Journal of Sol-Gel Science and Technology (v.64, #2)

Synthesis and characterization of FePt nanoparticles and FePt nanoparticle/SiO2-matrix composite films by Jun-Long Zhang; Ji-Zhou Kong; Ai-Dong Li; You-Pin Gong; Hai-Rong Guo; Qing-Yu Yan; Di Wu (269-275).
Superparamagnetic face-centered cubic (fcc) FePt nanoparticles were synthesized using a polyol process. The effect of reaction temperature and molar ratio of Fe(CO)5 to Pt(acac)2 on the structure, composition and morphology of nanoparticles has been investigated. The optimum processing condition has been obtained for producing well-monodisperse fcc-phase FePt nanoparticles with the 2:1 molar ratio of Fe-Pt at 220 °C. In order to circumvent the problem of FePt particle coalescence during high temperature annealing for the L10 ordering, FePt nanoparticle/SiO2-matrix composite films have been fabricated by sol–gel method. The experimental results confirm that the amorphous SiO2 matrix effectively inhibits the grain growth and particle aggregation during 700 °C annealing for 1 h. Well-monodisperse face-centered tetragonal (fct) FePt particles embedded in the SiO2 matrix can be obtained with the long-range chemical order parameter S of ~0.74, indicating partially ordered L10 phase transition in FePt/SiO2 composite films. The FePt/SiO2 system exhibits a hysteretic behavior with smaller coercive field of 1,450 Oe. The incomplete phase transition from cubic deredat height maxsium (A 1-disordered phase to tetragonal L10-ordered phase) might be responsible for it.
Keywords: L10-phase FePt; Sol–gel; Monodisperse particle; SiO2-matrix

Sol–gel preparation of double-layer tri-wavelength antireflective coating by Bo Xiao; Bibo Xia; Haibing Lv; Xingxiang Zhang; Bo Jiang (276-281).
Double-layer tri-wavelength antireflective (AR) coating effective simultaneously at 351, 527 and 1,053 nm has been designed and prepared by the sol–gel process. The refractive index and film thickness of bottom layer and up layer are 1.27 and 113 nm, and 1.17 and 245 nm, respectively. The bottom layer with refractive index of 1.27 was prepared from a mixture of acid-catalyzed and base-catalyzed silica sols, and the up layer with refractive index of 1.17 was prepared from polypropylene oxide modified silica sol. It was found that the addition of polypropylene oxide into the sol significantly decreased the refractive index and increased the hydrophobicity of the AR coating. The obtained tri-wavelength AR coating gives very high transmittance of 99.7, 99.1 and 98.0 % at 351, 527 and 1,053 nm, simultaneously.
Keywords: Sol–gel process; Antireflective coating; Hydrophobicity; Tri-wavelength

Nanoporous morphology of alumina films prepared by sol–gel dip coating method on alumina substrate by Manju Pandey; Kriti Tyagi; Prabhash Mishra; Debdulal Saha; K. Sengupta; S. S. Islam (282-288).
Nanoporous crack free alumina thin films were fabricated in two phases gamma (γ) and alpha (α) by sol–gel dip coating method. The thickness of the mesoporous films was increased with binder by varying its concentration, and with increasing the number of coating. The porosity, pore size, surface area and phase were controlled by sintering temperature. Interconnected pore structure of 8–15 nm diameter were successfully prepared by repeating the deposition several times. FESEM, BET, AFM and XRD techniques were employed for the microstructural characterization.
Keywords: Sol–gel; Thin-films; Binder; Dip-coating

Homogeneous and transparent ZrO2 thin films were prepared by sol–gel dip coating method. The prepared ZrO2 thin films were annealed in air and O2 atmosphere at 500, 700 and 900 °C for 1, 5 and 10 h. X-Ray diffraction (XRD) pattern showed the formation of tetragonal phase with a change of stress in the films. Scanning electron microscope (SEM) revealed the nucleation and particle growth on the films. An average transmittance of >80 % (in UV–Vis region) was observed for all samples. The refractive index and direct energy band gap were found to vary as functions of annealing atmosphere, temperature and time. Photoluminescence (PL) revealed an intense emission peak at 379 nm weak emission peaks at 294, 586 and 754 nm. An enhancement of PL intensity was observed in films annealed in O2 atmosphere. This is due to reconstruction of zirconium nanocrystals interfaces, which help passivate the non-radiative defects. At 900 °C, oxygen atoms react with Zr easily at the interface and destroy the interface states acting as emission centres and quench the PL intensity of the film. The enhancement of the luminescence properties of ZrO2 by the passivation of non radiative defects presents in the films make it suitable for gas sensors development, tuneable lasers and compact disc (CD) read-heads.
Keywords: ZrO2 ; Thin films; Sol–gel; Photoluminescence; XRD; Scanning electron microscope (SEM)

