol; Gelation; Coagulation;
End-to-end assembly of gold nanorods via oligopeptide linking and surfactant control by Titoo Jain; Renée Roodbeen; Nini E.A. Reeler; Tom Vosch; Knud J. Jensen; Thomas Bjørnholm; Kasper Nørgaard (83-90).
Display Omitted► End-to-end assembly of Au nanorod chains. ► Linking via an oligopeptide or a surfactant controlled self-linking process. ► Introducing chemical functionality into self-assembled nanochains. ► Nanogap width is controlled by length of oligopeptide. ► Reaction rate and extent is controlled by the surfactant concentration.We report two novel approaches for fabricating self-assembled chains of end-to-end linked Au nanorods separated by a nanogap. In one approach, bi-functional cysteine end-capped oligopeptides of different lengths are used as the linking agent. The widths of the produced nanogaps scale with the length and tertiary structure of the peptide linker. Functionalized oligopeptides containing an acetylene group are also employed as a linker, and the functional group is uniquely identified using surface-enhanced Raman spectroscopy. The development of an oligopeptide-linking platform is motivated by the ease of synthesis and high modularity of peptides; these features enable the possibility to integrate diverse functionality into molecular nanogap junctions – synthesized in water. The stepwise nanochain formation is followed via the evolution of the longitudinal plasmon absorption band in combination with transmission electron microscopy. The reaction rate and extent is tuned by controlling the concentration of the stabilizing CTAB surfactant in the solution. At very low surfactant concentrations, spontaneous end-to-end linking of the Au nanorods is observed even in the absence of linking peptide. The assembled AuNRs may act as next-generation electrodes in a platform for molecular electronics and synthetic biology.
Keywords: Gold nanorods; Self-assembly; Peptide; Nanogap; Synthetic biology;
Superior dispersion of highly reduced graphene oxide in N,N-dimethylformamide by Thanh Truong Dang; Viet Hung Pham; Seung Hyun Hur; Eui Jung Kim; Byung-Seon Kong; Jin Suk Chung (91-96).
Display Omitted► The hydrazine reduction of GO in DMF/water at different temperatures was investigated. ► The relationships between the highly reduced graphene oxide (HRG) properties were established. ► The HRGs exhibited a high electrical conductivity and good dispersibility in DMF. ► The reduction of GO in DMF-rich media at low temperature is the key factor.Here, we report the effect of temperature on the extent of hydrazine reduction of graphene oxide in N,N-dimethylformamide (DMF)/water (80/20 v/v) and the dispersibility of the resultant graphene in DMF. The highly reduced graphene oxide (HRG) had a high C/O ratio and good dispersibility in DMF. The good dispersibility of HRGs is due to the solvation effect of DMF on graphene sheets during the hydrazine reduction, which diminishes the formation of irreversible graphene sheet aggregates. The dispersibility of the HRGs was varied from 1.66 to 0.38 mg/mL when the reduction temperature increased from 25 °C to 80 °C. The dispersibility of the HRGs was inversely proportional to the electrical conductivity of the HRGs, which varied from 17,400 to 25,500 S/m. The relationships between the C/O ratio, electrical conductivity, and dispersibility of the HRGs were determined and these properties were found to be easily controlled by manipulating the reduction temperature.
Keywords: Hydrazine reduction; Graphene oxide; Chemically converted graphene; Colloidal suspension and organic solvent;
Thermo-responsive monodisperse core–shell microspheres with PNIPAM core and biocompatible porous ethyl cellulose shell embedded with PNIPAM gates by Ya-Lan Yu; Mao-Jie Zhang; Rui Xie; Xiao-Jie Ju; Ji-Yun Wang; Shuo-Wei Pi; Liang-Yin Chu (97-106).
Display Omitted► Novel core–shell microspheres are prepared for thermo-responsive controlled release. ► Microcapsules are composed of biocompatible shell and thermo-responsive core. ► Thermo-responsive gates are synthesized in situ in the membrane pores of capsules.Monodisperse microspheres composed of thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) core and biocompatible porous ethyl cellulose (EC) shell embedded with PNIPAM gates have been successfully prepared by microfluidic emulsification, solvent evaporation and free radical polymerization. Attributing to the coating of EC shell, the mechanical strength and biocompatibility of the core–shell microsphere are much better than those of the PNIPAM core itself. Fourier transform infrared (FT-IR) spectrometer and scanning electron microscopy (SEM) are employed to examine chemical compositions and microstructures of prepared microparticles. By the cooperative action of EC shell with PNIPAM gates and PNIPAM core, the proposed core–shell microspheres exhibit satisfactory thermo-responsive controlled release behaviors of model drug molecules rhodamine B (Rd B) and VB12. At temperatures above the volume phase transition temperature (VPTT) of PNIPAM, the release rate of solute molecules is much faster than that at temperatures below the VPTT. The controlled factor of the prepared core–shell microspheres for VB12 release reaches to as high as 11.7. The proposed microspheres are highly attractive for controlled drug delivery.
Keywords: Core-shell microspheres; Controlled release; Thermo-responsive behavior; Poly(N-isopropylacrylamide); Ethyl cellulose;
One-pot aqueous phase growth of biocompatible 15–130 nm gold nanoparticles stabilized with bidentate PEG by Eunkeu Oh; Kimihiro Susumu; Vaibhav Jain; Mijin Kim; Alan Huston (107-111).
Display Omitted► Synthesis of water-soluble gold nanoparticles using PEG-appended disulfide ligands. ► Size control from 15 to 130 nm. ► In situ functionalization of gold nanoparticles. ► Excellent colloidal stability in aqueous solutions in biological buffer condition.We describe a new, single pot, aqueous phase method for synthesizing water soluble gold nanoparticles (AuNPs) over a size range of 15–130 nm. Poly(ethylene glycol)-appended thioctic acid ligands were used to control the growth rates and stabilize the AuNPs. Critical factors that enable the controlled growth of the AuNPs over this size range include the pH, the choice of reducing agent, the reaction temperature and the sequential addition of gold precursor and ligand with specific ligand-to-gold ratios. We describe the synthetic procedure in detail. Optical and structural characterization of the AuNPs was accomplished using UV–vis absorption spectroscopy, dynamic light scattering, and transmission and scanning electron microscopy.
Keywords: Gold nanoparticles; Surface plasmon absorption; Surface ligands; Poly(ethylene glycol); TEM; SEM; Z-average;
Solubilization of two organic dyes by cationic ester-containing gemini surfactants by A.R. Tehrani-Bagha; R.G. Singh; K. Holmberg (112-118).
