Size-Dependent Catalysis in Fenton-like Chemistry: From Nanoparticles to Single Atoms.

State-of-the-art Fenton-like reactions are crucial in advanced oxidation processes (AOPs) for water purification. This review explores the latest advancements in heterogeneous metal-based catalysts within AOPs, covering nanoparticles (NPs), single-atom catalysts (SACs), and ultra-small atom clusters. A distinct connection between the physical properties of these catalysts, such as size, degree of unsaturation, electronic structure, and oxidation state, and their impacts on catalytic behavior and efficacy in Fenton-like reactions. In-depth comparative analysis of metal NPs and SACs was conducted focusing on how particle size variations and metal-support interactions affect oxidation species and pathways. The review highlights the cutting-edge characterization techniques and theoretical calculations, indispensable for deciphering the complex electronic and structural characteristics of active sites in downsized metal particles. Additionally, the review underscores innovative strategies for immobilizing these catalysts onto membrane surfaces, offering a solution to the inherent challenges of powdered catalysts. Recent advances in pilot-scale or engineering applications of Fenton-like based devices have also been summarized for the first time. The paper concludes by charting new research directions, emphasizing advanced catalyst design, precise identification of reactive oxygen species, and in-depth mechanistic studies. These efforts aim to enhance the application potential of nanotechnology-based AOPs in real-world wastewater treatment. This article is protected by copyright. All rights reserved.

Insights into the efficient water treatment over N-doped carbon nanosheets with layered minerals as template: The role of interfacial electron tunneling and transfer.

Peroxymonosulfate (PMS) oxidation reactions have been extensively studied recently. Due to the high material cost and low catalytic capability, PMS oxidation technology cannot be effectively applied in an industrial water treatment process. In this work, we developed a modification strategy based on enhancing the neglected electron tunneling effect to optimize the intrinsic electron transport process of the catalyst. The 2D nitrogen-doped carbon-based nanosheets with small interlayer spacing were prepared by self-polymerization of dopamine hydrochloride inserted into the natural layered bentonite template. Systematic characterizations confirmed that the smaller layer spacing in the 2D nitride-doped carbon-based nanosheets reduces the depletion layer width. The weak electronic shielding effect derived by the small layer spacing on the material subsurface enhanced the bulk electron tunneling effect. More bulk electrons could be migrated to the catalyst surface to activate PMS molecules. The PMS activation system showed ultrafast oxidation capability to degrade organic pollutants and strong ability to resist interference from environmental matrixes due to the optimized electron transfer process. Furthermore, the developed membrane reactor exhibited strong catalytic stability during the continuous degradation of P-Chlorophenol (CP).

Utilizing the oxygen-atom trapping effect of Co3O4 with oxygen vacancies to promote chlorite activation for water decontamination.

Heterogeneous high-valent cobalt-oxo [≡Co(IV)=O] is a widely focused reactive species in oxidant activation; however, the relationship between the catalyst interfacial defects and ≡Co(IV)=O formation remains poorly understood. Herein, photoexcited oxygen vacancies (OVs) were introduced into Co3O4 (OV-Co3O4) by a UV-induced modification method to facilitate chlorite (ClO2-) activation. Density functional theory calculations indicate that OVs result in low-coordinated Co atom, which can directionally anchor chlorite under the oxygen-atom trapping effect. Chlorite first undergoes homolytic O-Cl cleavage and transfers the dissociated O atom to the low-coordinated Co atom to form reactive ≡Co(IV)=O with a higher spin state. The reactive ≡Co(IV)=O rapidly extracts one electron from ClO2- to form chlorine dioxide (ClO2), accompanied by the Co atom returning a lower spin state. As a result of the oxygen-atom trapping effect, the OV-Co3O4/chlorite system achieved a 3.5 times higher efficiency of sulfamethoxazole degradation (~0.1331 min-1) than the pristine Co3O4/chlorite system. Besides, the refiled OVs can be easily restored by re-exposure to UV light, indicating the sustainability of the oxygen atom trap. The OV-Co3O4 was further fabricated on a polyacrylonitrile membrane for back-end water purification, achieving continuous flow degradation of pollutants with low cobalt leakage. This work presents an enhancement strategy for constructing OV as an oxygen-atom trapping site in heterogeneous advanced oxidation processes and provides insight into modulating the formation of ≡Co(IV)=O via defect engineering.

