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Heterogeneous Fenton catalysis offers a promising alternative to traditional Fenton oxidation for water treatment as its wider operating pH range and high cyclic performance. However, designing catalysts that can activate H2O2 both actively and selectively to mineralize refractory pollutants remains challenging. Here, a state‐of‐the‐art design principle of constructing spatially separated Fe‐M (M denotes an oxophilic first‐row transition metal) dual single‐atom sites is developed for Fenton‐like catalysis. This strategy enables accelerated redox cycles between the dual metal centers, leading to precise manipulation of Fe···O‐O···M intermediate in H2O2 activation. This, in turn, aids the homolytic decomposition of H2O2 toward selective and efficient •OH generation. Taking Fe‐Cu pairs as an example, the constructed dual sites outperform the individual Fe or Cu sites, demonstrating a higher activation selectivity (94%) for •OH production. Further benefitting from the electronic communications between Fe (electron acceptor) and Cu (electron donor), the SA‐Fe‐Cu‐CN catalyst exhibited an effective H2O2 decomposition with 0.94 mm of •OH yielded within 50 min. Compared to the typical homogeneous system, the SA‐Fe‐Cu‐CN/H2O2 system has higher mineralization capacities toward refractory pollutants and greater pH tolerance. The work provides a new strategy for the design of robust catalysts by creating spatially separated dual single‐atom sites toward multi‐reactant systems. [ABSTRACT FROM AUTHOR]

In this study, a Pd -loaded porous titanium anode was prepared using a simple spraying method, and an electrocatalytic oxidation system was constructed with Pd/Ti as anode and titanium mesh as cathode to achieve the efficient and stable removal of refractory organic pollutants from coking wastewater reverse osmosis concentrates. At a current density of 5 mA/cm^2, the Pd/Ti anode achieved a COD removal of 86.3% in 4 hours which was higher than that of the BDD (46.7%) and Ir/Ta (34.0%) electrodes. Gas chromatography-mass spectrometer analysis demonstrated that the electrocatalytic system with Pd/Ti as the anode could effectively convert refractory organic pollutants (e.g., 1,2-dimethyl-5-nitroadamantane) in the reverse osmosis concentrate into simple substances (e.g., 2-pentyn-1-ol). During the 28-hour long-term operation, the COD effluent was less than 50 mg/L, meeting the limit of the standard for direct discharge of wastewater in the Emission Standard for Pollutants in Coking Chemical Industry (GB 16171—2012). These results indicated that the Pd/Ti anode had the potential for eliminating refractory organic pollutants in reverse osmosis concentrates from coking wastewater with high efficiency and low consumption.

[Display omitted] Highly reactive nanoclusters of metal oxides are extremely difficult to be synthesized due to their thermodynamic instability. For the first time, CuO x nanoclusters supported on anatase TiO 2 nanotubes (NT) with many defects as anchoring sites were successfully prepared. Although the copper loading reached as high as 2.5 %, the size of CuO x nanoclusters in the sample of 2.5 %CuO x /NT were mainly around 1.0 nm. The aggregation of copper species during the calcination process was undoubtedly hampered by the anchoring effects of the abundant defects in NT support. Due to the highly exposed undercoordinated atoms of CuO x nanoclusters, the mixed valences of copper, and the strong interface interaction between CuO x nanoclusters and NT support, 2.5 %CuO x /NT-catalyzed ozonation showed the highest pseudo-first-order reaction rate constant of 8.5 × 10−2 min−1, 2.2 and 4.0 times that of NT-catalyzed ozonation and ozonation alone, respectively. Finally, the catalytic mechanism was revealed by both experiments and density functional theory calculations (DFT). The results demonstrated that the undercoordinated Cu in CuO x /NT could highly promote the adsorption of ozone with a high adsorption energy of −125.16 eV and the adsorbed ozone was activated immediately, tending to dissociate into a O 2 molecule and a surface O atom. Thus, abundant reactive oxygen species, e.g., hydroxyl radical (·OH), superoxide radical (·O 2 –) and singlet oxygen (1O 2), could be generated via chain reactions. Especially, ·OH mainly contributed to the removal of ibuprofen pollutants. This work sheds a light on the design and preparation of highly reactive nanoclusters of metal oxide catalysts for catalytic ozonation of refractory organic pollutants. [ABSTRACT FROM AUTHOR]

It is essential to develop an efficient technology for the elimination of refractory contaminants due to their high toxicity. In this study, a novel underwater bubbling pulsed discharge plasma (UBPDP) system was proposed for the degradation of Orange II (OII). The degradation performance experiments showed that by enhancing the peak voltage and pulse frequency, the degradation efficiency of OII increased gradually. The removal efficiencies under different air flow rates were close. Reducing OII concentration and solution conductivity could promote the elimination of OII. Compared with neutral and alkaline conditions, acidic condition was more beneficial to OII degradation. The active species including ·OH, ·O2−, 1O2, and hydrated electrons were all involved in OII degradation. The concentrations of O3 and H2O2 in OII solution were lower than those in deionized water. During discharge, the solution pH increased while conductivity decreased. The variation of UV–vis spectra with treatment time indicated the effective decomposition of OII. Possible degradation pathways were speculated based on LC-MS. The toxicity of intermediate products was predicted by the Toxicity Estimation Software Tool. Coexisting constituents including Cl−, SO42−, HCO3−, and humic acid had a negative effect on OII removal. Finally, the comparison with other technology depicted the advantage of the UBPDP system. [ABSTRACT FROM AUTHOR]

Pulp and paper wastewater (PPWW) contains numerous refractory and harmful contaminants that require advanced treatment to meet the discharge criteria. This study compared the efficacy of two PPWW treatments: ultraviolet/peroxymonosulfate (UV/PMS) and ultraviolet/H2O2 (UV/H2O2) working under similar circumstances. The initial pH value, oxidant dosage, UV radiation intensity, and pseudo-first-order constant kobs were systematically studied in both systems. Optimally, the UV/PMS process produced an effluent of higher quality than the UV/H2O2, as measured by the removal efficiencies of chemical oxygen demand (COD) in 60 min, which were 48.2 and 64.3% for the respective UV/H2O2 and UV/PMS processes and corresponding kobs values of 0.0102 and 0.0159 min−1, respectively. Radical scavenging experiments demonstrated that •OH was the primary reactive oxygen species in UV/H2O2 process, and •OH and SO4−• in the UV/PMS process. Moreover, ultraviolet-visible spectroscopy and gas chromatography coupled mass spectroscopy analyses showed that deep treatment of petroleum hydrocarbons with carbon chain lengths greater than 18 and macromolecular semi-volatile organic compounds in paper wastewater is difficult, whereas the UV/PMS process can significantly improve the removal of amides, esters, phenols, and other aromatic compounds. HIGHLIGHTS UV/PMS is a worthwhile in-depth study to achieve more effective treatment of actual wastewater.; It was difficult to completely degrade the organics in actual PPWW due to some long-chain alkanes and macromolecules containing benzene ring organic substances.;

The stable structure and toxic effect of refractory organic pollutants in wastewater lead to the problem of high energy consumption in water treatment technology. Herein, we propose a synergistic purification of refractory wastewater driven by microorganisms and surface microelectric fields (SMEF) over a dual-reaction-center (DRC) catalyst HCLL-S8-M prepared by an in situ growth method of carbon nitride on the Cu-Al2O3 surface. Characterization techniques demonstrate the successful construction of SMEF with strong electrostatic force over HCLL-S8-M based on cation-π interactions between metal copper ions and carbon nitride rings. With the catalyst as the core filler, an innovative fixed bed bioreactor is constructed to purify the actual kitchen-oil wastewater. The removal efficiency of the wastewater even with a very low biodegradability (BOD5/COD = 0.33) can reach 60% after passing through this bioreactor. An innovative reaction mechanism is revealed for the first time that under the condition of a small amount of biodegradable organic matter, the SMEF induces the enrichment of electric active microorganisms (Desulfobulbus and Geobacter) in the wastewater, accelerates the interspecies electron transfer of intertrophic metabolism with the biodegradable bacteria through the extracellular electron transfer mechanism such as cytochrome C and self-secreted electron shuttle. The electrons of the refractory organic pollutants adsorbed on the surface of the catalyst are delocalized by the SMEF, which can be directly utilized by microorganisms through EPS conduction. The SMEF generated by electron polarization can maximize the utilization of pollutants and microorganisms in wastewater and further enhance degradation without adding any external energy, which is of great significance to the development of water self-purification technology.

