Chen-Xuan Li

High-valent metal-oxo (HVMO) species generated from a homogeneous metal–ligand complex can provide high oxidation power to facilitate selective decontamination. However, sustaining a high reactivity of such a catalytic system is challenging due to the structural fragility of mononuclear-structured organic ligands that are susceptible to self-degradation. Moreover, because of the highly reactive and transient nature of the HVMO complex, its specific structural properties remain unclear, hindering the catalytic mechanism elucidation and system optimization. Here we propose the use of phenanthroline (phen) as a structurally robust alternative ligand for manganese ions (Mn²⁺) complexation and periodate (PI) activation, triggering the formation of a dinuclear Mn-oxo complex, [Mn₂^III,IV(μ-O)₂(phen)₄]³⁺. Impressively, this system achieved rapid sulfamethoxazole oxidation, exhibiting decontamination kinetics 2–5 orders of magnitude higher than those of conventional heterogeneous PI-based systems, and sustained high reactivity for a 10-h continuous operation via a resin-supported complex. Importantly, the structural-stable,diomand-core complex can be directly isolated from the reaction solution. Mechanical study revealed a unique dynamic “closed–open” structure of the Mn₂^III,IV(μ-O)₂ complex for driving pollutant degradation. The system also demonstrated high efficiency and robustness for treating real waters. This study lays a fundamental framework to revolutionize HVMO-based advanced oxidation processes toward sustainable, robust water purification.

A ‘polydopamine-glue’ strategy enables the one-pot fabrication of a multi-component membrane for highly efficient synergistic photocatalytic water purification.

Heterogeneous Mg-Fe oxide/biochar (MgFeO@BC) nanocomposites were synthesized by a co-precipitation method and used as biochar-based catalysts to activate peroxymonosulfate (PMS) for sulfamethoxazole (SMX) removal. The optimal conditions for SMX degradation were examined as follows: pH 7.0, MgFeO@BC of 0.4 g/L, PMS concentration of 0.6 mM and SMX concentration of 10.0 mg/L at 25 ℃. In the MgFeO@BC/PMS system, the removal efficiency of SMX was 99.0% in water within 40 min under optimal conditions. In the MgFeO@BC/PMS system, the removal efficiencies of tetracycline (TC), cephalexin (CEX), ciprofloxacin (CIP), 4-chloro-3-methyl phenol (CMP) and SMX within 40 min are 95.3%, 98.4%, 98.2%, 97.5% and 99.0%, respectively. The radical quenching experiments and electron spin resonance (ESR) analysis suggested that both non-radical pathway and radical pathway advanced SMX degradation. SMX was oxidized by sulfate radicals (SO₄^•−), hydroxyl radicals (•OH) and singlet oxygen (¹O₂), and SO₄^•− acted as the main active species. MgFeO@BC exhibits a higher current density, and therefore, a higher electron migration rate and redox capacity. Due to the large number of available binding sites on the surface of MgFeO@BC and the low amount of ion leaching during the catalytic reaction, the system has good anti-interference ability and stability. Finally, the intermediates of SMX were detected.

In this work, rice-husk-derived biochar (RBC) was synthesized by using simple one-step pyrolysis strategies and served as catalysts to activate peroxymonosulfate (PMS) for degrading sulfamethoxazole (SMX). When the annealing temperature (T) = 800 °C, RBC₈₀₀ exhibits the typical hardwood structure with several micropores and mesoporous. Furthermore, RBC₈₀₀ obtains more defect sites than RBC₆₀₀, RBC₇₀₀, and RBC₉₀₀. In the RBC₈₀₀/PMS system, the removal rate of the SMX reached 92.0% under optimal conditions. The kinetic reaction rate constant (k_obs) of the RBC₈₀₀/PMS system was 0.009 min⁻¹, which was about 1.50, 1.28, and 4.50 times that of the RBC₆₀₀/PMS (k_obs = 0.006 min⁻¹), RBC₇₀₀/PMS (k_obs = 0.007 min⁻¹), and RBC₉₀₀/PMS (k_obs = 0.002 min⁻¹) systems, respectively. In the RBC₈₀₀/PMS system, sulfate radical (SO₄^•−) is the main active species. Compared with other active sites, the hydroxyl group (C-OH) on the surface of RBC₈₀₀ interacts more strongly with PMS, which is more likely to promote the stretching of the O-O bond of the PMS, thus breaking into the activated state and significantly reducing the activation energy required for reaction. The degradation intermediates of SMX were speculated, and the toxicity analysis was conducted. Generally, this work reveals in depth the interaction between reactive sites of biochar-based catalysts and PMS at the molecular level.