Progress on mechanism and efficacy of heterogeneous photocatalysis coupled oxidant activation as an advanced oxidation process for water decontamination.

The rising debate on the dilemma of photocatalytic water treatment technologies has driven researchers to revisit its prospects in water decontamination. Nowadays, heterogeneous photocatalysis coupled oxidant activation techniques are intensively studied due to their dual advantages of high mineralization and high oxidation efficiency in pollutant degradation. This paved a new way for the development of solar-driven oxidation technologies. Previous reviews focused on the advances in one specific coupling technique, such as photocatalytic persulfate activation and photocatalytic ozonation, but lack a consolidated understanding of the synergy between photocatalytic oxidation and oxidant activation. The synergy involves the migration of photogenerated carriers, radical reaction, and the increase in oxidation rate and mineralization. This review systematically summarizes the fundamentals of activation mechanism, advanced characterization techniques and synergistic effects of coupling techniques for water decontamination. Besides, specific cases that lead researchers astray in revealing mechanisms and assessing synergy are critically discussed. Finally, the prospects and challenges are put forward to further deepen the research on heterogeneous photocatalytic activation of oxidants. This work provides a consolidated view of the existing heterogeneous photocatalysis coupled oxidant activation techniques and inspires researchers to develop more promising solar-driven technologies for water decontamination.

The Unique Fe3 Mo3 N Structure Bestowed Efficient Fenton-Like Performance of the Iron-Based Catalysts: The Double Enhancement of Radicals and Nonradicals.

Iron-based catalysts are widely used in Fenton-like water pollution control technology due to their high efficiency, but their practical applications are limited by complex preparation conditions and strong blockage of Fe2+ /Fe3+ cycle during the reaction. Here, a new iron-molybdenum bimetallic carbon-based catalyst is designed and synthesized using cellulose hydrogel for adsorption of Fe and Mo bimetals as a template, and the effective iron cycle in water treatment is realized. The integrated materials (Fe2.5 Mo@CNs) with "catalytic/cocatalytic" performance have higher Fenton-like activation properties and universality than the equivalent quantity iron-carbon-based composite catalysts (Fe@CNs). Through the different characterization methods, experimental verifications and theoretical calculations show that the unique Fe3 Mo3 N structure promotes the adsorption of persulfate and reduces the energy barrier of the reaction, further completing the double enhancement of radicals (such as SO4 ·- ) and nonradicals (1 O2 and electron transport process). The integrated "catalytic/cocatalytic" combined material is expected to provide a new promotion strategy for Fenton-like water pollution control.

Fenton-like activity and pathway modulation via single-atom sites and pollutants comediates the electron transfer process.

