Main Reaction Site Research Articles

Rapid oxidation of histamine H2-receptor antagonists by peroxymonosulfate during water treatment: Kinetics, products, and toxicity evaluation

Peroxymonosulfate (PMS) is an appealing oxidant for organic contaminant destruction relying on radical generation after activation. Herein, we report PMS-promoted rapid degradation of histamine H2-receptor antagonists (HRAs) through non-radical process for the first time. Five commonly used HRAs, i.e., ranitidine (RNTD), cimetidine (CMTD), famotidine (FMTD), nizatidine (NZTD) and roxatidine (RXTD), were examined their reactivity towards PMS. Results show that HRAs (except RXTD) exhibit high reactivity towards PMS, with apparent second-order rate constants from 403 to 872 M−1s−1 at pH 7.0. Radical scavenging experiments excluded the contribution of radicals to PMS-promoted degradation of HRAs, and this non-radical process was unaffected by the real water matrices. Structure-activity assessment and theoretical calculation indicated that the thioether sulfur in HRAs (except RXTD) was the main reactive site for PMS oxidation. Transformation product analysis further elucidated oxidation of the thioether sulfur to sulfoxide product through an oxygen atom transfer process. Moreover, the thioether sulfur on the straight chain was more susceptible to oxygen transfer with PMS than that on the thiazole ring of HRAs. Toxicity evaluation indicated the ecotoxicity of HRAs could be remarkably reduced after PMS oxidation. Hence, this work provides a promising strategy to rapidly remove HRAs and significantly reduce their toxicity in water treatment.

Deep insight into the effect of NaCl/HCl/SO2/CO2 in simulated flue gas on gas-phase arsenic adsorption over mineral oxide sorbents

Coal combustion is one of the major pathways by which arsenic enters the ecological environment. An effective method to control arsenic emissions in-furnace is to transform the arsenic from a vapour to fly ash particles using mineral sorbents. However, flue gas components have a significant effect on gas-phase arsenic adsorption, which limits the industrial application of mineral sorbents. In this paper, the effect mechanism of flue gas components (NaCl/HCl/SO2/CO2) on gas-phase arsenic adsorption over different mineral oxide sorbents was investigated. The results demonstrate that the order of arsenic adsorption is CaO > MgO/Fe2O3> NaCl > Al2O3 > SiO2. NaCl promotes the arsenic adsorption of CaO above 800 °C, and the arsenic removal efficiency of CaO with 5 % NaCl is 52.51 % at 900 °C. NaCl inhibits the arsenic adsorption of MgO and Fe2O3, and promotes arsenic adsorption by Al2O3 and SiO2. Acid gases inhibit arsenic adsorption by the sorbents and the order of the inhibition intensity of acid gases at 700 °C is HCl > SO2 > CO2. The active sites (CaO, FeO, or AlO bonds) in the sorbents are the main reaction sites for arsenic adsorption, and captured arsenic is in the form of AsO21− and AsO43-.

Electrochemical Performance of Graphitic Multi-walled Carbon Nanotubes with Different Aspect Ratios as Cathode Materials for Aluminum-ion Batteries.

Graphitic multi‐walled carbon nanotubes (MWCNTs) can function as high‐performance cathode materials for rechargeable Al‐ion batteries with well‐defined discharging plateaus and reasonable charge/discharge C‐rates. However, the main intercalation/deintercalation or adsorption/desorption path of AlCl4 − anions into or onto G‐MWCNTs has not been elucidated. Herein, we used battery cells comprised of G‐MWCNTs with different aspect ratios, Al metal, and AlCl3/1‐ethyl‐3‐methylimidazolium chloride ionic liquid as the cathode, anode, and electrolyte, respectively. The electrochemical performance of the Al||G‐MWCNT cell increased as the aspect ratio of the G‐MWCNT cathode increased (i. e., longer and thinner). The degree of defects of the G‐MWCNTs was similar (0.15–0.22); hence, the results confirm that the main and alternate paths for the AlCl4 − intercalation/de‐intercalation or adsorption/desorption into/from or onto/from the G‐MWCNT are the basal and edge planes, respectively. The step‐like structures of defects on the basal plane provide the main reaction site for AlCl4 − anions.

