Degradation Of Persistent Organic Pollutants Research Articles

Preparing a photocatalytic Fe doped TiO2/rGO for enhanced bisphenol A and its analogues degradation in water sample

For extending the light response to visible spectrum, an approach to efficient photocatalysts in sustainable energy technology has been a hot research topic. In this work, Fe doped TiO2/rGO (Fe-TiO2/rGO) was synthesized via one-step hydrothermal deposition method. The presence of Fe-Ti bond and Ti3+ in the photocatalyst was confirmed by XPS, EXAFS and Raman analyses. The batch experiments showed that as-synthesized Fe-TiO2/rGO nanocomposites exhibited high photocatalytic performance for bisphenol A (BPA) and its analogues degradation under visible light irradiation (λ ≥ 420 nm). Moreover, Fe-TiO2/rGO presented high photocatalytic activity at a high BPA concentration of 95 ppm as well as a wide pH value of 4.5–8.5. Additionally, the extended visible light absorption range Fe-TiO2/rGO was demonstrated by low temperature electron spin resonance, UV–vis diffuse reflectance spectra, the transient photocurrent density and electrochemical impedance spectroscopies measurements. The radical quenching and ESR active species trapping experiments implied the main role of superoxide radicals on the high efficient photodegradation of BPA. These findings are crucial for designing TiO2-based photocatalysts with high performance for degradation of persistent organic pollutants in wastewater treatment.

Construction of magnetic bifunctional β-cyclodextrin nanocomposites for adsorption and degradation of persistent organic pollutants

Herein, we report a novel magnetic bifunctional β-cyclodextrin nanocomposite (Fe3O4@β-CD-CDI) based on metal coordination, which may be used for adsorption and degradation of persistent organic pollutants in aqueous solution. More importantly, N,N’-carbonyldiimidazole (CDI) functionalized β-CD ligand (β-CD-CDI) was assembled on the surface of Fe3O4 by Zn-N interaction. The results of kinetic and isothermal adsorption model investigation indicated that the adsorption rate and capacity of Fe3O4@β-CD-CDI were better than other materials, suggesting the effective accessibility of adsorption sites. We further confirmed that Fe3O4@β-CD-CDI can be used as heterogeneous catalyst to remove BPA through Fenton-like reaction in the presence of hydrogen peroxide (H2O2). Moreover, the material effectively alleviated the secondary pollution owing to the existence of β-CD inner cavity. This study indicated that the magnetic Fe3O4@β-CD-CDI material has great potential applications in wastewater purification containing persistent organic pollutants.

Adsorption enhanced photocatalytic degradation sulfadiazine antibiotic using porous carbon nitride nanosheets with carbon vacancies

Residues of antibiotics are promoting antibiotic resistance of environmental microbiota which is identified as one of the most crucial global challenge for health security. Photocatalysis has been regarded as a desirable technology for organic pollutant removal, but is underappreciated in degradation of persistent organic pollutants due to the low adsorption capacity and photocatalytic efficiency of photocatalysts. In this study, a scalable photocatalyst of single/few-layered carbon nitride nanosheets with carbon vacancies (Cv-CNNs) is synthesized through a thermal process. Quantum mechanical simulation results reveal that the C vacancies can change the plane structure of CN sheets, enhancing adsorption capability of Cv-CNNs towards sulfadiazine (SDZ, a refractory antibiotic pollutant). Furthermore, the introduction of C vacancies in Cv-CNNs enhance the redox capacity, promoting photocatalytic hydrogen evolution and SDZ degradation. The removal efficiency of SDZ (5 mg L−1) reaches almost 100% within 20 min under visible-light irradiation. In addition, the photocatalyst delivers a high H2 evolution rate of 2.03 mmol h−1 g−1. The study provides a large-scale-production metal-free photocatalyst for practical application in antibiotics removal from wastewater or solar-to-hydrogen energy conversion.