The studies on the origin of versatile oxidation pathways toward targeted pollutants in the single-atom catalysts (SACs)/peroxymonosulfate (PMS) systems were always associated with the coordination structures rather than the perspective of pollutant characteristics, and the analysis of mechanism commonality is lacking. In this work, a variety of single-atom catalysts (M-SACs, M: Fe, Co, and Cu) were fabricated via a pyrolysis process using lignin as the complexation agent and substrate precursor. Sixteen kinds of commonly detected pollutants in various references were selected, and their lnkobs values in M-SACs/PMS systems correlated well (R2 = 0.832 to 0.883) with their electrophilic indexes (reflecting the electron accepting/donating ability of the pollutants) as well as the energy gap (R2 = 0.801 to 0.840) between the pollutants and M-SACs/PMS complexes. Both the electron transfer process (ETP) and radical pathways can be significantly enhanced in the M-SACs/PMS systems, while radical oxidation was overwhelmed by the ETP oxidation toward the pollutants with lower electrophilic indexes. In contrast, pollutants with higher electrophilic indexes represented the weaker electron-donating capacity to the M-SACs/PMS complexes, which resulted in the weaker ETP oxidation accompanied with noticeable radical oxidation. In addition, the ETP oxidation in different M-SACs/PMS systems can be regulated via the energy gaps between the M-SACs/PMS complexes and pollutants. As a result, the Fenton-like activities in the M-SACs/PMS systems could be well modulated by the reaction pathways, which were determined by both electrophilic indexes of pollutants and single-atom sites. This work provided a strategy to establish PMS-based AOP systems with tunable oxidation capacities and pathways for high-efficiency organic decontamination.

Impact of nanoplastics on membrane scaling and fouling in reverse osmosis desalination process.

Nanoplastics (NPs) are a prevalent type of emerging pollutant in marine environment. However, their fouling behavior and impact on reverse osmosis (RO) membrane performance remain unexplored. We investigated the relationship between polystyrene (PS), one of the most abundant NPs, with silica scaling and humic acid (HA) fouling in RO. The results demonstrated that the surface potential of NPs played an important role in the combined scaling and fouling process. Compared with the negatively charged NPs (original PS and carboxyl group modified PS, PS-COOH), the amino-functionalized PS (PS-NH2) with positive surface charge significantly accelerated membrane scaling/fouling and induced a synergistic water flux decline, due to the strong electrostatic attraction between PS-NH2, foulants, and the membrane surface. The amino groups acted as binding sites, which promoted the heterogeneous nucleation of silica and adsorption of HA, then formed stable composite pollutants. Thermodynamic analysis via isothermal titration calorimetry (ITC) further confirmed the spontaneous formation of stable complexes between PS-NH2 and silicates/HA. Our study provides new insights into the combined NPs fouling with other scalants or foulants, and offers guidance for the accurate prediction of RO performance in the presence of NPs.

Coagulation performance and mechanism of different hydrolyzed aluminum species for the removal of composite pollutants of polyethylene and humic acid.

Microplastics (MPs) and natural organic matter (NOM) composite pollutants have become emerging contaminants with potential threats. Coagulation has been widely used to remove MPs and NOM, but the underlying mechanisms for the removal of MPs-NOM composite pollutants by hydrolyzed Al species remain unclear. Therefore, the coagulation performance and mechanism of AlCl3, polyaluminum chloride with basicity of 2.2 (PAC22), and PAC25 in treating polyethylene (PE), humic acid (HA), and PE-HA composite systems were systematically investigated. The results showed that in the single PE system, PAC25 with hexagonal clusters achieved the maximum removal (68.09 %) (pH: 5, dosage: 0.5 mM) since adsorption bridging and sweeping effect were the main mechanisms for PE removal. The adsorption of HA on the PE surface enhanced its hydrophilicity and electrostatic repulsion, resulting in decreased PE removal. In the AlCl3-PE-HA system, the oligomeric Al first interacted with the -COOH and C-OH of HA through complexation, followed by the meso- and polymers of Al interacted with PE by electrostatic adsorption. The pre-formed medium polymeric Al species (Alb) and colloidal or solid Al species (Alc) in PAC22 and PAC25 formed complexes with the -OH and -COOH groups of HA, respectively, and then removed PE by adsorption bridging and sweeping effect.

Microcosmic mechanism analysis of the combined pollution of aged polystyrene with humic acid and its efficient removal by a composite coagulant.

