Unveiling the synergistic role of nitrogen vacancies and Z-scheme heterojunction in g-C3N4/β-Bi2O3 hybrids for enhanced CO2 photoreduction

Abstract

Rational design of highly efficient photocatalysts for CO2 conversion into carbonaceous fuels is of great significance to mitigate the global greenhouse effect and energy shortage problem. Among numerous materials studied for this purpose, the carbon nitride (g-C3N4) has been widely used in photocatalytic CO2 reduction (PCR) due to its decent optical properties, low cost and environment friendliness. However, its wide use still remains a substantial challenge due to inefficiency of the active site and rapid recombination of photogenerated electrons and holes. Herein, we suggest a Z-scheme system of nitrogen vacancies g-C3N4/β-Bi2O3 heterojunction photocatalyst based on self-assembly of nitrogen vacancies in g-C3N4 nanosheets and β-Bi2O3 micro-flowers, yielding an enhanced CO evolution rate of 30.56 μmol·g−1·h−1 under the simulated solar light without any cocatalysts and sacrificial agents. Our detailed studies indicate that the promoted PCR performance originates from the stronger adsorption capability of the *COOH intermediates due to the cleavage of the C-C bond in nitrogen vacancies g-C3N4 (NV-C3N4), turning the most endothermic step from the formation of *COOH intermediates to *CO. Moreover, the unique Z-scheme feature can efficiently facilitate the separation of photoelectron-hole pairs and enhance redox capability by optimizing the energy band structure. To sum up, this work provides deep insights and guidelines for rational design of highly efficient Z-scheme heterojunctions catalysts for CO2 photoreduction to solar fuels.