In this study, in order to develop a new photosensitive gel film, Nb2O5 gel films including a chelate ring were prepared by the sol–gel method. Photosensitive and patterning properties of the gel films were investigated. Properties such as refractive index for annealed films were also evaluated. In the electronic absorption spectra of the gel films, the absorption peak assigned a chelate ring was observed at 353 nm, this peak intensity decreased by UV irradiation. From this result, the obtained gel films exhibit photosensitivity. Fine patterns (minimal width of about 2 μm) could be fabricated. It was found that the value of refractive index reaches a maximum of 2.25 for the film heat-treated at 800 °C.
Keywords: Photosensitivity; Patterning; Nb2O5 ; UV-irradiation; Refractive index

Simplifying patterning process of ZnO nanowires by one step development and etching process by Yong Hee Kim; Nam Seob Baek; Kook Hwa Kim; Sang-Don Jung (304-308).
We present herein a simple protocol of growing a patterned ZnO nanowire by etching of ZnO seed layer in the tetramethyl ammonium hydroxide (TMAH) solution. The ZnO seed layer was fabricated by sol–gel method using zinc acetate solution and patterned by using photolithographic method. Patterned ZnO seed layer as etched in the TMAH solution, followed by growth of ZnO nanowires by hydrothermal method. Remarkable point of present ZnO seed layer patterning is that development of UV-exposed photoresist and etching of ZnO seed layer is subsequently processed in aqueous TMAH solution without interruption. The grown ZnO nanowires were analyzed using XRD patterns to exhibit high purity and degree of crystallinity, and showed very good pattern fidelity.
Keywords: ZnO nanowire; Patterned growth; Hydrothermal method; Tetramethylammonium hydroxide

Synthesis of silica nanoparticles using oil-in-water emulsion and the porosity analysis by Linggen Kong; Akira Uedono; Suzanne V. Smith; Yukihiro Yamashita; Ilkay Chironi (309-314).
A set of silica particles was synthesized in oil–in–water emulsion with particle diameters ranging from ~42 nm to ~115 nm approximately. The porosity of the nanoparticles was analyzed using conventional nitrogen sorption and positron annihilation lifetime spectroscopy (PALS) techniques. The isotherm obtained using nitrogen sorption indicated that the particles were ‘non-porous’, however fitting data with Density Functional Theory model revealed a low concentration pore with diameters from 1.4 nm to 1.7 nm. The pore size was independent of the particle size. In contrast, analysis with PALS revealed a single pore size of ~0.6 nm present in all samples. Difference in results obtained for micropores <4 nm diameter is proposed to be dependent on models used and sample conditions for analysis.
Keywords: Silica nanoparticles; Sol–gel; Porosity; PALS

Significant enhancement of luminescence intensity of CaTiO3:Eu3+ red phosphor prepared by sol–gel method and co-doped with Bi3+ and Mg2+ by Pu-jun Zeng; Li-ping Yu; Zhong-xian Qiu; Ji-lin Zhang; Chun-ying Rong; Cheng-zhi Li; Zai-hui Fu; Shi-xun Lian (315-323).
In this study, red phosphors Ca1−n Mg n TiO3:Eu3+,Bi3+ were prepared by the sol–gel method and the impact of single dopant, co-dopants and solid solutions on the photoluminescence of the samples has been also investigated. Our results show that the crystal structure of the host does not have distinct changes when doped with Eu3+, Bi3+ and/or Mg2+. The emission intensity at 615 nm of Eu3+ increased at the presence of Bi3+ ions owing to the energy transfer from Bi3+ ion to Eu3+ ion. Moreover, with the addition of Mg2+, the red emission of the phosphor was further enhanced due to the stronger absorption at 399 and 467 nm, which match well with the emission of near-UV (395–400 nm) and blue-LED (450–470 nm), respectively. Under the near-UV (399 nm) or blue light (467 nm) excitation, the fluorescence quantum yield of the optimal composition Ca0.9Mg0.1TiO3:0.18Eu3+,0.018Bi3+ is 0.36 and 0.41, respectively, which possesses the higher photoluminescence intensity than CaMoO4:0.2Bi3+,0.05Eu3+ and the commercially available Y2O2S:Eu3+ phosphors under near-UV excitation. Based on these results, we are currently considering the potential application of Ca0.9Mg0.1TiO3:Eu3+,Bi3+ as a near-UV or blue-chip convertible red-emitting phosphor.
Keywords: Red phosphor; Ca0.9Mg0.1TiO3:Eu3+,Bi3+ ; Sol–gel method; Near-UV or blue chip excitation

