An evaluation of g-C3N4 and BiVO4 for photocatalytic water treatment and disinfection

Photocatalysis has been found to be effective for the degradation of organic pollutants and for the inactivation of various pathogenic microorganisms in water, including disinfection resistant species. Development of a semiconductor photocatalyst that has a narrow band gap, responsive to visible light and suitable energy band structure is needed for effective redox capacity. In this study, we explored two different materials i.e., graphitic carbon nitride (g-C3N4) and bismuth vanadate (BiVO4) as photocatalysts for water treatment and attempted to correlate their physiochemical properties to the photocatalytic activity. g-C3N4 was investigated to analyse the effect of different precursors and reaction parameters on its physiochemical properties i.e., porosity, morphology, crystal structure, etc. and photocatalytic performance for phenol degradation and E. coli inactivation. The urea derived exfoliated g-C3N4 displayed high specific surface area (183.9 m2 g-1). The thiourea and urea derived exfoliated g-C3N4 samples exhibited better phenol degradation and E. coli disinfection performance than all other prepared g-C3N4 samples. However, the photocatalytic efficiency demonstrated by all the gC3N4 samples is still far behind the photocatalytic efficiency of P25-TiO2 under UVVis irradiation. The inefficient photocatalytic performance of g-C3N4 was explained through its physiochemical properties, i.e., bandgap energy, band edge positions, work function, photocurrent, open circuit photopotential, and flat band potential, etc. It was found to behave as an intrinsic semiconductor as the Fermi level of g-C3N4 was quantified approximately in the middle of the forbidden gap. A very small photocurrent and photoelectrochemical photocurrent switching (PEPS) effect was observed in photoelectrochemical results. Another photocatalyst BiVO4 was successfully synthesized with different morphologies (spheres, plates, pyramids/thorns) using hydrothermal and seed mediated methods. Although prepared samples did not show any photocatalytic activity for phenol degradation despite producing OH radicals (detected by RNO photocatalytic discolouration), possibly due to its positive conduction band edge potential which is insufficient to reduce oxygen.