Activation of persulfate/copper by hydroxylamine via accelerating the cupric/cuprous redox couple

Development of persulfate-based advanced oxidation processes to remove synthetic azo dyes from aqueous matrices

Azo dyes are largely used in many industries and discharged in large volumes of their effluents into the aquatic environment giving rise to non-esthetic pollution and health-risk problems. Due to the high stability of azo dyes in ambient conditions, they cannot be abated in conventional wastewater treatment plants. Over the last fifteen years, the decontamination of dyeing effluents by persulfate (PS)-based advanced oxidation processes (AOPs) has received a great attention. In these methods, PS is activated to be decomposed into sulfate radical anion (SO4•-), which is further partially hydrolyzed to hydroxyl radical (•OH). Superoxide ion (O2•-) and singlet oxygen (1O2) can also be produced as oxidants. This review summarizes the results reported for the discoloration and mineralization of synthetic and real waters contaminated with azo dyes covering up to November 2023. PS activation with iron, non-iron transition metals, and carbonaceous materials catalysts, heat, UVC light, photocatalysis, photodegradation with iron, electrochemical and related processes, microwaves, ozonation, ultrasounds, and other processes is detailed and analyzed. The principles and characteristics of each method are explained with special attention to the operating variables, the different oxidizing species generated yielding radical and non-radical mechanisms, the addition of inorganic anions and natural organic matter, the aqueous matrix, and the by-products identified. Finally, the overall loss of toxicity or partial detoxification of treated azo dye solutions during the PS-based AOPs is discussed.

Hydroxylamine promoted degradation of organic contaminants using peroxydisulfate activated by Fe-alginate

To overcome the shortcomings of Fe(Ⅱ)/peroxydisulfate (PDS) system including the limited working pH range and large iron sludge production, a Fe-doped alginate (Fe-Alg) catalyst was prepared and combined with hydroxylamine (HA) to continuously activate PDS for the removal of organic pollutants in neutral condition. Due to the strong reductive capability of HA, it could significantly enhance the catalytic capability of Fe-Alg for PDS. The results of characterization suggested that Fe(Ⅲ)/Fe(Ⅱ) was evenly distributed in Alg through its complexation with carboxyl groups, and the reduction of Fe(Ⅲ) to Fe(Ⅱ) initiated by HA enabled Orange G (OG) to be continuously degraded in the Fe-Alg/HA/PDS system. The results of quenching experiments suggested that S O 4 ∙ - and HO• played a dominant role for OG removal in the Fe-Alg/HA/PDS process. The effect of influence factors (e.g. initial pH, HA concentration, Fe-Alg dose and PDS concentration) and water matrix components (i.e. S O 4 2 - , N O 3 - , Cl-, HC O 3 - and dissolved organic matters (DOM)) on the performance of Fe-Alg/HA/PDS system was systematically investigated. Other refractory organic contaminants, including diclofenac (DCF), sulfamethoxazole (SMX), oxytetracycline (OTC) and bisphenol AF (BPAF) were also efficiently eliminated in Fe-Alg/HA/PDS system, suggesting the feasibility of this system for the treatment of organic pollutants. This work provides a method to optimize Fe(Ⅱ)/PDS system and a novel process applied to degrade refractory pollutants.

Hydroxylamine enhanced the degradation of diclofenac in Cu(II)/peracetic acid system: Formation and contributions of CH3C(O)O•, CH3C(O)OO•, Cu(III) and •OH

The slow reduction of Cu(II) into Cu(I) through peracetic acid (PAA) heavily limited the widespread application of Cu(II)/PAA system. Herein, hydroxylamine (HA) was proposed to boost the oxidative capacity of Cu(II)/PAA system by facilitating the redox cycle of Cu(I)/Cu(II). HA/Cu(II)/PAA system was quite rapid in the removal of diclofenac within a broad pH range of 4.5-9.5, with a 10-fold increase in the removal rate of diclofenac compared with the Cu(II)/PAA system at an optimal initial pH of 8.5. Results of UV-Vis spectra, electron paramagnetic resonance, and alcohol quenching experiments demonstrated that CH3C(O)O•, CH3C(O)OO•, Cu(III), and •OH were involved in HA/Cu(II)/PAA system, while CH3C(O)OO• was verified as the predominant reactive species of diclofenac elimination. Different from previously reported Cu-catalyzed PAA processes, CH3C(O)OO• mainly generated from the reaction of PAA with Cu(III) rather than CH3C(O)O• and •OH. Four possible elimination pathways for diclofenac were proposed, and the acute toxicity of treated diclofenac solution with HA/Cu(II)/PAA system significantly decreased. Moreover, HA/Cu(II)/PAA system possessed a strong anti-interference ability towards the commonly existent water matrix. This research proposed an effective strategy to boost the oxidative capacity of Cu(II)/PAA system and might promote its potential application, especially in copper-contained wastewater.

