Influence of W6+ cations on the photocatalytic activity of Zn2+Al3+W6+ layered double hydroxides in the degradation of diclofenac

Abstract

The photocatalytic activity of ZnAl and ZnAlW-x layered double hydroxides (where x = 1.5, 3.0 and 5.0 mol% of W6+ cations) prepared by the coprecipitation method was studied in the photo-degradation of diclofenac (DCF) in aqueous medium using UV light irradiation. The incorporation of W6+ cations within the ZnAl LDH brucite-type layer structure promotes the elimination of CO23– anions and H2O molecules from since the interlayer space as well as the decrease in the band gap energy and the retarding in the recombination rate of electron-hole pairs, giving rise to the improvement in the photocatalytic activity in the degradation of DCF in aqueous medium. Such improvement in the photocatalytic activity could be favored by the increase in the positive charge of the ZnAl LDH sheets due to the incorporation of W6+ cations, arising an increase in the attractive potential for the uptake of anionic diclofenac molecules within the inter-lamellar spacing to compensate the excess of positive charge. ZnAl LDH photoconverts 29.0% of DCF after 90 min of photoreaction. However, the photoconversion percentage of DCF increases with the molar concentration of W6+ to reach 68.0% in 40 min and 82.0% in 90 min of photoreaction respectively using either ZnAlW-1.5 or ZnAlW-3 LDHs. The kinetics studies confirmed that ZnAlW-1.5 and ZnAlW-3 LDHs are the photocatalysts with the highest activity for the elimination of DCF in aqueous medium. Total organic carbon analysis also confirmed the highest efficacy of ZnAlW-1.5 and ZnAlW-3 LDHs to mineralize diclofenac molecules in aqueous medium.