Electrosynthesis of Hydrogen Peroxide in a Novel Flow-through Electrochemical Reactor with in Situ generated Oxygen

Most of electrochemical advanced oxidation processes (EAOP´s) such as the electroFenton (EF), photo electroFenton (PEF), solar photo electroFenton (SPEF) and electro-peroxone (E-peroxone) processes use hydrogen peroxide (H2O2) as its core reactant due to its possibility to react with some catalysts (Fe2+, O3) yielding high oxidant hydroxyl radicals to be used in the degradation of persistent organic pollutants [1]. Carbonaceous materials like carbon felt, carbon cloth and reticulated vitreous carbon (RVC) are the most used because of its capability to accumulate H2O2 [2,3]. The use of these materials is often in gas diffusion electrodes which are based in the injection of air from an external source to an air chamber located behind the electrode allowing the dispersion of the gas inside the electrode promoting the oxygen reduction [3]. This work deals with the in situ electrosynthesis of H2O2 in a flow through reactor using RVC as cathode material and Ti|Ir-Ta oxides expanded mesh as anode to improve the oxygen evolution reaction with subsequent reduction of O2 on the RVC to yield H2O2. The electrochemical cell consists of a flow channel where the electrodes are placed along its length, allowing the electrolyte to flow through them forcing the transport of oxygen bubbles inside the porous carbon material for its reduction to H2O2. [1] Sirés I., Brillas., E. Remediation of water pollution caused by pharmaceutical residues sed on electrochemical separation and degradation technologies: A review. Environmental International, 40 (2018) 212-229. [2] Coria G., Pérez T., Sirés I., Nava J.L., Mass transport studies during dissolved oxygen reduction to hydrogen peroxide in a filter-press electrolyzer using graphite felt, reticulated vitreous carbon and boron-doped diamond as cathodes. Journal of Electroanalytical Chemistry, 757 (2015) 225-229. [3] Pérez T., Coria G., Sirés I., Nava J.L., Uribe A.R., Electrosynthesis of hydrogen peroxide in a filter-press flow cell using graphite felt as air-diffusion cathode. Journal of Electroanalytical Chemistry, 812 (2018) 54-58.

Highly active WO3@anatase-SiO2 aerogel for solar-light-driven phenanthrene degradation: Mechanism insight and toxicity assessment

The global energy crisis and water pollution drive the researchers to develop highly effective and less energy intensive water purification technologies. In this study, a highly active WO3@TiO2–SiO2 nanocomposite was synthesized and used for photocatalytic degradation of persistent organic pollutants under simulated solar light. The optimum WO3@TiO2–SiO2 prepared with 2 wt% WO3 loading and calcination at 800 °C exhibited higher photocatalytic activity, as the rate constant (k1) for phenanthrene degradation was ∼7.1 times of that for the commercial TiO2 (P25). The extremely large specific surface area (>400 m2/g) of WO3@TiO2–SiO2 afforded it with enlarged pollutants adsorption performance and abundant active surface sites. The heterojunction of anatase with SiO2 as well as loading of WO3 decreased the band gap energy (Eg) of TiO2, which extended the utilization spectrum of TiO2 to visible region. Formation of Ti–O–Si band indicated the excess charges can cause Brønsted acidity due to the absorption of protons to compensate the charges. Moreover, the migration of photo-excited electrons from the conduction band of anatase to WO3 and holes in the opposite direction restrained the electron-hole recombination. The photocatalytic degradation mechanism and pathway for phenanthrene degradation were proposed based on experimental analysis and density functional theory (DFT) calculation, and the toxicities of the degradation intermediates were evaluated by quantitative structure–activity relationship (QSAR) analysis. WO3@TiO2–SiO2 also showed good separation (settling) performance and high stability. Our work is expected to offer new insight into the photocatalytic mechanism for WO3, TiO2 and SiO2 based heterojunctions, and rational design and synthesis of highly efficient photocatalysts for environmental application.

