The aqueous degradation of butylated hydroxyanisole by UV/S2O8(2-): study of reaction mechanisms via dimerization and mineralization

Sulfate radical-based oxidation of the aminopyralid and picloram herbicides: The role of amino group on pyridine ring

The widespread utilization of pesticides has attracted increasing attention to their environmental impacts and effective removal strategies. In the present study, the degradation of herbicides picloram (PCLO) and aminopyralid (AMP) with similar structures were investigated systematically by thermo activated persulfate. Overweight SO₄^•- was determined to be the predominant oxidizing species by quenching experiment. Obtained by laser-flash photolysis (LFP), reaction rate constants of SO₄^•- towards AMP and PCLO were determined at 1.56 × 10⁹ M^-1s^-1 and 1.21 × 10⁹ M^-1s^-1, respectively. Product analysis revealed that both substances underwent similar oxidation paths, namely, successive oxidation on pyridine ring and formation of coupling-products as well as further hydroxylation and decarboxylation. Amino group on the pyridine ring was identified as the main reactive site, which was further confirmed by DFT calculation. It was susceptible attacked by SO₄^•- to form deamination, nitration, and self-coupling products. These couples could be further oxidatively dehydrated to form azo and a series of azo derivatives. EOCSAR program predicted significant hazards on aquatic species during the formation of these couplings and azo derivatives. Our work emphasized the potential ability and toxicity of contaminates to produce azo substances in the presence of amino groups on the pyridine ring.

Enhanced adsorption and catalytic peroxymonosulfate activation by metal-free N-doped carbon hollow spheres for water depollution

Rational design of metal-free carbon-based heterogeneous catatlyst for wastewater remediation via peroxymonosulfate (PMS) activation is highly desirable. Here, hollow structured porous carbon with abundant N, a high graphitization degree, and a large specific surface area and pore volume (1301 m²/g and 1.12 cm³/g) was synthesized by the pyrolysis of core-shell structured composites consisting of polystyrene (PS) cores and Zeolitic imidazolate frameworks-8 (ZIF-8) shells. The hollow structured carbon (CPS@ZIF-8) was characterized thoroughly and applied for phenol degradation by the activation of PMS. The effects of operation conditions such as the catalyst and PMS dose, phenol concentration, initial pH, and temperature on phenol removal were investigated comprehensively. Moreover, the main reactive species involved in phenol oxidation were investigated, and a plausible mechanism for the degradation of phenol is proposed. The results show that CPS@ZIF-8 exhibited an excellent phenol adsorption and degradation performance, which can be mainly ascribed to its large surface area, abundance of nitrogen and hollow porous structure. Moreover, both the nonradical pathway (involving ¹O₂) and the radical pathway (involving SO₄^- and O₂^-) were found to be involved in the decomposition of phenol.

Photochemical Water Oxidation Using a Doubly N-Confused Hexaphyrin Dinuclear Cobalt Complex

A doubly N-confused hexaphyrin dinuclear cobalt complex (Co₂DNCH) is revealed as an efficient water oxidation catalyst, outperforming the mononuclear cobalt porphyrin with the same aryl group as those in Co₂DNCH. By photoirradiation of a water/acetone-d₆ (9:1) mixture containing Co₂DNCH, [Ru^II(bpy)₃]²⁺, and S₂O₈^2- as the water oxidation catalyst, photosensitizer, and sacrificial electron acceptor, respectively, with visible light, O₂ was obtained as the maximum with turnover number = 1200, turnover frequency = 3.9 s^-1, and quantum yield = 0.30.

Degradation of benzotriazole by sulfate radical-based advanced oxidation process

Benzotriazole (BTA) is a recalcitrant contaminant that is widely distributed in aquatic environments. This study explored the effectiveness of sulfate radical-based advanced oxidation process in degrading BTA (SR-AOP). The sulfate radical was generated by heat activation of persulfate (PS). Our results show alkaline pH promoted the BTA degradation. The solution pH also affected the speciation of total radicals. Sulfate radical ( S O 4 ⋅ - ) predominated at acidic pH while hydroxyl radical (HO^•) predominated at basic pH. High temperature, high PS concentration and low BTA concentration promoted the BTA degradation. Influence of water matrix constituents on the reaction kinetics was assessed. We found that ≤10 mM of Cl^- promoted the reaction, but 100 mM Cl^- inhibited it. H C O 3 - was similar to Cl^-. Br^- and C O 3 2 - inhibited the reaction while S O 4 2 - did not affect the reaction. N O 3 - of ≤10 mM did not affect the reaction, but 100 mM of N O 3 - inhibited it. Eleven degradation intermediates were identified using ultra-high solution Orbitrap mass spectrometry. Based on the intermediates identified, possible reaction pathways were proposed. Overall, SR-AOP can effectively mineralize BTA, but water matrix constituents greatly influenced the reaction kinetics and thus should be carefully considered for its practical application. Abbreviations: BTA, benzotriazole; PS, persulfate; PMS, peroxymonosulfate; SPC, sodium percarbonate; AOP, advanced oxidation process; PS-AOP, persulfate-based advanced oxidation process; SR-AOP, sulfate radical-based advanced oxidation process; TAP, thermally activated persulfate; TOC, total organic carbon; TBA, tert-butyl alcohol.

Degradation kinetics and mechanism of bis(2-chloroethyl) ether by electromagnetic induction electrodeless lamp activated persulfate

Bis(2-chloroethyl) ether (BCEE) has become one of the most frequently detected chlorinated ether contaminants in the US and Europe, and is classified as a B2 carcinogen. In this study, the degradation rate of BCEE by mercury lamps, xenon lamp and electromagnetic induction electrodeless lamp (EIEL) activated persulfate were compared, and EIEL activated persulfate was confirmed to have higher degradation capability and lower energy consumption. In this sense, the degradation kinetics and mechanism in EIEL system were further investigated. The degradation reaction followed pseudo first-order, and the removal rate of BCEE exceeded 95% in 60 min when the initial pH, the concentration of BCEE and Na₂S₂O₈ were 3, 4 mg L^-1 and 15 mM, respectively. Presence of inorganic anions and humic acids would reduce the degradation rate constant. In accordance with the results of electron paramagnetic resonance and quenching experiments, SO₄^-· was dominant in the acidic regime and OH· was dominant in the alkaline regime. Meanwhile, OH· had higher degradation rate with BCEE when initial pH was 7. Seven degradation products were identified and the reaction pathways included OH· substitution and free radical coupling. Although the total organic carbon was eliminated slowly during the degradation of BCEE, the predicted toxicity of most degradation products to Fathead minnow, Daphnia magna and oral rat were lower than BCEE.

