Removal of atrazine by biochar-supported zero-valent iron catalyzed persulfate oxidation: Reactivity, radical production and transformation pathway

Development and testing of alginate/C3N4porphyrin bead as a self-initiated Fenton photocatalyst for highly efficient atrazine removal

Fenton reaction has been widely used for efficient treatment of organic wastewater. However, its applications are limited by such key factors as pH < 3. In this study, we developed, tested, and optimized an alginate/C3N4porphyrin bead (C3N4por-SA) as a recyclable photocatalyst in a photocatalysis-self-Fenton process to overcome these limitations. Porphyrin-modified C3N4 (C3N4por) was used as the H2O2 donator, while Fe(III) nodes served as the Fenton reagent. The as-prepared floating alginate/C3N4por bead utilized the light source as a driving force for the catalysis. Under visible light irradiation for 6 h, the model pollutant atrazine was degraded by 70.96 % by the optimized photocatalyst (named as C3N4por-SA-Fe1Ca5), demonstrating better photocatalytic performance than alginate/C3N4 beads. This improvement was attributed to the higher H2O2 yield from C3N4por. The alginate/C3N4por bead showed better photocatalytic activity even after several consecutive cycles and could easily be recovered for reuse. Furthermore, Fe(III)/Ca(II) bimetallic alginate bead exhibited better photocatalytic activity and a higher content of •OH radicals than the Ca(II) monometallic alginate beads, due to the ability of Fe(III) nodes to serve as a Fenton reagent. The influences of light sources, and commonly existing matters (namely SO42-, Cl-, CO32-, NO3-, and humic acid) were investigated. Moreover, the alginate/C3N4por bead demonstrated good photocatalytic performance in a simulated natural environment without the addition of extra H2O2, with an atrazine removal percentage of up to 96.3 % after 3-h irradiation. These findings indicated the great potential of alginate/C3N4por bead in practical applications.

Persulfate activation with biochar supported nanoscale zero- valent iron: Engineering application for effective degradation of NCB in soil

Nitrochlorobenzene (NCB) is very common in pesticide and chemical industries, which has become a major problem in soil environment. However, the remediation of NCB contaminated soil is received finite concern. Using biochar as a substrate for nanoscale-zero valent iron (nZVI/p-BC) to activate peroxodisulfate (PDS), a novel heterogeneous oxidative system had been applied in the current study to remediate NCB contaminants in soil. The degradation efficiencies and kinetics of m-NCB, p-NCB, and o-NCB by various systems were contrasted in soil slurry. Key factors including the dosage of nZVI/p-BC, the molar ratio of nZVI/PDS, initial pH and temperature on degradation of NCB were further examined. The results confirmed that the nZVI/p-BC/PDS displayed the remarkable performance for removing NCB compared with other systems. Higher temperature with nZVI/PDS molar ratio of 2:1 under the acidic condition favored the reduction of NCB. The treatment for NCB with optimal conditions were evaluated for the engineering application. The mechanism of nZVI/p-BC/PDS indicated that electron transfer between p-BC and nZVI was responsible for activation of PDS, generating active species (SO4•-, •OH and 1O2) via both the free and non-free radical pathways. Experimental results revealed prominent availability of nZVI/p-BC/PDS system in remediation of actual contaminated field by NCB.

Visible light irradiation enhanced sulfidated zero-valent iron/peroxymonosulfate process for organic pollutant degradation

This study developed a novel process named sulfidated zero-valent iron/peroxymonosulfate/visible light irradiation (S-mZVI/PMS/vis) for enhanced organic pollutant degradation. The S-mZVI/PMS/vis process exhibited remarkable catalytic activity, achieving a 99.6% rhodamine B (RhB) removal within 10 min. The degradation rate constant of RhB by the S-mZVI/PMS/vis process was found to be 6.49 and 79.84 times higher than that by the S-mZVI/PMS and PMS/vis processes, respectively. Furthermore, the S-mZVI/PMS/vis process worked efficiently across a wide pH range (3.0-9.0), and the result of five-cycle experiments demonstrated the excellent reusability and stability of S-mZVI. Radical quenching tests and electron paramagnetic resonance analysis indicated that ·O2-, 1O2, and h+ significantly contributed to the degradation of RhB through the S-mZVI/PMS/vis process. The visible light irradiation increased the Fe2+ concentration, improved the Fe3+/Fe2+ cycle, and consequently enhanced the PMS decomposition, reactive species production, and RhB degradation. This work offers a promising strategy to highly efficiently activate PMS for organic pollutants elimination from aqueous solutions.

Fast and efficient As(III) removal from water by bifunctional nZVI@NBC

As a notable toxic substance, metalloid arsenic (As) widely exists in water body and drinking As-contaminated water for an extended period of time can result in serious health concerns. Here, the performance of nanoscale zero-valent iron (nZVI) modified N-doped biochar (NBC) composites (nZVI@NBC) activated peroxydisulfate (PDS) for As(III) removal was investigated. The removal efficiencies of As(III) with initial concentration ranging from 50 to 1000 μg/L were above 99% (the residual total arsenic below 10 μg/L, satisfying the contaminant limit for arsenic in drinking water) within 10 min by nZVI@NBC (0.2 g/L)/PDS (100 μM). As(III) removal efficiency influenced by reaction time, PDS dosage, initial concentration, pH, co-existing ions, and natural organic matter in nZVI@NBC/PDS system were investigated. The nZVI@NBC composite is magnetic and could be conveniently collected from aqueous solutions. In practical applications, nZVI@NBC/PDS has more than 99% As(III) removal efficiency in various water bodies (such as deionized water, piped water, river water, and lake water) under optimized operation parameters. Radical quenching and EPR analysis revealed that SO4·- and ·OH play important roles in nZVI@NBC/PDS system, and the possible reaction mechanism was further proposed. These results suggest that nZVI@NBC activated peroxydisulfate may be an efficient and fast approach for the removal of water contaminated with As(III).

Novel mint-stalks derived biochar for the adsorption of methylene blue dye: Effect of operating parameters, adsorption mechanism, kinetics, isotherms, and thermodynamics

The pyrolysis of mint stalks and lemon peels was performed to synthesize mint-stalks (MBC) and lemon-peels (LBC) derived biochars for adsorbing methylene blue (MB). The preparation, characterization, and application of MBC in adsorption have not been reported in the literature. MBC showed higher surface area and carbon content than that of LBC. The removal ratios of MB were 87.5% and 60% within 90 min for MBC and LBC, respectively at pH 7, temperature of 30oC, adsorbent dose of 0.5 g/L, and MB concentration of 5 mg/L. The optimal MBC dose was 1 g/L achieving a removal efficiency of 93.6% at pH 7, temperature of 30oC, contact time of 90 min, and initial dye concentration of 5.0 mg/L. The adsorption efficiency decreased from 98.6% to 31.33% by raising the dye concentration from 3.0 mg/L to 30 mg/L. Further, the increase of adsorbent dose to 10 g/L could achieve 94.2%, 90.3%, 87.6%, and 84.1% removal efficiencies of MB in the case of initial concentrations of 200 mg/L, 300 mg/L, 400 mg/L, and 500 mg/L, respectively. MBC showed high stability in adsorbing MB under five cycles, and the performed analyses after adsorption reaffirmed the stability of MBC. The adsorption mechanism indicated that the adsorption of MB molecules on the biochar's surface was mainly because of the electrostatic interaction, hydrogen bonding, and π-π stacking. Pseudo-second-order and Langmuir models could efficiently describe the adsorption of MB on the prepared biochar. The adsorption process is endothermic and spontaneous based on the adsorption thermodynamics. The proposed adsorption system is promising and can be implemented on a bigger scale. Moreover, the prepared biochar can be implemented in other applications such as photocatalysis, periodate, and persulfate activation-based advanced oxidation processes.

