Recent Progress in the Photocatalytic Reduction of Carbon Dioxide

Abstract

Elimination or reduction of CO₂ in the atmosphere is a serious problem faced by humankind, and it has become imperative for chemists to find ways of transforming undesirable CO₂ to useful chemicals. One of the best means is the use of solar energy for the photochemical reduction of CO₂. In spite of considerable efforts, discovery of stable photocatalysts which work in the absence of scavengers has remained a challenge although encouraging results have been obtained in the photocatalytic reduction of CO₂ in both gas and liquid phases. Semiconductor-based catalysts, multicomponent semiconductors, metal-organic frameworks (MOFs), and dyes as well as composites involving novel composite materials containing C₃N₄ and MoS₂ have been employed for the photoreduction process. Semiconductor heterostructures, especially those containing bimetallic alloys as well as chemical modification of oxides and other materials with aliovalent anion substitution (N^3- and F^- in place of O^2-), remain worthwhile efforts. In this article, we provide a brief perspective of the present status of photocatalytic reduction of CO₂ in both liquid and gas phases.

Figure 1

(a) Schematic illustration of mechanism and (b) relative energy levels of photocatalytic reduction of CO₂ on a semiconductor photocatalyst.

Figure 2

Schematic of the possible CO₂ adsorption configurations on surfaces of photocatalysts. Reproduced with permission from ref (7).

Figure 3

Photocatalytic CO₂ reduction on (a) Ag-NaTaO₃:Ca, (b) Ag-NaTaO₃:Sr, and (c) Ag-NaTaO₃:Ba in the liquid phase under UV irradiation. Figure legends: hydrogen (open circle), oxygen (solid circle), and CO (triangle). Reproduced with permission from ref (26).

Figure 4

(a) Electronic absorption spectra of nitridation products of Zn₂GeO₄ and (b) corresponding photocatalytic methane product activities. (c) Curve depicting the recyclability and stablitity of the photocatalyst. Reproduced with permission from ref (27).

Figure 5

(a) Schematic diagram of the proposed mechanism of light-induced charge transfer in C₅H₅–RuH–TiO₂. (b) Electron decay kinetics CpRu₀.₅/TiO₂ and TiO₂. (c) Reduction of CO₂ to CH₄ on CpRu₀.₅/TiO₂ under visible-light irradiation. (d) Dependence of CH₄ evolution with varying the Ru content. Reproduced with permission from ref (28).

Figure 6

(a) Schematic diagram, (b) TEM, and (c) SEM images of Cu₃(BTC)₂@TiO₂ (BTC-benzene-1,3,5-tricarboxylate). (d) CO₂ uptake and (d) comparison of CO₂ reduction activities on Cu₃(BTC)₂@TiO₂ (BTC-benzene-1,3,5-tricarboxylate) and Cu₃(BTC)₂@TiO₂ (BTC-benzene-1,3,5-tricarboxylate). Reproduced with permission from ref (29).

Figure 7

Comparison of (a) density of states and (b) relative band positions in (001) and (101) facets of TiO₂. (c) Photocatalytic CO₂ reduction to CH₄ with different ratios of (001) to (010) facets in TiO₂. Reproduced with permission from ref (35).

Figure 8

(a) Comparison of tauc plots of N,F-TiO₂ (TiO₁.₈N₀.₁F₀.₁) and undoped TiO₂. (b) Comparison of reduction of CO₂ to CO on Ag, Au, and Pt deposited N,F-TiO₂ with bare N,F-TiO₂ under the irradiation of sunlight. (c) and (d) Comparison of reduction of CO₂ to CO on TiO₂:N,F-TiO₂ homojunctions with individual TiO₂ and N,F-TiO₂ under the irradiation of sunlight.

Figure 9

(a) Schematic illustration of the process of charge transfer and CO₂ reduction in Cu₂ZnSnS₄/TiO₂ heterostructures. (b) Comparison of photocatalytic activities of Cu₂ZnSnS₄/TiO₂ with different compositions and individual Cu₂ZnSnS₄ and TiO₂. Reproduced with permission from ref (44).

Figure 10

(a) Comparison of photocatalytic activities and (b) schematic illustration of process of charge transfer and CO₂ reduction in ZnO/Ag_1–xCu_x/CdS (x = 0–0.75) heterostructures.

Figure 11

(a) Schematic illustration of the process of Z-scheme charge transfer and CO₂ reduction in α-Fe₂O₃/Cu₂O heterostructures. (b) Comparison of yield of CO production with varying the Cu content in these heterostructures. Reproduced with permission from ref (38).

Figure 12

(a) Schematic illustration of the process of Z-scheme charge transfer and CO₂ reduction and (b) photocatalytic evolution of H₂, O₂, and CO in CuGaS₂–RGO–TiO₂ under UV–visible light irradiation. Reproduced with permission from ref (53).