Synthesis of C–N dual-doped Cr2O3 visible light-driven photocatalysts derived from metalorganic framework (MOF) for cyclohexane oxidation

Abstract

A series of novel C–N dual-doped Cr₂O₃ photocatalysts were synthesized from a chromium-containing MOF material, MIL-101(Cr), using a two-step method, including initial carbonization in nitrogen atmosphere without adding any carbon source and subsequent calcination in air. The physical and photophysical properties of the C–N dual-doped Cr₂O₃ photocatalysts were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) analysis, scanning electron microscopy (SEM), high resolution transmission electron microcopy (HRTEM), X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL), time-resolved PL decay (TRPL) and surface photovoltage (SPV). The results showed that the nitrogen atmosphere used in the carbonization process provided the nitrogen dopant and the organic ligands in the MOF acted as the carbon source in the dual-doped process. Carbon and nitrogen elements were doped in the Cr₂O₃ samples, which adopted substitutional rather than interstitial doping. In the process of synthesis, carbonization temperature was a crucial factor, which determined the doping amounts of the two elements as well as the crystallinities and morphologies of the as-prepared samples. Compared with C-doped Cr₂O₃, the C–N dual-doped Cr₂O₃ samples possessed better photocatalytic activity for cyclohexane oxidation with molecular oxygen under visible light irradiation. Based on the characterization and photocatalytic results, a C–N doping process, a possible mechanism for the visible light response of C–N dual-doped Cr₂O₃, and a reaction pathway of cyclohexane oxidation were proposed.