Prediction of Fenton oxidation positions in polycyclic aromatic hydrocarbons by Frontier electron density

Remediation of carcinogenic PAHs from landfill leachate by Electro-Fenton process - Optimization and modeling

PAHs is the group of emerging micro-pollutants present in most environmental matrices that has the tendency to bioaccumulate and cause carcinogenic effects to human health. The present research involved the quantification and treatment of leachate produced from secured landfill, to eliminate the PAHS. Electro-Fenton process, a class of advanced oxidation process, is adopted to degrade the PAHs using titanium electrodes as both anode and cathode. Artificial intelligence based statistical tool "Central Composite Design" a module of JMP -19 software was used to design the experiments and optimize the critical parameters involved in the research. It was observed that the value of P is significant (P < 0.05) for all the independent variables evidencing the significant correlation between experimental values and predicted values of the software. The value of R2 obtained was 0.96 and 0.97 for COD and PAHs respectively. The maximum removal efficiency of COD and PAH was found to be 84.24% and 90.78% respectively. The optimized conditions obtained from the central composite design were: pH = 5; Fe2+ = 0.1 g/L; H2O2 = 2 g/L; reaction time = 60 min; and electric intensity = 0.2 A. Additionally, optimized experimental conditions were used to study the removal efficiencies of individual 16 PAHs and are also reported. From the close proximity of experimental and predicted results of the software it can be proved that central composite design is efficient enough to be used as a statistical tool in design and analysis for treatment of landfill leachate.

Degradation and mechanism of PAHs by Fe-based activated persulfate: Effect of temperature and noble metal

The accumulation of contaminants like PAHs in soil due to industrialization, urbanization, and intensified agriculture poses environmental challenges, owing to their persistence, hydrophobic nature, and toxicity. Thus, the degradation of PAHs has attracted worldwide attention in soil remediation. This study explored the effect of noble metal and temperature on the degradation of various polycyclic aromatic hydrocarbons (PAHs) in soil, as well as the types of reactive radicals generated and mechanism. The Fe-Pd/AC and Fe-Pt/AC activated persulfate exhibited high removal efficiency of 19 kinds of PAHs, about 79.95 % and 83.36 %, respectively. Fe-Pt/AC-activated persulfate exhibits superior degradation efficiency than that on Fe-Pd/AC-activated persulfate, due to the higher specific surface area and dispersity of Pt particles, thereby resulting in increased reactive radicals (·OH, SO4-· and ·OOH). Additionally, thermal activation enhances the degradation of PAHs, with initial efficiencies of 64.20 % and 55.49 % on Fe-Pd/AC- and Fe-Pt/AC-activated persulfate systems respectively, increasing to 76.05 % and 73.14 % with elevated temperatures from 21.5 to 50 °C. Metal and thermal activation facilitate S2O82- activation, generating reactive radicals, crucial for the degradation of PAHs via ring opening and oxygen hydrogenation reactions, yielding low-ring oxygen-containing derivatives such as organic acids, keto compounds, ethers, and esters. Furthermore, understanding the impact of parameters such as activation temperature and the types of noble metals on the degradation of PAHs within the activated persulfate system provides a theoretical foundation for the remediation of PAH-contaminated soil.

Effect of common low-molecular-weight organic acid on the photodegradation of sertraline by ferrihydrite

Sertraline is one of the most commonly used antidepressant pharmaceuticals with ubiquitous distribution in the aqueous environment. However, the environmental behavior of sertraline in the co-presence of low-molecular-weight organic acid (LMWOA) and iron oxide mineral is still poorly understood. In this study, the photodegradation of sertraline was systematically investigated in a common photosensitizing system (ferrihydrite (Fh)-LMWOA). Six LMWOAs, including citrate acid (CA), tartrate acid (TA), malate acid (MA), lactate acid (LA), succinate acid (SA) and malonic acid (MOA) were chosen as the representatives. Our results implied that the different Fe3+ dissolution rates would lead to rather different sertraline degradation patterns following the order of Fh-CA > Fh-TA > Fh-MA > Fh-LA > Fh-SA > Fh-MOA. The reaction was initiated by the interaction between LMWOA and Fh via ligand-promoted-dissolution mechanism. Furthermore, the Fe3+ dissolution rates also showed a strong correlation with the metal-organic complexation constants, indicating that the photodegradation process is strongly related to the complexation ability of LMWOA with Fe3+. •OH, O2•- and CO2•- were detected, indicating that they contributed to the photodegradation of sertraline. •OH was demonstrated to be the dominant Reactive oxygen species (ROS) for the degradation of sertraline, and the detailed transformation pathways were proposed based on the product analysis and theoretical calculation. According to the ecological structure activity relationship estimation, the photodegradation products of sertraline possessed lower toxicity compared to the parent compound. These findings contribute to a more comprehensive understanding of the environmental fate of sertraline and evaluate its potential ecotoxicity in natural systems.

Hydroxyl radical-driven transformations of bisphenol A and 2,4-dinitroanisole: Experimental and computational analysis

This study used experimental and computational analysis to investigate the advanced oxidation of bisphenol A (BPA) and 2,4-dinitroanisole (DNAN). The pseudo first-order reaction rate constants depended on the molar peroxide ratio and were between 0.13 and 0.28 min-1 for BPA and between 0.018 and 0.032 min-1 for DNAN. The kinetic differences appear to be due in part to the energy requirements for oxidation, which depended on the reaction mechanism but were typically lower for BPA than they were for DNAN. Density functional theory (DFT) was used to develop transformation pathways that included experimentally-detected byproducts. The most energetically favored pathway for BPA oxidation begins with the formation of hydroxylated derivatives, while for DNAN, the most energetically favorable degradation pathway begins with the substitution of the methoxy group. Overall, these findings demonstrate the power of combining experimental and computational tools to reveal transformation mechanisms during water treatment. PRACTITIONER POINTS: Advanced oxidation transformations for two emerging water pollutants, bisphenol A and dinitroanisole, was investigated. The observed reaction kinetics depended on molar peroxide ratio in a manner that is in keeping with previous findings. Density functional theory-based analysis revealed reaction energy requirements and degradation pathways.

Generating high-valent iron-oxo ≡FeIV=O complexes by calcium sulfite activation in neutral microenvironments for enhanced degradation of CIP

Although alkaline sulfite activation of ferrate (Fe(VI)) has advantages of fast response and high activity for degradation of organic contaminants, the specific production pathways of active species and the pH conditions still hinder its widespread application. Based on this, our study constructed a novel advanced oxidation process of calcium sulfite (CaSO3) could activated Fe(VI) continuously by Ca2+ buffering and investigated the mechanism under different pH values and CaSO3 dosages with ciprofloxacin as a target organic pollutant. The results showed that Ca2+ stabilized the process at a neutral/weakly alkaline microenvironment of pH 7-8, which could alleviate the hydrolysis of ≡FeIV=O by protons and iron hydroxyl groups. Besides, the removal of pollutants occurred efficiently when sulfate (SO32-) was excessive and had a 3:1 ratio of SO32- to Fe(VI), achieving more than 99% removal of electron-rich phenolic organic pollutants within 2 min. By adding different radical scavengers and combining electrochemical analysis methods and electron paramagnetic resonance spectroscopy techniques to revealed that the main active species in Fe(VI)/CaSO3 process were ≡FeIV=O/≡FeV=O. Furthermore, the reactivity of various sulfate species (such as SO32-, SO3•-, SO4•-, SO5•-) with Fe(VI) was calculated using density functional theory (DFT), and it was found that Fe(VI)-SO32- reaction has a much lower energy barrier (-36.08 kcal/mol), indicating that SO32- can readily activate Fe(VI) and generate ≡FeIV=O to attack the atoms with high Fukui index (f -) in organic pollutants. The above results confirm the feasibility of Fe(VI)/CaSO3 process. Thus, this study can theoretically and practically prove that the main active species is ≡FeIV=O, rather than SO4•- or •OH in Fe(VI)/CaSO3 process.