Single Atom Catalyst in Persulfate Oxidation Reaction: From Atom Species to Substance

With maximum utilization of active metal sites, more and more researchers have reported using single atom catalysts (SACs) to activate persulfate (PS) for organic pollutants removal. In SACs, single metal atoms (Fe, Co, Cu, Mn, etc.) and different substrates (porous carbon, biochar, graphene oxide, carbon nitride, MOF, MoS2 , and others) are the basic structural. Metal single atoms, substances, and connected chemical bonds all have a great influence on the electronic structures that directly affect the activation process of PS and degradation efficiency to organic pollutants. However, there are few relevant reviews about the interaction between metal single atoms and substances during PS activation process. In this review, the SACs with different metal species and substrates are summarized to investigate the metal-support interaction and evaluate their effects on PS oxidation reaction process. Furthermore, how metal atoms and substrates affect the reactive species and degradation pathways are also discussed. Finally, the challenges and prospects of SACs in PS-AOPs are proposed.

Research Progress on the Degradation of Organic Pollutants in Water by Activated Persulfate Using Biochar-Loaded Nano Zero-Valent Iron

Biochar (BC) is a new type of carbon material with a high specific surface area, porous structure, and good adsorption capacity, which can effectively adsorb and enrich organic pollutants. Meanwhile, nano zero-valent iron (nZVI) has excellent catalytic activity and can rapidly degrade organic pollutants through reduction and oxidation reactions. The combined utilization of BC and nZVI can not only give full play to their advantages in the adsorption and catalytic degradation of organic pollutants, but also help to reduce the agglomeration of nZVI, thus improving its efficiency in water treatment and providing strong technical support for water resources protection and environmental quality improvement. This article provides a detailed introduction to the preparation method and characterization technology, reaction mechanism, influencing factors, and specific applications of BC and nZVI, and elaborates on the research progress of BC-nZVI in activating persulfate (PS) to degrade organic pollutants in water. It has been proven experimentally that BC-nZVI can effectively remove phenols, dyes, pesticides, and other organic pollutants. Meanwhile, in response to the existing problems in current research, this article proposes future research directions and challenges, and summarizes the application prospects and development trends of BC-nZVI in water treatment. In summary, BC-nZVI-activated PS is an efficient technology for degrading organic pollutants in water, providing an effective solution for protecting water resources and improving environmental quality, and has significant application value.

Advances in Fe-modified lignocellulosic biochar: Impact of iron species and characteristics on wastewater treatment

Lignocellulosic biomass is an attractive feedstock for biochar production owing to its high abundance and renewability. Various modified biochars have been extensively studied for wastewater treatment to improve the physical and chemical properties of lignocellulosic biochar (L-BC). Particularly, Fe-modified L-BCs have garnered attention owing to the abundance and eco-friendliness of Fe and the outstanding ability to remove various organic and inorganic contaminants via adsorption, oxidation, reduction, and catalytic reactions. Different iron species (e.g., Fe(0), Fe (hydr)oxide, Fe sulfide, and Fe-Metal) are formed during the preparation of Fe-L-BCs, which can completely differentiate the physical and chemical properties of BCs. This review discusses the advances in the synthesis of different Fe-L-BCs, specific changes in the physical and chemical properties of Fe-L-BCs upon Fe addition, and their impacts on wastewater treatment. The results of this review can demonstrate the unique advantages and drawbacks of Fe-L-BCs for the removal of different types of pollutants.

MicroRNA-217-5p triggers dopaminergic neuronal degeneration via autophagy activation under Atrazine exposure

Atrazine (ATR) is a widely used agricultural herbicide, and its accumulation in soil and water can cause various environmental health problems. ATR has neurotoxic effects on dopaminergic neurons, which can lead to a Parkinson's disease (PD)-like syndrome. Epigenetics regulates gene expression dynamically through DNA methylation, histone post-translational modification, microRNA (miRNA) interaction, and RNA methylation. MicroRNA (miRNA), representing one of the primary epigenetic mechanisms responsible for regulating gene expression, plays a crucial role in maintaining normal cellular function, while dysregulation of miRNA expression has been observed in PD. This study aims to investigate the regulatory mechanisms of miRNA in ATR exposure. The results show that ATR-exposure significantly upregulates the expression level of miR-217-5p. Both miR-217-5p overexpression and ATR exposure is able to trigger the autophagy process and apoptosis. Conversely, inhibiting the expression of miR-217-5p can reverse the levels of ATR-induced autophagy and apoptosis. Moreover, ATR causes damage to dopaminergic neurons, as indicated by the altered expression of tyrosine hydroxylase and α-synuclein. Taken together, these results suggest that ATR-induced autophagy can accelerate the progression of neurodegenerative diseases and that miR-217-5p is probably an important target involved in ATR-induced dopaminergic damage, shedding important light on the development of a novel strategy for treating neurodegenerative diseases.

A critical review of sustainable application of biochar for green remediation: Research uncertainty and future directions

Biochar, a carbon-rich material produced from the pyrolysis of organic biomass, has gained significant attention as a potential solution for sustainable green remediation practices. Several studies analyze biomass-derived biochar techniques and environmental applications, but comprehensive assessments of biochar limitations, uncertainty, and future research directions still need to be improved. This critical review aims to present a comprehensive analysis of biochar's efficacy in environmental applications, including soil, water, and air, by sequentially addressing its preparation, application, and associated challenges. The review begins by delving into the diverse methods of biochar production, highlighting their influence on physical and chemical properties. This review explores the diverse applications of biochar in remediating contaminated soil, water, and air while emphasizing its sustainability and eco-friendly characteristics. The focus is on incorporating biochar as a remediation technique for pollutant removal, sequestration, and soil improvement. The review highlights the promising results obtained from laboratory-scale experiments, field trials, and case studies, showcasing the effectiveness of biochar in mitigating contaminants and restoring ecosystems. The environmental benefits and challenges of biochar production, characterization, and application techniques are critically discussed. The potential synergistic effects of combining biochar with other remediation methods are also explored to enhance its efficacy. A rigorous analysis of the benefits and drawbacks of biochar for diverse environmental applications in terms of technical, environmental, economic, and social issues is required to support the commercialization of biochar for large-scale uses. Finally, future research directions and recommendations are presented to facilitate the development and implementation of biochar-based, sustainable green remediation strategies.

FeS and Fe3O4 Co-modified biochar to build a highly resistant advanced oxidation process system for quinclorac degradation in irrigation water

Advanced oxidation processes (AOPs), based on sulfate radical (SO4·-) produced by peroxymonosulfate (PMS), can effectively mineralize refractory organic pollutants. However, the coexistence of anions and natural organic matters in actual wastewater prevents the application of AOPs. A simple one-step method was used to prepare FeS/Fe3O4 co-modified biochar materials (FFB) that could activate PMS to degrade quinclorac (QNC) with a removal rate of 100%, even exhibiting optimum degradation of QNC reached 99.31% in irrigation water, demonstrating excellent anti-interference performance for co-existing anions and natural organic matter. Meanwhile, ecotoxicity analysis showed that the toxicity of degradation intermediates was lower than that of QNC. Characterization results demonstrated the even distribution of FeS and Fe3O4 onto biochar, supplying abundant Fe2+ to activate PMS producing reactive oxygen species (ROS), while the generated Fe3+ after reactive continue to be reduced with sulfur species to promote the cycle of Fe2+/Fe3+. The coexistence of ·OH, SO4·-, 1O2, and O2·- in the FFB/PMS-QNC system suggest the possession of two pathway with free radical and non-free radical pathways to degrade QNC. The density functional theory (DFT) was used to analyze the adsorption sites and adsorption energy of PMS, as well as the differential charge density, which further proved the generation of SO4·-, O2·- and 1O2. In addition, the electrochemical test results showed that electron transfer also played an important role in the degradation of QNC. This study provides a feasible approach for the removal of organic pollutants in actual water.

