Journal of Colloid And Interface Science (v.347, #2)

Cover 1 (OFC).

Adsorption of cysteine to ZnS colloids decreased attachment efficiency of the particles during aggregation. Serine did not adsorb to particles and, as a result, did not alter ZnS aggregation rates.Mineral sulfide colloids and nanoparticles are important for the aquatic fate and transport of toxic metals such as zinc and mercury in anaerobic environments. The persistence of metal sulfides in the colloidal form is likely to depend on surface interactions with dissolved natural organic matter. In this work, we investigated the sorption of cysteine and serine on ZnS and HgS particles and the implications for colloidal stability. These amino acids were used as model compounds for small molecular weight natural organic acids. Cysteine was found to increase colloidal stability by adsorbing to particle surfaces and modifying the surface potential of the particles. In contrast, serine did not adsorb in appreciable amounts and as a consequence, did not appear to alter surface properties and particle attachment efficiencies. The pH of the aqueous phase was another critical component for controlling aggregation kinetics of cysteine-coated ZnS particles. Colloidal stability was promoted at pH values greater than 7 due to deprotonation of functional groups on the mineral surface and sorbed cysteine molecules. These results indicate that specific surface coordination of thiol-containing natural organic acids is important for the colloidal stability of ZnS, HgS, and other metal sulfides in water.
Keywords: Metal sulfides; Nanoparticles; Attachment efficiency; Sulfhydryl; Natural organic matter; Amino acids; Environmental;

Synthesis, optical properties and growth process of In2S3 nanoparticles by Jiajia Ning; Kangkang Men; Guanjun Xiao; Liyan Zhao; Li Wang; Bingbing Liu; Bo Zou (172-176).
In2S3 nanoparticles with size of 6 nm have been synthesized. The absorption and emission spectra reflect the nucleation and growth process of nanoparticles in the reaction and obvious quantum size effect in nanoparticles.Cubic β-In2S3 nanoparticles (NPs) have been synthesized by a simple and facile way, which is 6 nm in size. Absorption and emission spectra of In2S3 NPs show obvious blue peak shift compared to band gap of bulk In2S3, indicating the strong quantum size confinement effect. The fluorescence quantum yield of In2S3 NPs is found to be 10%. During the synthesis process, the absorption spectra have no peak shift, which is responding to transition from valence band to the conduction band levels. This absorption spectra show that the nucleation and growth process of In2S3 NPs is very quick. The PL lifetime spectra and time resolved spectra give two emission processes in In2S3 NPs, which would be excitonic recombination and electron–hole recombination via defects levels. The blue shift of emission peaks show the emission process in In2S3 NPs is from mainly electron–holes recombination via defects levels to excitonic recombination. The Stokes shift becomes smaller which is mainly contributed by blue shift of emission and smaller contribution from the UV–Vis absorption. The absorption and emission spectra show the size and crystallinity of In2S3 NPs have no changes (HRTEM images provide enough proofs); however the surface-related defects changed greatly in the reaction process.
Keywords: β-In2S3 nanoparticles; Stokes shift; Nucleation and growth; Surface-related defect;

Geometrical study of electrorheological activity with shape-controlled titania-coated silica nanomaterials by Jin-Yong Hong; Moonjung Choi; Chanhoi Kim; Jyongsik Jang (177-182).
The electrorheological activity of titania-coated silica nanomaterials with three different shapes (nanosphere, nanorod, nanotube) exhibited a dependence on the aspect ratio.The titania-coated silica nanomaterials with three different shapes (nanosphere, nanorod, nanotube) are fabricated to examine the influence of particle geometry on ER fluid in nanometer-size region. The effect of particle geometry on ER activity is studied by varying the geometric aspect ratio of dispersing materials. The ER activities of titania-coated silica nanomaterials exhibit a dependence on their aspect ratio. Interestingly, the shear stress of titania-coated silica nanomaterials based ER fluids increases with increasing the aspect ratio. Geometrical study is performed to give deep insights into the primary factors that determine the ER activity. It is believed that the geometrical effect originated from high aspect ratio played a dominant role in enhancing the performance of ER fluid. Furthermore, the dielectric property analysis based on dielectric loss model clarifies that an increase in aspect ratio has been coupled with the larger achievable polarizability and short relaxation time of interfacial polarization. Consequently, the increment in aspect ratio has strong influence on ER activity, provides outstanding enhancement in shear stress value of titania-coated silica nanotube based ER fluid.
Keywords: Colloids; Functional coating; Silica; Stimuli–responsive materials; Structure–property relationships;