Engineering microstructure of hydroxyapatite by electron beam irradiation to induce controllable in vitro degradation

Controllable degradation behavior of hydroxyapatite (HA) plays a crucial role in successful long-term implantation of a bone tissue substitute. In this study, electron beam irradiation (EBI) was carried out as an efficient strategy to modify HA structure. The degradation characteristics, bioactivity and cell response of the irradiated HA were comprehensively evaluated. The results showed that EBI with absorbed dose of 3.42, 10.27 and 20.54 Gy did not introduce newly-formed phase or impurity, but created crystal defects and nanovoids, which were formed from oxygen deficiencies, into HA lattice with irradiation dose-dependence. The dissolution rate of the irradiated HA enhanced continuously with increasing irradiation dose, as a result of constantly increasing crystal defects and enlarging voids, where the main reactive sites for the degradation of HA formed. The Ca2+ and PO43- releasing of HA with the highest irradiation dose enhanced by 92.75% and 138.85% respectively compared to that of the pristine HA after 28 days’ immersion. SBF immersion results suggested the irradiated HA with raising EBI doses exhibited preferable performance in bioactivity as well. Moreover, the results from CCK-8 assay and SEM observation showed that the irradiated HA were beneficial to the proliferation and attachment of osteoblasts.

Defect-rich carbon based bimetallic oxides with abundant oxygen vacancies as highly active catalysts for enhanced 4-aminobenzoic acid ethyl ester (ABEE) degradation toward peroxymonosulfate activation

Meeting with severe environmental problems, highly efficient, environmental friendly and multiple reusable catalysts are demanding to develop. In this work, carbon based bimetallic oxides with oxygen vacancies were prepared toward peroxymonosulfate (PMS) activation for 4-aminobenzoic acid ethyl ester (ABEE) degradation. Among different molar ratios of ferrous ions and manganese ion, Fe1Mn1-Fe NC appeared optimum catalytic performance. The degradation of ABEE should contain free radical pathway and non-free radical pathway. All of sulfate radical, hydroxyl radical, superoxide radical and singlet oxygen were responsible for efficient degradation and mineralization of ABEE. Lattice oxygen was the main reactive site for ABEE degradation. Electron transport provided good synergistic redox reaction between Fe and Mn and promoted lattice oxygen released. New proposed pathway for ABEE degradation included electrophilic and radical addition, hydrogen abstraction reaction and diazotization. This work is expected to provide rational design of bimetallic materials with oxygen vacancy for in-situ environmental remediation.

Degradation of thiacloprid via unactivated peroxymonosulfate: The overlooked singlet oxygen oxidation

Unactivated peroxymonosulfate (PMS) degrading organic contaminants has been reported. Previous studies have focused on direct PMS oxidation, while the role of singlet oxygen (1O2) is often overlooked. Here, we studied the oxidation of thiacloprid (THIA) of the neonicotinoid insecticides by PMS without explicit activation. According to electron spin resonance spectroscopy and quenching experiments, the nonradical mechanism (i.e., direct PMS oxidation and 1O2 oxidation) was responsible for the THIA degradation. There are two pathways to generate 1O2. The pyridine nitrogen of THIA structure can combine with PMS to produce epoxide, which is beneficial to generation of 1O2. However, the contribution of 1O2 from PMS self-decomposition can be ignored. According to kinetic solvent isotropic effect analysis, the overall THIA degradation was attributed to 36.5% 1O2 oxidation and 63.5% direct PMS oxidation. A structure-activity assessment and density functional theory suggested that thioether sulfur, amidine nitrogen and the cyanoimino groups were the main reaction sites. Product analysis further confirmed the involvement of 1O2 and PMS. Moreover, three major THIA degradation pathways were proposed, including (i) heterolytic cleavage of peroxo bonds and transfer of oxygen atoms, (ii) electron transfer and (iii) oxidation of cyanoimino groups to generate nitroso/nitro-THIA. In addition, identification byproducts (Except for TP141) had lower ecotoxicity toxicity (using ECOSAR) in fish, daphnid and green algae. Effects of pH and natural water matrices on THIA oxidation via PMS were further evaluated. This study investigated the overlooked 1O2 oxidation reaction to elucidate the mechanism. The new mechanistic knowledge has important implications for other contaminants for their interactions with PMS.