Removal of sulfonamide antibiotics by a sonocatalytic Fenton-like reaction: Efficiency and mechanisms

With the widespread use of sulfonamide antibiotics (SAs), SAs are detected as residues in aquatic environments, posing a serious threat to human life and safety. Because of their high water solubility, fast transmission rate, and strong antibacterial properties, the safe disposal of SAs has become a key constraint for water quality assurance. Therefore, an ultrasound (US)-assisted zero-valent iron (ZVI)/persulfate (PS) system was proposed to explore the rapid and effective degradation of SAs. Comparative experiments were performed to study the removal of sulfadiazine (SDZ) by US, ZVI, PS, US/ZVI, US/PS, ZVI/PS, and US-ZVI/PS systems, respectively. Experimental results indicated that the highest removal efficiency of SDZ was ahieved in US-ZVI/PS system (97.4%), which were 2-44 times higher than that in other systems. Furthermore, the degradation efficiency of five typical SAs was achieved over 95%, demonstrating the effectiveness of the US ZVI/PS system for SAs removal. Also, quantum chemical computations for potential reactive sites of SAs and intermediate product detection by HPLC‒MS/MS were performed. The radical attack on active sites of SAs, such as N atom (number 7), was the main reason for SAs removal in US-ZVI/PS system. Besides, the common degradation pathways of six typical SAs were defined as S-N bond cleavage, C-N bond cleavage, benzene ring hydroxylation, aniline oxidation, and R substituent oxidation. Interestingly, the unique pathway of "SO2 group extraction" was observed in the degradation of six-membered ring SAs. Therefore, the US-ZVI/PS system is a promising and cost-effective method for the removal of SAs and other refractory pollutants.

Bacterial chemotaxis of herbicide atrazine provides an insight into the degradation mechanism through intermediates hydroxyatrazine, N-N-isopropylammelide, and cyanuric acid compounds

In recent times, the herbicide atrazine (ATZ) has been commonly used before and after the cultivation of crop plants to manage grassy weeds. Despite its effect, the toxic residues of ATZ affect soil fertility and crop yield. Hence, the current study is focused on providing insight into the degradation mechanism of the herbicide atrazine through bacterial chemotaxis involving intermediates responsive to degradation. A bacterium was isolated from ATZ-contaminated soil and identified as Pseudomonas stutzeri based on its morphology, biochemical and molecular characterization. Upon ultra-performance liquid chromatography analysis, the free cells of isolated bacterium strain was found to utilize 174 μg/L of ATZ after 3-days of incubation on a mineral salt medium containing 200 μg/L of ATZ as a sole carbon source. It was observed that immobilized based degradation of ATZ yielded 198 μg/L and 190 μg/L by the cells entrapped with silica beads and sponge, respectively. Furthermore, the liquid chromatography-mass spectroscopy revealed that the secretion of three significant metabolites, namely, cyanuric acid, hydroxyatrazine and N- N-Isopropylammelide is responsive to the biodegradation of ATZ by the bacterium. Collectively, this research demonstrated that bacterium strains are the most potent agent for removing toxic pollutants from the environment, thereby enhancing crop yield and soil fertility with long-term environmental benefits.

Fe3+-cysteine enhanced persulfate fenton-like process for quinclorac degradation: A wide pH tolerance and reaction mechanism

A green, high-efficiency, and wide pH tolerance water remediation process has been urgently acquired for the increasingly exacerbating contaminated water. In this study, a Fe³⁺/persulfate (Fe³⁺/PS) system was employed and enhanced with a green natural ligand cysteine (Cys) for the degradation of quinclorac (QNC). The introduction of Cys into the Fe³⁺/PS system widened the effective pH range to 9 with a superior removal rate for QNC. The mechanism revealed that the Fe³⁺/Cys/PS system can enhance the ability of degrading QNC by accelerating the Fe³⁺/Fe²⁺ redox cycle, maintaining Fe²⁺ concentration and thereby generating more HO^• and SO₄^•-. The impact factors (i.e., pH, concentrations of PS, Fe³⁺ and Cys) were optimized as well. This work provides a promising strategy with high catalytic activity and wide pH tolerance for organic contaminated water remediation.

Metal-carbon hybrid materials induced persulfate activation: Application, mechanism, and tunable reaction pathways

Proper wastewater treatment has always been the focus of human society, and many researchers have been working to find efficient and stable wastewater treatment technologies. Persulfate-based advanced oxidation processes (PS-AOPs) mainly rely on persulfate activation to form reactive species for pollutants degradation and are considered to be one of the most effective wastewater treatment technologies. Recently, metal-carbon hybrid materials have been diffusely used for PS activation because of their high stability, abundant active sites, and easy applicability. Metal-carbon hybrid materials can successfully overcome the shortcomings of onefold metal catalysts and carbon catalysts by combing the complementary advantages of the two components. This article reviews recent studies about metal-carbon hybrid materials-mediated PS-AOPs for wastewater decontamination. The interactions of metal and carbon materials, as well as the active sites of metal-carbon hybrid materials, are introduced first. Then, the application and mechanism of metal-carbon hybrid materials-mediated PS activation are presented in detail. Lastly, the modulation methods of metal-carbon hybrid materials and their tunable reaction pathways were discussed. The prospect of future development directions and challenges is proposed to facilitate metal-carbon hybrid materials-mediated PS-AOPs to take a step further for practical application.

Effective degradation of atrazine by spinach-derived biochar via persulfate activation system: Process optimization, mechanism, degradation pathway and application in real wastewater

Herein, biochar derived from spinach remnants was prepared for the first-time for the utilization in persulfate (PS) activation to effectively degrade atrazine. Characteristics of the prepared biochar were explored using advanced analyses. Control experiments implied the efficient activation of PS in the presence of the synthesized biochar. The highest degradation of atrazine (99.8%) could be attained at atrazine concentration of 7.2 mg/L, PS concentration of 7.7 mM, biochar dose of 1.88 g/L and reaction time of 120 min. The prepared biochar displayed a high recyclability performance attaining degradation ratios of 98.2, 96.53, 96.4, 92.8 and 88% in five sequential cycles under the optimum conditions. The degradation mechanism was explored showing that sulfate radicals were the prime reactive species in the degradation system. The degradation intermediates were specified, and the degradation pathways were propositioned. The highest REs in agrochemical industrial wastewater reached 80.21 and 83.43% of atrazine and TOC after 2 h. NH₃ (348.4 mg/L) was reduced to 168.3 mg/L (RE: 51.7%) while level of NO₃ (94.7 mg/L) was increased by 98.8% (188.3 mg/L) in the treated effluent due to oxidation of NH₃ to nitrite and then nitrate. Extension of reaction time could contribute to achieving full mineralization of the real wastewater due to the residual PS after 120 min. The effectiveness and low-cost of biochar@PS system as well as its high performance in degrading real wastewater support the efficiency of the prepared biochar to be applied on an industrial scale.

Complexation and degradation of tetracycline by activation of molecular oxygen with biochar-supported nano-zero-valent copper composite

Nano-zero-valent copper (nZVC) is a superior molecular oxygen (O₂) activator for the abatement of organic pollutants due to its high electron utilization rate. However, the activation efficiency of O₂ is compromised by the agglomeration tendency of nZVC particles and the concomitant reduction of the available active sites. To address this problem, the biochar (BC) with porous structure and abundant surface functional groups is utilized to disperse and stabilize nZVC for O₂ activation (simplified as the nZVC/BC/O₂ system) for efficient removal of tetracycline (TC). The nZVC/BC composite possesses a high specific area with well-distributed nZVC particles on the BC surface, which guarantees the superior dispersion and high reactivity in the activation of O₂. The efficacy of the nZVC/BC/O₂ system for TC abatement is evaluated and the underlying mechanism is elucidated. The results show that nZVC/BC/O₂ system can achieve excellent removal of TC with the efficiencies of more than 85% in the pH range of 4.0-9.0, which originated from the combined action of complexation and degradation. The degradation is dominated by reactive oxygen species (ROS) including •OH, •O₂^- and ¹O₂ generated by Cu⁰/Cu⁺ activated O₂ while the generation of Cu²⁺ via oxygen oxidation on the surface of nZVC/BC can remove TC by complexation adsorption. This study highlights the complexation and degradation in the removal of TC and can be expected to exhibit application prospects in the water and wastewater treatment.

