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Municipal solid waste (MSW) leachate contains various refractory pollutants that pose potential threats to both surface water and groundwater. This paper established a novel catalytic oxidation process for leachate treatment, in which OH is generated in situ by pumping both H 2 and O 2 in the presence of Pd catalyst and Fe 2+ . Volatile fatty acids in the leachate were removed almost completely by aeration and/or mechanical mixing. In this approach, a maximum COD removal of 56.7% can be achieved after 4 h when 200 mg/L Fe 2+ and 1250 mg/L Pd/Al 2 O 3 (pH 3.0) are used as catalysts. After oxidation, the BOD/COD ratio in the proposed process increased from 0.03 to 0.25, indicating that the biodegradability of the leachate was improved. By comparing the efficiency on COD removal and economical aspect of the proposed Pd-based in-situ process with traditional Fenton, electro-Fenton and UV-Fenton for leachate treatments, the proposed Pd-based in-situ process has potential economic advantages over other advanced oxidation processes while the COD removal efficiency was maintained. [ABSTRACT FROM AUTHOR]

Highlights: [•] Ecological effects of compost on soils contaminated by leachate were evaluated. [•] Etrahymena pyriformis was effective as the toxicity indicator. [•] Compost is effective to reduce biotoxicity risks of leachate-contaminated soils. [•] Excessive compost has no benefit for decreasing leaching toxicity further. [ABSTRACT FROM AUTHOR]

[Display omitted] • Health Care Wastes were classified into three categories. • Primary data of COVID-19 Health Care Wastes production in Wuhan were reported. • Health Care Wastes production was related to consumption of medical resources. • Multiple Linear Regression model was built to predict the production. • The MLR model has shown good agreement with the practical data. The fight against coronavirus disease 2019 (COVID-19) is still running its courses. Proper management and disposal of health care wastes (HCWs) are critical to win the fight. To achieve aforementioned tasks, prediction of their production is highly desired. In this study, primary data of production of three kinds of HCWs collected from Wuhan, the first epidemic epicenter worldwide and a mega city with more than 10 million population who has went through a lockdown period of 78 days, were reported for their first time. HCWs were classified into routine HCWs, infectious HCWs (IHCWs) and infectious municipal solid wastes. Among them, infectious HCWs from designated hospitals for COVID-19 were recognized as the most dangerous one. A multiple linear regression (MLR) model was built to predict the production of IHCWs with high significance. Numbers of patients were demonstrated high correlations with the production of IHCWs in an order of confirmed patients ＞ out-patients ＞ suspected patients. By the MLR model, production rates of IHCWs by confirmed, suspected and out patients were determined as 3.2, 1.8 and 0.1 kg/patient, respectively. In addition, constant production of IHCWs during the pandemic period was determined as 13 tons/d. This is the first study on quantitative evaluation of infectious HCWs during COVID-19 pandemic. The achievements in this study have potentials to shed light on global efforts to the prediction, management and disposal of vast HCWs generated in the war against COVID-19. [ABSTRACT FROM AUTHOR]

• A novel flower-like anisotropic MgAl-LDH/BC engineered biochar was synthesized. • Cationic Pb2+ and anionic CrO 4 2− can be simultaneously captured by MgAl-LDH/BC. • CrO 4 2− was mainly removal via reduction, and subsequently isomorphic substitution. • The mechanism for Pb2+ removal was the complexations and electrostatic attraction. • The fixed-bed column evaluated the feasibility of MgAl-LDH/BC. Cationic and anionic heavy metal contaminants generally co-exist in practical industrial effluent, and simultaneously removal of these species is a bottleneck for most of the bio-adsorbents because of their contrary charge. In this work, pinewood sawdust derived engineered biochar (BC) was fabricated with MgAl layered double hydroxide (MgAl-LDH) nanosheets, which could efficiently and simultaneously capture heavy metal cations and oxyanions from wastewater. The synergetic effect between loaded MgAl-LDH and BC substantially improves its adsorption performance towards both cationic and anionic contaminants, i.e., Pb2+ and CrO 4 2−. The adsorption capacity of MgAl-LDH/BC for Pb2+ reached 591.2 mg/g, which is 263% higher than that of BC, and in the case of CrO 4 2−, the adsorption capacity is 330.8 mg/g, 416% higher than that of BC. The elimination of Pb2+ was mainly attributed to forming complexations with surface functional groups. While for oxyanions removal, CrO 4 2− can be reduced to Cr3+ by functional groups, and then generated Cr3+ could replace Al3+ via morphic substitution, consequently formed an MgCr-LDH structure. Further, in the continuous fixed-bed column study, 225 bed volume of simulating electroplating wastewater co-existed with Pb2+ and CrO 4 2− can be efficiently treated. Hence, this study sheds light on the engineered biochar design to efficiently and simultaneously capture heavy metal cations and oxyanions and its feasibility on real wastewater purification. [ABSTRACT FROM AUTHOR]

• Hazardous chromate removed by thiol functional hydride material through a self-gating proton-coupled electron transfer process. • The reduction plus adsorption process highly efficient (899.66 mg of [Cr 2 O 7 2− / 1 g of nanocomposite), exceptionally rapid (<5 min), highly selective against background electrolytes. • During the reduction of [Cr 2 O 7 2−, thiol functional groups (S H) were oxidized into disulphide linkages (S S). • Disulphides can also be reversely reduced to thiols by thiosulphates (S 2 O 3 2−), which beneficial for regeneration of the material. We have proposed a novel strategy for the reduction plus adsorption process for hexavalent chromium elimination by thiol functional hybrid materials through a self-gating process. Namely, we exploit that coating dithiocarbamate chitosan at the surface of SBA-15 affords a core-shell composite that undergoes reversible shape transformations while thiol functional groups acted as proton-coupled electron donor for [Cr 2 O 7 2−. The reduction of [Cr 2 O 7 2− to Cr3+ was highly efficient and exceptionally rapid, occurred within 5 min with the reduction amount of 899.66 mg of [Cr 2 O 7 2− / 1 g of nanocomposite as a record high value. During the reduction of [Cr 2 O 7 2−, thiol functional groups (-SH) were oxidized into disulfide linkages (S S), and simultaneously chitosan matrix turned into shrunken structure because of the consuming of protons, preventing any release of Cr3+. Disulfides can also be reversely reduced to thiols by thiosulphates (S 2 O 3 2−), which was attractive for regeneration and recyclability of the nanocomposite. Moreover, the [Cr 2 O 7 2− elimination through self-gating process was highly selective against a huge concentration of background electrolytes. This alternative strategy ensures the outstanding and stable performance in applied fields, and could be conducted in various pollution control techniques like permeable reactive barriers. [ABSTRACT FROM AUTHOR]

