An efficient catalytic degradation of trichloroethene in a percarbonate system catalyzed by ultra-fine heterogeneous zeolite supported zero valent iron-nickel bimetallic composite

A systematic review on percarbonate-based advanced oxidation processes in wastewater remediation: From theoretical understandings to practical applications

Percarbonate encompasses sodium percarbonate (SPC) and composite in-situ generated peroxymonocarbonate (PMC). SPC emerges as a promising alternative to hydrogen peroxide (H2O2), hailed for its superior transportation safety, stability, cost-effectiveness, and eco-friendliness, thereby becoming a staple in advanced oxidation processes for mitigating water pollution. Yet, scholarly literature scarcely explores the deployment of percarbonate-AOPs in eradicating organic contaminants from aquatic systems. Consequently, this review endeavors to demystify the formation mechanisms and challenges associated with reactive oxygen species (ROS) in percarbonate-AOPs, alongside highlighting directions for future inquiry and development. The genesis of ROS encompasses the in situ chemical oxidation of activated SPC (including iron-based activation, discharge plasma, ozone activation, photon activation, and metal-free materials activation) and composite in situ chemical oxidation via PMC (namely, H2O2/NaHCO3/Na2CO3, peroxymonosulfate/NaHCO3/Na2CO3 systems). Moreover, the ROS generated by percarbonate-AOPs, such as •OH, O2•-, CO3•-, HO2•-, 1O2, and HCO4-, can work individually or synergistically to disintegrate target pollutants. Concurrently, this review systematically addresses conceivable obstacles posing percarbonate-AOPs in real-world application from the angle of environmental conditions (pH, temperature, coexisting substances), and potential ecological toxicity. Considering the outlined challenges and advantages, we posit future research directions to amplify the applicability and efficacy of percarbonate-AOPs in tangible settings. It is anticipated that the insights provided in this review will catalyze the progression of percarbonate-AOPs in water purification endeavors and bridge the existing knowledge void.

Removal enhancement of persistent basic fuchsin dye from wastewater using an eco-friendly, cost-effective Fenton process with sodium percarbonate and waste iron catalyst

In this comprehensive investigation, we evaluate the efficacy of the Fenton process in degrading basic fuchsin (BF), a resistant dye. Our primary focus is on the utilization of readily available, environmentally benign, and cost-effective reagents for the degradation process. Furthermore, we delve into various operational parameters, including the quantity of sodium percarbonate (SPC), pH levels, and the dimensions of waste iron bars, to optimize the treatment efficiency. In the course of our research, we employed an initial SPC concentration of 0.5 mM, a pH level of 3, a waste iron bar measuring 3.5 cm in length and 0.4 cm in diameter, and a processing time of 10 min. Our findings reveal the successful elimination of the BF dye, even when subjected to treatment with diverse salts and surfactants under elevated temperatures and acidic conditions (pH below 3). This underscores the robustness of the Fenton process in purifying wastewater contaminated with dye compounds. The outcomes of our study not only demonstrate the efficiency of the Fenton process but highlight its adaptability to address dye contamination challenges across various industries. Critically, this research pioneers the application of waste iron bars as a source of iron in the Fenton reaction, introducing a novel, sustainable approach that enhances the environmental and economic viability of the process. This innovative use of recycled materials as catalysts represents a significant advancement in sustainable chemical engineering practices.

Efficient composite chlorinated ethenes removal using gallic acid to enhance Fe/Ni nanoparticles activated persulfate

As the representative volatile chlorinated hydrocarbons detected in wastewater, the removal of composite chlorinated ethenes is a major challenge in wastewater treatment. In the present study, an efficient removal system for composite chlorinated ethenes was reported, in which gallic acid was used to enhance the activation of persulfate by Fe/Ni nanoparticles. The influences of gallic acid-Fe/Ni and persulfate concentrations, initial pH value, reaction temperature, inorganic anions, and natural organic matters were evaluated in the composite chlorinated ethenes removal. Our results showed that the gallic acid-Fe/Ni-persulfate system with 9.0 mM of gallic acid-Fe/Ni and 30.0 mM of persulfate yielded about 100% trichloroethylene removal and 97.3%-98.6% perchloroethylene removal in the pH range of 3.0-12.0. Electron paramagnetic resonance analysis and radical quenching experiments indicated that SO4•- and •OH were the predominant radical species under acidic and alkaline conditions. Ultraviolet visible spectroscopy and inductively coupled plasma optical emission spectrometer tests revealed the Fe-gallic acid chelation could regulate the concentration of iron ions and improve the reactivity of gallic acid-Fe/Ni. These results demonstrated that the gallic acid-Fe/Ni-persulfate system was a promising strategy for treating composite chlorinated ethenes-containing wastewater.

