A convenient double defect engineering avenue for NH2-MIL-125 to enhance photocatalytic hydrogen evolution and NO removal via accelerating the electron mobility

Defect engineering for MOFs is a promising approach to accelerate the charge transfer to further enhance the photocatalytic performance. Up to now, the current defect engineering strategy for MOFs mainly focuses on a single adjustment mode with the apparent ceiling effect, whether the further break out of the ceiling effect could be achieved through the combination of two or more adjustment modes is still in its infancy. In this work, the original NH₂-MIL-125 was firstly adjusted by a single adjustment mode in ethanol solvothermal method to obtain partially linker defective NM-125-X (where X signifies the distinct temperatures used in the solvothermal treatment, with optimal results observed at X = 120). Subsequently, the NM-125-120 was further re-regulated by adjusting the ligand defects through another adjustment mode in water heating agitation, resulting in the ultimate defective NM-125-120-65. The NM-125-120-65 obtained through double defect engineering avenue showed superior photocatalytic performance with the hydrogen production rate of 11585.23 μmol·g⁻¹, which was 1.23 and 14.05 times as those of partially defective NM-125-120 (9427.65 μmol·g⁻¹) and original NH₂-MIL-125 (824.85 μmol·g⁻¹), respectively. In addition, the NO removal rate of NM-125-120-65 was 64.8 % also higher than that of NM-125-120 (37.8 %) and NH₂-MIL-125 (23.6 %). Through a series of comparative experiments, especially TGA and XPS, it was noted that the ligand defective NH₂-MIL-125 can be formed by ethanol solvothermal method, and it was also confirmed that through further re-regulating the ligand defects in water heating agitation, the linker defects could also be further expanded. The PL emission spectra, IT diagrams, and EIS measurements displayed that the NM-125-120-65 had outstanding conductivity and excellent electron mobility compared to NM-125-120 and NH₂-MIL-125. This work provided a novel approach for the subsequent defect engineering by another adjustment mode based on the existing defective MOFs via double linker defect engineering adjustment modes, so as to further obtain better photocatalytic performance for solving the environmental and energy crisis.