Highly Selective Photocatalytic CO2 Reduction to CH4 by Ball-Milled Cubic Silicon Carbide Nanoparticles under Visible-Light Irradiation.

Hao Li,Jianwu Sun

doi:10.1021/acsami.0c19945

Abstract

The ultimate goal of photocatalytic CO2 reduction is to achieve high selectivity for a single product with high efficiency. One of the most significant challenges is that expensive catalysts prepared through complex processes are usually used. Herein, gram-scale cubic silicon carbide (3C-SiC) nanoparticles are prepared through a top-down ball-milling approach from low-priced 3C-SiC powders. This facile mechanical milling strategy ensures large-scale production of 3C-SiC nanoparticles with an amorphous silicon oxide (SiOx) shell and simultaneously induces abundant surface states. The surface states are demonstrated to trap the photogenerated carriers, thus remarkably enhancing the charge separation, while the thin SiOx shell prevents 3C-SiC from corrosion under visible light. The unique electronic structure of 3C-SiC tackles the challenge associated with low selectivity of photocatalytic CO2 reduction to C1 compounds. In conjugation with efficient water oxidation, 3C-SiC nanoparticles can reduce CO2 into CH4 with selectivity over 90%.

Highlights

Semiconductor-based photocatalysis has attracted worldwide attention due to its great potential in tackling environmental and energy issues.[1,2] Environmental photocatalysis can remove organic pollutants from water through deep oxidation, while energy photocatalysis aims to generate hydrogen through water splitting.[3−5] Recently, solar reduction of CO2 into C1 compounds (e.g., CO, CH4, CH3OH, and HCOOH) is considered as a new green and ideal process to address the global warming effect and simultaneously generate renewable fuels under ambient conditions.[6−11] In light of this fact, significant efforts have been devoted to synthesizing transition−metal complexes or semiconductors for photocatalytic CO2 reduction
3C-SiC nanoparticles showed additional Raman modes between 300 and 700 cm−1, due to the presence of the surface Si−O species (Figure 2a).[22]. This result was confirmed by the According to the scanning electron microscope (SEM) images, the as-grown 3C-SiC crystalline powder we adopted contained micron-sized particles
The phase structure of the as-prepared 3C-SiC nanoparticles was investigated by X-ray diffraction (XRD), whose diffraction peaks at 35.6, 41.4, and 60.0° corresponded well with the crystal faces (111), (200), and (220) of the cubic SiC structure, called as β-SiC (PDF#29-1129) (Figure 1d)

Summary

INTRODUCTION

To enable complete and efficient solar-driven CO2 reduction, the chosen semiconductor band gap should be smaller than 3.00 eV and better larger than 1.23 eV, so that conduction (CB) and valence bands (VB) will respectively satisfy the thermodynamic requirement for CO2 reduction and water oxidation. This essential criterion can be met by cubic silicon carbide (3C-SiC), a representative metal-free semiconductor with broad applications due to its suitable band gap, good thermal conductivity, high stability, and low cost. The influence of the surface states and the SiOx shell on the charge-carrier dynamics and photocatalytic CO2 reduction under visible light is comprehensively discussed

RESULTS AND DISCUSSION

CONCLUSIONS

EXPERIMENTAL SECTION

■ ACKNOWLEDGMENTS

■ REFERENCES