The agglomeration of rGO resulted from the morphological irregularities restrict its direct applications as catalyst for pollutants removal using advance oxidation processes (AOPs). In this study, we addressed this problem after incorporating the nanosheets of reduced graphene oxide (rGO) in the layers of hydroxides (LDHs) as Fe-rGO LDH hetero-composite. Based on the first order kinetic model, the fabricated composite showed excellent phenol removal with degradation rate constant of 0.16 min−1, 5–100 times higher than Fe-LDH/rGO or other control catalysts. This enhanced catalytic activity was resulted from the systematic assembly of both monolayered rGO and LDHs as superlattice materials, avoiding the aggregation of rGO during the reaction and thus promote the interfacial electron transfer among the active sites. Moreover, Fe-rGO LDH/PMS system exhibited consistent performance over a wide pH range (3.0 ─ 12.0) and broad spectrum of co-existing water constituents (anions and humic acid). The spectroscopic and analytical results suggested that the special arrangement of monolayered rGO in Fe-LDHs facilitated Fe sites to form a stable Fe intermediates after reacting PMS, offering a suitable centre to accept electron from another PMS to generate superoxides (•O 2 −). Finally, singlet oxygen (1O 2) was accounted as dominant reactive oxygen species (ROS) for pollutants removal. Image 1 [ABSTRACT FROM AUTHOR]

A rod-like SDBC-Mg(II) composite was synthesized and optimized in the conditions of 25% Mg(II) loading and 500 °C calcination temperature. As-prepared SDBC-25%Mg(II)-500 adsorbent attained equilibrium in 30 min, with an extraordinary capacity of 2931.76 mg g−1 (Pb(II)) and 861.11 mg g−1 (Cd(II)), revealing a promising adsorbent for the removal of such metals so far. The adsorption kinetics was well described by the pseudo-second-order model while the adsorption isotherm could be fitted by Redlich-Peterson model. Furthermore, SDBC-25%Mg(II)-500 has a high anti-interference and selectivity in the presence of competing ions/other environmental factors and, also effectively eliminates >99% of Pb2+, Cd2+, Ag+ and Cu2+ ions from pond water, lake water and tap water. The adsorption process demonstrated a synergetic adsorption mechanism comprised of ion exchange with Mg(II), coordination with surface and inner carboxylic or carbonyl functional groups and co-precipitations as metal silicates, which is responsible for its superb adsorption performance. Besides, surface carvings of Mg(II) and tunnels on the rods resulting from the sludge carbonization provided a high surface area (91.57 m2 g−1), extra sorption sites and room for easy pollutant diffusion which contributed to surface physical adsorption. Furthermore, this technique demonstrate an alternative pathway that will relieve the burdens of sewage sludge treatment process and turn this solid waste into highly efficient adsorbent for eliminating heavy metal ions from wastewater. This can be considered as a feasible waste resource utilization to meet with the requirement from both ecology and economy for auspicious applications in industries. Unlabelled Image • A surface carved and nanorod-like SDBC-Mg(II) was synthesized through a facile precipitation-calcination route • Sewage sludge used as carbon source which aided to create porous structures, carved Mg(II) and tunnel paths • The approach of resource recovery from waste sewage sludge itself is indicative to the sludge free wastewater treatment [ABSTRACT FROM AUTHOR]