The treatment of refractory organic wastewater pollution is a focus issue related to the national economy and the people′s livelihood. Electrochemical oxidation has attracted much attention in many wastewater treatment technologies because of its clean, efficient and flexible characteristics. Anode is the core of electrochemical oxidation, which determines the efficiency and cost of this technology. In recent years, with the development of anode materials, a new anode form, Magnetically Assembled Electrode (MAE), has emerged, which is between the traditional two-dimensional electrode and three-dimensional electrode. Its essence is a modular electrode, which uses a magnet to adsorb the magnetic sub electrode material on the two-dimensional main electrode, endows the electrode with a large number of catalytic active sites, makes the electrode have diversity, flexible and adjustable performance and good recyclability, and has the potential of stable and efficient treatment of dynamic wastewater. In this paper, flake magnetic cellulose nanofiber polyaniline composites (CNFs/PANI) are used as secondary electrode, typical DSA electrode Ti/PbO2 is used as main electrode, and a new MAE with good adsorption and degradation properties of azo dyes is constructed by combining adsorbent and electrocatalyst, so as to improve the efficiency of azo dye wastewater treatment. Taking the typical azo dye acid red g as the target, the electrochemical properties of the new MAE and the degradation effect of acid red g simulated wastewater were investigated. The results show that compared with the traditional two-dimensional Ti/PbO2 anode, the new MAE has more adsorption catalytic active sites and higher electrocatalytic activity. Due to the easy enrichment of acid red g to the surface of the new MAE, the new MAE can maintain high dye degradation efficiency even when the dye concentration decreases in the later stage of the degradation process. [ABSTRACT FROM AUTHOR]

[Display omitted] • Textile waste as raw material was used to develop Co-doped carbon fiber catalyst. • Abundant formation of C-O-Co bonds enhanced the electron transfer. • It realized high catalytic efficiency for various refractory organic pollutants. • It also displayed remarkable catalytic efficiency in purifying coking wastewater. • Three possible degradation pathways of BPA over Co 3 O 4 @TCF was proposed. Resource utilization of textile waste is an important way of achieving the "dual carbon" policy. A one-step calcination method using textile waste as a raw material was used to develop a novel Co-doped carbon fiber catalyst (Co 3 O 4 @TCF) with catalytic performance in the activation of peroxymonosulfate (PMS) to degrade refractory organic pollutants. Various refractory organic pollutants in the Co 3 O 4 @TCF/PMS system were degraded within a few min. In particular, 50 mg·L−1 of bisphenol A (BPA) was completely degraded within 8 min under the initial conditions of 30 °C, a Co 3 O 4 @TCF dosage of 0.25 g·L−1, a PMS concentration of 0.7 mmol·L−1, and a pH of 6.6. The degradation efficiency of BPA was 10 times higher than that of Co 3 O 4 @CF prepared from commercial carbon fibers, where the utilization efficiency of PMS was also significantly higher than that of the Co 3 O 4 @CF. In addition, the 3D-excitation-emission matrix (3D-EEM) results showed that Co 3 O 4 @TCF exhibited remarkable catalytic efficiency for purifying actual coking wastewater with and without BPA. The characterization results indicated the uniform dispersion of Co 3 O 4 and the abundant formation of C–O–Co bonds over Co 3 O 4 @TCF because of the rapid aromatization of cellulose in the textile waste, which facilitated electron transfer during PMS activation and the degradation of organic pollutants. The quenching experiments and electron paramagnetic resonance spectra verified the dominant role of 1O 2 in the Co 3 O 4 @TCF/PMS system for BPA degradation. Density functional theory calculations and liquid chromatography–mass spectrometry revealed three degradation pathways of BPA. By using textile waste to prepare carbon fiber-based catalysts for the activation of PMS to degrade refractory pollutants, new insights were provided in textile waste recycling, advanced oxidation, and pollutant control. [ABSTRACT FROM AUTHOR]

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In this study, a novel dopamine-imprinted MOFs (metal organic frameworks) was developed for the first time to achieve targeted degradation of refractory organic pollutants (ROPs) in advanced oxidation process. The targeted adsorption and degradation capacity of sulfamethoxazole (SMX) by molecularly imprinted catalyst (Fe-MOFs@MIP) was 3.17 times and 5.47 times that of Fe-MOFs, respectively. The results showed that the polydopamine (PDA) imprinted layer not only enhanced the targeted adsorption of SMX, but also improved the activity of the catalyst by promoting electron transfer. The physicochemical properties of Fe-MOFs@MIP were investigated. In situ Fourier transform infrared spectroscopy and molecular dynamics theory were used to investigate targeted adsorption mechanism. The active species were identified by quenching experiments and electron paramagnetic resonance (EPR). The reaction sites of SMX were predicted using density functional theory (DFT) and the possible degradation pathways of SMX were proposed. Finally, the targeted degradation mechanism of Fe-MOFs@MIP was elucidated. This study has a guiding significance for the deep removal of refractory organic pollutants in wastewater. • A simple and green method for the preparation of molecularly imprinted MOFs. • The efficient targeted degradation of SMX was realized. • PDA imprinting layer can promote electron transfer. • The synergistic effect of targeted adsorption and degradation of Fe-MOFs@MIP was elucidated. [ABSTRACT FROM AUTHOR]

Nowadays the concern on the treatment of refractory organic pollutants (e.g., Congo red and phenolic compounds) in industrial wastewaters and their treated effluents with conventional technologies has been still continuously increasing. In this study, a novel visible light photocatalyst material, Ag/AgBr and Al loading on the attapulgite (ATP), was prepared for efficiently catalyzing the photodegradation of the two refractory substances, and its photocatalytic performance and recyclability were assessed. Results from transmission electron microscopy and X-ray diffraction confirmed the successful loading of Ag/AgBr and Al on the ATP. The prepared Ag/AgBr-Al-ATP composite presented substantially better catalytic performance than Ag/AgBr alone probably because the ATP as a carrier of catalyst provided more contact surface for catalyst Ag/AgBr and Congo red/phenol. In the Ag/AgBr-Al-ATP composite, the photocatalyst AgBr content increased from 20.4 to 34.9% due to the modification of ATP by Al. Correspondingly, the Ag/AgBr-Al-ATP composite presented its excellent photocatalytic performance under visible light irradiation: photodegradation efficiencies of Congo red and phenol of 1.73 mg/100 mg and 0.86 mg/100 mg were achieved. With the increase of pH, the photolysis efficiencies of Congo red and phenol both first increased and then decreased, whereas the optimal photocatalytic performance occurred at pH 7 for Congo red and pH 10 for phenol. The Ag/AgBr-Al composite presented a high catalytic activity for photolysis of Congo red and phenol in all the four consecutive reused cycles. The results in this study comprehensively demonstrated a promising photocatalyst for efficient removal of the similar refractory organics presented in industrial wastewaters, which deserves further investigation and development. [ABSTRACT FROM AUTHOR]