The performance and mechanism of iron-mediated chemical oxidation: Advances in hydrogen peroxide, persulfate and percarbonate oxidation

Many studies have successfully built iron-mediated materials to activate or catalyze Fenton-like reactions, with applications in water and wastewater treatment being investigated. However, the developed materials are rarely compared with each other regarding their performance of organic contaminant removal. In this review, the recent advances of Fenton-like processes in homogeneous and heterogeneous ways are summarized, especially the performance and mechanism of activators including ferrous iron, zero valent iron, iron oxides, iron-loaded carbon, zeolite, and metal organic framework materials. Also, this work mainly compares three O-O bond containing oxidants including hydrogen dioxide, persulfate, and percarbonate, which are environmental-friendly oxidants and feasible for in-situ chemical oxidation. The influence of reaction conditions, catalyst properties and benefits are analyzed and compared. In addition, the challenges and strategies of these oxidants in applications and the major mechanisms of the oxidation process have been discussed. This work can help understand the mechanistic insights of variable Fenton-like reactions, the role of emerging iron-based materials, and provide guidance for choosing appropriate technologies when facing real-world water and wastewater applications.

Mechanism and security of UV driven sodium percarbonate for sulfamethoxazole degradation using DFT and metabolomic analysis

Recently, sodium percarbonate (SPC) as a solid substitute for H₂O₂ has aroused extensive attention in advanced oxidation processes. In current work, the degradation kinetics and mechanisms of antibiotic sulfamethoxazole (SMX) by ultraviolet (UV) driven SPC system were explored. The removal efficiency of SMX was enhanced as the increasing dosage of SPC. Moreover, hydroxyl radical (•OH), carbonate radical (CO₃^•-) and superoxide radical (O₂^•-) were verified to be presented by scavenger experiments and •OH, CO₃^•- exhibited a significant role in SMX degradation. Reactions mediated by these radicals were affected by anions and natural organic matters, implying that an incomplete mineralization of SMX would be ubiquitous. The screening four intermediates and transformation patterns of SMX were verified by DFT analysis. Metabolomic analysis demonstrated that a decreasing negative effect in E. coli after 24 h exposure was induced by intermediates products. In detail, SMX interfered in some key functional metabolic pathways including carbohydrate metabolism, pentose and glucuronate metabolism, nucleotide metabolism, arginine and proline metabolism, sphingolipid metabolism, which were mitigated after UV/SPC oxidation treatment, suggesting a declining environmental risk of SMX. This work provided new insights into biological impacts of SMX and its transformation products and vital guidance for SMX pollution control using UV/SPC technology.

Degradation of 1,2,3-trichloropropane by unactivated persulfate and the implications for groundwater remediation

Persulfate (PS) is widely used as an in situ chemical oxidation (ISCO) technology for groundwater and soil remediation. While conventional theory generally assumes that PS needs to be "activated" to produce reactive radicals for pollutant degradation, herein, PS without explicit activation system was discovered for the degradation of 1,2,3-TCP with the generation of reactive oxidation species (ROS). Comparison of five common ISCO oxidants (PS, peroxymonosulfate, hydrogen peroxide, potassium permanganate, and sodium percarbonate) indicated that only unactivated PS was able to degrade 1,2,3-TCP in both pure water and 12 natural water samples. 50 μM 1,2,3-TCP degradation can be continued as long as there is enough PS (50 mM). The degradation rate of 1,2,3-TCP increased 450 % when the PS concentration increased from 10 mM to 50 mM and 500 % when the temperature increased from 25 °C to 45 °C. Electron paramagnetic resonance (EPR) analyzes, hydroxyl radicals (·OH) probe reaction and radical quenching experiments confirmed the involvement of both sulfate radicals (SO₄·-) and ·OH that were responsible for 1,2,3-TCP degradation and ·OH played a more important role. HCO₃^-, Cl^- and NOM are three groundwater matrix species that are most likely to inhibit PS oxidation of 1,2,3-TCP. Compared to activated PS, unactivated PS is more promising and more practical for groundwater remediation, since it has several advantages: (1) longer lifetime and better long-term availability; (2) ability of enduring contaminant degradation; (3) applicable for low-permeability zones remediation and potential to alleviate contaminant rebound or tailing problems; (4) environmental friendly; and (5) lower cost. Overall, results of this study show that unactivated PS is a promising in situ remediation technology that may be a good candidate for the most challenging low permeable zone remediation.

