Photocatalytic debromination of polybrominated diphenyl ethers (PBDEs) on metal doped TiO2 nanocomposites: Mechanisms and pathways

Magnetically separable Pd-iron-oxides composites as highly efficient and recyclable catalysts for ultra-rapid degradation and debromination of polybrominated diphenyl ethers

When precious nano-metals are used as environmental catalysts, it is important to tune the particle sizes and the reusability of the nano-metals for achieving their highly efficient catalytic performance at a low cost. In the present work, magnetic iron oxides (FeOx-Y) nanoparticles were pre-prepared as supports of nano-metals, where Y represented the mole percentage of Fe(III) in the total iron (Y ≥ 50 %). FeOx-Y (support), PdCl42- (Pd source) and NaBH4 (reducing agent) were added into the organic pollutant solution containing 2,2',4,4'-tetrabromodiphenyl ether (BDE47). After the NaBH4 was added, the followed reaction realized not only the rapid in-situ preparation of a Pd-loaded FeOx-Y composite catalyst (Pd-FeOx-Y), but also the ultra-fast and complete debromination of BDE47 within 30 s. Comparing the case without adding FeOx-Y, the debromination efficiency of BDE47 was much promoted in the presence of FeOx-Y. The support-induced enhancing effect on the catalytic ability of Pd nanoparticles was improved by increasing the Fe(III) content in the support, being attributed to the much more hydroxyl groups on the support surface. Considering both the catalytic and recovery abilities of Pd-FeOx-Y, Pd-FeOx-75 was the optimal choice because it could be magnetically recovered and re-used for multiple cycles with high catalytic activities. The presently developed "catalyst preparation-pollutant degradation" one-pot system could be applied to conduct complete debromination of all the PBDEs.

Magnetic Fe-doped silicon carbide induced microwave activated persulfate for decabromodiphenyl ether removal: Mechanism and unique degradation pathway

In this work, the magnetic nanocomposite Fe@SiC was prepared by a hydrothermal method and determined by SEM, XRD, XPS, FTIR and VNA. Fe3O4 particles were loaded onto SiC with great success, and the synthesized composites had favorable microwave absorption properties. Fe@SiC was used to activate persulfate in a microwave field for the degradation of BDE209 in soil. Specifically, the synergistic interaction between microwaves and Fe@SiC showed excellent catalytic performance in activating PS to degrade BDE209 (90.1% BDE209 degradation in 15 min). The presence of •OH, O2•- and 1O2 was demonstrated based on quench trapping and EPR experiments. LC‒MS was applied to determine the intermediates and propose the possible degradation pathway for BDE209 in the MW/Fe@SiC/PS system, and it was found that BDE209 produced almost no lower brominated diphenyl ethers. Therefore, the toxicity of BDE209 was found to be reduced using toxicity assessment software. Overall, this work provides an effective approach for the degradation of BDE209 in environmental remediation.

Comparison of photocatalysis and photolysis of 2,2,4,4-tetrabromodiphenyl ether (BDE-47): Operational parameters, kinetic studies, and data validation using three modern machine learning models

Polybrominated diphenyl ethers (PBDEs) are halogenated organic compounds that are among the major pollutants of water, and there is an urgent need for their removal. This work compared the application of two techniques, i.e., photocatalytic reaction (PCR) and photolysis (PL), for 2,2,4,4- tetrabromodiphenyl ether (BDE-47) degradation. Although a limited degradation of BDE-47 was observed by photolysis (LED/N₂), photocatalytic oxidation by using TiO₂/LED/N₂ proved to be effective in the degradation of BDE-47. The use of a photocatalyst enhanced the extent of BDE-47 degradation by around 10% at optimum conditions in anaerobic systems. Experimental results were systematically validated through modeling with three new and powerful Machine Learning (ML) approaches, including Gradient Boosted Decision Tree (GBDT), Artificial Neural Network (ANN), and Symbolic Regression (SBR). Four statistical criteria (Coefficient of Determination (R²), Root Mean Square Error (RMSE), Average Relative Error (ARER), and Absolute Error (ABER)) were calculated for model validation. Among the applied models, the developed GBDT was the desirable model for predicting the remaining concentration (Ce) of BDE-47 for both processes. Total Organic Carbon (TOC) and Chemical Oxygen Demand (COD) results confirmed that BDE-47 mineralization required additional time than its degradation in both PCR and PL systems. The kinetic study demonstrated that BDE-47 degradation for both processes followed the pseudo-first-order form of the Langmuir-Hinshelwood (L-H) model. More importantly, the calculated electrical energy consumption of photolysis was shown to be ten percent higher than that for photocatalysis, possibly due to the higher irradiation time required in direct photolysis, which in turn increases electricity consumption. This study is useful in proposing a feasible and promising treatment process for the degradation of BDE-47.