Abstract The designing of selective and efficient adsorbent for removal of heavy metals from wastewater of diverse chemistry is a challenging task for researchers. Herein, FeMgAl derived from layered double hydroxides (LDH) with different intercalated anions (CO 3 2−, NO3−, S 5 2− and MoS 4 2−) as selective adsorbents were evaluated by considering capturing heavy metals from a complex aqueous environment such as: 1) adsorption of single metals ions from a mixture of Ag+, Hg2+, Pb2+, Cu2+, Cd2+, Co2+, Ni2+, Zn2+, 2) adsorption of heavy metals in the presence of huge amount of Ca2+, Mg+, Na+, Cl−, NO 3 − and SO 4 2− ions, 3) adsorption under different solution pHs, 4) solutions with high salinity etc. Out of the studied materials, fast kinetics, record capacities (582 for Hg2+ and 565 mg/g for Ag+) with enormous K d values (1.0 × 108–2.5 × 107) placed FeMgAl MoS 4 (Fe MoS 4 LDH) as the most selective and promising material. FeMgAl S 5 (Fe S 5 LDH) was also impressive due to its good capacities (279 mg/g for Hg2+ and 341 mg/g for Ag+ ions) with K d values (8.3 × 105–1.0 × 103). In contrast, FeMgAl CO 3 and FeMgAl NO 3 (Fe CO 3 LDH and Fe NO 3 LDH) showed very poor selectivity, lower capacities and very small K d values. Furthermore, Fe MoS 4 LDH and Fe S 5 demonstrated negligible efficiency loss in the presence of competitive cations/anions or with change in solution pH. As confirmed by X-ray Diffraction (XRD) and Fourier Transformed Infrared (FTIR) analysis, a mechanism for adsorbed metals in the form of various coordinated complexes inside LDH layers was proposed for Fe MoS 4 or Fe S 5 LDHs. In contrast, a dominant precipitation mechanism as metal-hydroxide or metal-carbonate was suggested for Fe CO 3 and Fe NO 3 LDHs. Graphical abstract Image 1 Highlights • Adsorption by Fe-LDHs with different intercalated anions was compared. • Intercalating with sulfides functional groups offered excellent selectivity. • Adsorption performance was consistent in diverse types of wastewater. • Distinguished adsorption mechanism was proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Surface selenation strategy is performed on metal cocatalysts for enhanced CO 2 -to-CH 3 OH conversion. • Stacked photocatalysts with metal core sandwiched between semiconductor and selenated shell are fabricated. • Metal core accelerates the migration of photoelectrons from semiconductor to selenated shell. • Selenated shell decreases the energy barriers for CH 3 OH production and inhibits the side H 2 evolution. Solar-driven reduction of CO 2 and H 2 O to methanol is highly desirable owing to multiple advantages of green and renewable liquid fuels, whose efficiency and selectivity are restricted by sluggish charge kinetics and unfavorable surface reaction dynamics in conversional semiconductor photocatalysts. This study proposes a surface selenation strategy on metal cocatalysts to improve the photocatalytic performance in CO 2 -to-CH 3 OH conversion. Electron microscopy observation shows the formation of a stacked structure with crystalline Rh core sandwiched between semiconductor substrate and amorphous selenated Rh (RhSe) shell after the treatment. The combination of experimental characterizations with theoretical simulations reveals that Rh core smoothens the migration of photoelectrons from light-harvesting semiconductor to RhSe shell, while the selenation of Rh shell not only reduces the rate-limiting barriers required for CH 3 OH production, but also inhibits the occurrence of side H 2 evolution. Enabled by such a design, significantly enhanced photocatalytic activities (41.2 μmol g cat -1 h-1) and selectivties (91.2%) in CH 3 OH generation are achieved by the Rh@RhSe semi-core-shell cocatalysts, 12.7 and 6.4 times as high as that of pristine Rh, respectively. Moreover, the generalized strategy can be extended to other metal cocatalysts for improved CO 2 -to-CH 3 OH transformation, which opens a new avenue for powering the future with liquid sunshine. [ABSTRACT FROM AUTHOR]

Pyrolysis under protective atmosphere was regarded as an indispensable process for the preparation of biomass-based adsorbents to achieve higher surface areas. In this paper, magnetic carbon composites (MCC) that fabricated under air atmosphere showed an adsorption capacity of 167.22 mg/g in 200 ppm Hg(II), which was significantly higher than magnetic biochar (MBC, 31.80 mg/g) that fabricated under traditional nitrogen protection, and this remarkable performance of MCC was consistent in a wide range of pHs. Based on BET, XRD, FTIR, SEM and Boehm titration, MCC was demonstrated with limited surface area (43.29 m 2 /g) but large amount of surface functional groups comparing with MBC. Additionally, γ-Fe 2 O 3 with a high degree of crystallization was generated in MCC, which led to a better magnetic property and recyclability. Moreover, characterizations, Langmuir isotherm and pseudo-second-order kinetics demonstrated the chemisorption was dominant for MCC in mercury capture, and surface complexation co-precipitate of Hg 4 Fe 8 O 16 C 56 H 40 were also formed. [ABSTRACT FROM AUTHOR]

To meet the current challenges of waste water, an efficient, environment friendly and economical treatment process is always desirable for the degradation of toxic organic compounds. Herein, we reported a stable and active bimetallic CuOx@Co-LDH catalyst for the degradation of phenol using persulfate (PS) under mild conditions. The system of PS/CuOx@Co-LDH completely degraded 0.1 mM of phenol in less than 40 min while at the same time, all the other tested catalysts including catalyst precursors remained sluggish. In view of the practical application, CuOx@Co-LDH/PS system demonstrated consistent performance over a broad pH range (pH 5.0–12.0), during which minimum leaching could be detected. Moreover, good resistance to various inorganic anions was demonstrated in CuOx@Co-LDH/PS system. The consistent performance of CuOx@Co-LDH/PS system may originate from the constant buffer pH of catalyst (9.5 ± 0.8), minimum leaching and the generation of diverse free radicals ( SO 4 − , OH or − O 2 ) under different pH conditions. Additionally, LDH structure offered strong synergetic interactions among active components which might also help in minimum leaching and good reactivity of CuOx@Co-LDH catalyst. The results of radical scavengers, EPR and XPS studies collectively proved the mechanism of diverse free radicals, which was accounted to the redox cyclic reactions of active sites (Cu (III) –Cu (II) –Cu (III) and Co (III) –Co (II) –Co (III) ) during degradation of phenol. [ABSTRACT FROM AUTHOR]

The designing of efficient, selective and stable adsorbents for heavy metals removal remained a challenging task, as most adsorbents did not exhibit consistent performance in diverse types of water. Unlike traditional adsorbents based on surface oxygen groups, thio-functionalized layered double hydroxide (LDH) as Mn-MoS 4 was designed by inserting MoS 4 2− anions into lamellar layers in LDH, and was applied as a highly stable, efficient and selective adsorbent for heavy metals removal. The record high distribution coefficient (K d ∼ 10 7 –10 8 mL/g), fast kinetics and enormous saturated uptake capacities (594, 564 & 357 mg/g) for Hg 2+ , Ag + and Pb 2+ placed Mn-MoS 4 as the most efficient adsorbent for the removal of such metals so far. Further, Mn-MoS 4 can completely tolerate the impact of huge concentration of background electrolytes (Ca 2+ , Mg 2+ , Na + , Cl − , NO 3 − & SO 4 2− ), and effectively control the concentrations of Hg 2+ , Ag + and Pb 2+ ions from tap water, lake water or industrial wastewater far below the limitation in drinking water. Similarly, Mn-MoS 4 is a potential filter due to its consistent performance over a broad pH range (from 2.0 to 11.0), changing ionic strength (up to 100 mM) or in the presence of organic matters. These remarkable features originate from the dominant chemical adsorption mechanism through inner-sphere coordination between thio groups as soft Lewis acid and Hg 2+ , Ag + and Pb 2+ as soft Lewis bases. More interestingly, LDH layers offer protective space for intercalated MoS 4 2− anions against oxidation, and facilitate Mn-MoS 4 with the advantage of easy storage and application over other adsorbents. [ABSTRACT FROM AUTHOR]

