Nonradical oxidation has been determined to be a promising pathway for the degradation of organic pollutants in heterogeneous catalytic ozonation (HCO). However, the bottlenecks are the rational design of catalysts to selectively induce nonradicals and the interpretation of detailed nonradical generation mechanisms. Herein, we propose a new HCO process based on single-atom iron catalysts, in which Fe-N 4 sites anchored on the carbon skeleton exhibited outstanding catalytic ozonation activity and stability for the degradation of oxalic acid (OA) and phydroxybenzoic acid (pHBA) as well as the advanced treatment of a landfill leachate secondary effluent. Unlike traditional radical oxidation, nonradical pathways based on surface-adsorbed atomic oxygen (*O ad ) and singlet oxygen ( 1 O 2 ) were identified. A substrate-dependent behavior was also observed. OA was adsorbed on the catalyst surface and mainly degraded by *O ad , while pHBA was mostly removed by O 3 and 1 O 2 in the bulk solution. Density functional theory calculations and molecular dynamics simulations revealed that one terminal oxygen atom of ozone preferred bonding with the central iron atom of Fe-N 4 , subsequently inducing the cleavage of the O−O bond near the catalyst surface to produce *O ad and 1 O 2 . These findings highlight the structural design of an ozone catalyst and an atomic-level understanding of the nonradical HCO process.

No abstract

Anaerobic digestion (AD) is a promising method to treat organic matter. However, AD performance was limited by the inefficient electron transfer and metabolism imbalance between acid-producing bacteria and methanogens. In this study, a novel binary electroactive material (Fe 3 O 4 @biochar) with pseudocapacitance (1.4 F/g) and conductance (10.2 μS/cm) was exploited to store-release electrons as well as enhance the direct electron transfer between acid-producing bacteria and methanogens during the AD process. The mechanism of pseudocapacitance/conductance on mediating interspecies electron transfer was deeply studied at each stage of AD. In the hydrolysis acidification stage, the pseudocapacitance of Fe 3 O 4 @biochar acting as electron acceptors proceeded NADH/NAD + transformation of bacteria to promote ATP synthesis by 21% which supported energy for organics decomposition. In the methanogenesis stage, the conductance of Fe 3 O 4 @biochar helped the microbes establish direct interspecies electron transfer (DIET) to increase the coenzyme F 420 content by 66% and then improve methane production by 13%. In the complete AD experiment, electrons generated from acid-producing bacteria were rapidly transported to methanogens via conductors. Excess electrons were buffered by the pseudocapacitor and then gradually released to methanogens which alleviated the drastic drop in pH. These findings provided a strategy to enhance the electron transfer in anaerobic treatment as well as guided the design of electroactive materials.