Direct fibre simulation of carbon nanofibres suspensions in a Newtonian fluid under simple shear by Mikio Yamanoi; C. Leer; F.W.J. van Hattum; O.S. Carneiro; J.M. Maia (183-191).
The current work studies the effect of simple shear flows on the dispersion of carbon nanofibres in a low viscosity Newtonian matrix by a direct fibre simulation and experiments.This work studies the effect of simple shear flows on the dispersion of carbon nanofibres (CNF) in a low viscosity Newtonian matrix. Analysis was performed by using a direct fibre simulation based on Particle Simulation Method (PSM) especially focusing on structure changes under shear flows. Suspensions of CNF/epoxy of different concentrations varying from 0.1 to 3.0 wt% were prepared by simple hand-mixing the as-received fibres with the epoxy resin. These suspensions were then subjected to different flow conditions (shear rates and strains) and their rheological behaviour was characterised. It is demonstrated that simulation can reproduce shear-thinning and structure developments induced by shear flow at different shear rates. Especially at low shear rates, flow induced helical bands were predicted by simulation, which was observed in experiments performed by other researchers and reported in the literature. From the results obtained it is concluded that the direct fibre simulator is a useful tool to design nano-scale fibre composites, allowing for optimisation of the critical parameters to determine the most adequate conditions leading to the required level of fibre dispersion.
Keywords: Fibre simulation; Carbon nanofibres; Rheology; Shear thinning; Van der Waals interaction;

Hydrodynamic radii and diffusion coefficients of particle aggregates derived from the bead model by Zbigniew Adamczyk; Krzysztof Sadlej; Eligiusz Wajnryb; Maria L. Ekiel-Jeżewska; Piotr Warszyński (192-201).
Modelling bioparticle shapes by strings of beadsThe multiple expansion method was applied for calculating friction tensors and hydrodynamic radii RH of rigid molecules of various shape, composed of ns equal sized, touching spheres. The maximum value of ns studied was 450, which covers most situations met in practice. Calculations were performed for linear chains, half-circles, circles (cyclic molecules) and S-shaped aggregates. It was shown that our results agreed with previous theoretical data obtained for linear chains and cyclic aggregates, for ns< 100. For larger ns , studied exclusively in our work, interpolating analytical expressions were formulated for the hydrodynamic radii RH . These expressions, involving logarithmic function of the aspect ratio parameter (length to width ratio of the macromolecules), are the main finding of our work. Using these expressions, the ratio of the hydrodynamic radius of cyclic-to-linear aggregate qf was calculated, which is a parameter of vital significance. It was determined that qf attained values close to 0.95 for ns ∼450. This suggests that the previous analytical results derived by Tchen , in the slender body limit, who predicted that qf  → 12/11 = 1.09, are not applicable for ns< 450. Using the RH values, the average translation diffusion coefficients and the sedimentation coefficients for these aggregate shapes were calculated. It was shown that our theoretical results are in good agreement with experimental data obtained for polyelectrolytes and for DNA fragments of various molecular mass. It was concluded that our results can be effectively used to determine the shape of macromolecules, in particular to discriminate between linear and cyclic DNA configurations.
Keywords: Aggregates of particles of various shapes; Bead model of particle aggregates; Diffusion coefficients of particle aggregates; DNA bead model of; DNA fragment hydrodynamic radii; Hydrodynamic radius of aggregates; Linear chain aggregates; Sedimentation coefficients of aggregates and macromolecules;