Silica imprinted materials containing pharmaceuticals as a template: textural aspects by Everton C. Morais; Gabriel G. Correa; Rodrigo Brambilla; Paolo R. Livotto; João Henrique Z. dos Santos; Mateus Borba Cardoso (324-334).
Silica-based materials were prepared by the acid catalyzed sol–gel method using different pharmaceuticals as a template. The template molecules investigated were fluoxetine, gentamicin, lidocaine, morphine, nifedipine, paracetamol and tetracycline. The resulting hybrid silicas underwent ultrasound extraction in the presence of several solvents and were characterized by elemental analysis, porosimetry by adsorption/desorption of nitrogen (BET method), small-angle X-ray scattering and X-ray diffraction. Drug extraction was carried out by the combination of solvent and ultra-sound. The textural characteristics of the hybrid xerogels and resulting imprinted materials were shown to be highly dependent on the molecular weight and molecular volume of the drug template. Increasing the molecular weight of the template results in a decrease in the encapsulation content of the resulting material. In the case of paracetamol and fluoxetine, the dimensions of the surface area are not sufficient to guarantee the adsorption of the smaller molecule. Instead, the shape generated through encapsulation and extraction during the production of the imprinted silica dictates the adsorption behavior.
Keywords: Molecular imprinting; Pharmaceuticals; Silica; Sol–gel; Adsorption

Cobalt-doped CCTO (CaCu3Ti4O12) ceramics were prepared by a conventional sol–gel synthesis method and the effects of Cobalt doping on the microstructures and dielectrical properties were investigated. The phase composition and microstructure were studied by means of X-ray diffraction (XRD) and high resolution scanning electron microscopy (HRSEM). Efficient crystalline phase formation accompanied by Cobalt induced lattice constant expansion was confirmed through XRD studies. HRSEM results show that doping effectively enhanced grain growth or densification. A compositional study reveals the variation of Cobalt diffusion in CCTO structure by the reduction of Ti presence according to the doping ratio. The dielectric constant reached a value as high as (εr = 25,400 at 1,000 and εr = 111,000 at 1,050 °C) at a cobalt-doping concentration of x = 0.2 at low frequency (50 Hz). The dielectrical constant and dielectric loss of the pure and cobalt-doped CCTO ceramics was measured for different concentrations and discussed in detail.
Keywords: Sol–gel; Ceramics; XRD; Microscopy

A novel lariat-silacrown ether based in sol–gel process: synthesis, characterization and interaction study with the copper(II) ion by Rômulo A. L. Campos; Ana Gabriela S. Bezerra; Mônica F. Belian; Valberes B. Nascimento; André Galembeck (342-346).
The synthesis and characterization of the lariat-silacrown ether (Sila15NH—IUPAC name: 3-[1-[[1-(3-aminopropyl)-2,5,8,11,14-pentaoxa-1-silacyclotetradec-1-yl] oxy]-2,5,8,11,14-pentaoxa-1-silacyclotetradec-1-yl]propan-1-amine) and its complex with copper(II) ion, Cu(II)–Sila15NH, are reported in this work. Tetraethylene glycol, 3-aminopropyl triethoxysilane and metallic sodium were employed as precursors and the lariat-silacrown ether obtained in a good yield (64 %) was characterized by elemental analysis, infrared spectroscopy (FTIR) and nuclear magnetic resonance of 1H, 13C and 29Si. The Cu(II)–Sila15NH was characterized by elemental analysis and FTIR. The straightforward Cu(II) complex formation suggests this property could be explored for analytical purposes.
Keywords: Lariat-silacrown ether; copper(II); Ionophore

Multifunctional nanomaterials with task-specific physicochemical properties, especially core–shell nanostructures with Fe3O4 core and NH2-functional shells (Fe3O4@SiO2–NH2), have been extensively investigated as high-performance adsorbents, catalysts and catalyst supports; and in most cases the controllable sol–gel technique is the choice for fabrication of this kind of widely applied materials. Herein, we demonstrated that mono-dispersed and spherical Fe3O4@SiO2–NH2 nanomaterials with magnetic response core, NH2-functional shell structure can be facilely prepared by co-condensation of TEOS with APTMS using a versatile sol–gel process. It was shown that the proper usage of APTMS and appropriate pre-hydrolysis time of TEOS were crucial and key steps for formation of highly uniform and desirable amino loading Fe3O4@SiO2–NH2 materials. The TEOS pre-hydrolysis and the critical time (around 90 min) before the addition of APTMS prove to be vital for uniform structure evolution, while the appropriate concentration of APTMS (~2.28 mmol L−1 in our system) leads to well-dispersed materials with relatively high loading of amino functionality. The as-prepared Fe3O4@SiO2–NH2 magnetic nanoparticles prepared under optimum conditions possessing superparamagnetic behavior, uniform core–shell structure (~200 nm in diameter), relatively large BET surface area (~138 m2/g) and high incorporation of amino-functionality (~2.90 wt %).
Keywords: Magnetic core–shell materials; Sol–gel; Preparation; APTMS; Physicochemical properties

