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Journal of Sol-Gel Science and Technology (v.62, #3)

Sol–gel preparation of calcium titanium phosphate: viscosity, thermal properties and solubility by M. Dressler; J. Börnstein; M. Meinel; U. Ploska; S. Reinsch; V. D. Hodoroaba; D. Nicolaides; K. J. Wenzel (pp. 273-280).
Calcium titanium phosphate (CTP) was prepared by the sol–gel route in order to prepare suitable coatings. This work addresses the question of how to prepare stable CTP sols. Their rheological properties as a function of process parameters like solid loading and water content are investigated. It was found that an increased solid loading as well as an increased water content lead to an increased initial viscosity as well as a more pronounced ageing induced viscosity rise. In addition, the thermal behavior of the resulting xerogels was analyzed. Furthermore, we studied the ion release behavior of the xerogels when brought in contact with water. Results suggest that calcium titanium phosphate shows a diffusion controlled ion release mode with a preferential release of Ca.

Keywords: Calcium titanium phosphate; Sol–gel processing; Rheology; Thermal analysis; Coatings; Solubility

Sol–gel synthesis of nanosilver embedded hybrid materials using combined organosilica precursors by Shang-Ru Zhai; Xu Shao; Di Zhou; Bin Zhai; Qing-Da An (pp. 281-286).
A facile sol–gel route to the fabrication of size-controllable nanosilver embedded hybrid materials at room-temperature is presented. The preparation process involves using three kind of organosilica precursors, i.e. tetraethoxysilane, 3-mercaptopropyltrimethoxysilane and polymethylhydrosiloxane, which behaved as framework constructor, complexing agent toward metal ions and in situ reducing agent for Ag+ ions, respectively, under alcohol-rich synthesis conditions. The prepared hybrid materials were characterized by Ultraviolet–visible diffuse reflectance spectra, Fourier transform infrared, transmission electron microscopy, X-ray diffraction, nitrogen adsorption–desorption measurements. It was shown that well-dispersed silver nanoparticles (AgNPs) with small particle size were successfully embedded in the hybrid skeleton, and the mean particle size of AgNPs could be controlled at ca. 2–5 nm.

Keywords: Polysiloxane; Hybrid; Nanoparticles; Redox chemistry; Complexing agent

Control over the self-assembly of polymers and layered molybdenum oxide: from the micrometer scale to the molecular scale by Ke Shao; Xiaoyan Chai (pp. 287-293).
We report adjustment on the self-assembly between polymer of polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA) and inorganic molybdenum oxide layers from the micrometer scale to the nanometer scale. Our method is to break the strong interactions between the organic polymers by introducing suitable bridging agents and adjust the reaction speeds of the two competitive reactions in the reaction system. We use I2 to complex with PVA and break the strong hydrogen interactions between the PVA chains, resulting in a PVA-I2/(MoxOy) n− complex, in which the organic and inorganic species self-assemble homogenously on the molecular scale. We also adjust the thickness of the inorganic (MoxOy) n− layers in the hybrid of PVP/(MoxOy) n− by controlling the reaction speeds of the two competitive reactions: hydrolysis of Mo7O24 6− into (MoxOy) n− and packing into thick inorganic layers on the one hand, and hybridization of (MoxOy) n− and PVP into layered hybrid on the other hand. Experimental results proved that when the hydrolysis is overwhelming, the inorganic molybdenum oxide chains pack into heavy layers and self-assemble with PVP polymers on the micrometer scale, and when the hybrid reaction dominates, the organic polymer and molybdenum oxide hybridize on the molecular scale. These findings open new routes to disperse organic polymer and inorganic species homogenously and fabricate novel organic/inorganic hybrid nanomaterials in situ.

Keywords: Organic/inorganic hybrid; Self-assembly

One-pot synthesis, characterization and properties of acid-catalyzed resorcinol/formaldehyde cross-linked silica aerogels and their conversion to hierarchical porous carbon monoliths by Ke Chen; Zhihao Bao; Ai Du; Xiurong Zhu; Jun Shen; Guangming Wu; Zhihua Zhang; Bin Zhou (pp. 294-303).
A rapid and facile synthesis of resorcinol/formaldehyde cross-linked silica (RF/SiO2) aerogels was carried out in one pot based on an acid-catalyzed route, instead of the previously reported base-catalyzed ones. The gelation time was reduced to several hours at room temperature while it took several days even under heating conditions in the base-catalyzed ones. The interpenetrating network of RF/SiO2 aerogels showed similar porous structures with those of silica aerogels or RF aerogels. Their thermal conductivity was as low as that of the typical glass wool materials. The mechanical properties are characterized by dynamic mechanical analysis and compression testing. At room temperature, the results of compression testing show that the compressive Young’s modulus or ultimate failure strength of RF/SiO2 aerogel specimen is higher than that of native SiO2 aerogels with a similar density. The one-pot method improves the efficiency and reduces the cost of RF/SiO2 aerogels. The hierarchical porous carbon monoliths are also converted from carbonized RF/SiO2 aerogels by an additional HF treatment. Hence, they could be further explored as multifunctional candidate materials for thermal, mechanical, and electrochemical applications.

