Construction of 2D Bismuth Silicate Heterojunctions from Natural Mineral toward Cost-Effective Photocatalytic Reduction of CO₂

Abstract

Photocatalytic reduction of carbon dioxide to chemical fuels is an attractive route to generate renewable energy and curtail the green house effect. However, it remains a great challenge to explore cost-effective photocatalysts using natural and readily available clay minerals. In this work, one-dimensional natural palygorskite (Pal) is treated with acid to remove most of the metal ions from the silica framework, and bismuth ions are incorporated to grow two-dimensional (2D) bismuth silicate (Bi 12 SiO 20 ) nanosheet under a microwave-hydrothermal process. Excess Bi ions generate bismuth oxide (BiO 2−x ) nanoparticles that respond to nearinfrared (NIR) light and coprecipitate on the surface of Bi 12 SiO 20 , which forms a well-defined S-scheme Bi 12 SiO 20 /BiO 2−x heterojunction facilitating the charge transfer and maintaining high redox potentials. The abundant active sites on the 2D Bi 12 SiO 20 sheet and the oxygen vacancies in BiO 2−x particles are found to favor the cooperative activation and adsorption of CO 2 . The influence of various amounts of BiO 2−x on CO 2 reduction performance is explored. Bi 12 SiO 20 /BiO 2−x -30 wt % shows the best photocatalytic reaction rate at 31.16 μmol•g −1 •h −1 for CH 3 OH formation during sunlight irradiation. In NIR light, the Bi 12 SiO 20 / BiO 2−x -30 wt % even achieves a CH 3 OH generation rate of 17.1 μmol•g −1 •h −1 . The current study potentially provides a sustainable approach for CO 2 conversion.

Photothermal Catalytic Reduction of CO2 by Cobalt Silicate Heterojunction Constructed from Clay Minerals

“…According to the DRIFTS analysis, a possible CO 2 reduction pathway is summarized in the following reactions [33]: [31]. Moreover, the sign of CH2* is detected at 1,385 cm −1 , confirming the hydrogenation of HCHO* [12]. The results show that the photocatalytic reduction of CO2 on the Co2SiO4/Co3O4-x surface go through a sequential process in which COO− and HCHO act as reaction intermediates generate methanol groups [32].…”

“…It is observed that the peak of COOH* species becomes stronger with increasing light-irradiation time, indicating that the COOH* is one of the key intermediate species for CO 2 -to-CH 3 OH conversion [31]. Moreover, the signal of CH 2 * is detected at 1385 cm −1 , confirming the hydrogenation of HCHO* [12]. The IR results show that the photocatalytic reduction of CO 2 on the Co 2 SiO 4 /Co 3 O 4 −x surface goes through a sequential process in which COO− and HCHO act as reaction intermediates to generate methanol groups [32].…”

“…Figure 1b shows the magnified view of Figure 1a from 36.5° to 39.5°. The peaks of Co2SiO4/Co3O4 composites are obviously shifted to a higher angle compared with Co3O4 and Co2SiO4, indicating a stronger interaction between Co2SiO4 and Co3O4 [12,14]. 2a, the morphology of Pal is a one-dimensional nanofiber structure with a diameter of about 30-50 nm.…”

“…Figure 2b,f indicates TEM and HRTEM of Co 2 SiO 4 . The microstructure of Co 2 SiO 4 is a two-dimensional flake, which may be due to the preservation of the silicon-oxygen tetrahedron structure in the skeleton after the destruction of Pal [12]. After the addition of Co 2+ , the chain-like structure of the silicon-oxygen tetrahedron regularly grows into two-dimensional cobalt silicate flakes under alkaline hydrothermal conditions.…”

“…In our previous work, a unique solar driven catalysis system was developed to convert cellulose into lactic acid using Cu-modified natural palygorskite (Pal) catalyst [11]. Liu [12] et al reported on one-dimensional Pal treated with acid to remove most of the metal ions from the silica framework, and bismuth ions were incorporated to grow a two-dimensional (2D) bismuth silicate (Bi12SiO20) nanosheet under a microwavehydrothermal process. Metal silicates can be prepared from silica and are often used in cement and glass processing, as well as in manufacturing [13].…”