Chemical reductive technologies for the debromination of polybrominated diphenyl ethers: A review

Polybrominated diphenyl ethers (PBDEs) are widely used as brominated flame retardants, which had attracted amounts of attention due to their harmful characteristics of high toxicity, environmental persistence and potential bioaccumulation. Many chemical reductive debromination technologies have been developed for the debromination of PBDEs, including photolysis, photocatalysis, electrocatalysis, zero-valent metal reduction, chemically catalytic reduction and mechanochemical method. This review aims to provide information about the degradation thermodynamics and kinetics of PBDEs and summarize the degradation mechanisms in various systems. According to the comparative analysis, the rapid debromination to generate bromine-free products in an electron-transfer process, of which photocatalysis is a representative one, is found to be relatively difficult, because the degradation rate of PBDEs depended on the Br-rich phenyl ring with the lowest unoccupied molecular orbital (LUMO) localization. On the contrary, the complete debromination occurs easily in other systems with active hydrogen atoms as the main reactive species, such as chemically catalytic reduction systems. The review provides the knowledge on the chemical reductive technique of PBDEs, which would greatly help not only clarify the degradation mechanism but also design the more efficient system for the rapid and deep debromination of PBDEs in the future.

Application of Photocatalysis and Sonocatalysis for Treatment of Organic Dye Wastewater and the Synergistic Effect of Ultrasound and Light

Organic dyes play vital roles in the textile industry, while the discharge of organic dye wastewater in the production and utilization of dyes has caused significant damage to the aquatic ecosystem. This review aims to summarize the mechanisms of photocatalysis, sonocatalysis, and sonophotocatalysis in the treatment of organic dye wastewater and the recent advances in catalyst development, with a focus on the synergistic effect of ultrasound and light in the catalytic degradation of organic dyes. The performance of TiO₂-based catalysts for organic dye degradation in photocatalytic, sonocatalytic, and sonophotocatalytic systems is compared. With significant synergistic effect of ultrasound and light, sonophotocatalysis generally performs much better than sonocatalysis or photocatalysis alone in pollutant degradation, yet it has a much higher energy requirement. Future research directions are proposed to expand the fundamental knowledge on the sonophotocatalysis process and to enhance its practical application in degrading organic dyes in wastewater.

Selected dechlorination of triclosan by high-performance g-C3N4/Bi2MoO6 composites: Mechanisms and pathways

Environmental-friendly and efficient strategies for triclosan (TCS) removal have received more attention. Influenced by COVID-19, a large amount of TCS contaminants were accumulated in medical and domestic wastewater discharges. In this study, a unique g-C₃N₄/Bi₂MoO₆ heterostructure was fabricated and optimized by a novel and simple method for superb photocatalytic dechlorination of TCS into 2-phenoxyphenol (2-PP) under visible light irradiation. The as-prepared samples were characterized and analyzed by XRD, BET, SEM, XPS, etc. The rationally designed g-C₃N₄/Bi₂MoO₆ (4:6) catalyst exhibited notably photocatalytic activity in that more than 95.5% of TCS was transformed at 180 min, which was 3.6 times higher than that of pure g-C₃N₄ powder. This catalyst promotes efficient photocatalytic electron-hole separation for efficient dechlorination by photocatalytic reduction. The samples exhibited high recyclable ability and the dechlorination pathway was clear. The results of Density Functional Theory calculations displayed the TCS dechlorination selectivity has different mechanisms and hydrogen substitution may be more favorable than hydrogen abstraction in the TCS dechlorination hydrogen transfer process. This work will provide an experimental and theoretical basis for designing high-performance photocatalysts to construct the systems of efficient and safe visible photocatalytic reduction of aromatic chlorinated pollutants, such as TCS in dechlorinated waters.

