Engineering rGO-Driven Z-Scheme Charge Dynamics in NH2-MIL-125(Ti)/ZIF-67 for Superior Green Energy Applications

Abstract

Photocatalytic H2O2 and H2 production address the energy crisis but demand efficient photocatalysts with broad solar absorption and reduced electron-hole recombination. However, pristine MOF-based photocatalysts often suffer from poor visible light absorption and fast charge recombination, limiting their efficiency. This study investigates the design and evaluation of a ternary-hybrid all-solid-state Z-scheme system composed of NH2-MIL-125(TI)(Ti) and ZIF-67, synthesized through a facile solvothermal approach followed by room temperature stirring. Integrating highly conductive rGO nanosheets as electron mediators promoted charge transfer and ROS generation, significantly improving photocatalytic efficiency. The hybrid catalyst achieved a H2O2 production rate of 2583 μmol/g/h with an apparent quantum efficiency of 5.47% at 400 nm and a H2 generation rate of 471 μmol/h, each marking a four-fold increase compared to the performance of the pristine MOFs. The synergetic interplay between rGO and the NH2-MIL-125(TI)/ZIF-67 binary framework was well-supported by PXRD studies, RAMAN spectra, EPR analysis, and electron microscopy studies, which is responsible for the superior visible light efficiency, better charge carrier separation, and a broader light absorption range of the ternary hybrid. The elemental composition was confirmed using ICP-OES analysis, CHNO analysis, and EDX spectra. The mechanistic investigation showed that in the ternary hybrid, electrons flow from NH2-MIL-125(TI)(Ti) to ZIF-67 through a Z-scheme charge dynamics via a solid-state electron mediator, rGO, and the charge transfer pathway was corroborated by analyses including XPS analysis, PL spectra, TRPL studies, and radical trapping experiments. This study offers valuable insights into designing efficient photocatalysts for sustainable green energy solutions.