Trace Cu(II)-Mediated Selective Oxidation of Benzothiazole: The Predominance of Sequential Cu(II)-Cu(I)-Cu(III) Valence Transition and Dissolved Oxygen

Trace Cu(II), which inherently exists in soil and some water/wastewater, can trigger persulfate oxidation of some pollutants, but the oxidation capability and mechanism are not well understood, especially toward refractory pollutants. We report in this research that benzothiazole (BTH), a universal refractory pollutant typically originating from tire leachates and various industrial wastewater, can be facilely and selectively removed by peroxydisulfate (PDS) with an equimolar BTH/PDS stoichiometry in the presence of environmental-relevant contents of Cu(II) (below several micromoles). Comprehensive scavenging tests, electron spin resonance analysis, spectroscopy characterization, and electrochemical analysis, revealed that PDS first reduces the BTH-coordinated Cu(II) to Cu(I) and then oxidizes Cu(I) to high-valent Cu(III), which accounts for the BTH degradation. Moreover, once the reaction is initiated, the superoxide radical is probably produced in the presence of dissolved oxygen, which subsequently dominates the reduction of Cu(II) to Cu(I). This facile oxidation process is also effective in removing a series of BTH derivatives (BTHs) that are of environmental concern, thus can be used for their source control. The results highlight the sequential Cu(II)-Cu(I)-Cu(III) transition during PDS activation and the crucial role of contaminant coordination with Cu(II) in oxidative transformation.

Transformation of hydroxylamine to nitrosated and nitrated products during advanced oxidation process

Recently, hydroxylamine (HAm) was introduced to drive advanced oxidation processes (AOPs) for removing organic contaminants. However, we found that HAm-driven Cu(II)/peroxymonosulfate oxidation of phenol produced p-nitrosophenol, 2-nitrophenol and 4-nitrophenol. The total nitro(so) products accounted for approximately 25.0 % of the phenol transformation at certain condition. SO₄^•- and •OH were identified as the primary and second significant oxidants, respectively. Reactive nitrogen species (RNS) were involved in phenol transformation. The pathway and mechanism of HAm transformation in HAm-driven transition metal ion-catalyzed AOPs were proposed for the first time in this study. The product of HAm via twice single-electron oxidation by Cu(II) is nitroxyl (HNO/NO^-), which is a critical oxidation intermediate of HAm. Further oxidation of HNO by SO₄^•- or •OH is the initial step in propagating radical chain reactions, leading to nitric oxide radical (•NO) and nitrogen dioxide radical (•NO₂) as the primary RNS. HAm is a critical intermediate in natural nitrogen cycle, suggesting that HAm can drive the oxidation processes of pollutants in natural environments. Nitro(so) products will be readily produced when AOPs are applied for ecological remediation. This study highlights the formation of toxic nitrosated and nitrated products in HAm-driven AOPs, and the requirement of risk assessments to evaluate the possible health and ecological impacts.

