The effect of sulfate pre-treatment to improve the deposition of Au-nanoparticles in a gold-modified sulfated g-C3N4 plasmonic photocatalyst towards visible light induced water reduction reaction

In continuation of our earlier work on Au–g-C3N4 and to improve its activity further, Au incorporated sulfated carbon nitride (g-C3N4) has been designed by using a simple impregnation cum borohydrate reduction method for the visible light induced water reduction reaction for hydrogen generation. The photocatalysts were characterized using various instrumental methods such as PXRD, UV-Vis DRS, SEM, HR-TEM, XPS, PL and TRPL spectral analysis. Functionalisation by the –HSO3 group and incorporation of AuNPs in the g-C3N4 skeleton lead to the extension of its pi-conjugated system, modification of its semiconductor properties, such as band structure engineering with a tunable bandgap, red-shift of the optical absorption band and promotion of charge migration and separation. The sulfate pre-treated g-C3N4 samples are supposed to have a defected surface due to oxygen vacancies, which increases the adsorption of AuNPs onto the vacant oxygen sites. Thus the AuNPs get adsorbed on the reduced surfaces, increasing the extent and effectiveness of the electronic communication between gold and the g-C3N4 interface. The improved photocatalytic activity could be attributed to the surface plasmon resonance (SPR) effect of AuNPs, which synergistically facilitates the photocatalysis process. The photocatalytic activity of Au-sulfated g-C3N4 for photocatalytic splitting of water to produce H2 was increased 1.5 times compared to that of Au–g-C3N4, 2.5 times compared to that of sulphated-g-C3N4 and 35 times compared to that of single-phase g-C3N4.