Enhanced mineralization of bisphenol A by eco-friendly BiFeO3-MnO2 composite: Performance, mechanism and toxicity assessment

An eco-friendly BiFeO₃-MnO₂ composite with dual functionalities of adsorption and catalysis was successfully constructed by using a simple one-step hydrothermal method for the removal of bisphenol A (BPA) pollution from water. Several characterization methods, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS), were applied to verify the combination of BiFeO₃ and MnO₂. BiFeO₃-MnO₂ (BFO-MO) exhibited excellent adsorption and catalytic activity compared with those of pure BiFeO₃. The adsorption process followed a pseudo-second-order kinetic model and matched the Langmuir isotherm model. Effects of the catalyst and peroxymonosulfate (PMS) concentrations, pH and real water matrix were also analyzed, and BFO-MO displayed perfect adsorption and degradation performance under different conditions. Meanwhile, mineralization performance was tested, and the total organic carbon removal rate was nearly 85%. Moreover, BFO-MO exhibited good stability and reusability after five cycles. Based on radical quenching experiments, SO₄^- and OH were the primary reactive species responsible for BPA oxidation, and the possible reaction mechanism of BFO-MO/PMS was proposed. Finally, the degradation intermediates were identified, and the toxicity of intermediates was assessed. The novel BFO-MO composite is a promising catalyst for synchronous adsorption and degradation to purify wastewater.

Degradation of sulfamethazine by biochar-supported bimetallic oxide/persulfate system in natural water: Performance and reaction mechanism

The rapid development of aquaculture results in the increased concentrations and kinds of antibiotics in water environment, and the sharply growing antibiotic contamination has caused increasing concerns. Herein, an innovative sulfamethazine (SMT) removal approach was developed by activation of persulfate (PS) using biochar-based materials prepared by co-precipitation and pyrolysis: Fe-Mg oxide/biochar (FeMgO/BC). Experiments on the activation of PS by FeMgO/BC under different factors were carried out. The involved mechanism and degradation pathway were also studied. Notably, the SMT removal rate reached 99 % under the optimum reaction condition, while the TOC removal efficiency reached 77.9 %. PS was activated by FeMgO/BC and the dominated active radical was SO_4•^-. Fe²⁺ from FeMgO and the hydroxyl and carboxyl groups on the surface of biochar contributed to the production of SO_4•^-. The dehydrogenation, bond cracking and unsaturated bond addition process occurred in the degradation of SMT. Furthermore, FeMgO/BC exhibits excellent reusability and stability. Considering the outstanding actual water application performances and the weak biotoxicity, FeMgO/BC shows a promising potential in the removal of antibiotics under actual water conditions.

Nonradical Oxidation of Pollutants with Single-Atom-Fe(III)-Activated Persulfate: Fe(V) Being the Possible Intermediate Oxidant

When applied for the remediation of polluted water/soil, peroxydisulfate (PDS) usually needs to be effectively activated to generate sulfate radical as the working oxidant. However, a significant part of the oxidation capacity of PDS is lost in this way because sulfate radical unselectively reacts with most of the substances in water/soil. PDS activation without generating radicals is preferred to maximize its oxidation capacity for targeted pollutants. Here, we report that single-atom Fe(III)- and nitrogen-doped carbon (Fe-N-C) can efficiently activate PDS to selectively remove some organic pollutants following an unreported nonradical pathway. The single-atom Fe(III) coordinated with pyridinic N atoms was confirmed to be the active site for the catalytic decomposition of PDS. However, the PDS decomposition did not produce radicals or reactive oxygen species. It is very likely that the coordinated Fe(III) is readily converted to Fe(V) through two-electron abstraction by PDS, and Fe(V) is responsible for the selective degradation of organic pollutants. The PDS/Fe-N-C-coupled process utilizes more oxidation capacity of PDS than both radical oxidation and other reported nonradical oxidation like PDS/CuO under the same experimental conditions. This process provides a new approach to selectively degrade some organic pollutants through PDS activation.

Novel Visible Light-Driven Photocatalytic Chlorine Activation Process for Carbamazepine Degradation in Drinking Water

Photolysis of free chlorine (HOCl/ClO^-) is an advanced oxidation process (AOP) to produce hydroxyl (HO^•) and other radicals for refractory micropollutant degradation. However, HOCl/ClO^- is only conducive to activation and production of radicals by ultraviolet (UV) light. For the first time, we show the use of visible light (>400 nm) to produce HO^• and ClO^•, through use of graphitic carbon nitride (g-C₃N₄) and photogenerated h_vb⁺, e_cb^-, and O₂^•- in the presence of HOCl/ClO^-, which was termed visible light g-C₃N₄-enabled chlorine AOP (VgC-AOP). The VgC-AOP increased the pseudo first-order degradation rate constant of a model micropollutant, carbamazepine, by 16 and 7 times higher than that without g-C₃N₄ and HOCl/ClO^-, respectively, and remained active over multiple use cycles. Effects of water quality [pH, alkalinity, Cu(II), and natural organic matter (NOM)] and the operational conditions (g-C₃N₄ and HOCl/ClO^- concentrations, irradiation wavelength, and dose) were investigated. Of particular significance is its superior performance in the presence of NOM, which absorbs less light at visible light wavelengths and scavenges less surface-bonded reactive species, compared against UV/TiO₂ or UV/chlorine AOPs. The VgC-AOP is practically relevant, feasible, and easily implementable and it expands the potential types of light sources (e.g., LEDs and solar light).

Enhancement of benzene degradation by persulfate oxidation: synergistic effect by nanoscale zero-valent iron (nZVI) and thermal activation

The feasibility of an advanced oxidation process based upon sodium persulfate (SPS) activated simultaneously by heat (50 °C) and nanoscale zero-valent iron (nZVI) on benzene removal was investigated. The experimental results strongly showed the synergistic effect of thermal and nZVI activation to SPS and benzene removal was enhanced with the increase of SPS/nZVI/benzene molar ratio. Specifically, 94% of benzene could be removed in 1 hr at 50 °C at the SPS/nZVI/benzene molar ratio of 10/5/1. The radical scavenger tests and electron paramagnetic resonance (EPR) analysis confirmed that SO₄•^- was the predominant species contributing to benzene degradation. Further, the effects of the solution matrix on benzene elimination were investigated. The results indicated that benzene destruction in the thermally activated SPS/nZVI system performed better under acidic conditions, and the high concentration of both Cl^- and HCO₃ ^- had adverse effects on benzene elimination. The test for the performance of benzene degradation in the actual groundwater demonstrated that benzene could be degraded entirely at SPS/nZVI/benzene molar ratio of 40/40/1 at 50 °C, indicating that the synergistic catalysis of thermal and nZVI activation to SPS is exploitable and the thermally activated SPS/nZVI system can be applicable to the remediation of benzene contaminated groundwater.