Dissolved black carbon incorporating with ferric minerals promoted photo-Fenton-like degradation of triclosan in acidic conditions

Dissolved black carbon (DBC) has been recognized as an important organic matter that influences the photochemical processes of organic pollutants. The excited triplet state (3DBC*) of DBC usually exhibits activity in neutral and basic aqueous conditions, rather than in acidic conditions. In this study, we found the crop (wheat, rice, maize) straw sourced DBC can substantially enhance the photodegradation of triclosan in relatively acidic conditions, and in the presence of ferric minerals (ferrihydrite and lepidocrocite), when exposed to simulated sunlight irradiation. This should be ascribed to the rapid non-reductive dissolution of ferric minerals by DBC, which leads to the generation of abundant hydrogen peroxides (H2O2) and hydroxyl radicals (•OH) through photo Fenton-like reactions. •OH is the dominant reactive species that leads to triclosan degradation in acidic conditions. Otherwise, triclosan itself is resistant to direct photolysis at pH < 5.0. The triplet state (3DBC*) plays a critical role in accelerating the Fe3+/Fe2+ cycling, which further promotes •OH generation. This study provides a new perspective on the role of DBC in surface water or mineral-water interfaces with acidic conditions and adds a more comprehensive understanding about the environmental implications of the DBC-ferric mineral system in sunlit surface water.

Computational Studies on the Reactivity of Polycyclic Aromatic Hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are widely present in the environment as toxic pollutants. In this study, quantum chemistry methods are used to study reactions of PAHs in both particle and gas phases. Seven theoretical methods are exploited to predict the reactive sites of 15 PAHs in the particle phase. Among these methods, the performance of the condensed Fukui function (CFF) is optimum. The gas-phase reactions of eight PAHs are also investigated. Except for fluorene, CFF predicts correctly the gas-phase mono-nitro products for seven systems. The products of fluorene predicted by CFF are 1-nitrofluorene and 3-nitrofluorene, which is however inconsistent with the experimental results. Transition state theory is then used to investigate the reaction mechanism of fluorene. Calculated rate constants for 3-nitrofluorene and 2-nitrofluorene formation are much bigger than that for 1-nitrofluorene formation, which is in agreement with the experimental results.

Formation of organic chloride in the treatment of textile dyeing sludge by Fenton system

In the oxidation treatment of textile dyeing sludge, the quantitative and transformation laws of organic chlorine are not clear enough. Thus, this study mainly evaluated the treatment of textile dyeing sludge by Fenton and Fenton-like system from the aspects of the influence of Cl^-, the removal of polycyclic aromatic hydrocarbons (PAHs) and organic carbon, and the removal and formation mechanism of organic chlorine. The results showed that the organic halogen in sludge was mainly hydrophobic organic chlorine, and the content of adsorbable organic chlorine (AOCl) was 0.30 mg/g (dry sludge). In the Fenton system with pH=3, 500 mg/L Cl^-, 30 mmol/L Fe²⁺ and 30 mmol/L H₂O₂, the removal of phenanthrene was promoted by chlorine radicals (•Cl), and the AOCl in sludge solid phase increased to 0.55 mg/g (dry sludge) at 30 min. According to spectral analysis, it was found that •Cl could chlorinate aromatic and aliphatic compounds (excluding PAHs) in solid phase at the same time, and eventually led to the accumulation of aromatic chlorides in solid phase. Strengthening the oxidation ability of Fenton system increased the formation of organic chlorines in liquid and solid phases. In weak acidity, the oxidation and desorption of superoxide anion promoted the removal and migration of PAHs and organic carbon in solid phase, and reduced the formation of total organic chlorine. The Fenton-like system dominated by non-hydroxyl radical could realize the mineralization of PAHs, organic carbon and organic chlorines instead of migration. This paper builds a basis for the selection of sludge conditioning methods.

Mechanistic insights into Fe(II)-citric acid complex catalyzed CaO2 Fenton-like process for enhanced benzo[a]pyrene removal from black-odor sediment at circumneutral pH

Polycyclic aromatic hydrocarbons (PAHs) are found ubiquitously in contaminated aquatic sediments. They are difficult to degrade, particularly the high-molecular-weight PAHs (e.g., benzo[a]pyrene, BaP). In this study, CaO₂ assisted with ferrous ion (Fe(II))-citric acid (CA) was applied for the first time in BaP degradation in aquatic sediment. Among the treatment processes we studied, CaO₂/Fe(Ⅱ)/CA could effectively degrade BaP at circumneutral pH (7.0 ± 0.3), reaching a maximum of nearly 80% under optimal conditions (0.84 mM CaO₂, 0.21 mM Fe(Ⅱ), and 0.35 mM CA in per gram of dry sediment). Contrary to some external environmental factors such as temperature, common metal ions, and natural organic matters, a certain amount of moisture content and inorganic anions (Cl^-, SO₄^2-) exhibited a positive effect on BaP degradation, which can probably be contributed to the improved mass transfer rate in the non-homogeneous sediment-water mixture and a higher level of free radicals. The degradation kinetic dominated by hydroxyl radicals included three main stages contribution ∼29.4%, ∼43.1%, and ∼2.4% to BaP degradation, respectively. Based on the theoretical calculations of density functional theory, a pathway for BaP degradation was proposed. For the treatment of actual contaminated sediment, the CaO₂/Fe(II)/CA process could realize the elimination of black-odor and effective removal of PAHs from the sediment, as well as negligible ecotoxicity on benthic organisms. This study provides a reference and guidance for the use of CaO₂ based Fenton-like systems in treating PAH-contaminated black-odor river sediments.

Heterogeneous Fenton-like removal of tri(2-chloroisopropyl) phosphate by ilmenite (FeTiO3): Kinetic, degradation mechanism and toxic assessment

Tri(2-chloroisopropyl) phosphate (TCPP), a common organophosphate flame retardant, was frequently detected in the environment and posed threats to human health. In this work, the main component of ilmenite FeTiO₃ was synthesized by the sol-gel method and employed as the catalyst for the degradation of TCPP by activating persulfate (PS) under UV irradiation. The degradation processes were fitted by the pseudo-first-order kinetic. The k_obs value in UV/FeTiO₃/PS system was up to 0.0056 min^-1 and much higher than that in UV/PS (0.0014 min^-1), UV/FeTiO₃ (0.0012 min^-1) and FeTiO₃/PS (0.0016 min^-1) systems, demonstrating a distinct synergistic effect in TCPP removal. The degradation efficiency of TCPP increased with the increase of UV intensity, PS concentration and catalyst dosage, and with the decrease of pH. By quenching experiment and EPR analysis, ·OH was confirmed to be the dominant radical in the reaction of the UV/FeTiO₃/PS system. The possible degradation pathways of TCPP were dechlorination, dealkylation, and further oxidation of alkyl groups based on the theoretical calculation of frontier molecular orbits. The toxicity of degradation intermediates evaluated by luminescence inhibition rate of photoluminescence was higher than TCPP. Thus, TCPP can be degraded in the UV/FeTiO₃/PS system effectively at the premise of introducing controlling measures to reduce the toxicity of degradation intermediates.

Remediation of PAHs contaminated industrial soils by hypochlorous acid: performance and mechanisms

Polycyclic aromatic hydrocarbons (PAHs) mainly originate from incomplete combustion of organic substances and are carcinogenic, mutagenic and teratogenetic, posing a high risk to the ecosystem and human health. The remediation of soils contaminated with PAHs has aroused wide public concern. In this study, hypochlorous acid (HOCl) was applied to realize PAHs removal from industrial contaminated soil with an extremely high degradation efficiency of 93.33% when the initial chlorine concentration was 5000 mg L⁻¹. The degradation behavior of PAHs by HOCl oxidation was investigated in detail. Parameters including chlorine dosage, pH and temperature that had effects on the degradation process were evaluated systematically. The removal of PAHs was followed well with the pseudo-first-order kinetic model. It is found that HOCl and OH˙ were major contributors to the degradation products of chlorinated and oxygenated PAHs. This research provided an easy-operating and energy-saving way to realize the remediation of PAHs contaminated industrial soil practically with high efficiency.

An extremely high degradation efficiency of 93.3% was realized for PAHs in contaminated industrial soil by HOCl oxidation.

