Photocatalytic removal of organic dye using green synthesized zinc oxide coupled cadmium tungstate nanocomposite under natural solar light irradiation

In this work, zinc oxide coupled cadmium tungstate (ZnO-CT) was prepared as a nano-photocatalyst through a green synthesis route using lemon leaf extract and characterized based on diverse microscopic and spectroscopic techniques. To explore the applicabilties of the prepared nanocomposite (NC), its photocatalytic activity has been investigated against Congo red (CR) dye under natural solar light irradiation conditions. ZnO- CT nano-photocatalyst showcases 97% photocatalytic degradation of the CR after 90 min of natural solar light irradiation with quantum yield of 1.16 × 10⁻⁸ molecules photon⁻¹. The ZnO-CT NC has shown the enhanced photocatalytic degradation performance against CR when compared to its pristine forms (e.g., ZnO (70%) or CT (44%)). According to the free radical trapping and quenching experiments, the photocatalytic activity of ZnO-CT NC appears to be driven efficiently by superoxide and hydroxyl radicals. The photocatalytic degradation kinetics for CR dye was also studied using the pseudo-first-order, diffusional, and Singh models. The high photocatalytic activity of ZnO-CT NC can be accounted for by the presence of electron-withdrawing functional groups like acids (-COOH) and aldehydes (-CHO) on its surface which helped maintain the prolonged recombination of charge carriers and enhanced stability of ZnO-CT (with moderately low leaching rate of cadmium ions (∼2–5%)).