A novel strategy for the removal of refractory organic contaminants was realized through sludge-derived biochar (SDBC)/persulfate (PS) system via both adsorption and advanced oxidation process under ambient conditions. SDBC was prepared by one single step of slow pyrolysis of municipal sewage sludge, appeared a porous structure, and contained abundant oxygen-containing functional groups as well as amorphous Fe species. Large surface area and porous structure of SDBC benefitted the adsorption and enrichment of contaminants, while oxygen-containing functional groups and Fe species on the surface were considered as reactive components for the activation of PS. Under conditions of [PS] 0 = 1.85 mM, [4-chlorophenol] 0 = 0.039 mM, [SDBC] 0 = 1 g L −1 , pH 0 = 6.30 and temperature = 25 °C, the removal of model compound of 4-chlorophenol achieved 92.3%, and this significant performance of SDBC/PS system was consistent in a broad pH window. Radical scavengers and electron paramagnetic resonance (EPR) studies suggested that SDBC successfully activated PS to produce various oxidative radicals. Meanwhile, recycle experiments and Fe 3+ leaching tests further demonstrated the stability of SDBC during the activation of PS. Municipal landfill leachate effluent through a membrane bio-reactor was testified as the refractory real wastewater, in which both the removal of total organic carbon and ammonia was significant. Thus, SDBC showed certain advantages in PS activation such as feasible preparation method, remarkable efficiency and stability. These advantages proved SDBC/PS system as an effective strategy of controlling waste by waste, and implicated its potential application in full-scale for the treatment of refractory organic contaminants. [ABSTRACT FROM AUTHOR]

Introducing cow manure compost as an amendment in landfill-leachate-contaminated soils is proved to be an effective technique for the immobilization of Cd in this study. Landfill-leachate-contaminated soil was collected from an unlined landfill in China and amended with a different blending quantity of cow manure compost (0, 12, 24, 36, and 48 g per 200 g soil), which was made by mixing cow manure and chaff at a ratio of 1/1 and maturing for 6 months. pH values of five different blending quantity mixtures increased by 0.2–0.4, and the organic matter levels increased by 2.5–7%, during a remediation period of 5 weeks. Four fractions of Cd named exchangeable Cd, reducible Cd, oxidizable Cd, and residual Cd in soil were respectively analyzed by a sequential extraction procedure. Introducing the cow manure compost application resulted in more than 40% lower exchangeable Cd but a higher concentration of oxidizable Cd in soils, and mass balance results showed nearly no Cd absorption by applied material, indicating that transformation of exchangeable Cd into oxidization forms was the main mechanism of Cd immobilization when cow manure compost was used as an amendment. The Pearson correlation showed that increasing of pH values significantly improved the efficiency of Cd immobilization, with a correlation coefficiency of 0.940 (p< 0.05). This is the first attempt at heavy metal immobilization in landfill-leachate-contaminated soil by cow manure compost, and findings of this work can be integrated to guide the application. Implications: Addition of cow manure compost (CMC) was effective in reducing exchangeable Cd in landfill-leachate-contaminated soils (LLCS). The immobilization effect of Cd was mainly assigned to the redistribution of labile soil Cd. Organic matter (OM) and pH value increased with CMC application. The pH values were more sensitive to Cd immobilization efficiency. It was proved that CMC can be safely and effectively used for the restoration of LLCS. [ABSTRACT FROM AUTHOR]