Photodegradation of chloramphenicol in micro-polluted water using a circulatory thin-layer inclined plate reactor

This study describes the photodegradation of chloramphenicol (CAP) in micro-polluted water with a thin-layer inclined plate reactor. Under simulated sunlight irradiation, the effect of reaction parameters including solution pH, initial CAP concentration, and co-existed humic acid (HA) or chloride was evaluated. The photodegradation of CAP was independent of initial pH in the range of 6.0-9.0, but sharply decreased by 25.5% with the increase of initial CAP concentration from 0.4 to 1.0 mg/L. The presence of HA exhibited a significant inhibitory effect, while Cl^- promoted the photoreaction. In this study, CAP was degraded through both direct and indirect photolysis, in which ¹O₂ was the main reactive species responsible for the indirect route. Its steady-state concentration in the micro-polluted water was determined to be 1.40 × 10^-13 mol/L. Transformation intermediates were identified to propose the degradation pathway of CAP, which substantially met the density functional theory (DFT) calculation results. Moreover, four other pharmaceuticals including tetracycline, doxycycline, oxytetracycline, and minocycline were also successfully photodegraded during 5 h irradiation. Therefore, the designed circulatory thin-layer inclined plate reactor is suggested to be effectively applied to the decontamination of organic micro-polluted water.

Evaluation of OH Radical Reaction Positions in 3-Ring PAHs Using Transition State Energy and Atomic Charge Calculations

In this study, transition state energy and atomic charge were calculated using the Gaussian 09 program with focus on three-ring PAHs, such as acenaphthylene and anthracene, which are most likely found in contaminated sites. The calculation results were then compared with the radical reaction positions reported in the existing literature. Because the energy difference between the reactant and the transition state according to the reaction position was very small, no distinct correlation was obtained when results were compared with those of the OH radical test findings reported in the literature. It was also found that the charge calculation makes it possible to accurately predict the radical reaction position of the target material. In addition, MK and HLY charges were found to be more accurate than CHelpG charges in predicting the radical reaction positions. The charge calculation can also be applied in predicting radical reaction positions for hazardous materials with different molecular structures.

The BODIPY-based chemosensor for the fluorometric determination of organochlorine pesticide dicofol

Dicofol is an organochlorine pesticide, which is widely used in fruits, tea and other crops, and is moderately toxic to humans. Therefore, the monitoring of organochlorine pesticide-dicofol is critical for food safety. In this work, a fluorometric chemosensor based on mercaptoethanol and boron dipyrromethene (BODIPY) was first constructed to detect the dicofol. The chemosensor displayed turn-off fluorescence behavior upon dicofol with a detection limit of 200 ppb. The nucleophilicity of the glutathione and other biological thiols was studied to evaluate the reactivity of thiols with dicofol. In practical applications, an obvious color difference was observed on a paper based microfluidic device modified by phenyltriethoxysilane (PTES). We designed an integrated device for pretreatment and paper-based detection, and successfully used for the detection of dicofol in tea. The applicability was demonstrated by detection of dicofol in real tea samples with good recovery ranging from 86% to 109%. The apparatus was convenient and could be used for on-site evaluation of dicofol.

Treatment of simulated textile sludge using the Fenton/Cl- system: The roles of chlorine radicals and superoxide anions on PAHs removal

The main content of this work is to investigate the removal of polycyclic aromatic hydrocarbons (PAHs: phenanthrene, anthracene, and fluoranthene) from simulated sludge solid phase employing an Fenton/Cl^- system under various Cl^- contents and pH values. The steady-state concentrations of the hydroxyl, chlorine, and dichloride anion radicals ([·OH]_ss, [·Cl]_ss, and [Cl₂^·-]_ss) in heterogeneous system were first measured using tert-butanol, nitrobenzene, and benzoic acid. The outcomes exhibited that increasing the Cl^- content from 50 to 2000 mg/L (pH = 3.0) or raising the pH from 3.0 to 5.0 (1000 mg/L Cl^-) caused [·OH]_ss to continuously decrease and [Cl₂^·-]_ss and the concentration of superoxide anions (HO₂·/O₂^·-) to continuously increase. When the pH was 3.0 and the Cl^- concentration was 1000 mg/L, [·Cl]_ss had a maximum value of 9.27 × 10^-14 M. Combining the results of PAH removal, radical quenching, and product analysis, it was found that ·Cl in the Fenton/Cl^- system promoted the oxidative degradation of phenanthrene without forming chlorination byproducts. Furthermore, HO₂·/O₂^·- was helpful in removing anthracene and fluoranthene. Under the environment of high Cl^- content (≥1000 mg/L), PAHs could be removed more effectively by using HO₂·/O₂^·-. This investigation underpins further study on the regulation of reactive species and the efficient degradation of target organic matter in Fenton/Cl^- system, and provides a basis for studying the formation of chlorinated or toxic byproducts in the process of treating textile dyeing sludge by Fenton.

Enhanced and selective phototransformation of chlorophene on aluminum hydroxide-humic complexes

Mineral-humic complexes, known as mineral-associated organic matter (MAOM), are ubiquitous in natural waters. However, the interaction between organic pollutants and MAOM remains elusive, which may affect their degradation process. In this study, photochemical transformation of chlorophene (CP) in the presence of MAOM, prepared by coating aluminum hydroxide with humic acid (HA-HAO), was investigated. Our results showed that the degradation of CP was significantly enhanced in the presence of HA-HAO, and the degradation rate constant was ~5 times as that with HA only. It was because the adsorption of CP to HA-HAO particles was greatly enhanced, and concentration of reactive oxygen species (ROS) was increased on HA-HAO surfaces, which further promoted the reactions between CP and ROS. The quenching experiments combined with EPR technology confirmed that superoxide anion (O₂^·-) was the primary reactive radical on CP photodegradation. More importantly, the degradation of CP with HA-HAO followed a hydroxylation process, rather than the oligomerization reaction with HA only. Spectroscopic analysis provided direct evidence for the formation of hydrogen bonding between CP phenolic hydroxyl group and surface oxygen of HAO, which would suppress the reactivity of phenolic hydroxyl group, consequently the ortho- and meta-positions of CP became more facile for the hydroxylation reaction. This study shows the importance of MAOM in altering the photochemical behavior and transformation pathway of organic contaminants.

Double photoelectron-transfer mechanism in Ag-AgCl/WO3/g-C3N4 photocatalyst with enhanced visible-light photocatalytic activity for trimethoprim degradation

Antibiotic contamination is increasing scrutinized recently. In this work, the Ag-AgCl/WO₃/g-C₃N₄ (AWC) nanocomposites were successfully synthesized using a two-step process involving electrostatic self-assembly and in-situ deposition for trimethoprim (TMP) degradation. The as-prepared photocatalysts were investigated and characterized by XRD, FTIR, XPS, TGA, SEM, TEM, UV-vis, PL and EIS. The experimental results indicated that 99.9% of TMP (4 mg/L) was degraded within 60 min when the concentration of AWC was 0.5 g/L. Reactive species scavenging experiments and electron spin resonance (ESR) experiments illustrated that superoxide radical (•O₂^-) and photogenerated holes (h⁺) were the main active species. The functional theory calculation and identification of intermediates via HPLC-MS revealed the possible degradation pathways of TMP. A double photoelectron-transfer mechanism in AWC photocatalyst was proposed. Five cycling photocatalytic tests and reactions under different solution matrix effects further supported that the AWC was a promising photocatalyst for the removal of TMP from the aquatic environment.

Fe-Activated Peroxymonosulfate Enhances the Degradation of Dibutyl Phthalate on Ground Quartz Sand

Soil contamination by organic compounds has received worldwide concern for decades. Here, we found that dibutyl phthalate (DBP) could be degraded on moist quartz sand (QS, crystal, a typical soil constituent) during stirring, and the removal rate reached 57.2 ± 3.1% after 8 h of reaction. The introduction of peroxymonosulfate (PMS) and zerovalent iron (Fe⁰) substantially improved the decomposition of DBP to 94.2 ± 1.6% in 8 h, suggesting they have great contributions. DBP decomposition was caused by multiple reactive species, such as surface silicon-based radicals (like ≡SiO^•) and other reactive species like superoxide radical (O₂^•-), hydroxyl radical (^•OH), and sulfate radical (SO₄^•-). In the QS/ultrapure water system, DBP was mainly attacked by O₂^•- or ≡SiO^•, with the formation of hydrolysis products. In the iron@QS/PMS system, due to the activation of PMS by Fe⁰, SO₄^•- and ^•OH were produced while the latter led to DBP degradation, and thus hydroxyl substitution products of DBP were ubiquitous. DBP was hardly removed on amorphous supporters like silica gel, alumina, and red soil even with the presence of PMS and Fe⁰, indicating the indispensable role of surface radicals on crystals like QS. This work presents a new remediation technology for polluted soil, especially aquifer.

