Optical properties and electrical resistivity of boron-doped ZnO thin films grown by sol–gel dip-coating method

Sol–gel dip-coating was used to grow ZnO thin films doped with various concentrations of B ranging from 0 to 2.5 at.% on quartz substrates. The effects of B doping on the absorption coefficient (α), optical band gap (E_g), Urbach energy (E_U), refractive index (n), refractive index at infinite wavelength (n_∞), extinction coefficient (k), single-oscillator energy (E_o), dispersion energy (E_d), average oscillator strength (S_o), average oscillator wavelength (λ_o), moments M₋₁ and M₋₃, dielectric constant (ε), optical conductivity (σ), and electrical resistivity (ρ) of the BZO thin films were investigated. The transmittance spectra of the ZnO and BZO thin films show that the transmittance of the BZO thin films was significantly higher than that of the ZnO thin films in the visible region of the spectrum and that the absorption edge of the BZO thin films was blue-shifted. The BZO thin films exhibited higher E_g, E_U, and E_o and lower E_d, λ_o, M₋₁ and M₋₃ moments, S_o, n_∞, and ρ than the ZnO thin films.     

Eu3+ probe ion for rare-earth dopant site structure in sol–gel derived LiYF4 oxyfluoride glass–ceramic

Sol–gel route using metal alkoxides and trifluoroacetic acid as precursors has been used to prepare oxyfluoride glass–ceramic containing Eu³⁺-doped LiYF₄ nanocrystals of about tens of nm size embedded in a silica matrix through controlled crystallization at higher temperatures of the xerogel. Photoluminescence spectra and decay curves recorded in the Eu³⁺-doped LiYF₄ polycrystalline pellet and glass ceramic have been discussed using group-theoretical arguments. In the glass–ceramic Eu³⁺ ions are embedded dominantly inside the LiYF₄ nanocrystals most probably as Eu–O center and/or dimer centers in low symmetry (C_2v) sites; oxygen ions were incorporated in their neighborhood during the glass ceramization.     

Water‐Resistant Poly(vinyl alcohol)‐Silica Hybrids through Sol‐Gel Processing

Poly(vinyl alcohol) (PVA)‐silica hybrids with exceptionally reduced solubility in water were synthesized. The hybrid xerogels were fabricated through sol‐gel processing of a mixture of PVA and the acid‐catalyzed silica precursor tetraethoxysilane. The effects of varying ratios of PVA and silica precursor on the surface structure, thermal properties, crystallinity, and solubility of the hybrids were investigated. Unlike the highly water‐soluble nature of PVA, all the hybrids displayed considerably reduced solubility in water. This anomalous behavior of PVA in the hybrids can be attributed to the unavailability of its pendant –OH groups. Water‐resistant PVA‐silica hybrids can find applications in various technologies requiring biocompatible systems that are stable in aqueous environments.     

Investigating the role of a Schiff-base ligand in the characteristics of TiO2 nano-particles: Particle size,optical properties,and photo-voltaic performance of dye-sensitised solar cells

A Schiff base ligand was employed to synthesise TiO₂ nano-particles by a two-step sol–gel method. The effect of the ligand on purity, particle size, optical properties and photo-voltaic performance of dye-sensitised solar cells was investigated. Various concentrations of the ligand were applied and each sample was characterised. Changing the ligand content had an effective role on the optical and photo-voltaic properties of the final product. The obtained products were characterised through powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectra, energy-dispersive X-ray spectrometry and ultraviolet–visible spectroscopy.     

