Green synthesis of Ag/ZnO catalysts using cassava starch applied to the degradation of emerging contaminants

This work describes a new synthetic route for the production of a low-cost and environmentally friendly catalyst: a zinc oxide-based system doped with silver, prepared using a novel sol–gel method with cassava starch to form the gel. The photocatalysts were characterized by different techniques: X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), photoacoustic spectroscopy (PAS), and point of zero charge (PZC). The XRF and EDS results indicated that photocatalysts doped with 2%, 5%, 8%, and 10%, silver could be obtained successfully. The synthesis method employed produced nanoparticles of ~30 nm, as confirmed by XRD and TEM results. The band gap energy values of the materials (ranging from 1.98 to 3.05 eV) fall within the range suitable for catalyst activation under UV radiation. Photocatalytic reactions were carried out with two emerging pollutants, 2,4-d-dichlorophenoxyacetic acid (2,4D) and caffeine, to verify the catalytic activity of the synthesized catalyst. The results indicated that the catalyst was efficient for the degradation of both pollutants. Tests using solar radiation led to 100% degradation of 2,4D. Cl⁻ ions did not influence the process negatively. The amount of caffeine removed by the photocatalytic process used in solar radiation was ~97% due to the low band gap energy values of the synthesized material.