Ultrasound-assisted heterogeneous peroxymonosulfate activation with Co/SBA-15 for the efficient degradation of organic contaminant in water

Recent advances in mechanistic insights into microplastics mitigation strategies via emerging advanced oxidation processes: Legislation, challenges, and future direction

Microplastics (MPs) pollution has emerged as a global environmental concern due to its detrimental impacts on ecosystems. Conventional wastewater/water treatment methods are inadequate for MPs removal due to their diminutive size ranging from micrometers to nanometers. Advanced oxidation processes (AOPs) have gained attention as a promising green strategy for the efficient and safe elimination of MPs from aqueous systems. In recent years, various AOPs, including direct photo-degradation, photocatalytic oxidation, electrochemical oxidation, sono-chemical oxidation, ozonation, as well as sulfate radicals-based AOPs (SR-AOPs), and the use of hybrid systems have all been extensively investigated for MP elimination. However, the molecular mechanisms of MP polymer chain scission by AOPs have not been thoroughly studied so far. In this review, we have attempted to provide a thorough overview of molecular mechanisms and highlighted recent advances in the degradation of commonly used MP by AOPs. The characteristics and limitations of each technique are thoroughly examined. Additionally, current policies and legislation on plastic pollution are discussed, emphasizing the need for regulatory frameworks to support effective MPs mitigation strategies. To advance the practical application of AOPs for MPs removal, future research direction should address the transition from controlled laboratory environments to complex field conditions, assess the sustainability of AOPs in terms of catalytic material design, selection of effective oxidants, power consumption, and operational costs. Given these challenges, recommendations for future research directions are proposed based on knowledge gaps in the reported literature. This review could offer a coherent summary of the molecular mechanisms involved in different MP elimination techniques, aiding in the advancement of more dependable AOPs technology with superior removal and degradation efficiency.

Degradation mechanism and toxicity assessment of clofibric acid by Fe2+/PS process in saline pharmaceutical wastewater

A considerable effort has been made to exploring the oxidation of clofibric acid (CA) in advanced oxidation processes (AOPs). However, few studies are available on degradation mechanism and toxicity assessment of CA in saline pharmaceutical wastewater. Here the effect of chlorine on the degradation kinetics of CA by Fe2+/ persulfate (PS) process were studied. Oxidation efficiency, mineralisation, intermediate by-products, reactive oxygen species (ROS) and toxicity assessment were examined. Notably, a high removal efficiency (70.91%) but low mineralisation (20.99%) of CA were observed at pH 3.0 during the Fe2+/PS system. Furthermore, we found Cl- exerted a beneficial impact on CA degradation. However, the degree of CA mineralisation was relatively minor. Under high salinity (100 mM) condition, the primary reactive species within the Fe2+/PS system were SO 4 ⋅ - , OH·, Cl2/HClO, and Fe(IV). Several undesirable chlorinated by-products were formed. A reasonable degradation pathway was proposed. According to the ecological structure-activity relationship (ECOSAR) programme, some transformation products exhibited higher toxicity levels than CA itself in both acute and chronic toxicity assessment, especially in high-salinity environments. These findings elucidate an increased challenges and ecological risk for CA oxidation by Fe2+/PS treatment in saline pharmaceutical wastewater.

Construction of highly dispersed iron active sites for efficient catalytic ozonation of bisphenol A

The essential factor of catalytic ozonation technology relies on an efficient and stable catalyst. The construction of highly dispersed active sites on heterogeneous catalysts is an ideal strategy to combine the merits of homogeneous and heterogeneous catalysis with high activity and stability. Herein, an iron-containing mesoporous silica material (Fe-SBA15) with sufficient iron site exposure and enhanced intrinsic activity of active sites was employed to activate ozone for bisphenol A (BPA) degradation. Approximately 100% of BPA and 36.6% of total organic carbon (TOC) removal were realized by the Fe-SBA15 catalytic ozonation strategy with a reaction constant of 0.076 min-1, well beyond the performance of FeOx/SBA15 mixture and Fe2O3. Radical quenching experiments and electron paramagnetic resonance (EPR) analysis demonstrated that the hydroxyl radicals (HO•) and superoxide radicals (O2•-) played an important role in the degradation process. The iron sites with recyclable Fe(III)/Fe(II) pairs act as both the electron donors and active sites for catalytic ozonation. The mesoporous framework of SBA15 in Fe-SBA15 stabilizes the iron sites that enhance its stability. With high catalytic performance and high reusability for catalytic ozonation of BPA, the Fe-SBA15 is expected to be a promising catalyst in catalytic ozonation for wastewater treatment.