Synthesis of porous silicon nitride using silica/carbon composite derived from phenol–resorcinol–formaldehyde gel

Mesoporous silicon nitride (Si₃N₄), which is one of the most promising structural materials for applications in high-temperature filtration, was synthesized from the carbothermal reduction and nitridation of a pyrolyzed silica-containing phenol-resorcinol-formaldehyde (PRF) gel. The PRF gel was synthesized by combining sol–gel and polymerization of phenol, resorcinol and formaldehyde using sodium carbonate as a catalyst. Silica was incorporated into the gel by addition of 3-aminopropyl trimethoxysilane (APTMS) as a silica precursor. After aging and being freeze-dried, the silica/PRF composite was pyrolyzed under nitrogen gas to convert it into porous silica/carbon composite. The combination of phenol-formaldehyde (PF) and resorcinol-formaldehyde (RF) gels into PRF gel, allows further enhancement in porosity of the silica/carbon composite via pre-calcination in the range of 400–500 °C, since carbon derived from PF gel and that from RF gel have different thermal stability. The final product obtained after final calcination to remove residual carbon has a surface area as high as 194 m²/g, which is significantly much higher than the conventional Si₃N₄ granules. Specific surface area of the product is affected by molar ratio of phenol-to-resorcinol, molar ratio of silica-to-carbon, and the pre-calcination temperature.     

Surface properties of new green building material after TiO2–SiO2 coatings deposition

The aim of this study was the surface functionalization of a new green ceramic material, obtained using packaging glass waste (PGW), to improve its cleanability. This objective was reached through the deposition by air-brushing of a nanostructured coating based on titania–silica sol–gel suspension. The coatings were deposited on both glazed and unglazed ceramic substrates and the thermal treatment conditions (temperature) were optimized. The obtained results suggest that the applied coatings are transparent and show a good scratch resistance and photocatalitic activity under the tested conditions. The photodegradation process and the mechanical properties are clearly affected by the thermal treatment and thus by the sample surface roughness. The best surface properties were obtained with a thermal treatment at temperature of 150 °C. These coatings do not exhibit either cracks from the substrate. All in all, the developed surface modified ceramic material is attractive as potential sustainable building material.     

High‐Temperature Capture of CO2 on Lithium‐Based Sorbents Prepared by a Water‐Based Sol‐Gel Technique

A convenient water‐based sol‐gel technique was used to prepare a highly efficient lithium orthosilicate‐based sorbent (Li₄SiO₄‐G) for CO₂ capture at high temperature. The Li₄SiO₄‐G sorbent was systematically studied and compared with the Li₄SiO₄‐S sorbent prepared by solid‐state reaction. Both sorbents were characterized by X‐ray diffraction, scanning electron microscopy, nitrogen adsorption, and thermogravimetry. The CO₂ sorption stability was investigated in a dual fixed‐bed reactor. Li₄SiO₄‐G exhibited a special Li₄SiO₄ structure with smaller crystalline nanoparticles, larger surface area, and higher CO₂ adsorption properties as compared with Li₄SiO₄‐S. The Li₄SiO₄‐G sorbent also maintained higher capacities during multiple cycles.     

Preparation of double-doped BaCeO3 and its application in the synthesis of ammonia at atmospheric pressure

Perovskite-type oxides BaCe_0.90Sm_0.10O_3–δ (BCS) and BaCe_0.80Gd_0.10Sm_0.10O_3–δ (BCGS) were synthesized by the sol–gel method and characterized by thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Using the sintered samples as solid electrolytes and silver–palladium alloy as electrodes, ammonia was synthesized from nitrogen and hydrogen at atmospheric pressure in a solid-state proton-conducting cell reactor. The maximum rate of production of ammonia was 5.82 × 10^–9 mols^–1 cm^–2.     

Improving the yield of Jatropha curcas's FAME through sol–gel derived meso-porous hydrotalcites

The conversion of fatty acid methyl ester (FAME) from triglycerides using heterogeneous catalysis has gained increasing interest due to the prospect of increased yield at reduced operating costs and reaction conditions. In this paper, meso-porous hydrotalcite was used to catalyze jatropha oil into FAME with relatively higher yield at atmospheric pressure and relatively low reaction temperature. The molar ratio of methanol to oil required was relatively low and the conversion was completed within few hours of reaction time. The reaction was promoted when moderate calcination temperature was applied, the disordered structure of the catalyst was maintained, counterbalance anions was removed, and phase transitions within the oxide lattice was induced. Despite the observed deactivation during successive reaction cycles due to adsorption of residual triglycerides, the catalyst performance was restored effectively by air-re-calcination.