Direct synthesis of TiO2 nanoparticles without heat treatment: Effect of order of addition and precursor/reducing ratio

Abstract

Titanium dioxide (TiO2) is the most used semiconductor for heterogeneous photocatalysis. However, there is a limitation on its application since TiO2 works as catalyst only under ultraviolet radiation. Therefore, the synthesis of high-performance TiO2 NPs by a direct method without further calcination could improve the use of this catalyst. The current work aimed to obtain anatase/rutile TiO2 nanoparticles for photocatalysis under UV light by a direct method without further heat treatment. A 2k factorial design was used to evaluate the effect of the order of addition and ratio of the precursor/reducing agents on the synthesis of the NPs. TiO2 nanoparticles with large surface area were synthesized via the controlled precipitation method. The NPs were characterized by the XRD, DSC/TG, FTIR, BET, DLS, ELS, UV–Vis, FESEM-EDS techniques, and by the photocatalytic activity test. The commercial TiO2 NP P25 Evonik was used as standard photocatalyst for comparison with the obtained samples. The specific surface area (BET) of the TiO2 NP samples was three to five times higher in comparison to P25. The photoactivity of the TiO2 NP samples and P25 was determined as the discoloration of methylene blue and rhodamine B dyes under UVA radiation (330 nm, 12 W/m2) for 180 min. The results showed that the discoloration efficiency of the synthesized TiO2 NP samples is equivalent to that of the P25 sample. The synthesis of TiO2 nanoparticles via the controlled precipitation method using only two reagents proved to be a viable and promising route. The method does not require heat treatment for titanium dioxide crystallization and is still capable of producing a mixture of ideal phases to delay the recombination of the photogenerated electron-hole pair, contributing to the increase of the photocatalytic efficiency. The TiO2 NP samples will be used to the degradation of recalcitrant pollutants in water as textile dyes and pharmaceutical byproducts.