[Display omitted] • A step-by-step oxidation process including electron transfer and 1O 2 was proposed. • Electron transfer and 1O 2 occurred on OMS-2 surface and in solution, respectively. • O 2 •− on the surface of OMS-2 could significantly extended its half-life. • The step-by-step oxidation driven by the adsorption-desorption of O 2 •− on OMS-2. This study proposed a step-by-step oxidation process based on the in-depth analysis of the catalytic mechanism of peroxymonosulfate (PMS) activated by the common MnO 2 -based catalyst-manganese octahedral molecular sieve (OMS-2). In the first stage, OMS-2-mediated electron transfer dominated the oxidation process. When PMS was completely consumed, the reaction entered the second stage, at which singlet oxygen (1O 2) gradually turned into primary oxidation source. OMS-2-mediated electron transfer was proved based on the results of electrochemical analysis, phosphate substitution experiments, and Raman tests. Meanwhile, the oxidation process of 1O 2 was unveiled by radical scavenging tests, electron paramagnetic resonance (EPR), and solvent-exchange experiment (from H 2 O to D 2 O). Moreover, superoxide radical (O 2 •−) generated from the reaction between PMS and metastable manganese intermediate was identified as the precursor of 1O 2. O 2 •− generated in the first stage could significantly extend its half-life by adsorbing on the (2 1 1) plane of OMS-2, and then desorbed in the second stage and contributed to the formation of 1O 2. More importantly, through the transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and DFT calculations, the essence of step-by-step oxidation driven by O 2 •− adsorption–desorption process was uncovered. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fe-HO/(NO 3) captured GO excellently than hydroxides with different anions. • NO 3 – release from the hydroxide galleries resulted in exfoliation of host layers. • Electrostatic interactions were the driving force for removal of GO. • GO removal was significantly affected by pH. • Coagulated end product was further used in secondary applications, i.e., AOPs and adsorption. The extensive use and inevitable release of graphene oxide (GO) to the environment have increased the threat of its exposure to living organisms. This study reports the design of Fe-based hydroxides with different interlayers anions, i.e., Cl−, SO 4 2−, CO 3 2−, and NO 3 − to capture GO from an aqueous medium. Various characterization techniques, including X-ray diffraction (XRD), Fourier transform infrared (FTIR), and scanning electron microscopy (SEM), confirmed the successful synthesis of these different materials. The Fe-hydroxides as Fe-HO/(NO 3) with NO 3 − interlayers anions effectively removed up to 190 mg/g GO and was tolerant to a high concentration of background electrolyte, different anions, and increasing ionic strength. These remarkable features of Fe-HO/(NO 3) originated from the weak bonding abilities of interlayers NO 3 − anions that facilitated simple self-exfoliation of hydroxide nanosheets, and thus promoted the electrostatic interactions between the positively charged layers of hydroxides and negatively charged GO particles. The coagulated end product (Fe-HO/(NO 3)@GO can be further used in advanced oxidation processes (AOPs) as catalyst or adsorbent for the treatment of different pollutants. We believe that this work not only explains the positive aspect of regulating anions in the hydroxides layers but also provides a direction to develop new materials for environmental remediation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Critical role of non-redox metals to regulate the activation mechanism. • Generating large number of surface bound isolated Cu2+ ions and OH groups. • Switching the PS activation from radical to non-radical. • Surface complexation and activation through electron transfer. • The activation mechanism is less susceptible to solution pH, ionic strength, anion. In advance oxidation processes (AOPs), modulating the activation mechanism from free radical to the non-radical pathway is the most attractive strategy for the treatment of recalcitrant pollutants. Herein, we achieved this goal after modifying the spinel CuFe 2 O 4 catalyst by introducing non-redox metals (M = Mg, Ca, Ba, and Zn) as CuMFe 2 O 4. The modified catalysts were evaluated for the removal of acetaminophen (ACE) using the persulfate (PS) activated system. The results revealed that the non-redox metals not only enhanced the catalytic activity of CuFe 2 O 4 in the order of Mg > Zn > Ca > Ba but also switched the original radical pathway of CuFe 2 O 4 /PS system to the non-radical one (i.e., direct electron transfer path) of CuMgFe 2 O 4 /PS system. The critical role of non-redox metals to modulate the reaction mechanism was studied in detail using the extensive radical scavengers, EPR analysis, target pollutants selectivity, electrochemical studies, decomposition of oxidants, and identification of degradation products. Additionally, various experiments and characterizations, including XRD, EPR, H 2 -TPR, XPS, and FTIR, showed that the changes in the activation mechanism and catalytic activity (6–8 folds higher in the case of CuMgFe 2 O 4) were related to the generation of a large amount of surface-bound isolated Cu2+ ions and abundant surface hydroxyl groups. The non-radical pathway of the CuMgFe 2 O 4 /PS system showed less susceptibility to the changing solution pH, excessive amount of humic acid (HA) or anions, and complete recyclability, and thus demonstrating good practical utility for wastewater. This study provides deep insight into the intrinsic role of non-redox metals to modulate both the activation mechanism and catalytic properties of the catalyst and to design new catalysts for the persulfate-based advance oxidation process. [ABSTRACT FROM AUTHOR]

[Display omitted] • Investigated the major role of active functionalities for the chromate removal. • Elucidated the detailed reaction mechanisms of the applied systems. • Conducted the detailed comparison among various functionalities. • Provided significant insights and perspectives for future studies. Highly efficient elimination of anionic chromate remains a critical task from the biological and ecological perspective owing to their carcinogenic effects on the biosphere and ecosphere. In literature, varieties of functional materials have been applied to remove Cr(VI) from the environmental sources. In which the chemical reduction of Cr(VI) to Cr(III) by a reductant and simultaneous adsorption of Cr species is an effective technique for the removal of Cr(VI). Many effective reductants were applied in the past years, which could be categorized according to their active functional atom/group. Although very few studies illustrated the complete coordination mechanisms between Cr ions and functional groups during the reduction coupled adsorption. This review focuses on recently investigated Cr(VI) reduction coupled adsorption systems based on the electron donor (reductant) functionalities with the interactions of Cr 2 O 7 2−, CrO 4 2− and Cr3+ ions by the metal and nonmetal functional groups. Also, the removal capacity and equilibrium time were analyzed based on the findings from isotherm and kinetic studies. To conclude, we offered our insights based on the coordination of chromium species with various functionalities into future research prospects and issues in the hope of motivating more researchers to involve in this new area of functional materials for environmental pollution control. [ABSTRACT FROM AUTHOR]

• The principle of unreducible metals regulating oxidation mechanism was revealed. • ROS was altered from radical to non-radical after doping unreducible metals. • The reducibility of Cu3+ are dependent on different unreducible metals. • O v raised pH pzc of CuM@Fe 3 O 4 and promoted the adsorption and activation of PMS. In this paper, we surprisingly found that the incorporation of unreducible metal oxides M x O y (M = Mg, Zn, Ca, Ba, Al) onto CuO hybrid magnetic nano ferric oxide (Cu@Fe 3 O 4) may alter the reaction pathway in persulfate activation, and increase the reaction rate constant. The activation of peroxymonosulfate (PMS) by Cu@Fe 3 O 4 led to a classic sulfate radical based oxidation process (SR-AOP) with an acetaminophen (ACE) degradation rate constant of 0.004 min−1, while 1O 2 -dominated nonradical oxidation process was disclosed in CuM@Fe 3 O 4 with wildly fluctuated reaction rate constants from 0.003 to 0.242 min−1. Mechanism studies indicated that singlet oxygen (1O 2) derived from the direct oxidation of superoxide anions radicals (O 2 −) or the recombination of O 2 − was the main reactive oxygen species (ROS) in CuM@Fe 3 O 4 /PMS system. A series of characterization experiments (pH pzc tests, XPS, H 2 -TPR, et al.) and DFT calculation disclosed that the addition of an unreducible metal M yielded many positive effects: (1) the formation of surface oxygen vacancies (O V) raised the zero point charge (pH pzc) of CuM@Fe 3 O 4 , thus enhanced the adsorption and activation of PMS; (2) promoting the generation of a new Cu species (Cu3+) on the surface of CuM@Fe 3 O 4 , which then participated in the generation of 1O 2. The different reducibility of Cu3+ led to differences in the catalytic properties of CuM@Fe 3 O 4. In addition, the effects of various water matrix species and the results of reusability experiment, mineralization experiment, and ecotoxicity test exhibited that CuM@Fe 3 O 4 /PMS system possessed excellent practical application value. [ABSTRACT FROM AUTHOR]