Aerobic Degradation Characteristics and Mechanism of Decabromodiphenyl Ether (BDE-209) Using Complex Bacteria Communities

Complex bacteria communities that comprised Brevibacillus sp. (M1) and Achromobacter sp. (M2) with effective abilities of degrading decabromodiphenyl ether (BDE-209) were investigated for their degradation characteristics and mechanisms under aerobic conditions. The experimental results indicated that 88.4% of 10 mg L^-1 BDE-209 could be degraded after incubation for 120 h under the optimum conditions of pH 7.0, 30 °C and 15% of the inoculation volume, and the addition ratio of two bacterial suspensions was 1:1. Based on the identification of BDE-209 degradation products via liquid chromatography-mass spectrometry (LC-MS) analysis, the biodegradation pathway of BDE-209 was proposed. The debromination, hydroxylation, deprotonation, breakage of ether bonds and ring-opening processes were included in the degradation process. Furthermore, intracellular enzymes had the greatest contribution to BDE-209 biodegradation, and the inhibition of piperyl butoxide (PB) for BDE-209 degradation revealed that the cytochrome P450 (CYP) enzyme was likely the key enzyme during BDE-209 degradation by bacteria M (1+2). Our study provided alternative ideas for the microbial degradation of BDE-209 by aerobic complex bacteria communities in a water system.

An updated review on environmental occurrence, scientific assessment and removal of brominated flame retardants by engineered nanomaterials

Due to the extensive manufacturing and use of brominated flame retardants (BFRs), they are known to be hazardous, bioaccumulative, and recalcitrant pollutants in various environmental matrices. BFRs make flame-resistant items for industrial purposes (textiles, electronics, and plastics equipment) that are disposed of in massive amounts and leak off in various environmental matrices. The consumption of plastic items has expanded tremendously during the COVID-19 pandemic which has resulted into the increasing load of solid waste on land and water. Some BFRs, such as polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCDs), are no longer utilized or manufactured owing to their negative impacts, which promotes the utilization of new BFRs as alternatives. BFRs have been discovered worldwide in soil, sludge, water, and other contamination sources. Various approaches such as photocatalysis-based oxidation/reduction, adsorption, and heat treatment have been found to eradicate BFRs from the environment. Nanomaterials with unique properties are one of the most successful methodologies for removing BFRs via photocatalysis. These methods have been praised for being low-cost, quick, and highly efficient. Engineered nanoparticles degraded BFRs when exposed to light and either convert them into safer metabolites or completely mineralize. Scientific assessment of research taking place in this area during the past five years has been discussed. This review offers comprehensive details on environmental occurrence, toxicity, and removal of BFRs from various sources. Degradation pathways and different removal strategies related to data have also been presented. An attempt has also been made to highlight the research gaps prevailing in the current research area.

Enhanced photocatalytic performance over PANI/NH2-MIL-101(Fe) with tight interfacial contact

Constructing a suitable heterojunction structure while maintaining a tight interface to promote the separation of photogenerated electrons is of great significance for improving the photocatalytic activity. In this paper, a new PANI/NH₂-MIL-101(Fe) II-scheme heterojunction was prepared by a hydrothermal method. PANI with a porous structure was firstly obtained by the template method, and then PANI fragments were loaded on the surface of NH₂-MIL-101(Fe) crystals under hydrothermal conditions to obtain a PANI/NH₂-MIL-101(Fe) photocatalyst. The photocatalytic degradation of TC under simulated sunlight can reach 90% within an hour, and the maximum hydrogen evolution rate is 7040 μmol g^-1 h^-1 under visible light. The enhanced catalytic performance of PANI/NH₂-MIL-101(Fe) was attributed to the appropriate matching of the VB and CB of PANI and NH₂-MIL-101(Fe), and secondly, the coordination bonds formed between PANI and NH₂-MIL-101(Fe) provided a channel for charge separation and transfer. Finally, a possible mechanism of the photocatalytic system was proposed through a free radical capture experiment and characterization analysis. More importantly, the experiment proved that the heterojunction formed by PANI and NH₂-MIL-101(Fe) can achieve the effect of complementing each other, which provides a feasible idea and method for the design of efficient heterojunction photocatalysts.