Occurrence of both hydroxyl radical and surface oxidation pathways in N-doped layered nanocarbons for aqueous catalytic ozonation

Metal-free catalysts such as N-doped nanocarbons are sustainable alternatives to metal-based catalysts for the degradation of persistent organic pollutants (POPs), but cost-efficient methods are required for their large-scale synthesis. In this study, a facile and scalable strategy was established for synthesizing layered N-doped nanocarbons via the pyrolysis of β-cyclodextrin (β-CD) and melamine in a N2 atmosphere. Compared with undoped pyrolyzed β-CD, N-doping led to a 30.3-fold enhancement in the pseudo-first-order rate constant for catalytic ozonation of oxalic acid (OA), and complete degradation of 50 mg/L OA was achieved in 45 min. Apart from the specific surface area boosting from 78.9 to 16.2 m2/g after N doping, the OA degradation results and material characterization also suggested that quaternary N was the main active site, which was further validated by density functional theory (DFT) simulations. DFT simulations also suggested that C atoms with high charge densities adjacent to N dopants exhibited considerable potential for the catalytic dissociation of ozone. Electron paramagnetic resonance (EPR), radical quenching, and in situ Raman studies indicated occurrence of surface oxidation pathway apart from the radical-based one. Ozone on the catalyst surface was decomposed into surface-adsorbed atomic oxygen (*Oad) and free peroxide (*O2 free). Both *Oad and OH, which was further evolved on the surface or in bulk solution, contributed to OA destruction. These insights into the catalytic ozonation mechanism on N-doped nanocarbons will advance their practical application to the catalytic degradation of organic pollutants.

Using an Ultrasonic Input for Ammonium Persulfate Electrosynthesis and Advanced Oxidation Processes

The persulfate anion is a powerful oxidant that can be used for effective degradation of persistent organic pollutants. In this work, it is shown that low-power ultrasonic irradiation does not adversely affect Faradaic yields of persulfate electrosynthesis from ammonium sulfate solutions, and that a combined sono-electrochemical treatment of sulfate solutions containing exemplar pollutant naphthol blue-black provides swift degradation of dye solutions as compared to treatments where the sonochemical and electrochemical steps are performed separately. The implications for the degradation of persistent organic pollutants are discussed.

Enhanced degradation of atrazine by nanoscale LaFe1-xCuxO3-δ perovskite activated peroxymonosulfate: Performance and mechanism

Cu-doped LaFeO3 perovskite (LaFe1-xCuxO3-δ, LFCx) synthesized using a sol-gel method was introduced in the heterogeneous activation of peroxymonosulfate (PMS) for atrazine degradation. The obtained LFCx catalysts were characterized by several technologies and the results showed that Cu was incorporated into the perovskites lattice successfully. In addition, the introduction of Cu resulted in the mixed valence state of Fe(III)/Fe(II) and Cu(II)/Cu(I) in perovskite structure. LaFe0.8Cu0.2O3-δ (LFC0.2) exhibited excellent catalytic activity and stability towards the degradation of atrazine. Atrazine (23 μM) was removed completely within 60 min in the presence of 0.5 g/L catalyst and 0.5 mM PMS. The efficient degradation was obtained when the initial pH ranged from 2 to 10. Sulfate radicals (SO4•-) and hydroxyl radicals (HO•) generated during activation process were determined as the main reactive species based on the electron spin resonance (ESR) studies and radical quenching experiments. The enhanced catalytic activity derived from the lower valence state of Fe and Cu as well as the synergetic effect between them. A surface catalyzed-redox cycle between Fe(III)/Fe(II) and Cu(II)/Cu(I), along with surface hydroxyl groups (-OH), were all responsible for the decomposition of PMS. The oxygen vacancies could promote the chemical bonding with PMS and enhance the reactivity of Fe and Cu. The 12 transformation products were determined by LC-MS and the degradation mechanisms were further proposed, which involved five different pathways. The perovskite that possesses bimetallic active sites can be a promising catalyst for PMS activation towards the degradation of persistent organic pollutants with high-efficiency.

