Key Takeaways & Executive Findings
- •• • The GM/UiO-66 ternary heterojunction achieves an NH3 generation rate of 25.1 μmol g−1 h−1 under simulated solar illumination, which is 1.9 times higher than pristine UiO-66 (13.5 μmol g−1 h−1), demonstrating a substantial enhancement in photocatalytic nitrogen fixation efficiency. • • The internal electric field at the heterointerface drives anisotropic migration of photogenerated charges, leading to rapid separation of electron–hole pairs and suppression of interfacial recombination, which is critical for improving quantum efficiency in photocatalytic systems. • • The intrinsic defect structure of GO provides key sites for N2 adsorption and activation, while π–π interactions between GO and UiO-66 accelerate electron transfer, highlighting the role of defect engineering and interfacial interactions in enhancing catalytic activity. • • The Schottky junction between UiO-66 and MXene promotes hole transfer, and the introduction of GO and MXene enhances visible-light absorption of UiO-66, collectively contributing to the improved photocatalytic performance under solar irradiation.
Abstract
The efficient conversion of dinitrogen (N2) to ammonia (NH3) under mild conditions remains a critical challenge for sustainable nitrogen fixation. This study reports a rationally designed ternary heterojunction, GO/MXene/UiO-66 (GM/UiO-66), which achieves directed charge transfer for enhanced photocatalytic nitrogen fixation. The internal electric field at the heterointerface drives anisotropic migration of photogenerated charges, leading to rapid separation of electron–hole pairs and suppression of interfacial recombination. The intrinsic defect structure of graphene oxide (GO) provides active sites for N2 adsorption and activation, while π–π interactions between GO and UiO-66 accelerate electron transfer. Additionally, the Schottky junction between UiO-66 and MXene facilitates hole (h+) transfer. The incorporation of GO and MXene extends visible-light absorption of UiO-66. Under simulated solar illumination, GM/UiO-66 exhibits an NH3 generation rate of 25.1 μmol g−1 h−1, which is 1.9 times higher than that of pristine UiO-66 (13.5 μmol g−1 h−1). This work presents a novel strategy for designing ternary heterojunction composites that optimize charge transfer and significantly improve photocatalytic performance.
1. Introduction
The industrial fixation of nitrogen to ammonia via the Haber–Bosch process is energy-intensive, consuming approximately 2% of global fossil energy and emitting over 3% of greenhouse gases annually. This has driven the search for alternative, sustainable routes under mild conditions. Photocatalytic nitrogen fixation using semiconductor materials offers a promising approach, but challenges remain in activating the inert N2 molecule and achieving efficient multi-electron transfer. Metal-organic frameworks (MOFs) such as UiO-66 have shown potential due to their high surface area and tunable structure, yet their photocatalytic efficiency is limited by rapid charge recombination and poor visible-light absorption.
To address these bottlenecks, this work constructs a ternary heterojunction by integrating graphene oxide (GO) and MXene with UiO-66. The design leverages the internal electric field at heterointerfaces to direct charge migration, the defect sites of GO for N2 activation, and the Schottky junction with MXene for hole transfer. This synergistic architecture not only enhances charge separation but also extends light absorption into the visible region, resulting in a 1.9-fold increase in ammonia production compared to pristine UiO-66. The findings provide a viable strategy for designing efficient photocatalysts for nitrogen fixation under ambient conditions.
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JI Houqiang, SUN Yangyang, HUANG Tianyu, LI Qian, ZHANG Yanfei, PANG Huan (2026). Directed charge transfer over GM/UiO-66 ternary heterojunction for enhanced photocatalytic nitrogen fixation. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3684-4
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Frequently Asked Questions
What is the underlying mechanism for the enhanced charge separation in the GM/UiO-66 heterojunction?
The enhanced charge separation is attributed to the internal electric field formed at the heterointerface, which drives anisotropic migration of photogenerated electrons and holes. Additionally, the Schottky junction between UiO-66 and MXene facilitates hole transfer, while π–π interactions between GO and UiO-66 accelerate electron transfer, collectively suppressing recombination.
How does the introduction of GO and MXene affect the light absorption properties of UiO-66?
The incorporation of GO and MXene extends the visible-light absorption range of UiO-66, as evidenced by enhanced photocatalytic activity under simulated solar illumination. This is likely due to the synergistic effects of the heterojunctions and the intrinsic light-harvesting capabilities of GO and MXene.
What is the significance of the NH3 generation rate of 25.1 μmol g−1 h−1 compared to other reported photocatalysts?
The NH3 generation rate of 25.1 μmol g−1 h−1 is 1.9 times higher than that of pristine UiO-66 (13.5 μmol g−1 h−1), demonstrating a substantial improvement. While direct comparison with other systems requires standardized conditions, this rate is competitive and highlights the effectiveness of the ternary heterojunction design.
What are the potential scalability and stability concerns for practical application of GM/UiO-66?
The study focuses on laboratory-scale synthesis and testing. For practical application, issues such as long-term stability under continuous illumination, photocorrosion, and the cost of scaling up production of GO, MXene, and UiO-66 need to be addressed. Further studies are required to evaluate the durability and economic feasibility.
How does the defect structure of GO contribute to N2 adsorption and activation?
The intrinsic defect sites in GO provide active coordination sites that can adsorb N2 molecules and facilitate their activation by weakening the N≡N triple bond. This is crucial for the initial step of nitrogen fixation, as it lowers the energy barrier for subsequent reduction reactions.
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