Remediation of industrial site soil contaminated with PAHs using stage persulfate oxidation activated by Fe2+ chelated with sodium citrate

The remediation for industrial site soil has attracted public concerns because of the hazardous and hydrophobic properties of organic pollutants existed in the soil. The persulfate oxidation activated by Fe²⁺ chelated with sodium citrate (PS/Fe²⁺/SC) was used to remediate different types of industrial site soils in the present study. The maximum removal rates of Σ16 PAHs in the Nanjing site soil (NJS) and Hefei site soil (HFS) were 73.6% and 85.8% after the second-stage oxidation, respectively. The late oxidation stages couldn't enhance the degradation efficiency of PAHs due to the increase of high crystalline Fe mineral phases both in the NJS and HFS, which significantly decreased the Fe²⁺/Fe³⁺ recycle and further inhibited the reactive oxygen species production during the remediation. The remediation using PS/Fe²⁺/SC could change the soil physicochemical properties, such as the functional groups, specific surface area (SSA), total pore volume (TPV) and some UV spectral parameters of soil particles. Additionally, the oxidation of PS/Fe²⁺/SC also altered the composition of soil dissolve organic matters, especially the fulvic acid, which further affected the Fe²⁺ oxidation. The study mainly discloses the mechanism of limitation using persulfate oxidation activated by Fe materials at late oxidation stage.

Photocatalysis of carbamazepine via activating bisulfite by ultraviolet: Performance, transformation mechanism, and residual toxicity assessment of intermediates products

Carbamazepine (CBZ) as an extensively distributed emerging pollutant has menaced ecological security. The degradation performance of CBZ by UV driven bisulfite process was investigated in this work. The kinetics results indicated that CBZ was high-efficiently degraded by UV/bisulfite following a pseudo first-order kinetic model (K_obs = 0.0925 min^-1). SO₄^•- and •OH were verified as the reactive oxidants by EPR test and the radicals scavenging experiment using MeOH and TBA. SO₄^•- played a dominant role for CBZ degradation. The Density functional theory (DFT) and LC-qTOF-MS/MS clarified that hydroxylation, ketonation, ring opening reaction, and ring contraction were main transformation patterns of CBZ. As to influence factors, CBZ degradation was significantly hindered in presence of CO₃^2-, HPO₄^2- and NOM. Toxicological analysis derived from metabonomics suggested that the remarkable alteration of metabolic profile was triggered by exposure to intermediates mixture. CBZ intermediates interfered in several key metabolic pathways, including pentose phosphate, amino acids, lysine degradation, glycerophospholipid, glutathione, nucleotides and carbohydrate, which was alleviated after UV/bisulfite treatment. This work provided a meaningful support to potential risk of CBZ intermediates products, which shed light on the future application in eliminating drugs using UV /bisulfite.

Efficient removal of Phaeocystis globosa from seawater with the persulfate activation by arbutin-modified cellulose nanocrystals

Harmful algal blooms (HABs) from seawater have a severe threat to human health, aquaculture, and coastal nuclear power safety. Thus, it is highly desirable to explore environmentally friendly, efficient, and economic methods for controlling HABs. Herein, the arbutin-modified cellulose nanocrystals (AT-CNC) activated persulfate (PS), as a novel heterogeneous Fenton-like process, was proposed to remove Phaeocystis globosa (P. globosa) from seawater. The AT-CNC was synthesized via the surface modification of AT on CNC. The effects of AT dosage, CNC dosage, and PS dosage on the removal performance of P. globosa were investigated. With the addition of 530 mg/L AT-CNC (6 wt% AT/CNC of AT loading) and 120 mg/L PS, the removal percentage of chlorophyll a (R_c), optical density at 680 nm (R_o) and turbidity (R_t) reached 97.7%, 91.9% and 85.2% at 24 h. According to electron paramagnetic resonance (EPR) spectra and radical quenching tests, the predominant free radicals inactivating P. globosa were hydroxyl radicals (^•OH). Additionally, the flocculation of the inactivated algae cells by AT-CNC was also critical for removing P. globosa. Moreover, a positive environmental impact was achieved in the AT-CNC-PS system due to the reduction of nitrogen, phosphorus and organic carbon contents. Based on the excellent removal performance for P. globosa, we believe that the AT-CNC activated persulfate is a promising option for HABs control.

Enhanced degradation of atrazine through UV/bisulfite: Mechanism, reaction pathways and toxicological analysis

Atrazine residue in the environment continues to threaten aquatic ecosystem and human health owing to its adverse effect. However, limited researches focused on degradation mechanism of atrazine by UV/bisulfite, especially risk of intermediates at cellular and molecular level has not been seriously elaborated. In current work, transformation patterns and residual toxicity of intermediates of atrazine by UV/bisulfite were systematically investigated. The atrazine degradation was described by a pseudo first-order kinetic model (K_obs = 0.1053 min^-1). The presence of H₂PO₄^-, HCO₃^- and HA had a powerful inhibition. Scavenging test of radicals illustrated that SO₄^•-, •OH and O₂^•- existed in UV/bisulfite system, SO₄^•- and •OH were mainly responsible for atrazine degradation. Eight degradation intermediates were identified, which were involved in dealkylation, alkyl oxidation, dechlorination-hydroxylation, and alkylic-hydroxylation. E. coli as a model microorganism was selected to assess the risk of degradation intermediates. The levels of reactive oxygen species, MDA and Na⁺/K⁺-ATPase were declined, suggesting that oxidative damage induced by these intermediates was weakened. According to differential metabolites expression analysis, several key metabolites including aspartate, L-tryptophan, L-asparagine, cytidine, cytosin, stearic acid, behenic acid, were up-regulated, and glutathione, cadaverin, L-2-hydroxyglutaric acid and phytosphingosine were downregulated, clarifying that effective detoxification of atrazine can be performed by UV/bisulfite.

Bisphenol A removal in treated wastewater matrix at neutral pH using magnetic graphite intercalation compounds as persulfate activators

Effluents of municipal wastewater treatment plants (WWTPs) are major sources for releasing contaminants of emerging concern (CECs) into the aquatic environment, which can result in negative effects on aquatic ecosystems and, as a consequence, on humans. Herein, the graphite intercalation concept was used to synthesize heterogeneous catalysts to degrade bisphenol A (BPA) as a model CEC in municipal WWTP effluents at neutral pH. The catalyst was synthesized using the simple molten salt method and showed several benefits, such as iron leaching prevention and stability in environmental matrices. Different methods were applied to describe the catalyst's structural characteristics. The proposed system removed 99.3% of BPA in 75 min using 2 g/L of the synthesized catalyst and 1.19 g/L (5 mM) persulfate at neutral pH. Quenching experiments showed that catalytic activities and BPA removals were significantly aided by both radical and non-radical pathways through the generation of free radicals and singlet oxygen (¹ O₂ ). Furthermore, the reuse of recycled synthesized catalyst was investigated on treated urban wastewater, and the results showed that the catalyst could degrade BPA from the wastewater in consecutive cycles, demonstrating its applicability under real conditions. PRACTITIONER POINTS: BPA was effectively removed from the effluents of municipal WWTPs at neutral pH. A new catalyst (magnetic GIC) was fabricated for heterogeneous catalytic systems. The catalyst activates persulfate to generate free radicals and ¹ O₂ , indicating that radical and non-radical pathways contribute to BPA degradation. The catalyst showed the ability to remove BPA even in the sixth cycle of use, demonstrating its stability and reusability.