Degradation and transformation of bisphenol A in UV/Sodium percarbonate: Dual role of carbonate radical anion

The bicarbonate and carbonate ions (HCO3− &CO32−) will consume hydroxyl radical (HO•) to generate carbonate radical anion (CO3•−) in hydroxyl radical based advanced oxidation processes (HO•−AOPs) resulting in reduced oxidation efficiencies of the systems. However, despite the HO• quenching effect of carbonate species, the contribution of CO3•− to the degradation of bisphenol A (BPA) was observed in UV/sodium percarbonate (UV/SPC). In order to study the performance of UV/SPC for BPA degradation and the role of CO3•− in this process, the degradation kinetics and mechanisms of BPA in UV/SPC and in UV/hydrogen peroxide (UV/H2O2) were compared at equivalent concentration of H2O2. In this study, the observed degradation rates of BPA by UV/SPC and by UV/H2O2 in Milli-Q water were similar. Variation of the BPA degradation rates in the presence of radical quenchers, tert-butanol and phenol, suggested that both CO3•− and HO• contributed to the degradation of BPA in UV/SPC. Second order rate constant of CO3•− towards BPA (kCO3•−+BPA = 2.23 × 108 M−1 s−1) and steady state concentrations of CO3•− ([CO3•−]ss = 2.3 × 10−12 M) and HO• ([HO•]ss = 1.82 × 10−14 M) in UV/SPC were determined with competition kinetics at 1 mM SPC and pH 8.5. The high [CO3•−]ss observed in UV/SPC compensated for the smaller kCO3•−+BPA compared to kHO•+BPA and the consumption of HO• making the degradation rate of BPA in UV/SPC comparable to that in UV/H2O2. Detailed studies on identification of transformation products (TPs) of BPA in UV/SPC revealed that phenol ring and isopropylidene bridge were the main reactive sites of BPA. Degradation pathways were proposed accordingly. The results of kinetic and mechanistic studies provide better fundamental understanding of the degradation of BPA in UV/SPC and HCO3−&CO32− impact on BPA degradation by HO•−AOPs. This also demonstrates potential for CO3•− based water purification technologies.

Degradation behaviors of Isopropylphenazone and Aminopyrine and their genetic toxicity variations during UV/chloramine treatment

Combination of ultraviolet and chloramine (i.e., UV/chloramine) treatment has been attracting increasingly attention in recent years due to its high efficiency in removing trace organic contaminants. This study investigated the degradation behaviors of two pyrazolone pharmaceuticals (i.e., Isopropyl phenazone (PRP) and Aminopyrine (AMP)) and their genetic toxicity variations during UV/chloramine treatment. The results showed that chloramine could hardly degrade PRP and AMP, while UV/chloramine greatly increased the observed first-order rate constant (kobs) of PRP and AMP degradation. The quenching and probe experiments illustrated that the reactive chlorine species (RCS) contributed dominantly to PRP removal, and hydroxyl radical (HO•) was the major contributor to the degradation of AMP, while the reactive amine radicals (RNS) could hardly degrade them. The overall degradation rates of PRP and AMP decreased as pH increased from 6.5 to 10. The kobs of PRP and AMP increased along with NH2Cl dosage increasing and reached a plateau at higher concentrations (0.2–0.5 mM). The present background carbonate (HCO3−, 1–10 mM), chloride (Cl−, 1–10 mM) and natural organic matter (NOM, 5-10 mg-C L−1) exhibited inhibition impacts on PRP and AMP degradation. In addition, the intermediates/products of PRP and AMP were identified and their general degradation pathways were proposed to be hydroxylation, deacetylation, and dephenylization. Specifically, Cl-substitution was inferred during PRP degradation, while demethylation in tertiary amine group was only observed in AMP degradation. These mechanisms including the main reactive sites of PRP and AMP were further confirmed by the frontier orbitals calculation. Moreover, the results of the genetic toxicity according to the micronucleus test of Viciafaba root tip indicated that UV/chloramine treatment could partially reduce the genetic toxicity of PRP and AMP.