• The nonradical mechanisms in PMS-based heterogeneous catalytic system were arranged. • The evolutionary pathways were summarized and analyzed. • Common identification methods were summarized and evaluated. • Nonradical exhibited its unique oxidation advantages. • Nonradical has extensive application prospect in environmental remediation. Recently, various nonradical oxidation mechanisms different from traditional free radicals have been discovered in peroxymonosulfate (PMS)-based heterogeneous catalytic system. These nonradical oxidation mechanisms have given rise to much controversy in many aspects due to their variety and complex evolutionary pathways. In this paper, we systematically summarized and compared these nonradical oxidation mechanisms. Mainly including the evolutionary pathways, identification methods (qualitative and quantitative), and oxidation characteristics. Moreover, the challenges and strategies for the further development of these oxidation mechanisms, as well as the research and application prospects are proposed. Our work can deepen systematic understanding of the nonradical oxidation mechanism among relevant researchers, and provides some enlightenment for using nonradical oxidation mechanism to deal with the environmental crisis. [ABSTRACT FROM AUTHOR]

Electrolytic manganese anode slag (EMAS) is the waste residue produced by electrolytic manganese metal industry. At present, no mature recycling system has been established, which causes a waste of resources and threatens the environment. Therefore, the resource utilization of EMAS has attracted increased attention. In this paper, the in-situ resource utilization of EMAS can be realized by pickling treatment was reported. Specifically, EMAS after pickling treatment (PEMAS) was first used as catalyst to activate PMS to degrade tetrachlorophenol (4-CP). Pickling could remove the inert inorganic components on EMAS and increase the specific surface area, pore volume and Mn distribution of the catalyst, thus improving the catalytic performance of the catalyst. Under the conditions of 4-CP of 40 ppm, PMS of 1 mM and PEMAS of 0.3 g L−1, 85% of 4-CP could be degraded within 50 min. Mechanism studies proved that the main active species were O 2 − and 1O 2. Some O 2 − contributed to the generation of 1O 2 and some O 2 − directly contributed to the degradation of 4-CP. During the reaction, the valence state of Mn transformed between Mn(III)/Mn(IV) and Mn(II)/Mn(III) and kept the cycle. Moreover, PEMAS/PMS system exhibited excellent independence of the solution pH, resistance to the versatile inorganic ions and background organic matters, and stability of recycling. In a word, this study has achieved the resource utilization of EMAS and the goal of treating waste with waste, which is a win-win strategy of economic and environmental benefits. Unlabelled Image • Pickling enhanced the catalytic activity and inhibited metal leaching of EMAS. • Pickling improved the morphology and Mn dispersion of EMAS. • PEMAS/PMS exhibited excellent stability, reusability, environmental adaptability. • The whole process conformed to the concept of green recycling. [ABSTRACT FROM AUTHOR]

• The sluggish FeIII/FeII cycles restrict Fe-based system from practical application. • Accelerating the FeIII/FeII redox centres is an innovative strategy. • Fe3+/MgAl-MoS 4 /PMS system was more reactive than the reported system. • Regeneration of Fe2+ was responsible for good PMS utilization and activity. • The unsaturated S2− and Mo4+ were disclosed to fuel electron to reduce Fe3+. The slow transformation of Fe3+ back to Fe2+ restrict the practical application of Fe-based catalytic treatment of organic pollutants. Herein, we report a new findings of MgAl-MoS 4 to accelerate the redox cycle of Fe3+/Fe2+ in Fe3+/PMS system. Based on the degradation of 4-chlorophenol (4-CP) profile, the rate constant of Fe3+/MgAl-MoS 4 /PMS system was 40 to 42 folds higher than MgAl-CO 3 /PMS, MgAl-MoS 4 /PMS and Fe3+/PMS respectively. Moreover, Fe3+/MgAl-MoS 4 /PMS system was superior both in the degradation efficiency of pollutants as well as in the stoichiometric efficiency of oxidants from the recently reported Fe3+/WS 2 /PMS, Fe3+/MoS 2 /PMS or other well-known nano-catalysts systems. This co-catalytic effect of MgAl-MoS 4 on the studied redox metals falls in the order of Fe3+ > V5+ > Cu2+ > Mn2+~Ag+. Furthermore, the Fe3+/PMS/MgAl-MoS 4 system shows smooth degradation over a wide pH (3.0–7.0) and complete stabilities in the recycled studies. Additionally, the presence of excessive amounts of inorganic anions or organic matters also did not influence the degradation profile. In mechanism studies, both the unsaturated S2− and Mo4+ of MgAl-MoS 4 were disclosed to fuel electron continuously during the reduction of Fe3+ ions, and thus accelerate the rate limiting step (Fe3+/Fe2+). Additionally, the layered structure, memory effect and suitable surface charge of LDH material also concentrates the reactants molecules and hence, the boosted effect of MgAl-MoS 4 was associated with the better adsorption of Fe3+ ions, the faster PMS decomposition, and the acceleration of Fe3+/Fe2+ redox cycle. This work indicates a breakthrough in the field of classical homogenous Fe/PMS system, offers the very first report on the role of Mo6+ and S2− to modulate the redox behaviour of homogenous Fe ions in persulfate based advanced oxidation processes. [ABSTRACT FROM AUTHOR]

