In this work, birnessite-type d-MnO 2 nanoflowers were uniformly deposited on 3D nickel foam (NF)... more In this work, birnessite-type d-MnO 2 nanoflowers were uniformly deposited on 3D nickel foam (NF) by one-step hydrothermal route for high-efficient activation of peroxymonosulfate (PMS) towards degradation of acid orange 7 (AO7). High specific surface area, large pore volume and 3D hierarchical structure promotes the mass and electron transfer for great catalytic activity. Low reaction energy barrier (E a = 2 7.5 kJ/mol) and outstanding reusability with extremely low manganese leaching during recycling (<0.06 mg/L) was achieved due to the 3D hierarchical structure which could effectively avoid the agglomeration of nano-sized MnO 2. SO 4 ÅÀ was confirmed to be the predominant reactive species for AO7 decomposition by electron spin resonance and quenching tests. The synergistic catalytic mechanism of MnO 2 / NF and the role of inner-sphere complexation between the active sites of MnO 2 and peroxymonosulfate were thoroughly investigated. Compared with traditional nano/micro-sized catalysts, 3D macroscopic MnO 2 /NF with facile recovery and high stability potentially facilitates fascinating applications as green heterogeneous catalysis approach.
Co 3 O 4 nanocrystals were supported on 3D monolith N-doped graphene aerogel (NGA). Co 3 O 4 /NGA... more Co 3 O 4 nanocrystals were supported on 3D monolith N-doped graphene aerogel (NGA). Co 3 O 4 /NGA possesses excellent longterm stability and recycling performance. Kinetic modeling was developed to simulate transformation of main active radicals. Macroscopic Co 3 O 4 /NGA can be easily separated and reused with low cobalt leaching.
h i g h l i g h t s g r a p h i c a l a b s t r a c t Novel Co 3 O 4 nanowires and nanoflowers ar... more h i g h l i g h t s g r a p h i c a l a b s t r a c t Novel Co 3 O 4 nanowires and nanoflowers are supported on nickel foam (NF) surface. Co 3 O 4 /NF exhibits excellent capacity for peroxymonosulfate activation. Macroscopic Co 3 O 4 /NF can be easily and completely recycled with low cobalt leaching. Co 3 O 4 /NF shows remarkable reusability with stable performance.
Both Cl À and base can affect PMS activation to produce reactive chlorine or oxygen species, but ... more Both Cl À and base can affect PMS activation to produce reactive chlorine or oxygen species, but the overall effects of chloride on this emerging PMS/base technology in saline wastewater treatment are unknown. Here effectiveness of PMS/base, PMS/Cl À and PMS/base/Cl À is compared with a gradient concentration of chloride and alkalinity, by probing the degradation of methylene blue (MB). Both PMS/ base and PMS/Cl À systems can rapidly degrade MB due to the generation of singlet oxygen and reactive chlorine, respectively. Interestingly, dye degradation and adsorbable organic halides (AOX) formation are inhibited in the PMS/base/Cl À system as high concentrations of Cl À and base co-exist. Reaction of PMS with chloride diminishes the effective concentration of PMS by base activation, whereas in return high alkalinity decreases the oxidation capacity of reactive species. Therefore, this finding may have significant technical implications for evaluating the applicability of the emerging PMS/base technology and optimizing the conditions for AOX abatement in PMS-based processes.
Halides (X −) in the industrial wastewater are usually thought to adversely affect the degradatio... more Halides (X −) in the industrial wastewater are usually thought to adversely affect the degradation kinetics and mineralization rates in several SO 4 %−-based advanced oxidation processes. However, their unfavorable effects might be overestimated, particularly the heat/persulfate (PS) system as tested in the present study. Here the degradation of phenol, benzoic acid, coumarin and acid orange 7 (AO7) was examined with the presence of chloride or bromide in a heat/PS process. Cl − was found to have a dual effect (inhibition followed by enhancement) on the decomposition rates of organic pollutants, whereas the effects of Br − are insignificant within the tested concentration (0-0.2 mM). However, some chlorinated or brominated compounds were still identified in this heat/PS system. Unexpectedly, the mineralization rates of AO7, phenol, benzoic acid and coumarin were not apparently inhibited. In addition, the formation of adsorbable organic halogen (AOX) in the heat/PS system was much less than those in the peroxymonosulfate (PMS)/Cl − or PMS/Br − systems. According to the results of kinetic modeling, SO 4 % − was the dominating radical for AO7 degradation without Cl − or Br − , but Cl 2 %− was the main oxidant in the presence of Cl − , SO 4 %− , Br % and Br 2-% were responsible for the oxidation of AO7 in the presence of Br −. The present study assumes that X 2 /HOX, rather than halogen radicals, is responsible for the enhanced formation of organohalogens. These findings are meaningful to evaluate the PS-based technologies for the high-salinity wastewater and to develop useful strategies for mitigating the negative effects of halides in advanced oxidation processes (AOPs).
The most efficient route was designed for 3D mesoporous α-Co(OH) 2 on Ni foam (NF). • Extraordina... more The most efficient route was designed for 3D mesoporous α-Co(OH) 2 on Ni foam (NF). • Extraordinary catalytic activity of Co (OH) 2 /NF for peroxymonosulfate was observed. • The cobalt leaching was alleviated by the macroscopic Co(OH) 2 /NF. • The readily recyclable monolith catalyst benefits the practical application.