Sulfur and nitrogen co-doped magnetic biochar coupled with hydroxylamine for high-efficiency of persulfate activation and mechanism study

Biochar has recently become a central issue in advanced oxidation processes (AOPs) based on peroxydisulfate (PDS) activation. However, the PDS activation by biochar must be improved. In this study, S, N co-doped magnetic biochar (IBC) was prepared by a simple impregnation-pyrolysis method using Eichhornia crassipes stems with inherent sulfur and nitrogen as the raw materials for biochar. The reductant hydroxylamine (HA) was employed to further enhance PDS activation by the IBC for organic pollutant degradation. Incorporating HA in PDS activation over IBC significantly improved its compatibility with complex water, catalytic degradation, stability performance, and mineralization rate of organic pollutants. The outstanding performance of the HA/PDS/IBC system for organic degradation was due to the increased free radicals SO₄^·-, O₂^·-, and non-radical ¹O₂ generated, as well as the electrons transferred between IBC, PDS, and organic pollutants, which were verified by electron paramagnetic resonance (EPR) detection and electrochemical characterizations. Furthermore, HA-enhanced Fe(III)/Fe(II) cycling, surface functional groups, and S and N doping contributed to the generation of reactive oxygen species (ROS). Moreover, the toxicity assessment indicated that the toxicity of the degradation intermediates decreased. Therefore, this research proposes a new insight into the enhanced degradation of pollutants by increasing PDS activation using biochar-based catalytic materials.

Enhancement on the degradation of naproxen in Cu0 activated peroxymonosulfate system by complexing reagents

In recent years, there has been growing interest in the mechanism (radical or nonradical) of persulfate activation processes. In this study, the enhancement of naproxen (NPX) degradation in a Cu⁰/peroxymonosulfate (PMS) system by complexing reagents was investigated. Surprisingly, neocuproine (NCP) alters the nature of reactive species in the Cu⁰/PMS system. A high-valent copper species, Cu(III)-NCP, was found to dominate NPX degradation rather than radicals under acid conditions for the first time. Moreover, systematically designed experiments revealed that the Cu(III)-NCP complex was a strong selective oxidant that reacted with organics through a single electron transfer pathway. Meanwhile, the degradation efficiency of NPX was highly dependent on the solution pH and dosage of Cu⁰ and NCP, but was irrelevant to the concentration of NPX. Additionally, the enhancement of NCP on other copper based PMS activation systems (i.e., Cu²⁺/HA/PMS and Cu⁰/HA/PMS systems) was investigated. Considering that the released copper can be removed by a simple precipitation method to meet the effluent standards, the new complex-enhanced Cu⁰/PMS system provided a new method to enhance the degradation efficiencies of pollutants by a copper-catalyzed Fenton-like system.

NDMA formation during ozonation of DMAPA: Influencing factors, mechanisms, and new pathway exploration

Aliphatic amines, common constituents that contribute to dissolved organic nitrogen (DON), can quickly react with ozone due to the lone electron pair on the nitrogen atom and this may produce carcinogen N-Nitrosodimethylamine (NDMA). 3-(Dimethylamino)-1-propylamine (DMAPA) was chosen as a representative to elucidate the NDMA formation characteristics, kinetic rates, reaction pathways, and influencing factors during ozonation in this study. The results demonstrated that NDMA generated directly from DMAPA during ozonation. Moreover, the NDMA yields increased with ozone dosages. The NDMA molar yield increased and then decreased when the pH raised from 5 to 9, achieving the maximum value at pH 8. Hydroxyl radical (∙OH) played a promotional role in NDMA formation, and its scavenger dramatically cut down its yields. Low levels of Br^- facilitated NDMA formation, while the value significantly reduced when Br^- was up to 1 mM. The NDMA amount was slightly raised by NO₂^-, but it was inhibited by NH₄⁺ and NO₃^-. Moreover, it was also depressed by co-existing components in actual lake water. Based on the result of the Gaussian calculation, the LC-MS/MS and GC-MS analysis, four possible transformation pathways were proposed. The radical recombination was verified to be the primary pathway for ozone promoting NDMA formation from DMAPA.

Metalation/Demetalation as a Postgelation Strategy To Tune the Mechanical Properties of Catenane-Crosslinked Gels

Mechanically interlocked molecules (MIMs) possess unique architectures and nontraditional degrees of freedom that arise from well-defined topologies that are achieved through precise mechanical bonding. Incorporation of MIMs into materials can thus provide an avenue to discover new and emergent macroscale properties. Here, the synthesis of a phenanthroline-based [2]catenane crosslinker and its incorporation into polyacrylate organogels are described. Specifically, Cu(I) metalation and demetalation was used as a postgelation strategy to tune the mechanical properties of a gel by controlling the conformational motions of integrated MIMs. The organogels were prepared via thermally initiated free radical polymerization, and Cu(I) metal was added in MeOH to the pretreated, swollen gels. Demetalation of the gels was achieved by adding lithium cyanide and washing the gels. Changes in Young's and shear moduli, as well as tensile strength, were quantified through oscillatory shear rheology and tensile testing. The reported approach provides a general method for postgelation tuning of mechanical properties using metals and well-defined catenane topologies as part of a gel network architecture.

