Activation of persulfate by stability-enhanced magnetic graphene oxide for the removal of 2,4-dichlorophenol

Research progress of persulfate activation technology

Persulfate-based advanced oxidation processes (PS-AOPs) have been widely investigated by academia and industry due to their high efficiency and selectivity for the removal of trace organic pollutants from complex water substrates. PS-AOPs have been extensively studied for the degradation of pesticides, drugs, halogen compounds, dyes, and other pollutants. Utilizing bibliometric statistics, this review presents a comprehensive overview of persulfate-based advanced oxidation technology research over the past decade. The number of published articles about persulfate activation has steadily increased during this time, reflecting extensive international collaboration. Furthermore, this review introduces the most widely employed strategies for persulfate activation reported in the past 10 years, including carbon material activation, photocatalysis, transition metal activation, electrochemical activation, ultrasonic activation, thermal activation, and alkali activation. Next, the potential activation mechanisms and influencing factors, such as persulfate dosage during activation, are discussed. Finally, the application of PS-AOPs in wastewater treatment and in situ groundwater treatment is examined. This review summarizes the previously reported experiences of persulfate-based advanced oxidation technology and presents the current application status of PS-AOPs in organic pollution removal, with the aim of avoiding misunderstandings and providing a solid foundation for future research on the removal of organic pollutants.

Synthesis of Acid Mine Drainage (AMD) Sludge-Derived Al-Fe3O4 as Fenton-like Catalysts for the Efficient Degradation of Tetracycline

In recent years, the development of environmentally friendly solid catalysts derived from sludge for the efficient removal of pollutants from wastewater has triggered widespread attention. Acid mine drainage (AMD) sludge is a waste produced in the process of acid mine wastewater treatment and contains multitudes of valuable metal resources. Hence it provides the original conditions for the synthesis of metal-based Fenton catalysts. In this article, the Fenton-like catalyst Al-Fe3O4 derived from AMD sludge was first synthesized by acid leaching coprecipitation methods, and the relationship among catalyst properties and pH, growth temperature, and growth time during coprecipitation was explored. Transmission electron microscope (TEM)/vibrating sample magnetometer (VSM)/particulate size description analyzer (DLS) results showed that the Al-Fe3O4 catalyst with high purity, large particle size, and strong magnetic properties was obtained under the conditions of pH 10, reaction temperature 60 °C, and growth for 45 min. In addition, the introduction of Al active sites promoted the activation of H2O2 and improved the catalytic activity of Al-Fe3O4, and the degradation efficiency of tetracycline was up to 93.9% within 60 min, which was 1.94 times that of pure Fe3O4. Moreover, Al-Fe3O4 exhibited excellent recyclability after four adsorption-desorption cycles. Hence, this study is expected to promote the resource utilization of industrial sludge and provide a new idea for the rapid removal of TC from aqueous solution.

The reaction pathway and mechanism of 2,4-dichlorophenol removal by modified fly ash-loaded nZVI/Ni particles

Nanoscale zero-valent iron (nZVI) is more valuable in environmental restoration than other materials. Chemical treatment of fly ash (CFA) was employed as a support material to disperse iron nickel bimetal nanoparticles (CFA-nZVI/Ni) to remove 2,4-dichlorophenol (2,4-DCP). Batch experiments showed that 2,4-DCP was completely removed by CFA-nZVI/Ni, and an optimal loading ratio was 8:1. The degradation of 2,4-DCP by CFA-nZVI/Ni was a chemical control reaction with an activation energy of 95.6 kJ mol^-1 and followed pseudo-first-order kinetics. The addition of Cl^- increased the removal rate of 2,4-DCP by 4%, while the addition of CO₃^2- and SO₄^2- decreased the removal rate of 2,4-DCP by 32% and 72.3%, respectively. The removal process of 2,4-DCP by CFA-nZVI/Ni included adsorption and reduction. The 2-CP (7.1 mg/L) and 4-CP (11.6 mg/L) could be converted to phenol using the CFA-nZVI/Ni system. Cl on the para-position of 2,4-DCP was simpler to remove than on the ortho-position. The following steps were taken in the electrophilic substitution reaction between substituted phenols and hydrogen radicals: 2,4-DCP > 2-CP > 4-CP > phenol. This research provides a novel concept to effectively remove 2,4-DCP and mechanism analysis.