Herein, we show the first report on the degradation of hazardous organic pollutants in very saline matrice (seawater) using acetone photoactivated process at 253.7 nm. Chloral black (CB), a very persistent dye of well‐established carcinogenic and mutagenic effects, was chosen a substrate model. The photodegradation of CB was monotonically increased in the presence of acetone. About 90% of CB (25.5 µM) was removed after 30 minutes in the presence of 50 mM of acetone whereas only 30% of removal was achieved under UV alone. The process is very sensitive to operational conditions. Chemical probes' tests using oxygen and KI have evidenced that methyl radical (CH3●) is the primarily radical involved in the CB degradation upon UV/acetone treatment. The formation of CH3● is thermodynamically favourable since the energy per Einstein of 253.7 nm light (~113 kcal) is large enough to break the C–C bond in the acetone molecule (70 kcal). [ABSTRACT FROM AUTHOR]

With the rapid growth of the metallurgical industry, there is a significant increase in the production of metallurgical slags. The waste slags pose significant challenges for their disposal because of complex compositions, low utilization rates, and environmental toxicity. One promising approach is to utilize metallurgical slags as catalysts for treatment of refractory organic pollutants in wastewater through advanced oxidation processes (AOPs), achieving the objective of "treating waste with waste". This work provides a literature review of the source, production, and chemical composition of metallurgical slags, including steel slag, copper slag, electrolytic manganese residue, and red mud. It emphasizes the modification methods of metallurgical slags as catalysts and the application in AOPs for degradation of refractory organic pollutants. The reaction conditions, catalytic performance, and degradation mechanisms of organic pollutants using metallurgical slags are summarized. Studies have proved the feasibility of using metallurgical slags as catalysts for removing various pollutants by AOPs. The catalytic performance was significantly influenced by slags-derived catalysts, catalyst modification, and process factors. Future research should focus on addressing the safety and stability of catalysts, developing green and efficient modification methods, enhancing degradation efficiency, and implementing large-scale treatment of real wastewater. This work offers insights into the resource utilization of metallurgical slags and pollutant degradation in wastewater. [Display omitted] • The source, production, properties of metallurgical slags are summarized. • Metallurgical slags can be as promising catalysts in AOPs for wastewater treatment. • The process factors and mechanism of organic pollutant degradation are discussed. • The advances and perspectives of using metallurgical slags for practical applications is described. [ABSTRACT FROM AUTHOR]

• Novel Graphene Electroactive Membrane (GEM) were fabricated. • GEM exhibited optimal performance for organic pollutant mineralization. • Main mechanism of GEM electro-catalysis was direct oxidation. • GEM electro-catalysis was controlled by adsorption-diffusion and electro-catalysis. This study was conducted to access the catalytic performances and reaction mechanisms of Graphene Electroactive Membrane (GEM). The GEM was prepared by vacuum-pressing method, and characterized by FESEM and FTIR. Catalytic performances were measured in the index of decolorization ratio and mineralization rate. Active species were recognized by scavengers for investigating reaction mechanisms. The impacts of current intensity and water flux on catalytic performances were presented to illustrate the mechanisms of GEM electro-catalysis deeply. According to the results, the method of GEM preparation was reliable and Graphene was an appropriate material for Electroactive Membrane (EM). Compared with EM electro-catalysis and GEM with no electro-catalysis (GEM-NEC), the mineralization rate increased by 56.1% and 28.8% respectively, and the decolorization rate increased by 45.5% and 29.8% respectively. The decolorization rate of GEM electro-catalysis with 0.2 M Ammonium Oxalate (Scavenger of electron hole) decreased 32.7% more than GEM electro-catalysis with no scavenger. Thus, direct oxidation was the main mechanism of GEM electro-catalysis, which was very different from traditional electro-catalysis. When current intensity was less than 20 mA and water flux was higher than 3 mL/min, decolorization ratio increased dramatically. Thus, electro-catalytic process and adsorption-diffusion process played important roles in GEM electro-catalysis process. The GEM electro-catalysis was an effective and stable advanced wastewater treatment for removal of organic pollutants. [ABSTRACT FROM AUTHOR]

Agro-based pulp and paper mills (PPMs) inevitably produce numerous refractory pollutants in their wastewater, including chlorolignin, chlorophenols, chlorocatechols, chloroguaiacol, cyanide, furan, dioxins, and other organic compounds, as well as various heavy metals, such as nickel (Ni), zinc (Zn), chromium (Cr), iron (Fe), lead (Pb), arsenic (As), etc. These pollutants pose significant threats to aquatic and terrestrial life due to their cytogenotoxicity, mutagenicity, impact on sexual organs, hormonal interference, endocrine disruption, and allergenic response. Consequently, it is crucial to reclaim pulp paper mill wastewater (PPMW) with high loads of refractory pollutants through effective and environmentally sustainable practices to minimize the presence of these chemicals and ensure environmental safety. However, there is currently no comprehensive published review providing up-to-date knowledge on the fate of refractory pollutants from PPMW in soil and aquatic environments, along with valuable insights into the associated health hazards and remediation methods. This critical review aims to shed light on the potential adverse effects of refractory pollutants from PPMW on natural ecosystems and living organisms. It explores existing effective treatment technologies for remediating these pollutants from wastewater, highlighting the advantages and disadvantages of each approach, all in pursuit of environmental safety. Special emphasis is placed on emerging technologies used to decontaminate wastewater discharged from PPMs, ensuring the preservation of the environment. Additionally, this review addresses the major challenges and proposes future research directions for the proper disposal of PPMW. It serves as a comprehensive source of knowledge on the environmental toxicity and risks associated with refractory pollutants in PPMW, making it a valuable reference for policymakers and researchers when selecting appropriate technologies for remediation. The scientific community, concerned with mitigating the widespread risks posed by refractory pollutants from PPMs, is expected to take a keen interest in this review. [Display omitted] [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Iodide was inserted in the interlayer of the multilayered Bi 2 WO 6 for better activity. • I 0.30 -Bi 2 WO 6 was highly effective for pollutants removal under visible light. • The enlarged layer spacing enhanced effective charge separation and transfer. • The main active species were holes whose oxidative power was enhanced after I− insertion. Abstract An iodine intercalated Bi 2 WO 6 was fabricated by a facile hydrothermal method (160 °C, 2 h) and characterized by field emission scanning electron microscope, high resolution transmission electron microscopy, nitrogen adsorption/desorption isotherms, X-ray diffraction and X-ray photoelectron spectroscopy, Fourier-transform infrared and UV-Vis diffuse reflectance spectra. The I 0.30 -Bi 2 WO 6 with an I/W molar ratio of 0.30 was highly effective for the degradation and mineralization of 2-chlorophenol, rhodamine B, bisphenol A, phenol, ciprofloxacin and sulfamethoxazole in water under visible light. Furthermore, the visible-light-driven photocatalytic activity of Bi 2 WO 6 was enhanced 3.1 times by the introduction of I−. The characterized results indicated that I− mainly inserted into the interlayer of Bi 2 WO 6 , expanding the layer spacing, favoring the efficient charge separation and transfer and prohibiting the recombination of the photogenerated electrons and holes. Specially, the XPS analysis indicated the I− ions substitued the absorbed oxygen to chemically bond in the layered Bi 2 WO 6 , resulting in the change of the electric charge distribution of Bi 2 WO 6. Moreover, the BET surface area was increased from 25.2 m2 g−1 for Bi 2 WO 6 to 66.7 m2 g−1 for I 0.30 -Bi 2 WO 6 for more surface active sites. In addition, the band gap was narrowed for expanded optical absorption in the visible light region. ESR and radicals trapping experiments verified holes were the main active species for the degradation of organic pollutants. Simultaneously, the more positive potential of valence band in iodine intercalated Bi 2 WO 6 could enhance the oxidative power of the photogenerated holes, resulting in the efficient removal of refractory organic pollutants in water. [ABSTRACT FROM AUTHOR]

