Anions-Impacted Water Purification from a Dual-Substrate Perspective

Heterogeneous chemical oxidation for water treatment based on direct electron transfer has attracted great interest due to its low oxidant consumption and selective oxidation capabilities. Under low oxidant dosages (e.g., less than ten times the pollutant concentration), the influence of common inorganic anions in wastewater cannot be ignored. However, the respective impacts of ions on the two substrates (i.e., oxidant and pollutant) have not yet been systematically studied yet. In this work, we reveal that several inorganic anions (e.g., NO₃^-, Cl^-, HCO₃^-, SO₄^2-, HPO₄^2-), which are commonly present in water and wastewater, have much greater influences on the oxidant than on the pollutant, with notable differences among the different ions. The origin of the ion effects was investigated from the aspects of substrate adsorption-activation and interfacial electron transfer. Experimental and theoretical studies demonstrate that the solution resistance, electrostatic interactions, interfacial bonding, and electronic interactions, as well as the ions' affinity for water, which correlates with the Hofmeister series, were collectively responsible for the ion effects. From a dual-substrate perspective, this work proposes a research paradigm that not only offers insights into the ion effects in heterogeneous chemical water treatment but also holds implications for the design of catalytic active sites and the optimization of reaction conditions in dual-reactant systems.