Facile Construction of S-Scheme Heterojunction of MgIn ₂ S ₄ /ZnS for Enhanced Photocatalytic Hydrogen Evolution under Simulated and Natural Solar Light

Hydrogen (H2) generation through photocatalytic water splitting continues to stand as one of the most promising alternatives to fossil fuels. For this purpose, photocatalysts must exhibit exceptional durability, efficiency, and the capability to harness solar energy fully for maximum output. In this work, we present the strategic design and fabrication of an advanced S-scheme heterojunction (HJ) photocatalyst comprising magnesium indium sulfide (MgIn2S4, MIS) and zinc sulfide (ZnS, ZS). This material was synthesized via a straightforward two-step hydrothermal route and evaluated for its effectiveness in driving light-induced H2 production from water splitting in the presence of a sacrificial agent. A series of characterizations illustrates the formation mechanism of the S-scheme HJ, the migration of photogenerated carriers, and related photocatalytic reactions. Experimental results confirm that the MIS/ZS S-scheme HJ can efficiently outperform pristine MIS and ZS. Among the MIS/ZS HJs (3, 5, 7, and 10 wt %), the 7-MIS/ZS HJ achieved the highest H2 evolution rate of 123.4 mmol·g–1·h–1, which is 8.8 and 28.05 times greater than those of pristine ZS and MIS, respectively. It also demonstrated an impressive apparent quantum yield of 22.42% at 370 nm, far surpassing those of its individual counterparts. This exceptional performance is attributed to the efficient S-scheme charge transfer, which promotes effective exciton separation and transport along with the robust structural stability inherited from ZS. Overall, this work provides a strong framework for designing durable, high-efficiency photocatalysts for water redox applications.