Here we demonstrated that the Co doped anatase titanium dioxide (Co@TiO 2) prepared by a facile wet chemical method could activate peroxymonosulfate (PMS) for efficiently degrading a wide range of refractory organic pollutants. The characterization results demonstrated that the doped Co replaced partial Ti while did not bring obvious structural change. The Co@TiO 2 /PMS system can efficiently remove about 100 % chlortetracycline (CTC) within 40 min and 100 % Rhodamine B (RhB) within 15 min. The Co@TiO 2 /PMS/CTC system maintained a good catalytic performance over a wide pH range from 3 to 11 and the removal efficiency of CTC improved with increasing pH. The Co@TiO 2 /PMS system had a good anti-interference ability, which was free from interference by inorganic ions (such as H 2 PO 4 2-, NO 3 - and SO 4 2-, etc.) and HA, and also in the different real water matrixes and refractory organic pollutants. Quenching experiments and electron spin resonance (EPR) measurements confirmed that the system had a typical radical process as hydroxyl radical (•OH), sulfate radical (SO 4 •−) and superoxide radical (O 2 •−) were the main reactive species for the degradation of CTC. Furthermore, the Co@TiO 2 also showed excellent stability and low metal leaching during long-term use because of the excellent chemical and physical stability of TiO 2. A Co-doped anatase TiO 2 catalyst was synthesized by a facile wet chemical strategy and used for degrading various organic contaminants via peroxymonosulfate activation. [Display omitted] • Co doped anatase TiO 2 was prepared by a facile wet chemical method. • Effects of doping amount and annealing temperature were studied. • Co@TiO 2 /PMS system noticeably removed 100 % CTC under a broad conditions within 40 min • The system had a typical radical process as •OH, SO 4 •− and O 2 •− were the main reactive species. • The fantastic adaptability of the Co@TiO 2 /PMS system was also demonstrated. [ABSTRACT FROM AUTHOR]

[Display omitted] • The applications of LDHs in different Fenton-based processes for water treatment are reviewed. • Regulation strategies for enhanced LDH activity in Fenton-based processes are assessed. • The mechanisms of electron transferring by LDHs are described. • The applications of LDHs in electrode material and hybrid reactors are studied. • Challenges and future outlooks concerning LDH-based materials are outlined. Wastewater treatment has become a great concern of this century owing to the advent of different types of refractory pollutants, which needs to be effectively treated with state-of-the-art catalysts and techniques. Layered double hydroxides (LDHs), as two-dimensional (2D) layered materials, are deemed to be promising candidates for environmental remediation due to outstanding advantages, such as high surface area, unique exchangeability of intercalated anions, porous, and stable layered structure. Fenton-based processes have been demonstrated their ability in removal of recalcitrant contaminants even in low quantities. Recently, LDHs and their derivatives have emerged as an important class of Fenton-based catalysts to overcome conventional Fenton process drawbacks, including narrow working pH, potential for secondary contamination, and sludge production. This review aims to summarize the current knowledge about LDHs, different synthesis procedure, and properties of LDHs materials. A systematical investigation on the recent progress in application of multi-metals LDH-based catalysts in Fenton, Fenton-like, photo-Fenton (PF), and electro-Fenton (EF) processes and the corresponding reaction mechanisms were provided. Furthermore, key strategies (oxygen vacancies, carbon materials, incorporation of different metals, magnetic materials) to increase active sites, electron transfer rates, and hydroxyl radicals (•OH) generation, were also described, which thereby lead to improvement in the LDHs performance. The role of LDHs in the design of electrodes and EF membranes were discussed in detail. This study also summarized the applications of LDHs materials as catalysts in Fenton-based processes for elimination of different organic pollutants. Finally, this review focuses on challenges, some crucial issues of current research, and future prospects of LDH-based Fenton catalysts in environmental remediation to achieve excellent catalytic performance. It is believed that this work provides valuable insights into the efficacious applications of LDH materials in the field of Fenton-based processes. [ABSTRACT FROM AUTHOR]

In present work, a novel catalyst of cobalt supported on silica-composited biochar (Co@ACFA-BC) derived from fly ash and agricultural waste was synthesized. A series of characterizations confirmed that Co 3 O 4 and Al/Si–O compounds were successfully embedded on the surface of biochar, which triggered superior catalytic activity for PMS activation towards phenol degradation. Particularly, the Co@ACFA-BC/PMS system could completely degrade phenol in the wide pH range, and was almost unaffected by environmental factors including humic acid (HA), H 2 PO 4 −, HCO 3 −, Cl−, and NO 3 −. Further quenching experiment and EPR analysis proved that both radical (SO 4 ·-, ·OH, O 2 ·-) and non-radical (1O 2) pathways were involved in the catalytic reaction system, and the excellent PMS activation was attributed to the electron pair cycling of Co2+/Co3+ and the active sites provided by Si–O–O and Si/Al–O bonds on the catalyst surface. Meanwhile, the carbon shell effectively inhibited the leaching of metal ions, enabling the Co@ACFA-BC catalyst to maintain excellent catalytic activity after four cycles. Finally, biological acute toxicity assay demonstrated that the toxicity of phenol could be significantly reduced after being treated by Co@ACFA-BC/PMS. Overall, this work provides a promising strategy for solid waste valorization and a feasible methodology for green and efficient treatment of refractory organic pollutants in water environment. [Display omitted] • A novel Co@ACFA–BC catalyst was synthesized from fly ash and agricultural waste. • Co@ACFA–BC showed superior activity for PMS activation. • Si–O–O and Si/Al–O bonds and high porosity led to efficient phenol enrichment. • Radical/non-radical cooperation and phenol degradation mechanisms were proposed. • Environmental risks of the Co@ACFA-BC system were assessed. [ABSTRACT FROM AUTHOR]

Sodium percarbonate (SPC) is widely used in Fenton-like technology for the organic wastewater treatment because of its low costs and convenient transportation. However, low utilization efficiency of hydrogen peroxide limits its application. In this work, a catalyst (CuCoFe-LDHs) was designed to activate SPC for degrading ciprofloxacin (CIP) effectively in heterogeneous Fenton system with higher H 2 O 2 utilization rate (62 %) and higher stability (degradation rate of CIP decreased 5.6 % after five cycles). Since SPC was dissolved in water, H 2 O 2 and CO 3 2- were generated, and CO 3 2- was transferred to HCO 3 - subsequently along with the variation of pH value. Plenty of •OH and •O 2 - was generated, and most of •OH was directly reacted with CIP. However, •O 2 -, was prone to react with HCO 3 - to form •CO 3 -, and then for degrading CIP. Compare with CuMgFe-LDHs catalyst, the electrochemical impedance spectroscopy (EIS) showed that CuCoFe-LDHs with stronger electron transfer ability. Therefore, the Co atom could facilitate the generation of specific free radical via enhancing electron transfer rate for the degradation of CIP in CuCoFe-LDHs. In summary, this study provides a cheap, recyclable, efficient and environmentally friendly wastewater treatment method for the degradation of refractory organic pollutants. [Display omitted] • CuCoFe-LDHs/SPC system with excellent CIP degradation performance is established. • SPC activated by CuCoFe-LDHs in heterogeneous system with high H 2 O 2 utilization. • The electron transfer between Co and O promote the generation of reactive species. • The CuCoFe-LDHs/SPC system with wider pH range and better recyclability. [ABSTRACT FROM AUTHOR]