Magnetic Nanocomposites for the Remote Activation of Sulfate Radicals for the Removal of Rhodamine B

The widespread presence of numerous organic contaminants in water poses a threat to the ecological environment and human health. Magnetic nanocomposites exposed to an alternating magnetic field (AMF) have a unique ability for magnetically mediated energy delivery (MagMED) resulting from the embedded magnetic nanoparticles; this localized energy delivery and associated chemical and thermal effects are a potential method for removing contaminants from water. This work developed a novel magnetic nanocomposite-a polyacrylamide-based hydrogel loaded with iron oxide nanoparticles. For this magnetic nanocomposite, persulfate activation and the contamination removal in water were investigated. Magnetic nanocomposites were exposed to AMF with a model organic contaminant, rhodamine B (RhB) dye, with or without sodium persulfate (SPS). The removal of RhB by the nanocomposite without SPS as a sorbent was found to be proportional to the concentration of magnetic nanoparticles (MNPs) in the nanocomposite. With the addition of SPS, approximately 100% of RhB was removed within 20 min. This removal was attributed primarily to the activation of sulfate radicals, triggered by MNPs, and the localized heating resulted from the MNPs when exposed to AMF. This suggests that this magnetic nanocomposite and an AMF could be a unique environmental remediation technique for hazardous contaminants.

Application of pier waste sludge for catalytic activation of proxy-monosulfate and phenol elimination from a petrochemical wastewater

This investigation aimed to remove phenol from real wastewater (taken from a petrochemical company) by activating peroxy-monosulfate (PMS) using catalysts extracted from pier waste sludge. The physical and chemical properties of the catalyst were evaluated by FE-SEM/EDS, XRD, FTIR, and TGA/DTG tests. The functional groups of O-H, C-H, CO₃^2-, C-H, C-O, N-H, and C-N were identified on the catalyst surface. Also, the crystallinity of the catalyst before and after reaction with petrochemical wastewater was 103.4 nm and 55.8 nm, respectively. Operational parameters of pH (3-9), catalyst dose (0-100 mg/L), phenol concentration (50-250 mg/L), and PMS concentration (0-250 mg/L) were tested to remove phenol. The highest phenol removal rate (94%) was obtained at pH=3, catalyst dose of 80 mg/L, phenol concentration of 50 mg/L, PMS concentration of 150 mg/L, and contact time of 150 min. Phenol decomposition in petrochemical wastewater followed the first-order kinetics (k> 0.008 min^-1, R²> 0.94). Changes in pH factor were very effective on phenol removal efficiency, and maximum efficiency (≈83%) was achieved in pH 3. The catalyst stability test was performed for up to five cycles, and phenol removal in the fifth cycle was reduced to 42%. Also, the energy consumption in this study was 77.69 kW h/m³. According to the results, the pier waste sludge catalyst/PMS system is a critical process for eliminating phenol from petrochemical wastewater.

High surface area acid-treated biochar from pomegranate husk for 2,4-dichlorophenol adsorption from aqueous solution

In the present study, zinc chloride (ZnCl₂) followed by acid treating was employed for the fabrication of activated biochar from pomegranate husk (APHBC) for 2,4-dichlorophenol (2,4-DCP) adsorption from an aqueous solution. The batch adsorption experiments were carried out as a function of solution pH, APHBC dose, initial 2,4-DCP concentration, contact time, and ionic strength. The APHBC showed a well-developed pore with specific surface areas of 1576 m²/g due to explosive characteristics of ZnCl₂. In addition, the XRD analysis showed that the diffraction peaks between 15 and 35° corresponded to amorphous carbon. The pore size distribution results showed that APHBC was dominantly mesoporous materials. The pH_pzc value of APHBC was 6.15 ± 0.15. According to batch experiments, the optimum adsorption conditions were pH of 3.0, contact time 60 min, APHBC dose of 1.75 g/L and without ionic strengths. The absorption capacity of 2,4-DCP at the initial concentration of 150.0 mg/L promptly decreased from 259.5 ± 12.9 to 74.5 ± 3.7 mg/g as the APHBC dose increased from 0.50 to 2.00 g/L. The isotherm and kinetics study of 2,4-DCP adsorption by APHBC revealed that Liu and Avrami fractional-order well fitted with experimental data, respectively.