Display Omitted► The solubilization power of cationic gemini surfactants is superior to that of the corresponding monomeric surfactant. ► A correlation between surfactant structure and solubilization power is demonstrated. ► It is shown that the dye resides just below the head group region of the cationic surfactant micelles.Solubilization of two different types of organic dyes, Quinizarin with an anthraquinone structure and Sudan I with an azo structure, has been studied in aqueous solutions of a series of cationic gemini surfactants and of a conventional monomeric cationic surfactant, dodecyltrimethylammonium bromide (DTAB). Surfactant concentrations both above and below the critical micelle concentration were used. The concentration of solubilized dye at equilibrium was determined from the absorbance of the solution at λ max with the aid of a calibration curve. The solubilization power of the gemini surfactants was higher than that of DTAB and increased with increasing alkyl chain length. An increase in length of the spacer unit resulted in increased solubilization power while a hydroxyl group in the spacer did not have much effect. Ester bonds in the alkyl chains reduced the solubilization power with respect to both dyes. A comparison between the absorbance spectra of the dyes in micellar solution with spectra in a range of solvents of different polarity indicated that the dye is situated in a relatively polar environment. One may therefore assume that the dye is located just below the head group region of the micelle. Attractive π-cation interactions may play a role for orienting the dye to the outer region of the micelle.
Keywords: Gemini surfactants; Ester bond; Solubilization; Anthraquinone dye; Azo dye; Quinizarin; Sudan I;
Size control of giant unilamellar vesicles prepared from inverted emulsion droplets by Kazuya Nishimura; Hiroaki Suzuki; Taro Toyota; Tetsuya Yomo (119-125).
Display Omitted► We tested the giant lipid vesicle formation process from uniform emulsion droplets. ► We clarified the relationship between the sizes of droplets and vesicles formed. ► Vesicles with desired size were obtained at an optimum centrifugal acceleration.The production of giant lipid vesicles with controlled size and structure will be an important technology in the design of quantitative biological assays in cell-mimetic microcompartments. For establishing size control of giant vesicles, we investigated the vesicle formation process, in which inverted emulsion droplets are transformed into giant unilamellar vesicles (GUVs) when they pass through an oil/water interface. The relationship between the size of the template emulsion and the converted GUVs was studied using inverted emulsion droplets with a narrow size distribution, which were prepared by microfluidics. We successfully found an appropriate centrifugal acceleration condition to obtain GUVs that had a desired size and narrow-enough size distribution with an improved yield so that emulsion droplets can become the template for GUVs.
Keywords: Giant lipid vesicles; Microfluidics; Water-in-oil emulsion; Micro-reaction compartment;
Cationic ester-containing gemini surfactants: Determination of aggregation numbers by time-resolved fluorescence quenching by A.R. Tehrani-Bagha; J. Kärnbratt; J.-E. Löfroth; K. Holmberg (126-132).
Display Omitted► Aggregation numbers have been determined by time resolved fluorescence quenching. ► Ester bonds in the surfactant tails promote micelle grow with concentration. ► A hydroxyl group in the spacer unit does not affect the micelle size.The micellar aggregation number of a series of ester-containing gemini surfactants has been determined with steady state and with time-resolved fluorescence quenching. The latter method gave values of aggregation number about twice those obtained with the former method. It was found that the length of the spacer was the most important factor affecting the aggregation number. The length and the nature of the surfactant alkyl chains were of less importance in spite of the fact that the length of the alkyl chains strongly affects the solution properties of the unimers.
Keywords: Gemini surfactant; Esterquat; Fluorescence quenching; Aggregation number;
Study of nano-emulsion formation by dilution of microemulsions by I. Solè; C. Solans; A. Maestro; C. González; J.M. Gutiérrez (133-139).
Display Omitted► Effect of dilution procedure and cosurfactant nature on O/W nano-emulsion formation by self-emulsification. ► Dilution of O/W microemulsions results in nano-emulsions regardless the dilution procedure. ► Dilution of W/O microemulsions only results in nano-emulsions when water is added stepwise. ► Nano-emulsion size decreases with cosurfactant alkyl chain length. ► Nano-emulsion stability increases with cosurfactant alkyl chain length.The influence of different dilution procedures on the properties of oil-in-water (O/W) nano-emulsions obtained by dilution of oil-in-water (O/W) and water-in-oil (W/O) microemulsions has been studied. The system water/SDS/cosurfactant/dodecane with either hexanol or pentanol as cosurfactant was chosen as model system. The dilution procedures consisted of adding water (or microemulsion) stepwise or at once over a microemulsion (or water). Starting emulsification from O/W microemulsions, nano-emulsions with droplet diameters of 20 nm are obtained, independently on the microemulsion composition and the dilution procedure used. In contrast, starting emulsification from W/O microemulsions, nano-emulsions are only obtained if the emulsification conditions allow reaching the equilibrium in an O/W microemulsion domain during the process. These conditions are achieved by stepwise addition of water over W/O microemulsions with O/S ratios at which a direct microemulsion domain is crossed during emulsification. The nature of the alcohol used as cosurfactant has been found to play a key role on the properties of the nano-emulsions obtained: nano-emulsions in the system using hexanol as cosurfactant are smaller in size, lower in polydispersity, and have a higher stability than those with pentanol.
Keywords: Nano-emulsions; Microemulsions; Low-energy methods; Self-emulsification; Dilution of microemulsions;
Water–AOT–alkylbenzene microemulsions: Influence of alkyl chain length on structure and percolation behavior by Markus Appel; Tinka Luise Spehr; Robert Wipf; Bernd Stühn (140-145).
Display Omitted► AOT-based water-in-oil droplet microemulsions with different alkylbenzenes as oil phase. ► Percolation behavior studied by conductivity measurements, structure studied by SAXS. ► Droplet radius increases linearly with molar water to surfactant ratio. ► Percolation can be induced by increasing alkyl chain length.We study the percolation behavior of the water-in-oil (w/o) droplet phase of AOT (sodium bis[2-ethylhexyl] sulfosuccinate)-based microemulsions with different alkylbenzenes (toluene, ethylbenzene, butylbenzene or octylbenzene) as oil phase. We use microemulsions of varying composition with molar water to surfactant ratios 0 ⩽ W ⩽ 50 and droplet (water plus surfactant) volume fractions 10% ⩽ ϕ ⩽ 50%. Using dielectric spectroscopy, a percolation transition is observed in w/o microemulsions with butylbenzene or octylbenzene. With increasing molecular weight of the alkylbenzene, the percolation temperature T P decreases. The structure of the microemulsions is determined by small angle X-ray scattering (SAXS). With increasing molar weight of the alkylbenzene, the stability range of the L 2 droplet phase extends to higher W. The larger amount of solubilizable water can be related to variable oil penetration of the AOT monolayer, which affects the spontaneous curvature of the surfactant shell.
Keywords: Microemulsion; AOT; Alkylbenzene; Dynamic percolation; Small angle X-ray scattering;
Mechanism of gelation in the hydrogenated soybean lecithin (PC70)/hexadecanol/water system by Yasuharu Nakagawa; Hiromitsu Nakazawa; Satoru Kato (146-151).