Efficient degradation of m-cresol during catalytic wet peroxide oxidation with biochar derived from the pyrolysis of persulfate-ZVI treated sludge

Sludge dewatering is crucial for cutting the cost of sludge post-disposal in wastewater treatment plants. Response surface methodology (RSM) was used in this study to sufficiently investigate the interaction among persulfate, zero-valent iron (ZVI) and reaction time on the sludge dewatering. Under the experimental condition at the central point in RSM, the sludge moisture content was reduced to 54%. The sludge-based biochar obtained from the pyrolysis of persulfate-ZVI treated sludge at the central point in RSM was marked as SC-M and tested for catalytic activity. With the catalyst SC-M, the removal rates of m-cresol and total organic carbon (TOC) were 98.1% and 84.2%, respectively. The persulfate-ZVI treatment for sludge dewatering facilitated increasing the proportion of iron species in SC-M, which contributed to its high catalytic activity. M-cresol degradation with SC-M was a two-period reaction including an induction period and a rapid reaction with the apparent activation energy at a low level. This study integrates the sludge dewatering by persulfate-ZVI treatment and m-cresol degradation by catalytic oxidation with the biochar SC-M prepared from the dewatered iron-rich sludge, providing an effective, economic and environment-friendly approach for sewage sludge utilization and management.

Biochar modification with hematite and goethite as efficient persulfate activation catalysts for sulfamethoxazole degradation: one-step biochar synthesis method and solution matrix effect on sulfamethoxazole removal kinetics

Using biochar to adsorb and degrade organic contaminants has attracted increasing attention due to its relatively low cost and high efficiency. In this work, two magnetic biochars were synthesized by pyrolyzing a mixture of naturally occurring hematite or goethite mineral and pine needle biomass. The biochar composite was characterized with X-ray diffraction, scanning electron microscopy, and surface area analyzer. The result demonstrated iron minerals have been deposited on carbon surfaces and been reduced to magnetite or wustite minerals. In comparison to the unmodified biochar, the iron mineral-modified biochar had better sorption ability, likely because the iron mineral particles on the carbon surface served as additional sorption sites for sulfamethoxazole (SMX) removal. After modification, the biochar also showed higher persulfate activation capacity with radical generation: at 4 h, neutral pH, 67.5 and 77.9% of persulfate is activated with hematite and goethite modified biochar, where only 11.7% persulfate is activated by unmodified biochar. With persulfate, goethite-modified biochar showed better SMX removal capacity than hematite-modified biochar with about 79% of SMX removed in 4 h. Solution chemistry such as pH and co-exist humic acid can affect SMX removal by affecting iron minerals. Because the magnetized biochar can be easily isolated and removed with external magnets, it can be used in various contaminant removal applications.

Insights into highly effective catalytic persulfate activation on oxygen-functionalized mesoporous carbon for ciprofloxacin degradation

Nanocarbons have been demonstrated as promising carbon catalysts for substituting metal-based catalysts for the green treatment of wastewater. In this study, oxygen-functionalized mesoporous carbon (OCMK-3) was prepared by wet oxidation and exhibited high catalytic performance against ciprofloxacin (CIP) by activation of persulfate. The effects of environmental parameters (pH, temperature, coexisting ions) and process parameters (temperature, sodium persulfate concentration, catalyst agent dosage, initial concentration) on the removal of CIP were investigated. Compared with the pristine ordered mesoporous carbon (CMK-3), the removal efficiency of CIP by OCMK-3 was increased by 32% under optimal conditions. This rise in activity was attributed to the increase in oxygen-containing functional groups, porosity, and specific surface area of OCMK-3 with improved structural defects and electron transfer efficiency. Furthermore, based on active species scavenging experiments, a dual-pathway mechanism of the radical and nonradical pathways was discovered. The rational degradation pathway of CIP was investigated based on liquid chromatography-mass spectrometry (LC-MS). In addition, the OCMK-3/PS system exhibited high decomposition efficiency in pharmaceutical wastewater treatment. This study provides an in-depth mechanism for the degradation of organic pollutants by carbon-based PS-AOPs and provides theoretical support for further studies.

Photocatalytic degradation of atrazine in aqueous solution using La-doped ZnO/PAN nanofibers

Polyacrylonitrile (PAN)-based-modified zinc oxide (ZnO) nanofibers were synthesized by using electrospinning and hydrothermal techniques. The synthesized nanofibers were characterized by field emission scanning electron microscopy and X-ray photoelectron spectroscopy and evaluated for their ability to promote the photocatalytic degradation of the toxic herbicide atrazine. The degradation conditions were optimized by varying catalyst types, catalyst quantity, pH, light source, and toxic concentration. The degradation products were confirmed by high-performance liquid chromatography and gas chromatography-mass spectrometry (GC-MS) analyses. The extent of mineralization was calculated using total organic carbon and real-time analyses. The diameter of the La-doped ZnO-loaded PAN nanofibers was larger than that of the ZnO-seeded PAN nanofibers. The additional peak at a binding energy of 533 eV in the bonding states of La-doped ZnO/PAN indicated the presence of oxygen vacancies in the ZnO matrix, which could enhance the catalytic activity of the material. Furthermore, the degradation of atrazine depended on all the above reaction parameters. The mass spectrum of the degradation product was recorded and exhibited a molecular ion peak at m/z 187 according to GC-MS. Finally, La-doped ZnO PAN nanofibers proved to be an excellent catalyst for decontaminating atrazine within 1 h and allowed to achieve a 98% degradation efficiency.

Application of Functional Modification of Iron-Based Materials in Advanced Oxidation Processes (AOPs)

Advanced oxidation processes (AOPs) have become a favored approach in wastewater treatment due to the high efficiency and diverse catalyzed ways. Iron-based materials were the commonly used catalyst due to their environmental friendliness and sustainability in the environment. We collected the published papers relative to the application of the modified iron-based materials in AOPs between 1999 and 2020 to comprehensively understand the related mechanism of modified materials to improve the catalytic performance of iron-based materials in AOPs. Related data of iron-based materials, modification types, target pollutants, final removal efficiencies, and rate constants were extracted to reveal the critical process of improving the catalytic efficiency of iron-based materials in AOPs. Our results indicated that the modified materials through various mechanisms to enhance the catalytic performance of iron-based materials. The principal aim of iron-based materials modification in AOPs is to increase the content of available Fe2+ and enhance the stability of Fe2+ in the system. The available Fe2+ is elevated by the following mechanisms: (1) modified materials accelerate the electron transfer to promote the Fe3+/Fe2+ reaction cycle in the system; (2) modified materials form chelates with iron ions and bond with iron ions to avoid Fe3+ precipitation. We further analyzed the effect of different modifying materials in improving these two mechanisms. Combining the advantages of different modified materials to develop iron-based materials with composite modification methods can enhance the catalytic performance of iron-based materials in AOPs for further application in wastewater treatment.

Activation of persulfate for highly efficient degradation of metronidazole using Fe(II)-rich potassium doped magnetic biochar

The content of active components in magnetic biochar, especially Fe(II), is closely related to its activation performance. Therefore, improving Fe(II) content in magnetic biochar is an ideal strategy to enhance the activation performance of magnetic biochar. In this study, the potassium-doped magnetic biochar was prepared and employed to activate persulfate for degradation of metronidazole. The degradation efficiency of metronidazole in potassium-doped magnetic biochar/persulfate system was 98.4%, which was 13.1 times higher than that in magnetic biochar/persulfate system. Free radicals quenching experiments and electron spin resonance analyses confirmed that surface-bound free radicals were responsible for metronidazole degradation followed the order of ¹O₂ > ·OH > SO₄·^- > O₂·^-. The doping of magnetic biochar with potassium increased its Fe(II) content, approximately 3.1 times higher than that of pristine magnetic biochar. The differences in Fe(II) content between potassium-doped magnetic biochar and magnetic biochar were the key reasons for the activation performance differences. Based on the ultra-high pressure liquid chromatography-quadrupole tandem time-of-flight mass spectrometer, the primary degradation intermediates of metronidazole were identified, and possible degrading pathways were proposed. Overall, this work provides an effective strategy to improve the activation performance of magnetic biochar.