Enhanced Perfluorooctanoic Acid Degradation by Electrochemical Activation of Sulfate Solution on B/N Codoped Diamond.

Electrochemical oxidation based on SO4•- and •OH generated from sulfate electrolyte is a cost-effective method for degradation of persistent organic pollutants (POPs). However, sulfate activation remains a great challenge due to lack of active and robust electrodes. Herein, a B/N codoped diamond (BND) electrode is designed for electrochemical degradation of POPs via sulfate activation. It is efficient and stable for perfluorooctanoic acid (PFOA) oxidation with first-order kinetic constants of 2.4 h-1 and total organic carbon removal efficiency of 77.4% (3 h) at relatively low current density of 4 mA cm-2. The good activity of BND mainly originates from a B and N codoping effect. The PFOA oxidation rate at sulfate electrolyte is significantly enhanced (2.3-3.4 times) compared with those at nitrate and perchlorate electrolytes. At sulfate, PFOA oxidation rate decreases slightly in the presence of •OH quencher while it declines significantly with SO4•- and •OH quenchers, indicate both SO4•- and•OH contribute to PFOA oxidation but SO4•- contribution is more significant. On the basis of intermediates analysis, a proposed mechanism for PFOA degradation is that PFOA is oxidized to shorter chain perfluorocarboxylic acids gradually by SO4•- and •OH until it is mineralized.

Efficient Photocatalytic Fuel Cell via Simultaneous Visible-Photoelectrocatalytic Degradation and Electricity Generation on a Porous Coral-like WO3/W Photoelectrode.

Photocatalytic fuel cells (PFCs) have proven to be effective for generating electricity and degrading pollutants with a goal to resolve environmental and energy problems. However, the degradation of persistent organic pollutants (POPs), such as perfluorooctanoic acid (PFOA), remains challenging. In the present work, a porous coral-like WO3/W (PCW) photoelectrode with a well-designed energy band structure was used for the photoelectrocatalytic degradation of POPs and the simultaneous generation of electricity. The as-constructed bionic porous coral-like nanostructure greatly improved the light-harvesting capacity of the PCW photoelectrode. A maximum photocurrent density (0.31 mA/cm2) under visible light (λ > 420 nm) irradiation and a high incident photon conversion efficiency (IPCE) value (5.72% at 420 nm) were achieved. Because of the unique porous coral-like structure, the suitable energy band position, and the strong oxidation ability, this PCW photoelectrode-based PFC system exhibited a strong ability for simultaneous photoelectrocatalytic degradation of PFOA and electricity generation under visible-light irradiation, with a power output of 0.0013 mV/cm2 using PFOA as the fuel. This work provides a promising way to construct a reliable PFC using highly toxic POPs to generate electricity.

Continuous rapid dechlorination of p-chlorophenol by Fe-Pd nanoparticles promoted by procyanidin

Nanoscale zero-valent iron has been widely applied in environmental remediation and toxic waste treatment, especially for the degradation of persistent organic pollutants (POPs). However, the dechlorination activity of Fe nanoparticles (Fe NPs) can be suppressed by the precipitation of iron oxides generated from the corrosion of Fe-Pd NPs under alkaline conditions, leading to a decreased dechlorination efficiency. Faced with this challenge, we report a highly effective dechlorination system that functions over a broad pH range and especially well under alkaline conditions in this work. Procyanidin (PROC), a natural polyphenol, was utilized as a stabilizer to manipulate the size distribution of Fe-Pd NPs and, more importantly, as a scavenger of Fe ions to prevent iron oxide precipitation. Experiments and theoretical calculations reveal that the generated Fe ions was mainly present in the form of bis- and tris-PROC-Fe complexes in the reaction solution. Compared with pristine Fe-Pd NPs, the PROC-modified Fe-Pd NPs had a dechlorination efficiency that was increased 20-fold (pH 9.0). Notably, a normalized rate constant was enhanced by more than 2 orders of magnitude compared to the previously reported dechlorination systems. The PROC-modified Fe-Pd NPs showed excellent dechlorination efficiency over a wide pH range (2.3–13.0).