When negatively charged colloidal particle suspensions are destabilized with cationic polyelectrolyte the colloidal stability approaches a plateau at higher polyelectrolyte dose.Sulfate-terminated latex particles were investigated in the presence of poly(diallyldimethyl ammonium chloride) (PDADMAC) at pH 4.0 in aqueous KCl electrolyte solutions by dynamic light scattering and electrophoresis, in particular, at high ionic strengths. The polyelectrolyte adsorbs to the latex particles quantitatively until the adsorption plateau is reached. The adsorbed amount at this plateau and the corresponding layer thickness increase with increasing ionic strength. The resulting layers have a thickness of several nanometers. Colloidal stability is qualitatively consistent with electrostatic double layer forces, especially since the system can be fully destabilized at high ionic strengths even at high polyelectrolyte doses. Additional attractive forces due to lateral charge heterogeneities seem to contribute to the destabilization of the system, even for the adsorbed layers in the saturated state. However, this layer does not provide any additional stabilization mechanism due to steric repulsion forces, since the adsorbed polyelectrolyte layers are thin and laterally heterogeneous even in their saturated state.
Keywords: Colloidal stability; Aggregation; Charge reversal; Overcharging; Adsorption;

Mathematical modeling of DNA-mediated selective aggregation of CdS quantum dots by Taehoon Kim; Dongcheol Choe; Sang-Woo Joo; So Yeong Lee; Kangtaek Lee (209-214).
We have successfully modeled the DNA-mediated selective aggregation of CdS quantum dots, which results in a fluorescence-quenching phenomenon.We report a mathematical modeling of the DNA-mediated selective aggregation of CdS quantum dots. Addition of hybridized double-stranded DNAs into the suspensions of CdS quantum dots at the optimal salt concentration causes a selective aggregation and a fluorescence-quenching phenomenon depending on the target DNA sequence. We monitor the aggregation process with quasi-elastic light scattering (QELS), zeta potential, and conductivity measurements at different salt concentrations. To model the aggregation process, we use the constant-number Monte Carlo method with the aggregation kernel that accounts for the interparticle interaction from the classical DLVO model. We find that the calculated results are in good agreement with the experiments, and that the fractal dimension of the quantum dot aggregates is 2.3. Modeling also allows us to estimate that the total number of initial quantum dots in aggregates at the beginning of the fluorescence-quenching phenomenon is approximately 200. The insights gained in this study should be useful in the design of biosensors based on the fluorescence-quenching phenomenon caused by the quantum dot aggregation.
Keywords: CdS quantum dot; Aggregation; DNA; Sensor; Constant-number Monte Carlo; Fluorescence quenching;

Highly dispersed ZnO quantum dots (QDs) in poly(vinyl pyrrolidone) (PVP) nanofibers with enhanced ultraviolet emission have been successfully prepared by electrospinning technique. By adjusting the electrospinning voltage, the UV emission intensity of the composites nanofibers could be controlled.Highly dispersed ZnO quantum dots (QDs) in poly(vinyl pyrrolidone) (PVP) nanofibers have been successfully prepared by electrospinning technique. The structure and optical properties were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), resonant Raman spectra, Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric and differential thermal analysis (TG–DTA), ultraviolet (UV)–vis absorption spectra, and photoluminescence (PL) spectra. In the PVP/ZnO QDs composite nanofibers, PVP molecules could effectively prevent the aggregation of ZnO QDs and passivate the surface defects of ZnO QDs. Thus, by comparing ZnO QDs, the composite nanofibers exhibited a blue-shifted band gap and enhanced ultraviolet (UV) emission. Furthermore, the composite nanofibers prepared at higher voltage showed more intense UV emission than which obtained at lower voltage, suggesting that the UV emission intensity of the composite nanofibers could be controlled by adjusting the electrospinning voltage.
Keywords: Electrospinning; Poly(vinyl pyrrolidone); ZnO quantum dots; Photoluminescence;

SEM photomicrograph of aragonite obtained by aging EG solutions containing 0.75 mol dm−3 urea, 0.25 mol dm−3 CaCl2 at 160 °C for 10 min.An innovative precipitation process, achieved through the thermal decomposition of urea in polyols containing hydrated calcium salts, was used to prepare calcite and aragonite at elevated temperatures (120–180 °C). The effect of various experimental conditions, such as the media of different polyols (ethylene glycol, EG; diethylene glycol, DEG; and tetraethylene glycol, TEG), the temperature, the reaction time, and the addition of magnesium salts, on the structure, size, and morphology of the obtained solids is described. It was found that the formation of calcium carbonate polymorphs, i.e., calcite or aragonite, their morphology and their size was predominantly influenced by the type of polyols used, and by the diverse growing mechanisms occurring in the different polyol systems. Structurally and morphologically different calcite precipitates were formed in the DEG and TEG solvents via classical crystallization processes, while colloidal and nanostructured aragonite particles were assembled in the EG through a recently reaffirmed mechanism based on the role of nanoscale aggregation processes in the formation of carbonate solids. This study highlights the importance of the presence and concentration of magnesium ions in the inhibition of the crystal growth of nanosized aragonite, and in the stabilization of amorphous calcium carbonate (ACC) precipitates in polyol solutions.
Keywords: Aggregation; Calcite; Aragonite; Polyols; Precipitation;