UV-Vis spectrophotometry coupled to chemometric analysis for the performance evaluation of atrazine photolysis and photocatalysis

In this study, a spectrophotometric-chemometric (Spec-Chem) approach was applied as an alternative to chromatography to monitor ATZ and by-products after photolytic and photocatalytic oxidation aiming to unveil the ATZ degradation mechanism. Spec-Chem is an accessible, easy-to-operate, low-cost analytical approach to monitor atrazine (ATZ) and by-products, and its applicability was validated by HPLC, the reference technique for the evaluation of pollutant degradation mechanisms. The chromatographic (DChro) and spectrophotometric (DSpec) data found 95% and 57% ATZ removal after 30 min, respectively, proving that the DSpec erroneously induces a 38% loss in removal efficiency. When DSpec was treated by multivariate curve resolution (MCR) analysis for providing chemometric data (DChem), it found ATZ removal and hydroxyatrazine (HAT) formation statistically equal to DChro (t-test, p = 0.05). After unraveling the ATZ degradation mechanism using Spec-Chem, a new hypothesis for the kinetic calculation of ATZ degradation was presented, where the concentrations of ATZ and HAT were used to find k and R² values representative for the ATZ degradation mechanism. The values found for k were compatible with the literature under similar conditions of ATZ degradation, and the linear correlation coefficients (R² = 0.99) showed an optimal fit for the proposed hypothesis. Thus, Spec-Chem was successfully applied to unravel the mechanism of photocatalytic degradation of ATZ in the presence of TiO₂, while k was obtained by the new hypothesis proposed that considered ATZ and HAT concentration as parameters of kinetic interest. Therefore, the importance of monitoring quantitatively ATZ and HAT were provided in this study, providing new information for the scientific community.

Optimization, equilibrium, adsorption behaviour of Cu/Zn/Fe LDH and LDHBC composites towards atrazine reclamation in an aqueous environment

Cu-Zn-Fe Layered double hydroxides (LDH) and LDH dispersed on bamboo biochar (LDHBC) was used to study the adsorption of Atrazine by characterizing the adsorption kinetics, isotherms and response surface methodology (RSM) to reveal interactive effects of pH, adsorbent dosage and adsorbate initial concentration towards LDH optimum performance. The estimate of parameters determined for Langmuir isotherm quantities were in the range (21.84-37.91 mg/g) for LDH and (63.64-87.04 mg/g) for LDHBC. Regeneration and reusability after five cycles detected that the adsorption efficiencies of the adsorbents were reduced to 36% for LDH and 66% for LDHBC. Box Behnken design analysis could further reveal optimized conditions for higher Atrazine removal by LDH up to 74.8%. The adsorption mechanisms could be determined by π-π interactions occurring at the interfaces by hydrogen bonding and pore filling effects.

Overestimate of remediation efficiency due to residual sodium persulfate in PAHs contaminated soil and a solution

Oxidation remediation is a commonly used technology for PAHs contaminated soil presently, but the overestimate of efficiency due to ongoing remediation by residual oxidants during extraction and testing has not been paid enough attention. In this study, persulfate was activated by Fe(II) to investigate the effects of residual oxidants on PAHs removal during detection process and the elimination effects of adding Na₂SO₃ and extending sampling time on residual oxidants. Results verified that the residual oxidants removed PAHs in extraction process, making the results lower than the actual values: the detection recovery rate η of ∑PAHs and 3-6 ring PAHs ranged from 24.3% (25% Na₂S₂O₈ treatment) to 87.4% (5% Na₂S₂O₈+4/4Fe²⁺ treatment), 20.1%-99.0%, 28.9%-87.9%, 20.8%-89.4%, and 18.6%-76.9%, respectively. After adding Na₂SO₃, the accuracy of detection results increased significantly: the η of ∑PAHs and 3-6 ring PAHs increased to 64.1%-96.5%, 58.8%-95.5%, 73.8%-114.4%, 60.6%-95.6%, and 45.4%-77.1%, respectively. After 49 days of adding oxidants, residual oxidants had no considerable effect on the detection of PAHs, indicating it was appropriate to start soil remediation verification sampling49 days after the remediation was completed. The observed results will help scientific evaluation of the remediation effects of chemical oxidation on organic contaminated soil.

Enhanced degradation of bisphenol S by persulfate activated with sulfide-modified nanoscale zero-valent iron

Sulfide-modified nanoscale zero-valent iron (S-nZVI) has been considered an efficient material to remove heavy metals and organic contaminants. The experiments of bisphenol S (BPS) degradation by persulfate (PS) activated with S-nZVI (S-nZVI/PS) or nZVI (nZVI/PS) were carried out in this paper. The results show that, compared to the bare nZVI/PS system, the S-nZVI/PS system shows higher activity in BPS degradation, especially at high BPS concentration. The reaction rate constant k_obs of BPS removal by the S-nZVI/PS system (0.142 min^-1) was much higher than that in nZVI/PS system (0.089 min^-1) because more oxidation species were generated in the S-nZVI/PS system. The results of electron paramagnetic resonance (EPR) and radical quenching tests show that both hydroxyl radical (·OH) and sulfate radical (SO₄^·-) were involved in the degradation of BPS and had a great contribution to BPS removal. Moreover, the effects of S/Fe molar ratio, S-nZVI dosage, initial pH, and initial concentration of PS or BPS on S-nZVI/PS were also studied. The results show that the S/Fe molar ratio has significant influence on the BPS degradation; over 97.7% of the removal efficiency was achieved at 0.035 of S/Fe molar ratio. And the removal efficiency of BPS degradation increased with the increase of the dosage of S-nZVI, PS concentration. Furthermore, BPS could be efficiently removed in solutions with a wide range of initial pH (3.13-9.35). The observed results show that it is promising in the removal of micro-pollutants from water by persulfate activated with S-nZVI.

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.

Role of sulfide-modified nanoscale zero-valent iron on carbon nanotubes in nonradical activation of peroxydisulfate

Sulfamethoxazole (SMX) is highly persistent and difficult to remove, making it urgent to find an efficient method for alleviating the enormous environmental pressure of SMX. In this study, sulfide-modified nanoscale zero-valent iron on carbon nanotubes (S-nZVI@CNTs) was prepared to activate peroxydisulfate (PDS) for the degradation of SMX. The results showed that SMX was completely removed within 40 min (k_obs=0.1058 min^-1) in the S-nZVI@CNTs/PDS system. By analyzing quenching experiments and electron paramagnetic resonance (EPR), singlet oxygen (¹O₂) was the main active species of the S-nZVI@CNTs/PDS system. ¹O₂ might be mediated by the abundant carbonyl groups (CO) on carbon nanotubes through spectroscopic analyses. In addition, sulfur doping transitioned the activation pathway to a nonradical pathway. Spectroscopic analyses and electrochemical experiments confirmed that the formation of CNTs-PDS complexes and S-nZVI could promote electron transfer on the catalyst surface. Furthermore, the main degradation intermediates of SMX were identified, and five possible transformation pathways were proposed. The S-nZVI@CNTs/PDS system possessed advantages including high anti-interference (Cl^-, NO^3-, HA), a strong applicability, recyclability and a low PDS consumption, offering new insight into the degradation of antibiotic wastewater.

Occurrence and spatial-temporal distribution of atrazine and its metabolites in the aquatic environment of the Volturno River estuary, southern Italy

The present study assesses the spatial distribution and temporal trends of the water dissolved phase (WDP), suspended particulate matter (SPM) and sediment partitioning of atrazine (ATR) and its metabolites in the Volturno River estuary. The load contribution of ATR and its metabolites in this river to the Central Mediterranean Sea was estimated. Samples were collected in 10 sampling sites during the four seasons. The total concentrations of ATR and DPs detected ranged from 18.1 to 105.5 ng L^-1 in WDP, from 4.5 to 63.2 ng L^-1 in SPM, and from 4.6 to 18.6 ng g^-1 in sediment samples, indicating high levels of these pollutants. Structural equation model and the ratio study indicated that the relationship between sediment and WDP pollutants occurred through the SPM. The pollutants load at the Volturno River in its mouth was evaluated in about 30.4 kg year^-1, showing that this river is an important source of these analytes through discharge into Central Mediterranean Sea. Principal component analysis indicated that ATR and its metabolites pollution moves from Volturno River mouth southward and increased in the rainy season. The desethylatrazine-to-atrazine ratio was higher than 0.5 for all samples analyzed, indicating an historical discharge and a long residence time of ATR in sediment about two decades after its ban, and classifying ATR as a nonpoint source contaminant. This study makes up the first record of ATR and its metabolites in superficial water of Southern Italy and provides helpful data as starting point for future studies.

