Visible light assisted reduction of 4-nitrophenol to 4-aminophenol on Ag/TiO₂ photocatalysts synthesized by hybrid templates

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• 作者：Mohamed Mokhtar Mohamed ; Merfat S. Al-Sharif
• 关键词：Photoreduction ; p-Nitrophenol ; Ag/TiO2 ; Hybrid template ; Characterization
• 刊名：Applied Catalysis B: Environmental
• 出版年：2013
• 出版时间：October-November, 2013
• 年：2013
• 卷：142-143
• 期：Complete
• 页码：432-441
• 全文大小：3204 K

文摘

Silver nanoparticles were successfully assembled in self-organized polyhedral TiO₂; synthesized by hybrid template consisting of pluronic-85, hexadecyltrimethylammoinm bromide and triethanol amine (TPHtAg₂), as well as in platelets TiO₂; synthesized only via hexadecyltrimethylammonium bromide (THAg₂). X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, diffuse reflectance UV-vis spectroscopy as well as N₂ sorptiometry were used for the characterization of phase composition, surface morphology, valent states of Ag/TiO₂, optical and surface texturing properties. These nanomaterials were tested as catalysts for 4-nitrophenol (4-NP) reduction in presence of aqueous NaBH₄ under visible-light irradiation. The results showed that the THAg₂ catalyst exhibited the best photocatalytic performance in the reduction of 4-NP into 4-aminophenol (4-AP) and revealed 98 % conversion following 2 min irradiation with rate constant equal 0.025 s^?1. On the other hand, the TPHtAgS₂ catalyst, derived from using Ag₂SO₄ as a precursor instead of AgNO₃, indicates a conversion comprised of 80 % at similar reaction conditions. The superiority of the photocatalytic reduction of THAg₂ was due to exposing Ag⁺ ions together with Ag⁰ nanoparticles (5 nm) and to the photo-induced role of carbon atoms; formed as a result of the non-complete decomposition of the template, and its synergistic effect with the anatase phase. On the contrary, TPHtAg₂ showed strong chemical interaction of Ag⁺ ions within the hybrid templates and as a result inhibits the reduction of Ag⁺ ion as well as the adsorption of 4-NP and eventually indicates no activity. The decreased activity and stability of TPHtAgS₂ compared with THAg₂ was due to increasing the particles size of Ag⁰ (10 nm), diminishing the accessibility and reactivity of Ag⁺ ions; which could have been worked as trapping sites with Ag^o, and the limited effect of residual S^2- ions, depicted from XPS measurements.