Photocatalytic oxidation of glyphosate and reduction of Cr(VI) in water over ACF-supported CoNiWO4-gCN composite under batch and flow conditions

Photocatalytic treatment of wastewater using nanomaterials is an efficient energy saving technology. Yet the practical application of the technology is limited because of difficulty in developing the stable, supported photocatalytic nanoparticles that can be used under continuous flow conditions. Here, we report an efficient removal of glyphosate (GLP) and Cr(VI) from water under batch as well as continuous flow conditions using the activated carbon fiber (ACF)-supported nanocomposite of CoNiWO4 (CNW) and g-C3N4 (gCN), as a photocatalyst. CNW-gCN/ACF is synthesized using a one-step strategy, and spectroscopic characterization techniques are used to corroborate the formation of the Z-scheme-based CNW-gCN heterojunction in the ACF substrate. Efficacy of the photocatalyst is assessed in visible light irradiation. The batch activity data of the individual pollutant show the complete oxidation of GLP at 30 ppm and reduction of Cr(VI) at 200 ppm concentration levels in 60 and 150 min, respectively at 1 g/L dose of CNW-gCN/ACF. Photocatalytic efficiency of CNW-gCN/ACF in the simultaneous removal of both pollutants from co-contaminated feed is found to be greater than that in single-feed system under identical experimental conditions. Tested under flow conditions, CNW-gCN/ACF shows approximately the same rates of oxidation and reduction as prevalent under batch conditions, indicating the efficient immobilization of the nanocatalyst particles in ACF, which not only prevents elution of the catalyst but also improves its reusability. The toxicity data indicate the treated water samples to be non-toxic. The current study provides an efficient method for developing supported nanomaterial photocatalysts for treating flowing co-contaminated wastewater.