Template-free hierarchical TiO2 synthesis: Investigations of structural, optical, and photocatalytic property relationships

Abstract

Researchers have recently been able to pinpoint a number of factors that affect the photocatalytic activity of semiconductors, but to date no clear correlation between them has been revealed. In this work, the photocatalytic activity of hierarchical titanium dioxide (TiO2) nanoparticles was studied in terms of phase concentration, morphology, surface area, and band gap energy (Eg). Particles were produced in acetone (AH), acetone–water (AHW), chloroform (CU), and chloroform-water (CUW). Anatase (A)-, rutile (R)-, and bronze (B)-containing TiO2 particles were ultimately formed. AH produced hollow and solid (A-R) urchins. AHW produced (A-R-B) spheres. CU formed (B) spheres. CUW provided (R) fibers. CU and CUW did not have many Ti3+ defects, in contrast to AH and AHW, which did. With the addition of water to acetone and chloroform, a significant reduction in specific surface area of TiO2 particles was observed, from 66.41 to 57.50 m2/g in AH and AHW and from 82.23 to 11.01 m2/g in CU and CUW, respectively. The Eg values of the associated particles were relatively comparable to one another (2.9–3.1 eV); however, their photocatalytic degradation performances were entirely distinct. In spite of having the lowest surface area, (R) fibers of CUW displayed the fastest photodegradation rate (0.20 h−1), which was followed by the hollow and solid (A-R) urchins of AH (0.04 h−1). The degradation rates of AHW and CU were similar. Surface area alone could not be correlated to the photocatalytic degradation capability, but this study originally showed that TiO2′s photocatalytic capability was mainly governed by its phase composition, not its hierarchical-morphology-driven surface area, despite having similar values of Eg. For the first time in the literature, (B) spheres were straightforwardly produced without the need for templates or high temperatures.