Photocatalytic evaluation of CuO and ZnO crystallites synthesized hydrothermally using binary eugenol/iso-eugenol mixtures: isomer effects on the capping propensity of biogenic agents

Abstract

This work aims to investigate isomer effects on the capping propensity of biogenic agents used in nanomaterial synthesis. Ten photocatalysts ((CuO-1–CuO-5) and (ZnO-1–ZnO-5)) of the CuO and ZnO series were hydrothermally synthesized using different molar ratios of eugenol + iso-eugenol (EIM) as biogenic capping agents to compare their capping propensity as isomeric forms. Experimental data analysis highlighted a variation in the surface morphology and crystallinity of both the systems synthesized using different EIM concentrations. The ZnO and CuO crystallites synthesized using different EIM mixtures depicted a range of photocatalytic descriptors and broader photocatalytic efficiencies. Furthermore, their optical properties such as band gap (E_g), absorption coefficient (α), refractive index (n), extinction coefficient (k) and optical conductivity (σ_opt) showed a favourable trend with an increase in the proportion of eugenol in the binary mixture. Based on the observed photocatalytic and electrochemical characteristics, ZnO-based photocatalysts were predicted to be more efficient than CuO catalysts. Furthermore, photocatalytic parameters predicted increasing photocatalytic efficiency from ZnO-1 to ZnO-5 and CuO-1 to CuO-5, which was consistent with the increasing proportion of eugenol in the binary mixture. This increase in the efficiency is attributed to a better charge transfer, reduced recombination rate and greater optical conductivity in the case of ZnO-5 and CuO-5, which was confirmed by EIS and UV-vis studies. Moreover, photocatalytic efficacy was evaluated for the degradation of dyes with different structural complexities under natural attenuation conditions (solar radiation, pH 7 and 25 °C) for a maximum of 450 min.