Display Omitted► The crude lecithin/hexadecanol bilayers formed a gel owing to low levels of impurities. ► A morphological change from vesicles to bilayer sheets causes the gelation. ► The hexadecanol molecules are intercalated between phospholipids to reduce the chain tilt. ► We propose the continuous water layers between bilayer sheets as a network in the gel. ► Trace acidic phospholipids in the lecithin may play a crucial role in the gel formation.The crude phospholipid mixture (PC70) forms a homogeneous gel with hexadecanol (HD) in water, whereas the purified lipid does not. The fact that the crude material PC70 can be utilized for homogeneous gel preparation suits the cosmetic industry very well from the viewpoint of cost performance. In order to clarify the mechanism of the gelation, we investigated the structures and physicochemical properties of the PC70/HD/water system by rheometry, freeze-fracture electron microscopy, differential scanning calorimetry (DSC) and synchrotron X-ray diffraction. Our results suggested that the gelation is induced by change in bilayer morphology from closed vesicles to sheet-like structures with open edges covered by minor lipid components that are stiffened due to intercalation of HD molecules between phospholipids. The morphological change may give rise to homogeneous distribution of the bilayer sheets throughout the solution and formation of water continuum that may work as a network in the gel.
Keywords: Hydrogenated soybean lecithin (PC70); Hexadecanol; Gelation; Sheet-like structure; Morphological change; Water continuum;
Sensitivity of cationic surfactant templates to specific anions in liquid interface crystallization by Paul J. Sanstead; Nick Florio; Kiersten Giusto; Catherine Morris; Sunghee Lee (152-159).
Display Omitted► Cationic monolayers at liquid interface of aqueous microdroplet were prepared. ► CTAB and DODAB monolayers promote crystal nucleation of K2SO4. ► Specific anions affect CTAB-promoted nucleation, but not DODAB. ► Interaction between surfactant monolayer and anions depends on surfactant nature.We investigated the specific effects of potassium salts of various anions upon the interfacially templated crystal nucleation of K2SO4. Previously, we have shown that the presence of several salts at low concentrations could induce changes in important crystallization characteristics templated by 1-octadecylamine at the liquid–liquid interface, and that these changes depended greatly on the specific identity of the salt. In this work we extend our surfactant monolayers to include dimethyldioctadecylammonium bromide (DODAB) and hexadecyltrimethylammonium bromide (CTAB). Addition of 10 mM of various potassium salts results in a diminution in efficiency of the templating capability of CTAB monolayer, as evidenced by higher C onset values and polycrystalline habit. The ability of the anions to perturb these values varied in a manner consistent with a Hofmeister series. However, DODAB maintained its templating effectiveness regardless of the nature of the salt or concentration. DODAB and CTAB are likely to be undergoing different reordering effects in the monolayer upon binding with chaotropic anions: a combined reduction in surface charge with different monolayer ordering results in a differing template ability. These studies have provided significant insights into the understanding of the interaction of ordered surfactant arrays with salts, and provide exciting possibilities for crystal engineering and materials design.
Keywords: Potassium sulfate; Templated crystallization; Specific anion effect; Microdroplet crystallization; Liquid interface; Surfactant;
A cinnamic acid-type photo-cleavable surfactant by Hideki Sakai; Shohei Aikawa; Wataru Matsuda; Takashi Ohmori; Yuko Fukukita; Yoji Tezuka; Atsutoshi Matsumura; Kanjiro Torigoe; Koji Tsuchiya; Koji Arimitsu; Kazutami Sakamoto; Kenichi Sakai; Masahiko Abe (160-164).
Display Omitted► We have developed a cinnamic acid-type photo-cleavable surfactant. ► This surfactant yields two functional materials as a result of the photo-cleavage. ► The photo-cleavage results in a significant change in interfacial properties. ► Hence, the surfactant is a photo-responsive function-exchangeable material. ► This is a new concept in stimulus-responsive amphiphilic materials.We have developed a novel cinnamic acid-type photo-cleavable surfactant. This surfactant experiences photo-cleavage through UV-induced cyclization in aqueous solutions. The photo-cleavage not only reduces its capabilities as a surfactant but also yields two functional materials including a coumarin derivative and an aminated polyoxyethylene compound. This means that the photo-cleavable surfactant synthesized in this study is a photo-responsive function-exchangeable material. In our current study, we have characterized the photo-cleavable behavior that occurs in aqueous solutions and a resulting change in interfacial properties. The photo-cleavage induces an increased interfacial tension of a squalane/water interface and a decreased solubilization capability of the surfactant micelles.
Keywords: Photo-cleavable surfactant; Cinnamic acid; Interfacial tension; Solubilization;
Surface and biological activity of sophorolipid molecules produced by Wickerhamiella domercqiae var. sophorolipid CGMCC 1576 by Xiaojing Ma; Hui Li; Xin Song (165-172).
Display Omitted► Sophorolipids (SLs) were produced by Wickerhamiella domercqiae. ► Six SL molecules with different structures were prepared and identified. ► Surface and biological activity of different SL molecules were compared. ► The different SL molecules showed distinct surface and biological activity. ► Some explanations were given for the influence of structures on activities.This work investigated the surface and biological activity of lactonic and acidic sophorolipid (SL) molecules differing in the acetylation degree of sophorose, carbon chain length and unsaturation degree of the fatty acid moiety. Six different SL molecules were prepared from crude SLs produced by Wickerhamiella domercqiae var. sophorolipid CGMCC 1576. The structures of the selected SL molecules were elucidated by MS and GC/MS. The surface properties of SLs including critical micelle concentration (CMC), minimum surface tension (Min. S.T.) and emulsification capacity to hydrocarbon and vegetable oils were studied, and the results demonstrated that SL molecules with different structures exhibited quite different surface properties. Cytotoxicities of different SL molecules to Chang liver cells determined by the MTT (3-(4,5-dimethythiazol-2-yl)-2,5-diphenyl tetrazolium bromide) method showed the effect of chemical structure of the SLs on their biological activities. Biodegradability of these SL molecules was tested using the river-water die-away method. The differences of surface and biological activity in different SL molecules will be of benefit for the applications of these SLs in specific fields such as the detergent, petroleum, pharmaceutical and environment industries.
Keywords: Sophorolipid; Surface property; Emulsification capacity; Cytotoxicity; Biodegradability;
Investigations of surfactant effects on gas hydrate formation via infrared spectroscopy by Chi Lo; Junshe Zhang; Ponisseril Somasundaran; Jae W. Lee (173-176).
Display Omitted► Explain the full role of SDS in nucleation and extended growth phase using IR spectroscopy. ► Observe both ice- and water-like OH stretches of hydrate–water interface at or above 100 ppm SDS. ► Detect both symmetric and asymmetric, free OH bands of the HB acceptor in the hydrate–water interface. ► Provide important insights to spatial positions of SDS molecules absorbed onto the interface from free/bonded OH bands.This infrared (IR) spectroscopic study addresses surfactant effects on cyclopentane (CP) hydrate–water interfaces by observing both ice-like (3100 cm−1) and water-like (3400 cm−1) bands in the bonded OH region together with free OH bands. IR spectroscopy of hydrates has not been actively employed due to the overwhelming signal saturation of the OH bonding. However, this work is able to utilize this large signal of the OH bonding to understand the water structure changes upon adding sodium dodecyl sulfate (SDS) to CP hydrate–water interfaces. The spectral data suggest a change to more ice like (3100 cm−1) features starting from 100 ppm to 750 ppm SDS, indicating favorable nucleation. At the same instance, water like (3400 cm−1) features are also shown in this range of SDS concentration, which suggests looser hydrogen bonding that is an indicator for facilitating hydrate growth. Additionally, this ATR-IR study firstly identifies both symmetric and anti-symmetric free OH bands of the hydrogen bond (HB) acceptors in the clathrate hydrate system. Relative area ratios of free and bonded OH bands provide important information about spatial arrangements of adsorbed SDS monomers.