The composite pollutants formed by aged polystyrene (APS) and natural organic matter are complex and harmful, which lead to the deterioration of water quality. In this work, the interaction mechanism between humic acid (HA) and APS was discussed by investigating the changes in their functional groups. Besides, a novel polyaluminum-titanium chloride composite coagulant (PATC) was prepared, and its binding behaviors with HA@APS under different pH conditions were analyzed from a microscopic perspective. It was found that at pH 4, π-π conjugation was the dominant interaction between HA and APS. And the main removal mechanism of HA@APS by PATC was surface complexation. With the increase of pH, π-π conjugation, n-π electron donor-acceptor interaction (EDA), and hydrogen bonding gradually dominated the interaction between APS and HA. At pH 7, PATC hydrolyzed to form various polynuclear Al-Ti species, which could meet the demand for different binding sites of HA@APS. Under alkaline conditions, HB and n-π EDA in HA@APS were weakened, while π-π conjugation held a dominant position again. At this time, the main coagulation mechanism of PATC changed from charge neutralization to sweeping action, accompanied by hydrogen bonding. ENVIRONMENTAL IMPLICATION: Microplastics (MPs) have attracted the public's attention due to their potential toxicity to humans. The combined pollution of aged microplastics and humic acid (HA) will bring great harm to aquatic environment. The development of novel composite coagulants is hopeful to efficiently remove MPs and their combined pollutants. Elucidating the interactions between HA and aged MPs is helpful to understand the transformation and fate of MPs in actual environments, and to reveal the removal mechanism of composite pollutants by coagulation. The findings presented here will provide theoretical guidance for addressing the challenges of coagulation technology in treating new pollutants in practice.

Intrinsic mechanism for the removal of antibiotic pollution by a dual coagulation process from the perspective of the interaction between NOM and antibiotic.

Antibiotics bring potential risks to human health and ecosystem, and their coexistence with natural organic matters (NOMs) could have harmful impacts on the environment. Herein, a polyaluminium chloride (PAC)-polydimethyl diallyl ammonium chloride (PDMDAAC) dual coagulation process was designed to remove the co-pollutants of chlortetracycline (CTC) and humic acid (HA), representing antibiotics and NOMs, respectively. The main research strength was given to understand molecular interactions and their mechanisms associated with the coagulation and flocculation. We found that the co-existing HA and CTC increased the hydrophily and stability of contaminants, and generated HA@CTC complexes with large particles size. The interaction mechanism between CTC and HA was mainly hydrogen bonding, hydrophobic association action, n-π* electron donor-acceptor interaction, and π-π* conjugation. Lewis acid-base interaction was the main force between HA and CTC. The bonding energies of OH…N, OH…O, and hydrophobic association were -12.2 kcal/mol, -13.1 kcal/mol, and -11.4 kcal/mol, respectively, indicating that hydrogen bonding was stronger than hydrophobic association. The interactions between HA and CTC could improve their removal efficiency in the coagulation process. This is due to that the functional groups (COOH and OH) in the HA@CTC could be adsorbed by Al based hydrolysates. Polar interaction dominated the CTC and HA removal, and PAC was more efficient than PDMDAAC to remove HA@CTC complexes due to its higher complexing capacity. Thanks to the low concentration of residual contaminants and the formation of large and loose flocs, the interaction of HA and CTC could alleviate membrane fouling during ultrafiltration process. This study will provide new insight into the efficient removal of combined pollution and membrane fouling control.

Simultaneous removal of antibiotics and antibiotic resistant genes using a CeO2@CNT electrochemical membrane-NaClO system.

