Template-free synthesis of hierarchical graphitic carbon nitride (H-gC3N4) embedded with NiO for water splitting and CO2 reduction with the role of hole scavenger: A comparative investigation

Abstract

Hierarchical graphitic carbon nitride (H-gC3N4) embedded with nickel oxide (NiO) were synthesized using a template-free hydrothermal approach. The performance of NiO/H-gC3N4 composite was investigated for photocatalytic water splitting in a slurry system to produce H2. Similarly, photocatalytic CO2 reduction to generate CO under visible light was conducted in a gas-phase photoreactor system. Optimized 2% NiO/H-gC3N4 composite enables H2 production of 1010 μmol g−1 h−1, which was 13.93 folds higher than using pure H-gC3N4. Similarly, the highest CO evolution rate of 96.7 μmol g−1 h−1 was obtained, 3.85 folds higher than using H-gC3N4. The enhanced photoactivity resulted mainly from the distinctive interlayer structure, improved light penetration, reduced charge carrier recombination and increased surface-reactive active sites. The methanol sacrificial reagent, owing to its capacity to generate extra protons, proved pathways in augmenting the yields of both H2 and CO. While the efficiency of water splitting for H2 production surpassed that of CO2 reduction, it exhibited lower stability. The recently developed composite demonstrated consistent and sustained photocatalytic efficiency for CO production throughout five consecutive cycles.