Keywords: Silica aerogels; Resorcinol/formaldehyde; Acid-catalyzed; Hybrid materials; Porous carbon

Photocatalytic and antibacterial activities of Ag-doped ZnO thin films prepared by a sol–gel dip-coating method by K. Thongsuriwong; P. Amornpitoksuk; S. Suwanboon (pp. 304-312).
Silver-doped ZnO thin films with various loadings of Ag in the range of 0–10 mol% were prepared by the sol–gel dip-coating method. All prepared films show X-ray powder diffraction patterns that matched with ZnO in its würtzite structure. The grain size decreased as the Ag loading increased. The prepared films, under UV blacklight illumination, produced a photocatalytic degradation of methylene blue, rhodamine B and reactive orange solutions. Furthermore, they inhibited the growth of Escherichia coli bacteria under UV blacklight irradiation and to a lesser extent in dark conditions. The photocatalytic and antibacterial activities of the prepared films increased with Ag loading, presumably because Ag enhanced the efficiency of generation of superoxide anion radicals (O2 ) and hydroxyl radicals (OH).

Keywords: Ag-doped ZnO thin film; Inorganic antibacterial agent; Photocatalytic degradation

Synthesis and characterization of Pr3+-doped glass scintillators prepared by the sol–gel method by Yan Sun; Masanori Koshimizu; Shunji Kishimoto; Keisuke Asai (pp. 313-318).
Transparent and crack-free Pr-doped silica glass scintillators were successfully synthesized using the sol–gel method. A peak found at 301 nm in the photoluminescence spectrum was ascribed to a radiative transition of the Pr3+ emission center. The associated excitation peak was located at 276 nm. The energy of the excitation peak (4.50 eV) was significantly lower than the energy gap (5.83 eV) of the 1S0 to 3H4 ff transition. Therefore, the ff transition was excluded as the origin, and the transition was attributed to 5d–4f. In the absorption spectrum, several bands of the ff transition were observed. Fourier transform infrared spectroscopy was employed to understand the microstructural features and OH group concentration in the Pr3+-doped silica glass. It was revealed that a Si–O network had been successfully formed, and that the OH group concentration decreased with increasing thermal treatment temperature reaching a saturation value for temperatures higher than 750 °C. The absence of praseodymium oxide nanocrystalline clusters was confirmed by transmission electron microscopy (TEM), even in the sample with the highest Pr ion concentration. Scintillation properties of the Pr3+-doped silica glass were also characterized. The scintillation decay time constants were estimated to be approximately 1.3 and 14 ns, which supports the assignment of the luminescence to the 5d–4f transition. The scintillation light yield of the Pr3+-doped silica glass was estimated to be approximately 130 photons/MeV.

Keywords: Photoluminescence; 5d–4f transition; Glass scintillator; Sol–gel method

Thermal annealing combination with pulse Nd-YAG laser treatment of ITO on polycarbonate using spin coating process by H. Salar Amoli; S. Shokatian; M. Abdous (pp. 319-323).
This work, we report a cost effective method to decompose ITO thin layer on polycarbonate as flexible substrate by means of spin coating technique. Three calcinations techniques were carried out. The coating were deposited by spin and cured by heat, ultraviolet (UV) irradiation and Nd-YAG pulse laser. The resistivity change on annealing of the amorphous film by thermal, UV and laser was investigated by X-ray diffraction, scanning electron microscopy, atomic force spectroscopy and UV–Vis spectrometer. It is shown that the resistance of coated film on polymer decreases dramatically to less than impedance spectroscopy (600 Ω) when using combination of low heat treatment and laser irradiation with a wavelength of 1,100 nm and energy of 6–25 J.

Keywords: Nd-YAG pulse laser; Annealing; Polycarbonate; Spin coating; Nanopowder ITO

Quinine doped hybrid sol–gel coatings for wave guiding and optical applications by E. Enríquez; M. A. Garcia; N. Carmona; J. F. Fernández; M. A. de la Rubia (pp. 324-332).
Pure and quinine doped silica coatings have been prepared over sodalime glasses. The coatings were consolidated at low temperature (range 60–180 °C) preserving optical activity of quinine molecule. We designed a device to test the guiding properties of the coatings. We confirmed with this device that light injected in pure silica coatings is guided over distances of meters while quinine presence induces isotropic photoluminescence. With the combined use of both type of coatings, it is possible to design light guiding devices and illuminate regions in glass elements without electronic circuits.