The simultaneous removal of antibiotic and antibiotic resistance genes (ARGs) are important to inhibit the spread of antibiotic resistance. In this study, a coupled treatment system was developed using a CeO2 modified carbon nanotube electrochemical membrane and NaClO (denoted as CeO2@CNT-NaClO) to treat simulated water samples containing antibiotics and antibiotic-resistant bacteria (ARB). As the mass ratio of CeO2 to CNT was 5:7 and the current density was 2.0 mA/cm2, the CeO2@CNT-NaClO system removed 99% of sulfamethoxazole, 4.6 log sul1 genes, and 4.7 log intI1 genes from the sulfonamide-resistance water samples, and removed 98% of tetracycline, 2.0 log tetA genes, and 2.6 log intI1 genes of the tetracycline-resistance water samples. The outstanding performance of the CeO2@CNT-NaClO system for simultaneously removing antibiotic and ARGs was mainly ascribed to the generation of multiple reactive species, including •OH, •ClO, •O2- and 1O2. Antibiotics can undergo efficient degradation by •OH. However, the reaction between •OH and antibiotics reduces the availability of •OH to permeate into the cells and react with DNA. Nevertheless, the presence of •OH enhancd the effects of •ClO, •O2-, and 1O on ARG degradation. Through the coupled action of •OH, •ClO, •O2-, and 1O2, the cell membranes of ARB experience severe damage, resulting in an increase in intracellular reactive oxygen species (ROS) and a decrease in superoxide dismutase (SOD) activity. Consequently, this coordinated mechanism leads to superior removal of ARGs.

Sono-enhanced heterogeneous Fenton catalysis: magnetic halloysite nanotube synthesis and accelerated free radical generation.

Although heterogeneous Fenton catalysis has captured increasing attention compared to its homogeneous counterpart, it still confronts some inherent drawbacks in use, such as the dilemma in solid-liquid separation and greater mass transfer resistance. Driven by the acoustic cavitation effect, herein, a sono-enhanced heterogeneous Fenton catalysis process was built to overcome the above two shortcomings, by rapidly synthesizing magnetic Fenton-like catalysts and accelerating electron transfer during the catalytic reaction. The results show that, compared to the traditional chemical coprecipitation method, Fe3O4 with smaller particle size and better crystallinity grew on the surface of halloysite nanotubes (HNTs) by using the sonochemical strategy, leading to displaying the higher catalytic activity toward the degradation of methylene blue (MB, improved by ~2.5 times). In parallel, more •OH and •O2- were produced after the ultrasound was further introduced to the routine Fenton-like catalysis system, thus highly accelerating the removal of MB (improved by ~50%). Besides, benefiting from the robust chemical integration of Fe3O4 and HNTs, Fe3O4@HNTs-S had a lower iron ion leaching in use, showing superior catalytic stability. The speed, simplicity, and generality, together with the enhanced mass transfer rate, make the use of ultrasound an enabling methodology to improve the heterogeneous Fenton catalysis.

Insights into S-doped iron-based carbonaceous nanocomposites with enhanced activation of persulfate for rapid degradation of organic pollutant.

In the work, S-doped iron-based carbon nanocomposites (Fe-S@CN) for activating persulfate (PS) were prepared by calcining iron-loaded sodium lignosulfonate. The characterization revealed that the main substances of Fe-S@CN were FeS and Fe3C, which were distributed on porous carbon nanosheets in rod-like morphology. In the Fe-S@CN/PS system, carbamazepine could be completely removed within 30 min, and the relative contribution of hydroxyl radicals (OH·), sulfate radicals (SO4·-) and total singlet oxygen (1O2) and superoxide radicals (O2·-) for carbamazepine removal were approximated as 8.7%, 19.2% and 72.1%, respectively. Electron paramagnetic resonance spectroscopy demonstrated that S doping promoted the formation of various active species. Compared with the catalyst without S doping, Fe-S@CN exhibited higher activation performance (1.48-fold) for PS due to the enhanced electron transfer rate and facilitated Fe2+/Fe3+ cycle. Density functional theory calculations showed that S doping promoted the binding between the catalyst and PS, and enhanced the overall internal electron density of the catalyst. Fe-S@CN exhibited excellent catalytic performance over a wide pH range (3.0-11.0). The active sites of Fe-S@CN used in the cycling experiments was also largely recovered after thermal regeneration. Overall, this study shows for the first time the impact of SLS as an S dopant on enhanced PS activation.