Polyionic Resin Supported Pd/Fe2O3Nanohybrids for Catalytic Hydrodehalogenation: Improved and Versatile Remediation for Toxic Pollutants

A series of Pd/Fe2O3 nanohybrids with low metal content supported with Amberlite resin formate (Pd/Fe2O3@ARF) was prepared and characterized by FTIR, XRD, XPS, EELS, SEM–EDAX, and HRTEM. The coexistence of mainly crystalline Pd and Fe2O3 nanoparticles (NPs) of average size ∼4–5 nm in the resin matrix was confirmed. These nanohybrids were used for hydrodehalogenation of polyhaloaromatics using NaBH4 as a reducing agent in water. Notably, the composite Pd/Fe2O3@ARF-110 exhibits excellent catalytic performance in the hydrodehalogenation of different haloaromatics. High TOF (in comparison to other related heterogeneous catalysts), recyclability, and chemoselectivity between halide and C═C bond make this nanohybrid catalyst very attractive for the degradation of persistent organic pollutants originated from industries. The experimental observations and other analytical studies suggest that the enhanced catalytic activity could be due to strong interactions between Fe2O3 and Pd NPs that facilitate the cleavage ...

Recent developments in fabrication and structure regulation of visible-light-driven g-C3N4-based photocatalysts towards water purification: A critical review

Graphitic carbon nitride (g-C3N4), a conjugated polymer semiconductor, has drawn increasing attention in environmental photocatalysis over the past decade, owing to its highly chemical stability, low cost and suitable electronic structure with a mild energy gap (∼ 2.7 eV). Whereas, its practical applications in wastewater purification are still faced with huge challenges, such as insufficient visible light absorption, low electronic conductivity, poor surface area and fast recombination of photoinduced charge carriers. The modification of g-C3N4 by coupling with other nanomaterials or forming unique nanostructures have been confirmed as valuable strategies. In this review, we give a comprehensive introduction about the recent developments in engineering g-C3N4 by constructing heterostructures or diverse morphologies to improve its photodegradation performance for the photocatalytic degradation of persistent organic pollutants. Such heterojunctions contain metal/g-C3N4, g-C3N4/C-based material and many other binary or ternary composites, and these special morphologies normally include nanorods, nanowires, nanotubes, nanosheets, porous architectures and other different tunable nanostructures. Several enhanced photocatalytic mechanisms for these nanohybrids under visible light irradiation have been explicated in detail, and future perspectives are also concluded in this review.

Catalytic electrochemical pre-treatment for the degradation of persistent organic pollutants

Summary Electrochemical advanced oxidation processes have been widely explored for the total degradation of biorecalcitrant compounds such as some pesticides and pharmaceuticals. More recently, coupling processes involving an electrochemical pre-treatment followed by a biological process have been proposed as cost-effective and reliable remediation methods for the mineralization of persistent compounds. This open the way to more selective electrochemical methods than those involving hydroxyl radicals since the aim of the pre-treatment is no more to achieve the total mineralization of non-biodegradable species, but is only the improvement of their biodegradability focusing on functional groups known to reduce it. In this context, catalytic electrochemical reductions and oxidations can find their place in a coupling process for the remediation of biorecalcitrant compounds as selective and well-controlled methods. This review summarizes some relevant and recent work on catalytic electrochemical processes performed in aqueous medium that have been used to improve the biodegradability of persistent organic pollutants.