Futility of traditional advanced oxidation processes (AOPs) in saline wastewater treatment has st... more Futility of traditional advanced oxidation processes (AOPs) in saline wastewater treatment has stimulated the quest for novel "halotolerant" chemical oxidation technology. Acetylacetone (AA) has proven to be a potent photo-activator in the degradation of dyes, but the applicability of UV/AA for saline wastewater treatment needs to be verified. In this study, degradation of crystal violet (CV) was investigated in the UV/AA system in the presence of various concentrations of exogenic Clor Br-. The results reveal that degradation, mineralization and even accumulation of adsorbable organic halides (AOX) were not significantly affected by the addition of Clor Br-. Rates of CV degradation were enhanced by elevating either AA dosage or solution acidity. An apparent kinetic rate equation was developed as r =-d[CV]/dt = k[CV] a [AA] b = (7.34 × 10-4 mM 1-(a+b) min-1) × [CV] a=0.16 [AA] b=0.97. In terms of results of radical quenching experiments, direct electron/energy transfer is considered as the major reaction mechanism, while either singlet oxygen or triplet state (3 (AA)*) might be involved. Based on identification of degradation byproducts, a possible degradation pathway of CV in the UV/AA system is proposed.
Release and rechlorination of chlorine atoms on the benzene ring have been observed during advanc... more Release and rechlorination of chlorine atoms on the benzene ring have been observed during advanced oxidation processes (AOPs), while the dechlorination on the side chain of the benzene ring has not been fully investigated previously. The degradation and dechlorination processes of chloramphenicol (i.e., thiamphenicol (TAP) and florfenicol (FFC)) were assessed through generation of the sulfate radical from Co(II)-mediated activation of peroxymonosulfate (PMS). High-resolution mass spectrometry (HRMS) analysis detected a few chlorinated and dechlorinated products during the Co 2+ /PMS reaction. The low efficiency of total organic carbon (TOC) removal in conjunction with slightly decreased absorbable organic halogen (AOX) values with high degradation rates, indicate that TAP and FFC could be degraded via the destruction of a small portion of the carbon moiety rather than through complete mineralization. The possible degradation pathways of TAP and FFC are proposed. All experimental results and further quantum chemistry calculations indicate dechlorination on the side chain of the benzene ring is more difficult than that directly on the benzene ring. This suggests organic pollutants containing chlorine atoms on the side chain of the benzene ring will be more resistant to oxidative attack and deserve more attention.
Abiotic oxidation of toxic As(III) to As(V) is being deemed as a necessary step for the overall a... more Abiotic oxidation of toxic As(III) to As(V) is being deemed as a necessary step for the overall arsenic decontamination in both natural and engineered systems. Direct oxidation of As(III) by chemical oxidants, such as ozone, permanganate, ferrate, chlorine and chloramine, or naturally occurring minerals like Mn, Fe oxides, seems straightforward. Both O 2 and H 2 O 2 are ineffective for arsenite oxidation, but they can be activated by reducing substances like Fe 2+ , Fe 0 to increase the oxidation rates. Photo-induced oxidation of As(III) has been demonstrated effective in Fe complexes or minerals, NO 3-/NO 2-, dissolved organic matter (DOM), peroxygens and TiO 2 systems. Although a variety of oxidation methods have been developed over the past two decades, there remain many scientific and technical challenges that must be overcome before the rapid progress in basic knowledge can be translated into environmental benefits. To better understand the trends in the existing data and to identify the knowledge gaps, this review describes in detail the complicated mechanisms for As(III) oxidation by various methods and emphasizes on the conflicting data and explanation. Some prevailing concerns and challenges in the sphere of As(III) oxidation are also pointed out so as to appeal to researchers for further investigations.
Iopromide (IOP) has been identified as one of the most persistent pharmaceuticals in wastewater t... more Iopromide (IOP) has been identified as one of the most persistent pharmaceuticals in wastewater treatment processes, however, kinetic and intrinsic factors constraining its fast removal in advanced oxidation processes (AOPs) are yet to be resolved. Here oxidation of IOP by heat-activated peroxydisulfate (PDS) was investigated both experimentally and theoretically. Rates of IOP degradation were enhanced by elevating solution temperature and acidity. An apparent kinetic rate equation was developed, based on the pseudo-first-order reaction model and assumption of steady state of SO 4 %−. The common water constituents showed inhibitory effects on IOP decomposition to various extent. An insufficient supply of SO 4 %− was considered as the major kinetic constraint. Eight byproducts were identified and most of which had intact triiodinated benzene ring. O-demethylation, oxidation of amino moiety and oxidation/elimination of alcohol groups are proposed as the primary degradation pathways, in accordance with the incomplete mineralization and non-detectable release of inorganic iodine. Quantum chemical calculations predict that oxidation of alkyl chains of IOP preferentially occurs and IOP byproducts with shorter side chains and intact triiodinated ring are more reactive than IOP. By virtue of the identified kinetic and intrinsic constraints, strategies to maximize degradation efficiency of IOP are proposed.
