Key Takeaways & Executive Findings
- •• • Fe3O4-Nv-12h achieves a total syngas production rate of 43.55 mmol g−1 h−1 with a CO/H2 ratio of approximately 1:1, representing an 805.2-fold enhancement over pristine Fe3O4, which is critical for industrial Fischer-Tropsch synthesis feedstocks. • • Nitrogen vacancy introduction modulates the electronic structure of Fe3O4, acting as electron traps to suppress photogenerated charge carrier recombination, as confirmed by EPR and XPS, directly addressing the bottleneck of low quantum efficiency in CO2 photoreduction. • • In situ FTIR spectroscopy identifies *COOH and *CO as key intermediates for CO formation, providing mechanistic evidence for the reaction pathway and enabling rational catalyst design for selective syngas production. • • The catalyst operates under visible light (λ ≥ 420 nm), utilizing a photosensitizer and TEOA sacrificial donor, achieving a performance that surpasses reported state-of-the-art photocatalytic CO2-to-syngas systems at a 1:1 ratio, demonstrating practical viability for solar-driven carbon neutralization.
Abstract
Photocatalytic reduction of CO2 to syngas (CO and H2) is pivotal for Fischer-Tropsch synthesis and carbon neutrality, yet suffers from rapid charge carrier recombination. Here, we report a solvent-induced defect engineering strategy to fabricate nitrogen vacancy (Nv)-modified Fe3O4 (Fe3O4-Nv-12h). Under visible light (λ ≥ 420 nm), Fe3O4-Nv-12h achieves a total syngas production rate of 43.55 mmol g−1 h−1 with a near 1:1 CO/H2 ratio, representing an 805.2-fold enhancement over pristine Fe3O4 and surpassing state-of-the-art systems. Electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) confirm that Nv introduction modulates the electronic structure, acting as electron traps to suppress recombination and enhance charge transport. In situ Fourier transform infrared (FTIR) spectroscopy identifies *COOH and *CO as key intermediates for CO formation. This work establishes an effective nitrogen vacancy modification strategy for efficient photocatalytic CO2 conversion to syngas, offering new avenues for high-performance catalyst design.
1. Introduction
Industrial Fischer-Tropsch synthesis (FTS) demands syngas with a CO/H2 ratio typically between 0.7 and 1.3, yet current photocatalytic routes suffer from low production rates due to rapid recombination of photogenerated charge carriers. While defect engineering has been explored, achieving both high activity and precise ratio control remains a critical bottleneck. Existing systems, such as MOF-based nanoreactors (0.26 mmol g−1 h−1) and Metal-Salen embedded MOFs (3.44 mmol g−1 h−1), demonstrate the challenge, with even the best reported black BaTiO3 nanofibers reaching only 12.53 mmol g−1 h−1.
This work introduces a solvent-induced defect engineering strategy to create nitrogen vacancies (Nv) in Fe3O4, resulting in Fe3O4-Nv-12h. The Nv act as electron traps, modulating the electronic structure to suppress charge recombination and enhance charge transport. This approach achieves a syngas production rate of 43.55 mmol g−1 h−1 with a near 1:1 CO/H2 ratio, an 805.2-fold improvement over pristine Fe3O4, directly addressing the productivity bottleneck while maintaining the required stoichiometry for FTS.
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Menglu Wei, Ting Zhou, Hongjing Chen, Ao Sun, Weidong Shi (2026). Nitrogen vacancy-modified Fe3O4 for efficient visible-light-driven CO2 photoreduction to syngas. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3922-2
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Frequently Asked Questions
What is the specific role of nitrogen vacancies in enhancing the photocatalytic activity of Fe3O4?
Nitrogen vacancies act as electron traps, as confirmed by EPR and XPS, which suppress photogenerated charge carrier recombination and promote charge transport. This modulation of the electronic structure facilitates the formation of key intermediates (*COOH and *CO) for CO production, leading to a 43.55 mmol g−1 h−1 syngas yield.
How does the CO/H2 ratio remain near 1:1 under visible light irradiation?
The near 1:1 CO/H2 ratio is achieved through balanced kinetics of CO2 reduction and proton reduction on the Fe3O4-Nv-12h surface. The nitrogen vacancies optimize the electronic structure to favor both pathways, as evidenced by the production rate of 43.55 mmol g−1 h−1 with a ratio of approximately 1:1, which is suitable for Fischer-Tropsch synthesis.
What are the long-term stability and recyclability of Fe3O4-Nv-12h under operational conditions?
The paper does not provide explicit long-term stability data, but the catalyst demonstrates high activity (43.55 mmol g−1 h−1) and structural integrity as confirmed by post-reaction characterization (XPS, EPR). Further studies are needed to assess deactivation over extended cycles, but the defect engineering approach is designed to maintain electronic structure stability.
How does the performance of Fe3O4-Nv-12h compare to other state-of-the-art photocatalytic syngas systems?
Fe3O4-Nv-12h achieves a syngas production rate of 43.55 mmol g−1 h−1, which is 805.2 times higher than pristine Fe3O4 and surpasses reported systems such as ReCo-NU(7/3) (0.26 mmol g−1 h−1), Metal-Salen MOFs (3.44 mmol g−1 h−1), and black BaTiO3 nanofibers (12.53 mmol g−1 h−1), all at a 1:1 CO/H2 ratio.
What is the industrial relevance of achieving a 1:1 CO/H2 ratio at such high production rates?
A 1:1 CO/H2 ratio is essential for Fischer-Tropsch synthesis to produce light olefins (ethene, propene, butene). The high production rate of 43.55 mmol g−1 h−1 makes this catalyst a promising candidate for scalable solar-driven CO2 conversion, potentially reducing reliance on fossil-fuel-derived syngas and contributing to carbon neutrality.
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