Abstract
Among all greenhouse gases, CO2 is considered the most potent and the largest contributor to global warming. In this review, photocatalysis is presented as a promising technology to address the current global concern of industrial CO2 emissions. Photocatalysis utilizes a semiconductor material under renewable solar energy to reduce CO2 into an array of high-value fuels including methane, methanol, formaldehyde and formic acid. Herein, the kinetic and thermodynamic principles of CO2 photoreduction are thoroughly discussed and the CO2 reduction mechanism and pathways are described. Methods to enhance the adsorption of CO2 on the surface of semiconductors are also presented. Due to its efficient photoactivity, high stability, low cost, and safety, the semiconductor TiO2 is currently being widely investigated for its photocatalytic ability in reducing CO2 when suitably modified. The recent TiO2 synthesis and modification strategies that may be employed to enhance the efficiency of the CO2 photoreduction process are described. These modification techniques, including metal deposition, metal/non-metal doping, carbon-based material loading, semiconductor heterostructures, and dispersion on high surface area supports, aim to improve the light absorption, charge separation, and active surface of TiO2 in addition to increasing product yield and selectivity.
Highlights
The global emission of greenhouse gases, such as CO2, continues to rise by ~3% each year [1].Higher atmospheric concentrations of greenhouse gases lead to surface warming of the land and oceans [2]
TiO2 photocatalysts, this paper provides emphasis on modification techniques that will enhance the CO2 photoreduction efficiency of TiO2 photocatalysts
CO2 photoreduction was limited was by the production of suggested thatrate theof rate of the process overallofprocess of CO2 photoreduction limited by the electrons andofprotons
Summary
The global emission of greenhouse gases, such as CO2 , continues to rise by ~3% each year [1]. A wide variety of fuels, including methanol, ethanol, methane, dimethyl ether, formic acid, petroleum-equivalent fuels, and others may be produced through different CO2 conversion processes These conversion processes produce large quantities of CO2 and will increase the concentration of CO2 in the atmosphere instead of reducing it [11,12]. The development of new, stable, inexpensive, abundant, nontoxic, selective, and visible light-responsive photocatalysts is being actively investigated [19,27] In this regard, some state-of-the-art photocatalysts, such are perovskite oxides and III-V semiconductors, have shown some great promise in driving the photocatalytic reduction of CO2 under direct sunlight. The current photocatalytic efficiency of perovskite oxides and III-V semiconductors is too low for practical CO2 reduction applications Their low selectivity and high instability have urged researches to continue with their investigations on. Future directions toward efficient photocatalytic systems for the reduction of CO2 have been presented
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