A facile and scalable one-pot synthesis method was designed to fabricate N-doped biochar from woo... more A facile and scalable one-pot synthesis method was designed to fabricate N-doped biochar from wood residue for peroxymonosulfate (PMS) activation. The urea:wood residue w/w ratio was varied from 0:1 to 100:1, and the intrinsic (surface chemistry) and extrinsic (morphology, specific surface area, etc.) properties of the N-doped biochar were systematically investigated. Notably, the urea:wood residue w/w ratio played a significant role in tuning the N species composition in the N-doped biochar. A higher urea:wood residue w/w ratio resulted in greater at.% of graphitic N and higher specific surface area. The results show that the catalyst prepared with urea:wood residue w/w ratio of 100:1 (NC800-20) manifested the greatest catalytic activity as PMS activator for organics removal due to its highly favorable combination of intrinsic (highest at.% graphitic N) and extrinsic (excellent specific surface area) properties. The catalyst loading, PMS dosage and pH were found to be operationally crucial for PMS activation. Under the best condition, the NC800-20 can be used to degrade various organic pollutants. The recyclability of NC800-20 was studied and while the catalytic activity gradually deteriorated over successive cycles, it can be completely restored by simple calcination at 500°C. The used catalyst was extensively characterized, revealing insights into the mechanism of PMS activation. The prevailing mechanism for PMS activation was the nonradical pathway. Overall, this research provides insights into preparing N-doped biochar with favorable extrinsic and intrinsic properties from biowaste for sustainable pollutant removal via PMS activation.
The identification of reactive radical species using quenching and electron paramagnetic resonanc... more The identification of reactive radical species using quenching and electron paramagnetic resonance (EPR) tests has attracted extensive attention, but some mistakes or misinterpretations are often present in recent literature. This review aims to clarify the corresponding issues through surveying literature, including the uncertainty about the identity of radicals in the bulk solution or adsorbed on the catalyst surface in quenching tests, selection of proper scavengers, data explanation for incomplete inhibition, the inconsistent results between quenching and EPR tests (e.g., SO 4 •− is predominant in quenching test while the signal of • OH predominates in EPR test), and the incorrect identification of EPR signals (e.g., SO 4 •− is identified by indiscernible or incorrect signals). In addition, this review outlines the transformation of radicals for better tracing the origin of radicals. It is anticipated that this review can help in avoiding mistakes while investigating catalytic oxidative mechanism with quenching and EPR tests.
The addition of MoS 2 greatly accelerated the conversion of Fe(III) to Fe(II). • MoS 2 enables Fe... more The addition of MoS 2 greatly accelerated the conversion of Fe(III) to Fe(II). • MoS 2 enables Fe(II)/PMS to efficiently degrade halogenated organic pollutants. • The unsaturated S on the fresh MoS 2 was found to assist in PMS decomposition. • The used or rinsed MoS 2 still exhibited excellent recyclability and reactivity.
T chemical calculation, eight main transformation pathways are proposed for the degradation of io... more T chemical calculation, eight main transformation pathways are proposed for the degradation of iomeprol and iohexol as follows: (a) deiodination; (b) hydrogen abstraction; (c) amide hydrolysis; (d) amino oxidation; (e) hydroxyl substituent; (f) transformed alkyl aromatic amides to aromatic carbamoyl; (g) dehydration; (h) oxidized primary alcohol groups to carboxyl groups.
The interaction of reductive metal ions and peroxymonosulfate (PMS) is necessary for the generati... more The interaction of reductive metal ions and peroxymonosulfate (PMS) is necessary for the generation of sulfate radials (SO 4 %−), however, this process is greatly restrained by the sluggish reduction of high-valent metal ions. Here we report that commercially available reductive metal (Mo or W) powders are capable of unlocking this kinetic constraint. The reduction of Fe(III) to Fe(II), decomposition of PMS, and degradation/mineralization of 4chlorophenol (4-CP) are all accelerated in the Mo/Fe 2+ /PMS process at a very low Fe 2+ /PMS ratio (Fe 2+ / PMS = 1/10). In such an accelerated system, common adverse effects of natural water constituents such as chloride and humic acid are largely mitigated. According to the fluorescence measurement and scavenging tests, sulfate and hydroxyl radicals dominate in Mo/Fe 2+ /PMS process. The addition of Mo or W is further confirmed to favor Cu 2+ /PMS process, but this is not the case for other metal ions (Mn 2+ , Ni 2+ , Ce 3+ and Co 2+). Reductive zero-valence and four-valence active sites (Mo 0 and Mo 4+ ; W 0 and W 4+) play key roles in overall
Bimetallic Fe−Mn oxide (BFMO) has been regarded as a promising activator of peroxysulfate (PS), t... more Bimetallic Fe−Mn oxide (BFMO) has been regarded as a promising activator of peroxysulfate (PS), the sustained activity and durability of BFMO for long-term activation of PS in situ, however, is unclear for groundwater remediation. A BFMO (i.e., Mn 1.5 FeO 6.35) was prepared and explored for PS-based in situ chemical oxidation (ISCO) of trichloroethylene (TCE) in sand columns with simulated/actual groundwater (SGW/AGW). The sustained activity of BFMO, oxidant utilization efficiency, and postreaction characterization were particularly investigated. Electron spin resonance (ESR) and radical scavenging tests implied that sulfate radicals (SO 4 •−) and hydroxyl radicals (HO •) played major roles in degrading TCE, whereas singlet oxygen (1 O 2) contributed less to TCE degradation by BFMO-activated Oxone. Fast degradation and almost complete dechlorination of TCE in AGW were obtained, with reaction stoichiometry efficiencies (RSE) of ΔTCE/ΔOxone at 3−5%, much higher than those reported RSE values in H 2 O 2-based ISCO (≤0.28%). HCO 3 − did not show detrimental effect on TCE degradation, and effects of natural organic matters (NOM) were negligible at high Oxone dosage. Postreaction characterizations displayed that the BFMO was remarkably stable with sustained activity for Oxone activation after 115 days of continuous-flow test, which therefore can be promising catalyst for Oxone-based ISCO for TCE-contaminated groundwater remediation.