Synthesis and characterisation of functionalized borosilicate nanoparticles for boron neutron capture therapy applications by S. Grandi; A. Spinella; C. Tomasi; G. Bruni; M. Fagnoni; D. Merli; P. Mustarelli; G. F. Guidetti; C. Achilli; C. Balduini (358-366).
Boron Neutron Capture Therapy (BNCT) is a promising therapy for the cure of diffuse tumors. The successful clinical application of BNCT requires finding new boron-based compounds suitable for an efficient 10B delivery to the cancerous tissues. The purpose of this work is to synthesize borosilicate nanoparticles by a sol–gel recipe, and to functionalize them with folic acid in order to promote their capture by the tumor cells. Whereas sol–gel is a promising technique for the synthesis of nanoparticles, in case of borosilicate systems this approach is affected by significant boron loss during preparation. Here we show that functionalization of borosilicate nanoparticles with folic acid can reduce the boron loss. Moreover, preliminary biocompatibility tests indicate that functionalization strongly changes the reactivity of NPs towards blood cells, so favouring the potential use of these materials for clinical applications.
Keywords: Nanoparticles; Borosilicate; Folic acid; BNCT

Influence of Ti addition on boehmite-derived aluminum silicate aerogels: structure and properties by Frances I. Hurwitz; Haiquan Guo; Richard B. Rogers; Erik J. Sheets; Derek R. Miller; Katy N. Newlin; Molly K. Shave; Anna R. Palczer; Michael T. Cox (367-374).
Aluminosilicate aerogels offer potential for extremely low thermal conductivities at temperatures greater than 900 °C, beyond where silica aerogels reach their upper temperature use limits. Aerogels have been synthesized at two Al:Si ratios, a 3Al:1Si mullite composition, and an 8Al:1Si alumina rich composition. Boehmite (AlOOH) is used as the Al source, and tetraethoxysilane as the Si precursor. The influence of Ti as a ternary constituent, introduced through the addition of titanium isopropoxide in the sol–gel synthesis, on aerogel morphology and thermal properties is evaluated. Four different boehmite precursor powders are evaluated. Morphology, surface area and pore size, and thermal transformation vary with the crystallite size of the starting boehmite powder, as does incorporation of titanium and evolution of Ti-containing crystalline phases. The addition of Ti influences sol viscosity, gelation time, surface area and pore size distribution, as well as phase formation on heat treatment.
Keywords: Aerogel; Boehmite; Aluminum silicate; Titanium isopropoxide; Al2TiO5 ; Mullite

Observation of enhanced room temperature multiferroicity in nanoparticles BiFeO3 by Sangram Keshari Pradhan; Binod Kumar Roul (375-380).
Impurity free monophasic rhombohedral BiFeO3 (BFO) nanoparticles are synthesized by sol–gel method. Effect of processing technique and particle size are found to influence the dielectric, ferroelectric, magnetic and leakage behavior of BFO ceramic prepared by sol–gel as well as conventional solid state reaction route. From XRD analysis it is observed that bulk BFO sample showed rhombohedral structure (R3c) along with other impurity phases, which become suppressed with the decrease of particles size to few nanometers. The dielectric behavior and leakage current characteristic of the samples were improved significantly in nanoparticles of BFO. Ferroelectric hysteresis loops of sintered bulk BFO ceramic is found to change its shape from semi elliptical lossy P–E features to a typical ferroelectric feature with improved remnant and saturation polarization value for the particle size down to nanometer scale. Furthermore, BFO nanoparticles also showed a good ferromagnetic M–H hysteresis loop with enhanced saturation magnetization value of 0.138 emu/mg.
Keywords: Ceramics; Leakage current; Ferroelectricity; Ferromagnetism

A sol–gel methodology for the preparation of lanthanide-oxide aerogels: preparation and characterization by Brady J. Clapsaddle; Björn Neumann; Arne Wittstock; David W. Sprehn; Alexander E. Gash; Joe H. Satcher Jr.; Randall L. Simpson; Marcus Bäumer (381-389).
Lanthanide oxide-based aerogels were synthesized employing the so-called epoxide addition sol–gel method already successfully applied for main- and transition metal oxide aerogels. Using chlorides and nitrates as precursors, our aim was to test the transferability of this robust sol–gel methodology to the entire lanthanide series. By adding the proton scavenging organic epoxide, propylene oxide, to hydrated lanthanide trichloride dissolved in ethanol or methanol, uniform monolithic alcogels were obtained. Subsequent processing in supercritical CO2 resulted in monolithic aerogels. No gelling process could be induced by using nitrates, in contrast to previous results with iron oxide or alumina aerogels. All materials were characterized by nitrogen adsorption/desorption analysis, transmission electron microscopy, and powder X-ray diffraction. With the exception of cerium, for which fractions of crystalline CeO2 were found already in the as-prepared material, XRD analysis revealed that the other materials were mainly amorphous. Subsequent heat treatment of the aerogels above 650 °C resulted in nanocrystalline phases for all aerogel materials. However, except for ceria, more detailed TEM and XRD studies provided evidence that crystalline oxychloride phases are formed in addition to fractions of oxide phases. The trends and possible explanations are discussed in this contribution.A sol–gel methodology using organic epoxides as proton scavengers has been used to synthesize oxide aerogels of the entire lanthanide series. As precursors, nitrates and chlorides were used but only in the latter case, gelation set in. After supercritical drying, aerogels with high surface areas and mesoporous, nanoparticulate structures were obtained. Further characterization revealed that cerium plays a special role, since it contained crystalline CeO2 fractions already before calcination. After calcination it was the only material consisting of a pure oxide phase. The syntheses with the other lanthanides resulted in mixtures with varying fractions of crystalline oxychlorides in addition to an oxide phase. The trends and possible explanations are discussed in this contribution.A sol–gel methodology using organic epoxides as proton scavengers has been used to synthesize oxide aerogels of the entire lanthanide series. As precursors, nitrates and chlorides were used but only in the latter case, gelation set in. After supercritical drying, aerogels with high surface areas and mesoporous, nanoparticulate structures were obtained. Further characterization revealed that cerium plays a special role, since it contained crystalline CeO2 fractions already before calcination. After calcination it was the only material consisting of a pure oxide phase. The syntheses with the other lanthanides resulted in mixtures with varying fractions of crystalline oxychlorides in addition to an oxide phase. The trends and possible explanations are discussed in this contribution.
Keywords: Aerogels; Catalysts; Lanthanide oxides; Lanthanide oxychlorides; Rare-earth oxide aerogel