Advanced oxidation processes for water purification using percarbonate: Insights into oxidation mechanisms, challenges, and enhancing strategies

Percarbonate (SPC) has drawn considerable attention due to its merits in the safety of handling and transport, stability, and price as well as environmental friendliness, which has been extensively applied in advanced oxidation processes (AOPs) for water decontamination. Nevertheless, comprehensive information on the application of SPC-AOPs for the treatment of organic compounds in aquatic media is scarce. Hence, the focus of this review is to shed light on the mechanisms of reactive oxygen species (ROS) evolution in typical SPC-AOPs (i.e., Fenton-like oxidation, photo-assisted oxidation, and discharge plasma-involved oxidation processes). These SPC-AOPs enable the formation of multiple reactive species like hydroxyl radical (^•OH), superoxide radical (O₂^•-), singlet oxygen (¹O₂), carbonate radicals (CO₃^•-), and peroxymonocarbonate (HCO₄^-), which together or solely contribute to the degradation of target pollutants. Simultaneously, the potential challenges in practical applications of SPC-AOPs are systematically discussed, which include the influence of water quality parameters, cost-effectiveness, available active sites, feasible activation approaches, and ecotoxicity. Subsequently, enhancing strategies to improve the feasibility of SPC-AOPs in the practical implementation are tentatively proposed, which can be achieved by introducing reducing and chelating agents, developing novel activation approaches, designing multiple integrated oxidation processes, as well as alleviating the toxicity after SPC-AOPs treatment. Accordingly, future perspectives and research gaps in SPC-AOPs are elucidated. This review will hopefully offer valuable viewpoints and promote the future development of SPC-AOPs for actual water purification.

Insights into a novel CuS/percarbonate/tetraacetylethylenediamine process for sulfamethazine degradation in alkaline medium

This work presents a novel CuS/percarbonate/tetraacetylethylenediamine (CuS/SPC/TAED) process for the degradation of sulfamethazine (SMT). Results indicated that the CuS/SPC/TAED process enabled the efficient generation of peracetic acid (PAA), which can be efficiently activated by CuS in alkaline reaction media, and 93.6% of SMT was degraded in 30 min. Mechanism study revealed that the available reactive oxygen species (ROS) including hydroxyl radical (^•OH), carbonate radical (CO₃^•-), superoxide radical (O₂^•-), singlet oxygen (¹O₂), and organic radicals (R-O^•). Among them, R-O^• (acetyloxyl radical (CH₃CO₂^•) and acetylperoxyl radical (CH₃CO₃^•)) were confirmed to be the primary species that contributed to SMT degradation. Simultaneously, the role of sulfur species and carbonate ions were explored. It was found that the reductive O₂^•- and sulfur species rendered the efficient redox of Cu species. Besides, the effects of key influencing factors including SPC/TAED mole ratio, CuS dosage, initial pH, temperature, and nontarget matrix constituents on SMT degradation were examined. Finally, the degradation intermediates of SMT was identified, and the toxicity of these products was estimated by quantitative structure-activity relationship (QSAR) analysis. Overall, this work offers a new and simple strategy for antibiotic-polluted water remediation.

Preparation, characterization, and applications of Fe-based catalysts in advanced oxidation processes for organics removal: A review

Fe-based catalysts as low-cost, high-efficiency, and non-toxic materials display superior catalytic performances in activating hydrogen peroxide, persulfate (PS), peracetic acid (PAA), percarbonate (PC), and ozone to degrade organic contaminants in aqueous solutions. They mainly include ferrous salts, zero-valent iron, iron-metal composites, iron sulfides, iron oxyhydroxides, iron oxides, and supported iron-based catalysts, which have been widely applied in advanced oxidation processes (AOPs). However, there is lack of a comprehensive review systematically reporting their synthesis, characterization, and applications. It is imperative to evaluate the catalytic performances of various Fe-based catalysts in diverse AOPs systems and reveal the activation mechanisms of different oxidants by Fe-based catalysts. This work detailedly summarizes the synthesis methods and characterization technologies of Fe-based catalysts. This paper critically evaluates the catalytic performances of Fe-based catalysts in diverse AOPs systems. The effects of solution pH, reaction temperature, coexisting ions, oxidant concentration, catalyst dosage, and external energy on the degradation of organic contaminants in the Fe-based catalyst/oxidant systems and the stability of Fe-based catalysts are also discussed. The activation mechanisms of various oxidants and the degradation pathways of organic contaminants in the Fe-based catalyst/oxidant systems are revealed by a series of novel detection methods and characterization technologies. Future research prospects on the potential preparation means of Fe-based catalysts, practical applications, assistive technologies, and impact in AOPs are proposed.