Current Developments in the Effective Removal of Environmental Pollutants through Photocatalytic Degradation Using Nanomaterials

Photocatalysis plays a prominent role in the protection of the environment from recalcitrant pollutants by reducing hazardous wastes. Among the different methods of choice, photocatalysis mediated through nanomaterials is the most widely used and economical method for removing pollutants from wastewater. Recently, worldwide researchers focused their research on eco-friendly and sustainable environmental aspects. Wastewater contamination is one of the major threats coming from industrial processes, compared to other environmental issues. Much research is concerned with the advanced development of technology for treating wastewater discharged from various industries. Water treatment using photocatalysis is prominent because of its degradation capacity to convert pollutants into non-toxic biodegradable products. Photocatalysts are cheap, and are now emerging slowly in the research field. This review paper elaborates in detail on the metal oxides used as a nano photocatalysts in the various type of pollutant degradation. The progress of research into metal oxide nanoparticles, and their application as photocatalysts in organic pollutant degradation, were highlighted. As a final consideration, the challenges and future perspectives of photocatalysts were analyzed. The application of nano-based materials can be a new horizon in the use of photocatalysts in the near future for organic pollutant degradation.

Photodegradation of Decabrominated Diphenyl Ether in Soil Suspensions: Kinetics, Mechanisms and Intermediates

Pollution by polybrominated diphenyl ethers (PBDEs) is a major concern due to their bioaccumulation, persistence, and carcinogenicity. This study aimed to investigate the decabrominated diphenyl ether (BDE-209) photodegradation in soil suspensions. The results indicate BDE-209 can degrade in soil suspensions and its degradation follows pseudo-first-order kinetics. The light sources and intensity effects were studied and the photodegradation rates were 500 W Mercury Lamp > 300 W Mercury Lamp > 500 W Xenon Lamp > 300 W Xenon Lamp, which indicates UV light is the main reason for BDE-209 degradation. Soil particle inhibits BDE-209 photodegradation due to the light-shielding effect. BDE-209 photodegradation rates increased from 0.055 to 0.071 h−1 with pH value increasing from 3.5 to 9.5. This may be because the products are more easily produced in higher pH soil suspensions. The presence of humic acid (HA) may inhibit BDE-209 photodegradation by photo-shielding. Fe3+ and Cu2+ have an adverse effect on BDE-209 photodegradation due to the photo competition. The •OH and 1O2 were detected in soil solutions. Analysis of the photoproducts of BDE-209 by gas chromatography mass spectrometry (GC-MS) and liquid chromatography time of flight mass spectrometry (LC-TOF-MS) showed that BDE-209 was mainly debrominated to the lower-brominated BDEs and the reactive oxygen radicals may not lead to BDE-209 degradation.

Novel strategies for 2,8-dichlorodibenzo-p-dioxin degradation using ternary Au-modified iron doped TiO2 catalysts under UV-vis light illumination

Polychlorinated dibenzo-p-dioxins (PCDDs), characterized by their extreme toxicity, high persistency and bioaccumulation, regard as one of the most concerned environmental pollutants on the priority list. In this study, microwave-hydrothermal and photoreduction methods were adopted for fabrication of ternary Au@Fe/TiO₂ composites for removal of 2,8-dichlorodibenzo-p-dioxin (2,8-DCDD) under UV-Vis light irradiation. The acquired materials were characterized and analyzed by XRD, TEM, XPS, UV-Vis DRS, PL, etc. As a result, the 1%Au@1%Fe/TiO₂ exhibited much higher photocatalytic activity that 96.3% of 2,8-DCDD was removed within 160 min with respect to that of Fe/TiO₂ (3.0 times) and TiO₂ (5.5 times). It revealed the active substances might be produced, which were verified by ESR analysis. In a comparison, the 1%Au@1%Fe/TiO₂ also exhibited high activity in that 97.2% of 2,8-DCDD was removed within 240 min under an anoxic atmosphere. The 1%Au@1%Fe/TiO₂ systems were all pH-dependent that 2,8-DCDD could be fully degraded in neutral conditions. The results of repeatability on 1%Au@1%Fe/TiO₂ showed that the sample was high stability. Fe doping improved the charge separation of TiO₂ and Au modification improved the activity via SPR effect and Mott-Schottky barrier. The degradation mechanisms and pathways were proposed and discussed in detail. The current work develops a new approach on photocatalytic oxidation and reductive dechlorination of dioxins and may open a new opportunity to extend the application range of TiO₂ catalysts.