Keywords: Infrared spectroscopy; Gas hydrates; Surfactant; SDS; Hydrate formation;
Multilayer film assembled from charged derivatives of chitosan: Physical characteristics and biological responses by Wilaiporn Graisuwan; Oraphan Wiarachai; Cheeraporn Ananthanawat; Songchan Puthong; Suphan Soogarun; Suda Kiatkamjornwong; Voravee P. Hoven (177-188).
Display Omitted► LBL assembly of charged derivative of chitosan was constructed. ► All multilayer films are relatively rigid and have high water content associated. ► Cytocompatibility of multilayer films depends upon the outermost layer. ► The HTACC/PAA showed moderate antibacterial activity against Escherichia coli and Staphylococcus aureus. ► Strong anticoagulant activity was observed on the multilayer films terminating with SFC.Polyelectrolyte multilayer films were successfully assembled from each of the three charged derivatives of chitosan; N-[(2-hydroxyl-3-trimethylammonium)propyl]chitosan chloride (HTACC), N-succinyl chitosan (SCC) and N-sulfofurfuryl chitosan (SFC), paired with one of the two oppositely charged polyelectrolytes, poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) on surface-treated poly(ethylene terephthalate) (treated PET) substrates by alternate layer-by-layer adsorption. Surface coverage and wettability of the multilayer films were determined by AFM and water contact angle measurements, respectively. Analysis by quartz crystal balance with dissipation (QCM-D) has suggested that all multilayer films are relatively rigid and have a high water content associated within their structures, accounting for up to 85–90% (w/w) for films having 7–10 layers. In vitro cytocompatibility tests for the fibroblast-like L929 cell line revealed a slight dependency for cell adhesion and proliferation on the outermost layer. The multilayer film containing HTACC exhibited moderate antibacterial activity against E. coli and S. aureus. Bearing negative charges, the multilayer films terminating with SFC and having at least 10 layers were capable of suppressing the adsorption of plasma proteins and platelet adhesion at a comparable level to the multilayer film assembled from heparin, a well-known antithrombogenic polymer.
Keywords: Charged derivative; Chitosan; Layer-by-layer; Cytocompatibility; Antibacterial activity; Antithrombogenicity;
Synthesis of temperature-responsive anion exchanger via click reaction by Kenji Murakami; Xue Yu; Takahiro Kato; Yukihiko Inoue; Katsuyasu Sugawara (189-195).
Display Omitted► PNIPAM was immobilized on the mesoporous silica via click reaction. ► Amount of immobilized PNIIPAM could be controlled by amount of added PNIPAM. ► Adsorbed amount of methyl orange depended on the temperature of aqueous solution. ► Anion-exchange rate decreased slightly with amount of immobilized PNIPAM.The temperature-responsive anion exchanger was synthesized by immobilizing the poly(N-isopropylacrylamide) (PNIPAM), a kind of the temperature-responsive polymer, on the external surface of mesoporous silica via click reaction. The structure of this synthesized composite was characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), elemental analysis, and nitrogen adsorption experiment. The amount of PNIPAM immobilized on the external surface of mesoporous silica, which was calculated from the weight loss measured by thermogravimetry, increased from 5.3 wt.% to 12.9 wt.% (dry) depending on the amount of PNIPAM added in the click reaction. The adsorption–desorption behavior of methyl orange (MO) ions in this synthesized anion exchanger was affected by the temperature of aqueous solution: the MO ions were adsorbed and desorbed reversibly and repeatedly with changing the pH of the solution at 25 °C, while the amount of adsorbed MO ions remained nearly constant at about 0.05 mmol/g independent of the pH of the solution at 40 °C. Also, the amount of PNIPAM immobilized on the mesoporous silica influenced the adsorption rate of MO ions, suggesting that the adsorption rate in this composite is controlled by the diffusion of MO ions through the PNIPAM layer.
Keywords: Mesoporous silica; Temperature-responsive anion exchanger; Poly(N-isopropylacrylamide); Click reaction;
Effect of temperature on the sorption of europium on alumina: Microcalorimetry and batch experiments by Jean-Pierre Morel; Nicolas Marmier; Charlotte Hurel; Nicole Morel-Desrosiers (196-201).
Display Omitted► Adsorption of Eu3+ on the alumina surface in acidic media, which includes the deprotonation of the surface, is a weakly endothermic process. ► The pK values calculated at 50 °C using the van’t Hoff equation and the calorimetrically-determined enthalpies are in good accordance with experiments. ► In the tested conditions, temperature has only a small effect on adsorption.The determination of enthalpies of reactions (aqueous and surface complexation) is used in this work to model the temperature effect on the adsorption processes. Microcalorimetry experiments were carried out to determine the enthalpy of adsorption of europium on γ-alumina at 25 °C. The stability constants at 50 °C were then calculated with the van’t Hoff equation, and a 2-pK approach was used to model the adsorptive behavior of Eu on alumina at 50 °C, as a function of pH. The results have shown that the adsorption of Eu3+ on the alumina surface is weakly endothermic. In the experimental conditions considered in the present study, the temperature has only a small effect on the adsorption reaction.
Keywords: Microcalorimetry; Adsorption; Europium; γ-Alumina; Surface complexation modeling;
Functionalization of organic membranes by polyelectrolyte multilayer assemblies: Application to the removal of copper ions from aqueous solutions by C. Magnenet; S. Lakard; C.C. Buron; B. Lakard (202-208).
Display Omitted► Modification of organic membranes by polyelectrolytes assemblies using layer-by-layer technique. ► Filtration of copper solutions through functionalized membranes. ► Possibility to remove 80–90% of the copper ions contaminating aqueous solutions.The functionalization of an organic polyethersulfone membrane (PES) was performed by alternating deposition of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrene sulfonate) (PSS), leading to the formation of a polyelectrolyte multilayer film (PEM). The resulting assembly was characterized by tangential streaming potential measurements to determine the charge of the modified membranes as a function of the polyelectrolyte solution concentration and as a function of the immersion time of the membrane in the polyelectrolyte solutions. Then, the modified membranes were used to perform the ultrafiltration of aqueous solutions containing copper(II) ions. Different operating conditions were tested including: polyelectrolyte concentration, polyelectrolyte nature, thickness of the PEM film or pH of the Cu2+ solutions. These filtration experiments demonstrated that it was possible to obtain a satisfactory retention of the copper ions (88%), thus proving that this type of assembly can be useful for the removal of copper ions from contaminated aqueous solutions.
