Acta Physico-Chimica Sinica | Professor Lai Yuekun's Research Group at Fuzhou University: Interface Engineering Type II Heterojunction ZnIn₂S₄/SCN for Enhancing Photocatalytic H₂O₂ Synthesis in Pure Water

First Authors: Yongkang Quan, Ruidong Li

A directional and high-speed e⁻/h⁺ transport channel was constructed, enabling the ZIS/SCN composite to exhibit excellent photocatalytic activity and stability under low-light conditions and in the absence of sacrificial agents.

In January 2026, Acta Physico-Chimica Sinica published online the latest research achievement of Professor Yuekun Lai's group from Fuzhou University in the field of carbon nitride photocatalysis. This work reports the construction of an interface-engineered heterojunction for photocatalytic H₂O₂ synthesis in pure water. The first authors of the paper are Yongkang Quan and Ruidong Li, and the co-corresponding authors are Jianying Huang and Yun Hao Ng.

Hydrogen peroxide (H₂O₂) is widely used as a green chemical in numerous industrial fields. Photocatalytic synthesis of H₂O₂ is considered a promising green synthesis route. However, single semiconductor materials are limited by insufficient photogenerated charge separation and low photocatalytic reaction efficiency. Constructing heterojunctions to enhance interfacial electron transfer and improve charge separation is essential for boosting photocatalytic activity. In this study, a Type-II ZIS/SCN heterojunction was constructed through a two-step method, forming a directional and high-speed e⁻/h⁺ transport channel. The built-in electric field (BEF) provides the driving force for e⁻/h⁺ transport and separation at the interface. Benefiting from the well-designed interfacial structure, the problems of high recombination rates of photogenerated electron-hole pairs and low photocatalytic activity in single semiconductor photocatalysts were effectively addressed. In this work, the ZIS/SCN Type-II heterojunction was successfully constructed by hydrothermal synthesis and thermal polymerization. ZIS/SCN exhibited excellent photocatalytic H₂O₂ synthesis performance without sacrificial agents, achieving a production rate of 257.0 μmol g⁻¹ h⁻¹ under 10 W LED irradiation, while maintaining good cycling stability over 10 cycles. This work highlights the importance of constructing heterojunction composite photocatalysts and is expected to overcome the inherent limitations of conventional photocatalysts. It also provides valuable reference for addressing energy shortages, realizing large-scale green production of H₂O₂ using solar energy, and efficiently treating organic wastewater.

Equipment Used in This Study

Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterization results show that SCN exhibits a porous layered structure. This structural feature contributes to the formation of an extended porous network with a large specific surface area, providing favorable conditions for subsequent semiconductor loading and charge transport.

X-ray photoelectron spectroscopy (XPS) was used to systematically analyze the chemical states and electronic interactions of the photocatalysts. The XPS survey spectrum shows that ZIS/SCN consists of C, N, Zn, In, and S elements, which is highly consistent with the elemental distribution revealed by SEM and TEM mapping analyses. XPS results show that the C 1s and N 1s binding energies in SCN both exhibit a positive shift of 0.2 eV, while the Zn 2p, In 3d, and S 2p binding energies in ZIS show corresponding negative shifts of 0.2 eV. These opposite and complementary binding energy shifts clearly confirm the directional electron transfer from SCN to ZIS at the heterojunction interface, and this charge transfer behavior directly drives the formation of the interfacial built-in electric field. When the two semiconductors are coupled, interfacial charge redistribution occurs based on the principle of energy level matching. As a result, atoms on the SCN side experience reduced electron cloud density due to electron loss, accompanied by increased binding energy, while atoms on the ZIS side experience increased electron cloud density due to electron accumulation, accompanied by decreased binding energy. It should be emphasized that the formation of the heterojunction only changes the local coordination environment and electron cloud distribution state of the atoms, without causing essential changes in the chemical valence states of the elements. These binding energy changes constitute direct evidence of interfacial interactions between semiconductors, revealing the direction of interfacial charge transfer from the perspective of microscopic electronic structure and clarifying the core mechanism behind enhanced photocatalytic performance.