Iron (II) phthalocyanine loaded tourmaline efficiently activates PMS to degrade pharmaceutical contaminants under solar light

Iron (II) phthalocyanine (FePc) is loaded on the surface of the tourmaline (TM) by the reflow method to obtain FePc/TM. This research effectively prevents the π-π stacking of FePc, increased the effective utilization rate of PMS activation under solar light, and further improved the catalytic performance of the catalytic system. The catalytic oxidation efficiency of FePc/TM on carbamazepine (CBZ) and sulfadiazine (SD) can reach 99% under solar light for 15 and 5 min, the total organic carbon (TOC) removal rate can reach 58% and 69% under solar light for 120 min. After 6 cycles, the CBZ removal rate remained above 95%. In addition, the FePc/TM catalytic system has an excellent removal rate for other pharmaceuticals. The results of spin-trapped electron paramagnetic resonance and classical quenching experiments show that FePc/TM can effectively activate PMS to generate active species under solar light, including superoxide radical (•O2-), singlet oxygen (1O2), hydroxyl radicals(•OH), and sulphate radicals (SO4•-). The intermediates of CBZ were identified by Ultra-high performance liquid chromatography and high resolution mass spectrometry, and the degradation pathway was proposed. As the reaction progresses, all CBZ and intermediates are reduced and converted into small acids, or mineralized to H2O, CO2. This work provides an alternative method for the design of efficient activation of PMS activation catalysts under solar light to eliminate residual pharmaceuticals in actual water bodies.

Employ a Clay@TMSPDETA hybrid material as an adsorbent to remove textile dyes from wastewater effluents

A grafting of N1-(3-trimethoxysilylpropyl)diethylenetriamine (TMSPDETA) on natural clay was carried out to obtain an organic-inorganic hybrid clay material that was applied as an adsorbent to the uptake of Reactive Blue 19 (RB-19) and Reactive Green 19 (RG-19) dyes from aqueous wastewaters. This research demonstrates the effect of TMSPDETA contents on amino-functionalized clay materials' hydrophobic/hydrophilic behavior. The resultant material was utilized to uptake reactive dyes in aqueous solutions. The clay@TMSPDETA hybrid material was characterized by isotherm of adsorption and desorption of nitrogen, FTIR, elemental analysis, TGA, pHpzc, total acidity, total basicity groups, and hydrophilic balance. The hybrid samples were more hydrophilic than the pristine clay for ratios from 0.1 up to 0.5 due to adding amino groups to the pristine clay. FTIR spectra suggest that TMSPDETA was grafted onto the clay. The hybrid material presents a surface area 2.17-fold (42.7 m2/g) lower than pristine clay (92.7 m2/g). The total volume of pores of hybrid material was 0.0822 cm3/g, and the pristine clay material was 0.127 cm3/g, corresponding to a diminution of the total pore volume (Vtot) of 1.54 times. The kinetic data followed the pseudo-second-order (PSO) model for RB-19 and RG-19 reactive dyes. The equilibrium data were better fitted to the Liu isotherm model, displaying a Qmax as 178.8 and 361.1 mg g-1 for RB-19 and RG-19, respectively, at 20.0 °C. The main mechanism of interactions of the reactive dyes with the hybrid clay is electrostatic interaction. The clay@TMSPDETA has a very good effect on treating synthetic dye-textile wastewater. The removal percentage of simulated wastewater was up to 97.67% and 88.34% using distilled water and plastic industry wastewater as the solvents, respectively. The clay@TMSPDETA-0.1 could be recycled up to 5 cycles of adsorption and desorption of both dyes, attaining recoveries of 98.42% (RB-19) and 98.32% (RG-19) using 0.1 M HCl + 10% ethanol.

