Deploying radical inter-transition from radical dotOH to supported NO3radical dot on Mono-dentate NO3--modified ZrO2 to sustain fragmentation of aqueous contaminants

Abstract

© 2023 Elsevier B.V.To advance aqueous pollutant degradation using [rad]OH, H2O2 ([rad]OH carrier) should be cleaved homolytically on a non-reducible metal oxide (ZrO2) rather than heterolytically on a reducible counterpart (MnO2), given the merits of H2O2 homolysis such as improved [rad]OH productivity, unnecessity to recover H2O2 activators (Lewis acidic metals; LA) via electron reduction, and minute LA leaching. This paper presents a methodology to exploit H2O2 homolysis with the rate-determining step of endothermic [rad]OH desorption, thereby proposing the coupling of H2O2 homolysis and exothermic radical inter-conversion of [rad]OH → NO3[rad]SUP (supported NO3[rad]) to create the overall [rad]OH → NO3[rad]SUP route. ZrO2 was modified with NO3− functionalities (NO3[rad]SUP precursors) to form ZrO2-N, where NO3-SUP species were located close to Zr4+ (LA) and Brönsted acidic -OH (BA) sites, whose acidic strengths must be elevated to facilitate [rad]OH desorption for reducing the energy barrier (EBARRIER) of the overall [rad]OH → NO3[rad]SUP route. NO3-SUP species were bound to the ZrO2 surface via mono-dentate configuration only, thereby avoiding LA loss (rate in a per-gram↑), escalating LA/BA strengths (EBARRIER↓), and imparting two free oxygens available to [rad]OH → NO3[rad]SUP (rate in a per-site↑). Moreover, NO3[rad]SUP species extract electrons from contaminants via electron transfer to recover NO3-SUP species used for recurring [rad]OH → NO3[rad]SUP, while sustaining pollutant fragmentation efficiency by circumventing surface poison accumulation. Hence, NO3[rad]SUP on ZrO2-N revealed higher efficiencies in fragmenting bisphenol A or recycling phenol degradation than [rad]OH evolved from ZrO2. In addition, ZrO2 outperformed MnO2 in exploiting NO3[rad]SUP species, thus showing greater recyclability in mineralizing textile wastewater, while leaching a negligible amount of Zr.