Keywords: Sol–gel coatings; Photoluminescence; Waveguides; Silica; Quinine

Thermo-optic characteristics in transparent glass fabric reinforced composite using inorganic–organic hybrid materials by Eun-Seok Kang; KyungHo Jung; Deok Hai Park; Namseok Kang; Byunggil Ryu (pp. 333-337).
The thermo-optic characteristics of the transparent glass fabric composite and matrix resin have been investigated. The inorganic–organic hybrid materials modified with sulfur are synthesized as transparent matrix resin with the same refractive index and Abbe number as glass. The optical characteristics of the transparent composite relate to temperature due to the fact that the thermo-optic coefficient (dn/dT) for glass fiber (1.00 × 10−5K−1) is different to that of inorganic–organic hybrid materials (−1.99 × 10−4K−1). As the temperature increases, the transparent composite gradually becomes opaque and hazy due to the increased difference in the refractive index between the glass fiber and the matrix. The change in optical characteristics is reversible, meaning that the transparent composites can be used in for various applications in optical devices.

Keywords: Thermo-optic coefficient; Sol–gel; Inorganic–organic hybrid materials; Transparent composite

Layer-by-layer self-assembly of TiO2 sol on wool to improve its anti-ultraviolet and anti-ageing properties by J. Liu; Q. Wang; X. R. Fan (pp. 338-343).
A new method for improving the anti-ultraviolet and anti-ageing abilities of wool fabric was reported in this paper. TiO2 sols and poly (sodium 4-styrene-sulfonate) (PSS) were coated on the wool fibers via layer-by-layer (LBL) electrostatic self-assembly deposition. The morphologies and compositions of TiO2 sol-coated wool fabrics were characterized using SEM, surface Zeta potential, apparent color depth (K/S), ultraviolet (UV) transmission and alkali solubility. The SEM pictures showed that there were quite a few deposits absorbed on the wool surface. The dyeing depth and Zeta potential presented obvious “layer–layer alternate vibration” along with the change of deposited materials, revealing the surface structure of the assembled wool fiber. The results of ultraviolet (UV) transmission and alkali solubility indicated that the modified wool fabrics obtained good anti-ultraviolet and anti-ageing properties. In addition, the sol-assembled wool fabrics had good washing fastness. The studies proved that the LBL electrostatic self-assembly deposition is a promising way to endow the textiles with surface functionality.

Keywords: TiO2 sol; Wool; Layer-by-layer electrostatic self-assembly; Anti-ultraviolet; Anti-ageing

Effect of annealing atmosphere on structural, optical and electrical properties of Al-doped Zn1−x Cd x O thin films by L. B. Duan; X. R. Zhao; J. M. Liu; W. C. Geng; H. N. Sun; H. Y. Xie (pp. 344-350).
1 at.% Al-doped Zn1−x Cd x O (x = 0–8 at.%) thin films were prepared on glass substrates by sol–gel method. The codoping films retained the hexagonal wurtzite structure of ZnO, and showed preferential c-axis orientation. The effect of annealing ambient (in vacuum and nitrogen) on the optical and electrical properties of (Cd,Al)-codoped ZnO films were investigated using transmission spectra and electrical measurements. The transmittances of the codoping films were obviously degraded by vacuum annealing to 50–60 %, but enhanced to 70–80 % after nitrogen annealing. The carrier concentration and Hall mobility both increased, and resistivity decreased with narrowing band gap of Al-doped Zn1−x Cd x O, below different critical concentrations x = 4 % (in vacuum) and x = 6 % (in nitrogen). It is revealed that the conductivity is also improved by Cd doping along with band gap modification. The variations in optical and electrical properties are ascribed to both the changes of the crystallinity and concentration of oxygen vacancies under different ambient. In view of transmittance and conductivity, nitrogen annealing might be a more effective post-annealing way than vacuum annealing for our (Cd,Al)-codoped ZnO films to meet the requirements of transparent conducting oxide (TCO).

Keywords: (Cd,Al)-codoped ZnO films; Transparent conducting; Band gap modification; Crystallinity; Oxygen vacancies

Degradation of methylene blue via Co–TiO2 nano powders modified by meso-tetra(carboxyphenyl)porphyrin by Rahmatollah Rahimi; Elham Honarvar Fard; Sara Saadati; Mahboubeh Rabbani (pp. 351-357).
TiO2 photocatalylysts as an environmental cleaning factor has drawn considerable attention due to the global increase in the level of environmental pollutions. Studies on the development of new TiO2 materials wherein its photocatalytic activity can be activated by visible light will be valuable for field application. In this study, porphyrins/Co-doped TiO2 were prepared by sol–gel method. The nanopowders were characterized by means of X-ray diffraction, energy dispersive X-ray spectroscopy, IR spectroscopy and transmission electron microscopy (SEM). In addition, the photocatalytic degrading efficiency of porphyrins/Co-doped TiO2 complexes on the methylene blue decomposition under irradiation with visible light is evaluated.

