Synergistic C-TiO/ZIF-8 type II heterojunction photocatalyst for enhanced photocatalytic degradation of methylene blue.

Zinc imidazolate framework (ZIF-8) and titanium dioxide (TiO) have been extensively studied as photocatalysts and have shown remarkable potential. In this study, we report the synthesis of a type II heterojunction photocatalyst based on carbon-doped TiO (C-TiO) and ZIF-8 as a potentially improved material for solar light-harvested methylene blue (MB) degradation. Pure ZIF-8 has a wide band gap of 4.9 eV, due to which the application of this material to visible light-assisted photocatalytic performance is a challenging task. Therefore, C-TiO has been chosen as a composite material with ZIF-8 owing to its narrow band gap compared to TiO. This enables the free radical-initiated photocatalytic reaction to shift into the visible region instead of the ultraviolet region. To construct the C-TiO/ZIF-8 heterostructure, the zinc-based ZIF matrix has been built upon the exterior of C-TiO nanoparticles. UV-Vis diffuse reflectance spectroscopy (UV-Vis-DRS) corroborated the decrease in the band gap of ZIF-8 after the fabrication of C-TiO/ZIF-8, while X-ray diffraction (XRD) analysis demonstrated a decrease in average d-spacing and average crystallite size of the synthesized photocatalyst. Raman spectra and X-ray photoelectron spectroscopy (XPS) analysis of the synthesized samples were also performed to further understand their chemical structure and elemental content. Ultraviolet photoelectron spectroscopy (UPS) and high-resolution transmission electron microscopy (HRTEM) analyses were performed to understand the valence band (VB) states and the morphology of C-TiO/ZIF-8. The comparison between pure ZIF-8 and C-TiO/ZIF-8 in the photocatalytic degradation of MB under visible light has also been drawn. A possible charge-transfer mechanism for the same has also been proposed. It is concluded that the synergistic effect of C-TiO and ZIF-8 in C-TiO/ZIF-8 produces an effective material for photocatalytic dye degradation.