Special issue: Plasma and Liquids

Special issue: Plasma and Liquids

Mechanochemical formation of chlorinated phenoxy radicals and their roles in the remediation of hexachlorobenzene contaminated soil

Mechanochemical degradation (MCD) is a promising eco-friendly method to dispose persistent organic pollutants (POPs). Mechanically induced free-radical attack was thought to be one of the key elements in initiating and accelerating the dechlorination and degradation of POPs. In this study, mechanochemical formation of free-radicals and their roles in the remediation of hexachlorobenzene (HCB) contaminated soil were explored using both of experimental analysis and quantum chemical calculations. It was found that chlorinated phenoxy radicals(CB-O) can be produced in the milling process and they played a vital role in the dechlorination of HCB, based on the results of electron spin-resonance (ESR) and X-ray photoelectron spectra (XPS). Two transition states of mechanochemical reaction along the formation of pentachlorinated phenoxy radical (PeCB-O) were located, with the energy barriers of 39.4 and 3.4 kJ/mol. The localized orbital locator (LOL), Mayer bond order and topological analysis were also implemented to depict the process in detail. Free-radical attack dominated dechlorination pathway of HCB in the MCD process was also verified by the Fukui function analysis. The study on the mechanically-induced generation of free-radicals and their associated modes of action on the degradation of HCB will provide a deep insight into mechanochemical remediation mechanism of POPs contaminated soil.

Solar light driven photocatalytic degradation of Ofloxacin based on ultra-thin bismuth molybdenum oxide nanosheets

Herein, we report the facile synthesis, characterization and solar-light driven photocatalytic degradation of ultra-thin bismuth molybdenum oxide (Bi2MoO6) nanosheets. The nanosheets were synthesized by hydrothermal process and characterized using several techniques such as powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDS), UV-diffusive reflectance spectroscopy (UV-DRS), transmission emission microscopy (TEM) and X-ray photon electron spectroscopy (XPS). The detailed morphological and structural studies confirmed the growth of ultra-thin Bi2MoO6 nanosheets in large density with orthorhombic crystal structure. The calculated bandgap energy from Tauc’s plot for the synthesized nanosheets was found to be 2.73eV, which shows maximum absorption toward higher wavelength. The XPS studies confirmed the successful formation Bi2MoO6 nanosheets. The synthesized material was used as efficient solar light driven photocatalyst for the photocatalytic degradation of Ofloxacin. The mineralization of ofloxacin was confirmed using total organic carbon (TOC) analysis and photocatalytic experiments were performed under optimized conditions. It was observed that TOC value decreased with increasing the irradiation time. Under optimized photocatalytic degradation conditions, the observed extent of degradation was found to be∼71%. The observed results confirm that the synthesized Bi2MoO6 nanosheets are efficient and promising visible light responsive catalyst for the degradation of persistent organic pollutants.

Catalytic activity enhancement of a Fe3O4@SiO2 yolk-shell structure for oxidative degradation of acetaminophen by decoration with copper

The occurrence of pharmaceuticals in the environment has received wide attention, and they have recently been considered as emerging organic contaminants. Since conventional wastewater processes are not particularly effective, the development of new technology that can completely remove pharmaceutical compounds in aquatic environments is an urgent need. Recently, iron-copper bimetallic catalysts have attracted increasing attention, and they are known as good Fenton reagents for the degradation of persistent organic pollutants. In this study, yolk-shell structured Fe3O4@SiO2 was prepared via a spontaneous self-transformation process, and it was decorated with copper nanoparticles (Fe3O4@SiO2@Cu) to produce a novel catalyst aimed at the rapid catalytic oxidation of acetaminophen in the heterogeneous Fenton reaction. Different ratios of Fe3O4 and copper were obtained by varying the precursor amounts of yolk-shell and copper salt. The catalyst properties were characterized by several techniques to verify the successful synthesis of the targeted materials. The results demonstrated that the Fe3O4@SiO2@Cu was controllably prepared, copper nanoparticles were firmly immobilized on the mesoporous silica shell, and the decoration of copper did not impact the yolk-shell structure of the precursor material. The catalytic activity of Fe3O4@SiO2@Cu was much better than that of Fe3O4@SiO2 for the degradation of acetaminophen. The catalytic performance of Fe3O4@SiO2@Cu increased with increasing copper content. Radical scavenging studies showed that •OH is the main reactive species contributing to acetaminophen degradation. In addition, the catalyst also exhibited good separation and satisfactory regeneration properties. The decoration of copper nanoparticles onto the yolk-shell structure Fe3O4@SiO2 was proved to be an attractive alternative method to obtain a novel bimetallic catalyst applied in heterogeneous Fenton-like system for the removal of persistent pharmaceuticals from wastewater.

