Dimensionality-Driven CQD/TiO2-g-C3N4 Ternary Composites for Boosting Photocatalytic and PEC Performance

Photocatalysis and photoelectrochemical (PEC) water splitting are hindered by challenges such as rapid electron-hole recombination, limited visible light absorption, and inefficient charge transport. To overcome these limitations, a ternary composite CQD/TiO₂-g-C₃N₄ was engineered by combining 0D carbon quantum dots (CQDs), 1D TiO₂ nanorods, and 2D g-C₃N₄ nanosheets. This multidimensional structure significantly improves charge separation and transfer that enhances both photocatalytic and PEC efficiency. X-ray diffraction confirmed successful integration of TiO₂ and g-C3N4, with crystallite sizes ranging from 8.1 to 9.3 nm. SEM and TEM analyses showed uniform dispersion of TiO₂ nanorods on g-C₃N₄ sheets, while CQDs (~5–6 nm) were attached to surface, establishing strong interfacial contact for efficient charge movement. UV-vis exhibited a redshift, indicating a narrower band gap, and PL analysis showed reduced electron-hole recombination. Under visible light, composite with 15.0 mL CQD displayed excellent photocatalytic activity, achieving 96.0% degradation of mixed dyes (MO + BPB) with clear linear degradation indicating consistant reaction rate and delivering a high PEC photocurrent density (~33 mA·cm⁻²). CQDs enhance charge separation and lower band gap while multidimension (0D–1D–2D) structure boosts charge transfer. The 0D–1D–2D architecture enhances charge mobility and light utilization, making this material highly effective for environmental cleanup and sustainable energy applications.