Enhanced Driving Force and Charge Separation Efficiency of Protonated g-C₃N₄ for Photocatalytic O₂ Evolution

Abstract

Photocatalysts based on g-C 3 N 4 by loading cocatalysts or constructing heterojunctions have shown great potential in solar-driven water oxidation. However, the intrinsic drawbacks of g-C 3 N 4 , such as poor mass diffusion and charge separation efficiency, remain as the bottleneck to achieve highly efficient water oxidation. Here we report a simple protonation method to improve the activity of g-C 3 N 4 . Studies using valence band X-ray photoelectron spectra and steady-state and time-resolved spectroscopy reveal that the promotion of catalytic ability originates from the higher thermodynamical driving force and longer-lived charge separation state, which may provide guidance in designing efficient polymeric semiconductor photocatalysts with desirable kinetics for water oxidation.

Relations between Structure, Activity and Stability in C3N4 Based Photocatalysts Used for Solar Hydrogen Production

“…Figure 1 shows H 2 evolution as a function of time for monophasic AIS and CN as well as for AIS-CN composites with different contents of AIS under (a) UV-vis and (b) visible light irradiation (λ > 420 nm) in the presence of triethanolamine (TEOA) as sacrificial agent. Pt nanoparticles (NPs) were deposited as co-catalyst on the surface of these materials by in-situ photoreduction of H 2 PtCl 6 . It appeared that the total Pt content determined by ICP-OES in Pt/CN is much lower than the theoretical value of 2 wt.%, after both 3 h and 20 h irradiation with UV-vis light (0.27 and 0.43 wt.%, respectively, Table 1) while it is only slightly lower for the respective Pt/10AIS-CN samples (1.86 and 1.87 wt.%).…”

“…This is probably due to the fact that not the whole amount of the solved [PtCl 6 ] 2− precursor but only a part of it is reduced and deposited as Pt NPs in basic TEOA solution. It has been shown that at high pH (as in the presence of TEOA) a stepwise hydrolysis occurs according to [PtCl 6 ] 2− → [Pt(OH) x Cl 6−x ] 2− → [Pt(OH) 6 ] 2− which hampers the formation of metallic Pt particles [19]. Moreover, the rather non-polar surface of CN might be less prone than the polar AIS surface to adsorb the polar Pt complex species.…”

Enhancement of catalytic activity and oxidative ability for graphitic carbon nitride

“…The best K-C3N4 showed remarkably improvement of photo-catalysis in degrading phenol and MB, around 3.3 and 5.8 times the height of bulk g-C3N4, respectively. The new peak level within shorter shelf time arises from the intermediates of phenol, including dihydroxybenzene, 4,4-dihydroxybiphenyl and maleic anhydride [9,[24][25][26]. The new peak level within shorter retention period in the HPLC chromatograms (Figure 27e and 27f) possibly results from the phenol's intermediary agents, such as dihydroxy benzene and among other media.…”

“…In addition, g-C3N4 is plentiful and can be made by one-step thermally condensing nitrogen-rich precursors such as cyanamide [5,7], dicyandiamide [8,9], melamine [10,11] and urea [12][13][14], thiourea [15,16]. Potential applications in hydrogen generation [5,[17][18][19][20][21][22][23][24][25], oxygen evolution [20,21,[26][27][28], carbon dioxide reduction [28][29][30][31][32][33][34][35][36][37], pollutant elimination [38][39][40][41][42][43][44][45][46][47][48][49][50]…”

Novel ternary Ag/CeVO4/g-C3N4 nanocomposite as a highly efficient visible-light-driven photocatalyst

“…Depended on the advantages of rich precursor source and lowcost raw materials, g-C 3 N 4 has been widely used in many photocatalytic application fields, such as photocatalytic hydrogen evolution [16], pollutant degradation, and CO 2 reduction. However, pure g-C 3 N 4 still has many drawbacks that restrict its practical applications, such as small surface area, fast recombination of electron-hole pairs, and low electrical conductivity [17,18]. Coupling with other semiconductors to form heterojunction structure and improve the visible light absorption performance is a good way to improve the photocatalytic performance of g-C 3 N 4 [19].…”