Sol–gel synthesis of TiO2 from TiOSO4: characterization and UV photocatalytic activity for the degradation of 4-chlorophenol

Abstract

Nanosized titanium dioxide (TiO2) powders were prepared by an aqueous sol–gel method using an inorganic titanium precursor, titanium oxysulfate (TiOSO4). The synthesized powders were characterized by XRD, N2 sorption analysis, SEM, TEM, FTIR and UV-vis DRS spectroscopy. The important synthesis parameters such as precursor concentration, precipitating pH value, peptization temperature, aging time and temperature, heating rate and time and calcination temperature were systematically investigated for their effect on the physicochemical and photocatalytic properties of TiO2. XRD analysis revealed that powders prepared at precipitating pH value ranges from 5 to 9, calcined at 300–600 °C were composed of anatase and brookite. UV-vis DRS analysis showed that the variation in band gap for composite mixture is related to the fraction of brookite and rutile phase. Using low precursor concentration (0.1 and 0.2 M) the final material was composed of anatase–brookite composite mixture, in contrast, at high precursor concentration (0.4 M), pure anatase TiO2 was formed. An increase in aging time beyond 24 h favors the phase transformation of brookite into anatase and increase in peptization temperature from 40 to 70 °C shows a great influence on crystal structure, leading to enhanced crystallization rate with the formation of pure anatase phase. The synthesized powders activity was tested in the degradation of an aqueous solution of 4-chlorophenol (4-CP) under UV light. The TiO2 powder prepared at pH 6 and calcined at 300 °C showed the highest activity, which is attributed to powder composite nature (anatase–brookite; 81–19 wt.%), relative high specific area (157.0 m2 g−1), high crystallinity and degree of hydroxyl groups and moderate band gap. In addition, in terms of reusability, recyclability and chemical stability, the developed photocatalyst showed very encouraging results.