Application of sulfate radicals-based advanced oxidation technology in degradation of trace organic contaminants (TrOCs): Recent advances and prospects

The large amount of trace organic contaminants (TrOCs) in wastewater has caused serious impacts on human health. In the past few years, Sulfate radical (SO₄^•-) based advanced oxidation processes (SR-AOPs) are widely recognized for their high removal rates of recalcitrant TrOCs from water. Peroxymonosulfate (PMS) and persulfate (PS) are stable and non-toxic strong oxidizing oxidants and can act as excellent SO₄^•- precursors. Compared with hydroxyl radicals(·OH)-based methods, SR-AOPs have a series of advantages, such as long half-life and wide pH range, the oxidation capacity of SO₄^•- approaches or even exceeds that of ·OH under suitable conditions. In this review, we present the progress of activating PS/PMS to remove TrOCs by different methods. These methods include activation by transition metal, ultrasound, UV, etc. Possible activation mechanisms and influencing factors such as pH during the activation are discussed. Finally, future activation studies of PS/PMS are summarized and prospected. This review summarizes previous experiences and presents the current status of SR-AOPs application for TrOCs removal. Misconceptions in research are avoided and a research basis for the removal of TrOCs is provided.

Carbon materials in persulfate-based advanced oxidation processes: The roles and construction of active sites

Many researchers have paid more attention to the progress of carbon materials owing to their advantages, such as high activity, low cost, large surface area, high conductivity and high stability. Carbon materials have been widely used in persulfate-based advanced oxidation processes (PS-AOPs), especially for graphene (G), carbon nanotubes (CNTs) and biochar (BC). Various strategies are applied to promote their activity, however, up to now, the relationship between the structures of carbon materials and their activities in PS-AOPs has not been specifically reviewed. The methods to switch reaction pathway (radical and nonradical pathways) in carbon-persulfate-based AOPs have not been systematically explored. Hereon, this review illustrated the active sites of G, CNTs, BC and other carbon materials, and generalized the modification methods to promote the activity of carbon materials and to switch reaction pathway in PS-AOPs. The roles of carbon materials in PS-AOPs were discussed around reactive oxygen species (ROS) and the structures. ROS are frequently complex in AOPs, but main ROS generation is related to the active sites on carbon materials. The structures of carbon materials (e.g., metal-carbon bonds, the electron-deficient C atoms, unbalanced electron distribution and graphitized structures) play a decisive role in the nonradical pathway. Finally, future breakthroughs of carbon materials were proposed for practical engineering and multi-field application.

Magnetized Activated Carbon Synthesized from Pomegranate Husk for Persulfate Activation and Degradation of 4-Chlorophenol from Wastewater

The compound 4-chlorophenol (4-CP) is known to be a highly toxic compound having harmful effects on human health and the environment. To date, the removal of 4-CP by advanced oxidation processes (AOPs) has attracted tremendous attentions. The persulfate-based AOPs show higher oxidation, better selectivity, wider pH range, and no secondary pollution compared to the traditional Fenton-based AOPs. Carbon materials with low cost and chemical stability are useful for the activation of persulfate (PS) to produce reactive species. Herein, we magnetized activated carbon synthesized from pomegranate husk (MPHAC). By using 4-CP as a model organic pollutant, tests of the activation of PS via MPHAC for the removal of 4-CP were performed. Batch processes were carried out to study the influence of different parameters (initial solution pH, catalyst dose, PS dose, and initial 4-CP concentration) on the adsorption of 4-CP on PHAC with ferric oxide (Fe3O4-PHAC). The results show that under the obtained optimal conditions (MPHAC dose: 1250 mg/L, PS dose: 350 mg/L, solution pH 5, an initial 4-CP concentration of 100 mg/L, and a contact time of 60 min), a 4-CP removal factor of 99.5% was reached by the developed MPHAC/PS system. In addition, it was found that reusing MPHAC in five successive cycles is feasible because the catalyst in the last cycle kept exhibiting a high potential for 4-CP absorption, indicating the economically viable procedure. Therefore, this study provides a comprehensive understanding on the degradation of 4-CP by the magnetized activated carbon persulfate system.