Role of SiF groups in enhancing interfacial reaction of Fe-MCM-41 for pollutant removal with ozone

Heterogeneous catalytic ozonation had met the bottlenecks when treating low concentration but high toxic pollutants: (i) the low mass transfer efficiency of ozone and pollutants to hydrophilic catalyst; (ii) the negative impact of coexisted water matrixes. Herein, to enhance the mass transfer efficiency of reactants toward hydrophilic Fe-MCM-41 as well as enhance the interfacial reaction, the fluoride planting Fe-MCM-41 (F-Fe-MCM-41) was synthesized and employed as catalyst in catalytic ozonation for nitrobenzene (NB). Both NB and TOC removal were promoted in F-Fe-MCM-41/O₃ with 99.0 % NB removal in 60 min and 88.6 % TOC removal in 120 min, which were superior to the degradation efficiency by O₃ and Fe-MCM-41/O₃. FTIR, EPR, Mössbauer spectra, ²⁹Si NMR, ¹⁹F NMR et al verified that the replacement of non-reactive silanols (-Si-OH) of Fe-MCM-41 with SiF groups could enhance its hydrophobicity, Lewis acidity and mass transfer effect. Comparative characterizations, experiments and theoretical calculations verified that interfacial reaction played the major role over liquid phase reaction for NB degradation in F-Fe-MCM-41/O₃. Moreover, the strengthened interfacial reaction also reduced the OH scavenging effect of water matrix, such as humic acid and carbonate. The interfacial adjustment method proposed in this study provided a novel insight into catalyst design and water treatment process.

A new water treatment technology for degradation of B[a]A by hydrodynamic cavitation and chlorine dioxide oxidation

Managing environmental contamination with Benz[a]anthracene (B[a]A) is essential due to its carcinogenic, teratogenic and mutagenic effects on humans and the environment. At present, the mainly B[a]A degradation methods used are photodegradation, bioremediation and traditional advanced oxidation, although they all have disadvantages. In this study, B[a]A was degraded by hydrodynamic cavitation (HC), chlorine dioxide (ClO₂), or an innovative combination of the two methods. According to high performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) analysed the degradation products and degradation pathway of B[a]A, with the kinetics of different degradation methods discussed. Under optimal conditions, HC combined with ClO₂ oxidation can further degrade products to achieve ring cleavage. Compared with the two separate degradation process methods, the combined method exerts a synergistic effect on the degradation of B[a]A, with an enhancement factor of 1.48. Experimental results showed that the combination method can realize enhanced complete degradation of B[a]A, reduce ClO₂ requirements, improve efficiency, reduce energy consumption and produce less harmful products with ring cleavage achieved.

Activation of peroxymonosulfate by Fe doped g-C3N4 /graphene under visible light irradiation for Trimethoprim degradation

Fe-doped g-C₃N₄ / graphene (rGO) composites were investigated as catalysts for the activation of peroxymonosulfate (PMS) to degrade Trimethoprim (TMP) under visible light irradiation. The rapid recombination of photogenerated electron-hole pairs in g-C₃N₄ may be suppressed by doping with Fe and incorporating rGO. The TMP degradation efficiency using 0.2% Fe-g-C₃N₄/2 wt% rGO/PMS was 3.8 times than that of g-C₃N₄/PMS. The degradation efficiency of TMP increased with higher catalyst dosages and PMS concentrations. Acidic condition (pH = 3) was observed to significantly enhance the TMP degradation efficiency from 61.4% at pH = 6 to nearly 100%. By quenching experiments and electron spin resonance (ESR), O₂^- was found to play an important role for the activation of PMS to accelerate the generation of reactive radicals for the TMP degradation. A total of 8 intermediates derived from hydroxylation, demethoxylation and carbonylation were identified through theoretical calculations and the HRAM/LC-MS-MS technique, and transformation pathways of TMP oxidation were proposed. TOC removal rate of TMP increased as reaction time was prolonged. Acute toxicity estimation by quantitative structure-active relationship analysis indicated that most of the less toxic intermediates were generated. The aim of this study was to elucidate and validate the functionality of a promising polymeric catalyst for the environmental remediation of organic contaminants.

Phosphate-modified m-Bi2O4 enhances the absorption and photocatalytic activities of sulfonamide: Mechanism, reactive species, and reactive sites

Widespread usage of the sulfonamide class of antibiotics is causing increasing ecotoxicological concern, as they have the capacity to alter ambient ecosystems. Photocatalytic technology is an attractive yet challenging strategy for the degradation of antibiotics. For this work, the phosphate modification of m-Bi₂O₄ (Bi₂O₄-P) was prepared via a one-step hydrothermal process involving sodium bismuthate and sodium phosphate, which was employed for the degradation of sulfamethazine (SMZ) under visible light irradiation. The 0.5% Bi₂O₄-P exhibited excellent photocatalytic performance, which was 1.9 times that of pure m-Bi₂O₄. The photocatalytic degradation kinetics and mechanism of SMZ was investigated at different pH, whereupon it was revealed that m-Bi₂O₄-P exhibited improved SMZ adsorption and photocatalytic activities in contrast to pure m-Bi₂O₄. Compared with other four sulfonamide antibiotics, structures that contained additional methyl on the pyrimidine could be more easily attacked by phosphate modified m-Bi₂O₄. Reactive species (RS) scavenging experiments revealed that h⁺ was primarily responsible for the degradation of SMZ. Further studies of RS by ESR technology, and the results of photoelectrochemical properties showed phosphate-modified m-Bi₂O₄ could make greater use of photogenerated carriers, thereby producing additional RS. Based on the HRAM LC-MS/MS and the Frontier Molecular Orbital Theory, the degradation pathways of SMZ were proposed.

Visible light and fulvic acid assisted generation of Mn(III) to oxidize bisphenol A: The effect of tetrabromobisphenol A

Bisphenol A (BPA) and tetrabromobisphenol A (TBBPA), endocrine disrupting compounds (EDCs), are of increasing concerns for many years. This paper presents the elimination of BPA under visible light (VL) (λ ≥ 420 nm) irradiated solutions containing fulvic acid (FA) and MnSO₄ (Mn(II)), and examines the possible effects of TBBPA on the transformation of BPA. After 72 h of reaction time, the removal efficiency of BPA in the studied system was 69%. Results of different experiments to identify oxidative species suggested the dominate role of soluble manganese (III) (Mn(III)) in the conversion of BPA. The transformation of BPA by the VL/FA/Mn(II) system was through self-oligomerization in absence of co-existence of TBBPA. In the co-existence of BPA with TBBPA, the removal of BPA was largely inhibited due to the competition with available Mn(III) and the possible occurrence of cross-coupling reactions between the two EDCs. This phenomenon was further elucidated by product analyses and density functional theory (DFT) calculations. The energy difference (ΔE) for generating a cross-coupling product was calculated as -23.4 kJ mol^-1, much lower than the positive values of ΔE for self-coupling products of BPA or TBBPA, demonstrating that cross-coupling reactions between BPA and TBBPA likely occurred easier than the respective self-coupling reactions. The toxicity test showed that the overall estrogenic activity of BPA reaction solution was significantly decreased by the VL/FA/Mn(II) system. In general, our study provided new insights into the transformation of co-existing EDCs by in situ formed Mn(III) in aqueous solution.

Degradation of propranolol by UV-activated persulfate oxidation: Reaction kinetics, mechanisms, reactive sites, transformation pathways and Gaussian calculation

Contamination with β-blockers such as propranolol (PRO) poses a potential threat to human health and ecological system. The present study investigated the kinetics and mechanisms of PRO degradation by UV-activated persulfate (UV/PS) oxidation. Here, the experimental results showed that the degradation of PRO followed pseudo-first-order reaction kinetics, the degradation rate constant (k_obs) was increased dramatically with increasing PS dosage or decreasing initial PRO concentration. And increasing the initial solution pH could also enhance the degradation efficiency of PRO. Radical scavenging experiments demonstrated that the main radical species was sulfate radicals (SO₄^•-), with hydroxyl radicals (HO·) playing a less important role. Meanwhile, the second-order rate constants of PRO degradation with SO₄^•- and HO· were determined to be 1.94 × 10¹⁰ M^-1 s^-1 and 6.77 × 10⁹ M^-1 s^-1, respectively. In addition, the presence of natural organic matter (NOM) and nitrate anion (NO₃^-) showed inhibitory effect on PRO degradation, whereas bicarbonate anion (HCO₃^-) and chlorine anion (Cl^-) greatly enhanced the degradation of PRO. Moreover, the transformation products of PRO were identified by applying ultra performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF-MS) technique. Molecular orbital calculations were used to estimate the reaction site of PRO with radicals, simultaneously. Hence, the transformation pathways including hydroxylation, dehydration, naphthalene ring opening, and the cleavage of aldehyde groups were proposed. This work enriches the mechanism of PRO degradation under UV/PS system on the basis of results obtained by experimental characterization and Gaussian theoretical calculation.

