Hydrogen production and pollutant reduction from wastewater using dual-functional graphitic carbon nitride-based photocatalysts: A review

Abstract

Hydrogen (H<inf>2</inf>) is a promising green energy carrier with high energy density and clean combustion, emitting no greenhouse gases. Conventional H<inf>2</inf> production methods such as steam reforming still depend on fossil fuels, requiring high temperatures and pressures, and generating significant emissions. As a sustainable alternative, photocatalysis using semiconductors has gained attention for H<inf>2</inf> production via water splitting. Among these, graphitic carbon nitride (g-C<inf>3</inf>N<inf>4</inf>), a metal-free conjugated semiconductor, offers notable advantages, tunable structure, high stability, non-toxicity, cost-effectiveness, and biodegradability. Beyond pure water, g-C<inf>3</inf>N<inf>4</inf> photocatalysts can also generate H<inf>2</inf> from diverse wastewaters, including antibiotic, dye, brewery, and petrochemical effluents, while simultaneously degrading pollutants. These pollutants act as hole scavengers and influence H<inf>2</inf> production, synergistically, neutrally, or adversely, depending on catalyst properties, operating conditions, and degradation intermediates. This review highlights properties of g-C<inf>3</inf>N<inf>4</inf>, synthesis methods, and dual roles in H<inf>2</inf> production and pollutant reduction, fostering advances in sustainable, multifunctional photocatalytic systems for clean energy and environmental remediation.