A review of the new multifunctional nano zero-valent iron composites for wastewater treatment: Emergence, preparation, optimization and mechanism

Nano zero-valent iron (NZVI) with high chemical reactivity and environmental friendliness had recently become one of the most efficient technologies for wastewater restoration. However, the unitary NZVI system had not met practical requirements for wastewater treatments. Expectantly, the development of NZVI would prefer multifunctional NZVI-based composites, which could be prepared and optimized by the combined methods and technologies. Consequently, a systematic and comprehensive summary from the perspective of multifunctional NZVI-composite had been conducted. The results demonstrated that the advantages of various systems were integrated by multifunctional NZVI-composite systems with a more significant performance of pollutant removal than those of the bare NZVI and its composites. Simultaneously, characteristics of the product prepared by the incorporation of numerous methods were superior to those by a simple method, resulting in the increase of the entirety efficiency. By comparison with other preparation methods, the ball milling method with higher production and field application potential was worthy of attention. After combining multiple technologies, the effect of NZVI and its composite systems could be dramatically strengthened. Preparation technology parameters and treatment effect of contaminants could be further optimized using more comprehensive experimental designs and mathematical models. The mechanism of the multifunctional NZVI system for contaminants treatment was primarily focused on adsorption, oxidation, reduction and co-precipitation. Multiple techniques were combined to enhance the dispersion, alleviating passivation, accelerating electron transfer efficiency or mass transfer action for optimizing the effect of NZVI composites.

Removal of organic compounds by nanoscale zero-valent iron and its composites

During the latest several decades, the continuous development of the economy and industry has brought more and more serious organic pollutants to the natural environment, which have inevitably aroused severe menace to human health and the environmental system. The nano zero-valent iron (NZVI) particles and NZVI-based materials have widely applied to remove organic pollutants. This article reviews the key advancements of different methods for the synthesis of NZVI and NZVI-based materials. Different modification methods (e.g., doped NZVI, encapsulated NZVI and supported NZVI) are also introduced detailedly for overcoming the defects of NZVI such as aggregation and easy oxidation. The removal of different organic pollutants including dyes, halogenated organic compounds, nitro-organic compounds, phenolic compounds, pesticides, and antibiotics are summarized. The interaction mechanisms, including adsorption, reduction, and active oxidation of organic pollutants by NZVI/NZVI-based composites, are discussed. The dyes are mainly removed by destroying their chromogenic group according to the reduction or the Fenton-like reaction with NZVI. The removal of halogenated organic compounds (HOCs) is realized by the dehalogenation process, including reductive elimination, hydrogenolysis, and hydrogenation. As for the nitro-organic compounds, three different reduction pathways as nitro-reduction (into amino), cleavage at the carbon‑nitrogen bond or denitration of the NO₂ group may take effect. The phenolic compounds can be mineralized into inorganic molecules, including CO₂ and H₂O, by Fenton oxidation. This review might provide the basis for future studies on developing more effective NZVI-based materials for the treatment of wastewaters contaminated by organic pollutants.

A review on percarbonate-based advanced oxidation processes for remediation of organic compounds in water

Sodium percarbonate (SPC) is considered a potential alternative to liquid hydrogen peroxide (H₂O₂) in organic compounds contaminated water/soil remediation due to its regularly, transportable, economical, and eco-friendly features. The solid state of SPC makes it more suitable to remediate actual soil and water with a milder H₂O₂ release rate. Apart from its good oxidative capacity, alkaline SPC can simultaneously remediate acidized solution and soil to the neutral condition. Conventionally, percarbonate-based advanced oxidation process (P-AOPs) system proceed through the catalysis under ultraviolet ray, transition metal ions (i.e., Fe²⁺, Fe³⁺, and V⁴⁺), and nanoscale zero-valent metals (iron, zinc, copper, and nickel). The hydroxyl radical (^•OH), superoxide radical (^•O₂^-), and carbonate radical anion (^•CO₃^-) generated from sodium percarbonate could attack the organic pollutant structure. In this review, we present the advances of P-AOPs in heterogeneous and homogeneous catalytic processes through a wide range of activation methods. This review aims to give an overview of the catalysis and application of P-AOPs for emerging contaminants degradation and act as a guideline of the field advances. Various activation methods of percarbonate are summarized, and the influence factors in the solution matrix such as pH, anions, and cations are thoroughly discussed. Moreover, this review helps to clarify the advantages and shortcomings of P-AOPs in current scientific progress and guide the future practical direction of P-AOPs in sustainable carbon catalysis and green chemistry.