The suitability and mechanism of polyaluminum-titanium chloride composite coagulant (PATC) for polystyrene microplastic removal: Structural characterization and theoretical calculation.

Microplastics (MPs) particles bring potential threats to the aqueous environment, and the coexistence of natural organic matter (NOM) enhances their toxicity. Coagulation is an efficient method for particle removal and exploring the binding sites and modes of the coagulant hydrolysates with MPs in the presence of NOM is essential to understand the coagulation mechanism. In this study, a novel polymerized polyaluminum-titanium chloride composite coagulant (PATC) was prepared and used to remove polystyrene (PS). It was found that PATC could compress or even destroy the surface layer of the negatively charged PS. In comparison to PAC and PTC, PATC was more efficient in decreasing the energy barrier of the PS particles and increasing their aggregation rate over a wider pH range. The results of the Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) calculation revealed that the interaction between the hydrolysates of PATC and PS was mainly polar interaction (VAB), such as hydrogen bonding. The peak intensity and peak shift in Fourier-transformed infrared (FTIR) and X-ray photoelectron spectra (XPS) were analyzed to further explore the interaction between the hydrolysates of PATC and PS. It was found that hydrogen bonding existed between the -OH group of PATC and the aliphatic C-H and C=O groups of PS. And the main interaction between HA and PS was the π-π* conjugation and hydrogen bonding between the -COOH, -OH, and C=O groups of HA and the C=O and aliphatic C-H groups of PS. Therefore, in the HA@PS system, the active sites of HA (e.g. -COOH and -OH) and PS (e.g., C=O and aliphatic C-H) binding with the coagulants were occupied, which accordingly led to the dramatic decline in the removal efficiency of both HA and PS. In actual lake water treatment, although the removal efficiency of PS was significantly poor, PATC performed better for PS removal than PAC and PTC. Besides, the effluent pH was maintained at 6.81±0.08, which met the requirements of the subsequent water treatment process. This study provides systematic knowledge for understanding the interaction between PS, NOM, and coagulant hydrolysates, and further confirms the application potential of PATC for MPs removal.

Revealing the Generation of High-Valent Cobalt Species and Chlorine Dioxide in the Co3O4-Activated Chlorite Process: Insight into the Proton Enhancement Effect.

A Co3O4-activated chlorite (Co3O4/chlorite) process was developed to enable the simultaneous generation of high-valent cobalt species [Co(IV)] and ClO2 for efficient oxidation of organic contaminants. The formation of Co(IV) in the Co3O4/chlorite process was demonstrated through phenylmethyl sulfoxide (PMSO) probe and 18O-isotope-labeling tests. Both experiments and theoretical calculations revealed that chlorite activation involved oxygen atom transfer (OAT) during Co(IV) formation and proton-coupled electron transfer (PCET) in the Co(IV)-mediated ClO2 generation. Protons not only promoted the generation of Co(IV) and ClO2 by lowering the energy barrier but also strengthened the resistance of the Co3O4/chlorite process to coexisting anions, which we termed a proton enhancement effect. Although both Co(IV) and ClO2 exhibited direct oxidation of contaminants, their contributions varied with pH changes. When pH increased from 3 to 5, the deprotonation of contaminants facilitated the electrophilic attack of ClO2, while as pH increased from 5 to 8, Co(IV) gradually became the main contributor to contaminant degradation owing to its higher stability than ClO2. Moreover, ClO2- was transformed into nontoxic Cl- rather than ClO3- after the reaction, thus greatly reducing possible environmental risks. This work described a Co(IV)-involved chlorite activation process for efficient removal of organic contaminants, and a proton enhancement mechanism was revealed.

Repeated fluctuation of Cu2+ concentration during photocatalytic purification of SMZ-Cu2+ combined pollution: Behavior, mechanism and application.

