Enhanced photocatalytic activities of a hierarchical ZnO/V2C MXene hybrid with a close coupling heterojunction for the degradation of methyl orange, phenol and methylene blue dye

Abstract

The rapid conversion of refractory organic dyes to CO₂ and H₂O by photocatalytic technology is an important way for water environment recovery, but it is still a major challenge due to the undesirable photocatalytic performance of photocatalysts including a low degradation rate and poor stability. Herein, a hierarchical porous ZnO/V₂C nanocomposite was constructed by the heterojunction between V₂C and ZnO nanosheets using a facile electrostatic self-assembly method. The hierarchical structure showed good photocatalytic performance in the degradation of three charged organic dye molecules including anionic methyl orange (MO), neutral phenol, and cationic methylene blue (MB). The degradation rates reached 77.94%, 73.24%, and 98.9%, respectively, under UV irradiation for 120 min. Also, the apparent degradation rate constants (k) were 0.01126 min⁻¹, 0.00788 min⁻¹, and 0.03424 min⁻¹, respectively, which were 3.92, 8.90, and 14.27 times higher than those of pure ZnO. This was probably attributed to the close coupling structure between ZnO and V₂C which can facilitate carrier transfer. The photogenerated electrons were transferred from the conduction band (CB) of ZnO to the CB of V₂C, which was conducive to promoting the separation and transfer of carriers and reducing the recombination of carriers, thereby significantly improving the photocatalytic degradation efficiency. In addition, the ZnO/V₂C hierarchical structure exhibited good photocatalytic stability. After 4 cycles, the degradation rate remained at 94.1%, while that of pure ZnO remained at 18.5% because the obtained ZnO/V₂C hierarchical structure could provide uniform surface active sites and porous structures, preventing the aggregation of ZnO or V₂C. This work could provide a feasible design strategy for the synergistic utilization of different dimensional materials.