Photoreduction of CO2 into sustainable and green solar fuels is generally believed to be an appealing solution to simultaneously overcome both environmental problems and energy crisis. The low selectivity of challenging multi-electron CO2 photoreduction reactions makes it one of the holy grails in heterogeneous photocatalysis. This Review highlights the important roles of cocatalysts in selective photocatalytic CO2 reduction into solar fuels using semiconductor catalysts. A special emphasis in this review is placed on the key role, design considerations and modification strategies of cocatalysts for CO2 photoreduction. Various cocatalysts, such as the biomimetic, metal-based, metal-free, and multifunctional ones, and their selectivity for CO2 photoreduction are summarized and discussed, along with the recent advances in this area. This Review provides useful information for the design of highly selective cocatalysts for photo(electro)reduction and electroreduction of CO2 and complements the existing reviews on various semiconductor photocatalysts.

Cocatalysts for Selective Photoreduction of CO2 into Solar Fuels.

As a promising approach to achieving two objectives with one strategy, photocatalytic CO2 conversion for C1/C2 “solar fuels” production can provide a package solution to the current global warming and growing energy demand by using inexhaustible solar energy and increasing atmospheric CO2. Although numerous efforts have been made to enhance the CO2 conversion efficiency through developing photocatalysts and CO2 reduction systems in recent years, some challenges still remain in improving the activity and selectivity of the CO2 photoreduction reactions. This review gives an overview of fundamental aspects and recent research advances of heterogeneous photocatalytic CO2 conversion systems in the last 3 years, and the catalysts are categorized as one-step excitation semiconductor systems, one-step excitation photosensitized semiconductor systems, and two-step excitation hybrid systems such as semiconductor heterojunction and Z-scheme systems. Also, some suggestions are given for further confirming that the ca...

Recent Advances in Heterogeneous Photocatalytic CO2 Conversion to Solar Fuels

In recent years, heterogeneous photocatalysis has received much research interest because of its powerful potential applications in tackling many important energy and environmental challenges at a global level in an economically sustainable manner. Due to their unique optical, electrical, and physicochemical properties, various 2D graphene nanosheets-supported semiconductor composite photocatalysts have been widely constructed and applied in different photocatalytic fields. In this review, fundamental mechanisms of heterogeneous photocatalysis, including thermodynamic and kinetics requirements, are first systematically summarized. Then, the photocatalysis-related properties of graphene and its derivatives, and design rules and synthesis methods of graphene-based composites are highlighted. Importantly, different design strategies, including doping and sensitization of semiconductors by graphene, improving electrical conductivity of graphene, increasing eloectrocatalytic active sites on graphene, strengthening interface coupling between semiconductors and graphene, fabricating micro/nano architectures, constructing multi-junction nanocomposites, enhancing photostability of semiconductors, and utilizing the synergistic effect of various modification strategies, are thoroughly summarized. The important applications including photocatalytic pollutant degradation, H2 production, and CO2 reduction are also addressed. Through reviewing the significant advances on this topic, it may provide new opportunities for designing highly efficient 2D graphene-based photocatalysts for various applications in photocatalysis and other fields, such as solar cells, thermal catalysis, separation, and purification.

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Graphene in Photocatalysis: A Review

The production of solar fuel through photocatalytic water splitting and CO2 reduction using photocatalysts has attracted considerable attention owing to the global energy shortage and growing environmental problems. During the past few years, many studies have demonstrated that graphene can markedly enhance the efficiency of photocatalysts for solar-fuel generation because of its unique 2D conjugated structure and electronic properties. Herein we summarize the recent advances in the application of graphene-based photocatalysts for solar-fuel production, including CO2 reduction to hydrocarbon fuel and water splitting to H2. A brief overview of the fundamental principles for splitting of water and reduction of CO2 is given. The different roles of graphene in these graphene-based photocatalysts for improving photocatalytic performance are discussed. Finally, the perspectives on the challenges and opportunities for future research in this promising area are also presented.

Graphene‐Based Photocatalysts for Solar‐Fuel Generation

Quantum dots (QDs) generally refer to nanoscale particles of conventional semiconductors that are subject to the quantum-confinement effect, though other nanomaterials of similar optical and redox properties are also named as QDs even in the absence of strictly defined quantum confinement. Among such nanomaterials that have attracted tremendous recent interest are carbon dots, which are small carbon nanoparticles with some form of surface passivation, and graphene quantum dots in various configurations. In this article, we highlight these carbon-based QDs by focusing on their syntheses, on their photoexcited state properties and redox processes, and on their applications as photocatalysts in visible-light carbon dioxide reduction and in water-splitting, as well as on their mechanistic similarities and differences.

Xueshan Li

Papers

Green synthesis and photo-catalytic performances for ZnO-reduced graphene oxide nanocomposites.

Preparation and characterizations of Cu2O/reduced graphene oxide nanocomposites with high photo-catalytic performances

Synthesis and characterizations of graphene–copper nanocomposites and their antifriction application