Key Takeaways & Executive Findings
- •• BiOCl atomic layers (BOCNSs-i) were prepared by exfoliating hydrothermally synthesized BiOCl via ultrasonication in isopropanol, achieving efficient photocatalytic CO2 overall splitting to CO and O2. • BOCNSs-i exhibits a CO evolution rate of 134.8 µmol g−1 h−1 under simulated solar light (1.7 suns) and 13.3 mmol g−1 h−1 under concentrated solar irradiation (34 suns), surpassing state-of-the-art BilOmXn photocatalysts. • The atomic-layer thickness shortens charge transfer distance and enhances built-in electric field, promoting charge carrier separation and migration to the surface. • Oxygen vacancies introduce electrons enriched Bi active sites that lower the energy barrier of the rate-determining step, while H2O vapor exchanges oxygen atoms with CO2 to further improve photocatalytic performance.
Abstract
Given the limited exposure of active sites and the retarded separation of photogenerated charge carriers in those developed photocatalysts, photocatalytic CO2 splitting into value-added chemicals has suffered from the poor activity and remained in great challenge for real application. Herein, hydrothermally synthesized BiOCl with layered structure (BOCNSs) was exfoliated into thickness reduced nanosheets (BOCNSs-w) and even atomic layers (BOCNSs-i) via ultrasonication in water and isopropanol, respectively. In comparison with the pristine BOCNSs, the exfoliated BiOCl, especially BOCNSs-i with atomically layered structure, exhibits much improved photocatalytic activity for CO2 overall splitting to produce CO and O2 at a stoichiometric ratio of 2:1, with CO evolution rate reaching 134.8 µmol g−1 h−1 under simulated solar light (1.7 suns). By surpassing the photocatalytic performances of the state-of-the-art BilOmXn (X: Cl, Br, I) based photocatalysts, the CO evolution rate is further increased by 99 times, reaching 13.3 mmol g−1 h−1 under concentrated solar irradiation (34 suns). This excellent photocatalytic performance achieved over BOCNSs-i should be benefited from the shortened transfer distance and the increased built-in electric field intensity, which accelerates the migration of photogenerated charge carriers to surface. Moreover, with oxygen vacancies (VO) introduced into the atomic layers, BOCNSs-i is exposed with the electrons enriched Bi active sites that could transfer electrons to activate CO2 molecules for highly efficient and selective CO production, by lowering the energy barrier of rate-determining step (RDS), *OH + *CO2− → HCO3−. It is also realized that the H2O vapor supplied during photocatalytic reaction would exchange oxygen atoms with CO2, which could alter the reaction pathways and further reduce the energy barrier of RDS, contributing to the dramatically improved photocatalytic performance for CO2 overall splitting to CO and O2.
1. Introduction
Solar-driven photocatalysis converting CO2 to fuels is a promising strategy to cope with greenhouse effect and energy dilemma [1–3]. However, the low-density exposure of reactive sites and the fast recombination of photogenerated electrons and holes in those developed photocatalysts significantly inhibit the photocatalytic CO2 reduction activity and thus impose the inevitable restriction on its practical implementation [4, 5]. With thickness reduced to be several nanometers and even atomic layers, two-dimensional (2D) ultrathin architectures acting as photocatalysts are believed to reduce charge carrier recombination on account of the shortened diffusion distance from bulk to surface. In addition, 2D ultrathin photocatalysts possess much increased specific surface areas that expose abundant reactive sites for sufficient atom utilization and thus much improved photocatalytic activities [5–8].
As a kind of well-studied 2D semiconductors for photocatalysis, bismuth oxyhalides, BilOmXn (X: Cl, Br, I), are featured with layered structure constructed by [BilOm] and [Xn] layers. Given the strongly covalent-bonded atoms in monolayers and the week van der Waals force between monolayers, BilOmXn is hospitable to be exfoliated to ultrathin nanosheets, endowed with anisotropic carrier transfer property, and thus promoted charge separation ability [9–11]. For example, in comparison with bulk Bi3O4Br, the Bi3O4Br nanosheets with ultrathin thickness of about 1.7 nm possessed a remarkably improved charge separation efficiency, owing to the shortened diffusion distance of photogenerated carriers from bulk to surface [12]. Interestingly, with thickness reduced from 120 to 30 nm by liquid-phase exfoliation, the built-in electric field was strengthened significantly in the obtained Bi3O4Cl single-crystal nanosheets, contributing to the much enhanced charge separation and photocatalytic activity.
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Ting Peng, Yiqing Wang, Chung-Li Dong, Ta Thi Thuy Nga, Binglan Wu, Yiduo Wang, Qingqing Guan, Wenjie Zhang, Shaohua Shen (2025). BiOCl Atomic Layers with Electrons Enriched Active Sites Exposed for Efficient Photocatalytic CO2 Overall Splitting. Nano-Micro Letters. https://doi.org/10.1007/s40820-025-01723-2
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Frequently Asked Questions
What is the main achievement of this study?
The study demonstrates that BiOCl atomic layers (BOCNSs-i) achieve highly efficient photocatalytic CO2 overall splitting to CO and O2, with a CO evolution rate of 134.8 µmol g−1 h−1 under simulated solar light and 13.3 mmol g−1 h−1 under concentrated solar irradiation, surpassing state-of-the-art bismuth oxyhalide photocatalysts.
How were BiOCl atomic layers prepared?
BiOCl atomic layers were prepared by hydrothermally synthesizing BiOCl nanosheets (BOCNSs) and then exfoliating them via ultrasonication in isopropanol, resulting in atomically thin layers (BOCNSs-i).
What role do oxygen vacancies play in the photocatalytic performance?
Oxygen vacancies introduced into the atomic layers create electrons enriched Bi active sites that facilitate electron transfer to CO2 molecules, lowering the energy barrier of the rate-determining step and enhancing selective CO production.
How does the thickness reduction improve charge separation?
Reducing the thickness to atomic layers shortens the charge transfer distance from bulk to surface and increases the built-in electric field intensity, which accelerates the migration of photogenerated charge carriers and reduces recombination.
What is the significance of the stoichiometric ratio of CO to O2?
The stoichiometric production of CO and O2 at a ratio of 2:1 confirms that the reaction is an overall water splitting process, where water is oxidized to O2 and CO2 is reduced to CO, indicating a complete photocatalytic cycle.
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