Novel carbon-coated zirconium oxide nanocomposites enable ultrahigh oxidant utilization efficiency for selective degradation of organic contaminants

Abstract

Self-quenching of radicals and their non-selective attack on co-existing substrates result in the low oxidant utilization efficiency in Fenton and Fenton-like systems. Herein, we developed a novel octahedral carbon-encapsulated zirconium oxide catalyst (ZrO2-C) featured by large specific surface area (219.5 m2/g), highly-dispersed sub-5 nm active sites, and strong metal-support interactions. The catalyst shows outstanding performance for peroxymonosulfate (PMS) activation, and a two-step catalytic mechanism is proposed. First, it interacts with PMS via inner-sphere coordination to form a metastable surface complex (Stage I); then, the reactive complex reacts with selected molecules via oxygen-atom-transfer route (Stage II). Surprisingly, only 1.21 PMS molecules was consumed for each molecule of carbamazepine (CBZ), almost close to the stoichiometric ratio. Based on a quantitative structure–activity relationship between the reaction rates and the molecular structures of fourteen substituted phenols, we demonstrated that this catalytic process was highly selective towards electron-rich compounds, that is, only those organics with EHOMO values higher than ca. −6.52 eV could be oxidized. Overall, this study provides mechanistic insights into the catalytic selectivity of Zr-based catalysts and advances their further application in Fenton-like systems.