Ethylammonium nitrate in high temperature stable microemulsions by Oliver Zech; Stefan Thomaier; Agnes Kolodziejski; Didier Touraud; Isabelle Grillo; Werner Kunz (227-232).
By replacing water in microemulsions by a room-temperature ionic liquid, a thermal stability between 30 °C and 150 °C at ambient pressure can be obtained.The increasing number of publications reflects the still growing interest in nonaqueous microemulsions containing room-temperature ionic liquids. Recently, we characterized microemulsions composed of the room-temperature ionic liquid ethylammonium nitrate (EAN) as polar phase, dodecane as continuous phase and 1-hexadecyl-3-methyl imidazolium chloride ([C16mim][Cl]), an IL that exhibits surfactant properties, and decanol as cosurfactant at ambient temperature. We demonstrate here the high thermal stability of these microemulsions. Along an experimental path, no phase change could be observed visually within a temperature range between 30 °C and 150 °C. The microemulsions are characterized with quasi-elastic light scattering measurements at ambient temperature and temperature dependent small angle neutron scattering (SANS) experiments between 30 °C and 150 °C. DLS measurements at ambient temperature indicate a swelling of the formed structures with increasing amount of EAN up to a certain threshold. The SANS experiments were performed below this threshold. The data evaluation of such concentrated systems like microemulsions is possible with the “generalized indirect Fourier transformation” method (GIFT). We evaluated the small angle scattering data via the GIFT method, for comparison we also applied the model of Teubner and Strey (TS) which was often used to describe scattering curves of microemulsions. The GIFT method gives good fits throughout the experimental path, while the TS model gives relatively poor fits. Both, light scattering and SANS results are in agreement with the existence of EAN droplets stabilized by surfactant with dodecane as continuous phase along the whole investigated temperature range. Moreover, these results clearly demonstrate the possibility to formulate high temperature stable microemulsions with ionic liquids at ambient pressure.
Keywords: Ionic liquid; Microemulsion; SANS; DLS; GIFT; High thermal stability;

Surface area per head group vs. number of carbon atoms in the dialkylamino group and the heterocycle group of novel quaternary ammonium surfactants and alkylphosphocholines.The physico-chemical properties of dialkylamino and nitrogen heterocyclic analogues of hexadecylphosphocholine (HPC) and cetyltrimethylammonium bromide (CTAB) were investigated. The surface properties, such as the critical micelle concentration (cmc), the surface tension value at the cmc (γ cmc), and the surface area at the surface saturation per head group (A cmc) were determined by means of surface tension measurements. Micelle size was determined using the dynamic light scattering method. The influence of dialkylamino groups and heterocyclic ring size on surface-active properties was investigated. Surface activity and micellar size of prepared analogues of HPC and CTAB were mutually compared.
Keywords: Alkylphosphocholines; Micelle size; Quaternary ammonium salts; Surface tension; Surface saturation; Zwitterionic surfactants;

Interaction between lysozyme and colloidal poly(NIPAM-co-acrylic acid) microgels by Christian Johansson; Jonas Gernandt; Melanie Bradley; Brian Vincent; Per Hansson (241-251).
The interaction between lysozyme and colloidal poly(NIPAM-co-acrylic acid) microgels is investigated in aqueous solutions at neutral pH. Lysozyme binding isotherms, obtained within the ionic strength range 10–220 mM, indicate that the maximum uptake at 10 mM is 2.4 g lysozyme per gram dry gel, and that the uptake capacity decreases with increasing ionic strength to ∼0 at 220 mM. Swelling isotherms, obtained from photon correlation spectroscopy measurements, show that the binding is accompanied by a substantial deswelling of the microgels. The microgel suspension is stable up to a protein-to-polymer charge ratio in the microgels of about 0.6, largely independent of ionic strength, whereas flocculation/sedimentation occurs at higher charge ratios. The charge ratio 0.6 corresponds to a zeta-potential of about −6 mV, as obtained from measurements of electrophoretic mobility. Binding and swelling isotherms are analyzed in detail and compared with predictions of theoretical model calculations. The influence of protein–protein attraction is highlighted, as well as the interplay between electrostatic interactions and network elasticity.
Keywords: Microgel; NIPAM; Acrylic acid; Lysozyme; Protein; Binding isotherm; Swelling isotherm; Colloidal stability; Electrophoretic mobility; Theoretical model;