One of the great challenges in the field of photocatalysis is to develop novel photocatalysts wit... more One of the great challenges in the field of photocatalysis is to develop novel photocatalysts with excellent solar-light-harvesting capacity and separation efficiency of photo-induced charge. Herein, novel CeO 2 / Bi 2 MoO 6 heterojunctions were fabricated through in-situ precipitation of CeO 2 nanoparticles (size: $26 nm) on the surface of flower-like Bi 2 MoO 6 superstructures (diameter: 2.1-3.5 lm) by a simple method. The as-prepared photocatalysts were systematically characterized by a range of techniques. The photocatalytic degradation of rhodamine B (RhB) dye, methyl orange (MO) dye and tetracycline (TC) antibiotic by this novel photocatalyst was investigated under visible-light irradiation. The CeO 2 / Bi 2 MoO 6 heterojunction with a CeO 2 /Bi 2 MoO 6 weight ratio of 0.05 (0.05Ce-Bi) exhibited the highest photocatalytic activity with the RhB degradation efficiency of 100% in 75 min, which was considerably higher than those of pristine CeO 2 (26.8%) and Bi 2 MoO 6 (80.3%) as well as their physical mixtures (74.8%). The more efficient separation of electron-hole pairs was identified as the primary reason of the enhanced
Recently there is vigorous growth of reports on persulfate (PS)-based advanced oxidation processe... more Recently there is vigorous growth of reports on persulfate (PS)-based advanced oxidation processes (AOPs), inclining to development of newfangled catalysts and treatment of a wide range of organic pollutants. PS-related non-radical oxidation pathways are lately proposed, whereas there still exist debatable observations and explanation on these issues. While non-radical reactions in heterogeneous systems have been well commented, this review focuses on the latest discovery of non-radical oxidation in homogeneous persulfate (especially peroxymonosulfate (PMS)) systems. The application of direct oxidation process is firstly summarized and the roles of PMS distal oxygen in attack on organic pollutants like antibiotics are highlighted. Besides, the effects of exogenic and endogenic halogen on the reactivity and mechanisms of HOX in PS activation are discussed. Then the formation and reaction pathways of singlet oxygen (1 O 2) triggered by phenol/carbonyl compounds and nucleophiles are elaborated. Recent discovery on formation of high valent metal species by PS activation and their reactivity is reviewed lastly. By sorting out a large number of cutting-edge research reports, this review conducts a detailed and critical analysis and overview on the homogeneous PS non-radical mechanisms, and points out the controversies and challenges so as to better understand the reaction mechanism and further improve their treatment performance.
Effective photogenerated charge separation and rapid Cu(II)/Cu(I) redox cycling is still challeng... more Effective photogenerated charge separation and rapid Cu(II)/Cu(I) redox cycling is still challenging for photocatalytic reactions and copper-based Fenton-like process, respectively. Herein, a novel heterogeneous Fentonlike catalyst of copper incorporated carbon ring-g-C 3 N 4 (Cu-C-CN) was prepared through a facile calcination method. The carbon ring could be intimately connected with g-C 3 N 4 via sp 2-hybridized CeN bonds to form an inplane π-conjugated structure. The carbon ring spliced g-C 3 N 4 (C-CN) can serve as an effective electron-hole separator owing to the varied electron affinity of two domains (e.g. carbon-ring and g-C 3 N 4). The copper species were further introduced to the framework of g-C 3 N 4 via the CueN bonds to act as acceptors of conductionelectrons from g-C 3 N 4 and H 2 O 2 activators. Taking the photodegradation of methylene blue (MB) as a model reaction, the decomposition efficiency over Cu-C-CN is 5.5 times higher than that of pristine g-C 3 N 4 , and would nearly linearly increase with pH. The notable enhancement in photodegradation efficiency could be ascribed to the synergetic collaboration between photocatalysis process and Fenton-like process to generate abundant %OH and e −. The Cu-C-CN catalyst shows high recycling stability with negligible Cu leaching due to the strong affinity of Cu 2+ to g-C 3 N 4 framework. The strategy of coupling Fenton-like catalysts, electron-deficient domains (e.g. carbon-ring) into semiconductor-based photocatalysis provides a facile and promising solution to the remediation of water pollution with solar energy.
