Extraordinary Promotion of Visible-Light Hydrogen Evolution for Graphitic Carbon Nitride by Introduction of Accumulated Electron Sites (BN₂)

Abstract

The application of accumulated electron sites on the catalyst surface for photocatalytic hydrogen production represents a prospective strategy for efficient utilization of solar energy. Herein, the accumulated electron sites (BN2) loaded on graphitic carbon nitride (G-CN) were prepared without effort by a two-step calcination method in which melamine was calcined and then heat-treated with NaBH4. When compared with that of the bulk G-CN, the rate toward water splitting to produce H2 of the represented catalyst (CN-B0.05) greatly increased by 2.3 times under illumination (λ ≥ 420 nm). The improved activity could be attributed to the decrease in interlayer distance and the potential barrier of interlayers which was beneficial to readily transfer electrons in the Z direction, improve the adsorption and activation of water, and decline the Gibbs free energies for H* adsorption. The increase in π–π conjugation facilitated enhancement of the separation efficiency of photogenerated electron–hole pairs and light-capturing capabilities in the visible region with the introduction of BN2 sites. An approach for efficient H2 production is demonstrated in this work.

Universal Water Disinfection by the Introduction of Fe–N3 Traps between g-C3N4 Layers under Visible Light

“…It could be seen that four fitted peaks of CNF100 samples were located in Fe 2p 3/2 and 2p 1/2 peaks at 713.7, 726.9 eV over Fe 3+ and 710.2, 723.4 eV over Fe 2+ , respectively (Figure 2D). 37,38 The three simulated peaks of N 1s spectra for the CN sample were observed at 398.6, 399.6, and 400.7 eV, corresponding to C�N−C, N−(C) 3 , and N−H groups in g-C 3 N 4 , 25,39 respectively (Figure 2E). Equally, the CNF 100 sample N 1s spectrum was successfully fitted by the above three peaks, suggesting that the structure of g-C 3 N 4 was still retained in CNF 100 .…”

“…The optical capture capability, as the factors to improve the photocatalytic activity, was obtained by admeasuring the diffuse reflectance spectroscopy (DRS) of the sample in the 200–800 nm range (Figure D). , As exhibited in Figure D, the light absorption for CN (λ < 450 nm) was attributed to the intrinsic response of the band gap, and the as-prepared CNF 100 demonstrated an increased light capture efficiency in the visible region relative to CN, especially from 400 to 600 nm. Similarly, the DFT theoretical used to calculate the total density of states (TDOS) was endowed with the homologous tendency.…”

“…Graphite carbon nitride (g-C 3 N 4 ), as a common semiconductor fungicide, has attracted great attention owing to its terrific biocompatibility and stability. ,, However, it has some shortcomings that limit application, such as high carrier recombination and a narrow visible light response range (400–450 nm). − Modification of transition metals has been recognized as an important strategy that can significantly improve the photocatalytic performance of g-C 3 N 4 . ,, Cu, Mn, or Co atoms anchoring could greatly increase the in-plane and interlayer carrier separation and transfer of g-C 3 N 4 , thereby improving the photocatalytic efficiency, which in turn exhibits excellent photocatalytic performance. − These statements confirm the fact that by introducing transition metals into g-C 3 N 4 , the charge transfer process has been closely studied to activate molecular oxygen to form highly oxidizing superoxide radicals under photoexcitation, but the accompanying energy transfer process to generate singlet oxygen has rarely been analyzed in detail, which makes it difficult to clarify the actual photocatalytic bactericidal mechanism. To be sure, g-C 3 N 4 is considered to be a strong exciton material with low dielectric properties, and its exciton binding energy (evaluation of exciton strength important index) is assumed to be extremely high, much greater than some typical inorganic semiconductors. , As mentioned above, the huge Coulomb interaction between photoexcited electron–hole pairs in g-C 3 N 4 prevents the dissociation of excitons and charge carriers, thus inhibiting the charge transfer efficiency. , Although the conspicuous influence of excitons reduces the charge transfer efficiency, it may touch some pivotal process of energy transfer under illumination, such as the molecular oxygen in the ground state is activated by high-energy excitons into singlet oxygen in the spin triplet state. , Inspired by the above, the g-C 3 N 4 catalyst modified by transition metals was developed, which can not only significantly improve the charge transfer of excitons but also enhance the energy transfer of charge carriers, activating molecular oxygen to generate a variety of active species.…”

“… 20 , 23 , 24 However, it has some shortcomings that limit application, such as high carrier recombination and a narrow visible light response range (400–450 nm). 25 − 27 Modification of transition metals has been recognized as an important strategy that can significantly improve the photocatalytic performance of g-C 3 N 4 . 12 , 28 , 29 Cu, Mn, or Co atoms anchoring could greatly increase the in-plane and interlayer carrier separation and transfer of g-C 3 N 4 , thereby improving the photocatalytic efficiency, which in turn exhibits excellent photocatalytic performance.…”