High-performance carbon black electrode for oxygen reduction reaction and oxidation of atrazine by electro-Fenton process

The aim of this study is to produce an electrode that can be used in H₂O₂ production and Electro-Fenton (EF) process by an effective, cheap, and easy method. For this reason, a superhydrophobic electrode with a higher PTFE ratio and high thickness was produced with a simple press. The produced electrode was used in the production of H₂O₂ and mineralization of Atrazine. First, the effect of pH, cathode voltage, and operation time on H₂O₂ production was evaluated. The maximum H₂O₂ concentration (409 mg/L), the highest current efficiency (99.80%), and the lowest electrical energy consumption (3.16 kWh/kg) were obtained at 0.8 V, 7.0 of pH, and 120 min, and the stability of the electrode was evaluated up to 720 min. Then, the effects of the operational conditions (pH, cathode voltage, operating time, and catalyst concentration) in electro-Fenton were evaluated. The fastest degradation of Atrazine (>99%) was obtained at 2.0 V, 3.0 of pH, and 0.3 mM of Fe²⁺ in 15 min. In the final part of the study, the degradation intermediates were identified, and the characterization of the electrode was evaluated by SEM, XRD, FT-IR, tensiometer, potentiostat, and elemental analyzer.

Comparative study on the removal of organic pollutants by magnetic composite and pre-magnetized zero-valent iron activated persulfate

The rapid development of global logistics has led to the overuse of packaging cartons, causing problems for municipal solid waste disposal. Diverse methods of exploiting the potential value of waste cartons are needed. Herein, we fabricated a magnetic composite (MC) from waste cartons via a one-step hydrothermal treatment and characterized. Using methylene blue (MB) as a model organic pollutant, tests of the activation of persulfate (PS) via the MC for the removal of MB were performed. Meanwhile, a comparison with activation with pre-magnetized zero-valent iron (Pre-ZVI/PS) was made. The comparative results show that the removal of MB was successfully accomplished with both Pre-ZVI/PS and MC/PS. Specifically, MC/PS could remove almost 100 % of MB, with the COD removal efficiency reaching over 70 % when the MB concentration was 50 mg/L at 80 min under different pH conditions. Even when reused twice, the MC still displayed robust activation performance. Additionally, we evaluated the lifetime of magnetic memory for Pre-ZVI, and first found its consecutive loss of pre-magnetization over 30 days, corresponding to the incremental attenuation of reaction rate constants in the Pre-ZVI-activated PS process. Overall, activating PS using the MC is a promising advanced oxidation technology and also provides a valuable reference on the valorization of lignocellulosic biomass.

Citrate iron complex induced dramatically enhanced oxidation of atrazine with bimetallic Bi/Fe0: Reactivity, oxidation and mechanism

The oxidative degradation of atrazine (ATR) using bimetallic Bi/Fe⁰ nanoparticles cooperated with citric acid (CA) and sodium citrate (NaCA) without extra addition of H₂O₂ or another oxidant was conducted. Almost 73% of ATR was removed in Bi/Fe⁰+NaCA + CA buffer system in 3 h, and the bimetallic Bi/Fe⁰ performs high stability and long service life in the buffer system according to the results of cyclic degradation experiments. The citrate iron complex of Fe(II)[Cit]^- played the key role for the degradation process since it could quickly react with the generated H₂O₂ to produce free radicals in the Bi/Fe⁰+NaCA + CA system, which broadened the applicable pH range of the traditional Fenton reaction and promoted the oxidative degradation process of ATR. The possible degradation pathways of ATR were also investigated. In the Bi/Fe⁰+NaCA + CA buffer system, twelve kinds of ATR intermediate products were detected, of which the main products were dechlorination products and alkyl oxidative products. Due to the pH controllable of the Bi/Fe⁰+NaCA + CA system, it could reduce the acidity impact on the environment and makes the additional impact on the environment lower. Therefore, this work provides a new strategy for the degradation of ATR.

Detection and remediation of pollutants to maintain ecosustainability employing nanotechnology: A review

Environmental deterioration due to anthropogenic activities is a threat to sustainable, clean and green environment. Accumulation of hazardous chemicals pollutes soil, water and air and thus significantly affects all the ecosystems. This article highlight the challenges associated with various conventional techniques such as filtration, absorption, flocculation, coagulation, chromatographic and mass spectroscopic techniques. Environmental nanotechnology has provided an innovative frontier to combat the aforesaid issues of sustainable environment by reducing the non-requisite use of raw materials, electricity, excessive use of agrochemicals and release of industrial effluents into water bodies. Various nanotechnology based approaches including surface enhance scattering, surface plasmon resonance; and distinct types of nanoparticles like silver, silicon oxide and zinc oxide have contributed significantly in detection of environmental pollutants. Biosensing technology has also gained significant attention for detection and remediation of pollutants. Furthermore, nanoparticles of gold, ferric oxide and manganese oxide have been used for the on-site remediation of antibiotics, organic dyes, pesticides, and heavy metals. Recently, green nanomaterials have been given more attention to address toxicity issues of chemically synthesized nanomaterials. Hence, nanotechnology has provided a platform with tremendous applications to have sustainable environment for present as well as future generations. This review article will help to understand the fundamentals for achieving the goals of sustainable development, and healthy environment.

Accelerated atrazine degradation and altered metabolic pathways in goat manure assisted soil bioremediation

The intensive and long-term use of atrazine in agriculture has resulted in serious environmental pollution and consequently endangered ecosystem and human health. Soil microorganisms play an important role in atrazine degradation. However, their degradation efficiencies are relatively low due to their slow growth and low abundance, and manure amendment as a practice to improve soil nutrients and microbial activities can solve these problems. This study investigated the roles of goat manure in atrazine degradation performance, metabolites and bacterial community structure. Our results showed that atrazine degradation efficiencies in un-amended soils were 26.9-35.7% and increased to 60.9-84.3% in goat manure amended treatments. Hydroxyatrazine pathway was not significantly altered, whereas deethylatrazine and deisopropylatrazine pathways were remarkably enhanced in treatments amended with manure by encouraging the N-dealkylation of atrazine side chains. In addition, goat manure significantly increased soil pH and contents of organic matters and humus, explaining the change of atrazine metabolic pathway. Nocardioides, Sphingomonas and Massilia were positively correlated with atrazine degradation efficiency and three metabolites, suggesting their preference in atrazine contaminated soils and potential roles in atrazine degradation. Our findings suggested that goat manure acts as both bacterial inoculum and nutrients to improve soil microenvironment, and its amendment is a potential practice in accelerating atrazine degradation at contaminated sites, offering an efficient, cheap, and eco-friendly strategy for herbicide polluted soil remediation.

Adsorptive removal of noxious atrazine using graphene oxide nanosheets: Insights to process optimization, equilibrium, kinetics, and density functional theory calculations

Atrazine is a toxic herbicide whose alarming rate of contamination in the drinking water and wastewater poses a severe threat to the environment and human health. Here in this study, the graphene oxide (GO) nanosheets were prepared using Hummers' method with minor modification and studied as a potential adsorbent for atrazine removal from simulated wastewater. The spectroscopy and microscopic analysis confirmed the successful formation of GO with a multilayer structure resembling the crumpled sheets with random stacking. The Response Surface Methodology (RSM) employing Box Behnken design (BBD) was successfully developed to predict the optimal conditions for maximal atrazine removal as adsorbent dosage 121.45 mg/L; initial feed concentration 27.03 mg/L; temperature 27.69 °C, pH 5.37, and time 180 min. The atrazine adsorption onto GO was found to be higher in acidic pH and lower temperature. Density functional theory (DFT) calculation of adsorbent-adsorbate complex in the implicit solvent medium suggests adsorption affinity energy of -24.4 kcal/mol for atrazine. A careful observation of the molecules configuration and binding energy showed that the π-π interactions and hydrogen bonds played a significant role in the adsorption phenomena. Langmuir isotherm suited well to the adsorption process with a maximum adsorption capacity of 138.19 mg/g, at 318 K. The fitness of kinetic models for atrazine adsorption onto GO nanosheets were in following order Ho < Sobkowsk-Czerwi < Avrami model based on their correlation coefficient (R²) values. Reusability analysis showed that GO nanosheets could be effectively recycled using 0.01 N NaOH up to six cycles of atrazine removal. Thus, this study provided a theoretical and experimental basis for the potential application of GO nanosheets as a novel adsorbent for the removal of hazardous atrazine.