Deep mineralization of bisphenol A by catalytic peroxymonosulfate activation with nano CuO/Fe3O4 with strong Cu-Fe interaction

Cu-Fe bimetal oxides yield excellent catalytic activity. However, there are some debates on Cu redox cycle and direction ofelectron transfer during PMS activation by these Cu-Fe bimetal oxides. In this paper, therefore, CuO/Fe3O4 nanoparticles with strong Cu-Fe interaction were prepared by pyrolysis of copper-hexacyanoferrate(III) at 600 °C for 1 h and used to investigate the effect of Cu-Fe interaction on catalytic performance of these Cu-Fe bimetal oxides. The as-prepared CuO/Fe3O4 as a catalyst presented much stronger reactivity than CuO and Fe3O4 for peroxymonosulfate (PMS) activation and bisphenol A (BPA) degradation. The use of 0.3 g L−1 CuO/Fe3O4 and 0.3 mmol L−1 PMS achieved deep mineralization (>99%) in 110 min for degradation of 20 mg L−1 BPA at initial pH 6.0. The k value for BPA degradation was 0.32 min−1 for CuO/Fe3O4, being about 5.3, 3.2 and 2.7 times that for the catalysts of Fe3O4, CuO and the mixture of CuO and Fe3O4, respectively. The synergistic effect between Cu and Fe sites on the surface of CuO/Fe3O4 nanoparticles was attributable to strong Cu-Fe interaction. Characterization by X-ray photoelectron spectra and temperature-programmed reduction with H2 as a reducing agent showed that the strong Cu-Fe interaction makes Cu species more easily donate electrons to PMS for radicals generation as the main reactive sites and reductive cycle of Fe species easier through accepting electrons from PMS, further promoting Cu catalytic cycle through an electron transfer between Cu and Fe. The clarification of structure activityrelationship (SAR) of interaction between bimetal species and their activity for peroxide activation facilitates deep understand of the catalytic mechanism and development of more efficient bimetal based catalysts.

Reactivity of unactivated peroxymonosulfate with nitrogenous compounds

A recent investigation has demonstrated that peroxymonosulfate (PMS), a peroxide commonly applied as a radical precursor during advanced oxidation processes (AOPs), can degrade organic contaminants without the involvement of radicals. However, little is known about this non-radical reaction mechanism. In this study, the reactivity of PMS with several nitrogenous compounds was investigated. Fluoroquinolone antibiotics (except for flumequine) were rapidly degraded by direct PMS oxidation, followed by aliphatic amines (e.g., metoprolol and venlafaxine) and nitrogenous heterocyclic compounds (e.g., adenine and caffeine) at pH 8. The degradation rate of fluoroquinolones followed a second-order kinetic and was highly pH and structure-dependent. Unlike the radical-based AOPs, the direct degradation of contaminants by PMS was less influenced by the scavenging effect of the water matrix. High-Resolution Mass Spectrometry (HRMS) analysis demonstrated that the piperazine ring of fluoroquinolones was the main reaction site. Results showed that the direct electron-transfer from nitrogenous moieties (piperazine ring) to PMS can produce amide and aldehyde compounds. An amide-containing transformation product of ciprofloxacin (m/z 320), showing the highest signal intensity on HRMS, was previously recorded during ozonation. Moreover, the hydroxylamine analogue of ciprofloxacin and enrofloxacin N-oxide were tentatively identified, and the formation of the latter was not impacted by the dissolved oxygen in water. These results suggested that PMS also reacts with nitrogenous compounds via oxygen transfer pathway. Agar disk-diffusion tests indicated that PMS treatment efficiently removed the antibacterial activity of ciprofloxacin with the complete degradation of parent antibiotic, except for the transformation products in an earlier stage, which might still exert antibacterial potency.