Effects of ferric ion on the photo-treatment of nonionic surfactant Brij35 washing waste containing 2,2',4,4'-terabromodiphenyl ether

The effects of ferric iron on the photo-treatment of simulated BDE-47 (2,2',4,4'- terabromodiphenyl ether)-Brij35 (Polyoxyethylene lauryl ether) washing waste were studied to evaluate the influences of ferric iron on BDE-47 removal and Brij35 recovery. The results show that Fe³⁺ accelerated BDE-47 degradation at lower concentrations (<0.5 mM) but attenuated it at higher concentrations (0.5-5 mM) and that Brij35 loss was increased with increasing Fe³⁺. These results likely are caused by changes in the rate of •OH production due to the ferric ion, association of Fe³⁺ and electron transfer from Brij35, and light attenuation at high concentration. The BDE-47 and Brij35 had different degradation rates at different pH values and at different dissolved oxygen concentrations. The BDE-47 products were identified by gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS). The results indicated that BDE-47 transformed into mainly lower-brominated products, a few bromodibenzofurans, some rearrangement products, and some hydroxylated polybrominated diphenyl ethers. A series of Brij35 oxidization products were detected by ultra-performance liquid chromatography-high resolution mass spectrometry (UPLC-HRMS), including hydroxylation products, carboxylation products, and some hydrophilic chain-breaking products. Brij35 was mainly oxidized by Fe³⁺ and/or reactive oxygen species (ROS) with the final products of CO₂ and H₂O. The iron ions apparently cycled from ferric to ferrous ions in the micelles such that the Fe³⁺-Brij35 complex dominated the main redox reaction, leading to both BDE-47 and Brij35 degradation. It appears that in any applied soil washing system, the ferric ions in the washing waste need to be removed because of the adverse effects on BDE-47 removal and eluate reuse.

Ecotoxico Linking of Phthalates and Flame-Retardant Combustion Byproducts with Coral Solar Bleaching

Persian Gulf coral reefs are unique biota communities in the global sunbelts in being able to survive in multiple stressful fields during summertime (>36 °C). Despite the high-growth emerging health-hazard microplastic additive type of contaminants, its biological interactions with coral-algal symbiosis and/or its synergistic effects linked to solar-bleaching events remain unknown. This study investigated the bioaccumulation patterns of polybrominated diphenyl ether (PBDE) and phthalate ester (PAE) pollutants in six genera of living/bleached corals in Larak Island, Persian Gulf, and their ambient abiotic matrixes. Results showed that the levels of ∑₁₈PBDEs and ∑₁₃PAEs in abiotic matrixes followed the order of SPMs > surface sediments > seawater, and the cnidarian POP-uptake patterns (soft corals > hard corals) were as follows: coral mucus (138.49 ± 59.98 and 71.57 ± 47.39 ng g^-1 dw) > zooxanthellae (82.05 ± 28.27 and 20.14 ± 12.65 ng g^-1 dw) ≥ coral tissue (66.26 ± 21.42 and 34.97 ± 26.10 ng g^-1 dw) > bleached corals (45.19 ± 8.73 and 13.83 ± 7.05 ng g^-1 dw) > coral skeleton (35.66 ± 9.58 and 6.47 ± 6.47 ng g^-1 dw, respectively). Overall, findings suggest that mucus checking is a key^/facile diagnostic approach for fast detection of POP bioaccumulation (PB) in tropical corals. Although studied corals exhibited no consensus concerning hazardous levels of PB (log BSAF < 3.7), our bleaching evidence showed soft corals as the ultimate "summer winners" due to their flexibility/recovering ability.

Current progress in degradation and removal methods of polybrominated diphenyl ethers from water and soil: A review

The widespread of polybrominated diphenyl ethers (PBDEs) in the environment has caused rising concerns, and it is an urgent endeavor to find a proper way for PBDEs remediation. Various techniques such as adsorption, hydrothermal and thermal treatment, photolysis, photocatalytic degradation, reductive debromination, advanced oxidation processes (AOPs) and biological degradation have been developed for PBDEs decontamination. A comprehensive review of different PBDEs remediation techniques is urgently needed. This work focused on the environmental source and occurrence of PBDEs, their removal and degradation methods from water and soil, and prospects for PBDEs remediation techniques. According to the up-to-date literature obtained from Web of Science, it could be concluded that (i) photocatalysis and photocatalytic degradation is the most widely reported method for PBDEs remediation, (ii) BDE-47 and BDE-209 are the most investigated PBDE congeners, (iii) considering the recalcitrance nature of PBDEs and more toxic intermediates could be generated because of incomplete degradation, the combination of different techniques is the most potential solution for PBDEs removal, (iv) further researches about the development of novel and effective PBDEs remediation techniques are still needed. This review provides the latest knowledge on PBDEs remediation techniques, as well as future research needs according to the up-to-date literature.