Enhanced organic pollutant removal in saline wastewater by a tripolyphosphate-Fe0/H2O2 system: Key role of tripolyphosphate and reactive oxygen species generation

The effects of tripolyphosphate (TPP) on organic pollutant degradation in saline wastewater using Fe⁰/H₂O₂ were systematically investigated to elucidate its mechanism and the main reactive oxygen species (ROS). Organic pollutant degradation was dependent on the Fe⁰ and H₂O₂ concentration, Fe⁰/TPP molar ratio, and pH value. The apparent rate constant (k_obs) of TPP-Fe⁰/H₂O₂ was 5.35 times higher than that of Fe⁰/H₂O₂ when orange II (OGII) and NaCl were used as the target pollutant and model salt, respectively. The electron paramagnetic resonance (EPR) and quenching test results showed that ^•OH, O₂^•-, and ¹O₂ participated in OGII removal, and the dominant ROS were influenced by the Fe⁰/TPP molar ratio. The presence of TPP accelerates Fe³⁺/Fe²⁺ recycling and forms Fe-TPP complexes, which ensures sufficient soluble Fe for H₂O₂ activation, prevents excessive Fe⁰ corrosion, and thereby inhibits Fe sludge formation. Additionally, TPP-Fe⁰/H₂O₂/NaCl maintained a performance similar to those of other saline systems and effectively removed various organic pollutants. The OGII degradation intermediates were identified using high-performance liquid chromatography-mass spectrometry (HPLC-MS) and density functional theory (DFT), and possible degradation pathways for OGII were proposed. These findings provide a facile and cost-effective Fe-based AOP method for removing organic pollutants from saline wastewater.

Immobilization CoOOH nanosheets on biochar for peroxymonosulfate activation: Built-in electric field mediated radical and non-radical pathways

The strong electron interaction between metal oxide-carbon-based catalyst components plays a vital role in the peroxymonosulfate (PMS) activation for pollutant degradation. Herein, a novel CoOOH nanosheets anchored on rape straw-derived biochar (BC) surface (labeled as CoOOH/BC) as an efficient PMS activator toward degrading sulfamethoxazole (SMX) was synthesized. Experimental results indicated that integrating CoOOH nanosheets on the BC surface could inhibit CoOOH aggregation to increase the specific surface areas, exert a component synergistic effect to enhance activation degradation activity, and improve the catalyst stability. As a result, a 96 % degradation efficiency of SMX was achieved within 20 min over 20 wt% CoOOH/BC composite catalyst under the optimal conditions. Density functional theory (DFT) calculations disclosed that a built-in electric field (BIEF) pointing from BC to CoOOH was constructed at their interface, which could mediate PMS activation for reactive oxygen species (ROS) generation and induce direct electron transfer from SMX to PMS, resulting in efficient SMX degradation via both radical and non-radical pathways. Moreover, quenching experiments and electron paramagnetic resonance (EPR) measurements confirmed that single oxide (¹O₂) and superoxide radical (O₂^·-) are the dominant active species in the current system. Additionally, the possible SMX degradation routes were reasonably proposed based on liquid chromatography-mass spectrometry (LC-MS) results. This work provides an in-depth understanding of the role of BIEF in PMS activation, and expands the application of biochar-based materials in the field of environmental remediation.

