Modification Strategies with Inorganic Acids for Efficient Photocatalysts by Promoting the Adsorption of O₂

Abstract

Efficient photocatalysis for degrading environmental organic pollutants on semiconductors requires photogenerated charge carrier separation to drive the photochemical processes. To ensure charge separation, it is indispensable to make charges captured effectively. Generally, the step for capturing the photogenerated electrons by the surface adsorbed O2 is relatively slow as compared to that for capturing holes by the surface adsorbed hydroxyl groups so that it is taken as the rate-determining step. However, it is frequently neglected. Thus, it is greatly desired to develop feasible strategies to promote the adsorption of O2 for efficient photocatalysts. In this paper, we have mainly discussed surface modification with inorganic acids, such as H3PO4, HF, and H3BO3, to enhance photogenerated charge carrier separation based on oxygen adsorption promotion for photocatalytic degradation of environmental pollutants. Among these acids, the function and mechanism of H3PO4 are highlighted because of its good performance and universality. Several important photocatalyst systems, mainly including TiO2, α-Fe2O3, and g-C3N4, along with the nanostructured carbons as electron acceptors in nanocomposites, are addressed to improve the ability to adsorb O2. A key consideration in this review is the development of a strategy for the promotion of adsorbed O2 for efficient photocatalysts, along with the process mechanisms by revealing the relationships among the adsorbed O2, photogenerated charge carrier separation, and photocatalytic performance. Interestingly, it is suggested that the enrichment in surface acidity be favorable for promotion of O2 adsorption, leading to the improved charge carrier separation and then to the enhanced photoactivities of various semiconductor photocatalysts. Moreover, several outlooks are put forward.

Accepting Excited High-Energy-Level Electrons and Catalyzing H2 Evolution of Dual-Functional Ag-TiO2 Modifier for Promoting Visible-Light Photocatalytic Activities of Nanosized Oxides

“…Similar to T/BV, the SS-SPS response of 7Ag-T/BV is gradually enhanced with increasing the content of O 2 ( Figure S3), indicating that the presence of O 2 is favorable for charge separation by capturing electrons. 8,22 The kinetic manners of photogenerated electrons and holes are studied by TS-SPV in N 2 . Generally speaking, the TS-SPV response is involved with two time ranges: fast (<10 −5 s) from the charge separation by the built-in electric field, and slow (>10 −4 s) from the charge diffusion process.…”

One‐Pot Hydrothermal Synthesis of Visible‐Light‐Responsive MoS2/g‐CNO Heterostructures for Organic‐Pollutant Degradation

“…The peaks at 2 θ = 32.6 and 57.9° are ascribed to the (100) and (110) planes of the 2H phase of MoS 2 , respectively (JCPDS 37‐1492). [1a] The broadness of the peaks is ascribed to a combination of factors such as small particle size, disorder in the crystallinity, and strains in the crystallites. [23g] The loss of the highest intensity (002) peak of 2H‐MoS 2 at 2 θ = 14.1° indicates that the layered crystalline nature of MoS 2 is absent.…”

“…The traditional methods employed for the degradation of pollutants are expensive, time‐consuming, and often produce toxic products that are retained in the effluent. Therefore, a “green” photocatalytic strategy that utilizes solar energy has been considered as an environmentally benign pathway for the removal of organic pollutants . Recently, a host of new developments such as electrochemical water splitting, hydrogen gas production, the reduction of CO 2 to CH 4 , electricity generation from newer photovoltaic cells, and the degradation of organic pollutants have been achieved by exploiting solar energy and by employing photocatalytic technology.…”

“…More recently, heterojunction structures based on g‐C 3 N 4 coupled with cocatalysts have received much attention, as they have the highest potential to further boost the photocatalytic performance through efficient charge separation. [1a], Several heterostructure systems based on g‐C 3 N 4 , metal chalcogenides/g‐C 3 N 4 , and so forth have been designed . To develop such productive heterojunctions, the desired constituents must satisfy the prerequisites of proper type II band‐edge alignment for maximum separation of the photoexcited charge carriers.…”

“…Hexagonal 2H‐MoS 2 is a layered material that satisfies the above‐mentioned prerequisites and is a suitable candidate for coupling with g‐C 3 N 4 . [1a], Different methods for the synthesis of MoS 2 ‐based layered composite materials have been reported. [1a], [3c], The formation of a heterojunction between two kinds of hexagonally layered materials is an effective way to transfer and separate photoexcited electrons and holes in densely stacked g‐C 3 N 4 to decrease the diffusion distance .…”