Studies of Triton X-165–β-cyclodextrin interactions using both extrinsic and intrinsic fluorescence by Atanu Mahata; Debosreeta Bose; Debanjana Ghosh; Barnali Jana; Bhaswati Bhattacharya; Deboleena Sarkar; Nitin Chattopadhyay (252-259).
β-cyclodextrin forms an inclusion complex with Triton X-165. This inhibits the micellization process of TX-165 resulting in an increase in its apparent CMC in the presence of β-CD.The interaction of β-cyclodextrin with the non-ionic micelle-forming surfactant Triton X-165 (TX-165) has been studied using steady state fluorescence and fluorescence anisotropy techniques. Both extrinsic and intrinsic fluorescence have been exploited for the purpose. Phenosafranin (PSF), a cationic phenazinium dye, has been used as the extrinsic probe while fluorescence of TX-165 has served as the intrinsic one. PSF shows discernible interactions with both TX-165 and β-CD. The experimental results reveal that the extent of interaction of PSF with TX-165 is greater than with β-CD. However, addition of β-CD to a micellar solution of TX-165 containing PSF leads to a disruption of the micelles whereby the fluorophore is released from the micellar environment to the bulk aqueous phase. It has been substantiated that an inclusion complex is formed between the non-ionic surfactant and the cyclodextrin. A 1:1 stoichiometry of the TX-165–β-CD inclusion complex has been proposed. Such a complexation between TX-165 and β-CD results in an inhibition in the micellization process of TX-165 leading to an enhancement in the apparent CMC value. The inferences are drawn from a series of experiments, viz., binding studies, determination of micropolarity, heavy-ion quenching studies and steady state fluorescence anisotropy experiments monitoring both extrinsic and intrinsic fluorescences.
Keywords: Triton X-165; β-cyclodextrin; Phenosafranin; Intrinsic fluorescence; Fluorescence anisotropy;

Preparation of TiO2-loaded activated carbon fiber hybrids and application in a pulsed discharge reactor for decomposition of methyl orange by Yanzong Zhang; Shihuai Deng; Baiye Sun; Hong Xiao; Li Li; Gang Yang; Qi Hui; Jun Wu; Jingtang Zheng (260-266).
The COD removal from Methyl Orange solution could be increased significantly by the combination of pulsed discharge and TiO2/ACF due to adsorption of ACF and photocatalysis of TiO2.TiO2-loaded activated carbon fiber (TiO2/ACF) hybrids were prepared in a sol through a dip-coating method and added to a pulsed discharge reactor to enhance the decomposition of methyl orange. The crystalline phase transformation and the surface morphology of TiO2/ACF were investigated after calcination at various temperatures. X-ray diffraction results revealed the intensity of the diffraction peaks resulting from anatase increased in accordance with increasing calcination temperatures. An anatase-to-rutile phase transformation was observed for calcination at 1173 K. Morphology studies indicate that the TiO2 film fractured into irregular flakes on the ACF surface. TiO2/ACF calcined at 1173 K demonstrated the highest photocatalytic activity compared with samples calcined at lower temperatures. The enhancement of chemical oxygen demand removal may be due to the adsorption of ACF and the photocatalytic ozonation of TiO2 in the combined treatment. The surface morphology of TiO2/ACF showed no change after re-use. Although micropores slightly increased, mesopores significantly decreased, and some oxygen-containing surface groups increased on the ACF surface after re-use, the photocatalytic activity of TiO2/ACF was not affected.
Keywords: Photocatalyst; Activated carbon fiber; Pulsed discharge; Combined treatment;