Enhanced kinetic performance of peroxymonosulfate/ZVI system with the addition of copper ions: Reactivity, mechanism, and degradation pathways

Advanced oxidation processes (AOPs) based on the bimetallic system has been demonstrated as a promising way to enhance the degradation of pollutants in the water. In this study, the degradation of Rhodamine B (RhB) in a zero-valent iron (ZVI)/ peroxymonosulfate system with Cu²⁺ was thoroughly investigated. RhB could be efficiently removed (99.3 %) in the optimal ZVI/PMS/Cu²⁺ system, while only 58.2 % of RhB could be degraded in the ZVI/PMS system. The influence of reaction parameters on the degradation of RhB was further investigated. Quenching experiments and electron paramagnetic resonance (EPR) tests revealed that various reactive oxygen species could be generated in the ternary system, of which, ¹O₂ and O₂^- were identified for the first time. The effect of various anions, NOM and different water matrix were also considered at different concentrations. A variety of byproducts and degradation pathways were identified using HPLC/MS/MS. Finally, the Quantitative Structure Activity Relationship (QSAR) method of Toxicity Estimation Software Tool (TEST) was applied to estimate the toxicity of the byproducts and the results indicated that the overall toxicity of the target was relatively reduced. This study demonstrated the potential for the removal of environmental reluctant pollutants in water via the combined radical and non-radical pathways.

A Comparative Study on Oxidation of Acidic Red 18 by Persulfate with Ferrous and Ferric Ions

Ferrous and ferric salts were tested for the persulfate activation (PS/Fe2+ and PS/Fe3+) and the oxidation of Acid Red 18 (AR18). A complete removal was attained after 90 min in both PS/Fe2+ and PS/Fe3+ processes with the persulfate concentration of 6 mM. High concentrations of PS, Fe2+, and Fe3+ promoted the AR18 degradation in both processes and the optimized pH were 3 and 3.3 for PS/Fe2+ and PS/Fe3+ processes, respectively. The mechanism of PS activation by Fe3+ was also investigated. It was found that hydroxyl radical (HO•) and sulfate radical (SO4−•) were formed and acted as dominating radicals in both processes. It is also deduced that Fe recycle offers Fe2+ for PS activation in PS/Fe3+ process to produce HO• and SO4−•. The less radical side reactions lead to a higher contribution of HO• and SO4−• on AR18 degradation in PS/Fe3+ process.

Methylene blue degradation by the VUV/UV/persulfate process: Effect of pH on the roles of photolysis and oxidation

This study investigated methylene blue (MB) degradation by the vacuum-ultraviolet/ultraviolet/persulfate (VUV/UV/PS) process using a mini-fluidic VUV/UV photoreaction system. Results show that MB degradation by the VUV/UV/PS process was significantly higher than that of the conventional UV/PS process, as the VUV photolysis of H₂O and PS generated more reactive oxygen species (ROSs). HO^• and SO₄^•-, identified as the main ROSs, were mostly consumed by dissolved organic carbon and Cl^‒ in real waters, respectively. Additionally, the impacts of solution pH and the concentrations of PS, humic acid, and inorganic ions (HCO₃^‒, Cl^‒, NO₃^‒, SO₄^2‒, Fe(II), and Fe(III)) were systematically evaluated. The solution pH significantly affected the photon absorption distributions, as well as the contributions of photolysis and oxidation to MB degradation, resulting in different variations in the degradation rate constant and total organic carbon removal ratio with increasing solution pH. At all tested pH levels (3.0-11.0), particularly under acidic conditions, HO and SO₄^- were two predominant contributors to MB degradation, while VUV and UV photolysis contributed more when the solution pH increased. This study provides a highly efficient process for organic pollutant removal, which could be applied in water treatment.

Formation of chloronitrophenols upon sulfate radical-based oxidation of 2-chlorophenol in the presence of nitrite

Sulfate radical (SO₄^-)-based advanced oxidation processes (SR-AOPs) are promising in-situ chemical oxidation technologies widely applied for soil/groundwater remediation. The presence of non-target water constituents may interfere the abatement of contaminants by SR-AOPs as well as result in the formation of unintended byproducts. Herein, we reported the formation of toxic chloronitrophenols during thermally activated persulfate oxidation of 2-chlorophenol (2CP) in the presence of nitrite (NO₂^-). 2-Chloro-4-nitrophenol (2C4NP) and 2-chloro-6-nitrophenol (2C6NP) were identified as nitrated byproducts of 2CP with total yield up to 90%. The formation of nitrated byproducts is a result of coupling reaction between 2CP phenoxyl radical (ClPhO) and nitrogen dioxide radical (NO₂). As a critical step, the formation of ClPhO was supported by density functional theory (DFT) computation. Both 2C4NP and 2C6NP could convert to 2-chloro-4,6-dinitrophenol (2C46DNP) upon further treatment via a denitration-renitration process. The formation rate of 2C4NP and 2C6NP was closely dependent on the concentration of NO₂^-, solution pH, and natural water constituents. ECOSAR calculation suggests that chloronitrophenols are generally more hydrophobic and ecotoxic than 2CP. Our result therefore reveals the potential risks in the abatement of chlorophenols by SR-AOP, particularly when high level of NO₂^- is present in water matrix.

Efficient activation of intercalated persulfate via a composite of reduced graphene oxide and layered double hydroxide

Efficient activation of peroxydisulfate (PDS, S₂O₈^2-) was achieved in this study by a hybrid of reduced graphene oxide (rGO) and layered double hydroxide (LDH). The peroxydisulfate was intercalated into the interlayers of LDH that was combined with rGO. This sample contributed to 92.4 % of phenol (PhOH) removal at 25 °C with a PDS loading amount of 0.4 mmol/g, which is better than its LDH-PDS counterpart. A high activation of PDS in rGO/LDH-PDS was also observed during the oxidation of 4-bromophenol (4-BrPhOH), 2,4-dibromophenol (2, 4-BrPhOH), 2,6-dibromophenol (2, 6-BrPhOH) and bisphenol A (BPA). As a redox reaction of PDS in LDH, this result determined that the composite of rGO/LDH caused more PDS to be activated than LDH. As the defective rGO sites activated the PDS on the surface or edges of LDH layers, the breaking of the OO bond in PDS generated SO₄^·- radicals from intercalated peroxydisulfate. This result was supported by the radical scavenger experiment, electron paramagnetic resonance measurements, and the increased number of oxygen functional groups in the reacted rGO. Our work thus provided a novel strategy for PDS activation to use in environmental remediation.

