Improving g-C3N4:WO3 Z-scheme photocatalytic performance under visible light by multivariate optimization of g-C3N4 synthesis

Abstract This study reports the optimization of the g-C3N4 synthesis by the melamine-annealing route using the Response Surface Methodology (RSM) and its direct coupling to WO3 by a simple sono-assisted synthesis of g-C3N4:WO3 heterojunctions, with good materials homogenization, effective interface, and proper energy levels. The optimized synthetic conditions were: 605 °C, 183 min, and 5 °C min−1, producing a high-quality material in comparison with the ones reported in papers published between 2016 and 2020, as far as bandgap energies and specific surface areas are concerned (SSA/Eg ratio). The highest photocatalytic activity was observed in the 80:20 (wt.%) heterostructure. That material presented a high visible response, being capable of completely degrading the model-pollutant approximately four times faster than g-C3N4. The efficient flux of photo-generated electrons though a Z-Scheme heterojunction promoted a superior superoxide radical formation, resulting in increased pollutant degradation. Finally, a complete mechanism for the heterostructure photocatalysis was proposed based on theoretical and experimental results.