Preferential removal of silicon nitride over silicon dioxide using 0.25 wt.% ceria abrasives and 0.32 wt.% poly(acrylicacid-co-diallyldimethylammonium chloride). At this concentration, the polymer adsorbs strongly on ceria, blocking the interaction of surface Ce3+ species with the oxide film and suppresses its removal but has no effect the nitride removal rate. At lower values of X, the ratio of the amount of polymer to ceria, the blockage is not complete.We show that by adding poly(acrylicacid-co-diallyldimethylammonium chloride), a cationic polymer with a weight average molecular weight of about 4200 g/mole, to ceria-based dispersions, it is possible to achieve a silicon nitride removal rate (RR) of >100 nm/min and a silicon dioxide RR of <2 nm/min at pH 4 and 4 psi down pressure during chemical mechanical polishing. Furthermore, the RRs of the silicon dioxide films can be tuned by varying the polymer to abrasive weight ratio in the dispersion while the nitride RR is unaffected. We also characterized the role of adsorption of this polymer additive on ceria, silica and silicon nitride powders using zeta potential, adsorption isotherms, UV–Vis spectroscopy, contact angle, thermo-gravimetric analysis and friction coefficient measurements. Our results show that the polymer film formed on the ceria particle surface is strongly bound to it, survives use in polishing and appears to control its reactivity with the silicon dioxide surface in conjunction with electrostatic interactions.
Keywords: CMP; Reverse selectivity; Colloids; High silicon nitride over silicon dioxide removal; Ceria; Polymers;

The synthesized nano-goethite and nano-hematite are effective materials for Cu2+ removal and, together with their photocatalytic activity, may be applied to alleviate environmental contaminations.Goethite and hematite nanomaterials (nano-goethite and nano-hematite) can be synthesized using a coprecipitation method. Nano-hematite is synthesized via the reaction of HCl and FeCl3 solution at 100 °C for 2 days, while nano-goethite is prepared by adding Fe2(SO4)3 into the 2.5 M NaOH solution for 4 h, and then heated at 40 °C for 2 days. Afterward the photocatalytic decomposition of methylene blue solution is performed by UV-light irradiation, and the adsorption procedure is carried out by batch experiments. It is observed that both nano-hematite and nano-goethite exhibit some photocatalytic activity and possess a high adsorption capacity for copper ions. The maximum Cu(II) adsorption capacity is 149.25 and 84.46 mg/g for nano-goethite and nano-hematite, respectively. Further, the experimental data are well fitted to the pseudo-second-order equation. It also suggests that the Langmuir isotherm is more adequate than the Freundlich isotherm in simulating the adsorption isotherm of Cu2+, and the Cu2+ adsorption onto nanomaterials is a spontaneous process. Therefore, these findings indicate that nano-goethite and nano-hematite are effective materials for Cu2+ removal and, together with its photocatalytic activity, may be applied in the removal of heavy metal ions from aqueous streams.
Keywords: Nano-goethite; Nano-hematite; Photocatalyst; Cu2+ adsorption;

Mechanisms of uranyl and phosphate (co)sorption: Complexation and precipitation at α-Al2O3 surfaces by Catherine Galindo; Mirella Del Nero; Remi Barillon; Eric Halter; Benoit Made (282-289).
P–O stretching vibration bands in a surface precipitate of uranyl phosphate on α-Al2O3.This study presents new in situ electrophoretic and ATR-FTIR data on the surface species controlling the cosorption of uranyl and phosphate ions in α-Al2O3 suspensions at acidic pH (3.3). It was shown that the uranyl sorption (i) was promoted in the presence of phosphate, (ii) induced significant changes in zeta potential of P-loaded alumina, and (iii) was governed by two mechanisms, surface complexation and surface precipitation, with the predominant species being mainly dependent on phosphate surface coverage. Formation of surface precipitates of uranyl phosphate at high phosphate surface coverage was inferred from the high negative charges imparted to the surface by uranyl and phosphate (co)sorption, and from assignments of IR bands at 1107, 1024, and 971 cm−1 to P–O-stretching vibrations for phosphate coordinated to uranyl, at the alumina surface. The ATR-FTIR study showed that the precipitates of uranyl phosphate formed at the surface of α-Al2O3 for aqueous concentrations of uranyl at trace levels. It also evidenced that formation of surface precipitates of U(VI)–phosphate was occurring along with the transformation of alumina into secondary surface precipitates of Al-phosphate, at very high phosphate concentrations. These findings are relevant to the mechanisms of adsorption of trace uranyl on naturally occurring oxide surfaces, in soils with low pH where cosorption of phosphate and uranyl ions is known to play a crucial role in the long-term retention of U.
Keywords: Alumina–solution interface; Uranyl; Phosphate; Surface precipitation; In situ ATR-FTIR spectroscopy; Zeta potential;