Application of percarbonate and peroxymonocarbonate in decontamination technologies

Sodium percarbonate (SPC) and peroxymonocarbonate (PMC) have been widely used in modified Fenton reactions because of their multiple superior features, such as a wide pH range and environmental friendliness. This broad review is intended to provide the fundamental information, status and progress of SPC and PMC based decontamination technologies according to the peer-reviewed papers in the last two decades. Both SPC and PMC can directly decompose various pollutants. The degradation efficiency will be enhanced and the target contaminants will be expanded after the activation of SPC and PMC. The most commonly used catalysts for SPC activation are iron compounds while cobalt compositions are applied to activate PMC in homogenous and heterogeneous catalytical systems. The generation and participation of hydroxyl, superoxide and/or carbonate radicals are involved in the activated SPC and PMC system. The reductive radicals, such as carbon dioxide and hydroxyethyl radicals, can be generated when formic acid or methanol is added in the Fe(II)/SPC system, which can reduce target contaminants. SPC can also be activated by energy, tetraacetylethylenediamine, ozone and buffered alkaline to generate different reactive radicals for pollutant decomposition. The SPC and activated SPC have been assessed for application in-situ chemical oxidation and sludge dewatering treatment. The challenges and prospects of SPC and PMC based decontamination technologies are also addressed in the last section.

Magnetic Nanoparticle Composites: Synergistic Effects and Applications

Composite materials are made from two or more constituent materials with distinct physical or chemical properties that, when combined, produce a material with characteristics which are at least to some degree different from its individual components. Nanocomposite materials are composed of different materials of which at least one has nanoscale dimensions. Common types of nanocomposites consist of a combination of two different elements, with a nanoparticle that is linked to, or surrounded by, another organic or inorganic material, for example in a core-shell or heterostructure configuration. A general family of nanoparticle composites concerns the coating of a nanoscale material by a polymer, SiO2 or carbon. Other materials, such as graphene or graphene oxide (GO), are used as supports forming composites when nanoscale materials are deposited onto them. In this Review we focus on magnetic nanocomposites, describing their synthetic methods, physical properties and applications. Several types of nanocomposites are presented, according to their composition, morphology or surface functionalization. Their applications are largely due to the synergistic effects that appear thanks to the co-existence of two different materials and to their interface, resulting in properties often better than those of their single-phase components. Applications discussed concern magnetically separable catalysts, water treatment, diagnostics-sensing and biomedicine.

The performance of chlorobenzene degradation in groundwater: comparison of hydrogen peroxide, nanoscale calcium peroxide and sodium percarbonate activated with ferrous iron

The chlorobenzene (CB) degradation performances by various oxidants, including hydrogen peroxide (H₂O₂), nanoscale calcium peroxide (nCaO₂) and sodium percarbonate (SPC), activated with ferrous iron (Fe(II)) were investigated and thoroughly compared. The results showed that all tested systems had strong abilities to degrade CB. The CB removal rate increased with increasing dosages of oxidants or Fe(II) because the generation of reactive oxygen species could be promoted with the chemical dosages' increase. Response surface and contour plots showed that CB could achieve a better removal performance at the same H₂O₂ and Fe(II) molar content, but the Fe(II) dosage was higher than that of oxidants in the nCaO₂ and SPC systems. The optimal molar ratios of H₂O₂/Fe(II)/CB, nCaO₂/Fe(II)/CB and SPC /Fe(II)/CB were 5.2/7.6/1, 8/8/1, and 4.5/8/1, respectively, in which 98.1%, 98%, and 96.4% CB removals could be obtained in 30 min reaction. The optimal pH condition was around 3, while CB removal rates were less than 20% in all three systems when the initial pH was adjusted to 9. The oxidative hydroxyl radicals (HO•) and singlet oxygen (¹O₂) had been detected by the electron paramagnetic resonance test. Based upon the results of liquid chromatograph-mass spectrometer analysis, the pathways of CB degradation were proposed, in which ¹O₂ roles were elaborated innovatively in the CB degradation mechanism. The CB degradation performance was significantly affected in actual groundwater, while increasing the molar ratio of oxidant/Fe(II)/CB was an effective way to overcome the adverse effects caused by the complex of actual groundwater matrix.