Keywords: Photocatalytic activity; Porphyrin/cobalt doped TiO2 ; Methylene blue degradation

In situ crystalline investigation of sol–gel deposited barium stannate (BaxSnO2+y; x:y ≈ 1:1) nanoparticles in alkaline medium by Chinedu Ifeanyichukwu Amaechi (pp. 358-363).
Fine layers of barium stannate nanoparticles have been synthesized by sol–gel technique with tin chloride pentahydrate (SnCl4·5H2O) and barium sulphate (BaSO4). Physico-chemical properties of barium stannate, BaxSnO2+y; x:y ≈ 1:1 were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and UV–Visible spectrophotometry technique. A growth mechanism based on the combination of particle sticking and molecule level heterogeneous growth is proposed. It has been found that the particle size of all the samples was distributed in the range 3.0–6.5 Ǻ while optical absorption spectrum indicates that BaxSnO2+y nanoparticles have a direct band gap of 3.9 eV.

Keywords: Barium stannate; Particle size; Band gap; Sol–gel

Synthesis of NiO nanomaterials with various morphologies and their electrocatalytic performances for p-nitrophenol reduction by Lu Pan; Li Li; Yonghong Chen (pp. 364-369).
In the work, several facile and easily controlled procedures were designed to successfully synthesize a few NiO samples with various morphologies, including nanosheets, nanobelts, nanoparticles and empty microspheres, via a hydrothermal method. The as-prepared samples were characterized by X-ray powder diffractometer, TEM and field emission scanning electron microscopy technologies. The results revealed that the as-synthesized NiO samples displayed expected nanosheets, nanobelts, nanoparticles and empty microspheres in shape. The electrocatalytic performance of each NiO sample modified on a glassy carbon electrode for p-nitrophenol reduction in a basic solution using cyclic voltammetry method was investigated. The results indicated that the glassy carbon electrode modified with each NiO sample showed enhanced electrocatalytic activity by comparing a bare glassy carbon electrode, and especially NiO nanopatricles and empty microsphere exhibited the higher electrocatalytic activty for p-nitrophenol reduction.

Keywords: NiO; Nanomaterials; Morphology; Electrocatalysis; p-Nitrophenol

Biocompatible titania hydrogels with chemically triggered release of a photosensitive dye by Renata Rychtarikova; Gulaim A. Seisenbaeva; Gabriela Kuncova; Vadim G. Kessler (pp. 370-377).
5,10,15,20-Tetrakis(4-sulfonatophenyl)porphyrin was entrapped into biocompatible hydrogels formed by self-assembling micelles of the titanium dioxide prepared by hydrolysis of titanium ethoxide modified with triethanolamine (TEA). The materials were characterized by their optical and photosensitive properties. The immobilization led to changes of the absorption spectra of the dye and decreased its molar absorption coefficient. The TiO2 matrix did not degrade the entrapped porphyrin upon u.v. irradiation. The formation of TEA–titanium(IV) chelates facilitated a controlled and triggered release of the immobilized dye from the hydrogels in lactate and citrate buffers. The released dye prolonged the sterility of citrate–phosphate buffer and its illumination with visible light inhibited growth of Aspergillus niger.

Keywords: Sol–gel; Photosterilization; Immobilization; Biocompatible titanium dioxide; Porphyrin

Comments on the wetting behavior of non-porous substrates for ceramic coated-conductor applications by Pieter Vermeir; Frank Deruyck; Jonas Feys; Petra Lommens; Joseph Schaubroeck; Isabel Van Driessche (pp. 378-388).
This work gives an overview of the possibilities to improve the wetting behavior of precursors for coated conductors on non-porous substrates. Within this work, all coatings were performed on a metallic Ni–W/La2Zr2O7/CeO2 substrate using water-based Y, Ba, Cu containing precursors. The results described in this paper can be used for different technologies of chemical solution deposition, as there are ink jet printing, dip coating, spin coating etc. Starting from the forces involved during wetting, a separation between solid and liquid modifications was made. This study revealed that if a good cleaning procedure of the substrate, whether or not combined with a targeted modification of the precursor is applied, water-based solutions can be used without restriction towards their wetting behaviour leading to a sustainable technology within the coating industry. Within this work, special attention is given to (1) fast determination of the substrate cleaning procedure quality by the creation of wetting envelopes and (2) the use of a screening design of experiment to study the effects of intrinsic solution factors, such as precursor formulation, influencing the coating behavior. All modification discussed are expandable to all kinds of precursors and substrates.