• Hydrogen bonding is formed between dissolved organic matter (DOM) and photocatalyst. • Hydrogen bonding leads to a promotional effect of DOM on photocatalytic degradation. • Hydrogen bonding modulates interfacial electron transfer between DOM and photocatalyst. • Hydrogen bonding stabilizes excited-state DOM. • Hydrogen bonding strategy applies to real river water treatment. Removing refractory organic pollutants in real water using photocatalysis is a great challenge because coexisting dissolved organic matter (DOM) can quench photogenerated holes and thus prevent generation of reactive oxygen species (ROS). Herein, for the first time, we develop a hydrogen bonding strategy to avoid the scavenging of photoexcited holes, by which DOM even promotes photocatalytic degradation of refractory organic pollutants. Theoretical calculations combined with experimental studies reveal the formation of hydrogen bonding between DOM and a hydroxylated S-scheme heterojunction photocatalyst (Mo-Se/OHNT) consisting of hydroxylated nitrogen doped TiO 2 (OHNT) and molybdenum doped selenium (Mo-Se). The hydrogen bonding is demonstrated to change the interaction between DOM and Mo-Se/OHNT from DOM-Ti (IV) to a hydrogen bonded complexation through the hydroxyl/amine groups of DOM and the OHNT in Mo-Se/OHNT. The formed hydrogen network can stabilize excited-state of DOM and inject its electron to the conduction band rather than the valence band of the OHNT upon light irradiation, realizing the key to preventing hole quenching. The electron-hole separation in Mo-Se/OHNT is consequently improved for generating more ROS to be involved in removing refractory organic pollutants. Moreover, this hydrogen bonding strategy is generalized to nitrogen doped zinc oxide and graphitic carbon nitride and applies to real water. Our findings provide a new insight into handling the DOM problem for photocatalytic technology towards water and wastewater treatment. [Display omitted] [ABSTRACT FROM AUTHOR]

Wet air oxidation (WAO) is one of the most economical and environmentally-friendly advanced oxidation processes. It makes a promising technology for the treatment of refractory organic pollutants in industrial wastewaters. In wet air oxidation aqueous waste is oxidized in the liquid phase at high temperatures (125–320 °C) and pressures (0.5–20 MPa) in the presence of an oxygen-containing gas (usually air). The advantages of the process include low operating costs and minimal air pollution discharges. The present review is concerned about the literature published in the treatment of refractory organic pollutants in industrial wastewaters, such as dyes. Phenolics were taken as model pollutants in most cases. Reports on effect of treatment for the WAO of refractory organic pollutants in industrial wastewaters are reviewed, such as emulsified wastewater, TNT red water, etc. Discussions are also made on the mechanism and kinetics of WAO and main technical parameters influencing WAO. Finally, development direction of WAO is summed up.

• MIL100@MIP has achieved preferential targeted degradation of the refractory organics. • The degradation efficiency of SMX was significantly improved. • The target adsorption capacity of the imprinted catalysts was optimized by constructing different recognition sites. • Theoretical calculations were used to elucidate the process of targeted adsorption. • The mechanism of targeted degradation of SMX by MIL100@MIP was proposed. In this study, the role of weak interactions in the targeted adsorption of refractory organic pollutants by imprinted catalysts (MIL100@MIP) was elucidated. Through the imprinting technique, the targeted adsorption capacity for sulfamethoxazole (SMX) was increased by 3 times. With the synergy of adsorption and degradation, the removal of SMX reached 49.03 mg/g in MIL100@MIP/PS system. Methacrylic acid (MAA), acrylamide (AM), and 4-vinyl pyridine (4-VP) were used to construct different imprinting recognition sites. UV–vis spectral analysis indicated that MIL100@MIP adsorbed SMX through weak interactions. Dynamic experiments showed that MIL100@MIP-4-VP exhibited the best adsorption performance. Density functional theory (DFT) calculations and wave function analysis indicated that π-π stacking played a dominant role in the SMX adsorption process. The solvent effect was investigated by dynamics simulation. Finally, three possible SMX degradation pathways and the catalytic mechanism of MIL100@MIP were proposed based on the EPR and intermediate product analysis. This study has valuable guidance for improving the targeted degradation performance of imprinted catalytic materials. [ABSTRACT FROM AUTHOR]

The presence of refractory organic pollutants (ROPs) in the ecosystem is a serious concern because of their impact on environmental constituents as well as their known or suspected ecotoxicity and adverse health effects. According to previous studies, carbonaceous materials, such as biochar (BC), have been widely used to remove pollutants from ecosystems owing to their desirable features, such as relative stability, tunable porosity, and abundant functionalities. Nitrogen (N)-doping and iron/nitrogen (Fe/N) co-doping can tailor BC properties and provide supplementary functional groups as well as extensive active sites on the N-doped and Fe/N co-doped BC surface, which is advantageous for interaction with and removal of ROPs. This review investigates the impact of N-doped and Fe/N co-doped BC on the removal of ROPs through adsorption, activation oxidation, and catalytic reduction due to the synergistic Fe, N, and BC features that modify the physicochemical properties, surface functional groups, and persistent free radicals of BC to aid in the degradation of ROPs. Owing to the attractive properties of N-doped and Fe/N co-doped BCs for the removal of ROPs, this review focuses and evaluates previous experimental investigations on the manufacturing (including precursors and influencing parameters during manufacturing) and characterizations of N-doped and Fe/N co-doped BCs. Additionally, the effective applications and mechanisms of N-doped and Fe/N co-doped BCs in adsorption, activation oxidation, and reductive remediation of ROPs are investigated herein. Moreover, the application of N-doped and Fe/N co-doped BC for progressive environmental remediation based on their effectiveness against co-pollutants, regeneration, stability, affordability, and future research prospects are discussed. [Display omitted] • Synergy of BC with N and Fe/N can offer effective ROPs interaction and removal. • N-doped and Fe/N co-doped BC for ROPs adsorption/oxidation are reviewed. • Manufacture, characterization, and removal efficiency of BCs are summarized. • Adsorption and activation oxidation mechanisms of ROPs are discussed. • Effectiveness for co-pollutants, regeneration, stability, and cost of BCs are assessed. [ABSTRACT FROM AUTHOR]

We synthesized the magnetic recyclable Ti 3 C 2 derived N-TiO 2 @C@Fe 3 O 4 for photo-Fenton degradation of organic pollutants through high-temperature calcination and solvothermal methods. Ti 3 C 2 was first calcined into TiO 2 @C with a homogeneous titanium source and a two-dimensional carbon framework. Then the magnetic nanoparticles (Fe 3 O 4) were loaded by solvothermal method, which effectively solved the problem of repeated circulation of powder catalysts. N-TiO 2 @C@Fe 3 O 4 could be used as an excellent co-catalyst to improve the decomposition efficiency of H 2 O 2 in advanced oxidation processes (AOPs). This significantly reduced the amount of H 2 O 2 and Fe2+ in the photo-Fenton system. The N-TiO 2 @C@Fe 3 O 4 photo-Fenton system could degrade 96.5% of Rhodamine B (RhB) within 300 s and maintain a recycling rate of more than 90% after 10 cycles. This system also had favorable applicability to the same wastewater of antibiotics. This mechanism was proposed that the N-TiO 2 @C@Fe 3 O 4 photo-Fenton system activated H 2 O 2 to generate hydroxyl radicals (·OH) and superoxide radicals (·O 2 −) to further attack RhB. This research provided novel insights for the photo-Fenton collaborative catalytic system to achieve advanced oxidation treatment of pollutants in the water environment. Magnetically recoverable Ti 3 C 2 -derived N-TiO 2 @C@Fe 3 O 4 had been successfully designed for photo-Fenton degradation of refractory organic pollutants in water by high-temperature calcination and solvothermal methods. N-doped TiO 2 effectively reduced the bandgap and improved the light utilization, generating photogenerated electrons (e-) and holes (h+). The carbon matrix rapidly captured photogenerated electrons, suppressing carrier recombination and further enhancing the e-/h+ separation efficiency. The generated hydroxyl radicals (·OH) and superoxide radicals (·O 2 −) played a key role in the degradation of dyes and antibiotics. [Display omitted] • The N-doped and carbon layer reduced the band gap and improved the light utilization efficiency. • Magnetic recyclable N-TiO 2 @C@Fe 3 O 4 showed excllent cycle stability for degrading RhB. • ·OH and ·O 2 − played an important role in the optical Fenton process. • The mechanism of N-TiO 2 @C@Fe 3 O 4 photo-Fenton system to degrade RhB was proposed. [ABSTRACT FROM AUTHOR]