Kinetic and Theoretical Study of the Atmospheric Aqueous-Phase Reactions of OH Radicals with Methoxyphenolic Compounds

Methoxyphenols, which are emitted through biomass burning, are an important species in atmospheric chemistry. In the present study, temperature-dependent aqueous-phase OH radical reactions of six methoxyphenols and two related phenols have been investigated through laser flash photolysis and the density functional theory. The rate constants obtained were in a range of (1.1-1.9) × 10¹⁰ L mol^-1 s^-1 with k(3-MC) > k(Cre) ≈ k(Syr) ≈ k(MEP) > k(Res) > k(3-MP) > k(2-EP) ≈ k(2-MP). We derived the parameters of these reactions from the obtained T-dependent rate constants and found a mean Arrhenius activation energy of 16.9 kJ mol^-1. The diffusion rate constants were calculated for each case and compared to the measured ones. Generally, the rate constants are found to be close to fully diffusion-controlled (k_diff = (1.4-1.5) × 10¹⁰ L mol^-1 s^-1 for all reactions). A structure-function relationship was established through the measurement result, which could be used for predicting unknown rate constants of other phenolic compounds. All of these findings are expected to enhance the predictive capabilities of models, such as the chemical aqueous-phase radical mechanism.

Mechanism insight of acetaminophen degradation by the UV/chlorine process: kinetics, intermediates, and toxicity assessment

The removal of acetaminophen (AAP) in aqueous solution by the UV/chlorine process was evaluated. The effect of chlorine dose, the initial AAP concentration, pH value, and UV intensity on the reaction were also investigated. The degradation mechanism and the ecological risk were further discussed. The results indicated that AAP degradation fitted pseudo-first-order kinetics. Compared with UV alone or dark chlorination, the combination of UV and chlorine significantly accelerated the degradation process. The AAP degradation was positively affected by chlorine dose and UV intensity, while negatively affected by the initial AAP concentration and ammonia nitrogen concentration during the UV/chlorine process. The frontier orbital theory analysis shows that the C5 position in the benzene ring of AAP is likely to be the first site attacked by HO• and Cl• radical to form the products. Twelve intermediates were identified by Q-TOF and GC-MS. The possible degradation pathways were also proposed. Luminescent bacteria experiment and ECOSAR prediction both revealed that acute toxicity of AAP degradation could only be partially reduced. Ecological risks during the UV/chlorine process need to be further evaluated.

Removal of Bound PAH Residues in Contaminated Soils by Fenton Oxidation

The availability of bound residues of polycyclic aromatic hydrocarbons (PAHs), in reference to their parent compounds, can be enhanced by microbial activity and chemical reactions, which pose severe risks for the ecosystems encompassing contaminated soils. Considerable attention has been raised on how to remove these bound residues from PAH-contaminated soils. This paper provides a novel application of Fenton oxidation in the removal of bound residues of model PAHs, such as naphthalene (NAP), acenaphthene (ACP), fluorene (FLU) and anthracene (ANT), from naturally contaminated soils. The citric acid-enhanced Fenton treatment resulted in the degradation of bound PAH residues that followed pseudo-first-order kinetics, with rate constants within 4.22 × 10−2, 1.25 × 10−1 and 2.72 × 10−1 h−1 for NAP, FLU, and ANT, respectively. The reactivity of bound PAH residues showed a correlation with their ionization potential (IP) values. Moreover, the degradation rate of bound PAH residues was significantly correlated with H2O2-Fe2+ ratio (m/m) and H2O2 concentrations. The highest removal efficiencies of bound PAH residues was up to 89.5% with the treatment of chelating agent oxalic acid, which was demonstrated to be superior to other acids, such as citric acid and hydrochloric acid. This study provides valuable insight into the feasibility of citric acid-Fenton and oxalic acid-Fenton treatments in rehabilitating bound PAH residues in contaminated soils.

Transformation of gaseous 2-bromophenol on clay mineral dust and the potential health effect

Iron-bearing clays are ubiquitously distributed as mineral dusts in the atmosphere. Bromophenols were reported as the major products from thermal decomposition of the widely used brominated flame retardants (BFRs). However, little information is available for the reactivity of iron associated with mineral dusts to interact with the atmospheric bromophenols and the subsequent toxic effects. Herein, three common clay minerals (montmorillonite, illite and kaolinite) were used to simulate mineral dusts, and the reactions with gaseous 2-bromophenol were systematically investigated under environmentally relevant atmospheric conditions. Our results demonstrate that structural Fe(III) in montmorillonite and Fe(III) from iron oxide in illite mediated the dimerization of 2-bromophenol to form hydroxylated polybrominated biphenyl and hydroxylated polybrominated diphenyl ether. The surface reaction is favored to occur at moisture environment, since water molecules formed complex with 2-bromophenol and the reaction intermediates via hydrogen bond to significantly lower the reaction energy and promote the dimerization reaction. More importantly, the formed dioxin-like products on clay mineral dust increased the toxicity of the particles to A549 lung cell by decreasing cell survival and damaging cellular membrane and proteins. The results of this study indicate that not only mineral dust itself but also the associated surface reaction should be fully considered to accurately evaluate the toxic effect of mineral dust on human health.

Fenton-like and potassium permanganate oxidations of PAH-contaminated soils: Impact of oxidant doses on PAH and polar PAC (polycyclic aromatic compound) behavior

Potassium permanganate and Fenton-like oxidations were applied on two PAH-contaminated soils collected on former coking plant and gas plant sites. The impact of oxidant dose on the polycyclic aromatic compound (PAC) evolution, including 16 US-EPA PAHs, 11 oxygenated- and 4 nitrogen heterocyclic-PACs (O- and N-PACs) was studied for both treatments. The content of extractable organic matter and PACs was determined prior and after oxidation. Overall, permanganate treatment was more efficient than Fenton-like to decrease the PAH content, this latter being limited by the contamination availability. However, permanganate treatment resulted in incomplete PAH degradation, leading to the formation of O-PACs, that was limited with the application of higher dose. It underlines the importance of the dose and the oxidant type in the selection of oxidation parameters for remediation purpose, as improper use of oxidant can lead to the accumulation of oxidation by-products that could be as toxic as the parent compounds.

Characterization of particulate-bound polycyclic aromatic compounds (PACs) and their oxidations in heavy polluted atmosphere: A case study in urban Beijing, China during haze events

Characterizations on polycyclic aromatic compounds (PACs) during frequent haze periods have been conducted in an urban site of Beijing, China. Particulate polycyclic aromatic hydrocarbons (PAHs) and oxygenated-PAHs (OPAHs) and other carbonaceous matters were quantified. The average PM_2.5 during haze events (256.3 ± 103.7 μg/m³) were one magnitude over than that of clear periods (CRs, 24.7 ± 27.7 μg/m³).The average total quantified PAHs (ΣPAHs) and OPAHs (ΣOPAHs) during haze events were 423.9 ± 178.4 ng/m³ and 581.4 ± 299.8 ng/m³, respectively, which were approximately 10 times higher than those of 40.3 ± 68.2 ng/m³ and 54.4 ± 82.4 ng/m³ in clear days. Four-rings PAHs had the highest compositions. 1,8-Naphthalic anhydride (1,8-NA) is the most abundant OPAHs, accounted for 49.8% of ∑OPAHs, followed by 9,10-anthraquinone (9,10-AQ) (13.8%) and benzo(a)anthracene-7,12-dione (BaAQ) (8.31%). In haze events, the contents of 5- to 7-rings PAHs decreased by 2.32% compared with those of clear days, while lower molecular weight fractions of 3- and 4-rings PAHs increased. The relationships between PAHs, OPAHs and relative humidity (RH) were found to be exponential. High oxygenation rate (R₀) ratios of OPAH/PAH represents higher rates in secondary formation or degradation and gas- particle conversion for each PAH or OPAH during the wintertime. Significant positive correlation between BeP and OPAHs (r = 0.97), combined with the results of photochemical aging and negatively correlation with O₃, suggest that secondary atmospheric reactions of PAHs played an important role in the burden of OPAHs.