Environmentally friendly fabrication of new β-Cyclodextrin/ZrO2 nanocomposite for simultaneous removal of Pb(II) and BPA from water

Heavy metals and endocrine disrupters often co-exist in wastewater, while their possible competition behaviours make uptake removal more challenging. Therefore, β-Cyclodextrin based nanocomposite adsorbent was successfully fabricated (β-Cyclodextrin/ZrO₂) for the simultaneous uptake of Pb(II) and Bisphenol A from wastewater. FTIR, XRD, and XPS confirmed the successful fabrication of the β-Cyclodextrin/ZrO₂ nanocomposite. In this setting, oxygen-containing groups are primarily responsible for the Pb(II) binding, while the β-Cyclodextrin cavities adsorb Bisphenol A through host-guest interaction, enabling the simultaneous removal of Pb(II) and Bisphenol A. In the mono contaminant system, the nanocomposite displayed prominent removal ability toward Pb(II) and Bisphenol A with adsorption characteristics of pseudo-second-order, Langmuir, and Freundlich isotherm model. The maximum adsorption capacities were identified for Pb(II) and Bisphenol A to be 274.4 mg/g and 174.9 mg/g at 298 K, respectively. Most importantly, the β-Cyclodextrin/ZrO₂ could efficiently attain simultaneous removal of Pb(II) and Bisphenol A by avoiding their competitive behaviours was due to the different adsorption mechanisms (electrostatic interaction and host-guest interaction). Moreover, the adsorbed Pb(II) and Bisphenol A could be successfully recovered with a slight decline in nanocomposite removal performance even after 4 cycles in the binary-component system. All these findings provide insights into the fabrication of highly effective adsorbent with separated adsorption sites to treat wastewater bearing heavy metal and endocrine disrupters.

Degradation Efficiency and Kinetics Analysis of an Advanced Oxidation Process Utilizing Ozone, Hydrogen Peroxide and Persulfate to Degrade the Dye Rhodamine B

In this study, the effectiveness of a rhodamine B (RhB) dye degradation process at a concentration of 20 mg/L in different advanced oxidation processes—H2O2/UV, O3/UV and PDS/UV—has been studied. The use of UV in a photo-assisted ozonation process (O3/UV) proved to be the most effective method of RhB decolorization (90% after 30 min at dye concentration of 100 mg/L). The addition of sulfate radical precursors (sodium persulfate, PDS) to the reaction environment did not give satisfactory effects (17% after 30 min), compared to the PDS/UV system (70% after 30 min). No rhodamine B decolorization was observed using hydrogen peroxide as a sole reagent, whereas an effect on the degree of RhB degradation was observed when UV rays strike the sample with H2O2 (33% after 30 min). The rhodamine B degradation process followed the pseudo-first-order kinetics model. The combined PDS/O3/UV process has shown 60% color removal after 30 min of reaction time at an initial dye concentration of 100 mg/L. A similar effectiveness was obtained by only applying ozone or UV-activated persulfate, but at a concentration 2–5 times lower (20 mg/L). The results indicated that the combined PDS/O3/UV process is a promising method for high RhB concentrations (50–100 mg/L) comparing to other alternative advanced oxidation processes.

A Review on the Degradation of Pollutants by Fenton-Like Systems Based on Zero-Valent Iron and Persulfate: Effects of Reduction Potentials, pH, and Anions Occurring in Waste Waters

Among the advanced oxidation processes (AOPs), the Fenton reaction has attracted much attention in recent years for the treatment of water and wastewater. This review provides insight into a particular variant of the process, where soluble Fe(II) salts are replaced by zero-valent iron (ZVI), and hydrogen peroxide (H2O2) is replaced by persulfate (S2O82-). Heterogeneous Fenton with ZVI has the advantage of minimizing a major problem found with homogeneous Fenton. Indeed, the precipitation of Fe(III) at pH > 4 interferes with the recycling of Fe species and inhibits oxidation in homogeneous Fenton; in contrast, suspended ZVI as iron source is less sensitive to the increase of pH. Moreover, persulfate favors the production of sulfate radicals (SO4•-) that are more selective towards pollutant degradation, compared to the hydroxyl radicals (•OH) produced in classic, H2O2-based Fenton. Higher selectivity means that degradation of SO4•--reactive contaminants is less affected by interfering agents typically found in wastewater; however, the ability of SO4•- to oxidize H2O/OH- to •OH makes it difficult to obtain conditions where SO4•- is the only reactive species. Research results have shown that ZVI-Fenton with persulfate works best at acidic pH, but it is often possible to get reasonable degradation at pH values that are not too far from neutrality. Moreover, inorganic ions that are very common in water and wastewater (Cl-, HCO3-, CO32-, NO3-, NO2-) can sometimes inhibit degradation by scavenging SO4•- and/or •OH, but in other cases they even enhance the process. Therefore, ZVI-Fenton with persulfate might perform unexpectedly well in some saline waters, although the possible formation of harmful by-products upon oxidation of the anions cannot be ruled out.

Colloidal activated carbon as a highly efficient bifunctional catalyst for phenol degradation

A preparation of colloidal activated carbon (CAC) for phenol remediation from groundwater was introduced. The CAC prepared by a simple pulverization technique was an excellent metal-free catalyst for persulfate (PS) activation due to high contact surface area. The removal efficiency of phenol in the PS/CAC system (~100%) was higher than that in the PS/activated carbon (AC) system (90.1%) and was superior to the conventional PS/Fe²⁺ system (27.9%) within 30 min. The phenol removal reaction occurred both in bulk solution and at the surface of the CAC, as confirmed by Langmuir-Hinshelwood (L-H) kinetic model fitting, FT-IR, and electron spin resonance (ESR) analyses. The downsizing of particle size from AC to CAC played a critical role in the radical oxidation mechanism by leading to the formation of predominant superoxide radical (O₂^•-) species in the PS/CAC system. Anions NO₃^-, SO₄^2-, and Cl^- slightly inhibited the phenol removal efficiency, whereas CO₃^2-, HCO₃^- and PO₄3^- did not. Ferulic acid (C₁₀H₁₀O₄) was detected as an organic byproduct of phenol oxidation. The use of CAC as a metal-free bifunctional catalyst has an important implication in the PS activation for phenol degradation in groundwater.

Modified nanoscale zero-valent iron in persulfate activation for organic pollution remediation: a review

Under the action of different activators, persulfate can produce sulfate radicals (SO₄·^-) with strong oxidizing ability, which can destruct many organic compounds. Meanwhile, persulfate is widely used in groundwater and soil remediation because of its fast reaction and wide application. With the high specific surface area and reactivity of nanoscale zero-valent iron (nZVI), it can enhance the degradation efficiency of the persulfate system on organic pollutants in soil and water as a persulfate activator. However, nZVI is easy to get oxidized and has a tendency to aggregation. To solve these problems, a variety of nZVI modification methods have been put forward and put into to applications in the activation of persulfate. This article will give a systematic introduction of the background and problems of nZVI-activated persulfate in the remediation of organic pollution. In addition, the modification methods and mechanisms of nZVI are summarized, and the applications and progress of modified nZVI-activated persulfate are reviewed. The factors that affect the removal of organic compounds by the activation system are discussed as well. Worldwide, the field studies and full-scale remediation using modified nZVI in persulfate activation are yet limited. However, the already known cases reveal the good prospect of applying modified nZVI in persulfate activation to organic pollution remediation.