Mechanistic Characteristics of Surface Modified Organic Semiconductor g-C₃N₄ Nanotubes Alloyed with Titania

The visible-light-driven photocatalytic degradation of Bisphenol A (BPA) was investigated using the binary composite of alkaline treated g-C₃N₄ (HT-g-C₃N₄) deposited over commercial TiO₂ (Evonik Degussa GmbH, Essen, Germany). The existence and contribution of both TiO₂ and g-C₃N₄/HT-g-C₃N₄ in the composite was confirmed through various analytical techniques including powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflectance spectra (UV-vis-DRS), and photoluminescence (PL) analysis. The results showed that the titania in the binary composite exhibited both pure rutile and anatase phases. The morphological analysis indicated that the spongy "morel-like" structure of g-C₃N₄ turned to nanotube form after alkaline hydrothermal treatment and thereby decreased the specific surface area of HT-g-C₃N₄. The low surface area of HT-g-C₃N₄ dominates its promising optical property and effective charge transfer, resulting in a deprived degradation efficiency of BPA two times lower than pure g-C₃N₄. The binary composite of HT-g-C₃N₄/TiO₂ exhibited excellent degradation efficiency of BPA with 2.16 times higher than the pure HT-g-C₃N₄. The enhanced photocatalytic activity was mainly due to the promising optical band gap structure with heterojunction interface, favorable specific surface area, and good charge separation.