Enhanced degradation performance of bisphenol M using peroxymonosulfate activated by zero-valent iron in aqueous solution: Kinetic study and product identification

In the present work, we first examined the performance of zero-valent iron (Fe⁰) activated peroxymonosulfate (PMS) for the removal of that bisphenol M (BPM). In 90 min, 95.9 ± 1.0% of BPM (initial concentration of 10 μM) could be removed in the optimal reaction conditions: [BPM]₀:[PMS]₀ = 1:40 (molar ratio), [PMS]₀:[Fe⁰]₀ = 1:3 (molar ratio), pH = 8.0 (maintained by 0.1 M phosphate buffer solution), T = 35 °C. Common environmental ions like HCO₃^-, Cl^-, NO₃^- accelerated BPM degradation while NH₄⁺ hindered it. In radical quenching tests, sulfate radicals (SO₄^-) were found to play a dominant role in BPM degradation, while hydroxyl radicals (OH) were also detected. By high-performance liquid chromatography-tandem mass spectrometry analysis, 13 products of BPM including small molecules, oligomers and hydroxylated derivatives were identified, and five possible degradation pathways were then proposed. The predicted acute toxicity of the reaction products was reduced after BPM was treated by Fe⁰/PMS. All these results prove that Fe⁰/PMS is an efficient, convenient, and environmentally friendly treatment method for the removal of BPM.

Sono-advanced Fenton-like degradation of aromatic amines in textile dyeing sludge: efficiency and mechanisms

In this paper, a novel strategy integrating ultrasound (US) with a Fenton-like (zero-valent iron/EDTA/air, ZEA) process was proposed for the removal of the refractory and carcinogenic aromatic amines (AAs) in textile dyeing sludge for the first time. The operating condition was optimized as 1.08 W/cm³ ultrasonic density, 15 g/L ZVI, and 1.0 mM EDTA, which could reach degradation efficiencies of 51.79% in US, 72.88% in ZEA, and 92.40% in US/ZEA system after 90-min reaction. Quenching experiments showed that electron transfer reactions generated by the iron ligands in ZEA brought about various reactive oxidative species (ROS), in which Fe (IV), O₂˙^-, and ˙OH dominated the degradation. US induced sludge disintegration by ultrasonic shear, proven by particle size decrease and supernatant organic matter upsurge, which helps ROS contact with those pollutants in the sludge cavities. Besides, US facilitated the iron redox cycle for oxygen activation by promoting the corrosion of ZVI and stripping considerable ferric ions from sludge iron oxides which were verified by SEM, XRF, and XPS. Graphical abstract.

Photogeneration of hydroxyl radical in Fe(III)-citrate-oxalate system for the degradation of fluconazole: mechanism and products

The photochemical role of Fe(III)-citrate complex is significant in natural waters due to its ubiquitous existence and excellent photoreactivity at near neutral pH. Although there are many reports on the photoinduced degradation of pollutants in the Fe(III)-citrate system, the optimum pH for its photoreactivity is yet not clearly understood. Here, for the first time, we demonstrated that the optimum pH was 5.5 for the photoproduction of ^•OH in the Fe(III)-citrate system via kinetics modeling based on the steady-state approximation. According to the experimental results, the ^•OH photoproduction increased with increasing pH until 5.5 and then decreased in Fe(III)-citrate solution, which agreed well with the prediction trend of kinetic modeling. The effect of the common ligand oxalate on the photoreactivity of Fe(III)-citrate system was also investigated. The addition of oxalate promoted the photoproduction of ^•OH in Fe(III)-citrate solutions, and the measured [^•OH]_ss increased with oxalate concentration under a fixed Fe(III)-to-citrate ratio. Little synergistic effect exists in Fe(III)-citrate-oxalate system at pH 4.0-5.5. In contrast, an appreciable synergistic effect was observed at near neutral pH (6.0-8.0). Higher oxalate-to-citrate ratio facilitated the synergistic effect. Furthermore, antifungal drug fluconazole could be removed efficiently in the Fe(III)-citrate-oxalate system. The photodegradation kinetics also verified the optimum pH of Fe(III)-citrate system and synergistic effect of oxalate. By LC-ESI-MS/MS analyses, the photoproducts of fluconazole in the Fe(III)-citrate-oxalate system were identified and the reaction mechanism involving hydroxylation substitution and subsequent cleavage of heterocyclic amine was proposed. These findings suggest that Fe(III)-citrate exhibits best photoreactivity at pH 5.5, and the coexistence of reactive ligands will enhance its photoreactivity at circumneutral pH, indicating potential application in wastewater treatment via addition of appropriate citrate and co-ligands.

Photodegradation of amitriptyline in Fe(III)-citrate-oxalate binary system: Synergistic effect and mechanism

Fe(III) and carboxylic acids are ubiquitous in surface water and atmospheric water droplets. Numerous documents have reported the photochemistry of Fe(III)-carboxylate complexes, typically including Fe(III)-oxalate and Fe(III)-citrate. Our previous study preliminarily showed that oxalate enhances the photoreactivity of Fe(III)-citrate system. Here, we further investigate the synergistic effect of Fe(III)-citrate-oxalate binary system at different conditions with pharmaceutical amitriptyline (AMT) as the model pollutant. In the Fe(III)-oxalate system, the photodegradation of AMT decreased with increasing pH from 3.0 to 8.0. In the Fe(III)-citrate system, the optimal pH for AMT degradation is around 5.0 in the same pH range. For the Fe(III)-citrate-oxalate system, the photodegradation of AMT decreased with increasing pH, indicating the combined effect of both oxalate and citrate on the photoreactivity. The addition of oxalate to the Fe(III)-citrate system markedly accelerated the photodegradation of AMT. The Fe(III)-carboxylate binary system exhibited excellent photoreactivity and up to 90% AMT was removed after 30 min at pH 6.0 with Fe(III)/citrate/oxalate ratio of 10:150:500 (μM). Synergistic effect was observed in Fe(III)-citrate-oxalate binary system in the pH range of 5.0-8.0. The presence of oxalate promoted the depletion of citrate in the Fe(III)-citrate system. The higher concentration ratios of oxalate to citrate facilitated the synergistic effect in the Fe(III)-citrate-oxalate system. By LC-MS analyses, a possible pathway of AMT degradation was proposed based on hydroxyl radicals (OH) mechanism. This finding could be helpful for the better understanding of synergistic mechanism of Fe(III)-citrate-oxalate binary complexes, which will be of great potential application in environmental photocatalysis at near neutral pH.

Interactions of Gaseous 2-Chlorophenol with Fe3+-Saturated Montmorillonite and Their Toxicity to Human Lung Cells

The interactions of gaseous 2-chlorophenol with Fe³⁺-saturated montmorillonite particles in a gas-solid system were investigated to simulate the reactions of mineral dusts with volatile organic pollutants in the atmosphere. Results suggested that Fe³⁺-saturated montmorillonite mediated the dimerization of gaseous 2-chlorophenol to form hydroxylated polychlorinated biphenyl, hydroxylated polychlorinated diphenyl ether, and hydroxylated polychlorinated dibenzofuran. The toxicity of Fe³⁺-montmorillonite particles to A549 human lung epithelial cells before and after interaction with 2-chlorophenol was examined to explore their adverse impact on human health. Based on cell morphological analysis, cytotoxicity tests, and Fourier-transform infrared imaging spectra, surface-catalyzed reactions of Fe³⁺-montmorillonite with 2-chlorophenol increased the toxicity of montmorillonite particle on A549 cells. This was supported by increased cellular membrane permeability, the release of extracellular lactate dehydrogenase, and cell damages on cellular DNA, proteins, and lipids. Since mineral dusts are important components of particulate matter, our results help to understand the interactions of volatile organic pollutants with particulate matter in the atmosphere and their adverse impacts on human health.

