Characterization and enhanced photocatalytic performance of nanocrystalline Ni-substituted Zn ferrites synthesized by DEA-assisted sol–gel auto-combustion method

Nanocrystalline Ni-substituted Zn ferrites with compositions of Ni_xZn_1?xFe₂O₄ (x = 0–1.0) were synthesized by sol–gel auto-combustion method using metal nitrate as the reactants. Diethanolamine was selected as the fuel instead of conventional fuels such as urea, citric acid, tartaric acid or glycine. Characterization of after-calcined ferrite samples were conducted in terms of crystal structure, molecular vibrations, morphology and magnetic properties through X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscope and vibrating sample magnetometer analysis, respectively. The photocatalytic activities of these ferrites were studied in term of degradation of Rhodamine B under daylight-irradiation. The corresponding results indicate that nickel loading content has significant effect on physical, magnetic, optical and photocatalytic properties of the ferrite. Comparing to the undoped Zn ferrite, Ni_0.6Zn_0.4Fe₂O₄ shows the enhancement in photocatalytic activity accompanying the degradation of Rhodamine B aqueous solution up to 77 % within 4 h. The result suggests the feasibility of this material as potential sunlight-activated photocatalyst in wastewater treatment and environment cleaning applications.     

Crystallization process of lanthanum-substituted bismuth titanate synthesized by a facile sol–gel method

We present a facile sol–gel route to synthesize lanthanum-substituted bismuth titanate (BLT). The chemical reactions and crystallization process of this method using the initial materials of bismuth subnitrate [4BiNO₃(OH)₂·BiO(OH)], lanthanum nitrate [La(NO₃)₃·6H₂O] and tetrabutyl titanate [Ti(C₄H₉O)₄] were investigated by thermogravimetric and differential thermal analysis, IR spectroscopy, gas chromatography/mass spectrometry, Raman spectroscopy and XRD. The evaporation of the dissolved CO₂ in the amorphous BLT matrix is associated with the crystallization of BLT. The BLT gel is pure BLT perovskite when calcination temperature is higher than 500 °C. The grain size of the obtained nanoparticles ranges from 15 to 82 nm. The Arrhenius curve is obtained from the representation of the reduced sizes with respect to the calcination temperature. The activation energy of grain growth in BLT nanoparticles is 0.36 eV, which shows a rapidly growth process in the temperature range of 500–850 °C.     

Low temperature synthesis of Li5La3Nb2O12 with cubic garnet-type structure by sol–gel process

A cubic Li₅La₃Nb₂O₁₂ phase with a garnet framework was synthesized by the sol–gel process, in which lithium hydroxide, niobium oxide and acetic lanthanum were used as starting materials, while water was used as solvent. Pure garnet-like Li₅La₃Nb₂O₁₂ powders were obtained after heating the gel precursor at 700 °C for 6 h with 10 % excess lithium salt. The calcination temperature is nearly 250 °C lower than that by the solid state reaction. The phase transforms from cubic to tetragonal symmetry with loss of lithium at 717 °C, but the garnet framework remains stable to above 900 °C. A pellet annealed at 900 °C for 6 h had a room-temperature Li⁺-ion conductivity σ_Li (22 °C) = 1.0 × 10^?5 S cm^?1, a little higher than that attained by solid-state synthesis. The Li₅La₃Nb₂O₁₂ compound was chemically stable against two commonly used cathode materials, LiMn₂O₄ and LiCoO₂, up to 900 °C and against metallic lithium.     

Photocatalytic reduction of cadmium over CuFeO2 synthesized by sol–gel

The Cd²⁺ photo-electrodeposition was successfully carried out in air-equilibrated aqueous CuFeO₂ suspension. The delafossite CuFeO₂ is p-type semiconductor characterized by a low optical gap, properly matched to the sun spectrum, and a long term chemical stability in neutral solution. It has been elaborated by the sol–gel technique where the specific surface area is increased via the surface/bulk ratio. The TG/DSC plots and IR spectra show that the solid phases are formed only at temperatures exceeding 400 and at 700 °C, the system is mixed phases. When fired at 950 °C under nitrogen flow, the delafossite has been identified (CuO + CuFe₂O₄ → CuFeO₂ + ½O₂). All the XRD lines index in a hexagonal unit cell with the lattice constants a = 284.2 and c = 169.4 pm. The photocurrent onset potential (+0.35 V_SCE) is close to the flat band potential (+0.23 V_SCE) determined from the capacitance measurement. CuFeO₂/Cd²⁺ solution is a self photo-driven system, the absorption of light promotes electrons into CuFeO₂–CB with a potential (?0.93 V_SCE) sufficient to reduce Cd²⁺. This occurs because of the dark Cd²⁺ adsorption on the surface powder. The system was optimized with respect to the following physical parameters: pH 6.8, Cd²⁺ (100 ppm) and a mass concentration C_m (1 mg catalyst/ml solution). The hetero-system CuFeO₂/TiO₂ has been also reported for a comparative purpose. Prolonged irradiation (>50 min) was accompanied by a pronounced decrease in the rate of Cd-deposition owing to the competitive water reduction. Indeed, the generated bi-functional CuFeO₂/Cd particles account for the low over-potential of hydrogen and favour its evolution in aqueous solution.     