Bicarbonate enhanced heterogeneous activation of peroxymonosulfate by copper ferrite nanoparticles for the efficient degradation of refractory organic contaminants in water

Nowadays, the treatment of residual refractory organic contaminants (ROCs) is a huge challenge for environmental remediation. In this study, a potential process is provided by copper ferrite catalyst (CuFe₂O₄) activated peroxymonosulfate (PMS, HSO₅^-) in the bicarbonate (HCO₃^-) enhanced system for efficient removal of Acid Orange 7 (AO7), 2,4-dichlorophenol, phenol and methyl orange (MO) in water. The impact of key reaction parameters, water quality components, main reactive oxygen species (ROS), probable degradation mechanism, rational degradation pathways and catalyst stability were systematically investigated. A 95.0% AO7 (C₀ = 100 mg L^-1) removal was achieved at initial pH (pH₀) of 5.9 ± 0.1 (natural pH), CuFe₂O₄ dosage of 0.15 g L^-1, PMS concentration of 0.98 mM, HCO₃^- concentration of 2 mM, and reaction time of 30 min. Both sulfate radical (SO₄^-•) and hydroxyl radical (^•OH) on the surface of catalyst were proved as the predominant radical species through radical quenching experiments and electron paramagnetic resonance (EPR) analysis. The buffer nature of HCO₃^- was partially contributed for the enhanced degradation of AO7 under CuFe₂O₄/PMS/HCO₃^- system. Importantly, according to ¹³C nuclear magnetic resonance (NMR) and EPR analysis, the positive effect of bicarbonate may be mainly attributed to the formation of peroxymonocarbonate (HCO₄^-), which may enhance the generation of ^•OH. The magnetic CuFe₂O₄ particles can be well recycled and the leaching concentration of Cu was acceptable (<1 mg L^-1). Considering the widespread presence of bicarbonate in water environment, this work may provide a safe, efficient, and sustainable technique for the elimination of ROCs from practical complex wastewater.

Photoelectrocatalytic inactivation mechanism of E. coli DH5α (TET) and synergistic degradation of corresponding antibiotics in water

The occurrence and proliferation of antibiotic-resistance genes (ARGs) / antibiotic-resistant bacteria (ARB) have been currently aggravating due to the increase of antibiotic residues in the aquatic environment. The interaction of ARB/ARGs with antibiotics inevitably occurred during water purification, yet their synergistic purification mechanism remains unclear. Herein, a systematic approach was developed to understand, in-depth, the synergistic mechanism in the coexisted E. coli DH5α (TET) inactivation and tetracycline hydrochloride (TET) degradation using photoelectrocatalysis (PEC) as a model technology. Results showed that low dosage (0 - 40 ppm) of TET exerted a negative influence on ARB inactivation with prolonged bactericidal time from 60 to 160 min. Addition of TET in environmental concentration (5 - 60 ppm) resulted in sub-lethal damage and prolonged PEC treatment time (100 - 160 min), accounting for inhibition effects on ARB inactivation. The major reactive species (RSs) involved in ARB inactivation and TET degradation were evidenced as photogenerated hole, ^•OH and O₂^•-, whereas hole and O₂^•- were demonstrated to be the major disinfectants for ARB/ARG inactivation. The bacterial defense system displayed increased antioxidative activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) to protect ARB cells against oxidative stress. Exposure to 60 ppm TET was a threshold where certain ARB cells were induced into viable but nonculturable bacterial cell (VBNC) state, as evidenced by plate counting and ATP activity analysis, together with the integral cell membranes observed by flow cytometry (FCM) and scanning electron microscope (SEM). These findings appeal for appropriate technical adjustments for water and wastewater treatment to ensure safety of water.

Iron-based materials for simultaneous removal of heavy metal(loid)s and emerging organic contaminants from the aquatic environment: Recent advances and perspectives

The existence of heavy metals and emerging organic contaminants in wastewater produces serious toxic residues to the environment. Developing cheap and efficient materials to remove these persistent pollutants is crucial. Iron-based materials are cost-effective and environmentally friendly catalysts, and their applications in the environmental field deserve attention. This paper critically reviewed the removal mechanisms of heavy metals and emerging organic pollutants by different influencing factors. The removal of pollutants (heavy metals and emerging organic pollutants) in a multi-component system was analyzed in detail. The mechanisms of synergism, antagonism and non-interference were discussed. This paper had a certain reference value for the research of wastewater remediation technology which could simultaneously remove various pollutants by iron-based materials.

