The use of visible light active materials in water decontamination is an interesting strategy to improve the feasibility of photocatalytic systems. Tungsten trioxide (WO 3 ) presents typically low-cost and simple production, good stability, and activity in the visible spectrum, especially compared to other metal oxides, such as TiO 2 . Herein, two synthesis routes, sol-gel and hydrothermal, were explored, and key parameters (synthesis temperature and time, precursor ratio, pH, and calcination temperature) were varied to better understand their effect on the catalyst’s activity in the photocatalytic removal of a mixture of methyl-, ethyl-, and propylparabens under natural sunlight. Hydrothermal synthesis led to materials with better activity, achieving removals of 36.5 – 41.2 %, after 120 min under natural sunlight, using a catalyst synthesized at 150 ºC, pH of 0.5, during 24 h, and calcined at 500 ºC. The sol-gel method resulted in materials with an overall higher surface area, up to 81.9 m 2 g -1 , and synthesized in milder conditions, although the best catalyst produced achieved only up to 23.9 – 26.3 % parabens removal, synthesized with a 8:6 Na 2 WO 4 ·2H 2 O:C 6 H 8 O 7 ratio, for 24 h at 25 ºC, and calcined at 500 ºC. The higher crystallinity degree obtained through the hydrothermal route may play a more relevant role in the final contaminants’ abatement. Besides, the good photochemical characteristics of WO 3 , the synthesis method and its conditions have a crucial role in photocatalytic activity.
Fernandes et al. (Wed,) studied this question.