• A series of Co 9 S 8 nanorods with different S doping ratios were prepared from Co 3 O 4 precursor; • Dominantly ROS changed from nonradical to radical one along with S doping; • The concentration of 1O 2 was in a good linear relationship with ΔO L ; • S2− enhanced the conversion effectiveness of PMS to SO 4 -. The introduction of non-metal heteroatoms is an effective way to improve the catalytic properties of heterogeneous catalysts to peroxymonosulfate. Unfortunately, the influence of foreign elements on the catalytic process has not been deeply revealed. Herein, we reported a series of Co 9 S 8 nanorods catalysts from Co 3 O 4 precursor with different S doping ratios. S doping effectively enhanced the catalytic properties, and the catalytic process gradually switched from non-radical (1O 2) into radical (SO 4 −) with the increase of S doping ratio. Moreover, quenching experiments, EPR, XPS, and radicals quantification indicated that the concentration of 1O 2 exhibited a linear relationship with ΔO L. Indicating that 1O 2 was derived from the reaction between PMS and O L. S doping also altered the valency of cobalt. In Co 3 O 4 /PMS, ROS was generated through Co3+/Co2+ catalytic circle. However, in Co 9 S 8 /PMS, Co3+/Co2+/Co0 were all involved and accounted for the generation of ROS due to the low redox potential of S2-. Our work may provide some new clues and strategies for studying the influence of foreign elements on the catalytic process in PMS-based heterogeneous catalytic system. [ABSTRACT FROM AUTHOR]

• Pb2+ and Cr 2 O 7 2− were eliminated by CSC@SDBC via pH tunable reduction plus adsorption mechanisms. • Adsorption of Pb2+ optimized at pH 5.5 and reduction coupled adsorption of Cr 2 O 7 2− enhanced at pH 3. • Various techniques and models were employed to understand the adsorption mechanisms. • Pb2+ and Cr species were adsorbed on CSC@SDBC with the aid of the CS 2 and NH functional groups. • Adsorption mathematical models were applied for CSC@SDBC fixed-bed columns to predict industrial applicability. Over the past, extensive works executed to treat anionic and cationic heavy metal ions from wastewater. Although very few adsorbents were developed to adsorb anionic and cationic heavy metal ions from the same system. In this study, we explored the pH tunable complete reduction plus adsorption mechanism of Pb2+ and Cr 2 O 7 2− by dithiocarbamate-based composite. The pH study recommended that; adsorption of Pb2+ occurred at pH 5.5, besides Cr 2 O 7 2− reduction coupled adsorption executed at pH 3. Furthermore, quick adsorption occurred within 60 min with adsorption capacities of 228.69 and 219.75 mg g−1 for Pb2+ and Cr 2 O 7 2−, respectively. Adsorption isotherm well described by the Redlich-Peterson model, also adsorption processes were fitted by pseudo-second-order kinetics model. Interestingly, characteristic techniques, a physical monolayer model and thermodynamic models were applied to the experimental results to further understand the adsorption mechanisms. The results indicated that the physical model with two types of interaction energies was more appropriate to interpret the adsorption mechanism. Based on the physical model, three thermodynamic functions were calculated and interpreted to attribute new macroscopic interpretations at the molecular level of the adsorption systems. Inspiringly, the metal-composite system highly effective for 5 regeneration cycles and fixed-bed column could decontaminate 17.2 L of ~10 mg L−1 Pb2+ and 7.3 L of ~10 mg L−1 Cr 2 O 7 2− to the EPA's wastewater discharge limit by 5 g of CSC@SDBC with the yielding of 400 and 346 mL of eluent, respectively. Theoretically, a liter of CSC@SDBC column may efficiently adsorb 145,646 mg of Pb2+ and 57,518 mg of Cr 2 O 7 2− from industrial effluent, these were calculated from the Bohart-Adams model. These collective batch and fixed-bed systems were cost-effective and environmentally tolerable techniques to remove anionic and cationic heavy metal ions from industrial wastewater. [ABSTRACT FROM AUTHOR]

• BL firstly acted as the biomass feedstock to synthesize engineered ZVI/biochar. • Graphitic structure in red mud/black liquor (RM/BL) enhanced the electron transfer. • ZVI acted as an electron tank for Fe(II) during Cr(VI) reduction. • Chemical reduction and formation of complexations were the dominant mechanisms. • The industrial applicability of magnetic RM/BL was evaluated by fixed-bed column study. Black liquor (BL) is an agro-industrial residue with high number of lignocellulosic components which could be recognized as a biomass feedstock. In this work, BL coupled with red mud (RM), were applied to prepare cost-effective zero-valent iron (ZVI) embedded in biochar. The oligomers in BL acted as reductants for RM to generate ZVI, while the organic components could be converted into biochar during pyrolysis. The RM/BL demonstrated excellent performance in the removal of Cr(VI) (349.5 mg/g), as the mechanisms were reduction and adsorption. The fixed-bed column study was conducted and 1.7 L simulated wastewater could be treated by 1.0 g RM/BL. After reaction, 95.5% ± 0.8% and 82.5%±3.2% Cr-loaded adsorbents could be recovered by an external magnet for batch and fixed-bed experiments, respectively. All these results shed light on valorizing these two widespread agro-industrial byproducts, and bridged the knowledge gap between magnetic bio-adsorbent preparation and its industrial practicality on wastewater purification. [ABSTRACT FROM AUTHOR]