Graphene quantum dots on stainless-steel nanotubes for enhanced photocatalytic degradation of phenanthrene under visible light

A novel nanocomposite of stainless-steel nanotubes with graphene quantum dots (SSNT@GQD) was synthesized to degrade phenanthrene photocatalytically under visible light. Photocatalytic performance of bare stainless-steel nanotubes (SSNT) is not satisfactory due to the fast recombination of photoinduced electron-hole pairs. This phenomenon was effectively overcome by inclusion of GQDs and addition of persulfate as an external electron acceptor to improve charge separation. The pseudo-first-order rate constant of phenanthrene degradation by SSNT@GQD with persulfate under visible light was 0.0211 ± 0.0006 min^-1, about 42 times higher than that of persulfate and visible light, 0.0005 ± 0.0000 min^-1. Effects of different water quality parameters were investigated, including levels of initial pH, natural organic matters, bicarbonate, and chloride. Sulfate radicals, superoxide radicals, and photo-generated holes were the key reactive species in this photocatalytic process. Based on the analysis of intermediates using purge and trap-GC-MS, possible photocatalytic degradation pathways of phenanthrene in this process were proposed. The SSNT@GQD showed high figure of merit (99.5 without persulfate and 78.7 with persulfate) and quantum yield (1.56 × 10^-5 molecules photon^-1 without persulfate and 4.64 × 10^-5 molecules photon^-1 with persulfate), indicating that this material has excellent potential for practical photocatalysis applications.

Integration of •SO4--based AOP mediated by reusable iron particles and a sulfidogenic process to degrade and detoxify Orange II

The sulfate radical (•SO₄^-)-based advanced oxidation processes (AOPs) for the degradation of refractory organic pollutants consume a large amount of persulfate activators and often generate toxic organic by-products. In this study, we proposed a novel iron-cycling process integrating •SO₄^--based AOP mediated by reusable iron particles and a sulfidogenic process to degrade and detoxify Orange II completely. The rusted waste iron particles (Fe⁰@Fe_xO_y), which contained Fe^II/Fe^III oxides (Fe_xO_y) on the shell and zero-valent iron (Fe⁰) in the core, efficiently activated persulfate to produce •SO₄^- and hydroxyl radicals (•OH) to degrade over 95% of Orange II within 120 min. Both •SO₄^- and •OH destructed Orange II through a sequence of electron transfer, electrophilic addition and hydrogen abstraction reactions to generate several organic by-products (e.g., aromatic amines and phenol), which were more toxic than the untreated Orange II. The AOP-generated organic by-products were further mineralized and detoxified in a sulfidogenic bioreactor with sewage treatment together. In a 170-d trial, the organic carbon removal efficiency was up to 90%. The inhibition of the bioreactor effluents on the growth of Chlorella pyrenoidosa became negligible, due to the complete degradation and mineralization of toxic AOP-generated by-products by aromatic-degrading bacteria (e.g., Clostridium and Dechloromonas) and other bacteria. The sulfidogenic process also well recovered the used Fe⁰@Fe_xO_y particles through the reduction of surface Fe^III back into Fe^II by hydrogen sulfide formed and iron-reducing bacteria (e.g., Sulfurospirillum and Paracoccus). The regenerated Fe⁰@Fe_xO_y particles had more reactive surface Fe^II sites and exhibited much better reactivity in activating persulfate in at least 20 reuse cycles. The findings demonstrate that the integrated process is a promising solution to the remediation of toxic and refractory organic pollutants because it reduces the chemical cost of persulfate activation and also completely detoxifies the toxic by-products.

Efficient decomposition of perfluorooctanic acid by persulfate with iron-modified activated carbon

Using persulfate (PS) oxidation to remove the persistent perfluorooctanoic acid (PFOA) in water typically requires an elevated temperature or an extended reaction time. Under relatively ambient temperatures (15-45 °C), feasibility of employing PS with iron-modified activated carbon (AC) for PFOA oxidation was evaluated. With presence of Fe/AC in PS oxidation, 61.7% of PFOA was decomposed to fluoride ions and intermediates of short-chain perfluorinated carboxylic acids (PFCAs) with a 41.9% defluorination efficiency at 25 °C after 10 h. Adsorption of PFOA onto Fe/AC can be regarded as a pre-concentration step prior to subsequent oxidation of PFOA. Fe/AC not only removes PFOA through adsorption, but also activates PS to form sulfate radicals that accelerate the decomposition and mineralization of PFOA. With Fe/AC in the PS system, activation energies (E_a) of PFOA removal and defluorination were significantly reduced from 66.8 to 13.2 and 97.3 to 14.5 kJ/mol, respectively. It implies that PFOA degradation and defluorination could proceed at a lower reaction temperature within a shorter reaction time. Besides, the surface characteristics of AC and Fe/AC before and after PS oxidation were evaluated by XPS and SEM. A quenching test used MeOH as an inhibitor and EPR spectra of free radicals were conducted to develop the proposed reaction mechanisms for PFOA oxidation.

Sonophotocatalytic treatment of AB113 dye and real textile wastewater using ZnO/persulfate: Modeling by response surface methodology and artificial neural network

The present study investigates the synergistic performance of the sonophotolytic-activated ZnO/persulfate (US/UV/ZnO/PS) process in the decolorization of acid blue 113 (AB113) dye from aqueous solution and its feasibility for the treatment of real textile wastewater. Decolorization of AB113 solution was modeled by central composite design-response surface methodology (CCD-RSM) and artificial neural network (ANN) approaches and optimized by CCD-RSM and genetic algorithm (GA) approaches. Statistical metrics indicated that both CCD-RSM and ANN approaches seemed satisfactory. However, the results of statistical fit measures indicated a relative superiority of CCD-RSM as compared to the ANN approach. The results of optimization of the process parameters by CCD-RSM and GA approaches appeared to be similar as follows: pH = 6.1, reaction time = 25 min, US power density = 300 W/L, ZnO = 0.88 g/L and PS = 2.43 mmol/L. The synergistic effect of the hybrid US/UV/ZnO/PS process in comparison with its individual processes (US, UV, ZnO, and PS) was found to be 54.3%. Quenching experiments discovered that and HO are the main oxidizing radicals in a mildly acidic condition of the reaction solution. The removal efficiency of AB113 in the presence of some anions decreased in the order of bicarbonate > sulfate > phosphate > nitrate > chloride. Further, the reusability feasibility of ZnO showed that the ZnO material retained its photocatalytic property after five successive cycles of reusability test, while Zn²⁺ ion concentration in the reaction solution was measured to be 2.81 mg/L. The findings also indicated that the integrated process application suppresses extremely chemical and electrical costs. The study of the feasibility of the US/UV/ZnO/PS process in the treatment of real textile wastewater was done by determining COD, TOC and BOD₅/COD ratio. Results demonstrated that the 96.6 and 97.1% reduction of COD and TOC was achieved after 5 and 7 h reaction time, respectively. The obtained BOD₅/COD ratio changed from about 0.15 (for non-treated wastewater) to about 0.61 with increasing reaction time from zero to 90 min. In conclusion, the hybrid US/UV/ZnO/PS system can be proposed as a novel and promising approach to be utilized as a pretreatment technique before a biological treatment process to facilitate the biological treatment of recalcitrant textile wastewater.