Ozonation of the 5-fluorouracil anticancer drug and its prodrug capecitabine: Reaction kinetics, oxidation mechanisms, and residual toxicity

Anticancer drugs (ADs) have been detected in the environment and represent a risk to aquatic organisms, necessitating AD removal in drinking water and wastewater treatment. In this study, ozonation of the most commonly used antimetabolite ADs, namely 5-fluorouracil (5-FU) and its prodrug capecitabine (CAP), was investigated to determine reaction kinetics, oxidation mechanisms, and residual toxicity. The specific second-order rate constants between aqueous ozone and 5-FU, 5-FU−, 5-FU2−, CAP, and CAP− were determined to be 7.07(±0.11)×104 M−1·s−1, 1.36(±0.06)×106 M−1·s−1, 2.62(±0.17)×107 M−1·s−1, 9.69(±0.08)×103 M−1·s−1, and 4.28(±0.07)×105 M−1·s−1, respectively; furthermore, the second-order rate constants for •OH reaction with 5-FU and CAP at pH 7 were determined to be 1.85(±0.20)×109 M−1·s−1 and 9.95(±0.26)×109 M−1·s−1, respectively. Density functional theory was used to predict the main ozone reaction sites of 5-FU (olefin) and CAP (olefin and deprotonated secondary amine), and these mechanisms were supported by the identified transformation products. Carboxylic acids constituted a majority of the residual organic matter for 5-FU ozonation; however, carboxylic acids and aldehydes were important components of the residual organic matter generated by CAP. Ozone removed the toxicity of 5-FU to Vibrio fischeri, but the residual toxicity of ozonated CAP solutions exhibited an initial increase before subsequent removal. Ultimately, these results suggest that ozone is a suitable technology for treatment of 5-FU and CAP, although the residual toxicity of transformation products must be carefully considered.

Energy-saving hydrogen production coupling urea oxidation over a bifunctional nickel-molybdenum nanotube array

Hydrogen production via water electrolysis is promising but impeded by sluggish cathodic and anodic reactions. Consequently, highly-efficient and earth-abundant electrocatalysts are attracting considerable attention. Herein we report a bifunctional NiMo alloy nanotube for efficient hydrogen production coupled with anodic urea oxidation in a hybrid water electrolysis system. Specifically, ultralow potentials of −44 mV and 1.36 V (vs. RHE) are required to deliver 10 mA cm−2 current density for cathodic and anodic reactions, respectively. Density functional theory (DFT) calculation results show the Mo center is the main reaction site for the chemisorption and OH bond cleavage of H2O while Ni center is identified as the hydrogen-evolving site. Based on this bifunctional NiMo electrocatalyst, a hybrid water electrolysis cell is proposed and the overall cell voltage of ∼1.43 V is achieved for outputting 10 mA cm−2 current density during the 10 h operation. The understandings in alternative electrode reactions coupled with highly-efficient and earth-abundant electrocatalysts for hybrid water electrolysis in this work holds encouraging potential in future energy conversion technologies and urea-related water treatments.

Formation of Nitrophenolic Byproducts during Heat-Activated Peroxydisulfate Oxidation in the Presence of Natural Organic Matter and Nitrite.