A novel Fenton-like filter is constructed for highly efficient and stable degrading refractory organics continuously, and fantastically galvanic effect enhanced peroxymonosulfate activation is revealed based on the differential concentration in the filter and the conductivity of carbon based Co-N/CF and electrolyte. [Display omitted] • Fenton-like filtration device based on Co-N/CF has been presented. • A non-radical pathway mechanism involved in Co-N/CF/PMS system is proposed. • Significantly enhanced treating performance is achieved in the presence of electrolyte. • An intriguing galvanic-effect-enhanced PMS activation in the Fenton-like filter is revealed. • The Fenton-like filter displays excellent catalytic activity and avoids the trouble of catalyst recovery. Peroxymonosulfate (PMS) activation by heterogeneous catalysts is a promising method for removing organic contaminants in wastewater. However, recovery and stability of the catalyst limit its practical applications. Here we demonstrate that Co incorporated chitosan and immobilized on carbon-fiber (CF) sheets (Co-N/CF) by annealing can catalytically activate PMS for efficiently degrading refractory organic pollutants, and show excellent stability and recovery within a Fenton-like filtration device. Batch tests reveal the excellent activity of the Co-N/CF and the optimized synthesis condition. Radical-quenching experiments and EPR measurements confirm that the generated singlet oxygen (1O 2) is the main reactive species. Excellent continuously treating performance is obtained under various conditions, including different initial organic concentration, various organic pollutants, PMS dosage, pH, co-existing anions, and natural organic matter. For example, under the conditions of 20 mg L−1 RhB, 25 ppm PMS and a flux rate of 15 mL min−1, the reactor can maintain 100% RhB removal rate for more than 32 h while the Co leaching is much lower than the standard value. Interestingly, in the presence of electrolytes, the removal rate can keep 100% under a much higher flux rate over 450 mL min−1, which is about 16 times higher than the wastewater without electrolyte. Based on the differential concentration in the filter and the conductivity of carbon based Co-N/CF and electrolyte, an in-situ galvanic effect between the upper and lower Co-N/CF plates can be formed, which can boost the generation of reactive species, thereby significantly improving the degradation performance. Present study provided a rational strategy for PMS activation in equipment level, and also presented a new insight into the mechanism of PMS heterogeneous activation. [ABSTRACT FROM AUTHOR]

Recently, peroxymonosulfate-based advanced oxidation process has been widely applied in the removal of refractory organic pollutants. In the present study, cobalt-doped graphene aerogel (Co-GA) composites have been fabricated as a promising activator for peroxymonosulfate (PMS) via in-situ synthesis successfully. The physical-chemical properties of composite catalysts were carefully characterized and the activation performance was evaluated by the degradation of sulfamonomethoxine (SMM), ciprofloxacin (CIP), sulfanilamide (SN) and rhodamine B (RhB) aqueous solution, respectively. The results showed that Co-GA could effectively degrade refractory organics and keep macroscopic morphology intact under the reaction conditions of 15 mg/L simulated wastewater, 0.3 g/L PMS, 0.2 g/L Co-GA. Furthermore, the effect of reaction parameters on SMM degradation was investigated. Co-GA/PMS system exhibited consistent performance over a wide pH range (3-11). The degradation mechanism of SMM is free radical oxidation dominated by sulfate radical (SO 4 •−) combined with non-radical reaction initiated by GA. Benefiting from its flexibility and recyclability, the as-prepared Co-GA is suitable for practical wastewater purification. [Display omitted] • Co-GA was obtained via a simple hydrothermal method. • Co-GA used as activator of PMS could keep macroscopic morphology in the application of wastewater treatment. • SO 4 ‾ · and non-radical reaction pathway were involved in the removal of SMM. [ABSTRACT FROM AUTHOR]

Electrochemistry-mass spectrometry is used to simulate redox reactions in many research disciplines because this technique is fast and provides information on compound metabolites. However, the analysis of the degradation of refractory organic pollutants by reactive oxygen species is difficult to achieve by the electrochemistry step. Therefore, here we use online electro-Fenton-mass spectrometry to study for the first time the oxidation of 2,4′,5-trichlorobiphenyl [polychlorinated biphenyl (PCB) 31] by reactive oxygen species and the binding reactions of PCB degradation products with model substances of natural organic matter. The degradation products were identified by coupled Q Trap mass spectrometry. We observed a binding of a degradation product with γ- l-glutamyl- l-cysteinyl-glycine. We propose a transformation pathway. We conclude that online electro-Fenton-mass spectrometry is a promising technique to study the oxidation of refractory organic pollutants and further binding of degradation products with natural organic matter. [ABSTRACT FROM AUTHOR]

A large-scale combined ponds-wetland system was applied for advanced treatment of refractory pollutants in petrochemical industrial wastewater. The system was designed to enhance bioactivity and biological diversity, which consisted of anaerobic ponds (APs), facultative ponds (FPs), aerobic pond and wetland. The refractory pollutants in the petrochemical wastewater to be treated were identified as alkanes, chloroalkanes, aromatic hydrocarbons, and olefins, which were significantly degraded and transformed along with the influent flowing through the enhanced bioactive ponds-wetland system. 8 years of recent operational data revealed that the average removal rate of stable chemical oxygen demand (COD) was 42.7 % and that influent COD varied from 92.3 to 195.6 mg/L. Final effluent COD could reach 65.8 mg/L (average). COD removal rates were high in the APs and FPs and accounted for 75 % of the total amount removed. This result indicated that the APs and FPs degraded refractory pollutants through the facilitation of bacteria growth. The changes in the community structures of major microbes were assessed by 16SrDNA-denaturing gradient gel electrophoresis. The same analysis was used to identify the main bacterial function for the removal of refractory pollutants in the APs and FPs. The APs and FPs displayed similar microbial diversities, and some of the identified bacteria degraded and removed refractory pollutants. The overall results proved the applicability, stability, and high efficiency of the ponds-wetland system with enhanced bioactivity in the advanced removal of refractory pollutants from petrochemical industrial wastewater. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel underwater arc discharge plasma reactor was designed. • A low-temperature plasma-catalyst-oxidant method for the efficient degradation of phenolic and nitrochlorobenzene organic pollutants was constructed. • The synergistic catalytic mechanism between plasma and Fe 2 O 3 -CoFe 2 O 4 for PMS activation was revealed. This study employed a self-designed underwater arc discharge (UAD) plasma reactor, which combined advanced oxidation process (Fe 2 O 3 -CoFe 2 O 4 /PMS) and low-temperature plasma technology to efficiently degrade refractory organic pollutants (i.e. phenol, p-chlorophenol, p-nitrochlorobenzene). The results illustrated that the plasma/PMS/Fe 2 O 3 -CoFe 2 O 4 system possessed high degradation efficiency and TOC removal rate towards three target pollutants (phenol: 99.8%, 96.12%; 4-CP: 98.4%, 86.48%; p-NCB: 99.9%, 88.31%). With the help of in-situ variable temperature EPR and Indigo colorimetry method, ·OH, SO 4 ·-, O 2 ·-, 1O 2 and O 3 were identified as the main reactive oxygen species (ROS) for the degradation of target pollutants, revealing the synergistic catalytic mechanism between plasma and Fe 2 O 3 -CoFe 2 O 4 for PMS activation and inferring the degradation pathways of target pollutants. The results confirmed that the plasma/PMS/Fe 2 O 3 -CoFe 2 O 4 system was feasible for the degradation of refractory organic pollutants, has the advantages of high efficiency and low energy consumption, and could provide an effective strategy for the treatment of refractory organic pollutants in groundwater/soil. [ABSTRACT FROM AUTHOR]

Highlights: [•] Catalytic wet air oxidation of refractory organics in NF-reject. [•] Removal of potential EDCs after CWAO. [•] Mineralization higher with Pd/AC compared to Pd2+ and without catalyst. [•] Pd catalyst stable under CWAO treatment, graphitization of support observed. [ABSTRACT FROM AUTHOR]