Ascorbic acid enhanced ferrous/persulfate system for degradation of tetracycline contaminated groundwater

Persulfate (PS) activated by Fe(ii) has been widely investigated for degradation of contaminants.

Iodometric spectrophotometric determination of peroxydisulfate in hydroxylamine-involved AOPs: 15 min or 15 s for oxidative coloration?

In this study, iodometric spectrophotometry, the most-used method for detecting peroxydisulfate (PDS), was modified by increasing the concentration of potassium iodide (KI) for realizing the immediate PDS determination and avoiding the interference of hydroxylamine. Kinetic studies showed that the reaction between PDS and I^- to generate the yellow-colored I₃^- followed the kinetic equation as [Formula: see text] . Detection time of the iodometric spectrophotometry was shortened from 15 min to 15 s when KI concentration was increased from 0.6 M to 4.8 M. Different with the previous iodometric spectrophotometry, the modified method using 4.8 M KI as the indicator was well tolerable to the interference of hydroxylamine at acidic pH conditions. The calibration curve of the modified method showed a well linear relationship (R² = 0.999) between the absorbance of I₃^- at 352 nm and PDS concentration in the range of 0-80 μM. The modified method was highly sensitive with the absorptivity of 2.5 × 10⁴ M^-1 cm^-1 and the limit of detection of 0.11 μM. Moreover, the modified method was successfully applied for monitoring the change of PDS concentration during the degradation of diclofenac with four different PDS-based AOPs, the calculated reaction stoichiometric efficiency (RSE(%)=DiclofenacdegradedPDSconsumed×100%) followed the order as heat/PDS system > hydroxylamine/Fe²⁺/PDS system > hydroxylamine/Cu²⁺/PDS system > Fe²⁺/PDS system.

Hydroxylamine driven advanced oxidation processes for water treatment: A review

Hydroxylamine (HA) driven advanced oxidation processes (HAOPs) for water treatment have attracted extensive attention due to the acceleration of reactive intermediates generation and the improvement on the elimination effectiveness of target contaminants. In this review, HAOPs were categorized into three parts: (1) direct reaction of HA with oxidants (e.g., hydrogen peroxide (H₂O₂), peroxymonosulfate (PMS), ozone (O₃), ferrate (Fe(VI)), periodate (IO₄^-)); (2) HA driven homogeneous Fenton/Fenton-like system (Fe(II)/peroxide/HA system, Cu(II)/O₂/HA system, Cu(II)/peroxide/HA system, Ce(IV)/H₂O₂/HA system); (3) HA driven heterogeneous Fe/Cu-Fenton/Fenton-like system (iron-bearing material/peroxide/HA system, copper-bearing material/peroxide/HA system, bimetallic composite/peroxide/HA system). Degradation efficiency of the target pollutant, reactive intermediates, and effective pH range of various HAOPs were summarized. Further, corresponding reaction mechanism was elaborated. For the direct reaction of HA with oxidants, improvement of pollutants degradation was achieved through the generation of secondary reactive intermediates which had higher reactivity compared with the parent oxidant. For HA driven homogeneous and heterogeneous Fe/Cu-Fenton/Fenton-like system, improvement of pollutants degradation was achieved mainly via the acceleration of redox cycle of Fe(III)/Fe(II) or Cu(II)/Cu(I) and subsequent generation of reactive intermediates, which avoided the drawbacks of classical Fenton/Fenton-like system. In addition, HA driven homogeneous Fe/Cu-Fenton/Fenton-like system with heterogeneous counterpart were compared. Further, formation of oxidation products from HA in various HAOPs was summarized. Finally, the challenges and prospects in this field were discussed.