Comparison of the oxidation of halogenated phenols in UV/PDS and UV/H2O2 advanced oxidation processes

UV/peroxydisulfate (PDS) and UV/hydrogen peroxide (H₂O₂) can effectively degrade halophenols (HPs, e.g., 2,4-bromophenol and 2,4,6-trichlorophenol); meanwhile, information about the discrepancies in the related degradation kinetics and mechanisms of these two processes is limited. To gain this knowledge, the degradation of two typical HPs (i.e., bromophenols and chlorophenols) in UV/PDS and UV/H₂O₂ processes were investigated and compared. The results showed that the degradation rates of HPs with different substitution positions in the UV/PDS process were in the order of para-substituted HPs (i.e., 4-BP and 4-CP) > ortho-substituted HPs (i.e., 2-BP and 2-CP) > meta-substituted HPs (i.e., 3-BP and 3-CP), while in the UV/H₂O₂ process, these rates were in the order of para-substituted HPs > meta-substituted HPs > ortho-substituted HPs. These discrepancies were ascribed to the different reaction activities of SO₄˙⁻ and HO˙ with HPs, which were calculated based on the competition method. Further density functional theory (DFT) calculations suggested that SO₄˙⁻ reacts more readily with HPs via electron transfer than HO˙. In the presence of water matrices (such as Cl⁻, HCO₃⁻ and natural organic matter (NOM)), the degradation of 2-BP in both UV/PDS and UV/H₂O₂ treatment processes was inhibited due to the scavenging of free radicals by these background substances. The degradation products and pathways further confirmed that SO₄˙⁻ is a strong one-electron oxidant that reacts with HPs mainly via electron transfer, while HO˙ reacts with HPs via electron transfer and hydroxyl addition.

The oxidation of halogenated phenols with different substitution positions in UV/PDS and UV/H₂O₂ processes was compared.

Degradation of phenol by coal-based carbon membrane integrating sulfate radicals-based advanced oxidation processes

Phenol, as a representative organic pollutant in aquatic environments, has posed a serious threat to humans and ecosystem. In this work, a novel integration system combined coal-based carbon membrane with sulfate radicals-based advanced oxidation processes (SR-AOPs) was designed for degradation of phenol. The integrated system achieved 100% removal efficiency under the optimal condition (peroxydisulfate dosage is 0.2 g/L, at alkaline condition with 2 mL/min flow velocity). The quenching experiments revealed that the efficient removal of phenol by the integrated system were attributed to the co-existence of radical and nonradical mechanisms. This study proposes a green and efficient technique for the removal of phenol.

Oxidative Degradation of Methylene Blue via PDS-Based Advanced Oxidation Process Using Natural Pyrite

H₂O₂- and PDS-based reactions are two typical advanced oxidation processes (AOPs). In this paper, a comparative study of H₂O₂/PDS-based AOPs employing natural pyrite as a catalyst to degrade methylene blue (MB) was reported. The adaptive pH range in pyrite/PDS extended from 3 to 11, in contrast to the narrow effective pH range of 3–7 in pyrite/H₂O₂. As a result of the iron leaching, a synergistic effect of both homogeneous and heterogeneous catalysis was observed in pyrite/PDS, whereas heterogeneous catalytic oxidation dominated pyrite/H₂O₂. Furthermore, the batch results showed that the MB removal by pyrite/PDS was highly dependent on chemical conditions (e.g., pH, pyrite and PDS concentration, temperature). Powerful SO₄^•− was generated by pyrite rapidly under acidic or weakly acidic conditions, while SO₄^•− and PDS were assumed by OH⁻ under alkaline condition. The lower pyrite loading (from 0.1 to 0.5 g/L) was affected the removal efficiency obviously, while the scavenging of SO₄^•− did not seem to be remarkable with the excessive amounts of pyrite (>0.5 g/L). Excessive amounts of PDS (>2 mmol/L) might negatively affect the pyrite/PDS system. The reaction temperature that increased from 20 to 40 °C had a positive effect on the degradation of MB. SEM and XRD showed that the passivation of catalyst did not occur due to the strong acid-production ability of pyrite/PDS, inhibiting the formation of Fe-oxide covering the pyrite surface.

Binuclear cobalt phthalocyanine supported on manganese octahedral molecular sieve: High-efficiency catalyzer of peroxymonosulfate decomposition for degrading propranolol

Propranolol (PRO) is widely detected in the aquatic environment and proved to be detrimental to multifarious aquatic organisms. In view of some virtues of sulfate radicals than hydroxyl radicals, advanced oxidation technologies that involve the activation of peroxymonosulfate (PMS) have stimulated wide-ranging research on the PRO removal. In this paper, a composite (C₂NOMS-2) of amino-functionalized manganese octahedral molecular sieve (NOMS-2) and binuclear cobalt phthalocyanine (Co₂CPc) was synthesized easily, and utilized as a catalyzer for PMS to degrade PRO in water. The apparent rate constants of PRO degradation by PMS with C₂NOMS-2 as a catalyst was found to be higher than with NOMS-2, Co₂CPc and the composite of uninuclear cobalt phthalocyanine (CoCPc) and NOMS-2. The catalytic ability of C₂NOMS-2 was investigated under various reaction conditions: catalyst dosages (0.5-2.0 g/L), PMS doses (50-500 mg/L), initial pH (5-11), reaction temperature (20-35 °C), and natural water constituents (Cl^-, HCO₃^-, and sodium huminate). Radical scavenging tests and electron paramagnetic resonance spectroscopy showed that ¹O₂ was the most critical reactive oxygen species, and conceivable mechanisms of PMS activation with C₂NOMS-2 were proposed established on the curve estimation of high-resolution XPS spectra, revealing that the generation of reactive oxygen species was mainly resulted from the cycles of Mn³⁺/Mn⁴⁺, Co³⁺/Co²⁺ and surface lattice oxygen/surface adsorbed oxygen. The intermediate products of propranolol degradation were identified by LC-MS/MS. Cycling experiments and ion dissolution detection suggested that C₂NOMS-2 could maintain satisfactory stability in an aqueous system.