Keywords: Polyelectrolyte multilayer films; Layer-by-layer adsorption; Organic membrane; Filtration; Heavy metal removal;
Enhanced adsorption of paracetamol on closed carbon nanotubes by formation of nanoaggregates: Carbon nanotubes as potential materials in hot-melt drug deposition-experiment and simulation by Artur P. Terzyk; Agnieszka Pacholczyk; Marek Wiśniewski; Piotr A. Gauden (209-216).
Display Omitted► Paracetamol adsorption on a series of eight closed carbon nanotubes was measured. ► Paracetamol forms nanoaggregates in interstitial channels. ► After heating, nanoaggregates are destroyed and molecules forming them are readsorbed. ► The effect of nanoaggregates formation can be used in hot-melt deposition leading to the formation of new drug delivery system.We present the new results of systematic studies of paracetamol adsorption on closed, commercially available, unmodified carbon nanotubes. The results of thermal analysis, static adsorption measurements and the comparison with phenol adsorption data lead to suggestion that the formation of paracetamol nanoaggregates in the interstitial spaces between nanotubes occurs. This effect is also confirmed by the results of (performed in two ways) independent dynamic measurements and by molecular dynamics simulation technique. Next, we show that the behavior of adsorbed paracetamol during heating leads to the creation of a new drug delivery system. The properties of this system depend on the type of applied nanotubes and the parameters of the process called hot-melt drug deposition. Thus, we conclude that confined nanoaggregate formation, as well as hot-melt deposition should be promising effects in the preparation of highly effective, new drug delivery systems.
Keywords: Adsorption; Adsorption from solution; Carbon nanotubes; Paracetamol; Thermal analysis; Hot-melt deposition; Drug delivery;
Facile synthesis and photocatalytic properties of Ag―AgCl―TiO2/rectorite composite by Yanqing Yang; Gaoke Zhang; Wei Xu (217-223).
Display Omitted► Ag―AgCl―TiO2/rectorite composite was prepared by a deposition–photoreduction method. ► The composite exhibited excellent visible light photocatalytic activity. ► h+ and O 2 • - were considered the major reactive species in the photocatalytic process.In this study, we prepared a new visible light induced plasmonic photocatalyst Ag―AgCl―TiO2/rectorite using a facile deposition–photoreduction method. The catalysts were characterized using X-ray diffraction (XRD), UV–visible diffused reflectance spectra (UV–vis DRS), Raman spectra, high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). The as-prepared Ag―AgCl―TiO2/rectorite powders exhibited an efficient photocatalytic activity for the degradation of acid orange (ARG) and 4-nitrophenol (4-NP) under visible light irradiation (λ > 400 nm). Moreover, the mechanism suggested that the high photocatalytic activity is due to the charge separation and the surface plasmon resonance of metallic Ag particles in the region of visible light. The active species measurements suggested that HO • is not the dominant photooxidant. Direct hole transfers and O 2 • - were involved as the active species in the photocatalytic reaction.
Keywords: Photocatalyst; Deposition–photoreduction method; Visible light; ARG; Surface plasmon resonance;
Adsorptive characteristics of phosphate from aqueous solutions by MIEX resin by Lei Ding; Chao Wu; Huiping Deng; Xinxi Zhang (224-232).
Display Omitted► Various impact factors have effects on the removal of phosphate to some degree. ► The equilibrium data can be described by Freundlich and Koble–Corrigan models. ► The adsorption of phosphate on MIEX resin may be controlled by chemisorptions. ► The adsorption of phosphate on MIEX resin is mainly governed by film diffusion. ► Coexistent anions influence the adsorption of phosphate on MIEX resin.This study investigated the potential of MIEX resin as the adsorbent for the removal of phosphate from aqueous solutions. In our batch experiments, we studied the effect of some parameters on the removal of phosphate. It was observed that uptake of phosphate was mainly affected by initial phosphate concentration, adsorbent dosage, initial pH of solution, and coexistent anions. The adsorption equilibrium data at 288 K fitted well to Freundlich and Koble–Corrigan isotherm models. The kinetics studies displayed that the adsorption process followed the pseudo-second-order model. The diffusion studies showed that the intra-particle diffusion was not the only rate-controlling step and, the diffusion process of phosphate from solution to MIEX resin was controlled by film diffusion. The thermodynamics parameters were evaluated. The results showed that the adsorption process was spontaneous thermodynamically, endothermic, and entropy driven. These results have established a good potentiality for MIEX resin to be used as an adsorbent for the removal of phosphate from aqueous solutions. This work will deepen our understanding of the adsorptive characteristics of phosphate by MIEX resin and provide a better way to remove phosphate from wastewater.
Keywords: Phosphate; MIEX resin; Adsorption; Isotherm; Kinetics; Thermodynamics;
Influence of ceria modification on the properties of TiO2–ZrO2 supported V2O5 catalysts for selective catalytic reduction of NO by NH3 by Yaping Zhang; Xiaoqiang Zhu; Kai Shen; Haitao Xu; Keqin Sun; Changcheng Zhou (233-238).
Display Omitted► A quadri-component V2O5–CeO2/TiO2–ZrO2 was prepared and applied in the SCR reaction. ► Such a complex showed a stable and high activity than the tri-component counterpart. ► The Ce-modified catalysts possessed a large amount of Brønsted and Lewis acid sites. ► The addition of CeO2 promoted the formation of active intermediate on the surface.TiO2–ZrO2 (hereafter denoted as Ti–Zr) supported V2O5 catalysts with different loadings of CeO2 were synthesized, and their physicochemical properties were characterized by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), in situ Fourier transform infrared spectroscopy (in situ FT-IR) and temperature-programmed reduction (TPR). Their catalytic activities toward the NO x reduction reaction with NH3 were tested. We found that with the addition of CeO2, more NO was removed in a wide temperature range of 220–500 °C. As the CeO2 content was increased from 10% to 20% (i.e., the molar ratio of Ce to Ti–Zr), NO conversion increased significantly; after that, increasing CeO2 content, however, decreased NO conversion. In particular, the addition of CeO2 to V2O5/Ti–Zr suppressed the coke deposition and rendered a stable and high catalytic activity. The characterization results indicated that: (1) the deposited vanadium and cerium oxides were highly dispersed over the Ti–Zr support, and in addition to ZrV2O7, a common binary compound observed in V2O5/Ti–Zr, CeVO4 and Ce3ZrO8 was formed upon increasing CeO2 content; (2) the introduction of CeO2 to V2O5/Ti–Zr sample promoted the redox ability of the resulting catalysts; and (3) the Ce-containing catalysts possessed the greater amount of surface acidic and active intermediate.
Keywords: Ceria modification; V2O5; TiO2–ZrO2; Selective catalytic reduction;
Solute–solvent halogen bonding during adsorption on silver nanostructures by Donald A. Perry; Taylor M. Razer; James S. Cordova; Elizabeth M. Schiefer; TsungYen Chen; Katherine M. Primm; Ashley M. Bonde; Alexandru S. Biris (239-244).
