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Phenolic organic contaminants (POCs) in water environment have been usually degraded by advanced oxidation processes (AOPs) based on sulfate radicals ( SO 4 · - ) and hydroxyl radicals ( OH). In this paper, the first step of SO 4 · - / · OH -initiated oxidation reactions toward 19 POCs were investigated using density functional theory (DFT) in order to explore and compare the reactivity of POCs with two free radicals in the aqueous phase. The oxidation reactions initiated by SO 4 · - / · OH were confirmed that POCs can follow three reaction mechanisms: radical adduct formation (RAF), hydrogen atom abstraction (HAA), and single electron transfer (SET). The rate constants of all primary oxidation reactions were calculated using transition state theory (TST). The results turn out that the stronger the electron donating effects of the substituent on POCs, the better the reactivity of POCs with two free radicals. SET mechanisms are main reaction pathways for SO 4 · - -initiated oxidation reactions. Furthermore, the ecotoxicity assessment shows that most OH adducts have higher toxic on aquatic organisms than corresponding reactants. For all the POCs covering in this work, the order of acute toxicity is p-DP > o-AP > m-AP (p-AP) > MP > CP > NP > m-DP (o-DP) > phenol > YP, while the chronic toxicity is in the order p-DP > o-AP > m-AP (p-AP) > MP > CP > NP > YP > phenol > m-DP (o-DP). Thus, the application of AOPs for the removal of POCs should be taken seriously.

The magnetic biochar (γ-Fe2O3@BC) derived from banana peels was synthesized by a facile one-pot thermal process and used as the cost-effective and recyclable persulfate (PS) activator for organic contaminants degradation. The results showed that the encapsulated iron oxide nanoparticles not only introduced the magnetism into biochar for easy separation, but also influenced the catalytic ability for PS activation. The γ-Fe2O3@BC was found to be highly effective for bisphenol A (BPA) degradation without pH adjustment. A complete removal of BPA was obtained within 20 min with an observed rate constant (kobs) of 0.1849 min−1, which was almost two times as large as that (0.0956 min−1) of pure biochar. Further, it exhibited high mineralization efficiency for the degradation of various organic contaminants. The high catalytic activity could be attributed to large BET surface area, dispersed iron species, abundant oxygen functional groups and rich doped nitrogen. Radical quenching experiments and electron spin resonance (ESR) studies confirmed that OH , SO4 − and O2 − were all involved in the radical oxidation process which was responsible for BPA degradation. A mechanism of PS activation by the γ-Fe2O3@BC catalyst was proposed based on the synergistic effect of biochar and iron.

In this work, monochlorophenols (MCPs) isomers degradation was investigated by Co-doped g-C3N4 (CCN) using peroxymonosulfate (PMS) as the oxidant. The effects of the doping amount of Co, the concentration of PMS, the loading of catalyst and initial pH of the solution on the catalyst activity were systematically studied. The results showed that MCPs could be degraded effectively by CCN/PMS system. The degradation reaction followed pseudo-first order kinetics. Sulfate radical (SO4 −) was found as the major active radicals in the degradation process. MCPs were degraded effectively with the degradation rate order of 2-chlorophenol (2-CP) > 3-chlorophenol (3-CP) > 4-chlorophenol (4-CP). Except for the influence of structural characteristics of MCPs, this degradation rate order was also related to the adsorption behavior of CCN, which was based on the intermolecular interaction. Based on the analysis of the degradation products of MCPs, 1,4-benzoquinone or chlorinated 1,4-benzoquinone had been found to be the main intermediates.

The solar/chlorine and UV/chlorine systems as emerging advanced oxidation technologies (AOTs) are used for degrading trace organic contaminants (TrOCs) through generating various radical species. The pH is a vital parameter that significantly affects the degradation efficiency of contaminants. In this study, six aromatic acids and bases (AABs) are selected to investigate the pH-dependent degradation mechanisms and kinetics by two newly-discovered radicals (ClO• and BrO•). Among the 16 dissociation species, the structures with electron-rich rings possess stronger reactivities to ClO• and BrO• than those with electron-poor rings, which is similar to the result of HO•. However, ClO• and BrO• are considered to be more selective and pH-sensitive reacting with AABs than HO• based on the corresponding second-order rate constants (M−1 s−1). Compared with acidic pH, the basic pH could improve the degradation rate of most aromatics in both systems. As pH increases from 6 to 8, the contribution percentages of ClO• in terms of the removal of the aromatics (except for benzoic acid) in solar/chlorine rise more rapidly (from 0.33 ∼ 61.34% to 94.23 ∼ 99.09%) than those in UV/chlorine system (from 19.14 ∼ 99.60% to 96.75 ∼ 99.88%). The pH-dependent contributions of various radical species are attributed to structure-dependent reactivities of compounds and pH-dependent concentrations of radical species. As the dose of Br- increases from 0 to 10 μM, the contributions of BrO• to the removal of aromatics (except for benzoic acid) increase from 0% to 10.28 ∼ 19.32%, thanks to the increased [BrO•]ss. This work is necessary for enhancing the understanding of the pH-dependent contributions of individual species during the removal of dissociable aromatic contaminants in light/chlorine systems.