Efficient Degradation of Norfloxacin and Simultaneous Electricity Generation in a Persulfate-Photocatalytic Fuel Cell System

Photocatalytic fuel cell (PFC) has been verified to be a promising technique to treat organic matter and recover energy synchronously. Sulfate radicals (SO4·−), as a strong oxidant, have obvious advantages in the degradation of refractory pollutants compared with hydroxyl radicals (·OH), which is the dominant radical in PFC. This study reports a coupling method of PFC and persulfate (PS) activation to promote the degradation of antibiotic norfloxacin (NOR) and simultaneous electricity generation. The added PS as an electron acceptor could be activated by photoelectric effects to produce SO4·− at the electrodes-electrolyte interface. In the solution, PS as supporting electrolyte could accelerate the electron transfer and also be activated by ultraviolet (UV) light irradiation, which could extend the radical oxidation reaction to the whole solution and improve the PFC performance. The performance comparison among different systems indicated the excellent synergistic effect of PFC and PS activation for improving NOR degradation and electricity generation. The effects of influencing factors including initial pH, PS concentration, and initial NOR concentration on the degradation of NOR were investigated extensively to find out the optimal conditions. Moreover, according to the results of radical capture experiments, the significantly contribution of both SO4·− and ·OH to the degradation of NOR was demonstrated and a tentative function mechanism for the NOR degradation in the proposed system was provided. Finally, total organic carbon and real wastewater treatment confirmed the high mineralization and practical applicability of the proposed PFC/PS system.

An often-overestimated adverse effect of halides in heat/persulfate-based degradation of wastewater contaminants

Halides (X^-) in the industrial wastewater are usually thought to adversely affect the degradation kinetics and mineralization rates in several SO₄^--based advanced oxidation processes. However, their unfavorable effects might be overestimated, particularly the heat/persulfate (PS) system as tested in the present study. Here the degradation of phenol, benzoic acid, coumarin and acid orange 7 (AO7) was examined with the presence of chloride or bromide in a heat/PS process. Cl^- was found to have a dual effect (inhibition followed by enhancement) on the decomposition rates of organic pollutants, whereas the effects of Br^- are insignificant within the tested concentration (0-0.2 mM). However, some chlorinated or brominated compounds were still identified in this heat/PS system. Unexpectedly, the mineralization rates of AO7, phenol, benzoic acid and coumarin were not apparently inhibited. In addition, the formation of adsorbable organic halogen (AOX) in the heat/PS system was much less than those in the peroxymonosulfate (PMS)/Cl^- or PMS/Br^- systems. According to the results of kinetic modeling, SO₄^- was the dominating radical for AO7 degradation without Cl^- or Br^-, but Cl₂^- was the main oxidant in the presence of Cl^-, SO₄^-, Br and Br₂- were responsible for the oxidation of AO7 in the presence of Br^-. The present study assumes that X₂/HOX, rather than halogen radicals, is responsible for the enhanced formation of organohalogens. These findings are meaningful to evaluate the PS-based technologies for the high-salinity wastewater and to develop useful strategies for mitigating the negative effects of halides in advanced oxidation processes (AOPs).

Insight into the mechanisms for hexavalent chromium reduction and sulfisoxazole degradation catalyzed by graphitic carbon nitride: The Yin and Yang in the photo-assisted processes

As robust polymeric catalysts, graphitic carbon nitride (g-C₃N₄) has been known to have great application potential in environmental remediation. However, the mechanisms in the photo-assisted catalytic processes during the reduction or oxidation of pollutants are still difficult to discern and therefore not well studied. In this work, visible-assisted catalytic reduction of hexavalent chromium (Cr(VI)) or oxidation of sulfisoxazole (SIZ) by g-C₃N₄ with the addition of formic acid (FA) or potassium peroxydisulfate (PS) were systematically investigated. Effects of operation parameters such as g-C₃N₄ dosage, FA concentration, Cr(VI) concentration, solution pH, PS concentration were studied. The results showed g-C₃N₄ can be effective and robust catalyst for both the reduction (Yin) and oxidation (Yang) reactions in the environmental remediation. Mechanisms were studied by using electron spin resonance (ESR) spectroscopy. The results revealed the CO 2^- is the predominant radical for Cr(VI) reduction in the g-C₃N₄/FA/Vis system and the SO₄^- and OH are all the main radicals for the oxidation of SIZ in the g-C₃N₄/PS/Vis system. The photo-generated carriers by g-C₃N₄, act as radical initiator, were responsible for the production of the reactive radical species in aqueous solution. This work not only shed a new light on the application of semiconductor polymers for the removal of micropollutants and also will expand the applicability of the polymeric photocatalysts for environmental remediation.

The efficiency of UV/S2O8 2- photo-oxidation process in the presence of Al2O3 for the removal of dexamethasone from aqueous solution: kinetic studies

This study aimed to investigate the efficiency of the UV/S₂O₈ ^2- photocatalytic process in the presence of Al₂O₃ nanoparticles for the removal of dexamethasone from aqueous solution. In this experimental study, the variables pH, persulfate concentration, initial concentration of dexamethasone, the catalyst dose were studied in order to investigate the process efficiency. Furthermore, the efficiency of UV/S₂O₈ ^2- in the presence and absence of catalyst was investigated. The Al₂O₃ nanoparticle catalyst was characterized using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses and scanning electron microscopy (SEM) image. The results showed that a decrease in pH and the initial concentration of dexamethasone increased the process efficiency. Given the increased concentrations of the persulfate and Al₂O₃, the removal efficiency was partially increased. In UV/S₂O₈ ^2-/Al₂O₃ under optimum conditions (pH = 3, t = 30 minutes, dexamethasone concentration = 20 mg/L, 0.5 mM of persulfate, and UV radiation = 55 watts), 94% of the dexamethasone was removed. The kinetic response showed that the reaction data corresponded to the pseudo-first-order kinetic model. The results showed that the UV/S₂O₈ ^2- photochemical process can efficiently remove dexamethasone from aqueous solution in the presence of Al₂O₃ catalyst and the mineralization efficiency reached about 98%. Therefore, this process is recommended due to its high efficiency and availability for the removal of pharmaceutical compounds.