Display Omitted► Silver nanoparticles can induce ionization of 4-iodobenzoic acid in mono- and multi-layer. ► Halogen bonds form between 4-iodobenzoate ions and CCl4 in multilayer. ► DFT and SERS suggest strong interaction between CCl4 and benzoate oxygen atoms. ► Halogen bonding was not observed in the system without silver nanoparticles.We offer here evidence for halogen bonding induced by silver nanoparticles (SNPs) in a multilayer containing 4-iodobenzoate ion (4IBI) and CCl4. SERS experiments show in the monolayer that CCl4 does not adsorb and 4-iodobenzoic acid (4IBA) adsorbs as 4IBI. SEIRA experiments reveal that 4IBI forms in the multilayer during deposition from CCl4 on SNPs. Further infrared experiments on clean BaF2 prove that 4IBI formation caused by underlying SNPs was necessary for CCl4 inclusion in a 4IBI multilayer. Several potential scenarios involving intermolecular attraction between CCl4 and 4IBI are proposed to explain the results. Although halogen bonding involving solvents has been theoretically and experimentally demonstrated in solution phase chemistry, in bulk crystals, and at the monolayer level, here it is shown that halogen bonding interactions can also be significant in multilayer films. Results from this work will likely impact a range of applications across diverse fields where halogen bonding in thin films and nucleation chemistry are important.
Keywords: 4-Iodobenzoic acid; 4-Iodobenzoate; SEIRA; SERS; Carbon tetrachloride;
Preparation of superhydrophobic Fe2O3 nanorod films with the tunable water adhesion by Zhiwei Hu; Wen Li (245-249).
Display Omitted► A simple and inexpensive method to prepare α-Fe2O3 nanorods. ► Films with a hierarchical microtexture. ► Extraordinary superhydrophobicity and controllable water adhesion.We describe a simple and inexpensive method to prepare α-Fe2O3 nanorods films on glass slides fabricated via a simple hydrothermal procedure at 120 °C. Such films exhibit a hierarchical microtexture, and after the surface modification, they show extraordinary superhydrophobicity and the controllable water adhesion. Such superhydrophobic surfaces of the ferric oxides imply wide industrial applications.
Keywords: Superhydrophobic; Adhesion; α-Fe2O3;
Pitch reduction lithography by pressure-assisted selective wetting and thermal reflow by Hyung Sik Um; Jae Joon Chae; Sung Hoon Lee; Yudi Rahmawan; Kahp Y. Suh (250-254).
Display Omitted► We present a new pitch reduction lithographic technique by selective wetting. ► A meniscus was exploited to reduce the feature size of original line pattern. ► The line width was controllable by concentration and ashing time. ► The pattern shape was reconfigurable under different reflow conditions.We report on a new pitch reduction lithographic technique by utilizing pressure-assisted selective wetting and thermal reflow. The primary line-and-space pattern of low molecular weight polystyrene (PS) (Mw = 17,300) was formed by solvent-assisted capillary force lithography (CFL), on which a diluted photoresist (PR) solution was selectively filled into the spaces by the application of a slight pressure (200 g cm−2). Subsequent removal of the PS pattern by toluene and ashing process led to a line pattern with approximately 50% pitch reduction. It was observed that the size reduction and space to width ratios were controllable by changing PR concentration and ashing time.
Keywords: Pitch reduction; Patterning; Capillary force lithography; Reflow;
Effects of UV irradiation on the wettability of chitosan films containing dansyl derivatives by A.P.P. Praxedes; A.J.C. da Silva; R.C. da Silva; R.P.A. Lima; J. Tonholo; A.S. Ribeiro; I.N. de Oliveira (255-261).
Display Omitted► The addition of dansyl derivatives modifies the morphology of chitosan-based films. ► Wetting properties of chitosan films are strongly sensitive to the pulsed UV laser. ► The dansyl immobilization in chitosan backbone reduces the film photostability. ► UV irradiation enhances the surface energy of films even below the ablation threshold.The morphological and wetting properties of chitosan films containing dansyl derivatives have been investigated. By means of dynamic contact angle measurements, we study the modification of surface properties of chitosan-based films due to UV irradiation. The results were analyzed in the light of the molecular-kinetic theory which describes the wetting phenomena in terms of the statistical dynamics for the displacement of liquid molecules in a solid substrate. Our results show that the immobilization of dansyl groups in the chitosan backbone leads to a pronounced enhancement of the UV sensitivity of polymeric films.
Keywords: Chitosan; Dansyl; UV irradiation; Wetting phenomena;
Adhesion forces between AFM tips and superficial dentin surfaces by I.M. Pelin; A. Piednoir; D. Machon; P. Farge; C. Pirat; S.M.M. Ramos (262-268).
Display Omitted► The average adhesion forces on the processed dentin substrates are measured. ► We quantitatively analyze the effect of acid etching on the surface heterogeneity and the surface roughness. ► We determine, for the first time, the specific contribution of the organic constituents to the dentin adhesion.In this work, we study the adhesion forces between atomic force microscopy (AFM) tips and superficial dentin etched with phosphoric acid. Initially, we quantitatively analyze the effect of acid etching on the surface heterogeneity and the surface roughness, two parameters that play a key role in the adhesion phenomenon. From a statistical study of the force–distance curves, we determine the average adhesion forces on the processed substrates. Our results show that the average adhesion forces, measured in water, increase linearly with the acid exposure time. The highest values of such forces are ascribed to the high density of collagen fibers on the etched surfaces. The individual contribution of exposed collagen fibrils to the adhesion force is highlighted. We also discuss in this paper the influence of the environmental medium (water/air) in the adhesion measurements. We show that the weak forces involved require working in the aqueous medium.
Keywords: Adhesion forces; AFM; Dentin; Etching; Collagen;
Modeling the liquid filling in capillary well microplates for analyte preconcentration by Yang Yu; Xuewei Wang; Tuck Wah Ng (269-273).
Display Omitted► Capillary microplate wells with hydrophobic surfaces offers preconcentration with self-filling. ► Simulations show that the gravitational effect cannot be ignored for high liquid volumes. ► A modifying equation from a series of simulation results accounted for the gravitational effect. ► The presence of multiple holes under the droplet did not affect the simulation outcomes much.An attractive advantage of the capillary well microplate approach is the ability to conduct evaporative analyte preconcentration. We advance the use of hydrophobic materials for the wells which apart from reducing material loss through wetting also affords self entry into the well when the droplet size reduces below a critical value. Using Surface Evolver simulation without gravity, we find the critical diameters Dc fitting very well with theoretical results. When simulating the critical diameters D c G with gravity included, the gravitational effect could only be ignored when the liquid volumes were small (difference of 5.7% with 5 μL of liquid), but not when the liquid volumes were large (differences of more than 22% with 50 μL of liquid). From this, we developed a modifying equation from a series of simulation results made to describe the gravitational effect. This modifying equation fitted the simulation results well in our simulation range (100° ⩽ θ ⩽ 135° and 1 μL ⩽ V ⩽ 200 μL). In simulating the condition of multiple wells underneath each droplet, we found that having more holes did not alter the critical diameters significantly. Consequently, the modifying relation should also generally express the critical diameter for multiple wells under a droplet.