Sludge treatment by integrated ultrasound-Fenton process: Characterization of sludge organic matter and its impact on PAHs removal

In this work, the impact of organic matter on the degradation of polycyclic aromatic hydrocarbons (PAHs) in textile dyeing sludge by ultrasound-Fenton process has been studied. Sludge organic matter (SOM) was characterized and the degradation efficiencies of PAHs at various oxidation intensities (Fenton's reagent of 20, 70, and 140mmol/L, ultrasonic densities of 0.36, 0.90, and 1.80W/cm³, and reaction time of 15, 25, and 40min) were determined. The results showed that 75.52-84.40% of PAHs and 16.32-31.13% of SOM had degraded after ultrasound-Fenton treatment, confirming the competitive relation between both of them for degradation. The aliphatic SOM fractions were preferentially oxidized owing to their easily degradable properties, while equimolar amounts of the aromatic moieties would require more oxidant compared to the aliphatic fractions. Correlation analysis demonstrated that SOM with its lower content, stronger polarity, and a higher proportion of labile organic fraction was more favourable for PAHs degradation. In addition, the SOM fractions were decomposed to biodegradable matter after treatment, which further enhance the biodegradability of sludge. This study provides insights into the role of SOM in PAHs removal by AOPs, and confirms that the ultrasound-Fenton treatment could not only effectively degrade PAHs, but also modify SOM.

A novel method for photo-oxidative degradation of diatrizoate in water via electromagnetic induction electrodeless lamp

In this study, an electromagnetic induction electrodeless lamp (EIEL) was first introduced into UV advanced oxidation processes (AOPs) for photodegradation of Diatrizoate (DTZ), which was the most persistent iodinated X-ray contrast medium (ICM), and traditional Hg lamps were taken as references. Direct photolysis rate of DTZ under EIEL irradiation was 1.34 times as that under Hg irradiation, but the electric energy consumption was 0.87 times. In this sense, the combination of EIEL and oxidants (O₂, H₂O₂ and S₂O₈^2-(PS)) was further investigated. The remarkably increased photodegradation rates were observed in UV/PS system due to primary contribution rate of SO₄^- (62.5%) based on the results of radical concentrations and second-order rate constants of DTZ with SO₄^- and OH. Inorganic ions influencing the photodegradation process were investigated. The effect of natural organic materials (NOMs) in UV/PS system was studied based on contribution ratios of light screening effect and quenching. Transformation mechanisms of DTZ in UV/PS system included deiodination, intramolecular cyclization, decarboxylation, deacetylation and deamination, which were further confirmed by frontier electron density calculations. The study indicated that UV/PS with EIEL irradiation has the potential to remove pharmaceuticals in contaminated aquatic environments.

Rapid degradation of atrazine by hydroxyl radical induced from montmorillonite templated subnano-sized zero-valent copper

In this study, subnano-sized zero-valent copper (ZVC) was synthesized using montmorillonite clay mineral as the template. The discrete distribution of surface charge on montmorillonite effectively separates the formed ZVC particles and inhibits their aggregation. X-ray diffraction result indicates that the size of ZVC particles on montmorillonite is ∼6 Å, which is much smaller than nano-ZVC prepared by conventional method. The montmorillonite templated ZVC (ZVCMMT) shows superior reactivity as indicated by the degradation of atrazine, over 90% atrazine (15 μM) could be degraded in a few min. Hydroxyl radical is confirmed as the reactive species, which is produced from the activation of oxygen by ZVC. It was also shown that the degradation process is strongly dependent on the hydration status of synthesized ZVCMMT. The freeze dried ZVCMMT exhibits higher reactivity compared to freshly prepared ZVCMMT, which can be explained by the higher adsorption of atrazine and oxygen residue on freeze dried ZVCMMT surface. In addition, the toxicity of atrazine is significantly decreased after the reaction with ZVCMMT, indicating that ZVCMMT could be used as a promising material for rapid remediation of persistent organic contaminants.

Electrochemistry coupled to (LC-)MS for the simulation of oxidative biotransformation reactions of PAHs

Electrochemistry coupled to liquid chromatography and mass spectrometry was used for simulating the biological and environmental fate of polycyclic aromatic hydrocarbons (PAHs) as well as for studying the PAH degradation behavior during electrochemical remediation. Pyrene and benzo[a]pyrene were selected as model compounds and oxidized within an electrochemical thin-layer cell equipped with boron-doped diamond electrode. At potentials of 1.2 and 1.6 V vs. Pd/H₂, quinones were found to be the major oxidation products for both investigated PAHs. These quinones belong to a large group of PAH derivatives referred to as oxygenated PAHs, which have gained increasing attention in recent years due to their high abundance in the environment and their significant toxicity. Separation of oxidation products allowed the identification of two pyrene quinone and three benzo[a]pyrene quinone isomers, all of which are known to be formed via photooxidation and during mammalian metabolism. The good correlation between electrochemically generated PAH quinones and those formed in natural processes was also confirmed by UV irradiation experiments and microsomal incubations. At potentials higher than 2.0 V, further degradation of the initial oxidation products was observed which highlights the capability of electrochemistry to be used as remediation technique.

Photo-degradation ibuprofen by UV/H2O2 process: response surface analysis and degradation mechanism

The removal of ibuprofen (IBP) in aqueous solution using UV/H₂O₂ process was evaluated. The response surface methodology (RSM) and Box-Behnken design were employed to investigate the effects of process parameters on IBP removal, including the initial IBP concentration, H₂O₂ dosage, UV light intensity, and initial pH value of solution. The RSM model developed herein fits well with the experiments, and provides a good insight into the OH radical irritated degradation mechanisms and kinetics. High resolution accurate mass spectrometry coupled with liquid chromatography was used to identify the degradation intermediates. A total of 23 degradation products were identified, including mono-hydroxylated products and dihydroxylated products. A series of OH radical-initiated reactions, including hydroxylation, dihydroxylation, decarboxylation, demethylation, ring break, lead to the final mineralization of IBP to CO₂ and H₂O. UV/H₂O₂ technology could be a promising technology for IBP removal in aqueous solution.

Degradation of polycyclic aromatic hydrocarbons in different synthetic solutions by Fenton's oxidation

The Fenton oxidation using phenanthrene (Phe), fluoranthene (Fle) and benzo[a]pyrene (BaP) as representative polycyclic aromatic hydrocarbon (PAH) contaminants was examined. The effect of the H₂O₂ concentration, the temperature and the competition between the PAHs in different solutions (methanol, surfactant and quartz) was investigated. The Fenton oxidation process was performed at pH = 2.5. The best conditions were recorded by adding 15 g H₂O₂ L^-1 with a molar H₂O₂/Fe²⁺ ratio of 10/1 at T = 60°C. Phe, Fle and BaP were efficiently degraded in aqueous solution (Phe = 99%, Fle = 99% and BaP = 90%). The present study demonstrated that Phe, Fle and BaP were degraded to intermediate compounds and also oxidized to carbon dioxide. Among the by-products obtained, phthalic acids and benzoic acid were recorded as the major products.

Size distribution and sources of 37 toxic species of particulate polycyclic aromatic hydrocarbons during summer and winter in Baoshan suburban area of Shanghai, China

The objectives of this study were to assess the size-segregated distribution and sources of 37 different species of particulate polycyclic aromatic hydrocarbons (PAHs) in a suburban area of Shanghai metropolitan City, China. The ambient particulate sampling was carried out on the rooftop of a five-stories building in Baoshan campus of Shanghai University. An Andersen high-volume air sampler was employed to collect ambient size-segregated particulate matter during summer of August to September and winter of November to December 2015. The high toxic PAHs were determined by a gas chromatography mass spectrometry. The concentrations of total PAHs in suspended particulate matter (SPM) and PM1.1 (suspended particulate matter below 1.1μm in diameter) in the suburban area of Shanghai were 4.58-14.5ng/m(3) and 1.82-8.56ng/m(3), respectively in summer, and 43.6-160ng/m(3) and 23.2-121ng/m(3), separately in winter. 1,8-Naphthalic anhydride (1,8-NA) showed the highest concentration among 37 different species of PAHs in the suburban area of Shanghai. The concentrations of high molecular PAHs (e.g. 5-6 ring PAHs) followed a nearly unimodal size distribution with the highest peaks in PM1.1. The diagnostic ration qualitatively indicated that PAHs in SPM of Shanghai were mainly derived from motor-vehicle or petroleum combustion in summer and from coal and biomass combustion in winter. According to the calculated toxicity equivalency factors based on the methods of Nisbet and Lagoy and the potency equivalency factors (PEF) recommended by U.S. EPA, the highest contributors in the total carcinogenicity of the PAHs in SPM and PM1.1 were dibenzo[a,h]pyrene (46.2% and 45.0% in summer), benzo[a]pyrene (44.4% and 43.8% in winter) and benz[j]aceanthrylene (80.2% and 83.1% in summer and 83.1% and 84.0% in winter), respectively. Therefore, benzo[a]pyrene seemed to be a lower contributor than other carcinogenic PAHs.