Fabrication and characterization of Zn3V2O8 phosphor by sol–gel process

By choosing zinc acetate dehydrate (Zn(CH₃COO)₂·2H₂O) and ammonium metavanadate (NH₄VO₃) as starting materials, we succeeded in fabricating Zn₃V₂O₈ phase suitable for broad light emission by sol–gel process. X-ray diffraction (XRD), scanning electron microscope, photoluminescence (PL) and PL quantum yield (PL-QY) measurements have been performed for analyzing the relation between crystallographic and light emission characteristics. The PL-QY is determined by both the crystalline phase purity of the Zn₃V₂O₈ phase defined by XRD patterns and the crystalline size. With optimizing the sintering condition at a slightly Zn-rich side, a pure Zn₃V₂O₈ phase with enough large crystalline size was obtained with the PL-QY value of 52 %, which was higher than our previously obtained value by solid state reaction.     

Preparation of superhydrophobic silica nanoparticles by microwave assisted sol–gel process

Hydrophobic silica nanoparticles were obtained by microwave assisted sol–gel method using a two-step procedure. In the first step different size silica particles were generated from tetraethyl orthosilicate and in the second one the silica particles were hydrophobized using hexadecyl trimethoxysilane (HDTMOS). Under microwave irradiation, high conversion degrees were obtained at relatively short reaction times. The HDTMOS added in the second step instead of coating the silica nanoparticles generated new ones and therefore the final product showed a bimodal size distribution. All the synthesized nanoparticles gave rise to high water contact angles (≈150°) and low hysteresis values.     

Crystallization kinetics of MgO–Y2O3 composite nanopowder synthesized via combustion sol–gel method

Journal of Thermal Analysis and Calorimetry - The aim of this study is to synthesize MgO–Y2O3 nanocomposite by combustion sol–gel method from sucrose as a combustion agent. The...     

Preparation of three-component TEOS-based composites for stone conservation by sol–gel process

Tetraethoxysilane (TEOS) is the most commonly used silicon-based stone consolidant in art conservation. However, it is known that the resulting silica gel phase tends to develop cracks inside the stone as the gel shrinks during aging and drying. Such phenomenon may lead to severe damage to the protected objects. By introducing silica nanoparticles into TEOS, a so-called particle modified consolidant (PMC), may minimize such shrinkage by reducing the volume loss and forming mesoporous structure to weaken the capillary forces. But many previous results show significant color changes on the surface of PMC-treated stones which can not be tolerated in the conservation treatments of cultural heritage. In this work, we designed a three-component composite consolidant which consists of 15 nm silica particles, α,ω-hydroxyl-terminated polydimethylsilane (PDMS-OH) and TEOS. Among the three components, TEOS provides the consolidation function, silica nanoparticles prevent the cracking and increase the salt resistance and PDMS-OH further reduces cracking, decreases the color alteration and increases the resistance to wetting of the stone. Experimental results show that the three components have significant synergistic effect, which makes the material exhibiting best overall performance in terms of cultural heritage protection.     

Microencapsulation of an acrylate monomer in silica particles by sol–gel process

The sol–gel synthesis strategies combined with the templated growth of organic–inorganic hybrid networks provide access to an immense new area of innovative multi-functional advanced materials. One possible way to prepare such new advanced materials is to encapsulate liquid active agents (such as monomers, dyes, catalysts and hardeners) in microcapsules. Silica microcapsules of tetraethylortosilicate (TEOS) and 3-(trimethoxysilyl)propyl methacrylate (MPTS) were prepared in a precursor-monomer/NH₄OH water microemulsion system. Trimethylolpropane triacrylate (TMPTA)—a trifunctional monomer useful in manufacturing of coatings, inks and adhesives—and a corresponding photoinitiator (DAROCUR 1173) were entrapped inside the obtained microcapsules. MPTS was used to increase compatibility between TMPTA and the sol–gel precursors. As stability agent we added a “home made” product resulted from functionalization of poly (ethylene glycol) methyl ether (MPEG) with (3-isocyanatopropyl) triethoxysilane (NCOTEOS). Were obtained microcapsules containing incorporated monomer and having average particle size in range of 0.5–50 μm. Thermal analysis, morphology study and the increase of the silica microcapsules average diameter, measured by DLS technique confirm the monomer encapsulation.     

Preparation and characterization of nanocrystalline Ca-doped CeO2 by sol–gel process

The reactivity of CeO₂ is determined by grain size and oxygen vacancies, which can be achieved by doping elements with less oxidation state into CeO₂. In this study nanocrystalline Ca-doped CeO₂ sol was synthesized from the reaction of hydrate cerium (III) nitrate and calcium nitrate tetrahydrate in alcohol solution after being calcined at 600?°C. X-ray diffraction as well as selected area electron diffraction gave evidence that the synthesized Ca-doped CeO₂ samples were well crystalline and had a cubic fluorite structure. TEM observation revealed that Ca-doped CeO₂ was composed by nanoparticles with grain size around 8?nm. The Raman spectrum of pure CeO₂ consists of a single triple degenerate F_2g model characteristic of the fluorite-like structure. In the Ca-doped CeO₂ sample, two additional low-intensity Raman bands were detected, thus confirming the formation of the solid solution. The synthesized nanometric powder is expected to be used in solid oxide fuel cells as well as in the catalytic treatment of automobile exhaust fumes.     

Synthesis of superhydrophobic fluoro-containing silica sol coatings for cotton textile by one-step sol–gel process

Journal of Sol-Gel Science and Technology - Superhydrophobic coatings were successfully fabricated on cotton textiles through a simple one-step sol–gel process. A fluorinated copolymer...     

Comparative study of the thermal behavior of Sr–Cu–O gels obtained by sol–gel and microwave-assisted sol–gel method

Journal of Thermal Analysis and Calorimetry - In the literature data, several papers reported the synthesis by various chemical or physical methods of the SrCu2O2 (SCO) having possible applications...