Recent developments in metal-doped SBA-15 catalysts for heterogeneous catalysis and sustainable chemistry

The development of new advanced sustainable materials for heterogeneous catalysis requires control of the structural parameters of the active sites. Mesoporous silica, especially SBA-15, has some unique and important features such as highly ordered mesopores, greater hydrothermal stability, greater wall thickness, large surface area, and adjustable pore volume. All these properties render it a promising material for catalysis, adsorption, supporting materials, biomedical applications, and environmental remediation. However, pure SBA-15 lacks acidic characteristics, which hinders its catalytic activity. Therefore, the functionalized SBA-15 improves the catalytic activity for versatile applications. Thus, in this study, we attempted to summarize the synthesis procedures, various functionalization processes, and application of metal-modified SBA-15 in organic synthesis, fine chemical synthesis, photocatalysis, and decontamination of water. Furthermore, the physicochemical properties, sustainability, and efficacy are discussed in detail for future reference and scope of studies.

Green and efficient synthesis of Co-MOF-based/g-C3N4 composite catalysts to activate peroxymonosulfate for degradation of the antidepressant venlafaxine

Based on single metal-organic framework (MOF) composite catalyst ZIF-67/g-C₃N₄ (ZG), the composite catalysts ZIF-67/MOF-74(Ni)/g-C₃N₄ (ZNG) and ZIF-67/MIL-100(Fe)/g-C₃N₄ (ZMG) with double MOFs were synthesized, used to effectively activate peroxymonosulfate (PMS) for degrade venlafaxine (VEN). Various characterization methods (XRD, FT-IR, Raman, SEM, EDS, TEM and TG) showed that ZIF-67 and g-C₃N₄; ZIF-67, MOF-74(Ni) and g-C₃N₄; as well as ZIF-67, MIL-100(Fe) and g-C₃N₄ successfully formed heterostructures. The series of catalytic degradation results showed that within 120 min, the degradation rate of VEN by ZMG achieved 100% and the mineralization rate reached 51.32%. The removal rate of VEN by ZNG was 91.38%, while that by ZG was only 27.75%. Free radical quenching tests and EPR further confirmed the production of OH and SO₄^-, which could be conducive to the degradation of VEN. The mechanism analysis of PMS activation confirmed that the interaction of Fe²⁺/Co³⁺ was stronger than that of Ni²⁺/Co³⁺, and it was an important driving force to significantly enhance the synergistic effect. Finally, Gauss theory calculation and HPLC-MS/MS were used to analyze the intermediate products of VEN. It was verified that the main chemical reactions in the degradation process of VEN were hydroxylation, dehydration, demethylation and tertiary amine substitution.

Different activation methods in sulfate radical-based oxidation for organic pollutants degradation: Catalytic mechanism and toxicity assessment of degradation intermediates

With the continuous development of industrialization, a growing number of refractory organic pollutants are released into the environment. These contaminants could cause serious risks to the human health and wildlife, therefore their degradation and mineralization is very critical and urgent. Recently sulfate radical-based advanced oxidation technology has been widely applied to organic pollutants treatment due to its high efficiency and eco-friendly nature. This review comprehensively summarizes different methods for persulfate (PS) and peroxymonosulfate (PMS) activation including ultraviolet light, ultrasonic, electrochemical, heat, radiation and alkali. The reactive oxygen species identification and mechanisms of PS/PMS activation by different approaches are discussed. In addition, this paper summarized the toxicity of degradation intermediates through bioassays and Ecological Structure Activity Relationships (ECOSAR) program prediction and the formation of toxic bromated disinfection byproducts (Br-DBPs) and carcinogenic bromate (BrO₃^-) in the presence of Br^-. The detoxification and mineralization of target pollutants induced by different reactive oxygen species are also analyzed. Finally, perspectives of potential future research and applications on sulfate radical-based advanced oxidation technology in the treatment of organic pollutants are proposed.