Studies on size distribution and health risk of 37 species of polycyclic aromatic hydrocarbons associated with fine particulate matter collected in the atmosphere of a suburban area of Shanghai city, China

Polycyclic aromatic hydrocarbons (PAHs) in suspended particulate matter (SPM) contribute significantly to health risk. Our objectives were to assess the size distribution and sources of 26 PAHs and 11 polycyclic aromatic compounds (PACs) in SPM in the suburban area, Shanghai city, China. Air sampling was carried out on the rooftop of a five-stories building in the campus of Shanghai University. An Andersen high-volume air sampler was employed to collect ambient size-segregated particles from August to September 2015. The toxic particulate PAHs were determined by the gas chromatography mass spectrometry. The concentrations of total PAHs (TPAHs) in SPM and PM1.1 (suspended particulate matter below 1.1 μm) were in the ranges of 4.58-14.5 ng m(-3) and 1.82-8.56 ng m(-3), respectively. 1,8-naphthalic anhydride showed the highest concentrations among 37 species of PAHs and PACs ranging 7.76-47.9 ng m(-3) and 1.50-17.6 ng m(-3) in SPM and PM1.1, respectively. The concentrations of high molecular weight 5-6 ring PAHs followed a nearly unimodal size distribution with the highest peak in PM1.1, while other lower molecular weight PAHs were not dependent on particle sizes. The toxicity analysis indicated that the carcinogenic potency of particulate PAHs primarily existed in PM1.1. Regarding meteorological parameters and other pollutants, the positive effect of humidity and NO2 over PAHs was confirmed. Diagnostic ration indicated that the particulate PAHs in Shanghai were mainly derived from motor-vehicle or petroleum combustion. The highest benzo[a]pyrene equivalent (BaPeq) in SPM and PM1.1 were 2.15 ng m(-3) and 1.43 ng m(-3) calculated by the toxicity equivalency factor, and 69.31 ng m(-3) and 47.81 ng m(-3) estimated by the potency equivalency factors, respectively. The highest contributors in the total carcinogenicity of the particulate PAHs were dibenzo[a,h]pyrene (46.2% and 45.0%) and benz[j]aceanthrylene (80.2% and 83.1%), respectively while benzo[a]pyrene is lower contributor than other carcinogenic PAHs.

Degradation of polycyclic aromatic hydrocarbons (PAHs) in textile dyeing sludge with ultrasound and Fenton processes: Effect of system parameters and synergistic effect study

To establish an efficient oxidation process for the degradation of polycyclic aromatic hydrocarbons (PAHs) in textile dyeing sludge, the effects of various operating parameters were optimized during the ultrasound process, Fenton process and the combined ultrasound-Fenton process. The results showed that the ultrasonic density of 1.80w/cm(3), both H2O2 and Fe(2+) dosages of 140mmol/L and pH 3 were favorable conditions for the degradation of PAHs. The degradation efficiency of high molecular weight PAHs was close to or even higher than that of light molecular weight PAHs. The highest degradation efficiencies of Σ16 PAHs were obtained within 30min in the order of: Fenton (83.5%) >ultrasound-Fenton (75.5%) >ultrasound (45.5%), then the efficiencies were decreased in the other of: ultrasound-Fenton (73.0%) >Fenton (70.3%) >ultrasound (41.4%) in 60min. The extra PAHs were released from the intracellular substances and the cavities of sludge due to the disruption of sludge during the oxidation process. Also, the degradation of PAHs could be inhibited by the other organic matter in the sludge. The combined ultrasound-Fenton process showed more efficient than both ultrasound process and Fenton process not only in the surface of sludge but also in the sludge interior.

Decolorization of azo dye C.I. Reactive Black 5 by ozonation in aqueous solution: influencing factors, degradation products, reaction pathway and toxicity assessment

In this study, ozonation treatment of C.I. Reactive Black 5 (RB5) was investigated at various operating parameters. The results showed that the aqueous solution initially containing 200 mg/L RB5 was quickly decolorized at pH 8.0 with an ozone dose of 3.2 g/h. Reaction intermediates with m/z 281, 546, 201, 350, 286 and 222 were elucidated using liquid chromatography-mass spectrometry, while sulfate ion, nitrate ion and three carboxylic acids (i.e., oxalic acid, formic acid, and acetic acid) were identified by ion exchange chromatography. Thus, the cleavage of the azo bond and the introduction of OH groups in the corresponding positions were proposed as the predominant reaction pathway. The detachment of sulfonic groups was also commonly observed during the ozonation treatment. The proposed degradation mechanism was confirmed by frontier electron density calculations, suggesting the feasibility of predicting the major events in the whole ozonation process with the computational method. Compared with RB5 degradation, the reduction of total organic carbon (TOC) proceeded much more slowly, and approximately 54% TOC was removed after 4 h of ozonation. Acute toxicity tests with Photobacterium phosphoreum showed that the toxicity of reaction solution was firstly increased and then decreased to a negligible level after 160 min.

Role of goethite during air-oxidation of PAH-contaminated soils

The impact of goethite on air-oxidation of PAH-contaminated soils was studied through two sets of experiments. (i) Soil extractable organic matter (EOM) and (ii) whole coking plant soils were oxidized at 60 and 100 °C for 160 d, with/without goethite. Organic matter (OM) mineralization was monitored via CO2 production and polycyclic aromatic compounds (PACs) oxidation was investigated by GC–MS analyses. The decrease in EOM and PAH contents, and the oxygenated-PAC production observed during EOM oxidation, were enhanced by the presence of goethite. PACs were likely transformed at the goethite surface through electron transfer process. Mass carbon balance revealed a transfer from EOM to the insoluble organic fraction indicating condensation/polymerization of organics. Soil oxidation induced a decrease in EOM, PAH but also in oxygenated-PAC contents, underscoring different oxidation or polymerization behavior in soil. The goethite addition had a lesser impact suggesting that indigenous minerals played an important role in PAC oxidation.

Impact of clay mineral on air oxidation of PAH-contaminated soils

This work investigated the impact of a clay mineral (bentonite) on the air oxidation of the solvent extractable organic matters (EOMs) and the PAHs from contaminated soils. EOMs were isolated from two coking plant soils and mixed with silica sand or bentonite. These samples, as well as raw soils and bentonite/soil mixtures, were oxidized in air at 60 and 100 °C for 160 days. Mineralization was followed by measuring the CO2 produced over the experiments. EOM, polycyclic aromatic compound (PAC), including PAH, contents were also determined. Oxidation led to a decrease in EOM contents and PAH concentrations, these diminutions were enhanced by the presence of bentonite. Transfer of carbon from EOM to insoluble organic matter pointed out a condensation phenomenon leading to a stabilization of the contamination. Higher mineralization rates, observed during the oxidation of the soil/bentonite mixtures, seem to indicate that this clay mineral had a positive influence on the transformation of PAC into CO2.

Identification of persulfate oxidation products of polycyclic aromatic hydrocarbon during remediation of contaminated soil

The extent of PAH transformation, the formation and transformation of reaction byproducts during persulfate oxidation of polycyclic aromatic hydrocarbons (PAHs) in coking plant soil was investigated. Pre-oxidation analyses indicated that oxygen-containing PAHs (oxy-PAHs) existed in the soil. Oxy-PAHs including 1H-phenalen-1-one, 9H-fluoren-9-one, and 1,8-naphthalic anhydride were also produced during persulfate oxidation of PAHs. Concentration of 1,8-naphthalic anhydride at 4h in thermally activated (50°C) persulfate oxidation (TAPO) treatment increased 12.7 times relative to the oxidant-free control. Additionally, the oxy-PAHs originally present and those generated during oxidation can be oxidized by unactivated or thermally activated persulfate oxidation. For example, 9H-fluoren-9-one concentration decreased 99% at 4h in TAPO treatment relative to the control. Thermally activated persulfate resulted in greater oxy-PAHs removal than unactivated persulfate. Overall, both unactivated and thermally activated persulfate oxidation of PAH-contaminated soil reduced PAH mass, and oxidized most of the reaction byproducts. Consequently, this treatment process could limit environmental risk related to the parent compound and associated reaction byproducts.