Regulations On The Composition And Structure Of Silicon Carbide Nanosheets For Photoreduction Of Carbon Dioxide

The excessive consumption of fossil energy brings out the increasing atmospheric carbon dioxide?CO₂?,which is the main reason of climate change.In this case,photocatalytic reduction of CO₂ into hydrocarbon fuels represents an ideal strategy to simultaneously solve the energy and environmental issues.To advance the application of this technique,the exploitation of low-cost,highly active,and selective photocatalysts for CO₂ reduction is urgently required.In this paper,two-dimensional?2D?reduced graphene oxide?RGO?was chosen as the template and carbon source to synthesis silicon carbide nanosheets?SiC NSs?.In view of the key factors affecting its performance for photocatalytic CO₂ reduction,some effective strategies were applied to improve the conversion efficiency and selectivity,including the fabrication of 2D/2D heterojunctions of Si C/RGO,the synthesis of Pt/SiC NSs loaded with ultrasmall Pt nanoparticles?NPs?and the construction of Fe@C/SiC NSs decorated with Fe@C NPs.Firstly,SiC NSs were synthesized by in-situ conversion of RGO with silicon atoms at 1400 ^oC.The obtained SiC NSs were well crystallized with a transverse-size of about1?m and a longitudinal-size of 3.1?3.7 nm.The selectivity of CO₂-to-methane?CH₄?conversion over SiC NSs achieved as high as 90.6%,mainly contributed by the following two aspects.On the one hand,the high-level conduction band of SiC NSs provided a strong driving force to transfer much more photogenerated electrons and implement deep-reduction of CO₂ for selective CH₄ generation.On the other hand,the ultrathin nanostructure of SiC NSs could not only facilitate the carriers'diffusion but also provide abundant active sites for initially absorbing and activating CO₂ molecules.To improve the CO₂ conversion efficiency of SiC NSs,2D/2D heterojunctions of SiC/RGO were in-situ fabricated by the growth of SiC NSs on RGO surface.With proper RGO content?11.3 wt%?,the SiC/RGO 2D/2D heterojunctions exhibited superior performance of CO₂ reduction with CH₄ yield of 6.72?mol h^-11 g^-11 and selectivity of 92.3%.The CH₄ yield was 3 times of that of SiC NSs.It was found that the robust 2D/2D interface allowed fast transfer of energetic electrons from SiC to RGO.The highly aggregated electrons on RGO would facilitate the 8-electrons-reaction for selective CH₄ generation.To further improve the electrons'density on cocatalyst and realize efficient CO₂-to-CH₄ conversion,untrasmall Pt NPs in size of?1.75 nm were uniformly loaded on SiC NSs using a method of solvothermal reduction.The Pt/SiC NSs significantly improved the CO₂-to-CH₄ conversion efficiency to be 13.60?mol h^-11 g^-1,achieving 3.0times higher than that of SiC NSs.Specially,the energetic electrons from SiC possessed strong reduction ability,and the Pt NPs could effectively trap these energetic electrons.Thanks to such a synergistic effect,the absorbed CO₂ on Pt would be deeply reduced for selective CH₄ generation.To develop efficient and inexpensive photocatalysts for CO₂ reduction,Fe@C/SiC NSs were prepared from the raw materials of Fe?acac?3 and GO by successive freeze-drying,carbonization and controlled carbothermal reaction.In Fe@C/SiC NSs,Fe NP mainly in metal state was encapsulated by fewer-layers carbon to form core-shell nanostructure with size of 20?40 nm.Compared with Pt/SiC NSs,Fe@C/SiC NSs presented a similar generation rate of CH₄(13.1 vs 13.6?mol h^-11 g^-1),while exhibited a higher generation rate of CO(7.0 vs 1.8?mol h^-11 g^-1),indicating its higher CO₂conversion efficiency.It was found that Fe NP in Fe@C core-shell nanostructure could provide electrons outward and adjust the electronic structure of carbon layers,making the electrons transfer more easier at Fe@C/SiC interface.In conclusion,the composition-structure-performance relationship was established in ultrathin Si C NSs for photocatalytic CO₂ reduction.The effects of ultrathin nanostructures,surface chemical groups,2D/2D heterojunctions effect and relative electrons'density on the CO₂ conversion efficiency and selectivity over SiC NSs were revealed.The work here might provide experimental and theoretical guides for the development of more efficient and selective photocatalysts for CO₂ reduction.