Although the effect of Cu2+ on antibiotic removal during photocatalytic reaction has been studied in depth, there is less known about the effect of antibiotics on Cu2+ removal. In this study, we report for the first time that, during the photocatalytic purification of sulfamerazine (SMZ) and Cu2+ combined pollution, Cu2+ concentration showed an obvious five-stage fluctuation, which was completely different from the simple promotion or inhibition reported in previous studies. By employing HPLC-MS analysis and density functional theory (DFT) calculation, the repeated fluctuation of Cu2+ concentration was found to be closely related to the SMZ degradation process, mainly resulting from solution pH drop and formation of Cu-containing intermediates which acted as sacrificial agents for Cu2+ reduction. In addition, compared with the SMZ-free system, the presence of SMZ can greatly enhance the deep removal of Cu2+ (minimum Cu2+ concentration was only 0.17 mg/L vs. 1.28 mg/L without SMZ), and there was a wide time interval to ensure the efficient recovery of Cu metal. More interestingly, the in-situ obtained Cu-decorated TiO2 photocatalyst performed well in water splitting, nitrogen fixation and bacterial sterilization. Results of this study confirmed the great potential of photocatalytic technology in purifying antibiotic-heavy metal combined pollution.

Super-amphiphilic graphene promotes peroxymonosulfate-based emulsion catalysis for efficient oil purification.

Oil fractions containing highly toxic and hazardous organic contaminants can not only cause severe environmental disasters, but also an undesired waste of resources. Given the exceptional performance of persulfates in the removal of persistent and refractory organic pollutants from aqueous media, herein, a peroxymonosulfate-based Pickering emulsion catalytic (PPEC) system was constructed for the hazardous oil purification, using super-amphiphilic graphene as a solid emulsifier and a heterogeneous catalyst simultaneously. Combined detailed instrumental analysis with theoretical calculations, we find that the incorporation of pyridinic N and its oxide significantly facilitated the formation of super-amphiphilic graphene and successfully induced the formation of Pickering emulsion. In addition to stabilizing the PPEC system, super-amphiphilic graphene can also achieve efficient removal of Sudan III (simulated lipophilic organic pollutant) by activating peroxymonosulfate (PMS) to generate •O2- and 1O2. Results showed that 80 mg/L Sudan III (20 mL) could be fully degraded within 30 min using 10 mL 5 mmol PMS. More significantly, our proposed PPEC system also exhibited excellent property in the purification of practical waste engine oil. This study provides new insights into the purification and recovery of waste oil.

Pilot-scale advanced treatment of actual high-salt textile wastewater by a UV/O3 pressurization process: Evaluation of removal kinetics and reverse osmosis desalination process.

Advanced oxidation processes (AOPs) such as ozonation and Fenton processes are widely used in the treatment of high-salt wastewater. The UV/O3 pressurization process was designed and applied at the pilot-scale for treatment of actual high-salt textile wastewater. The UV/O3 pressurization process achieved the highest decolorization (85 %) and chemical oxygen demand (CODCr, 43.2 %) removal efficiency at an O3 dosage of 200 g·t-1 and a pressure of 0.2 MPa. Compared to ordinary ozonation, the UV/O3 pressurization process improved the solubility and gas-liquid mass transfer efficiency of O3 in wastewater and generated a large number of O3 microbubbles. Hydroxyl radical (·OH), superoxide radicals (O2·-) and single oxygen (1O2) all played a significant role on the removal of pollutants in wastewater during the UV/O3 pressurization process. The reverse osmosis (RO) process was used to evaluate the effect of UV/O3 pressurization and Fenton pre-oxidation processes on the desalination process as the last process in treating high-salt organic wastewater. The pre-oxidation processes improved the initial RO water flux. Compared with the Fenton process, the UV/O3 pressurization process had less membrane fouling (thin fouling layer vs thick fouling layer), and final water flux (59.4 LMH) was higher than that of Fenton process (34.9 LHM). The total dissolved solids (TDS), Cl- and SO42- of the effluent from UV/O3 pressurization process (37.2, 7.6 and 3.0 mg·L-1) were better than that of Fenton process (65.7, 13.9 and 7.1 mg·L-1). Therefore, the UV/O3 pressurization process without secondary pollution is more suitable for the advanced treatment of high-salt organic wastewater than the Fenton process.