Abstract: In this study, laboratory-scale anaerobic fluidized bed bioreactors (AFBBRs) using granular activated carbon as bedding material were employed for treating a primary treated sewage effluent (PTSE) with or without refractory organic pollutants (ROPs). A new starch based flocculant (NSBF) combining a nature starch based cationic flocculants and trace nutrients was prepared and applied in the AFBBR. The impact of NSBF on the performance of AFBBR was mainly evaluated in terms of organic and nutrient removal and microbial activity. Membrane fouling based on critical flux was assessed when the bioreactor used as pretreatment for microfiltration. The results indicated that the addition of NSBF in AFBBR (NSBF–AFBBR) not only attained improved organic (9–10%) and nutrient removal (10–20%), higher biomass growth (3.0gbiomass/LGAC) and net bed expansion (18cm), but also doubled the critical flux (from 15L/m3 h to 30L/m3 h) in the microfiltration system. In addition, NSBF–AFBBR could retain 10% better DOC removal efficiency at different recirculation rates for treating PTSE with ROPs. When increasing organic loading rate from 21.6kgCOD/m3 d to 43.2kgCOD/m3 d, NSBF–AFBBR achieved comparatively constant organic removal of 55% whereas the efficiency in AFBBR alone decreased dramatically from 47% to 34%. Thus, NSBF could act as a performance enhancer for AFBBR. [Copyright &y& Elsevier]

In this study, a natural starch-based cationic flocculant (SBCF) was first evaluated using a granular activated carbon fluidized-bed bioreactor (GAC-FBBR) to treat a high strength synthetic domestic wastewater (primary treated sewage effluent) containing refractory organic matters. The positive effect of SBCF on microorganisms and organic removal was obviously observed. When the optimal dose of SBCF (22 mg/L) combined with three major inorganic micronutrients (CaCl2, MgSO4, and FeCl3) at different concentrations, the best modified dosages of 0.5 mg/L of FeCl3, 5 mg/L of MgSO4 and 2 mg/L CaCl2 could significantly improve the microbial activity and organic removal simultaneously. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dual electron transfer from TCH and N vacancy to metal for efficient PMS activation. • DFT calculation revealed the direct electron transport from pollutant to Co (III). • Lower EE/O value in PMS/vis system brought more economic benefit. • Recyclable FeCoO x /g-C 3 N 4 -N vac oxidized high-toxic pollutant to less-toxic products. The construction of surface defect was a promising modification strategy to accelerate peroxymonosulfate (PMS) activation mediated by metal for water purification, but intrinsic impact on electron transfer path has been unclear. In this study, nitrogen vacancies (V n) were introduced into graphite carbon nitride and coupled with iron-cobalt bimetals (FeCoO x /CN-V n). Experimental and theoretical results confirmed that V n not only provided abundant electrons to reduce Fe(III)/Co(III) into Fe(II)/Co(II), but also induced the extraction of electrons from pollutant to electron-poor Co(III) for a faster Co(III)/Co(II) cycle. The sustainable dual-path electron transfer effectively overcame the obstacle of low-valence metal regeneration in conventional PMS-based oxidation, increasing the degradation rate constant of tetracycline hydrochloride, a typical refractory pollutant, from 0.2479 to 0.6674 min−1 in the first 2 min. The impacts of environmental factors (pH, PMS dosage, types of oxidants, water matrix) were investigated. Also, the effect of co-existing inorganics and organics was explored using a response surface quadratic model. The evaluation of electrical energy consumption and stability confirmed the outstanding practical application prospect of FeCoO x /CN-V n. Finally, degradation pathways of TCH were elucidated and toxicity of the products was evaluated using quantitative structure activity relationship (QSAR). This study not only furnished a novel insight into the defect-assisted PMS activation, but also achieved in-situ utilization of contaminant for efficient wastewater treatment. [ABSTRACT FROM AUTHOR]

The increasing demand for water in the manufacturing sector in a quest to meet the needs of the ever-growing population is inherently associated with a corresponding increase in the number and quantity of toxic and refractory wastes and dyes released into the environment. In most cases, polluted water from industries is discharged into surface water sources without the thorough treatment required to meet the lawfully set effluent control standards. Of the available water treatment technologies, TiO 2 photocatalysis has greater potential but its large-scale use is impeded by several technical factors associated with TiO 2 such as its high bandgap, particle agglomeration, fast electron-hole recombination, poor adsorption capacity towards organics, and difficulties in recovery after water treatment. Immobilizing TiO 2 nanoparticles (NPs) onto clays (phyllosilicates) eliminates these issues through the formation of the Ti-O-Si and Al-O-Ti bonds between TiO 2 NPs and the aluminosilicate layers of the clay supports. Recent interest is on the fabrication of porous ternary or quaternary TiO 2 /Clay nanocomposites with improved physicochemical and optoelectronic properties such as improved surface area, surface acidity, narrowed bandgap, extended electron-hole separation, and recombination time among others. Our review focuses on the different synthetic methods to fabricate binary, ternary, and quaternary TiO 2 /clay-based nanocomposites and drawing a correlation between their properties and their ability to photodegrade multifarious organic water pollutants. The application of TiO 2 /clay nanocomposites and their engineered products such as photoresponsive thin films and membranes in the remediation of real-life wastewater matrices and full-scale real-life wastewater treatment systems is also discussed. [Display omitted] • Role of support in TiO 2 /clay composites catalysts for remediation of water-containing organic pollutants by photocatalysis. • Efficiency of TiO 2 /clay over TiO 2 photocatalysts. • Application of TiO 2 /clay catalysts in photocatalytic degradation of organic pollutants in water. • Preparation methods of TiO 2 /clays nanocomposites. [ABSTRACT FROM AUTHOR]

Recently, an increasing number of publications concerned on the catalytic oxidation of refractory organic pollutants in wastewater dependent on the iron-based catalysts. Until now, the iron-based catalysts are diversity including Fe2+/Fe3+, ZVI, iron oxides (FeOOH, Fe 2 O 3 , Fe 3 O 4 , FeO), iron sulfides (Fe x S y) and Fe-bimetallic due to various valences and phases. A comprehensive understanding on the synthesis and applications of them as catalysts were little concerned. In this work, the methods for synthesis and control of the size, morphology, crystal phase and chemical valent properties of the iron-based catalysts were reviewed by classifying as Fe2+/Fe3+, ZVI, iron oxides, pyrite, Fe-MOF and Fe-bimetallic. Their applications in Fenton/Fenton-like oxidation, ozonation, wet air oxidation, PMS/PS activation, photocatalytic oxidation etc., for refractory organic pollutants oxidation were summarized. Generation of free radicals for oxidation of refractory organic pollutants in different systems was regarded as the main catalytic mechanisms. Refining controlled growth of size, morphology, crystal phase and chemical valence of iron-based catalysts will be prospective and challenge in synthesis of iron-based catalysts. Co-catalytic reaction will be promising for accelerating the electron transfer for generation of radicals. Quantitative analysis of the free radical is remained the challenge to understand the catalytic oxidation mechanism. We look forward to the fact that this review could inspire the readers to refine the synthesis of iron-based catalysts with special catalytic property for constructing the catalytic oxidation process and to understand the mechanism of degradation of refractory organic pollutants in wastewater. [Display omitted] • Synthesis of iron-based catalysts in various valent were reviewed. • Diversity of iron species resulted in various catalytic oxidation processes. • Electron transfer contributed to the iron induced catalytic oxidation. • Coupling catalytic oxidation with biological is promising for refractory organic pollutants degradation. [ABSTRACT FROM AUTHOR]