Superstructures have attracted attention because of their potential applications in chemistry and materials science. In this work, we report the preparation of a porous 3D superstructure of nitrogen-doped carbon decorated with ultrafine cobalt nanodots (Co@NCSS) derived from the self-assembly of polyimide nanoparticles. Utilizing modified ultra-small cobalt nanodots as main catalytically active sites, and the excellent quality and electron transport efficiency generated by this 3D porous superstructure, Co@NCSS exhibited excellent catalytic performance as a peroxymonosulfate (PMS) activator towards the degradation of several sulfonamides. Based on radical scavenging tests and electron paramagnetic resonance (EPR), singlet oxygen (1O2) was the dominant oxidative species. Furthermore, through the identification of degradation intermediates by HPLC-MS and DFT calculation, the pathway of sulfamethoxazole (SMX) degradation by Co@NCSS/PMS was analyzed. The possible catalytic mechanism of Co@NCSS/PMS for SMX degradation is also proposed in this paper. Co@NCSS has the potential to be an ideal material for removing antibiotics from wastewater.

The activation of peroxymonosulfate (PMS) by multivalent transition metal oxides has been widely studied in organic pollutants degradation. Compared with that of valence electrons, the role of localized electrons of transition metal oxides in the activation of PMS has remained elusive. Herein, ZnO, as a typical irreducible oxide, was used as an ideal model to determine the role of the localized electrons of O-vacancies (Vo) in the PMS heterolysis process. Combined experimental and theoretical analysis demonstrated that O-vacancies, serving as the catalytically active sites, provide enough localized electron retransmission to the adsorbed HSO5−, via a single electron transfer reaction resulting in formation of OH− and SO4 −. In addition, O-vacancies promote PMS dehydration to form metastable −SO4-O-O-O4S− that rapidly decompose into O2 −, which is responsible for the 1O2 production. This work introduces a unique strategy for obtaining electronic-level insights into the role of catalyst defects in promoting efficient PMS activation.

Advanced oxidation processes (AOPs) based on the activation of persulfate (PS) by minerals have been widely used in environmental remediation. Herein, two goethite materials with different contents of exposed {0 2 1} facet were synthesized and used as the catalysts for PS activation to degrade tetracycline. Results showed that exposed facets significantly affected their catalytic activity. Goethite exposed with more {0 2 1} facet exhibited better catalytic performance. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and electrochemical analysis suggested that the surface Fe(II)/Fe(III) redox cycle, the abundant surface hydroxyl density and the easier generation of active radicals by activating PS were responsible for the excellent catalytic performance of goethite with more {0 2 1} facet exposed. Furthermore, the density functional theory (DFT) calculations further confirmed that {0 2 1} facet was more favorable for the activation of PS than {1 1 0} facet. The electron paramagnetic resonance (EPR) and radical scavenging experiments indicated that both sulfate radicals and hydroxyl radicals participated in the degradation process. This study provides new insights into the PS heterogeneous activation by facet-dependent goethite in environmental catalysis.

In this study, a novel peroxymonosulfate (PMS) activator, periclase (MgO) was applied to the activation of PMS for the degradation of organic contaminants in aqueous solution. It was found that MgO exerts an excellent and stable catalytic performance for PMS activation to degrade a wide range of pollutants including bisphenol A (BPA), phenol, chlorophenol, and dye, with degradation efficiencies of 100%, 100%, 41%, and 59%, respectively. Results from a combination of electron spin resonance (ESR), free radical quenching, chemical probe and isotope labeling investigations confirm that singlet oxygen (1O2) was the dominant reactive species generated in the PMS/MgO system and accounted for BPA degradation. The steady-state concentration of 1O2 was 13.2 × 10−13 M. Further evidence from X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FTIR) spectroscopy, and density functional theory (DFT) suggested that 1O2 was generated by the self-decomposition of PMS induced by surface hydroxyl groups on MgO. In addition, the degradation of BPA was hardly affected by anions and humic acid (HA) that commonly existed in the environmental matrices. The naturally occurring periclase also has high catalytic ability for PMS activation and BPA degradation. Compared with other transition metals-based radical pathways and carbonaceous materials-based non-radical pathways of PMS activation, MgO exerts a comparable catalytic performance but less potential risk and cheaper. This study developed a novel environmentally friendly catalyst with low cost and high efficiency for the selective degradation of organic pollutants in wastewater treatment.

It has been found that soot particles with a graphene-like structure play an important role in heterogeneous oxidation. However, little is known about the mechanism at the atomic-level. Therefore, we studied the heterogeneous ozonolysis mechanism of syringol onto graphene (GP) sheets using density functional theory (DFT) methods. The results show that the GP sheet plane plays an adsorbent role in the ozonolysis of syringol. Results suggest that the adsorbed syringol will prefer to degrade in wet weather. Moreover, Criegee intermediates generated from the primary ozonolysis steps will undergo subsequent reactions in the presence of NO and H2O. The total rate constants for the ozonolysis of syringol are 4.62 × 105 and 4.77 × 107 M−1 s−1 in the condensed phase and aerosol particles, respectively (298 K, 1 atm). Based on toxicity assessments, most transformation products are eco-friendly. Our results provide a better understanding of the environmental fate of syringol and can be a supplement to the experimental research in the future.