The H₂O₂ generation performance of the prepared photocatalysts was evaluated in pure water using a 10 W LED light source (λ ≥ 420 nm). The H₂O₂ production rate of ZIS/SCN reached 257.0 μmol g⁻¹ h⁻¹, significantly higher than those of CN (24.5 μmol g⁻¹ h⁻¹), SCN (54.6 μmol g⁻¹ h⁻¹), and ZIS (67.5 μmol g⁻¹ h⁻¹). This result indicates that heterojunction construction strengthens the interfacial BEF effect, promotes charge transfer, and reduces carrier recombination, thereby improving the efficiency of photocatalytic H₂O₂ production. Under an O₂ atmosphere, the H₂O₂ generation rate was significantly increased to 328.3 μmol g⁻¹ h⁻¹, confirming the key promoting role of O₂ as a reactant in the oxygen reduction reaction (ORR). The collected photocatalytically generated H₂O₂ could efficiently degrade the organic pollutant methylene blue (MB, 10 mg L⁻¹) through a Fenton reaction within 10 min, achieving a removal rate of 95.2%, demonstrating its practical value in organic wastewater treatment.

Photoelectrochemical tests indicate that constructing the ZIS/SCN heterojunction is more favorable for enhancing visible-light absorption and the separation of photogenerated carriers.

The average charge density difference along the Z direction at the ZIS/SCN heterojunction interface visually presents the dynamic changes in charge density between SCN and ZIS during heterojunction formation. The results show that strong interactions exist between the two components: SCN undergoes electron depletion, while ZIS exhibits electron accumulation, resulting in charge redistribution at the heterojunction interface. From a thermodynamic perspective, the free energy changes of ORR during photocatalytic H₂O₂ generation over SCN, ZIS, and ZIS/SCN were investigated.

Electron paramagnetic resonance (EPR) and in situ Fourier transform infrared spectroscopy (In situ FT-IR) were used to analyze the intermediates formed during the photocatalytic reaction. When the two semiconductors are coupled, electrons spontaneously transfer from SCN to ZIS due to the difference in Fermi levels between ZIS and SCN, forming positively and negatively charged enrichment regions at the ZIS/SCN interface, respectively. Under light irradiation, electron-hole pairs are generated; photogenerated electrons migrate from SCN to ZIS, while photogenerated holes transfer in the opposite direction. This leads to electron enrichment on ZIS for participation in the oxygen reduction reaction (ORR), while holes are accumulated to participate in oxidation reactions, thereby achieving effective spatial separation of electrons and holes.

A ZIS/SCN Type-II heterojunction was successfully constructed through a two-step strategy combining thermal polymerization and hydrothermal synthesis. The formation of this Type-II heterojunction effectively promoted the separation and migration of photogenerated carriers, significantly improving the efficiency of photocatalytic H₂O₂ synthesis in pure water. DFT calculations indicate that the construction of the ZIS/SCN heterojunction optimizes the rate-determining step in H₂O₂ generation, making the production of H₂O₂ more thermodynamically favorable. In addition, in situ FT-IR and EPR spectroscopy results demonstrate that photocatalytic H₂O₂ production over ZIS/SCN follows a two-electron ORR pathway. This study realizes efficient green synthesis of H₂O₂ through the ORR pathway and provides important inspiration and reference for the design of heterojunction photocatalysts.

Yuekun Lai is a Professor and Ph.D. Supervisor at Fuzhou University, a National Leading Talent in Science and Technology Innovation, and was consecutively selected as a Clarivate “Highly Cited Researcher” from 2018 to 2023 in Materials Science and Cross-Field categories. He is a Distinguished Professor under the Fujian “Minjiang Scholar” Program and a recipient of the Fujian Provincial Outstanding Youth Fund and the “Hundred Talents Program”. He has long been engaged in research on multiphase separation, filtration and purification, environmental and energy chemical catalysis, bioinspired interfacial special wettability membranes, flexible sensing materials, and device development. He has co-authored more than 200 SCI papers in well-known domestic and international journals, with over 25,000 SCI citations and an h-index of 88. He has filed more than 50 invention patents, including 10 PCT international patents, and has been granted one U.S. patent and more than 20 Chinese invention patents. He serves as an Editor of the mainstream international chemical engineering journal Chemical Engineering Journal, Section Editor-in-Chief of Polymers, and an editorial board member of Green Energy & Environment, Advanced Fiber Materials, Acta Physico-Chimica Sinica, Nanomaterials, and Scientific Reports.

Research group website: https://yklai.fzu.edu.cn/

Yongkang Quan, Ruidong Li, Yunfei Yang, Shuguo Ding, Rongxing Chen, Jianying Huang^*, Yun Hao Ng^* and Yuekun Lai ^*, Interface-engineered Type-II heterojunction ZnIn₂S₄/SCN for enhanced photocatalytic H₂O₂ synthesis from pure water. Acta Physico-Chimica Sinica, 2026: 100237.

https://doi.org/10.1016/j.actphy.2026.100237