In recent years, refractory organic pollutants (ROPs) have been progressively detected in wastewater. Persulfates (peroxymonosulfate and peroxydisulfate)-based advanced oxidation processes (PS-AOPs) are efficient for ROPs degradation. Biochar and its composites, which have the dual advantages of adsorption and catalysis, have been widely used in PS-AOPs. Research advances on PS activation by biochar-based materials are systematically summarized, including biochar modifications, characterizations, radical determinations, and catalytic mechanism. Biochar modifications applied to PS-AOPs are introduced involving morphology regulation, heteroatomic doping, and metals loading. Characterization techniques are described to reveal the physicochemical properties of biochar-based catalysts. Various methods for radical determinations are discussed. The catalytic mechanism in the PS-AOPs is depicted from the point of radical pathway and non-radical pathway. Based on current knowledge, the perspectives and challenges that may be encountered in basic research and practical applications are put forward. This review offers novel insights into catalyst design and better understanding of PS-AOPs. [Display omitted] • Persulfates-based advanced oxidation processes were reviewed to for ROPs removal. • Heteroatomic doping and metals loading are promising to improve catalytic ability of biochar. • Catalytic mechanism was discussed from radical pathway and non-radical pathway. • The perspectives and challenges for biochar catalyzed PS-AOPs are proposed based on current knowledge. [ABSTRACT FROM AUTHOR]

The study reported one concept for fabrication of honeycomb block AC@Ti-Cu-Ni-Zn-Sb-Mn particles serving as packed bed particle electrodes for the degradation of PAP in wastewater. The proposed three-dimensional electrochemical systems exhibit excellent removal efficiency toward PAP. The particle electrodes activated O 2 to generate H 2 O 2 further forming OH. The pathway study suggested that the quinoneimine is the major intermediate and OH radicals play important roles in the reaction. [Display omitted] • Honeycomb block particle electrodes were synthesized through a facile method. • Ti-Cu-Ni-Zn-Sb-Mn were in-situ loaded on particle electrodes as catalysts. • The AC@Ti-Cu-Ni-Zn-Sb-Mn activated O 2 to generate H 2 O 2 further forming OH. • PAP is mainly degraded by indirect oxidation of OH radical. Emerging contaminants such as pharmaceuticals has been one of the most challenging environmental problems. In this work, we developed a one-step facile sol–gel method of loading TiO 2 , CuO, NiO, ZnO, Sb 2 O 3 and MnO onto honeycomb block activated carbon (AC@Ti-Cu-Ni-Zn-Sb-Mn), further applying as particle electrodes in a three-dimensional electrochemical system for the efficient degradation of p-aminophenol (PAP). Factors associated with the preparation of AC@Ti-Cu-Ni-Zn-Sb-Mn particle electrodes were investigated. The AC@Ti-Cu-Ni-Zn-Sb-Mn particle electrodes were analyzed by scanning electron microscope (SEM), energy dispersive spectrum analysis (EDX), X-Ray Diffraction analysis (XRD), Brunner-Emmet-Teller (BET) and X-ray Photoelectron spectroscopy (XPS). The effects of conductivity, pH value, aeration intensity, current density, conductivity and initial concentration on PAP degradation were also studied. Importantly, the PAP degradation results show that the activity of the particle electrodes supported by block honeycomb activated carbon is much better than that of the particle electrodes supported by granular activated carbon. The removal efficiency of PAP achieved approximately 99.87% under the optimized condition. The pathway study suggested that the quinoneimine is the major intermediate during the three-dimensional electrochemical degradation and OH radicals play important roles in the reaction. Overall, its facile fabrication and efficient electrochemical degradation performance indicate that the proposed honeycomb block particle electrodes have potential for practical applications of refractory organic pollutants. [ABSTRACT FROM AUTHOR]

Growing environment problem and emphasis of environmental protection motivate intense research efforts in exploring technology to improve treatment efficiency on refractory organic pollutants. Hence, finding a method to make up for the deficiency of anaerobic digestion (AD) is very attractive and challenging tasks. The recent spark in the interest for the usage of some nanomaterials as an additive to strengthen AD system. The adoption of iron compounds can influence the performance and stability in AD system. However, different iron species and compounds can influence AD system in significantly different ways, both positive and negative. Therefore, strengthening mechanism, treatment efficiency, microbial community changes in Nanoscale Zero Valent Iron (nZVI) and Fe 3 O 4 nanoparticles (Fe 3 O 4 NPs) added AD systems were summarized by this review. The strengthening effects of nZVI and Fe 3 O 4 NPs in different pollutants treatment system were analyzed. Previous study on the effects of nZVI and Fe 3 O 4 NPs addition on AD have reported the concentration of nZVI and Fe 3 O 4 NPs, and the types and biodegradability of pollutants might be the key factors that determine the direction and extent of effect in AD system. This review provides a summary on the nZVI and Fe 3 O 4 NPs added AD system to establish experiment systems and conduct follow-up experiments in future study. • The summary of nZVI and Fe 3 O 4 NPs added anaerobic digestion mechanisms. • The effect of pollutants digestion in nZVI and Fe 3 O 4 added anaerobic system. • The microbial community changes in different anaerobic digestion system. • The theory basis for experiments and applications in nZVI and Fe 3 O 4 added system. [ABSTRACT FROM AUTHOR]

• Various photo-activation methods and mechanisms for PS and PMS were summarized. • Photo-activated sulfate radical-based AOPs are efficient for degrading refractory organic pollutants. • The main parameters affecting the oxidation efficiency of photo-activated SR-AOPs were discussed. In recent decades, a growing number of refractory organic pollutants with serious health risks are frequently detected in aquatic environment. Sulfate radical (SO 4 −)-based advanced oxidation process (SR-AOP) under light irradiation (ultraviolet (UV) light, visible light or simulated solar light) is considered as a prospective method for refractory organic pollutants degradation. The satisfactory removal depends on the generation of active radicals SO 4 − as well as OH from the activation of persulfate (PS) and peroxymonosulfate (PMS). In this paper, different methods of PS/PMS photo-activation, including catalyst-free, metal catalyst and metal-free catalyst activation, under different light sources as well as their activation mechanisms are reviewed comprehensively. The effects of key parameters are commendably assessed, such as PS/PMS concentration, catalyst dosage, initial contaminant concentration, pH, and coexisting organic or inorganic matters. This study will help to deeply understand the photo-activated SR-AOP for the refractory organic pollutants removal and present better perspectives for future researches. [ABSTRACT FROM AUTHOR]

The quality of the bio-treated coking wastewater (BTCW) is difficult to meet increasingly stringent coking wastewater discharge standards and future wastewater recycling needs. In this study, the pre-treatment process of BTCW was installed including the two up-flow fixed-bed bioreactors (UFBRs) which were separately filled with alkali-pretreated or no alkali-pretreated corncobs used as solid carbon sources as well as biofilm carriers. Results showed that this pre-treatment process could significantly improve the biodegradability of BTCW and increase the C/N ratio. Thus, over 90% of residual nitrate in BTCW were removed stably. Furthermore, GC-MS analysis confirmed that the typical refractory organic matters decreased significantly after UFBRs pre-treatment. High-throughput sequencing analysis using 16S rRNA demonstrated that dominant denitrifiers, fermentative bacteria and refractory-organic-pollutants-degrading bacteria co-existed inside the UFBRs system. Compared with no alkali-pretreated corncobs, alkali-pretreated corncobs provided more porous structure and much stable release of carbon to guarantee the growth and the quantity of the functional bacteria such as denitrifiers. This study indicated that the UFBRs filled with alkali-pretreated corncobs could be utilized as an effective alternative for the enhanced treatment of the BTCW. Image 1 • Corncobs can be used as carbon source and biofilm carriers for BTCW pre-treatment. • UFBRs with corncobs could improve the biodegradability and C/N ratio of BTCW. • Refractory organics and nitrate were synergistically removed in UFBRs. • Alkali-pretreated corncobs as ideal carriers enhance the growth of diverse bacteria. [ABSTRACT FROM AUTHOR]