Dye adsorption onto activated carbons from tyre rubber waste using surface coverage analysis by Edward L.K. Mui; W.H. Cheung; Marjorie Valix; Gordon McKay (290-300).
Pore volumes of activated carbons from tyre chars pre-treated by H2SO4. Acid-treated chars reveal the lower reactivity that enables gasification to proceed under reaction limited phase. Both micro- and mesopores continue to develop even at 16 h of gasification.Two types of activated carbons from tyre char (with or without sulphuric acid treatment) were produced via carbon dioxide activation with BET surface areas in the range 59–1118 m2/g. Other characterisation tests include micropore and mesopore surface areas and volumes, pH, and elemental compositions, particularly heteroatoms such as nitrogen and sulphur. They were correlated to the adsorption capacity which were in the range of 0.45–0.71 mmol/g (untreated) and 0.62–0.84 mmol/g (acid-treated) for Acid Blue 25. In the case of larger-sized molecules like Acid Yellow 117, capacities were in the range of 0.23–0.42 mmol/g (untreated) and 0.29–0.40 mmol/g (acid-treated). Some tyre carbons exhibit a more superior performance than a microporous, commercial activated carbon (Calgon® F400). By modelling the dye adsorption equilibrium data, the Redlich–Peterson isotherm is adopted as it has the lowest SSE. Based on the surface coverage analysis, a novel molecular orientation modelling of adsorbed dyes has been proposed and correlated with surface area and surface charge. For the acid dyes used in this study, molecules were likely to be adsorbed by the mesopore areas.
Keywords: Adsorption; Dye; Surface coverage; Micropore; Mesopore; Surface charge;

Staphylococcal lipases stereoselectively hydrolyse the sn-2 position of monomolecular films of diglyceride analogs. Application to sn-2 hydrolysis of triolein by Habib Horchani; Nadia Ben Salem; Ali Chaari; Adel Sayari; Youssef Gargouri; Robert Verger (301-308).
The staphylococcal lipases significantly hydrolyse the secondary ester group of diglyceride analogs, with a strong preference for the R configuration.Using the monomolecular film technique, a kinetic study on the stereoselectivity of nine staphylococcal lipase forms was carried out with three pairs of enantiomers from diglyceride analogs (didecanoyl-deoxyamino-O-methyl glycerol, DDG) containing a single hydrolysable decanoyl ester group and two lipase-resistant groups. Our results show that the kinetic profiles of the wild type, the recombinant untagged and the recombinant tagged forms of staphylococcal lipases are significantly different. As with most of the lipases investigated so far, these staphylococcal lipases showed higher catalytic rates with primary esters than with secondary esters. However, it is noteworthy that all these staphylococcal lipases were found to significantly hydrolyse the secondary ester group of diglyceride analogs, with a strong preference for the R configuration. This stereopreference, which was predicted on the basis of Kazlauskas’ rule, was comparable to that of Candida rugosa and Pseudomonas glumae lipases. As was to be expected, all the staphylococcal lipases tested efficiently hydrolysed triolein at the sn-2 position. This hydrolytic activity was quantified by performing thin-layer chromatography to analyse the hydrolytic products of triolein. From the qualitative point of view, the sn-2 preferences observed with triolein and diglyceride analogs bearing a secondary ester function were in good agreement.Diglyceride analogs might therefore provide useful initial screening tools for use in future searches for strictly sn-2 specific lipases.
Keywords: Staphylococcal lipases; Sn-2 preference; Stereoselectivity; Diglyceride analogs; Monomolecular films;