In this work, birnessite-type d-MnO 2 nanoflowers were uniformly deposited on 3D nickel foam (NF)... more In this work, birnessite-type d-MnO 2 nanoflowers were uniformly deposited on 3D nickel foam (NF) by one-step hydrothermal route for high-efficient activation of peroxymonosulfate (PMS) towards degradation of acid orange 7 (AO7). High specific surface area, large pore volume and 3D hierarchical structure promotes the mass and electron transfer for great catalytic activity. Low reaction energy barrier (E a = 2 7.5 kJ/mol) and outstanding reusability with extremely low manganese leaching during recycling (<0.06 mg/L) was achieved due to the 3D hierarchical structure which could effectively avoid the agglomeration of nano-sized MnO 2. SO 4 ÅÀ was confirmed to be the predominant reactive species for AO7 decomposition by electron spin resonance and quenching tests. The synergistic catalytic mechanism of MnO 2 / NF and the role of inner-sphere complexation between the active sites of MnO 2 and peroxymonosulfate were thoroughly investigated. Compared with traditional nano/micro-sized catalysts, 3D macroscopic MnO 2 /NF with facile recovery and high stability potentially facilitates fascinating applications as green heterogeneous catalysis approach.
Co 3 O 4 nanocrystals were supported on 3D monolith N-doped graphene aerogel (NGA). Co 3 O 4 /NGA... more Co 3 O 4 nanocrystals were supported on 3D monolith N-doped graphene aerogel (NGA). Co 3 O 4 /NGA possesses excellent longterm stability and recycling performance. Kinetic modeling was developed to simulate transformation of main active radicals. Macroscopic Co 3 O 4 /NGA can be easily separated and reused with low cobalt leaching.
h i g h l i g h t s g r a p h i c a l a b s t r a c t Novel Co 3 O 4 nanowires and nanoflowers ar... more h i g h l i g h t s g r a p h i c a l a b s t r a c t Novel Co 3 O 4 nanowires and nanoflowers are supported on nickel foam (NF) surface. Co 3 O 4 /NF exhibits excellent capacity for peroxymonosulfate activation. Macroscopic Co 3 O 4 /NF can be easily and completely recycled with low cobalt leaching. Co 3 O 4 /NF shows remarkable reusability with stable performance.
Both Cl À and base can affect PMS activation to produce reactive chlorine or oxygen species, but ... more Both Cl À and base can affect PMS activation to produce reactive chlorine or oxygen species, but the overall effects of chloride on this emerging PMS/base technology in saline wastewater treatment are unknown. Here effectiveness of PMS/base, PMS/Cl À and PMS/base/Cl À is compared with a gradient concentration of chloride and alkalinity, by probing the degradation of methylene blue (MB). Both PMS/ base and PMS/Cl À systems can rapidly degrade MB due to the generation of singlet oxygen and reactive chlorine, respectively. Interestingly, dye degradation and adsorbable organic halides (AOX) formation are inhibited in the PMS/base/Cl À system as high concentrations of Cl À and base co-exist. Reaction of PMS with chloride diminishes the effective concentration of PMS by base activation, whereas in return high alkalinity decreases the oxidation capacity of reactive species. Therefore, this finding may have significant technical implications for evaluating the applicability of the emerging PMS/base technology and optimizing the conditions for AOX abatement in PMS-based processes.
Halides (X −) in the industrial wastewater are usually thought to adversely affect the degradatio... more Halides (X −) in the industrial wastewater are usually thought to adversely affect the degradation kinetics and mineralization rates in several SO 4 %−-based advanced oxidation processes. However, their unfavorable effects might be overestimated, particularly the heat/persulfate (PS) system as tested in the present study. Here the degradation of phenol, benzoic acid, coumarin and acid orange 7 (AO7) was examined with the presence of chloride or bromide in a heat/PS process. Cl − was found to have a dual effect (inhibition followed by enhancement) on the decomposition rates of organic pollutants, whereas the effects of Br − are insignificant within the tested concentration (0-0.2 mM). However, some chlorinated or brominated compounds were still identified in this heat/PS system. Unexpectedly, the mineralization rates of AO7, phenol, benzoic acid and coumarin were not apparently inhibited. In addition, the formation of adsorbable organic halogen (AOX) in the heat/PS system was much less than those in the peroxymonosulfate (PMS)/Cl − or PMS/Br − systems. According to the results of kinetic modeling, SO 4 % − was the dominating radical for AO7 degradation without Cl − or Br − , but Cl 2 %− was the main oxidant in the presence of Cl − , SO 4 %− , Br % and Br 2-% were responsible for the oxidation of AO7 in the presence of Br −. The present study assumes that X 2 /HOX, rather than halogen radicals, is responsible for the enhanced formation of organohalogens. These findings are meaningful to evaluate the PS-based technologies for the high-salinity wastewater and to develop useful strategies for mitigating the negative effects of halides in advanced oxidation processes (AOPs).
The most efficient route was designed for 3D mesoporous α-Co(OH) 2 on Ni foam (NF). • Extraordina... more The most efficient route was designed for 3D mesoporous α-Co(OH) 2 on Ni foam (NF). • Extraordinary catalytic activity of Co (OH) 2 /NF for peroxymonosulfate was observed. • The cobalt leaching was alleviated by the macroscopic Co(OH) 2 /NF. • The readily recyclable monolith catalyst benefits the practical application.
