Insights into Enhanced Visible-Light Photocatalytic Hydrogen Evolution of g-C₃N₄and Highly Reduced Graphene Oxide Composite: The Role of Oxygen

Abstract

The reduced graphene oxide (RGO)-based composites have attracted intensive attention in experiment due to its superior performance as photocatalysts, but still lacking is the theoretical understanding on the interactions between constituents, and the connection between such interaction and the enhanced photoactivity. Herein, the interaction between the g-C 3 N 4 and RGO sheets is systematically explored by using state-of-the-art hybrid density functional theory. We demonstrate that the O atom plays a crucial role in the RGO-based composites. Compared to the isolated g-C 3 N 4 monolayer, the band gap of composites obviously decreases, and at higher concentration, the levels in the vicinity of Fermi level are much more dispersive, indicating the smaller effective mass of the carrier. These changes are nonlinear on the O concentration.Interestingly, appropriate O concentration alters the direct-gap composite to indirect-gap one.Most importantly, at a higher O concentration, a type-II, staggered, band alignment can be obtained in the g-C 3 N 4 -RGO interface, and negatively charged O atoms in the RGO are active sites, leading to the high hydrogen-evolution activity. Furthermore, the calculated absorption spectra varying with the O concentration shed light on different experimental results. The findings pave the way for developing RGO-based composites for photocatalytic applications.

Design of graphene-like gallium nitride and WS2/WSe2 nanocomposites for photocatalyst applications

“…Consequently, the valence band offset (VBO) between the GaN and WS2 (WSe2) is about 0.2 eV (0.1 eV for GaN/WSe2), whereas the conduction band offset (CBO) between them is about 1.1 eV (1.2 eV for GaN/WSe2). Based on the analysis and the DOSs presented above, the band edge potentials of the nanocomposites versus the normal hydrogen electrode (NHE) are depicted in Figs 3a and b [33,55,56]. The VBM energies of these two heterostructures are more positive than the oxidation potential (1.23 eV) of H2O/O2 for water splitting, and their CBM energies are more negative than the reduction potential for the reduction of H + to produce H2.…”

g-C3N4-Based Nanomaterials for Visible Light-Driven Photocatalysis

“…Other g-C 3 N 4 nanocomposites were investigated with a range of materials and morphologies [39,82,91,, to access different charge transfer mechanisms between g-C 3 N 4 and the other components. These include a g-C 3 N 4 -based type II heterojunction [103], g-C 3 N 4 -based p-n heterojunction [91,129], g-C 3 N 4 -based Z-scheme heterojunction [113,130], g-C 3 N 4 /metal heterojunction [100,102], and a g-C 3 N 4 /carbon heterojunction [131]. The design of g-C 3 N 4 heterojunction photocatalysts is an attractive strategy to tune the electronic structure and redox potentials for visible-light absorption photocatalytic H 2 generation.…”

2D/2D Graphitic Carbon Nitride (g-C3N4) Heterojunction Nanocomposites for Photocatalysis: Why Does Face-to-Face Interface Matter?

“…It is discernable that the 2D graphene has directed a worldwide trend in the materials research stemming from its large surface area, remarkable electronic, optical and mechanical features, and high chemical stability (Putri et al, 2015(Putri et al, , 2016bVoon et al, 2016;Xiang et al, 2016). Up to now, a plethora of literature reports has been devoted to fabricate 2D/2D graphene/ g-C3N4 nanohybrids for photoredox catalysis in H2 evolution, pollutant degradation, and CO2 reduction (Xiang et al, 2011;Li et al, 2013;Xu et al, 2015;Wan et al, 2016). In a work by Ong et al (2015a), sandwich-like graphene/g-C3N4 nanocomposites were prepared via a one-step impregnation-thermal reduction process by employing graphene oxide and urea as the precursors ( Figure 5A).…”