Advanced oxidative processes (AOP) have the potential to address a slew of both emerging contaminates and persistent pollutants in drinking water sources. In this work, we detail the development of a chemical-additive-free AOP system employing a ZnO-SiO2-Ag photocatalytic nanocomposite immobilized in a polymer foam for non-selective degradation without expensive chemical additives (chlorine, peroxides, or ozone). We developed a statistical design of experiments (DOE) framework for a limited data environment to explore the polymer foam scaffold fabrication. This framework was also used to verify hypotheses concerning greener solvent selection and processes variables. Sol-gel synthesis of ZnO-SiO2-Ag nanocomposites produced materials with 64-95% ZnO as determined by ICP-MS. These nanocomposites generate the reactive oxygen species (ROSs) necessary for contaminant degradation using the UV-light that is standard in drinking water treatment industries. X-ray Diffraction (XRD) confirms a crystalline phase of zinc oxide with a mean crystalline diameter of 22-38 Å. The SiO2 domains are amorphous and provide increased surface area and stability to the nanocomposite. As nano-Ag is known to exhibit antimicrobial properties, inhibition zones against E. coli were measured to verify that the heterogeneous foam also shows antimicrobial behavior. The ROS generation and lifetimes of the nanocomposite were determined by measuring the chemiluminescence of luminol in the presence of horseradish peroxidase. Chemiluminescence confirmed a ten-fold increase in ROS generation with the inclusion of Ag and lifetimes up to 30 seconds after light exposure. Current work entails flow-through testing with UV-A light and High-Performance Liquid Chromatography to evaluate the performance of the nanocomposite/polymer foam system for caffeine, antibiotics, and other trace pharmaceuticals and calculate the quantum efficiencies. This polymer foam photocatalyst composite material presents a sustainable and safe solution for the nontargeted treatment of emerging contaminants in drinking water.

Immobilized ZnO-SiO2-Ag nanocomposite for the degradation of emerging contaminants

ACS Spring 2022

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