Biochar derived from red algae for efficient remediation of 4-nonylphenol from marine sediments

4-Nonylphenol (4-NP), a phenolic endocrine disruptor chemical (EDC), is known to have high toxicity to aquatic organisms and humans. The remediation of 4-NP-contaminated marine sediments was studied using red algae-based biochar (RAB) thermochemically synthesized from Agardhiella subulata with simple pyrolysis process under different temperatures of 300-900 °C in CO₂ atmosphere. The RAB was characterized by XRD, Raman, FTIR spectroscopy, and zeta potential measurements. The calcium in RAB efficiently activated sodium percarbonate (SPC) to generate reactive radicals for the catalytic degradation of 4-NP at pH 9.0. The oxygen-containing functional groups reacted with H₂O₂, which increased the generation of reactive radicals under alkaline pH condition. Ca²⁺ ion was the active species responsible for 4-NP degradation. CaO/CaCO₃ on RAB surface enhanced direct electron transfer, increased HO production, and 4-NP degradation in marine sediments. Langmuir‒Hinshelwood type kinetics well described the 4-NP degradation process. Remediation of contaminated sediments using RAB could be a sustainable approach toward closed-loop biomass cycling in the degradation of 4-NP contaminants.

High Degradation of Trichloroethylene in Water by Nanostructured MeNPs@CALB Biohybrid Catalysts

In this study, a methodology was developed for the rapid degradation of trichloroethylene (TCE) and 1,1-dichloroethylene (1,1-DCE) in distilled water and room temperature without the production of toxic chlorinated by-products. This process was carried out using bionanohybrids of different metals (Pd, Fe, Cu and Zn) obtained by enzyme–metal coordination called MeNPs@CALB, which present different metal species and nanoparticle sizes. The Cu2O@CALB biohybrid, which contained Cu2O nanoparticles, showed excellent catalytic performance in TCE degradation by removing 95% (>125 ppm) in 10 min using 1.5 g/L of catalyst. On the other hand, in the degradation reaction of 1,1-DCE, Cu2O@CALB eliminated 94% (93 ppm) in 1 min. Cu2O@CALB exhibited excellent stability and recyclability under sustainable conditions, maintaining its effectiveness in more than 90% for three cycles.

Enhanced removal of tetrachloroethylene from aqueous solutions by biodegradation coupled with nZVI modified by layered double hydroxide

Chlorinated volatile organic compounds, such as tetrachloroethylene (PCE), are the most commonly detected toxic contaminants in groundwater. In this study, the performance of PCE removal by a microbial consortium combined with nZVI modified by layered double hydroxide (nZVI-LDH) was evaluated. The enriched PCE-degrading consortium consisted of 44.49% Clostridium and other potential PCE degraders, and 0.5-2.5 mg/L PCE was completely biodegraded within 4 days. The characterization of nZVI-LDH indicated that LDH was coated on the surfaces of nZVI particles with an increased surface area. The PCE removal kinetics by nZVI-LDH was well described by a second-order model, and the removal rate constant of nZVI-LDH was 0.12 L h/mg, higher than that of native nZVI (0.02 L h/mg). Interestingly, the presence of Cu²⁺ improved the removal efficiency of PCE by nZVI-LDH, owing to its role as a catalyst or medium for charge transfer during reduction. Removal of PCE was enhanced by coupling the PCE-degrading consortium and nZVI-LDH. The initial removal of PCE was mainly dominated by the abiotic degradation and adsorption of nZVI-LDH, and biodegradation then played a major role in the exhaustion of nZVI-LDH. These results suggest that biodegradation coupled with nZVI-LDH has a great potential for applications in the remediation of chlorinated-solvent contaminated groundwater.

Percarbonate promoted antibiotic decomposition in dielectric barrier discharge plasma

A coupling technique introducing sodium percarbonate (SPC) into a dielectric barrier discharge (DBD) plasma was investigated to enhance the degradation of antibiotic tetracycline (TC) in aqueous. The dominant effects of SPC addition amount and discharge voltage were evaluated firstly. The experiments indicated that the moderate SPC dosages in the DBD presented an obvious synergistic effect, improving the TC decomposition efficiency and kinetics. Elevating the voltage was conducive for the promotion of antibiotic abatement. After 5 min treatment, the removal reached 94.3% at the SPC of 52.0 μmol/L and voltage of 4.8 kV for 20 mg/L TC. Especially the defined synergy factors were greater than one since the SPC being added, and the energy yield was increased by 155%. Besides, the function mechanism was explained by the hydrogen peroxide and ozone quantitative determinations and radical scavenger test, and the results confirmed that the collaborative method could increase the generation of reactive species, and the produced hydroxyl and superoxide radicals both played the significant roles for the TC elimination. Furthermore, the decomposition and mineralization of the synergism were verified by UV-vis spectroscopy, TOC and COD analyses, and the degradation byproducts and transformation pathways were identified based on the analysis of HPLC-MS finally.