Keywords: Microplate; Capillary; Surface Evolver; Analyte preconcentration;
Roughness assessment and wetting behavior of fluorocarbon surfaces by Antonia Terriza; Rafael Álvarez; Ana Borrás; José Cotrino; Francisco Yubero; Agustín R. González-Elipe (274-282).
Display Omitted► Fluorocarbon films with different F/C ratios are prepared by adjusting the plasma. ► Wetting behavior of C―F films depends strongly on their surface roughness. ► Superhydrophobic C―F surfaces require both a high F/C ratio and a high roughness. ► AFM roughness may be erroneous if measured on small observation scales. ► Wenzel model needs consistent roughness data to assess the wetting of rough surfaces.The wetting behavior of fluorocarbon materials has been studied with the aim of assessing the influence of the surface chemical composition and surface roughness on the water advancing and receding contact angles. Diamond like carbon and two fluorocarbon materials with different fluorine content have been prepared by plasma enhanced chemical vapor deposition and characterized by X-ray photoemission, Raman and FT-IR spectroscopies. Very rough surfaces have been obtained by deposition of thin films of these materials on polymer substrates previously subjected to plasma etching to increase their roughness. A direct correlation has been found between roughness and water contact angles while a superhydrophobic behavior (i.e., water contact angles higher than 150° and relatively low adhesion energy) was found for the films with the highest fluorine content deposited on very rough substrates. A critical evaluation of the methods currently used to assess the roughness of these surfaces by atomic force microscopy (AFM) has evidenced that calculated RMS roughness values and actual surface areas are quite dependent on both the scale of observation and image resolution. A critical discussion is carried out about the application of the Wenzel model to account for the wetting behavior of this type of surfaces.
Keywords: CFX thin films; Roughness; Wetting; Plasma deposition; Wenzel model; AFM;
Micromechanical cohesion force measurements to determine cyclopentane hydrate interfacial properties by Zachary M. Aman; Sanjeev E. Joshi; E. Dendy Sloan; Amadeu K. Sum; Carolyn A. Koh (283-288).
Display Omitted► Direct measurements of hydrate cohesion shown in water, hydrocarbon and gas phases. ► Unconverted water on the hydrate surface increases cohesive forces through a capillary bridge. ► Hydrate adhesive force on stainless steel reduced by 96% through a wax coating on the surface.Hydrate aggregation and deposition are critical factors in determining where and when hydrates may plug a deepwater flowline. We present the first direct measurement of structure II (cyclopentane) hydrate cohesive forces in the water, liquid hydrocarbon and gas bulk phases. For fully annealed hydrate particles, gas phase cohesive forces were approximately twice that obtained in a liquid hydrocarbon phase, and approximately six times that obtained in the water phase. Direct measurements show that hydrate cohesion force in a water-continuous bulk may be only the product of solid–solid cohesion. When excess water was present on the hydrate surface, gas phase cohesive forces increased by a factor of three, suggesting the importance of the liquid or quasi-liquid layer (QLL) in determining cohesive force. Hydrate-steel adhesion force measurements show that, when the steel surface is coated with hydrophobic wax, forces decrease up to 96%. As the micromechanical force technique is uniquely capable of measuring hydrate-surface forces with variable contact time, the present work contains significant implications for hydrate applications in flow assurance.
Keywords: Hydrate; Agglomeration; Micromechanical; Cohesion force; Interfacial tension; Liquid bridge; Wettability;
Interaction of chitosan and mucin in a biomembrane model environment by Cristiane A. Silva; Thatyane M. Nobre; Felippe J. Pavinatto; Osvaldo N. Oliveira (289-295).
Display Omitted► Electrostatic interactions govern interaction between mucin and chitosan in a cell membrane model. ► Mucin expands Langmuir monolayers from negatively charged phospholipid. ► Chitosan is able to remove mucin from a phospholipid monolayer. ► Desorption of mucin from LB films was induced by chitosan.Chitosans have been widely exploited in biological applications, including drug delivery and tissue engineering, especially owing to their mucoadhesive properties, but the molecular-level mechanisms for the chitosan action are not known in detail. It is believed that chitosan could affect the mucus by interacting with the proteins mucins, in a process mediated by the cell membrane. In this study we used Langmuir monolayers of dimyristoylphosphatidic acid (DMPA) as simplified membrane models to investigate the interplay between the activity of mucins and chitosan. Surface pressure and surface potential measurements were performed with DMPA monolayers onto which chitosan and/or mucin was adsorbed. We found that the expanding effect from mucin was considerably reduced when chitosan was injected after mucin had been adsorbed on the DMPA monolayer. The results were consistent with the formation of complexes between mucin and chitosan, thus highlighting the importance of electrostatic interactions. Furthermore, chitosan could remove mucin that was co-deposited along with DMPA in Langmuir–Blodgett (LB) films, which could be ascribed to molecular-level interactions between chitosan and mucin inferred from the FTIR spectra of the LB films. In conclusion, the results with Langmuir and LB films suggest that electrostatic interactions are crucial for the mucoadhesive mechanism, which is affected by the complexation between chitosan and mucin.
Keywords: Cell membrane models; Langmuir monolayers; Chitosan; Mucins; Mucoadhesion;
Interfacial layers from the protein HFBII hydrophobin: Dynamic surface tension, dilatational elasticity and relaxation times by Nikola A. Alexandrov; Krastanka G. Marinova; Theodor D. Gurkov; Krassimir D. Danov; Peter A. Kralchevsky; Simeon D. Stoyanov; Theodorus B.J. Blijdenstein; Luben N. Arnaudov; Eddie G. Pelan; Alex Lips (296-306).
Display Omitted► After expansion, surface tension relaxes exponentially indicating barrier control. ► The barrier is due to the energy of monomer detachment from a HFBII tetramer. ► After compression, the surface tension relaxation indicates diffusion control. ► This could be surface diffusion during HFBII “condensation” on surface aggregates. ► The condensation reduces the dilatational elasticity at higher surface pressures.The pendant-drop method (with drop-shape analysis) and Langmuir trough are applied to investigate the characteristic relaxation times and elasticity of interfacial layers from the protein HFBII hydrophobin. Such layers undergo a transition from fluid to elastic solid films. The transition is detected as an increase in the error of the fit of the pendant-drop profile by means of the Laplace equation of capillarity. The relaxation of surface tension after interfacial expansion follows an exponential-decay law, which indicates adsorption kinetics under barrier control. The experimental data for the relaxation time suggest that the adsorption rate is determined by the balance of two opposing factors: (i) the barrier to detachment of protein molecules from bulk aggregates and (ii) the attraction of the detached molecules by the adsorption layer due to the hydrophobic surface force. The hydrophobic attraction can explain why a greater surface coverage leads to a faster adsorption. The relaxation of surface tension after interfacial compression follows a different, square-root law. Such behavior can be attributed to surface diffusion of adsorbed protein molecules that are condensing at the periphery of interfacial protein aggregates. The surface dilatational elasticity, E, is determined in experiments on quick expansion or compression of the interfacial protein layers. At lower surface pressures (<11 mN/m) the experiments on expansion, compression and oscillations give close values of E that are increasing with the rise of surface pressure. At higher surface pressures, E exhibits the opposite tendency and the data are scattered. The latter behavior can be explained with a two-dimensional condensation of adsorbed protein molecules at the higher surface pressures. The results could be important for the understanding and control of dynamic processes in foams and emulsions stabilized by hydrophobins, as well as for the modification of solid surfaces by adsorption of such proteins.