Co-continuous morphology on spin coating produced thin TiO2 films by Sanja Stanojevic; Anne Ochsenbein; Ralf Busch (390-403).
Biological research has shown good cell response to dense TiO2 films. Good surface chemistry of the implant can be further improved by introducing optimal topology, which in the case of osseointegration means porosity features in the nm and μm range. TiO2 films are produced by spin coating and the obtained morphologies are characterized qualitatively and quantitatively from the scanning electron microscope images of the surface and in focused ion beam cross-sections. Infrared spectroscopy, thermogravimetry/differential thermal analysis, and X-ray diffraction were used to characterize chemical changes and crystallization processes in the bulk gels and thin films. Mechanical properties of the films are characterized using Nano Scratch Test. Results show that the increase in acetyl acetone (ACAC) concentration from 1 mol ACAC:1 mol Ti(IV) n-butoxide used for dense films to 1.5:1 and simultaneous polyethylene glycol (PEG) presence led to a change in morphology from a dense to highly porous, co-continuous morphology. This is a result of pronounced phase separation with respect to gelation due to (1) the presence of uncomplexed ACAC, which is highly dissimilar, in a sense of polarity, to the other components of the sol and (2) the additional reaction between PEG and TiO2 oligomers. This porous morphology is found to be very sensitive to production parameters such as viscosity, spinning velocity and the amount of PEG added to the sol. It was also detected that, in addition to the phase separation, PEG also influences the crystallization process of the film.
Keywords: Titanium dioxide; Spin coating; Thin films; Phase separation; Co-continuous morphology

Luminescent thin films and nanoparticles of europium doped hybrids based on organosilyl β-diketonate by Xianmin Guo; Jean-Louis Canet; Damien Boyer; Pierre Adumeau; Rachid Mahiou (404-410).
Novel organic–inorganic hybrid materials shaped as transparent films and core–shell nanoparticles were prepared by the sol–gel process from a new organo-alkoxysilane based on a β-diketonate (DBM-OH) and doped with trivalent europium ions. The resultant hybrid materials were characterized by Raman spectroscopy and electronic microscopy. Films thickness and nanoparticles size were respectively measured around 1 μm and 30 nm. The photoluminescence study, including the recording of excitation and emission spectra as well as the determination of the decay times, was investigated at room temperature. The results have pointed out an efficient ligand-to-Eu3+ intramolecular energy transfer resulting in a high quantum yield as determined by using an integrating sphere.
Keywords: Nanoparticles; Thin films; Optical materials; Photoluminescence spectroscopy

Different nanoporous silica materials, MCM-41, MCM-48 and SBA-15, were modified by pyridine and their applications for oral drug delivery system were evaluated. These pyridine functionalized nanoporous silicas were loaded with a water insoluble diorganotin(IV) dichloride complex as an antitumor drug model and its release from them were investigated by changing pH. An efficient pH-responsive carrier system was constructed by coordination of the pyridine group in modified nonoporous materials to tin complex. In vitro, releasing of loaded tin complex was studied in three different kinds of fluids, including a simulated gastric medium and a simulated body fluid. The loading and releasing of the diorganotin(IV) dichloride from various modified nanoporous silicas and also a non-porous silica (SiO2) were investigated, and the results were compared. In addition, the effect of some factors such as pH, time of loading and releasing were investigated through this study.
Keywords: Drug delivery; Nanoporous silica; Methylphenyltin(IV) dichloride; Pyridine functionalized