Sulfate radical (SO4•-)-based advanced oxidation is a viable in situ remediation technology for degrading organic contaminants in the subsurface. In this study, we demonstrated that SO4•- could induce the activation of nitrite, an anion commonly present in the subsurface environment, leading to the formation of nitrophenolic byproducts. Fourier-transform infrared spectroscope and 15N nuclear magnetic resonance analysis revealed that the inorganic nitrite was incorporated into natural organic matter (NOM) to form organic nitrogen upon SO4•- oxidation. Nitrophenolic byproducts, including 2-hydroxy-5-nitrobenzoic acid, 4-nitrophenol, and 2,4-dinitrophenol, were identified using high-resolution mass spectrometry in combination with a 15N labeling technique. Formation of nitrated byproducts was ascribed to the scavenging of SO4•- by nitrite, which not only generated the nitrating agent NO2• but also inhibited the degradation of organic compounds, making them more available to the reactions with NO2•. The phenolic moieties in NOM served as the main reactive sites for NO2• attack. The nitration begins with H abstraction on the phenoxy oxygen, followed by the addition of another NO2• to its ortho or para site. Decarboxylation followed by NO2• addition can also generate nitrophenolic byproducts. To the best of our knowledge, this is the first study reporting the nitration of NOM and formation of toxic nitrophenolic byproducts during SO4•--based oxidation. It sheds light on the potential risks of this technology in subsurface remediation practices.

A quantum chemical study on the reactivity of four licorice flavonoids scavenging ·OOCl3C

Isoliquiritigenin, liquiritigen, uralenol, and neouralenol are four natural licorice flavonoid compounds extracted from licorice, which have the ability of scavenging free radicals. In this paper, the density functional theory (DFT) was used to study the microscopic reaction mechanism of the four kinds of licorice flavonoids respectively scavenging ·OOCl3C in vivo. At the level of M06-2X/6-311+G(d,p), the geometries of all stationary points for hydrogen atom transfer (HAT) and radical adduct formation (RAF) pathways were optimized. The thermodynamic parameters and kinetic parameters of each reaction pathway were obtained, and the potential energy surface information of each reaction pathway was obtained too. Using the continuum solvation model based on solute electron density (SMD), the influence of the solvation effect on the reaction was calculated. The main mechanisms and reactive sites for the capture of ·OOCl3C by four licorice flavonoids, liquiritigen, isoliquiritigenin, uralenol, and neouralenol, were determined. Research indicates liquiritigen captures ·OOCl3C by HAT mechanism. The HAT pathway on the B′ ring of liquiritigen is the main reactive site. Isoliquiritigenin captures ·OOCl3C in the body through HAT and RAF mechanism. The RAF pathway is the dominant reaction pathway. The C1 site on the carbon–carbon double bond linking the two benzene rings is the main reactive site. Uralenol and neouralenol capture ·OOCl3C by HAT mechanism. The main reactive site of uralenol is B6 site, and the main reactive site of neouralenol is B′ 2 site. By this study, the potential energy surface information difficult to capture by experimental research is obtained, which provides a reliable theoretical basis for the further screening of highly active natural free radical scavengers of flavonoids in licorice and provides the support for the improvement of the development and application technology of licorice.

Oxidation and molecular properties of microcystin-LR, microcystin-RR and anatoxin-a using UV-light-emitting diodes at 255 nm in combination with H2O2

On the use of UV light emitting diodes (UV-LEDs), emitting at 260–290 nm, has attracted attention for treating cyanotoxins, although most previous studies related with UV/H2O2 process have been used conventional mercury UV lamp (λ = 254 nm). Therefore, the aim of the study was to investigate the UV-LEDs, having a wavelength of 255 nm, coupled with H2O2 process for the removal of microcystin-LR (MC-LR), microcystin-RR (MC-RR), and anatoxin-a (ANTX) and to verify the degradation kinetics, mechanism and impact of water quality parameters in relation to their molecular properties. Among three UV-LEDs (λ = 255, 266, and 280 nm), the shortest one was the most effective to remove MC-LR coincided with its decadic molar absorption coefficient. The degradation rate constants of MC-LR, MC-RR, and ANTX were 0.0644, 0.0241, and 0.0076 cm2 mJ−1, respectively, during the UV-LED/H2O2 process. For MC-LR and MC-RR degradation, reaction with OH is a major mechanism along with direct photolysis as a minor factor. ANTX degradation is predominantly attributed to OH. The second-order rate constant for ANTX is one order of magnitude lower than others because ANTX is recalcitrant to oxidation. The MC-LR degradation occurred at the diene and aromatic ring of Adda, Mdha, and amide bond and the main reactive oxidation site of MC-RR was the Adda chain. In contrast, photo-oxidation transformed ANTX to higher molecular weight compounds via polymerization instead of degradation. When MC-LR, MC-RR, and ANTX were co-present, lower concentration of dissolved organic carbon and higher acidity with bicarbonate was favorable to remove MC-LR and MC-RR according to their scavenging factors and reaction with CO−3. However, ANTX is relatively resistant to degradation at pH 3.2.