Adsorptive removal of Cyanosine from wastewater using coconut husks by Vinod K. Gupta; Rajeev Jain; Meenakshi Shrivastava (309-314).
Effect of pH on the adsorption of Cyanosine over AC and ACH.A waste material – coconut husk has been used as a low cost adsorbent and its efficiency in Cyanosine sorption was compared with activated carbon. The influence of various factors such as adsorbent dose, adsorbate concentration, particle size, temperature, contact time and pH was studied. The adsorption of the dye over both the adsorbents was found to follow Langmuir and Freundlich adsorption isotherm models. Based on these models, different useful thermodynamic parameters have been evaluated. The adsorption of Cyanosine over activated carbon and activated coconut husks follows first order kinetics and the rate constants for the adsorption processes increase with temperature in the case of AC and decrease in the case of ACH.
Keywords: Adsorption; Coconut husk; Cyanosine dye; Adsorption kinetics; COD;

(Semi)-analytical solutions are derived for the displacement of a liquid by a gas. Contact angle may depend on interface velocity. Five liquid withdrawal scenarios may occur.The displacement of a gas by a liquid in both horizontal and inclined capillary tubes where the tube inlet is connected to a liquid reservoir of constant pressure can be described by the Lucas–Washburn theory. One can also use the Lucas–Washburn theory to model the reverse flow, that is, liquid withdrawal, even though the latter case has received relatively little attention. In this paper, we derive analytical solutions for the travel time of the gas–liquid interface as a function of interface velocity. The interface position can be obtained by numerically integrating the numerically inverted interface velocity. Therefore we refer to these solutions as (semi)-analytical. We neglect inertial forces. However, we account for a dynamic contact angle where the nondimensional non-equilibrium Young force depends on the capillary number in the form of either a power law or a power series. We explore the entire nondimensional parameter space. The analytical solutions allow us to show that five different liquid withdrawal scenarios may occur that differ in the direction of flow and the sign of the acceleration of the gas–liquid interface: horizontal, upward, steady-state downward, accelerating downward, and decelerating downward flow. In the last case, the liquid is withdrawn from the tube either completely or partially. The (semi)-analytical solutions are also valid within the limit where the contact angle is constant.
Keywords: Capillary flow; Dynamic contact angle; Liquid withdrawal; Drainage; Analytical solution; Lucas–Washburn;

Concentrating molecules in a simple microchannel by Hai Jiang; Yasaman Daghighi; Chan Hee Chon; Dongqing Li (324-331).
Concentrating sample molecules from a dilute solution in a microfluidic channel by electrokinetic means.A simple method is proposed and tested to concentrate sample molecules from a dilute solution in a microchannel by electrokinetic means. The microfluidic chip has a straight microchannel connecting two wells and three electrodes. This method uses electrokinetic trapping and flow control simultaneously to concentrate a charged species of interest. A numerical model of the sample concentration process is presented in this paper. Using a fluorescent dye as the sample molecules, experimental investigation into the concentration process was performed. The 90 times of the concentration increase was achieved in 110 s. The numerical simulations of the concentrating and the subsequent dispensing processes agree well with the experimental results.
Keywords: Concentration; Closed-end microchannel; Electrokinetics; Electrophoresis; Microfluidics;

Synthesis and use of self-assembled rhamnolipid microtubules as templates for gold nanoparticles assembly to form gold microstructures by Asma Rehman; Zulfiqar Ali Raza; Saif-ur-Rehman; Zafar M. Khalid; Chandramouleeswaran Subramani; Vincent M. Rotello; Irshad Hussain (332-335).
Self-assembled microtubules of natural rhamnolipids can produce gold nanoparticles at their surface. Heat treatment of resulting composites yielded porous gold microwires with fairly controlled nanoscale features.Natural unmodified rhamnolipids are thermally self-assembled into soft microtubules, which can produce gold nanoparticles onto themselves due to the presence of rhamnose sugar moieties at their surface. The loading of gold nanoparticles on composite microtubules can be controlled by varying the concentration of gold salt to rhamnolipid and the reaction temperature. The composite rhamnolipid–gold nanoparticle microtubules are then heat treated to produce porous gold microwire-like structures with fairly controlled nanostructured features, which may have interesting applications in catalysis, biosensing and electronics.
Keywords: Rhamnolipids; Gold nanoparticles; Biotemplate; Porous microwires;