Synergistic activation of peroxydisulfate with magnetite and copper ion at neutral condition

Magnetite is known to exhibit high catalytic reactivity in Fenton-like reactions merely at low pH conditions. Here we report the association of Cu²⁺ ion can significantly enhance peroxydisulfate (PDS) activation with magnetite under environmental aquatic conditions (near neutral pH). Cu²⁺ is able to synergistically activate PDS with magnetite to generate radicals, e.g., SO₄^·-, at neutral or slightly alkaline pH, and such synergistic activation of PDS is promising to degrade various contaminants in groundwater. In-depth study reveals Cu²⁺ ion adsorbed on magnetite plays a crucial role in PDS activation. The adsorbed Cu²⁺ is labile to be reduced by the structural Fe(II) on magnetite to generate Cu⁺, which is relatively stable in the presence of magnetite at neutral or alkaline pH, but extremely unstable at acidic pH. The generated Cu⁺ on magnetite surface, rather than Cu²⁺, contributes to PDS activation in the reaction system, and the recycling of Cu⁺/Cu²⁺ sustains continuous activation of PDS. This study is among the first to report the synergistic activation of PDS by magnetite and Cu²⁺ ion at neutral pH, and unambiguously discern the role of Cu⁺ in PDS activation. The new mechanistic knowledge provides a more accurate understanding of PDS activation by natural minerals in environmental remediation.

Application of copper tailings combined with persulfate for better removing methyl orange from wastewater

In this paper, wasted copper tailings (CT) were used to activate persulfate (PS) to degrade azo dye methyl orange (MO). The results show that a large amount of FeS₂ contained in CT can slowly release Fe²⁺ in the aqueous solution to activate PS to generate reactive oxygen species to degrade MO. When the dosage of CT and PS was 2 g/L and 3 mM respectively, the MO degradation efficiency of 20 mg/L in the CT/PS system was 96.52% within 60 min. At the same time, it is found that CT has a certain adsorption capacity for MO, and the intra-particle diffusion model can well describe the adsorption process of MO by CT. The effects of related reaction parameters (CT dosage, PS dosage, initial MO concentration and solution pH) on MO degradation in CT/PS system were investigated. Compared with the direct addition of an equal amount of Fe²⁺ as in the CT/PS system, for homogeneous activated PS to degrade MO (Fe²⁺/PS), the results showed that the degradation efficiency of Fe²⁺/PS system for MO was lower than that of CT/PS system due to excessive Fe²⁺ consumption of SO₄ ^·-. By comparing the Fe²⁺ and Fe³⁺ concentrations in the two systems, it was found that the CT/PS system could maintain a low Fe²⁺ concentration during the reaction process, and the Fe²⁺ released by CT could be used by PS to degrade MO more efficiently. The free radical scavenging experiments showed that the reactive oxygen species in the CT/PS system was mainly SO₄ ^·-. This study not only proposed a new CT utilization approach, but also solved the problem of reduced degradation efficiency of organic pollutants caused by excessive Fe²⁺ in the Fenton-like reaction.

Cu(II)-enhanced degradation of acid orange 7 by Fe(II)-activated persulfate with hydroxylamine over a wide pH range

The activation of persulfate by Fe(II) coupled with hydroxylamine (the HA/Fe(II)/PS system) was highly effective for the degradation of refractory organic contaminants under acidic pH conditions. However, owing to the precipitation of ferric hydroxide and/or the slow reduction from Fe(III) to Fe(II), the HA/Fe(II)/PS system was invalid under neutral and alkaline pH conditions. In this study, it was observed that the degradation of acid orange 7 (AO7) was strongly enhanced over the wide pH range of 2-9 when trace Cu(II) (0.5-5 μM) was spiked into the HA/Fe(II)/PS system. It was evident that Cu(I) was generated via the reduction of Cu(II) by HA in the bimetallic system at both pH 3 and pH 8, and the steady concentration of Fe(II) in the bimetallic system was much higher than that in the HA/Fe(II)/PS system due to the rapid reaction between Fe(III) and Cu(I). Quenching experiments using tert-butyl alcohol, methanol and sodium bromide as the scavengers and electron spin resonance experiments confirmed that the primary reactive species responsible for AO7 degradation were sulfate radical at both pH 3 and pH 8, rather than hydroxyl radical and Cu(III). Nevertheless, sulfate radical was mainly produced by Fe(II)-activated PS at pH 3, while both Cu(I) and Fe(II) made important contributions to the generation of sulfate radical at pH 8. The bimetallic system was also highly effective in degrading other organic contaminants, such as phenol, diclofenac, reactive red 2 and orange G. This study might provide a promising idea based on Fe(II)-activated PS for degrading organic contaminants over a wide pH range.