The impact of surface properties and dominant ions on the effectiveness of G-nZVI heterogeneous catalyst for environmental remediation

The surface properties of nanocomposites are influenced by the existence of inorganic species that may affect its performance for specific catalytic applications. The impact of different ionic species on particular catalytic activity had not been investigated to date. In this study, the surface charge (zeta potential) of graphene-oxide-supported nano zero valent iron (G-nZVI) was tested in definitive cationic (Na⁺, K⁺, Ca²⁺ and Mg²⁺) and anionic (Br^-, Cl^-, NO₃^-, SO₄^2-, and HCO₃^-) environments. The efficiency of G-nZVI catalyst was inspected by measuring the generation of reactive oxygen species (ROS) for the degradation of 1,1,1-trichloroethane (TCA) in sodium percarbonate (SPC) system. Tests conducted using probe compounds confirmed the generation of OH and O₂^- radicals in the system. In addition, the experiments performed using scavenging agents certified that O₂^- were primary radicals responsible for TCA removal, along with prominent contribution from OH radicals. The study confirmed that G-nZVI catalytic capability for TCA degradation is notably affected by various cationic species. The presence of Ni²⁺ and Cu²⁺ significantly enhanced (94%), whereas Na⁺ and K⁺ had minor effects on TCA removal. Overall, the results indicated that groundwater ionic composition may have low impact on the effectiveness of G-nZVI-catalyzed peroxide TCA treatment.

Particles and porous tablets based on Fe0/ZSM-5 composites prepared by ball-milling for heavy metals removal: Dissolved Fe2+, pH, and mechanism

Novel, low-cost Fe⁰/ZSM-5-based particles and porous tablets were prepared by a ball-milling method and used for the removal of Pb²⁺ in solution. Solid-phase characterization by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS) and transmission electron microscopy (TEM) revealed that the Fe⁰ microparticles were evenly loaded and tightly immobilized on the surface of ZSM-5 because of the extrusion/welding impact during ball-milling. For different Pb²⁺ concentrations, batch experiments indicated that the removal of Pb²⁺ increased with the decline of dissolved Fe²⁺ and pH value in the solution for particles; opposite results were obtained for the tablets. The differences in the contact between both materials and Pb²⁺ were the main factor controlling Pb²⁺ removal in the solution. Investigation into the effect of initial pH value revealed that high pH reduced the number of electrons released from Fe corrosion. Consequently, low levels of removed Pb²⁺ and dissolved Fe²⁺ were synchronously observed. Also, simulated electroplating wastewater was treated using the prepared particles and porous tablets, and the removal order of Pb²⁺>Cr⁶⁺>Cu²⁺≈Cd²⁺ was observed. The Fe⁰/ZSM-5 particles and tablets prepared through ball-milling show potential as materials for treatment of Pb²⁺ and other toxic metals.

Enhanced Catalytic Dechlorination of 1,2-Dichlorobenzene Using Ni/Pd Bimetallic Nanoparticles Prepared by a Pulsed Laser Ablation in Liquid

Bimetallic nanoparticles (NPs) exhibit advantageous electrical, optical, and catalytic properties. Among the various NP synthesis methods, pulsed laser ablation in liquid (PLAL) is currently attracting much attention because of its simplicity and versatility. In this study, a pulsed laser was used to produce nickel/palladium (Ni/Pd) bimetallic NPs in methanol and deionized water. The morphological and optical properties of the resulting Ni/Pd bimetallic NPs were characterized. The synthesized Ni/Pd bimetallic NPs were used for the dechlorination of 1,2-dichlorobenzene (1,2-DCB) under various conditions. The dechlorination rates of 1,2-DCB while using single (Ni and Pd) and bimetallic (Ni powder/Pd and Ni/Pd) NPs were investigated. The results showed that the Ni/Pd bimetallic NPs with 19.16 wt.% Pd exhibited much enhanced degradation efficiency for 1,2-DCB (100% degradation after 30 min). Accordingly, the results of enhanced the degradation of 1,2-DCB provide plausible mechanism insights into the catalytic reaction.