Keywords: Wetting; Chemical solution deposition; Coating; Water-based

Hydridosilazanes hydrolysis-condensation reactions studied by 1H and 29Si liquid NMR spectroscopy by Nicolas Dargère; Véronique Bounor-Legaré; Fernande Boisson; Philippe Cassagnau; Grégory Martin; Phillipe Sonntag; Nicolas Garois (pp. 389-396).
Hydridosilazane compounds containing Si–N and Si–H bonds can be used as precursors of SiOx materials. The hydrolysis-condensation reactions of tetramethyldisilazane, as a polyhydridosilazane model compound, were investigated by 1H and 29Si liquid NMR spectroscopy. These reactions were carried out at room temperature for up to 120 min in presence of water. The identified products are short linear siloxane species (hydride terminated polydimethylsiloxanes MHDxMH) and cyclosiloxanes. Silicon hydride persistence in the reactional mixture suggested that silazane group is more sensitive to hydrolysis reaction than silicon hydride group. Moreover, additional experiments evidenced that the low steric hindrance of the silicon hydride influences the silazane hydrolysis kinetic. Hence the presence of ammonia released during silazane hydrolysis reaction was demonstrated to be a catalyst of the silicon hydride hydrolysis reaction.

Keywords: Hydridosilazane; Hydrolysis-condensation reaction; Liquid NMR

Structural and optical characterization of sol–gel derived boron doped Fe2O3 nanostructured films by C. Aydın; Sh. A. Mansour; Z. A. Alahmed; F. Yakuphanoglu (pp. 397-403).
Pure and boron (B) doped iron oxide (Fe2O3) nanostructured thin films were prepared by sol–gel spin coating method. The effects of B (0.1, 0.2, 0.5 and 1 %) content on the crystallinity and morphological properties of Fe2O3 films were investigated by X-ray diffractometer and atomic force microscopy. X-ray diffraction patterns revealed that the Fe2O3 films have a rhombohedral crystalline phase of α-Fe2O3 phase (hematite) with nanostructure and their crystallite size (D) is changed from 27 ± 2 to 45 ± 5 nm with B dopant content. The minimum crystallite size value of 27 ± 2 nm was obtained for 0.2 % B doped Fe2O3 film. Carrying out UV–VIS absorption study for both doped and undoped films at room temperature, it was realized that allowed optical transitions may be direct or indirect transitions. The direct and indirect energy gap values for pure Fe2O3 were obtained to be 2.07 and 1.95 eV, respectively. The optical band gap value of the films was changed with 0.1 % B doping to reach 1.86 eV for direct band gap and 1.66 eV in case of indirect band gap.

Keywords: Nanostructure; Sol–gel; Hematite Fe2O3 ; Optical properties

Fabrication of titania and titania–silica aerogels using rapid supercritical extraction by Lauren B. Brown; Ann M. Anderson; Mary K. Carroll (pp. 404-413).
Titania (TiO2) and titania–silica (TiSi) aerogels are suitable for photocatalytic oxidation of volatile organic compounds for pollution mitigation; however, methods for fabricating these aerogels can be complex. In this work we describe the use of a rapid supercritical extraction (RSCE) technique to prepare TiO2 and TiSi aerogels in as little as 8 h. The RSCE technique uses a metal mold and a four-step hydraulic hot press procedure to bring the solvents in the sol–gel pores to a supercritical state and control the supercritical fluid release process. Resulting TiO2 aerogels were powdery with BET surface areas of 130–180 m2/g, pore volumes ~0.5 cm3/g and skeletal densities of 3.6 g/mL. Monolithic TiSi aerogels were made using two different methods. An impregnation process, in which titania precursor was added to a silica sol–gel, took 4–8 days to complete with a 7-h RSCE and resulted in translucent aerogels with high surface area (560–650 m2/g) and pore volume (2.0–2.6 cm3/g), bulk densities ranging from 0.1 to 0.4 g/mL and skeletal densities of 2.3 g/mL. A co-precursor method for preparing TiSi aerogels took 8 h to complete. The precursor chemical mixture was poured directly into the mold and processed in a 7-h RSCE process. The resulting aerogels were opaque, with high surface areas (510–580 m2/g), low bulk density (0.03 g/mL), skeletal densities of 2 g/mL and pore volumes of 2.6–3.5 cm3/g. Preliminary solar simulator studies show that TiO2 and TiSi aerogels are capable of photocatalytic degradation of methylene blue in aqueous solution.

Keywords: Aerogel; RSCE; Titania; Titania–silica; Photocatalytic applications

Electric-field-induced antiferroelectric to ferroelectric and ferroelectric to paraelectric phase transition at various temperatures in (Pb, La)(Zr, Ti)O3 antiferroelectric thick films by Jun Liu; Wenping Geng; Xiujian Chou; Wendong Zhang (pp. 414-418).
(Pb, La)(Zr, Ti)O3 antiferroelectric thick films with (100)-preferred orientation were fabricated on Pt(111)/Ti/SiO2/Si(100) substrates via a sol–gel method. The electric-field-induced antiferroelectric (AFE) to ferroelectric (FE) phase transition characteristics were studied by C (capacitance)–E (electric field) measurements at different temperature. The films were in AFE state under 0 kV/cm below 122 °C, and the switching field values decreased, with increasing temperature. The films were in FE state between 122 and 135 °C, and when the temperature above 135 °C, the films were in PE state. The temperature-dependent dielectric parameters were deconvoluted using a Gaussian fit multi-peaks showed that two typical phase transitions were discovered. The first peak is the AFE-to-FE phase transition and the second peak is the FE-to-PE phase transition which has been verified by C–E tests.

