Effect of MCAA Synthesis and Calcination Temperature on Heterojunction Formation and Photocatalytic Activity of Biphasic TiO 2 (B/A)

This study investigates the impact of calcination temperature and the use of monochloroacetic acid (MCAA) as a complexing agent during the synthesis of TiO 2 heterojunctions on the photocatalytic performance of TiO 2 containing a heterojunction of anatase (A) and brookite (B). The TiO 2 samples were dried at 100 °C and subjected to calcination in the temperature range of 200–500 °C. As the calcination temperature increased, changes in chemical composition, phase composition, specific surface area, pore size distribution, and band gap energy were observed, influencing the photocatalytic behavior during Acid Orange (AO7) photodegradation. With increasing calcination temperature, the anatase content slightly increased to 81.8 wt.%, while the brookite content decreased. Additionally, the anatase crystallite size increased from 5 to 7 nm, and the brookite crystallite size increased from 8 to 11 nm. These phase changes were characterized by a slight decrease in the brookite/anatase (B/A) molar ratio from 0.27 to 0.22. Concurrently, the specific surface area of TiO 2 samples decreased from 180 to 70 m 2 g −1 , accompanied by alterations in the pore size distribution. The decrease in photocatalytic activity was evident, as the apparent rate constant k app of AO7 photodegradation declined from 2.1 × 10 –3 min −1 (100 °C) to 0.7 × 10 –3 min −1 (500 °C). This reduction was attributed to the partial destruction of anatase/brookite heterojunctions on the photocatalyst surface, which underwent changes in size and surface structure due to sintering. Moreover, the presence of Ti 3+ , Ti 4+ , Ti–O, and Ti–OH hydroxyl groups played a significant role in the degradation process. Overall, this investigation sheds light on the crucial role of calcination temperature in modulating the photocatalytic properties of TiO 2 heterojunctions and highlights the importance of heterojunction in enhancing photocatalytic activity. Graphical Abstract