Synthesis and Surface Modification of TiO2-Based Photocatalysts for the Conversion of CO2

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.

Enhancing the Photocatalytic Activity of TiO2 Catalysts

“…For instance, CO 2 reduction is a representative example of exhibiting the importance of reaction selectivity. [13,22,28] The narrow energy states and reduction potentials of CO 2 reduction make many reactions possible to occur, and it can produce a lot of byproducts. The selective photocatalytic CO 2 reduction not only facilitates the efficient production of target molecules but also makes it easier to separate products.…”

“…As a photocatalyst, TiO 2 has been investigated to degrade organic pollutants and to produce fuels from water and carbon dioxide (CO 2 ). [9][10][11][12][13] For photocatalytic fuel production, appropriate band position, fast charge mobility, and suppression of charge recombination are essential. Although several obstacles to realizing efficient photocatalytic activity remain, the main challenges for TiO 2 -based photocatalysts are systems are discussed.…”

Impact of Titanium Dioxide (TiO2) Modification on Its Application to Pollution Treatment—A Review

“…Another way is to deposit precious metals or metal oxides on the surface of TiO 2 and add electron capture agents or use photo-catalysis to prevent TiO 2 photo-generated electron-hole pair recombination thus improve the photocatalytic efficiency of TiO 2 [38][39][40]. In addition, dye photosensitization and providing a suitable carrier for TiO 2 would be the efficient methods to modify TiO 2 [41].…”

N-TiO2-x Nanocatalysts: PLAL Synthesis and Photocatalytic Activity

“…TiO 2 nanostructures provide increased surface area at which photoinduced reactions may occur, enhancing the light absorption rate, increasing the surface photoinduced carrier density, enhancing the photoreduction rate, and resulting in higher surface photoactivity. At the same time, the high surface-volume ratio of the nanoparticles enhances the surface absorption of OH− and H 2 O, increasing the photocatalytic reaction rate [4,5]. Based on the basic research results, industrial applications of photocatalytic TiO 2 have been achieved since the end of the 1990s and will develop further in the 21st century.…”