Keywords: Antiferroelectric thick films; Sol–gel; Phase transition

Color tuning by co-doping of Er doped TiO2 phosphors within a fixed Er concentration by B. S. Cao; Y. Y. He; Z. Q. Feng; H. Z. Zhang; Z. S. Wei; B. Dong (pp. 419-423).
In this paper, we report the color tuning of Er doped TiO2 upconversion phosphors within a fixed Er concentration using 976 nm semiconductor laser diode excitation. By codoping with Mo, Yb or Li ions in the Er doped TiO2, the green and red upconversion emissions from the 2H11/2/4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er ions were enhanced selectively and the color output of Er doped TiO2 could be tuned by different intensity ratios of green to red emissions. The two-photon absorption processes were responsible for the green and red upconversion emissions of Er–Mo, Er–Yb and Er–Li codoped TiO2 phosphors, and the corresponding enhanced mechanisms were discussed. It is expected that these color tuned phosphors within a fixed Er concentration have great potential for applications in biology, displays and other optical technology.

Keywords: Er doped TiO2 ; Codoping; Color tuning; Upconversion

Superhydrophobic surface by immobilization of polystyrene on vinyl-modified titania nanoparticles by W. L. Liu; L. Wang; L. D. Zhang; W. H. Xu; S. H. Chen; X. Q. Wang; X. L. Duan (pp. 424-431).
The organic–inorganic nanocomposite films were fabricated by grafting polystyrene (PS) onto the vinyltriethoxysilane (VTEOS) modified titanium dioxide nanopowders using free radical polymerization. The composition of the surfaces and the structure for the PS grafted titania (PS-g-TiO2) were examined by infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis, and the rough surface was confirmed by the evaluation of the morphological characteristics of the coating using hybrid particles. The wetting properties of the VTEOS modified titania and PS-g-TiO2 films were investigated, which show the maximum static water contact angles of 160° and 154°, and minimum sliding angles of 3° and 4°, respectively.

Keywords: Superhydrophobic; Titanium dioxide nanoparticles; Vinyltriethoxysilane; Polystyrene; Grafting

Synthesis, characterization and visible-light photocatalytic activity of TiO2–SiO2 composite modified with zinc porphyrins by Jin-Hua Cai; Yuan-Jian Ye; Jin-Wang Huang; Han-Cheng Yu; Liang-Nian Ji (pp. 432-440).
Three types of silica gel supported titanium dioxide particles immobilizing Zn(II) carboxylphenyl porphyrins appending p-CH3, p-H and p-Cl phenyl substituents (designated as ZnMP–TiO2–SiO2, ZnPP–TiO2–SiO2 and ZnCP–TiO2–SiO2, respectively) have been synthesized and characterized using SEM, XRD, IR, AFS, DRS, UV–Vis, XPS and TG. The photodegradation of α-terpinene in aqueous suspension was used to determine the photocatalytic activity of TiO2–SiO2 samples which had been impregnated with Zn(II) porphyrins, as sensitizers. The experimental results confirmed that the photocatalytic activitys of these composites are much higher than those of the nonmodified TiO2–SiO2 under visible light irradiation and follow the order of ZnMP–TiO2–SiO2 > ZnPP–TiO2–SiO2 > ZnCP–TiO2–SiO2.

Keywords: Photocatalytic degradation; Visible light irradiation; Zn(II) carboxylphenyl porphyrins; Titanium dioxide

Hydrophobic siloxane paper coatings: the effect of increasing methyl substitution by Elisa Cappelletto; Emanuela Callone; Renzo Campostrini; Fabrizio Girardi; Simona Maggini; Claudio della Volpe; Stefano Siboni; Rosa Di Maggio (pp. 441-452).
Paper is an organic material widely used in cultural heritage and mainly composed of cellulose mixed with lignin, hemicellulose and small amounts of additives. This paper deals with siloxane coatings on pure cellulose paper, applied by sol–gel dipping in sols prepared with different siloxane precursors (tetraethoxysilane, methyl triethoxysilane, dimethyl diethoxysilane, trimethyl monoethoxysilane). The coated samples were characterized using various techniques (Fourier Transform Infrared Spectroscopy FT-IR, Nuclear Magnetic Resonance NMR and Scanning Electron Microscopy and Energy Dispersive Spectroscopy SEM–EDS), measuring their mechanical properties, flame resistance and contact angles, and a colorimetric test. The coated samples’ behavior was more hydrophobic the higher the methyl number of siloxane precursor, regardless of the coating’s thickness. Increasing the thickness improved the mechanical and thermal properties. The thickest coatings were obtained using a double coating process and a basic catalyst for the hydrolysis step, but this latter condition facilitated the formation of surface agglomerates, which make the paper too stiff and yellow.