Facile synthesis of Fe-modified lignin-based biochar for ultra-fast adsorption of methylene blue: Selective adsorption and mechanism studies

A novel Fe-modified lignin-based biochar (Fe-LB) was fabricated via a facile one-step carbonization method for methylene blue (MB) removal from wastewater. Fe-LB exhibited a high specific surface area (885.97 m²/g) and micropore volume (0.3203 m³/g), and demonstrated high affinity for MB with the maximum adsorption capacity of 2.7-fold by Fe-LB than LB. It was found that quick adsorption could be achieved in 15 min with the MB removal efficiency of 100% and adsorption capacity reached 200 mg/g. Selective adsorption studies indicated that Fe-LB preferentially adsorbed MB in high salt and multiple dye systems (binary, ternary, and quaternary) over a wide pH range from 2 to 12. The removal efficiency of CR was greatly improved due to the synergistic effect between MB and CR in the binary system. This work demonstrated that Fe-LB can effectively remove dye contaminants and possessed great potential in the treatment of MB polluted dye wastewater.

Phenol removal kinetics from synthetic wastewater by activation of persulfate using a catalyst generated from shipping ports sludge

Disposal sludges from shipping docks contain elements that have the potential to catalyze the desired treatment process. The current work was designed to decompose phenol from wastewater by activation peroxymonosulfate (PMS) using a catalyst made from sea sediments (at 400 °C for 3 h). The catalyst had a crystalline form and contained metal oxides. The parameters of pH (3-9), catalyst dose (0-80 mg/L), phenol concentration (50-250 mg/L), and PMS dose (0-250 mg/L) were tested to specify the favorable phenol removal. The phenol removal of 99% in the waste sludge catalyst/PMS system was achieved at pH 5, catalyst quantity of 30 mg/L, phenol content of 50 mg/L, PMS dose of 150 mg/L, and reaction time of 150 min. From the results, it was implied that the pH factor was more important in removing phenol with the studied system than other factors. By-products and phenol decomposition pathways were also provided. The results showed that the sea sediment catalyst/PMS system is a vital alternative for removing phenol from wastewater medium.

Influence of catalyst zeta potential on the activation of persulfate

The effect of the zeta potential of nano zero-valent iron (nZVI) and carbocatalyst on the activation of persulfate was investigated. The oxidation experiments were performed on three different compounds, with variously modified nZVI and three distinct carbocatalysts. From the obtained results, an evident linear correlation between nanoparticles' zeta potential and reaction rate constants of these three compounds oxidation may be observed. This phenomenon is not mechanism-specific and occurs for the radical and non-radical processes. The present work indicates the critical influence of the surface charge of nZVI and carbocatalysts on the persulfate catalytic activation.

Efficient removal of bisphenol S by non-radical activation of peroxydisulfate in the presence of nano-graphite

An environmentally friendly and efficient catalyst is important for the persulfate activation and pollutants removal from water. In this study, nano-graphite (NG) prepared by detonation method, was firstly applied as the superb carbon catalyst to activate peroxydisulfate (PDS) for the degradation of bisphenol S (BPS) via a non-radical pathway. Results showed that NG had a very high catalytic performance and degraded most of BPS within 20.0 min, out-performing many popular metal-based catalysts. The doped N atoms (i.e. graphitic N and pyridinic N) in NG were identified as the possible reactive sites for the PDS activation. It is proposed that PDS could form the metastable surface-bound PDS complexes on the NG surface, which promoted the BPS degradation. The NG/PDS system had a strong anti-interference ability for the environmental background substances and a wide operative pH range, so it had a good application prospect in the actual wastewater environment. This study not only provides an efficient method for the removal of bisphenol pollutants, but also deepens the insight into the reaction mechanisms.