Complexation Enhances Cu(II)-Activated Peroxydisulfate: A Novel Activation Mechanism and Cu(III) Contribution

While aqueous free Cu(II) ion is known to be ineffective to activate peroxydisulfate (PDS), here we report for the first time that Cu(II) complexes are potentially effective activators for PDS when the coordination involves suitable ligands. Using cefalexin (CFX) as a representative, studies show that the complex of Cu(II) with CFX can efficiently activate PDS to induce rapid degradation of CFX. Transformation products of CFX by PDS/Cu(II) differ substantially from those generated from the typical radical oxidation process, for example, PDS/Ag(I), but quite resemble the products from oxidation of CFX by Cu(III). Complexation with CFX increases the electron density of Cu(II), favoring electron transfer from Cu(II) to PDS to generate radicals and Cu(III). The produced Cu(III), rather than radicals, plays the primary role in the overall CFX degradation and regenerates Cu(II) in a catalytic cycle. This novel activation process can occur for a wide range of contaminants (cephalosporin, penicillin, and tetracycline antibiotics) and ligands when coordinated with Cu(II), and N-containing functional groups (e.g. amines) were found to form effective Cu(II) complexes for PDS activation. The new findings of this study further broaden the knowledge on PDS activation by aqueous Cu(II), and verify the contribution of Cu(III) to contaminant elimination.

Decolorization and Mineralization of Rhodamine B in Aqueous Solution with a Triple System of Cerium(IV)/H2O2/Hydroxylamine

Hydroxylamine (HA) can react with hydrogen peroxide (H₂O₂) to generate hydroxyl radical (HO^•), but the reaction rate between them is very slow (2.2 × 10^-4 M^-1 s^-1). We propose a new system to accelerate the formation of aminoxyl radical (NH₂O^•) by the addition of cerium [Ce(IV)] to induce the continuous production of HO^• through reaction with H₂O₂. We also investigate the decolorization and mineralization of rhodamine B (RhB) and mechanism in the Ce(IV)/H₂O₂/HA system. The initial pH plays a significant role in decolorization of RhB. In this work, observation of the rapid decolorization process after 60 min revealed that approximately 80% of RhB was degraded at the initial pH of 4.0. The HO^• radicals were considered as the primary reactive oxidant in the system, during its investigation through coumarin capturing, benzoic acid capturing, and radical quenching experiments. The results of the present study suggest that the addition of Ce(IV) can greatly enhance the production of HO^•, and the rapid decolorization and mineralization of RhB can occur through the Ce(IV)/H₂O₂/HA system at acidic pH conditions.

Degradation of acetaminophen with ferrous/copperoxide activate persulfate: Synergism of iron and copper

To enhance the advanced oxidation process based on persulfate, CuO was introduced into the Fe²⁺/PS system to achieve a synergistic effect between Fe and Cu. Results showed that Fe²⁺ was able to adsorb onto the CuO surface to form Fe(II) and further reduced Cu(II) into Cu(I), which can further release into the solution to participate in oxidation reactions. In this case, SO₄^·- can be generated via Fe²⁺ and Cu⁺ reactions with PS and ·OH from Cu⁺ reaction with dissolved oxygen (DO). The degradation efficiency of APAP was studied under the optimal condition (initial pH 6.5, PS = 0.8 g L^-1, Fe²⁺ = 0.7 mM, CuO = 0.3 g L^-1), and the results indicated that the Fe²⁺/CuO/PS system can achieve a higher degradation rate of APAP (92% within 90 min) rather than Fe²⁺/PS and CuO/PS system (79% and 10%). Quenching experiment was performed to verify the active radicals in the Fe²⁺/CuO/PS system. Sulfate and hydroxyl radicals were generated in the Fe²⁺/CuO/PS system. Besides, some critical factors, such as Fe²⁺ concentration, catalyst dosage, PS concentration, initial pH (buffers and nonbuffers), and dissolved oxygen were evaluated in bath experiments. Results indicated that dissolved oxygen was essential in the Fe²⁺/CuO/PS system. APAP degradation experiments were conducted in surface water, and the intermediates were detected via GC-MS. The results indicated that the Fe²⁺/CuO/PS system is effective in the treatment of APAP in natural waters.