Keywords: HFBII hydrophobin; Surface relaxation times; Hydrophobic force; Dilatational surface elasticity; Storage and loss moduli;
Wettability determined by capillary rise with pressure increase and hydrostatic effects by Bigui Wei; Qing Chang; Caiyun Yan (307-311).
Display Omitted► We investigate the hydrostatic effects in the capillary rise. ► Derived an improved expression. ► Feasibility confirmed by high correlation coefficients and good reproducibility. ► The validity of the improved expression was confirmed. ► It becomes possible to more precisely measure the wettability of small particles.Capillary rise is the basis of some methods that are widely applied for the determination of contact angles as well as wettabilities of small particles. The equivalent hydraulic radius r d in the Classical Washburn equation is assumed to be particle-specific. But it seems that r d is not always constant when the type of liquids is different. The new equation with the pressure increment and the hydrostatic effects are theoretically derived based on the Washburn equation, so contact angles of small particles can be measured experimentally independently of r d. The result shows the validity of the proposed method, and therefore, it becomes possible to accurately measure the wettability of small particles.
Keywords: Contact angle; Capillary rise; Washburn equation; Wettability; Particle;
Magnetic Fe3O4@mesoporous silica composites for drug delivery and bioadsorption by Shanshan Huang; Chunxia Li; Ziyong Cheng; Yong Fan; Piaoping Yang; Cuimiao Zhang; Kuiyue Yang; Jun Lin (312-321).
Display Omitted► 4 Magnetic Fe3O4@MS with different morphologies and pore structures were synthesized. ► 4 Low cytoxicity of these magnetic composites make them potential drug carriers. ► 4 Fe3O4@MS with large pore sizes can be vectors for aspirin and BSA.Magnetic Fe3O4@mesoporous silica (MS) composites were synthesized by generating Fe3O4 nanoparticles in the mesoporous silica matrix using the sol–gel method in nitrogen atmosphere. The mesoporous silica hosts include SBA-15 particles owning highly ordered p6mm mesostructure, siliceous mesostructured cellular foams (MCFs), and fiber-like mesoporous silica (FMS) with unique pore structures. The X-ray diffraction (XRD), transmission electron microscopy (TEM), and N2 adsorption/desorption results show that Fe3O4 functionalized MCFs and FMS possess suitable mesoporous structure for the adsorption of both small-molecular drug and large biomolecules. The biocompatibility tests on L929 fibroblast cells using MTT assay reveal low cytotoxicity of these systems. These Fe3O4@mesoporous silica composites show sustained release properties for aspirin in vitro. The release of the aspirin molecules from the pores of the Fe3O4@mesoporous silica composites is basically a diffusive process. Fe3O4@MCFs and Fe3O4@FMS owning larger pore size are good candidates for the adsorption of bovine serum albumin (BSA). These magnetic composites can be potential vectors for drug delivery and bioadsorption.
Keywords: Magnetic mesoporous silica; Biocompatibility; Drug delivery; BSA adsorption;
Study of colloidal particle Brownian aggregation by low-coherence fiber optic dynamic light scattering by Hui Xia; Ru Yi Pang; Rui Zhang; Cai Xia Miao; Xiao Yun Wu; Xue Shun Hou; Cheng Zhong (322-326).
Display Omitted► The aggregation of particles in dense suspensions can be measured using low-coherence FODLS. ► The aggregation rate increases with the electrolyte concentration. ► The aggregation rate increases with the particle concentration. ► The aggregation process is a reaction-limited aggregation process.The aggregation kinetics of particles in dense polystyrene latex suspensions is studied by low-coherence fiber optic dynamic light scattering. Low-coherence fiber optic dynamic light scattering is used to measure the hydrodynamic radius of the aggregates. The aggregation kinetics data obtained can be fitted into a single exponential function, which is the characteristic of slow aggregation. It is found that the aggregation rate of particles increased with higher electrolyte levels and with larger particle concentrations. The experimental results can be explained by use of the Derjaruin–Landau–Verwey–Overbeer (DLVO) theory.
Keywords: Aggregation; Low-coherent fiber optic dynamic light scattering; Slow aggregation; DLVO theory;
Study and enhance the photovoltaic properties of narrow-bandgap Cu2SnS3 solar cell by p–n junction interface modification by Qinmiao Chen; Xiaoming Dou; Yi Ni; Shuyi Cheng; Songlin Zhuang (327-330).
Display Omitted► Photovoltaic properties of narrow-bandgap Cu2SnS3 (CTS) are studied for the first time. ► CTS can be a promising candidate as bottom cell absorber layer for low-cost thin film tandem solar cell application. ► A p–n junction interface modification method that can enhance the performance of the studied CTS solar cell is demonstrated.Photovoltaic properties of narrow-bandgap Cu2SnS3 (CTS) are studied for the first time by employing a superstrate solar cell structure of fluorine-doped tin oxide (FTO) glass/TiO2/In2S3/CTS/Mo. The structural, optical, and electronic characteristics of the CTS make it great potential as bottom cell absorber material for low-cost thin film tandem solar cell application. Furthermore, by inserting a thin low temperature deposited In2S3 layer between the In2S3 buffer layer and the CTS absorber layer, an enhancement in the performance of the solar cell can be achieved, leading to about 75% improvement (η = 1.92%) over the unmodified device (η = 1.10%).
Keywords: Narrow-bandgap Cu2SnS3; Photovoltaic properties; p–n junction interface modification;
Competitive ligand exchange on akaganéite surfaces enriches bulk chloride loadings by Xiaowei Song; Jean-François Boily (331-333).
Display Omitted► We report evidence for linked surface-bulk reactions. ► Competitive adsorption impacts hollandite-type material properties. ► Pools of surface-bound electrolyte ions are readily dislodged by foreign ions.Akaganéite (β-FeOOH) is a nanosized iron oxyhydroxide mineral with a hollandite structure containing chloride ions in 0.4 × 0.4 nm wide channels. Proton and chloride co-sorption into these channels induces variations in bulk O–H stretching vibrations, crystallographic lattice size, and thermal stability, as a result of hydrogen bond formation with chloride ions. In this work, we show that chloride ions bound to akaganéite surfaces can be dislodged into aqueous solutions by competitive adsorption of foreign ions and then transferred alongside co-sorbed protons into the akaganéite bulk. Fourier transform infrared and X-ray photoelectron spectroscopic measurements show that HClO4, H2SO4, and benzoic acid, and thereby, many other anions of various charge-to-size ratios can all effectively contribute to this phenomenon. This linked surface-bulk reactivity should be accounted for in mixed anion systems containing akaganéite-like materials.
Keywords: β-FeOOH; Competitive adsorption; Chloride occupancy; FTIR;