Persulfate Fe-based catalytic oxidation is considered as one of the most attractive strategy for the growing concerns of water pollution. However, the undesirable FeIII/FeII redox cycle restrict them from attending the sustainable activity during practical applications. This study was intended to develop a new strategy to regulate the redox cycles of FeIII/FeII by introducing the second redox center of MoS 4 2− in the interlayers of Fe-based layered double hydroxide (FeMgAl–MoS 4 LDH). Based on the first-order kinetic model, the fabricated FeMgAl–MoS 4 catalyst was 10–100 fold more reactive than the bench marked peroxymonosulfate (PMS) activators including FeMgAl LDHs and other widely reported nano-catalysts such as Co 3 O 4 , Fe 3 O 4 , α-MnO 2 , CuO–Fe 3 O 4 and Fe 3 O 4. The enhanced catalytic activity of FeMgAl–MoS 4 LDH was related to the continuous regeneration of active sites (FeII/MoIV), excellent PMS utilization efficiency and generation of abundant free radicals. Moreover, the FeMgAl–MoS 4 /PMS system shows an effective pH range from 3.0 to 7.0 and the degradation kinetics of parahydroxy benzoic acid (PHB) were not effected in the presence of huge amount of background electrolytes and natural organic matters. Based on the in-situ electron paramagnetic resonance spectroscopy (EPR), chemical scavengers, XPS analysis and gas chromatography couple with mass spectrometer (GC-MS), a degradation pathway based on dominant free radicals (•SO 4 − and •OH), passing through the redox cycles of FeIII/FeII and MoVI/MoIV was proposed for PMS activation. We believe that this strategy of regulating the redox center through MoS 4 2− not only provides a base to prepare new materials with stable catalytic activity but also broaden the scope of Fe-based material for real application of contaminated water. Image 1 • Intercalated MoS 4 2− is essential to control the FeIII/FeII redox cycles. • FeMgAl–MoS 4 catalyst was 10–100 fold more reactive than most PMS activators. • Excellent PMS utilization resulted from the continuous circulation of redox metals centers. • Consistent performance could be maintained under various water parameters. [ABSTRACT FROM AUTHOR]

• Cu-rGO LDH nanohybrid fabricated by intercalating rGO inside the LDH galleries. • Cu-rGO LDH exhibited higher surface area and electrical conductivity. • Cu-rGO LDH/PMS induced nonradical pathway. • 1O 2 generated through SO 5 − owing to electron conduction between PMS and Cu2+. A new strategy was applied by periodic stacking of active sites of Cu and reduced graphene oxide (rGO) in the form of Cu-rGO LDH nanohybrid material. The experimental results revealed that newly prepared Cu-rGO LDH nanohybrid material was extremely reactive in PMS activation as evident from the degradation rate of 0.115 min−1, much higher than Mn-rGO LDH (0.071 min−1), Zn-rGO LDH (0.023 min−1) or other benchmarked material used during the degradation of bisphenol A (BPA). This excellent activity of Cu-rGO LDH nanohybrid was attributed to the better PMS utilization efficiency as compared to the other catalysts. Additionally, the characterization techniques disclosed that the layer by layer arrangement of active sites in the Cu-rGO LDH catalyst promotes interfacial electron mobility owing to the synergistic association between Cu in LDH and interlayered rGO. Based on the in-situ electron paramagnetic resonance spectroscopy (EPR) and chemical scavengers, singlet oxygen (1O 2) was unveiled as dominant reactive species for pollutant removal, resulting from the recombination of superoxides (O 2 −) or reduction of active Cu centers. We believe that this novel Cu-rGO LDH/PMS system will open up a new avenue to design efficient metal-carbon nanohybrid catalysts for the degradation of emerging aquatic pollutants in a real application. [ABSTRACT FROM AUTHOR]

• Synergistic effect of Cu and Co oxides was find on various supports. • Incorporation of Cu changed the activation pathway of PMS by Co catalysts. • Surface hydroxyl groups on catalysis was studied quantitatively. • Electron transfer between Cu and Co improved the stoichiometric efficiency of PMS. Synergistic effect was commonly observed in bimetallic oxide catalysts in sulfate radical-based advanced oxidation processes by forming spinel structures. In this paper, we found the incorporation of Cu demonstrated the most remarkable promotional effect to Co oxides comparing with Fe and Mn in PMS activation, and no spinel structure of mixed metals was found. Moreover, the synergism between oxides of Cu and Co was observed on various supports including MgAl layered double hydroxides, mesoporous MnO 2 and ZnO. Under conditions of 0.2 g L−1 catalysts, 2 mM PMS, and 40 ppm 4-chlorophenol (4-CP), CuCo@ZnO/PMS system demonstrated excellent performance that 96.0% 4-CP could be removed, while the removal efficiency of 4-CP in Cu@ZnO/PMS and Co@ZnO/PMS systems was only 12.1% and 45.4%, respectively. The simultaneous incorporation of Co and Cu bimetallic oxides in CuCo@ZnO led to a higher surface hydroxyl density, and this surface hydroxyl density showed a linear relationship to their first order kinetic constant in 4-CP degradation. Moreover, the results of peroxymonosulfate (PMS) decomposition, quantification of sulfate radical (SO 4 −), EPR, XPS, H 2 -TPR, and CV indicated that the synergism of Cu/Co also arose from the electron transfer between Cu(I) and Co(III), which altered the redox circle of Co(II)/Co(III) and increased the steady concentration of oxidative radicals. Due to this synergism, the degradation percentage of organic contaminants, stability of heterogeneous catalysts and the stoichiometric efficiency of PMS were all improved. These findings were highly suggestive to the further development of bimetallic heterogeneous catalysts in persulfate based advanced oxidation processes. [ABSTRACT FROM AUTHOR]

In this study, we report on an active and stable CoMgAl layered double hydrotalcite (LDH) catalyst for phenol degradation by heterogeneous activation of peroxymonosulfate (PMS). The CoMgAl-LDH catalyst was synthesized by hydrothermal method. The PMS/CoMgAl-LDH system overcomes the drawbacks of traditional Fenton processes. Various effects, e.g., scavengers, chloride ion, catalyst dosage, PMS concentration, temperature, and pH, were also inspected to evaluate the system. The results indicated that the PMS/CoMgAl-LDH system had extremely high efficiency for phenol degradation; 0.1 mM phenol could be completely degraded by 0.3 g/L catalyst and 3 mM PMS within 60 min at 30 °C. The CoMgAl-LDH catalyst appeared to possess outstanding reusability and stability. After four rounds of recycling, nearly 100% of the phenol was removed within 80 min by the PMS/CoMgAl-LDH system, with only 0.05 mg/L Co2+ leaching. A sulfate radical was the main oxidation species in the PMS/Co-LDH system. The degradation rate of phenol was influenced by temperature, and the activation energy was 65.19 kJ/mol. These advantages proved the PMS/CoMgAl-LDH system is an effective strategy for the treatment of organic contaminants. [ABSTRACT FROM AUTHOR]