Process optimization on methyl orange discoloration in Fe3O4/RGO-H2O2 Fenton-like system

The development of a catalyst with high catalytic activity was one of the most important issues for the heterogeneous Fenton-like process. In this study, nanocomposites of Fe₃O₄ anchored onto reduced graphene oxide (RGO) were prepared by a moderate alkaline-thermal precipitation method and developed as highly efficient heterogeneous Fenton-like catalysts. The characterization results indicated that Fe₃O₄ nanoparticles (NPs) were tightly anchored onto few-layer RGO sheets via a strong interaction. Contrast experiments showed that Fe₃O₄/RGO nanocomposites had much better Fenton-like catalytic activity than Fe₃O₄ NPs. The process optimization of methyl orange (MO) discoloration in Fe₃O₄/RGO-H₂O₂ system was accomplished by central composite design under response surface methodology. A second-order polynomial model was established to predict the optimal values of MO discoloration and its significance was evaluated by analysis of variance. Three-dimensional response surfaces for the interaction between two variables were constructed. Based on the model prediction, the optimum conditions for MO discoloration in Fe₃O₄/RGO-H₂O₂ system were 2.9 for solution pH, 16.5 mM H₂O₂ concentration, 2.5 g/L catalyst dosage and 33.5 min of reaction time, with the maximum predicted value for MO discoloration ratio of 99.98%.

Degradation of trichloroethylene in aqueous solution by rGO supported nZVI catalyst under several oxic environments

The reduced graphene oxide (rGO) supported nano zero-valent iron (nZVI) (nZVI-rGO) was synthesized successfully and applied in the several oxic environments to remove trichloroethylene (TCE). The nZVI-rGO had a better catalytic performance than bare nZVI for the TCE removal. Both aggregation of nZVI and agglomeration of rGO were in part prevented by loading the nZVI nanoparticles on the rGO sheet. Among all the oxic environments, the better removal of TCE was followed as the order of PMS > SPS > H₂O₂. Chemical scavenger tests were carried out to identify the reactive oxygen species (ROSs) generated in the removal of TCE, showing that in PMS and SPS systems, SO₄^- and HO were main radicals responsible for TCE removal, while HO and O₂^- were main radicals in H₂O₂ system. The possible mechanisms were proposed with nZVI-rGO under several oxic environments. The recyclability of nZVI-rGO, dechlorination and mineralization of TCE were investigated. These fundamental data confirmed the effectiveness of nZVI-rGO to remove TCE and could help selecting the suitable oxidants to use with nZVI-rGO in the actual field groundwater remediation.

Efficient transformation in characteristics of cations supported-reduced graphene oxide nanocomposites for the destruction of trichloroethane

Experiments were conducted to investigate the use of graphene-oxide supported metallic nanocomposites for improving the degradation of trichloroethane (TCA) by sodium percarbonate (SPC). Two methods of production, chemical reduction (CR) and solvo-thermal (ST), were tested for preparation of single (Fe) and binary (Fe-Cu) nanocomposites supported by reduced graphene oxide (rGO). A variety of analytical techniques including N2 adsorption Brunauer-Emmett-Teller (BET), x-ray diffraction (XRD), fourier-transfrom infrared spectroscopy (FTIR), and transmisison electron microscopy (TEM) were applied to characterize the physicochemical and microstructural properties of the synthesized nanocomposites. The characterization indicated that the CR method produced nanocomposites that comprised only mesoporous structure. Conversely, both micro and mesoporous structures were present for samples produced with the ST method. The synthesized single and bimetallic composites produced from the ST method showed higher surface areas, i.e. 93.6 m²/g and 119.2 m²/g as compared to the ones synthesized via the CR method, i.e. 13.8 m²/g and 38.0 m²/g respectively. The results of FTIR and XRD analyses confirmed that the ST method produced highly crystalline nanocomposites. SEM and TEM analysis validated that metallic particles with definite morphology well distributed on the surface of rGO. X-ray photoelectron spectroscopy (XPS) analysis confirmed the homogeneity nanocomposites and occurrence of variation in copper oxidation states during degradation process. EDS mapping validate the homogeneous distribution of Cu and Fe at reduced graphene oxide surface. The Fe-Cu/rGO (ST) activated SPC system effectively degraded TCA (92%) in 2.5 h at low nanocomposite dose compared to the Fe-Cu/rGO (CR) and only Fe, for which the maximum degradation efficiencies achieved were 81% and 34%. In conclusion, excellent catalytic characteristics were observed for the ST-synthesized single and bimetallic (Fe/rGO, Fe-Cu/rGO) catalysts. These catalysts were successful in improving the degradation of TCA via activated SPC.