Nitrogen-doped porous carbon TiO2 produced by thermolysis of MIL-125-NH2 under an inert atmosphere for enhanced visible light photocatalytic activity

Abstract

Metal-organic frameworks have gained significant attention as precursors for the synthesis of functional materials with tailored properties. In this study, we present the synthesis and characterization of nitrogen-doped porous carbon TiO2 (N-C/TiO2) by thermolysis of MIL-125-NH2. The effect of calcination temperature (ranging from 300 to 900°C) and atmospheric conditions on the phase transition, elemental composition and morphological structure is thoroughly investigated. Through X-ray diffraction (XRD) analysis, we identified the formation of the rutile phase in the N-C/TiO2 nanoporous structure, which leads to the creation of oxygen vacancies and metal defects. Interestingly, the orthorhombic shape of MIL-125-NH2 is retained in the final N-C/TiO2 product, indicating the robustness of the conversion process. The UV-Vis diffuse reflectance (UV-Vis) and photoluminescence (PL) analysis demonstrated that the phase transition results in a narrowed band gap energy and reduced recombination of photogenerated electron-hole pairs. The photocatalytic activity of the synthesized N-C/TiO2 is evaluated by the degradation of methylene blue (MB) dye under visible light irradiation. Our results revealed that superoxide radicals are the primary species responsible for the photocatalytic reaction. Furthermore, the N-C/TiO2 photocatalyst exhibits excellent stability and recyclability for five consecutive photocatalytic cycles. Overall, this study provides novel insights into the synthesis, characterization and photocatalytic activity of N-C/TiO2 material derived from MIL-125-NH2, emphasizing the significance of calcination temperature and atmospheric conditions. The developed N-C/TiO2 poses great potential for various environmental and energy applications where enhanced visible light photocatalytic activity is desired.