Keywords: Sol–gel; Methyl-functionalized silanes; Solid-state NMR; Contact angle measurement

Magnesium doped ZnO nanoparticles embedded ZnO nanorod hybrid electrodes for dye sensitized solar cells by C. Justin Raj; S. N. Karthick; K. V. Hemalatha; Min-Kyu Son; Hee-Je Kim; K. Prabakar (pp. 453-459).
We report a novel type of Mg doped ZnO nanoparticles (ZMP) embedded on hydrothermally grown ZnO nanorod (ZR) based photoanode dye sensitized solar cells. The crystallinity, composition and morphology of the photoanodes were characterized by using X-ray diffraction analysis, X-ray photoelectron spectroscopy and scanning electron microscopy. The amount of dye absorbed in the photoanode was observed using UV visible spectral analysis. The improved internal resistance and charge-transfer kinetics of the fabricated cells were analyzed using electrochemical impedance spectroscopy. The ZMP embedded electrode of low thickness (~2.5 μm) gained an enhanced short-circuit current density of 8.56 mA/cm2, open-circuit photo voltage of 0.71 V, fill factor of 0.51, and overall conversion efficiency of 2.91 % under 1 sun illumination. This shows high conversion efficiency and performance than that of ZnO nanorod (η ~ 0.22 %) and bare ZnO nanoparticles (ZP) embedded ZnO nanorod (η ~ 1.04 %) based cells. The presence of Mg ions in the ZnO nanoparticle hinders the interfacial recombination of the photo-excited electrons with the electrolyte and also shows better dye absorption than that of ZR. These factors can significantly enhance solar-cell performance and increase the efficiency of the ZMP based dye sensitized solar cells.

Keywords: Nanostructured materials; Dye sensitized solar cells; Zinc oxide; Photoanode; Nanorods; Thin films

AFM measurements of forces between silica surfaces by Hasan Guleryuz; Arne K. Røyset; Ingeborg Kaus; Claudine Filiàtre; Mari-Ann Einarsrud (pp. 460-469).
Interaction forces and adhesion between a silica sphere and a flat silica surface in aqueous electrolyte solutions were investigated by atomic force microscopy. The forces were measured as a function of surface separation, pH and NaCl concentration as the surfaces were approaching each other. The adhesion force was determined upon retraction with respect to pH, NaCl concentration and contact time. The magnitude of the long range repulsive force was decreasing with decreasing pH. A short range repulsive force was observed at pH = 2, but no long range repulsive forces were observed at this pH. Force measurements showed that adhesion of silica surfaces in water was obstructed by short and long range repulsive forces. Adhesion was enhanced when both the long and the short range repulsive force was mitigated. A maximum adhesion force of 7.8 mN/m was measured at pH = 12.5 when the short range force vanished and the long range repulsive force was reduced by increasing the NaCl concentration. At pH = 12.5, the work of adhesion was calculated to be 1.2 mJ/m2 according to the Derjaguin–Muller–Toporov (DMT) model. Adhesion energy was much less at pH = 2 (0.3 mJ/m2) due to persistive short range repulsion.

Keywords: Silica; AFM; Colloidal probe; Adhesion; Chemical force spectroscopy

Highly functionalized bridged silsesquioxanes by Guannan Zhou; Thomas Simerly; Leonid Golovko; Igor Tychinin; Vladimir Trachevsky; Yury Gomza; Aleksey Vasiliev (pp. 470-482).
The objective of this work was to synthesize functionalized mesoporous silsesquioxanes with high concentrations of amine groups. During typical sol–gel syntheses, these materials are obtained by co-condensation of organic precursors with suitable linkers, such as tetraethoxysilane, necessary to prevent the mesoporous structure from collapsing. Thus, concentrations of amine groups in organosilicas usually do not exceed 2.7–3.4 mmol g−1. The use of bridged bis-trimethoxysilanes, however, allowed formation of mesoporous materials with no linker. Polycondensation of bis-trimethoxysilanes containing amine groups was conducted in acidic, neutral and basic media, resulting in high yields of solid bridged silsesquioxanes. Gelation occurred quickly if no acid or base was added to the reaction mixture. The hybrid organic/inorganic nature of obtained materials was confirmed by FT-IR and MAS CP NMR spectroscopy. Elemental analysis showed that amino group concentration in the products was 3.3–4.1 mmol g−1. Measurement of particle size distribution confirmed that choice of reaction media significantly affects particle sizes and agglomeration degrees, with the largest agglomerates (up to 50 μm) formed in basic media. A morphology study, using small-angle X-Ray scattering, displayed two-level fractal structures composed of aggregated 6.5–10.5 nm particles. Reactions in the presence of a surfactant resulted in formation of mesoporous structures. Furthermore, the obtained bridged silsesquioxanes were thermally stable down to 260 °C, but could reversibly absorb water and CO2 at temperatures below 120 °C. Thus, condensation of the bridged precursor without a linker resulted in formation of a highly functionalized mesoporous material.