Generation of reactive oxygen species by promoting the Cu(II)/Cu(I) redox cycle with reducing agents in aerobic aqueous solution

This study investigated the generation of reactive oxygen species (ROS) (O₂ ^-•, H₂O₂, and HO•) by promoting the Cu(II)/Cu(I) redox cycle with certain reducing agents (RAs) in aerobic aqueous solution, and benzoic acid (BA) was employed as indicator for the hydroxyl radical (HO•). Hydroxylamine (HA) can reduce Cu(II) to Cu(I) to induce chain reactions of copper species resulting in the generation of the superoxide radical (O₂ ^-•) and hydrogen peroxide (H₂O₂), and the intermediate Cu(I) can further activate H₂O₂ via a Fenton-like reaction to produce HO•, creating the remarkable BA degradation. O₂ is indispensable, and unprotonated HA is the motive power in the O₂/Cu/HA system. Moreover, pH is a crucial factor of the O₂/Cu/HA system due to the protonated HA not being able to reduce Cu(II) into Cu(I). The oxidation of HA can be effectively induced by trace amounts of Cu(II), and both a higher HA dosage and a higher Cu(II) dosage can enhance H₂O₂ generation and BA degradation. In addition, some other RAs that can reduce Cu(II) into Cu(I) could replace HA in the O₂/Cu/HA system to induce the generation of these ROS in aerobic aqueous solution.

Thermally activated persulfate oxidation of NAPL chlorinated organic compounds: effect of soil composition on oxidant demand in different soil-persulfate systems

This study investigates the interaction of persulfate with soil components and chlorinated volatile organic compounds (CVOCs), using thermally activated persulfate oxidation in three soil types: high sand content; high clay content; and paddy field soil. The effect of soil composition on the available oxidant demand and CVOC removal rate was evaluated. Results suggest that the treatment efficiency of CVOCs in soil can be ranked as follows: cis-1,2-dichloroethene > trichloroethylene > 1,2-dichloroethane > 1,1,1-trichloroethane. The reactions of soil components with persulfate, shown by the reduction in soil phase natural organics and mineral content, occurred in parallel with persulfate oxidation of CVOCs. Natural oxidant demand from the reaction of soil components with persulfate exerted a large relative contribution to the total oxidant demand. The main influencing factor in oxidant demand in paddy-soil-persulfate systems was natural organics, rather than mineral content as seen with sand and clay soil types exposed to the persulfate system. The competition between CVOCs and soil components for oxidation by persulfate indicates that soil composition exhibits a considerable influence on the available oxidant demand and CVOC removal efficiency. Therefore, soil composition of natural organics and mineral content is a critical factor in estimating the oxidation efficiency of in-situ remediation systems.

Radicals induced from peroxomonosulfate by nanoscale zero-valent copper in the acidic solution

A highly efficient advanced oxidation process for the degradation of benzoic acid (BA) during activation of peroxomonosulfate (PMS) by nanoscale zero-valent copper (nZVC) in acidic solution is reported. BA degradation was almost completely achieved after 10 min in the nZVC/PMS process at initial pH 3.0. PMS could accelerate the corrosion of nZVC in acidic to release Cu⁺ which can further activate PMS to produce reactive radicals. Both sulfate radical (SO₄^-•) and hydroxyl radical (•OH) were considered as the primary reactive oxidant in the nZVC/PMS process with the experiments of methyl (MA) and tert-butyl alcohol quenching. Acidic condition (initial pH ≤ 3.0) facilitated BA degradation and pH is a decisive factor to affect the oxidation capacity in the nZVC/PMS process. Moreover, BA degradation in the nZVC/PMS process followed the pseudo-first-order kinetics, and BA degradation efficiency increased with the increase of the nZVC dosage.