Fe/ZnIn₂S₄/Ni micro heterojunctions with enhanced charge transfer for efficient photocatalytic hydrogen and imine production

Replacing the challenging water oxidation with thermodynamically favorable organic oxidation presents a promising strategy for the efficient simultaneous production of hydrogen and value-added chemicals. However, photocatalytic activity is hindered by inefficient separation of photogenerated electron–hole pairs and limited redox active sites. Herein, Fe/ZnIn₂S₄/Ni (Fe/ZIS/Ni) micro heterojunctions were rationally engineered for synergistically photocatalytic hydrogen evolution and selective oxidation of benzylamine. Using Fe-based metal–organic frameworks (MIL-88A) as the self-etching morphology template and iron source, ZIS was grown in situ to obtain Fe-doped ZIS (Fe/ZIS). Then nickel was introduced into Fe/ZIS to locally construct Ni-doped ZIS (ZIS/Ni) microregion, thereby forming numerous microscopic heterojunctions (Fe/ZIS/Ni). The introduction of Fe effectively lowers the energy band (EB) position of Fe/ZIS, while the introduction of Ni elevates the EB position of ZIS/Ni microregion. Such difference in the EB structures of Fe/ZIS and ZIS/Ni promote the formation of local electric field, effectively suppresses the recombination of photogenerated carriers and enhances their efficient separation and migration. Moreover, the nanosheet assembly structure increases the availability of active sites and enhances the uptake of reactants. The optimized Fe/ZIS/Ni catalyst achieves remarkable hydrogen evolution and N-benzylidenebenzylamine (NBI) production rates of 7.9 and 6.8 mmol·g⁻¹·h⁻¹, respectively. Additionally, the selectivity for the oxidation of benzylamine to NBI exceeds 95%. This work establishes a novel design paradigm for developing high-performance photocatalytic systems that integrate renewable H₂ production with selective organic transformations.