Multifunctional MgAl LDH/Zn-MOF S-scheme heterojunction: efficient hydrogen production, methyl red removal, and CO2 adsorption

Abstract

Metal–organic frameworks (MOFs) and layered double hydroxides (LDHs) are undoubtedly promising and valuable materials for developing advanced catalysts to achieve efficient hydrogen evolution. The unique structures, environmentally friendly nature, and high redox activities of these materials make them ideal for catalytic applications. In this study, a delicately constructed S-scheme heterojunction photocatalyst, denoted as MgAl LDH/Zn-MOF, was designed and synthesized through the in situ nucleation of Zn-MOF nanostructure on MgAl LDH nanosheets, based on their excellent electronic properties and opposite surface potential. The MgAl LDH/Zn-MOF photocatalyst exhibited enhanced photocatalytic hydrogen evolution activity (129 mmol g⁻¹) compared to Zn-MOF and MgAl LDH alone. This was mainly due to the formation of the MgAl LDH/Zn-MOF S-scheme heterojunction, which effectively accelerated the recombination of several electrons (from the conduction band of Zn-MOF) and holes (from the valence band of MgAl LDH), thus preventing the recombination of other electrons (from the conduction band of MgAl LDH) and holes (from the valence band of Zn-MOF), which is a critical requirement for efficient hydrogen evolution. Further, the MgAl LDH/Zn-MOF has a high potential for methyl red removal (97% following the intraparticle diffusion model with a maximum R² value of 0.996). The CO₂ adsorption isotherms of the MgAl LDH/Zn-MOF revealed a gravimetric CO₂ uptake capacity of 129.7 mg g⁻¹ (at 298 K and 40 bar) and stable cyclic adsorption performance. These findings demonstrate the potential of MOFs and LDHs for developing advanced catalysts for efficient hydrogen evolution and highlight the importance of heterojunction design.