Sol–gel derived organic–inorganic hybrid sorbent for removal of Pb2+, Cd2+ and Cu2+ from aqueous solution by Hong-Tao Fan; Zi-Jie Su; Xue-Lei Fan; Meng-Meng Guo; Juan Wang; Song Gao; Ting Sun (418-426).
This manuscript reported sol–gel derived organic–inorganic hybrid sorbent for the removal of Cd2+, Pb2+ and Cu2+ ions from aqueous solutions. The hybrid sorbent (S2/SiO2) had been synthesized by a simple co-condensation of bis[3-(triethoxysilyl)propyl]disulfide and tetraethoxysilane via sol–gel transformation. The S2/SiO2 was characterized by scanning electron microscopy, Fourier-transform infrared spectroscopy, elemental analysis and thermogravimetric analysis. The influences of different adsorption parameters, such as pH value of solution, contact time and initial concentrations of metal ions on the adsorption amount of Cd2+, Pb2+ and Cu2+ were examined. The optimum pH for adsorption was found to be in the range of 3.7–8.5. The adsorption rates of Cd2+, Pb2+ and Cu2+ by S2/SiO2 were rapid. Ho’s pseudo-second-order model best described the kinetics of the adsorption reaction. The adsorption process of metals followed Langmuir isotherm model, and the experimental values of maximum adsorption capacities for Cd2+, Pb2+ and Cu2+ were 26.8, 56.7 and 13.3 mg g−1, respectively. The positive values of ΔH o suggested endothermic nature of Cd2+, Pb2+ and Cu2+ adsorption on S2/SiO2 sorbent. Increase in entropy of adsorption reaction was shown by the positive values of ΔS o and the negative values of ΔG o indicating that the adsorption was spontaneous in nature.
Keywords: Sol–gel; Bis[3-(triethoxysilyl)propyl]disulfide; Hybrid; Cadmium; Copper; Lead

An investigation on the assembling of WO3 particles on the matrix of silica solution by Guohua Gao; Wei Feng; Guangming Wu; Jun Shen; Zenghai Zhang; Xiaobo Jin; Zhihua Zhang; Ai Du (427-435).
A facile way to prepare modified WO3 structure by silica support through sol–gel method is reported. The WO3/SiO2 complex film was synthesized from a two steps process and dip-coating method. The films were characterized with laser particle analyzer, IR, Raman. The studies of gelation time and particle size distribution of WO3/SiO2 sol indicate that the silica addition could largely reduce the polycondensation of WO3 clusters. The reaction between WO3 and SiO2 were further systematically investigated using IR spectra, and an insight of this reaction was illuminated. Results reveal that Si–OH in SiO2 sols tended to crosslink with WO3 at the corner-sharing W–O sites, by which only edge-sharing WOx clusters could be detected. This modified the WO3 structure was also approved by the Raman spectra, TEM and AFM images. Moreover, gas sensing properties of the WO3/SiO2 films were tested. The assembled WO3 films exhibited more stable gas sensing stability than pure WO3 films.
Keywords: WO3 ; Sol–gel; Assembling; Silica solution; Gas sensing

Inks of titanium diisopropoxide bisacetylacetonate ([(CH3)2CHO]2Ti(C5H7O2)2) are suitable for the fabrication of photonic bandgap materials by direct ink writing (DIW). Using this method we are able to obtain micro-periodic titania (TiO2) structures with high refractive index by calcining the structures built with those inks. Calcining at high temperatures causes titania grain growth and surface roughness of the structure, which has an influence over its optical properties. In order to inhibit the grain growth of titania nanocrystals when the structures are calcined, we have synthesized using the sol–gel technique titanium diisopropoxide bisacetylacetonate inks doped with Cerium (III) nitrate hexahydrate (Ce(NO3)3·6H2O) and Zirconyl nitrate hydrate (ZrO(NO3)2·xH2O). The grain growth process of titania powders derived from the calcined doped sol–gel inks during various heat-treatment programs has been investigated by the X-ray line-broadening analysis. It was demonstrated how the dopants reduce the grain growth of the rutile phase after heat treatment. The influence of the dopants on the rheological behaviour of doped inks were studied and compared with the undoped. The flow and oscillation curves as a function of time demonstrate that doped inks have the same rheological behaviour than undoped inks. Thermogravimetric analysis also proves that doped inks keep the same mass loss after calcination than undoped inks. These results show how doped inks can be applied for DIW in the same conditions than undoped inks with a significant reduction of titania grain growth.
Keywords: Direct ink writing; Sol–gel; TiO2 ; Photonic crystals

