One-Dimensional Multichannel g-C₃N_4.7 Nanostructure Realizing an Efficient Photocatalytic Hydrogen Evolution Reaction and Its Theoretical Investigations

Abstract

The emerging metal-free carbon nitride (C3N4) offers prominent possibilities for realizing the highly effective hydrogen evolution reaction (HER). However, its poor surface conductivity and insufficient catalytic sites hinder the HER performance. Herein, a one-dimensional vermicular rope-like graphitic carbon nitride nanostructure is demonstrated that consists of multichannel tubular pores and high nitrogen content, which is fabricated through a cost-effective approach having the final stoichiometry g-C3N4.7 for HER application. The present g-C3N4.7 is unique owing to the presence of abundant channels for the diffusion process, modulated surface chemistry with rich-electroactive sites from N-electron lone pairs, greatly reduced recombination rate of photoexcited exciton pairs, and a high donor concentration (4.26 × 1017 cm3). The catalyst offers a visible-light-driven photocatalytic H2 evolution rate as high as 4910 μ mol h–1 g–1 with an apparent quantum yield of 14.07% at band gap absorption (2.59 eV, 479 nm) under 7.68 mW cm–2 illumination. The number of hydrogen gas molecules produced is 1.307 × 1015 s–1 cm–2, which remained constant for a minimum of 18 h of repeated cycling in the HER without any degradation of the catalyst. In density functional theory calculations, a significant change in the band offset is observed due to N doping into the system in favor of electron catalysis. The theoretical band gap of a monolayer of g-C3N4.7 was enormously reduced because of the presence of additional densities of states from the doped N atom inside the band gap. These impurity or donor bands are formed inside the band gap region, which ultimately enhance the hydrogen ion reduction reaction enormously.

Atomic‐level investigation on significance of photoreduced Pt nanoparticles over g‐C3N4/bimetallic oxide composites

“…The peaks at 284.6 and 286.1 eV in the C 1s spectra (Figure 6a) represent the C−C bond and the sp 2 carbon linked to nitrogen (C−N−C) moiety, respectively. The peaks at 287.7 and 289.6 eV originate from carbon atoms that are either coupled to oxygen molecules in the air and are sp 2 ‐hybridized within the aromatic rings of CN‐NT, respectively [67,68] . In Figure 6b N 1s spectra, peak at 398.1 eV demonstrates the existence of a secondary nitrogen atom that is covalently bound to two carbon atoms C=N−C.…”

Hydrogen Evolution Activity of Nitrogen-Rich g-C3–xN4+x Synthesized by Solid–Gas Interface Method

“…The CN-NH 3 exhibited the highest gas evolution rate of 634 μmol g –1 with 10% TEOA (sacrificial agent SA) as the hole scavenger. This is because the donor density of the CN-NH 3 photocatalyst has increased considerably due to the substitution of N at the β-carbon position and also the presence of surface terminating −NH x groups . The E CB of CN-NH 3 becomes more negative due to the electron donating peripheral −NH x groups than the pristine g -C 3 N 4 and thereby increases the reduction rate of protons.…”

“…This is because the donor density of the CN-NH 3 photocatalyst has increased considerably due to the substitution of N at the β-carbon position and also the presence of surface terminating −NH x groups. 31 The E CB of CN-NH 3 becomes more negative due to the electron donating peripheral −NH x groups than the pristine g-C 3 N 4 and thereby increases the reduction rate of protons. Additionally, HRTEM results show fully exfoliated and porous nanosheets due to the presence of NH 3 during the thermal condensation of melamine.…”

“…To date, syntheses of N-modified g -C 3 N 4 samples have been reported mostly by wet chemical processing of precursors for which nitrogen sources are in the form of either solid or liquid states. ,, The N-modified graphitic carbon nitride phases with different compositions recently reported are g -C 2 N 3 , g -C 3 N 3 , g -C 3 N 3.5 , g -C 3 N 4.8 , g -C 3 N 4.5 , g -C 3 N 4.7 , and mesoporous g -C 3 N 5 . , A new method of synthesizing photoactive nitrogen-rich carbon nitrides is reported here. In this method, complete thermal condensation of melamine in either a N 2 or NH 3 atmosphere, viz., solid–gas interface approach, produced g-C 3– x N 4+ x .…”

Hydrogen evolution via noble metals based photocatalysts: A review

“…Nickel is a suitable metal in the development of composites and its preparation is low cost because it is an abundant element in the earth's crust [112]. Recently, many researchers have drawn attention to graphitic carbon nitride-based nanocomposites [113]. Important aspects of the activity of g-C3N4-based photocatalyst are: (i) the ability to absorb light, (ii) charge dissociation and transportation and (iii) reactive surface [114].…”