TiO2 Doped with Noble Metals as an Efficient Solution for the Photodegradation of Hazardous Organic Water Pollutants at Ambient Conditions

This work highlights new insights into the performance of TiO2 doped with noble metal catalysts for the photocatalytic degradation of organic water pollutants. Different samples of titanium dioxide doped with noble metals (Au and Pd) were successfully synthesized via incipient wet impregnation (IWI) and ultrasound-assisted impregnation (US) methods. X-ray diffraction, scanning electron microscopy and UV-Vis reflectance spectroscopy were used for the characterization of the obtained materials. Their photocatalytic efficiency was investigated in aqueous suspension thorough a series of laboratory tests performed under ultraviolet (UV-A) irradiation conditions using 2,4 dinitrophenol (2,4 DNP) as a target molecule. The results clearly show that the method used for the catalyst synthesis affects its photocatalytic activity. It was found that the samples prepared by the IWI method exhibited high photocatalytic activity, and the removal rate obtained with TiO2-Pd/IWI was higher than that found for TiO2-Au/IWI. Furthermore, for the best catalyst, some extra photocatalytic experiments were conducted with rhodamine 6G (R6G), a highly stable molecule with a very different chemical structure to 2,4 DNP, in order to check the reactivity of this material. Moreover, the recycling experiments carried out with TiO2-Pd/IWI clearly demonstrated the high photocatalytic stability of this material for the degradation of 2,4 DNP. All of the collected data confirmed the interesting photocatalytic potential of the selected catalyst in the elimination of organic pollutants with no obvious change in its reactivity after four reaction cycles, which is very promising for promoting future applications in water depollution.

Degradation of 2, 2', 4, 4'-Tetrabrominated diphenyl ether (BDE-47) via the Fenton reaction driven by the dissimilatory metal-reducing bacterium Shewanella oneidensis MR-1

A microbially facilitated approach was developed to degrade 2, 2', 4, 4'-tetrabrominated diphenyl ether (BDE-47). This approach consisted of biological production of Fe(II) and H₂O₂ by the dissimilatory metal-reducing bacterium Shewanella oneidensis MR-1 during the repetitive anoxic/oxic cycles and abiotic production of hydroxyl radical (HO^●) with the biologically produced Fe(II) and H₂O₂ via Fenton reaction. Under the condition tested, BDE-47 did not inhibit the growth of S. oneidensis MR-1. Water soluble Fe(III)-citrate and the solid minerals ferrihydrite [Fe(III)₂O₃•0.5H₂O] and goethite [Fe(III)OOH] were tested in this study. Under anoxic condition, the amounts of Fe(II) produced by S. oneidensis MR-1 varied among the Fe(III)s tested, which decreased in the order of Fe(III)-citrate > ferrihydrite > goethite. Under subsequent oxic condition, H₂O₂ was produced via O₂ reduction by S. oneidensis MR-1. The amounts of H₂O₂ detected also varied, which decreased in the order of the reactions with Fe(III)-citrate > goethite > ferrihydrite. S. oneidensis MR-1 maintained its ability to produce Fe(II) and H₂O₂ for up to seven anoxic/oxic cycles. At each end of anoxic/oxic cycle, HO^● was detected. The amount of HO^● produced decreased in the order of the reactions with ferrihydrite > goethite > Fe(III)-citrate, which was opposite to that of H₂O₂ detected. Compared to the controls without HO^●, the amounts of BDE-47 in the reactions with HO^● decreased. The more HO^● in the reaction, the less amount of BDE-47 detected. Furthermore, no BDE-47 degradation was observed when HO^● was scavenged or ferrihydrite was either omitted or replaced by nitrate. Finally, identification of degradation products, such as hydroxylated BDE-47 and trisBDE, dibromophenol and monobromophenol, suggested that OH-addition and Br-substitution by HO^● were the main mechanisms for degrading BDE-47. Collectively, all these results demonstrated for the first time that the Fenton reaction driven by S. oneidensis MR-1 degraded BDE-47 effectively.