Efficient degradation of diclofenac by LaFeO3-Catalyzed peroxymonosulfate oxidation---kinetics and toxicity assessment

Diclofenac was frequently found in various waters, indicating conventional wastewater treatment methods ineffective in its removal. In this study, LaFeO₃ (LFO) was synthesized and its catalytic activity of LFO as the activator of different oxidants such as persulfate (PS), hydrogen peroxide and peroxylmonosulfate (PMS) was evaluated in terms of DCF degradation. The influence of calcination temperature was examined on the catalytic activity of LFO. The effects of various parameters including pH levels, PMS concentration, LFO dose and initial DCF concentration were investigated on DCF degradation rate. The marginal effects of PMS concentration and LFO dose were compared. Langmuir-Hinshelwood (LH) model was used to quantitatively describe DCF degradation reaction in LFO/PMS system. The two constants, k (Limiting reaction rate at maximum coverage) and K (Equilibrium adsorption constant), were determined on the basis of LH model. The performance of LFO/PMS process was also estimated in the presence of various inorganic anions. The potential toxicity of LFO and PMS were evaluated using phytoplankton and the toxicity evolution during DCF degradation was also investigated using luminescent bacteria. This contribution provides a basic study regarding the potential application of heterogeneous PMS activation by perovskite LFO for both DCF removal and toxicity elimination.

Thermochemical degradation of furfural by sulfate radicals in aqueous solution: optimization and synergistic effect studies

In this study, thermochemical degradation of furfural by sulfate radical has been investigated to find the best-operating conditions. For this purpose, the response surface methodology (RSM) based on central composite design (CCD) was applied to optimize the five independent variables of thermally activated persulfate (TAP)/nZVI oxidation process including pH, PS concentration, furfural concentration, nZVI dosage, and heat. The ANOVA results ("P > F value" < 0.0001 and [Formula: see text] = 0.9701) showed the obtained quadratic model is acceptable to predict furfural removal. Based on the reduced quadratic model PS concentration, nZVI dosage, and heat revealed the positive effects on removal efficiency, while pH and furfural concentration had a negative effect. Accordingly, 98.4% of furfural could be removed within 60 min of reaction under the optimum conditions: pH 5.26, PS concentration of 20.52 mM, furfural concentration of 84.32 mg/L, nZVI dosage of 1.15 mg/L, and a temperature of 79 °C. In such circumstances, the furfural removal efficiency for TAP, PS/nZVI, PS, and nZVI was 94.5, 9, 3, and 2%, respectively. Therefore, based on the synergy index (SI) values, the combination of PS, nZVI, and heat can lead to a synergistic effect in the performance of the thermochemical process.

Rethinking sulfate radical-based oxidation of nitrophenols: Formation of toxic polynitrophenols, nitrated biphenyls and diphenyl ethers

Sulfate radical (SO₄^-)-based oxidation of nitrophenols (NPs) have been widely studied; however, formation of potentially more toxic polynitroaromatic intermediates has been overlooked. In this contribution, we systematically investigated the degradation of four NPs by a SO₄^--based oxidation process. Degradation efficiency of NPs followed the order: 2-nitrophenol (2-NP) > 4-nitrophenol (4-NP) > 2,4-dinitrophenol (2,4-DNP) > 2,6-dinitrophenol (2,6-DNP). HPLC and LC-MS/MS analysis confirmed the formation of 2,4-DNP, 2,6-DNP and 2,4,6-trinitrophenol (2,4,6-TNP) during NPs transformation by SO₄^-, suggesting that both denitration and renitration processes occurred. Nitrogen dioxide radicals (NO₂) and phenoxy radicals are responsible for the formation of polynitrophenols. Coupling products including nitrated biphenyls and diphenyl ethers were also detected, which were proposed to be formed by combinations of resonance-stabilized radicals. Electron spin density and charge density calculation showed that ortho C-ortho C and ortho C-phenolic O were the most likely combination ways responsible for coupling products formation. ECOSAR program predicted that polynitrated diphenyl ethers and biphenyls had higher ecotoxicological effects on aquatic species such as fish and daphnia. Therefore, the formation of toxic polynitroaromatic intermediates in SO₄^--based advanced oxidation processes should be scrutinized before this technology can be safely utilized for water and wastewater treatment.

Enhanced dewaterability of waste activated sludge by a combined use of permanganate and peroxymonosulfate

Ever-increasing efforts have been made to develop rapid and practical conditioning methods of sludge dewatering. This study demonstrated an innovative combination of potassium permanganate (KMnO₄) and peroxymonosulfate (PMS) for sludge dewatering. The combined use of KMnO₄ and PMS (KMnO₄/PMS) showed its superiority in improving sludge dewaterability over the separate use of KMnO₄ or PMS. By dosing 4 mmol g⁻¹ VSS KMnO₄ and 3 mmol g⁻¹ VSS PMS, the dewaterability of waste activated sludge (WAS) significantly enhanced as capillary suction time (CST) decreased from 73.65 s to 24.65 s while the water content of dewatered sludge cake (W_C) decreased from 78.96% to 70.47%. Apart from CST and W_C, the KMnO₄/PMS process could also affect negative zeta potential, sludge flocs size and the concentrations of protein and polysaccharide in extracellular polymeric substances (EPS). The enhanced sludge dewaterability and changes of the physicochemical characteristics of the WAS samples during the KMnO₄/PMS process were actually ascribed to sulfate radicals (SO₄˙⁻) and hydroxyl radicals (HO˙) in situ generated via PMS activation by manganese oxides (MnO_x) in the states of MnO₂ and Mn₃O₄ transferred from KMnO₄ oxidation, which was verified by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) techniques and radical scavenging experiments. Moreover, the Fourier transform infrared spectroscopy (FTIR) analysis further confirmed that the in situ generated SO₄˙⁻ and HO˙ could improve sludge dewaterability. Thus, the KMnO₄/PMS process could be considered as a promising conditioning method of sludge dewatering.

Ever-increasing efforts have been made to develop rapid and practical conditioning methods of sludge dewatering.

Applicability study on the degradation of acetaminophen via an H2O2/PDS-based advanced oxidation process using pyrite

H₂O₂- and PDS-based reactions are two typical advanced oxidation processes (AOPs) with different adaptive pH ranges. However, the underlying mechanisms that caused the distinct applicability of these two AOPs have rarely been explored. Herein, a comparative study of H₂O₂/PDS-based AOPs employing pyrite as a catalyst to degrade acetaminophen (ACT) was reported. The poor ACT degradation in H₂O₂/pyrite under alkaline conditions was proven to be caused by a lack of OH production instead of by the weaker oxidation property of OH. The continuous exposure surface behavior induced by the intense acid-production reaction between PDS and pyrite prevented the coverage of iron-containing compounds on the pyrite surface. Therefore, the adaptive pH range in PDS/pyrite could extend from 4 to 10, in contrast to the narrow effective pH range of 4-6 in H₂O₂/pyrite. Oxidant consumption indicated that H₂O₂/pyrite possesses a higher oxidation efficiency than PDS/pyrite. The homogenous catalytic effect was non-negligible in PDS/pyrite, whereas heterogeneous catalytic oxidation dominated H₂O₂/pyrite under acidic conditions. The quenching experiment and electron spin resonance (ESR) spectroscopy demonstrated that the dominant radical species in H₂O₂/PDS-based AOPs via pyrite at a pH of 4 were OH and OH/SO₄^-, respectively, thus causing different degradation pathways of ACT. In addition, a higher proportion of S consumption was found in H₂O₂/pyrite, indicating that sulfur also plays a role during the catalytic reaction. The distinct surface reactions between pyrite and H₂O₂/PDS led to different water treatment applications.