In-situ synthesis of CuS@carbon nanocomposites and application in enhanced photo-fenton degradation of 2,4-DCP

Novel CuS nanoparticles embedded into carbon nanosheets (CuS@CNs) were prepared in situ by applying wheat straw cellulose/feather protein hydrogel beads as templates and were used to photocatalytically activate H₂O₂ to degrade 2,4-dichlorphenol (2,4-DCP). The photo-Fenton catalytic properties of the nanocomposite catalysts obtained under different synthetic conditions, including different Cu²⁺ concentrations, S^2- concentrations and calcination temperatures, were evaluated. The results showed that CuS@CNs with 0.1 M Cu²⁺, 0.1 M S^2- at 800 °C presented excellent photo-Fenton degradation performance for 2,4-DCP (25 mg/L) in the presence of H₂O₂ and could remove 90% of 2,4-DCP in 2.5 h. The water quality parameters (pH, Cl^-, HCO₃^-, H₂PO₄^- and SO₄^2-) exhibited different effects on the photocatalytic degradation process. The catalytic activity of the CuS@CNs used in the cycle could be recovered after thermal regeneration. Radical quenching and electron paramagnetic resonance (EPR) experiments confirmed that ·OH species were main active radicals contributing to the degradation of 2,4-DCP. The photocatalytic mechanism of CuS@CNs was also explored by photoelectrochemical (PEC) measurements and UV-vis diffuse reflectance spectroscopy (DRS). Incorporation of carbon nanosheets could significantly improve the separation of photogenerated charge carriers to stimulate pollutant degradation by CuS. Based on the detected intermediates, the degradation pathway of 2,4-DCP in the CuS@CNs/H₂O₂ reaction system was also proposed.

Activation of inorganic peroxides with magnetic graphene for the removal of antibiotics from wastewater

Magnetic graphene catalysts were prepared for the removal of antibiotics (sulfamethoxazole, norfloxacin, tetracycline and flumequine) from water. Different proportions of magnetite-graphene from 1:0 to 0:1 were considered to study the catalytic activation of inorganic peroxides, i.e. peroxymonosulfate (PMS), peroxydisulfate and hydrogen peroxide. The presence of graphene was mainly responsible for the activation, which was most effective in the presence of PMS. A ratio of 20% of magnetite in the solid was enough to achieve complete degradation of antibiotics with high recovery by application of a magnetic field. The performance of the catalyst was further evaluated in a simulated urban wastewater, studying the main parameters affecting the process and the stability in sequential reuses. The non-radical mechanism during the catalytic activation of PMS was hypothesized from kinetic scavenging probes tests. The electron transfer was suggested as the mechanism of the reaction from electron paramagnetic resonance analysis in the presence of D₂O. The prepared magnetic catalyst showed high catalytic activity and stability to remove antibiotics from water.

Sulfate radical-based oxidation of an alcohol ethoxylate (Brij30®) by the PS/UV-C process

In this study, sulfate radical-based oxidation of an alcohol ethoxylate (AE) was explored by the persulfate (PS)/UV-C process. Poly(oxyethylene)(4)laurylether, commercially known as Brij30^®, was used as a model AE. PS/UV-C oxidation of aqueous Brij30^® (8-20 mg/L) was performed at initial PS concentrations varying between 0.50 and 6.50 mM and at initial pH values of 3.0 and 6.0. Results indicated that an increase in both initial PS and Brij30^® concentrations did not have a significant effect on Brij30^® removal efficiency and that Brij30^® abatements of more than 90% could be achieved after 60 min of treatment time. Total organic carbon (TOC) removals were significantly improved with increasing initial PS concentrations for both initial pH values. On the other hand, an increase in initial Brij30^® concentration had a negative effect on mineralization. By employing the competitive kinetic method, the second-order reaction rate coefficient of Brij30^® with the sulfate radical (SO₄ ^•-) was determined as 1.62 × 10⁹ ± 3.5 × 10⁷ M^-1s^-1. The second-order reaction rate constant of TOC, originating from Brij30^® and reaction intermediates, was found to be 9.09 × 10⁵ ± 2.91 × 10⁵ M^-1s^-1 and 1.13 × 10⁶ ± 0.46 × 10⁶ M^-1s^-1 for pH values of 6.0 and 3.0, respectively. Toxicity of PS/UV-C treated aqueous Brij30^® solutions towards Vibrio fischeri was also investigated to determine the possible toxic behavior of oxidation products.