Keywords: Sol–gel synthesis; Silsesquioxanes; Mesoporous materials; Microstructure; Amine groups

Structural and magnetic properties of TbxY3−xFe5O12 (0 ≤ x ≤ 0.8) thin film prepared via sol–gel method by Ftema W. Aldbea; N. B. Ibrahim; Mustaffa Hj. Abdullah; Ramadan E. Shaiboub (pp. 483-489).
Terbium-doped yttrium iron garnet (TbxY3−x Fe5O12; x = 0.0, 0.2, 0.4, 0.6 and 0.8) nanoparticles thin films have been prepared onto quartz substrate by sol–gel method followed by spin coating process. Annealing of the films was processed at 900 °C in air for 2 h. The structures were investigated by using an X-ray diffractometer (XRD) and a field emission scanning electron microscope (FE-SEM). The magnetic properties were studied by a vibrating sample magnetometer (VSM). The XRD patterns of the films were consistent with a single phase garnet structure. The lattice parameter was initially increased with Tb3+ concentration due to the larger size of the Tb3+ ion compared to Y3+ ion, but a decrease in lattice parameter was observed at higher Tb3+ concentration due to the effect of film’s thickness. FE-SEM micrographs reveal that the particles were highly agglomerated. The grain’s sizes for all films were in the range of 40–59 nm. The magnetic measurements at room temperature (25 °C) show that the saturation magnetization (Ms) of the films was reduced with the increase in Tb3+ ions, which due to the antiparallel alignment between Tb3+ ions and Fe3+ ions. The films illustrate normal shapes of hysteresis loops except Tb0.2Y2.8Fe5O12 and Tb0.4Y2.6Fe5O12 films exhibiting two steps increments before being saturated. The coercivity values (Hc) demonstrate non linear dependency with the terbium concentration (x).

Keywords: Garnet; Sol–gel; Spin coating; Magnetic properties

Recoverable and thermally stable superhydrophobic silica coating by Satish A. Mahadik; D. B. Mahadik; V. G. Parale; P. B. Wagh; Satish Gupta; A. Venkateswara Rao (pp. 490-494).
A facile route to methyltrimethoxysilane (MTMS) based recoverable superhydrophobic silica coatings with dual-scale roughness obtained through the single step base catalyst sol–gel process. Superhydrophobic silica coatings have shown static water contact angle near about 170 ± 1° and dynamic water contact angle up to 2 ± 1°. Superhydrophobic-superhydrophilic switching feature also achieved by alternating heat treatment and bath surface modification with Trimethylchlorosilane (TMCS) at room temperature (26 °C). Furthermore, the superhydrophobic state could be transformed into superhydrophilic state by slow rate heat treatment. These studies present a very simple strategy for the fabrication of recoverable superhydrophobic surfaces.

Keywords: Superhydrophobicity; Superhydrophilicity; Colloidal processing; Sol–gel preparation; Deposition

Microwave assisted hydrothermal synthesis of zinc hydroxystannate films on glass substrates by Mohammad Abbas Mahmood; Joydeep Dutta (pp. 495-504).
Zinc stannate (ZnSnO3, Zn2SnO4) and its precursor, i.e. zinc hydroxystannate (ZnSn(OH)6), have emerged as technological nanomaterials for different applications. Herein, we report synthesis of polycrystalline zinc hydroxystannate (ZHS) film on glass substrate through facile and efficient microwave assisted hydrothermal growth. The method comprises of three steps; deposition of ZnO seed films on glass substrates through spray pyrolysis, growth of ZnO nanorod arrays over the seeded substrates through microwave assisted hydrothermal method and transformation of the as-synthesized ZnO nanorod arrays into the ZHS films through microwave treatment in aqueous precursor solution of SnCl4 and NaOH. The films were characterized by energy dispersive X-ray spectroscopy, X-ray diffraction and scanning electron microscopy (SEM). The films contain two crystalline phases namely ZnO with [002] as preferred growth direction and ZnSn(OH)6 preferably grown along [200] vector. The obtained ZHS films consist of crystals of exclusively cubic structure with sizes up to several microns. Microwave irradiation time, NaOH/SnCl4 molar ratio, concentration of Sn4+ ions, and the applied power are the four parameters which influence the size, aerial density and growth rate of ZHS microblocks.

Keywords: Microwave; Hydrothermal; Nanorod; Array; Zinc hydroxystannate; Film

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