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Studies of the characteristic and reaction mechanism of silica xerogel by sol–gel method catalyzed by alkylbiguanide as a strong organic base
摘要： Treatment of tetraethyl orthosilicate with 1,2-diisopropyl-4,4,5,5-tetra-methyl biguanide (A) as a highly strong base immediately gave silica gel by means of hydrolysis and condensation reaction at room temperature. The resulting wet gel was transparent and showed high density after dryness. From the results of gas adsorption and BET analysis, silica gel obtained by the treatment of strong base A had larger specific surface area and pore volume than silica gel that was prepared by a regular or less strong base such as tetramethylammonium hydroxide (TMAH). FTIR analysis revealed that the peak strength of Si-OH bond at 960 cm?1 of silica gel prepared by highly strong base A was smaller than that of TMAH. To understand the mechanism behind such difference, a mixture of diphenylsilandiol and dimethoxydiphenylsilane were reacted with highly strong base A, and the resulting products comprised linear-chain siloxane oligomer and octaphenylcyclotetrasiloxane. Our results indicate that silanol generated by hydrolysis of TEOS is activated by A and the activated silanol undergoes subsequent direct reaction with unhydrolyzed alkoxy silane to give condensation products in ethanol. Such a direct polycondensation between silanol and alkoxy silane brought by highly strong base A led to three-dimensional crosslinking having a higher bulk density of silica gel.
关键词： Biguanide,Silica xerogel,Sol–gel processes,Strong organic base
更新于2025-09-10 09:29:36
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Synthesis of novel ZnO/carbon xerogel composites: Effect of carbon content and calcination temperature on their structural and photocatalytic properties
摘要： This paper reports the development of new ZnO/carbon xerogel composites (XZn w) for photocatalytic applications. The use of black wattle tannin as a precursor to the carbon xerogel aimed at reducing costs and environmental impacts. The composites were characterized by di?use re?ectance spectroscopy (DRS), BET surface area, scanning electron microscopy (FEG-SEM), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), infrared spectroscopy (IR), and X-ray di?raction (XRD). The photocatalytic performance of the materials was evaluated in the decomposition process of methylene blue, a known toxic pollutant. The impacts of the catalyst dosage and calcination temperature on the photocatalytic process were also examined systematically. The X-ray pro?les of the XZn w evidenced the existence of the hexagonal structure of the zinc oxide (wurtzite) in the composites. The XPS and XRD analyses con?rmed the incorporation of carbon in the zinc oxide crystalline structure. The higher carbon content resulted in a larger surface area. All composites presented the ability to absorb radiation in less energetic wavelengths, contrary to pure zinc oxide that only absorbs radiation of wavelengths below 420 nm. The optimal dosage and calcination temperature were found to be 0.2 g L?1 and 300 °C. All the developed composites displayed signi?cant photocatalytic activities in the decomposition of methylene blue under both visible and solar light. The composites had superior photocatalytic e?ciency under visible light when compared to pure zinc oxide. The XZn 0.5 presented the best degradation e?ciency under visible radiation. All materials presented similar photocatalytic responses under solar light, evidencing the synergy between the carbon xerogel and the zinc oxide. The photocatalytic mechanism was evaluated by trapping experiments to be mainly controlled by the electron vacancies that are generated during the photoexcitation of the composites.
关键词： Zinc oxide,Methylene blue,Carbon xerogel,Tannin,Photocatalysis
更新于2025-09-10 09:29:36
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Characteristic of silica xerogel from rice husk ash wastes sintered by microwave and conventional
摘要： An attempt was made to produce silica from an agricultural waste, rice husks ash (RHA), as well as studied them. The high percentage silica content from ash of rice husks was used as silica source for sodium silica solution. Different heating temperature, time and acid treatments was studied for silica extraction. The composite is characterized and its microwave properties is investigated after sintering from 400 to 1200 oC. The results show the existing phases crystoballite at 1100 oC in microwave sintering. Preliminary experiment for reflection losses of silica alumina composite show that there are relation between degree of crystallinity and their reflection loss.
关键词： rice husk ash,microwave,alumina,Silica xerogel,sintering
更新于2025-09-04 15:30:14
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Magnetodielectric effect in a metamaterial consisting of xerogel with embedded ε-Fe2O3 iron oxide nanoparticles
摘要： The ε-Fe2O3 iron oxide is a fairly rare polymorphic modification, which only exists in the form of nanoparticles embedded, as a rule, into a silica gel matrix. This magnetically ordered iron oxide, which exhibits a significant room-temperature coercivity, is a ferroelectric; therefore, the magnetoelectric and magnetodielectric properties of this material evoke keen interest. In this work, we investigate the magnetodielectric (MD) effect in a metamaterial consisting of xerogel SiO2 with embedded ε-Fe2O3 nanoparticles 9 nm in size on average in a concentration of 20 mass.%. This bulk material exhibits the MD effect in a wide temperature range. The temperature behavior of the permittivity is related to the magnetic state of the ε-Fe2O3 oxide, which undergoes the magnetic transition from the magnetically hard to magnetically soft phase in the temperature range of 80–150 K, indicating the interplay of the ε-Fe2O3 magnetic and charge subsystems.
关键词： ε-Fe2O3,magnetodielectric effect,xerogel,multiferroics,nanoparticles
更新于2025-09-04 15:30:14
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Novel and inexpensive Nb2O5/tannin-formaldehyde xerogel composites as substitutes for titanium dioxide in photocatalytic processes
摘要： This project studied the preparation of new Nb2O5/tannin-formaldehyde xerogel composites (XTF-wNb) for photocatalytical applications. The choice of tannin biomass and niobium recycled scraps as precursors is aimed at reducing costs and environmental impacts. The composites were characterized by diffuse re?ectance spectroscopy (DR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), infrared spectroscopy (IR), and X-ray diffraction (XRD). The photocatalytic properties of the composites were evaluated by methylene blue decomposition. The in?uence of the catalyst dosage and the initial concentration of dye in the adsorption and photocatalysis processes were studied. The X-ray pro?les of the XTF-wNb show the presence of niobic acid in the structure of the materials, proving the presence of the inorganic oxide in the matrix of these composites. The tannin/Nb ratio had a signi?cant in?uence on the morphology of the formed composites, causing changes in the shape and size of the particles composing each material. All materials have pHPZC < 5. The XTF-24Nb was the most effective photocatalyst, its photocatalytic ef?ciency superior to the one of titanium dioxide, evidencing the bene?cial effect of the xerogel coupling on the photocatalytic properties of the material.
关键词： Photocatalysis,Niobium oxide,Xerogel,Tannin
更新于2025-09-04 15:30:14