Futility of traditional advanced oxidation processes (AOPs) in saline wastewater treatment has st... more Futility of traditional advanced oxidation processes (AOPs) in saline wastewater treatment has stimulated the quest for novel "halotolerant" chemical oxidation technology. Acetylacetone (AA) has proven to be a potent photo-activator in the degradation of dyes, but the applicability of UV/AA for saline wastewater treatment needs to be verified. In this study, degradation of crystal violet (CV) was investigated in the UV/AA system in the presence of various concentrations of exogenic Clor Br-. The results reveal that degradation, mineralization and even accumulation of adsorbable organic halides (AOX) were not significantly affected by the addition of Clor Br-. Rates of CV degradation were enhanced by elevating either AA dosage or solution acidity. An apparent kinetic rate equation was developed as r =-d[CV]/dt = k[CV] a [AA] b = (7.34 × 10-4 mM 1-(a+b) min-1) × [CV] a=0.16 [AA] b=0.97. In terms of results of radical quenching experiments, direct electron/energy transfer is considered as the major reaction mechanism, while either singlet oxygen or triplet state (3 (AA)*) might be involved. Based on identification of degradation byproducts, a possible degradation pathway of CV in the UV/AA system is proposed.
Release and rechlorination of chlorine atoms on the benzene ring have been observed during advanc... more Release and rechlorination of chlorine atoms on the benzene ring have been observed during advanced oxidation processes (AOPs), while the dechlorination on the side chain of the benzene ring has not been fully investigated previously. The degradation and dechlorination processes of chloramphenicol (i.e., thiamphenicol (TAP) and florfenicol (FFC)) were assessed through generation of the sulfate radical from Co(II)-mediated activation of peroxymonosulfate (PMS). High-resolution mass spectrometry (HRMS) analysis detected a few chlorinated and dechlorinated products during the Co 2+ /PMS reaction. The low efficiency of total organic carbon (TOC) removal in conjunction with slightly decreased absorbable organic halogen (AOX) values with high degradation rates, indicate that TAP and FFC could be degraded via the destruction of a small portion of the carbon moiety rather than through complete mineralization. The possible degradation pathways of TAP and FFC are proposed. All experimental results and further quantum chemistry calculations indicate dechlorination on the side chain of the benzene ring is more difficult than that directly on the benzene ring. This suggests organic pollutants containing chlorine atoms on the side chain of the benzene ring will be more resistant to oxidative attack and deserve more attention.
Abiotic oxidation of toxic As(III) to As(V) is being deemed as a necessary step for the overall a... more Abiotic oxidation of toxic As(III) to As(V) is being deemed as a necessary step for the overall arsenic decontamination in both natural and engineered systems. Direct oxidation of As(III) by chemical oxidants, such as ozone, permanganate, ferrate, chlorine and chloramine, or naturally occurring minerals like Mn, Fe oxides, seems straightforward. Both O 2 and H 2 O 2 are ineffective for arsenite oxidation, but they can be activated by reducing substances like Fe 2+ , Fe 0 to increase the oxidation rates. Photo-induced oxidation of As(III) has been demonstrated effective in Fe complexes or minerals, NO 3-/NO 2-, dissolved organic matter (DOM), peroxygens and TiO 2 systems. Although a variety of oxidation methods have been developed over the past two decades, there remain many scientific and technical challenges that must be overcome before the rapid progress in basic knowledge can be translated into environmental benefits. To better understand the trends in the existing data and to identify the knowledge gaps, this review describes in detail the complicated mechanisms for As(III) oxidation by various methods and emphasizes on the conflicting data and explanation. Some prevailing concerns and challenges in the sphere of As(III) oxidation are also pointed out so as to appeal to researchers for further investigations.
Iopromide (IOP) has been identified as one of the most persistent pharmaceuticals in wastewater t... more Iopromide (IOP) has been identified as one of the most persistent pharmaceuticals in wastewater treatment processes, however, kinetic and intrinsic factors constraining its fast removal in advanced oxidation processes (AOPs) are yet to be resolved. Here oxidation of IOP by heat-activated peroxydisulfate (PDS) was investigated both experimentally and theoretically. Rates of IOP degradation were enhanced by elevating solution temperature and acidity. An apparent kinetic rate equation was developed, based on the pseudo-first-order reaction model and assumption of steady state of SO 4 %−. The common water constituents showed inhibitory effects on IOP decomposition to various extent. An insufficient supply of SO 4 %− was considered as the major kinetic constraint. Eight byproducts were identified and most of which had intact triiodinated benzene ring. O-demethylation, oxidation of amino moiety and oxidation/elimination of alcohol groups are proposed as the primary degradation pathways, in accordance with the incomplete mineralization and non-detectable release of inorganic iodine. Quantum chemical calculations predict that oxidation of alkyl chains of IOP preferentially occurs and IOP byproducts with shorter side chains and intact triiodinated ring are more reactive than IOP. By virtue of the identified kinetic and intrinsic constraints, strategies to maximize degradation efficiency of IOP are proposed.