Recent advances in cobalt-activated sulfate radical-based advanced oxidation processes for water remediation: A review

Sulfate radical-based advanced oxidation processes (SR-AOPs) have attracted increasing attention for the degradation of organic contaminants in water. The oxidants of SR-AOPs could be activated to generate different kinds of reactive oxygen species (ROS, e.g., hydroxyl radicals (OH), sulfate radicals (SO₄^-), singlet oxygen (¹O₂), and superoxide radicals (O₂^-)) by various catalysts. As one of the promising catalysts, cobalt-based catalysts have been extensively investigated in catalytic activity and stability during water remediation. This article mainly summarizes recent advances in preparation and applications of cobalt-based catalysts on peroxydisulfate (PDS)/peroxymonosulfate (PMS) activation since 2016. The review covers the development of homogeneous cobalt ions, cobalt oxides, supported cobalt composites, and cobalt-based mixed metal oxides for PDS/PMS activation, especially for the latest nanocomposites such as cobalt-based metal-organic frameworks and single-atom catalysts. This article also discussed the activation mechanisms and the influencing factors of different cobalt-based catalysts for activating PDS/PMS. Finally, the future perspectives on the challenges and applications of cobalt-based catalysts are presented at the end of this paper.

Synergistically enhanced heterogeneous activation of persulfate for aqueous carbamazepine degradation using Fe3O4@SBA-15

The exploration of low-cost, high-performance and stable catalytic materials for sulfate radical-based advanced oxidation processes (SR-AOPs) is of great importance. This study presents Fe₃O₄-wrapped SBA-15 mesoporous silica catalyst (Fe₃O₄@SBA-15) for persulfate (PS) activation. The Fe₃O₄@SBA-15 with an Fe₃O₄ to SBA-15 weight ratio of 3:1 exhibited an impressive carbamazepine (CBZ) removal efficiency of ~100% after 30 min of SR-AOP at an initial pH of 3.0, a temperature of 25 °C, an initial PS concentration of 300 mg L^-1 and a catalyst concentration of 0.50 g L^-1. The primary oxidizing species produced in the system were identified as SO₄^- and HO by electron paramagnetic resonance spectra and radical quenching experiments. Benefiting from the synergetic effects of improved Fe₃O₄ dispersion and enhanced adsorption of CBZ and PS by SBA-15, the as-obtained heterogeneous Fe₃O₄@SBA-15 catalysts offer large numbers of active sites for free radical generation and high surface concentrations of CBZ and PS for SR-AOPs, as verified by physicochemical characterization and Langmuir-Hinshelwood model analysis. In addition, the activity of Fe₃O₄@SBA-15 was maintained throughout six successive cycling tests. Various inorganic anions, including Cl^-, NO₃^-, HCO₃^-, and CO₃^2-, as well as organic material in natural water, exert a negative impact on the Fe₃O₄@SBA-15 catalyzed SR-AOPs and deserve special attention.

Efficient degradation of bisphenol A in water by heterogeneous activation of peroxymonosulfate using highly active cobalt ferrite nanoparticles

Cobalt ferrite CoFe₂O₄ catalyst was fabricated and systematically investigated as an efficient peroxymonosulfate (PMS, HSO₅^-) activator for the degradation of recalcitrant organic contaminants (ROCs) in water treatment. Both SO₄^- and OH on the surface of catalyst were unveiled to be primarily responsible for bisphenol A (BPA) degradation by a comprehensive study using electron paramagnetic resonance (EPR), radical scavengers and quantification of SO₄^-, and the negligible contribution of singlet oxygen (¹O₂) was also observed. BPA degradation was accelerated in the presence of humic acid, and it increased first but then decreased with the further addition of fulvic acid. Moreover, the presence of chloride and bicarbonate ions can enhance both BPA and TOC removal. The toxicity of the target aqueous solution ascended slowly at the early stage but then declined dramatically and almost vanished as the reaction proceeded. The removal efficiencies of other typical ROCs (clofibric acid, 2,4-dichlorophenol, etc.) and the decontamination of natural surface water spiked with BPA were also evaluated. This CoFe₂O₄/PMS process could be well applied as a safe, efficient, and sustainable approach for ROCs remediation in complex wastewater matrix.