A Statistical Model and DFT Study of the Fragmentation Mechanisms of Metronidazole by Advanced Oxidation Processes.

The degradation pathway of the antibiotic metronidazole (MNZ) in wastewater was investigated computationally with a physical statistical method and a quantum chemical approach. In both cases, density functional theory (DFT) at the M06-2X/6-311+G(d,p) level was used to calculate the structures and property parameters of all molecules. On one hand, decay of the isolated MNZ molecule excited at a given excitation energy was studied using the statistical molecular fragmentation (SMF) model. On the other hand, the reaction mechanisms of MNZ oxidized by hydroxyl radicals (•OH) in advanced oxidation processes (AOPs) were analyzed. Both studies show that the main reaction sites in MNZ are, by decreasing importance, -NO2, -CH2OH, and -CH2CH2OH. The main degradation reactions are (i) alcohol group oxidation including the abstraction of hydrogen on C in the -CH2OH group and oxidation of the hydroxyl group to the aldehyde and further to the carboxylic acid and (ii) addition-elimination reactions happening on the imidazole ring which finally replace the nitro by hydroxyl radicals. The results gained are in a good agreement with the available experimental data on MNZ degradation by AOPs. The structures of intermediates, transition states, and free energy surfaces are helpful in elucidating the details of the elimination mechanism, supplementing current experimental knowledge.

Investigation on degradation behavior of dissolved effluent organic matter, organic micro-pollutants and bio-toxicity reduction from secondary effluent treated by ozonation

The environmental risk of secondary effluent has caused increasing attention in recent years, the negative effect of dissolved effluent organic matters (dEfOM) and organic micro-pollutants (OMPs) was a hot research point. In this research, the degradation behavior of dEfOM and fourteen OMPs in the ozonation was revealed using spectroscopic and chromatographic tools. Ozonation was effective for reducing UV254, but had limited effect in dissolved organic carbon reduction. The dEfOM with shorter absorption wavelength was preferentially removed in the ozonation (230 nm > 240 nm > 254 nm) and high molecular weight humics was largely reduced by the ozonation. Soluble microbial by-products were more reactive with ozone than humic acid as reflected by the fluorescence. Degradation behavior of the OMPs was identified based on their elimination kinetics and molecular structures and a simplified classification method was proposed. The group I OMPs (logkO3>5) showed high removal efficiency with 1 mg/L of ozone, while the removal of group II OMPs (1< logkO3<5) was largely dependent on the ozone dose. The CC bond, deprotonated amidogen, phenolic, aniline and anisole groups in these OMPs structures were the main reaction sites with ozone. The group III OMPs without active groups in the molecules showed slight removal in the ozonation. Moreover, genotoxicity and estrogenic activity were simultaneously analyzed for further evaluation on the risk of the effluent. The genotoxicity and estrogenic activity of the secondary effluent were 73.46 μg 4-NQO/L and 519.86 ng E2/L, respectively and an ozone dose of 10 mg/L could reduce the bio-toxicity to the detection limit.