A facile and scalable one-pot synthesis method was designed to fabricate N-doped biochar from woo... more A facile and scalable one-pot synthesis method was designed to fabricate N-doped biochar from wood residue for peroxymonosulfate (PMS) activation. The urea:wood residue w/w ratio was varied from 0:1 to 100:1, and the intrinsic (surface chemistry) and extrinsic (morphology, specific surface area, etc.) properties of the N-doped biochar were systematically investigated. Notably, the urea:wood residue w/w ratio played a significant role in tuning the N species composition in the N-doped biochar. A higher urea:wood residue w/w ratio resulted in greater at.% of graphitic N and higher specific surface area. The results show that the catalyst prepared with urea:wood residue w/w ratio of 100:1 (NC800-20) manifested the greatest catalytic activity as PMS activator for organics removal due to its highly favorable combination of intrinsic (highest at.% graphitic N) and extrinsic (excellent specific surface area) properties. The catalyst loading, PMS dosage and pH were found to be operationally crucial for PMS activation. Under the best condition, the NC800-20 can be used to degrade various organic pollutants. The recyclability of NC800-20 was studied and while the catalytic activity gradually deteriorated over successive cycles, it can be completely restored by simple calcination at 500°C. The used catalyst was extensively characterized, revealing insights into the mechanism of PMS activation. The prevailing mechanism for PMS activation was the nonradical pathway. Overall, this research provides insights into preparing N-doped biochar with favorable extrinsic and intrinsic properties from biowaste for sustainable pollutant removal via PMS activation.
The identification of reactive radical species using quenching and electron paramagnetic resonanc... more The identification of reactive radical species using quenching and electron paramagnetic resonance (EPR) tests has attracted extensive attention, but some mistakes or misinterpretations are often present in recent literature. This review aims to clarify the corresponding issues through surveying literature, including the uncertainty about the identity of radicals in the bulk solution or adsorbed on the catalyst surface in quenching tests, selection of proper scavengers, data explanation for incomplete inhibition, the inconsistent results between quenching and EPR tests (e.g., SO 4 •− is predominant in quenching test while the signal of • OH predominates in EPR test), and the incorrect identification of EPR signals (e.g., SO 4 •− is identified by indiscernible or incorrect signals). In addition, this review outlines the transformation of radicals for better tracing the origin of radicals. It is anticipated that this review can help in avoiding mistakes while investigating catalytic oxidative mechanism with quenching and EPR tests.
The addition of MoS 2 greatly accelerated the conversion of Fe(III) to Fe(II). • MoS 2 enables Fe... more The addition of MoS 2 greatly accelerated the conversion of Fe(III) to Fe(II). • MoS 2 enables Fe(II)/PMS to efficiently degrade halogenated organic pollutants. • The unsaturated S on the fresh MoS 2 was found to assist in PMS decomposition. • The used or rinsed MoS 2 still exhibited excellent recyclability and reactivity.
T chemical calculation, eight main transformation pathways are proposed for the degradation of io... more T chemical calculation, eight main transformation pathways are proposed for the degradation of iomeprol and iohexol as follows: (a) deiodination; (b) hydrogen abstraction; (c) amide hydrolysis; (d) amino oxidation; (e) hydroxyl substituent; (f) transformed alkyl aromatic amides to aromatic carbamoyl; (g) dehydration; (h) oxidized primary alcohol groups to carboxyl groups.
The interaction of reductive metal ions and peroxymonosulfate (PMS) is necessary for the generati... more The interaction of reductive metal ions and peroxymonosulfate (PMS) is necessary for the generation of sulfate radials (SO 4 %−), however, this process is greatly restrained by the sluggish reduction of high-valent metal ions. Here we report that commercially available reductive metal (Mo or W) powders are capable of unlocking this kinetic constraint. The reduction of Fe(III) to Fe(II), decomposition of PMS, and degradation/mineralization of 4chlorophenol (4-CP) are all accelerated in the Mo/Fe 2+ /PMS process at a very low Fe 2+ /PMS ratio (Fe 2+ / PMS = 1/10). In such an accelerated system, common adverse effects of natural water constituents such as chloride and humic acid are largely mitigated. According to the fluorescence measurement and scavenging tests, sulfate and hydroxyl radicals dominate in Mo/Fe 2+ /PMS process. The addition of Mo or W is further confirmed to favor Cu 2+ /PMS process, but this is not the case for other metal ions (Mn 2+ , Ni 2+ , Ce 3+ and Co 2+). Reductive zero-valence and four-valence active sites (Mo 0 and Mo 4+ ; W 0 and W 4+) play key roles in overall
Bimetallic Fe−Mn oxide (BFMO) has been regarded as a promising activator of peroxysulfate (PS), t... more Bimetallic Fe−Mn oxide (BFMO) has been regarded as a promising activator of peroxysulfate (PS), the sustained activity and durability of BFMO for long-term activation of PS in situ, however, is unclear for groundwater remediation. A BFMO (i.e., Mn 1.5 FeO 6.35) was prepared and explored for PS-based in situ chemical oxidation (ISCO) of trichloroethylene (TCE) in sand columns with simulated/actual groundwater (SGW/AGW). The sustained activity of BFMO, oxidant utilization efficiency, and postreaction characterization were particularly investigated. Electron spin resonance (ESR) and radical scavenging tests implied that sulfate radicals (SO 4 •−) and hydroxyl radicals (HO •) played major roles in degrading TCE, whereas singlet oxygen (1 O 2) contributed less to TCE degradation by BFMO-activated Oxone. Fast degradation and almost complete dechlorination of TCE in AGW were obtained, with reaction stoichiometry efficiencies (RSE) of ΔTCE/ΔOxone at 3−5%, much higher than those reported RSE values in H 2 O 2-based ISCO (≤0.28%). HCO 3 − did not show detrimental effect on TCE degradation, and effects of natural organic matters (NOM) were negligible at high Oxone dosage. Postreaction characterizations displayed that the BFMO was remarkably stable with sustained activity for Oxone activation after 115 days of continuous-flow test, which therefore can be promising catalyst for Oxone-based ISCO for TCE-contaminated groundwater remediation.