Simultaneous adsorption and oxidative degradation of Bisphenol A by zero-valent iron/iron carbide nanoparticles encapsulated in N-doped carbon matrix

The increased release and accumulation of Bisphenol A (BPA) in contaminated wastewater has resulted in the world wide concerns because of its potential negative effects on human health and aquatic ecosystems. Starting with metal-organic frameworks, we present a simple method to synthesize magnetic porous microcubes (N-doped Fe⁰/Fe₃C@C) with graphitized shell and highly dispersed active kernel via the pyrolysis process under N₂ atmosphere. Batch adsorption experimental results showed that N-doped Fe⁰/Fe₃C@C had high adsorption capacity for BPA (∼138 mg g^-1 at pH = 7 and 298 K). Degradation of BPA adsorbed on N-doped Fe⁰/Fe₃C@C was further investigated as a function of BPA concentration, persulfate amount, temperature and solution pH. It was found that potassium peroxodisulfate could be activated by N-doped Fe⁰/Fe₃C@C, and a large number of free radicals were generated which was crucial for the degradation of BPA. The concentration of BPA was barely changed in the individual persulfate system. BPA (10 mg L^-1) was almost completely degraded within 60 min in the presence of N-doped Fe⁰/Fe₃C@C (∼0.2 g L^-1). When the BPA content increased to 25 mg L^-1, the removal efficiency of BPA achieved to 98.4% after 150 min. From the XRD, Raman, and XPS analysis, the main adsorption mechanism of BPA was π-π interactions between the π orbital on the carbon basal planes and the electronic density in the BPA aromatic rings. While the superior degradation was attributed to the radical generation and evolution in phenol oxidation. This work not only proved the potential application of N-doped Fe⁰/Fe₃C@C in the adsorption and degradation of BPA, but also opened the new possibilities to eliminate organic pollutants using this kind of magnetic materials in organic pollutants' cleanup.

Carbon and hydrogen stable isotope analysis for characterizing the chemical degradation of tributyl phosphate

Tributyl phosphate (TBP) belongs to the group of trialkyl substituted organophosphate esters. Its chemical reactivity depends on the stability of various chemical bonds. TBP was used as a model compound for the development of a concept using stable isotope fractionation associated with bond cleavage reactions for better understanding the fate of TBP in the environment. Carbon isotope enrichment factors (ε_C) of TBP hydrolysis were found to be pH dependent (-3.8 ± 0.3‰ at pH 2, -4.6 ± 0.5‰ at pH 7, -2.8 ± 0.1‰ at pH 9, no isotope fractionation at pH 12), which is in accordance with the mode of a S_N2 hydrolytic bond cleavage. Hydrogen isotope fractionation was negligible as no H bond cleavage is involved during hydrolysis. The apparent carbon kinetic isotope effect (AKIE_C) ranged from 1.045 to 1.058. In contrast to hydrolysis, both carbon and hydrogen isotope fractionation were observed during radical oxidation of TBP by OH and SO₄^-, yielding ε_C from -0.9 ± 0.1‰ to -0.5 ± 0.1‰ and ε_H from -20 ± 2‰ to -11 ± 1‰. AKIE_C and AKIE_H varied from 1.007 to 1.011 and from 1.594 to 2.174, respectively. The correlation of ²H and ¹³C isotope fractionation revealed Λ values ranging from 17 ± 1 to 25 ± 6. Results demonstrated that the correlation of ²H and ¹³C isotope fractionation of TBP allowed to identify radical reactions and to distinguish them from hydrolysis. The presented dual isotope analysis approach has diagnostic value for characterizing the chemical transformation of TBP in the environment.

Ultrasensitive Fluorescence Detection of Peroxymonosulfate Based on a Sulfate Radical-Mediated Aromatic Hydroxylation

Recently, peroxymonosulfate (PMS)-based advanced oxidation processes have exhibited broad application prospects in the environment field. Accordingly, a simple, rapid, and ultrasensitive method is highly desired for the specific recognition and accurate quantification of PMS in various aqueous solutions. In this work, SO₄^•--induced aromatic hydroxylation was explored, and based on that, for the first time, a novel fluorescence method was developed for the PMS determination using Co²⁺ as a PMS activator and benzoic acid (BA) as a chemical probe. Through a suite of spectral, chromatographic, and mass spectrometric analyses, SO₄^•- was proven to be the dominant radical species, and salicylic acid was identified as the fluorescent molecule. As a result, a whole radical chain reaction mechanism for the generation of salicylic acid in the BA/PMS/Co²⁺ system was proposed. This fluorescence method possessed a rapid reaction equilibrium (<1 min), an ultrahigh sensitivity (detection limit = 10 nM; quantification limit = 33 nM), an excellent specificity, and a wide detection range (0-100 μM). Moreover, it performed well in the presence of possible interfering substances, including two other peroxides (i.e., peroxydisulfate and hydrogen peroxide), some common ions, and organics. The detection results for real water samples further validated the practical utility of the developed fluorescence method. This work provides a new method for the specific recognition and sensitive determination of PMS in complex aqueous solutions.

Oxidation of Rhodamine B by persulfate activated with porous carbon aerogel through a non-radical mechanism

In this study, porous carbon aerogel (CA) was synthesized with D-glucose, ammonium persulfate and aniline by a hydrothermal carbonization method. It was reported for the first time as an excellent catalyst for activating persulfate (PS) to degrade rhodamine B (RhB). The morphology of CA was characterized, exhibiting microporous and mesoporous structures. The solution pH of 3, 5, 7 and 9 showed slight impact on the degradation of RhB; however, when the pH increased to 11, the removal of RhB decreased. The PS concentration and CA dosage played a key role in the RhB degradation, and the activation energy was calculated to be 22.11 kJ/mol. Electron paramagnetic resonance (EPR) spectra suggested that neither sulfate radical (SO4^-) nor hydroxyl radical (OH) was generated from the PS activation. The radical quenching experiments also confirmed that CA activated PS in a non-radical pathway. It was indicated that PS bonded with CC in the sp² hybridized system could directly degrade RhB. The defective edges at the boundary of CA also facilitated the RhB removal. This work presented a green material with both excellent catalytic performance and high regeneration possibility in the heterogeneous metal-free PS activation, providing a new strategy in water treatment.