One-step synthesis of Enteromorpha graphene aerogel modified by hydrophilic polyethylene glycol achieving high evaporation efficiency and pollutant tolerance.

Photothermal evaporation using solar energy is a sustainable way to produce fresh water from seawater. Aiming to explore functional materials as a solar-energized evaporator with enhanced evaporation rate and pollutant tolerance, this study was to synthesize a self-floating composite graphene aerogel (GA) doped with Enteromorpha and modified polyethylene glycol (PEG), named as PEGA using solar energy for desalination. Physio-chemical properties and evaporative mechanism of PEGA were experimentally investigated and analyzed with respect to molecular weight, PEG dosage, and ratio of Enteromorpha and graphene oxide. Experimental data revealed that the modification of PEG improved hydrophilic functional ability of PEGA, resulting in increasing the evaporation rate and photothermal conversion efficiency up to 2.55 kg/(m2·h) and 105.71 %, respectively. The ion removal rate of seawater exceeds 99.99 % via the PEGA conducted solar evaporation. Furthermore, PEGA possessed an excellent property of salinity emulsion pollution tolerance. Particularly, the evaporation rate of the PEG-modified biomass-based aerogel was 2.84 kg/(m2·h) in a 15 wt% NaCl solution (1 sun, 6 h) and 2.50 kg/(m2·h) at 1 h. The formation of hydrogen bonds between -OH of PEG and water molecules assist to conduct water along the graphene matrix to improve water evaporation. The cost of the graphene aerogel modified by Enteromorpha was reduced by 38.88 % less than the original graphene aerogel. The results from this study will greatly promote the application of graphene aerogel for desalination via solar evaporation.

Revealing the fundamental role of MoO2 in promoting efficient and stable activation of persulfate by iron carbon based catalysts: Efficient Fe2+/Fe3+ cycling to generate reactive species.

Electron-rich iron sites are the main sites for iron-based catalysts to activate persulfate (PS) to generate reactive species, while blocked Fe2+/Fe3+ cycling usually reduces the catalytic performance of iron-based materials and hinders the generation of reactive species in the reaction. To solve the bottleneck, we synthesized an iron-carbon nanocomposite catalyst loaded with MoO2 (Fe/Mo-CNs). The promotion of MoO2 on the Fe2+/Fe3+ cycle in the system allowed Fe/Mo-CNs to exhibit excellent catalytic performance and environmental adaptability. The degradation rate of bisphenol S (BPS) by the Fe/Mo-CNs/PS system was significantly increased to 0.080 min-1 compared with the iron-carbon based catalyst/persulfate system, and the degradation efficiency of BPS was maintained at around 85% after four cycles. Density functional theory (DFT) calculations showed that the introduction of MoO2 reduced the reaction energy barrier of persulfate activated by catalysts to produce reactive species, especially promoted the production of more high valent iron (Fe(IV)). Fe(IV) and reactive oxygen species (SO4·-, ·OH, ·O2- and 1O2) worked together on the efficient degradation of BPS. In addition, the test of an automatic circulating degradation plant had proved that Fe/Mo-CNs had a good practical application prospect. BPS was mainly degraded by ring cleavage and O=S=O bond cleavage, and the toxicity of BPS and its intermediates were also evaluated. This work clarifies the mechanism of improving the catalytic performance of heterogeneous iron-based catalysts by MoO2 in sulfate radical-based advanced oxidation processes (SR-AOPs), providing a new idea for solving the blockage of Fe2+/Fe3+ cycle in SR-AOPs.