One of the great challenges in the field of photocatalysis is to develop novel photocatalysts wit... more One of the great challenges in the field of photocatalysis is to develop novel photocatalysts with excellent solar-light-harvesting capacity and separation efficiency of photo-induced charge. Herein, novel CeO 2 / Bi 2 MoO 6 heterojunctions were fabricated through in-situ precipitation of CeO 2 nanoparticles (size: $26 nm) on the surface of flower-like Bi 2 MoO 6 superstructures (diameter: 2.1-3.5 lm) by a simple method. The as-prepared photocatalysts were systematically characterized by a range of techniques. The photocatalytic degradation of rhodamine B (RhB) dye, methyl orange (MO) dye and tetracycline (TC) antibiotic by this novel photocatalyst was investigated under visible-light irradiation. The CeO 2 / Bi 2 MoO 6 heterojunction with a CeO 2 /Bi 2 MoO 6 weight ratio of 0.05 (0.05Ce-Bi) exhibited the highest photocatalytic activity with the RhB degradation efficiency of 100% in 75 min, which was considerably higher than those of pristine CeO 2 (26.8%) and Bi 2 MoO 6 (80.3%) as well as their physical mixtures (74.8%). The more efficient separation of electron-hole pairs was identified as the primary reason of the enhanced
Recently there is vigorous growth of reports on persulfate (PS)-based advanced oxidation processe... more Recently there is vigorous growth of reports on persulfate (PS)-based advanced oxidation processes (AOPs), inclining to development of newfangled catalysts and treatment of a wide range of organic pollutants. PS-related non-radical oxidation pathways are lately proposed, whereas there still exist debatable observations and explanation on these issues. While non-radical reactions in heterogeneous systems have been well commented, this review focuses on the latest discovery of non-radical oxidation in homogeneous persulfate (especially peroxymonosulfate (PMS)) systems. The application of direct oxidation process is firstly summarized and the roles of PMS distal oxygen in attack on organic pollutants like antibiotics are highlighted. Besides, the effects of exogenic and endogenic halogen on the reactivity and mechanisms of HOX in PS activation are discussed. Then the formation and reaction pathways of singlet oxygen (1 O 2) triggered by phenol/carbonyl compounds and nucleophiles are elaborated. Recent discovery on formation of high valent metal species by PS activation and their reactivity is reviewed lastly. By sorting out a large number of cutting-edge research reports, this review conducts a detailed and critical analysis and overview on the homogeneous PS non-radical mechanisms, and points out the controversies and challenges so as to better understand the reaction mechanism and further improve their treatment performance.
Effective photogenerated charge separation and rapid Cu(II)/Cu(I) redox cycling is still challeng... more Effective photogenerated charge separation and rapid Cu(II)/Cu(I) redox cycling is still challenging for photocatalytic reactions and copper-based Fenton-like process, respectively. Herein, a novel heterogeneous Fentonlike catalyst of copper incorporated carbon ring-g-C 3 N 4 (Cu-C-CN) was prepared through a facile calcination method. The carbon ring could be intimately connected with g-C 3 N 4 via sp 2-hybridized CeN bonds to form an inplane π-conjugated structure. The carbon ring spliced g-C 3 N 4 (C-CN) can serve as an effective electron-hole separator owing to the varied electron affinity of two domains (e.g. carbon-ring and g-C 3 N 4). The copper species were further introduced to the framework of g-C 3 N 4 via the CueN bonds to act as acceptors of conductionelectrons from g-C 3 N 4 and H 2 O 2 activators. Taking the photodegradation of methylene blue (MB) as a model reaction, the decomposition efficiency over Cu-C-CN is 5.5 times higher than that of pristine g-C 3 N 4 , and would nearly linearly increase with pH. The notable enhancement in photodegradation efficiency could be ascribed to the synergetic collaboration between photocatalysis process and Fenton-like process to generate abundant %OH and e −. The Cu-C-CN catalyst shows high recycling stability with negligible Cu leaching due to the strong affinity of Cu 2+ to g-C 3 N 4 framework. The strategy of coupling Fenton-like catalysts, electron-deficient domains (e.g. carbon-ring) into semiconductor-based photocatalysis provides a facile and promising solution to the remediation of water pollution with solar energy.
Rationally driving sunlight to carry out chemical reactions, for example, photochemistry and phot... more Rationally driving sunlight to carry out chemical reactions, for example, photochemistry and photocatalysis, has appeared as a beautiful episode within the long story of solar-energy utilization by human beings. Before approaching the application scale of solar panel or solar thermal energy, considerate efforts are still required from effective collaborations among academia, industries, and governments. Over past few decades, the photocatalysis frontier has been continuously explored by means of interdisciplinary research. Emerging understanding in the nanoscale is most likely to lead photocatalysis into the future. This Special Issue of Nanomaterials aims at presenting " dedicated collections " , showcasing the advances emerging in the research frontiers involving any aspect of the nanoscale in photocatalysis.
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Papers by Zhaohui Wang