Effect of TiO(2) Morphology on the Properties and Photocatalytic Activity of g-C(3)N(4)/TiO(2) Nanocomposites Under Visible-Light Illumination.

This study focused on the preparation and investigation of g-C(3)N(4)/TiO(2) photocatalysts using different TiO(2) morphologies (anatase nanoparticles (TPs), poorly crystalline nanotubes (aTTs), and well-crystalline anatase nanorods (TRs)) and self-synthesized g-C(3)N(4) (CN). The synthesis of the g-C(3)N(4)/TiO(2) composites was carried out using a mortar mixing technique and a g-C(3)N(4) to TiO(2) weight ratio of 1:1. In addition, the g-C(3)N(4)/TiO(2) composites were annealed in a muffle furnace at 350 °C for 2 h in air. The successful formation of a g-C(3)N(4)/TiO(2) composite with a mesoporous structure was confirmed using the results of XRD, N2 physisorption, and FTIR analyses, while the results of microscopic analysis techniques confirmed the preservation of TiO(2) morphology in all g-C(3)N(4)/TiO(2) composites investigated. UV-Vis DR measurements showed that the investigated g-C(3)N(4)/TiO(2) composites exhibited visible-light absorption due to the presence of CN. The results of solid-state photoluminescence and electrochemical impedance spectroscopy showed that the composites exhibited a lower charge recombination compared to pure TiO(2) and CN. For example, the charge transfer resistance (RCT) of the CNTR/2 composite of TR and CN calcined in air for 2 h was significantly reduced to 0.4 MΩ, compared to 0.9 MΩ for pure TR and 1.0 MΩ for pure CN. The CNTR/2 composite showed the highest photocatalytic performance of the materials tested, achieving 30.3% degradation and 25.4% mineralization of bisphenol A (BPA) dissolved in water under visible-light illumination. In comparison, the pure TiO(2) and CN components achieved significantly lower BPA degradation rates (between 2.4 and 11.4%) and mineralization levels (between 0.6 and 7.8%). This was due to (i) the presence of Ti(3+) and O-vacancies in the TR, (ii) enhanced heterojunction formation, and (iii) charge transfer dynamics enabled by a dual mixed type-II/Z scheme mechanism.