Unraveling the Co(IV)-Mediated Oxidation Mechanism in a Co₃O₄/PMS-Based Hierarchical Reactor: Toward Efficient Catalytic Degradation of Aromatic Pollutants

A metal (oxide)/peroxymonosulfate (PMS)-based hierarchical reactor has recently been developed as an emerging technology involving a heterogeneous advanced oxidation process for wastewater treatment. HO•, SO4•–, and 1O2 were regarded as predominant reactive oxidants that contributed to the degradation of pollutants in these reactors. However, the possible contribution of potentially generated high-valent metal to pollutant degradation in the reactor was rarely studied. Herein, we unraveled the Co­(IV)-mediated oxidation mechanism in a Co3O4/PMS-based hierarchical reactor for the degradation of aromatic pollutants. The Co3O4/PMS-based hierarchical reactor demonstrated an efficient degradation of aromatic organic pollutants (>90%). Electron paramagnetic resonance characterization, radical quenching, and probe oxidation experiments confirmed that Co­(IV) was the dominant reactive species in the Co3O4/PMS-based hierarchical reactor. Further scavenger experiments validated that Co­(IV) played the most crucial role in the removal of the aromatic pollutant. The majority of Co­(IV) originated from the immobilized Co3O4 rather than the leaching of Cox+ ions in the Co3O4/PMS-based hierarchical reactor. Our study revealed the critical role of high-valent metal species in the reactor for the degradation of aromatic pollutants, which will facilitate the understanding of mechanisms involved in heterogeneous metal (oxide)/PMS-based systems

Single-Atom Cobalt-Modified Catalytic Membrane for Pollutant Degradation with High Tolerance of Environmental Interferences

Peroxymonosulfate (PMS)-based catalytic oxidation processes represent promising means of degrading organic contaminants for wastewater treatment. However, these systems typically use dispersions of catalytic particles that require challenging recovery steps, and the radical-based oxidation processes are inefficient due to reactions with background species present in natural waters. Herein, we incorporate single-atom cobalt into a catalytic membrane (Co–C3N4) for the selective production of high-valent cobalt-oxo species (Co(IV)=O). The generation of Co(IV)O is confirmed by 18O isotopic labeling and scavenger experiments. Furthermore, density functional theory calculations show that Co(IV)O formation rather than radical formation is thermodynamically favorable in the Co–C3N4/PMS process. The Co–C3N4 membrane activates PMS with a rate constant of kobs = 11.1540 min–1, which is nearly 105 times greater than that for traditional heterogeneous catalytic dispersions (i.e., kobs = 0.1065 min–1). Additionally, the Co(IV)O-mediated oxidation process degrades contaminants with low ionization potentials at accelerated rates (e.g., kobs = 17.2860 min–1 for guaiacol). The process also demonstrates improved resistance to background ions and humic acid, in comparison with conventional radical-based oxidation processes. Our study presents a facile approach to engineer single-atom catalytic membranes for high-valent metal-oxo-mediated PMS-based catalytic oxidation processes, providing promising opportunities for efficiently removing persistent pollutants while mitigating interference from background species

Antibiotic Removal, Toxicity Reduction, and Antibiotic Resistance Development Inhibition Using Janus Electrochemical Membrane Filtration

Electrochemical membrane filtration (EMF) technology, which combines the advantages of membrane filtration and electrochemical oxidation, is an effective technology for removing micropollutants from water and wastewater. However, the investigations on antibiotic removal, toxicity reduction, and antibiotic resistance development inhibition in EMF systems are insufficient. In this study, a Janus EMF system using a Fe–Pt Janus electrochemical ceramic membrane was utilized to remove sulfadiazine (SDZ) from synthetic and real surface water. The results showed that a stable removal efficiency of SDZ (63.9%–79.3%) could be achieved with a contact time of 39 s in a 7-day continuous experiment. The toxicity assessment using Vibrio fischeri and Photobacterium phosphoreum revealed that EMF using Na2SO4, NaHCO3, or surface water solution as the matrix could stably reduce toxicity, while EMF in NaCl solution dramatically increased the permeate toxicity. The change in toxicity could be attributed to the reduction of SDZ as well as the generation of different degradation products. Furthermore, exposure experiments demonstrated that the EMF could alleviate the development of antibiotic-resistant genes revealed by three model microbiotas (activated sludge, farmland soil, and mice gut). Our results highlight that the EMF system has a great potential for antibiotic removal, toxicity reduction, and antibiotic resistance development inhibition

Selective Synergistic Catalytic Elimination of NO_<i>x</i> and CH₃SH via Engineering Deep Oxidation Sites against Toxic Byproducts Formation

NOx and CH3SH as two typical air pollutants widely coexist in various energy and industrial processes; hence, it is urgent to develop highly efficient catalysts to synergistically eliminate NOx and CH3SH. However, the catalytic system for synergistically eliminating NOx and CH3SH is seldom investigated to date. Meanwhile, the deactivation effects of CH3SH on catalysts and the formation mechanism of toxic byproducts emitted from the synergistic catalytic elimination reaction are still vague. Herein, selective synergistic catalytic elimination (SSCE) of NOx and CH3SH via engineering deep oxidation sites over Cu-modified Nb–Fe composite oxides supported on TiO2 catalyst against toxic CO and HCN byproducts formation has been originally demonstrated. Various spectroscopic and microscopic characterizations demonstrate that the sufficient chemisorbed oxygen species induced by the persistent electron transfer from Nb–Fe composite oxides to copper oxides can deeply oxidize HCOOH to CO2 for avoiding highly toxic byproducts formation. This work is of significance in designing superior catalysts employed in more complex working conditions and sheds light on the progress in the SSCE of NOx and sulfur-containing volatile organic compounds