Understanding the ozonated degradation of sulfadimethoxine, exploration of reaction site, and classification of degradation products

Ozonation has been demonstrated to be an efficient method of water treatment. In this study, the degradation of 20 mg/L of sulfadimethoxine (SDM) in different water matrices during ozonation was investigated. At pH 7.0, 100% removal of SDM was achieved by ozonation within 10 min. The degradation of SDM was more pronounced at acidic pH than under ambient environmental conditions, and was also dependent on different water matrices. Both direct and indirect oxidation of SDM by ozone were observed, and it was also shown that both ozone molecules and hydroxyl radicals were involved in the SDM degradation process, whereas it was found that the saturated ring of SDM made it O3-recalcitrant. Seven transformation products (TPs) were identified during SDM ozonation, allowing three degradation pathways to be proposed. Additionally, the main reaction sites, including N (7) and C (2) on the aniline ring, and the __S__N__ bond, were confirmed both experimentally and theoretically. The toxicity evolution during the degradation process was investigated, and the results showed no toxic intermediate products obtained during ozonation.

Oxidation of fluoroquinolone antibiotics by peroxymonosulfate without activation: Kinetics, products, and antibacterial deactivation

While fluoroquinolone (FQ) antibiotics are susceptible to degradation by sulfate and/or hydroxyl radicals formed in peroxymonosulfate (PMS) based advanced oxidation processes, here we report that unactivated PMS itself exhibits a specific high reactivity toward FQs for the first time. Reaction kinetics of PMS with two model FQs, ciprofloxacin (CF) and enrofloxacin (EF), showed a strong pH dependency with apparent second-order rate constants of 0.10–13.05 M−1s−1 for CF and 0.51–33.17 M−1s−1 for EF at pH 5–10. This pH dependency was well described by species-specific parallel reactions. On the basis of reaction kinetics and structure–activity assessment, the tertiary and secondary aliphatic N4 amines on the FQs’ piperazine ring were proposed to be the main reaction sites. High performance liquid chromatography/electrospray ionization tandem mass analysis showed the formation of hydroxylated, N-oxide, and dealkylated products. Bacterial growth inhibition bioassays using Escherichia coli showed that oxidation products of FQs by PMS retained negligible antibacterial potency in comparison to parent FQs. Kinetic modeling using the rate constants estimated from pure water well predicted the oxidation kinetics of low levels of CF and EF by PMS in surface water. The degradation efficiency of FQs by PMS in surface water was slightly lower than that by ozone, comparable to that by ferrate, and much higher than that by permanganate. These results suggest that PMS is a promising oxidant for the treatment of FQs in water.

Prednisolone degradation by UV/chlorine process: Influence factors, transformation products and mechanism

Prednisolone (PDNN) as an emergent micropollutant directly influences the regional ecological security. In this study, the degradation of PDNN by ultraviolet activated chlorine (UV/chlorine) oxidation process was comprehensively evaluated. The quenching experiment suggested that the PDNN degradation in UV/chlorine process was involved in the participation of hydroxyl radical (OH) and reactive chlorine species (RCS). Influence factors including chlorine dosage, pH, common anion and cation, fulvic acid (FA) on PDNN degradation via UV/chlorine process were investigated. A low chlorine (≤7.1 mg L−1) promoted the PDNN degradation, while a high chlorine dosage (>7.1 mg L−1) was adverse. The pH (4.0–10.0) showed negligible effect, while the investigated anions (Cl−, Br−, HCO3− and SO42−), NH4+ and FA exerted negative impact on PDNN degradation. An efficient process to minimize pharmaceutical micropollutants was the disposal of human urine containing a high concentration of pharmaceutical and potential toxic metabolites. An inhibitory effect was observed in the synthetic urine (fresh urine and hydrolyzed urine). The intermediates/products were identified and the mechanism of PDNN degradation was proposed. PDNN gone through three degradation routes, involving the direct addition of α, β-unsaturated ketone at C1 or C5, the photolysis of C17 and H-abstraction of C11. The main reactive sites were further determined by comparison of the frontier orbitals calculation and the proposed mechanism. Based on the toxicological tests for PDNN degradation, TP396 (TP396-C1Cl and TP396-C5Cl) and TP414-2-1 (TP414-C1ClC5OH) exhibited much higher toxicity than PDNN, and prolonging reaction time was necessary to achieve PDNN detoxification.