The design and characterisation of sol–gel coatings for the controlled-release of active molecules by M. Hernández-Escolano; M. Juan-Díaz; M. Martínez-Ibáñez; A. Jimenez-Morales; I. Goñi; M. Gurruchaga; J. Suay (442-451).
The controlled release of active agents from a matrix has become increasingly important for oral, transdermal or implantable therapeutic systems, due to the advantages of safety, efficacy and patient convenience. Controlled-release hybrid (organic–inorganic) sol–gel coating synthesis has been performed to create a sol with an active molecule included (procaine). Synthesis procedures included acid-catalysed hydrolysis, sol preparation, the addition of a procaine solution to the sol, and the subsequent gelation and drying. The alkoxide precursors used were triethoxyvinylsilane and tetraethyl-orthosilicate (TEOS) in molar ratios of 1:0, 9:1, 8:2 and 7:3. After the determination of the optimal synthesis parameters, the material was physicochemically characterised by silicon-29 nuclear magnetic resonance (29Si-NMR) and Fourier transform infrared spectroscopy, contact angle analysis and electrochemical impedance spectroscopy tests. Finally, the materials were assayed in vitro for their ability to degrade by hydrolysis and to release procaine in a controlled manner. The sustained release of procaine over a 3-day period was demonstrated. A close correlation between release and degradation rates suggests that film degradation is the main mechanism underlying the control of release. Electrochemical analysis reveals the formation of pores and water uptake during the degradation. The quantity of TEOS is one of the principal parameters used to determine the kinetics of degradation and procaine release.
Keywords: Sol–gel coatings; Controlled-release; Electrochemical properties

Fire retardancy effects in single and double layered sol–gel derived TiO2 and SiO2-wood composites by M. Shabir Mahr; T. Hübert; B. Schartel; H. Bahr; M. Sabel; H. Militz (452-464).
Sol–gel derived TiO2 and SiO2-wood inorganic composites are prepared by direct vacuum infiltration of silicon and titanium alkoxide based precursors in pine sapwood in one or two cycles followed by a controlled thermal curing process. The resulting flame retardancy effect is investigated under two different fire scenarios using cone calorimetry and oxygen index (LOI). Heat release rates (HRR) especially the values for the second peak, are reduced moderately for all single layered composites. This effect is more pronounced for double layered composites where HRR was reduced up to 40 % showing flame retardancy potential in developing fires. Beside this, smoke release was lowered up to 72 % indicating that these systems had less fire hazards compared to untreated wood, whereas no meaningful improvement is realized in terms of fire load (total heat evolved) and initial HRR increase. However impressively, the LOI of the composites were increased up to 41 vol% in comparison to 23 vol% for untreated wood displaying a remarkable flame retardancy against reaction to a small flame. An approximate linear interdependence among the fire properties and the material loading as well as fire residue was observed. A residual protection layer mechanism is proposed improving the residue properties for the investigated composites.
Keywords: Wood; Sol–gel; Composite materials; Cone calorimeter; Fire retardance; Flammability

Thickness effects in naturally superhydrophilic TiO2–SiO2 nanocomposite films deposited via a multilayer sol–gel route by C. Holtzinger; L. Rapenne; P. Chaudouët; G. Berthomé; M. Langlet (465-479).
TiO2–SiO2 nanocomposite films of various thicknesses have been deposited via a multilayer sol–gel route. These films exhibit a natural and persistent superhydrophilicity, which allows considering new applications for easy to clean surfaces. Atomic force microscopy, scanning and transmission electron microscopy, as well as ellipsometry and UV/visible spectrometry measurements, were performed to study how the multilayer procedure influenced the morphology and composition of composite films in relation to their thickness. The natural and photo-induced wettability of these films was studied and discussed in relation to morphology, composition, and thickness features. It is concluded that, while such features did not significantly influence the natural wettability of nanocomposite films, their photo-induced wettability was considerably enhanced when increasing their thickness, which favored a faster superhydrophilicity photo-regeneration when this natural property started to disappear after a long aging period in ambient atmosphere.
Keywords: Superhydrophilicity; TiO2–SiO2 composites; Sol–gel coatings; Surfaces; Enhanced cleanability

Fabrication of surface: relief gratings and their laser induced damage resistance properties by Zhezhe Wang; Gaoyang Zhao; Lin Lin; Zhuohong Feng; Zhiqiang Zheng (480-484).
This work demonstrates a promising method for fabricating ZrO2 surface–relief gratings by photosensitive sol–gel method combining with two-beam laser interference. UV-photosensitive ZrO2 resist with high resolution are prepared by using metal–chelate complexes as precursors. Two-beam laser interference lithography is carried out by a Kr ion laser with a wavelength of 350.7 nm and ZrO2 gratings with the minimum line-width of 150 nm are obtained. Laser induced damage resistance properties of ZrO2 gratings are investigated by a Q-switched solid state laser with the wavelength of 527 nm and the pulse width of 8.65 ns as the incident source. The results show that the LIDT of ZrO2 gratings on glass substrate heated at 600 °C is about 4.59 ± 0.06 J/cm2.
Keywords: Surface–relief gratings; LIDT; Photosensitive sol–gel; Laser interference