Photoassisted degradation of 2,2',4,4'-tetrabrominated diphenyl ether in simulated soil washing system containing Triton X series surfactants

This study aims to use ultraviolet (UV) irradiation to decompose polybrominated diphenyl ethers (PBDEs) in the elutes and then reuse the surfactants. The results indicate that UV can remove 2,2',4,4'-tetrabrominated diphenyl ether (BDE-47) from surfactant eluents and Triton X series surfactants also can remove BDE-47 from the soil. Triton X-100 (TX-100) is the most promising surfactant during the washing and photodegradation processes. Quench experiments suggest that both ¹O₂ and OH• were involved in the TX-100 decomposition but only ¹O₂ is responsible for the degradation of BDE-47. In analysis of the photoproducts of BDE-47 by Gas Chromatography Mass Spectrum (GC-MS) and Liquid Chromatography High Resolution Mass Spectrometry (LC-HRMS), BDE-47 was mainly debrominated to the lower-brominated BDEs and then oxidized to ring-opening products. The little loss of TX-100 can mainly be attributed to the breakage of polyethylene oxide (PEO) chain. Nevertheless, the washing wastes treated by UV light can exhibit higher solubility for BDE-47 than before, indicating they can be reused for BDE-47 removal from soil. The toxicity assessment experiments were performed using Escherichia coli (E.coli) as an indicator. The results indicate that the removal of BDE-47 by UV irradiation can reduce the toxicity of eluent.

Recent advances in the removal of persistent organic pollutants (POPs) using multifunctional materials:a review

Persistent organic pollutants (POPs) have gained heightened attentions in recent years owing to their persistent property and hazard influence on wild life and human beings. Removal of POPs using varieties of multifunctional materials have shown a promising prospect compared with conventional treatments. Herein, three main categories, including thermal degradation, electrochemical remediation, as well as photocatalytic degradation with the use of diverse catalytic materials, especially the recently developed prominent ones were comprehensively reviewed. Kinetic analysis and underlying mechanism for various POPs degradation processes were addressed in detail. The review also systematically documented how catalytic performance was dramatically affected by the nature of the material itself, the structure of target pollutants, reaction conditions and treatment techniques. Moreover, the future challenges and prospects of POPs degradation by means of multiple multifunctional materials were outlined accordingly. Knowing this is of immense significance to enhance our understanding of POPs remediation procedures and promote the development of novel multifunctional materials.

Evaluation of the Performance of Low-Cost Air Quality Sensors at a High Mountain Station with Complex Meteorological Conditions

Low-cost sensors have become an increasingly important supplement to air quality monitoring networks at the ground level, yet their performances have not been evaluated at high-elevation areas, where the weather conditions are complex and characterized by low air pressure, low temperatures, and high wind speed. To address this research gap, a seven-month-long inter-comparison campaign was carried out at Mt. Tai (1534 m a.s.l.) from 20 April to 30 November 2018, covering a wide range of air temperatures, relative humidities (RHs), and wind speeds. The performance of three commonly used sensors for carbon monoxide (CO), ozone (O3), and particulate matter (PM2.5) was evaluated against the reference instruments. Strong positive linear relationships between sensors and the reference data were found for CO (r = 0.83) and O3 (r = 0.79), while the PM2.5 sensor tended to overestimate PM2.5 under high RH conditions. When the data at RH >95% were removed, a strong non-linear relationship could be well fitted for PM2.5 between the sensor and reference data (r = 0.91). The impacts of temperature, RH, wind speed, and pressure on the sensor measurements were comprehensively assessed. Temperature showed a positive effect on the CO and O3 sensors, RH showed a positive effect on the PM sensor, and the influence of wind speed and air pressure on all three sensors was relatively minor. Two methods, namely a multiple linear regression model and a random forest model, were adopted to minimize the influence of meteorological factors on the sensor data. The multi-linear regression (MLR) model showed a better performance than the random forest (RF) model in correcting the sensors’ data, especially for O3 and PM2.5. Our results demonstrate the capability and potential of the low-cost sensors for the measurement of trace gases and aerosols at high mountain sites with complex weather conditions.