The Precision Defect Engineering with Nonmetallic Element Refilling Strategy in g‐C₃N₄ for Enhanced Photocatalytic Hydrogen Production

Abstract

energy crisis and greenhouse effect caused by the excessive use of fossil fuels. [1] Graphite carbon nitride (g-C 3 N 4 ) is regarded as one of the most promising photocatalysts due to its facile preparation, unique layered structure, and inherently visible light absorption. [2] However, pristine g-C 3 N 4 also suffers from a high photoexcited charge carrier recombination rate and limited visible light absorption range, resulting in undesirable photocatalytic H 2 production. Among various modification strategies, non-metallic element doping is considered to be one of the most economical and effective methods. [3] It can not only effectively improve the visible light response, but also induce electron rearrangement, which is beneficial to H 2 O adsorption and dissociation of OHH. Numerous reports have shown that doping with non-metallic elements, such as S, P, O, and B, can effectively improve hydrogen evolution performance. [4] The conjugated π bond in g-C 3 N 4 makes it difficult to replace the C and N of the melon unit. Therefore, a high-temperature calcination method is often used to prepare doped g-C 3 N 4 . [5] Interestingly, heteroatom doping is prone to a ring-opening reaction, which is often accompanied by the generation of defects. [2a,5b] Although both doping and defect engineering can enhance photocatalytic activity, the unregulated doping sites and inappropriate defect concentrations and types still result in performance losses. It is theoretically believed that photocatalysis performance can be further improved by precisely adjusting the correlation between the defect location and the non-metallic heteroatom.It is generally believed that the nitrogen vacancy (V N ) has a charge in g-C 3 N 4 , which is conducive to the adsorption of heteroatom reagents. Therefore, directional doping of heteroatoms can be achieved by the construction of nitrogen vacancies. Nitrogen vacancies in g-C 3 N 4 have been reported to facilitate the hydrogen evolution reaction (HER) in photocatalysis by increasing bulk carrier concentration. [6] However, vacancy concentration and photocatalytic efficiency are not linearly related. Numerous reports have shown that the hydrogen production activity of samples first increases and then decreases with increasing defect concentration. [7] At present, researchers have reached a consensus on the mechanism of photocatalysis improvement by defect engineering: an appropriate amount of nitrogen vacancies can capture electrons and accelerate the Traditional defect engineering and doping strategies are considered effective means for improving H 2 evolution, but the uncontrollability of the modification process does not always lead to efficient activity. A defect-induced heteroatom refilling strategy is used here to synthesize heteroatoms introduced carbon nitride by precisely controlling the "introduction" sites on efficient N1 sites. Density functional theory calculations show that the refilling of B, P, and S sites have stronger H 2 O adsorption and dissociation capacity than tradition...

Dual-defect semiconductor photocatalysts for solar-to-chemical conversion: advances and challenges

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Nitrogen defects and porous self-supporting structure carbon nitride for visible light hydrogen evolution

“…This is attributed to the n → π* transition of the lone pair electron in the N-defect within its heptazine structure. 42 The self-supporting multi-channel structure can effectively increase the light scattering effect inside the catalyst. The synergistic effect of the two improves the utilization of light.…”

Template-Free Synthesis of Boron-Doped Graphitic Carbon Nitride Porous Nanotubes for Enhanced Photocatalytic Hydrogen Evolution

“…Energy shortage and environmental degradation are two major global problems that can be solved by the development of renewable and clean energy . Hydrogen energy, known as the “ultimate energy source” can be revolutionary owing to its high energy density and nonpolluting nature. − The efficient conversion of solar into hydrogen energy has become a research focus in the field of renewable energy. − Graphitic carbon nitride is a promising photocatalytic material for hydrogen evolution, which has been widely studied in recent years. − Accordingly, a series of modification strategies have been explored to improve its performance, such as crystal structure engineering, − composite structure design, − morphology control, , and defect creation. ,, …”