Abstract
•Ag0/Ag+/TiO2 composites were prepared via hydrothermal process with either CTAB or hybrid polymers.•The catalyst derived from CTAB revealed high activities on the reduction of 4-nitrophenol.•Conversion rate of 98% after 2min irradiation under visible light was perceived.•Residual carbons together with anatase percentages played main role in the reduction.
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 2min irradiation with rate constant equal 0.025s−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 (5nm) 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 (10nm), diminishing the accessibility and reactivity of Ag+ ions; which could have been worked as trapping sites with Ago, and the limited effect of residual S2- ions, depicted from XPS measurements.