Nanocrystalline manganese aluminate (MnAl2O4) has been synthesized by Pechini and sequential homogenous precipitation methods and the results have been compared. The Taguchi L4 statistical design was utilized to optimize the production of MnAl2O4 nanoparticles by Pechini method. The MnAl2O4 nanocrystallites obtained by Pechini and sequential homogenous precipitation methods had the average particle size of 26.5 and 49.5 nm, respectively. The products were characterized with X-ray diffraction, laser light scattering, thermogravimetry analysis, Fourier transform infrared, UV–visible, energy dispersive X-ray, scanning electron microscope and inductively coupled plasma analyses. The photocatalytic activities of MnAl2O4 nanoparticles synthesized by two methods were investigated using aqueous solution of methylene blue under irradiation of visible light.
Keywords: Manganese aluminate nanoparticles; Pechini method; Sequential homogenous precipitation; Taguchi optimization

Synthesis and properties of Mo and W ions co-doped porous nano-structured VO2 films by sol–gel process by Yuanjie Xu; Wanxia Huang; Qiwu Shi; Yang Zhang; Linwei Song; Yaxin Zhang (493-499).
Porous nano-structured vanadium dioxide (VO2) films doped with Mo and W ions had been synthesized by sol gel process by employing a sol containing ammonium molybdate and ammonium tungstate with the addition of cetyltrimethyl ammonium bromide (CTAB). The effects of molybdenum and tungsten co-doping and CTAB addition on the structure, morphologies, crystalline and optical properties of VO2 films were investigated systematically in this study. The composition and microstructure were detected by X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. The Mo and W ions co-doped porous nano-structured VO2 films showed excellent infrared transmittance (nearly 70 %), large transmittance difference (55 %) before and after the phase transition, low transition temperature (35 °C), wide hysteresis width (22 °C) and fast phase transition. The results suggest that such Mo and W ions co-doped porous nano-structured VO2 film is an ideal fundamental material for optical data storage.
Keywords: Mo and W ions co-doped; Vanadium dioxide; Sol–gel process; Porous film; Optical properties

Organic–inorganic tandem route to polymer nanocomposites: kinetic products versus thermodynamic products by Lingli Ni; Nadia Moreau; Abraham Chemtob; Céline Croutxé-Barghorn (500-509).
We report a facile single-step photochemical methodology to afford alkylsiloxane-polymer hybrid films which relies on the tandem photoacid-catalyzed polymerization of n-alkyltrimethoxysilane precursors and a diglycidyl ether organic monomer. Photoacids liberated by the UV decomposition of iodonium salt triggers simultaneously the sol–gel process and epoxy cationic polymerization. Such conditions are intended to favour the formation of kinetic products trapped by cross-linking reactions instead of the thermodynamically most stable structures, whose preference would be for macrophase segregation. Organosilane precursor exhibiting different structures and chain lengths (n-butyl, n-octyl, n-dodecyl, n-hexadecyl, isobutyl and isooctyl) were systematically investigated to afford a range of transparent alkylsiloxane-polyether hybrids. The competitive organic–inorganic reaction kinetics were investigated using in situ real-time Fourier transform infrared spectroscopy. A main emphasis has been on discussing the effect of the alkyl substituent structure on the photoinduced polymerization kinetics and the silicate networks characterized by 29Si solid-state NMR. To avoid phase separation, the rate of formation of the two phases was tailored to favour concomitancy upon modulating several experimental parameters: film thickness, alkyl structure, photoacid generator concentration. Finally, the viscoelastic and surface properties were also assessed by dynamic mechanical analysis and water contact angle measurements, respectively.
Keywords: Hybrid; Film; Cationic polymerization; RT-FTIR; Single-step; UV

Synthesis of garnet structured Li7+x La3Y x Zr2-x O12 (x = 0–0.4) by modified sol–gel method by C. Deviannapoorani; L. Dhivya; S. Ramakumar; R. Murugan (510-514).
Preparation of lithium garnet Li7La3Zr2O12 (LLZ) in cubic phase by solid state method requires high temperature sintering around 1,200 °C for 36 h in Al2O3 crucible with intermittent grinding. Synthesis of LLZ in cubic phase at lower temperatures by wet chemical methods was reported earlier, however that decompose at high temperature around 850 °C. In this work we report the systematic studies on synthesis of garnet structured electrolytes by modified sol–gel method by the simultaneous substitution of Li+ and Y3+ for Zr4+ according to the formulae Li7+x La3Y x Zr2-x O12 (x = 0, 0.1, 0.2, 0.3 and 0.4). The present investigation revealed that the cubic garnet phase is obtained at much lower temperature for Li7La3Zr2O12 and the simultaneous increase of both Li+ and Y3+ in Li7+x La3Y x Zr2-x O12 requires slightly higher sintering temperatures for the formation of cubic garnet phase. SEM micrographs of the Li7+x La3Y x Zr2-x O12 (x = 0, 0.1, 0.2, 0.3 and 0.4) annealed at minimum sintering temperature required for the formation of cubic garnet phase revealed the increase in grain size and relatively dense structure with increase of x in Li7+x La3Y x Zr2-x O12.
Keywords: Sol–gel processes; Calcination; X-ray methods; Batteries