Hydrothermal synthesis of graphene grafted titania/titanate nanosheets for photocatalytic degradation of 4-chlorophenol: Solar-light-driven photocatalytic activity and computational chemistry analysis

Graphene grafted titania/titanate nanosheets (G/TNS) were synthesized through a one-step hydrothermal treatment. The 2.0wt% grafted composite material appears as flower-like nanoscale sheets, and contains Ti crystalline phases of both anatase and sodium titanate. Graphene acted as a two-dimensional template for growth of Ti-nanosheets while inhibiting transformation of TiO2 into titanate during the hydrothermal reaction. G/TNS with 2.0wt% graphene showed the highest photocatalytic degradation rate for 4-chlorophenol, and >99.2% of removal was achieved at 120min. The pseudo-first order rate constant (k1) was determined to be 0.041min−1, which is ∼8 times higher than that of anatase and ∼21 times than unmodified TNS. The findings indicate that the grafted graphene greatly promotes the material response to visible light because: (1) it facilitates rapid transfer of photo-excited electrons, thus inhibiting recombination of the h+−e− pairs, and (2) narrowed band gap energy leading to enhanced visible light absorption. Evidently, the 2-D sheet-like structures are conducive to high electron transfer efficiency and high solar-light-driven photocatalytic activity. The OH radicals were found to be the primary reactive oxygen species for 4-CP degradation. Density functional theory (DFT) analysis indicates that the sites on 4-CP with high Fukui index (f−) can be easily attacked by OH, and the theoretical calculation results were consistent with experimentally identified 4-CP degradation pathway. In addition, G/TNS showed good reusability and >90% of 4-CP still could be removed even after 5 reuse cycles. The new composite material is promising for photocatalytic degradation of persistent organic pollutants under solar light.

Magnetite nanoparticles enhance the performance of a combined bioelectrode-UASB reactor for reductive transformation of 2,4-dichloronitrobenzene

Direct interspecies electron transfer (DIET) among the cometabolism microbes plays a key role in the anaerobic degradation of persistent organic pollutants and stability of anaerobic bioreactor. In this study, the COD removal efficiency increased to 99.0% during the start-up stage in the combined bioelectrode-UASB system (R1) with magnetite nanoparticles addition, which was higher than those in the coupled bioelectrode-UASB (R2; 83.2%) and regular UASB (R3; 71.0%). During the stable stage, the increase of 2,4-dichloronitrobenzene (2,4-DClNB) concentration from 25 mg L−1 to 200 mg L−1 did not affect the COD removal efficiencies in R1 and R2, whereas the performance of R3 was deteriorated obviously. Further intermediates analysis indicated that magnetite nanoparticles enhanced the reductive dechlorination of 2,4-DClNB. High-throughput sequencing results showed that the functional microbes like Syntrophobacter and Syntrophomonas which have been reported to favor the DIET, were predominant on the cathode surface of R1 reactor. It is speculated that the addition of magnetite nanoparticles favors the cooperative metabolism of dechlorinating microbes and electricigens during 2,4-DClNB degradation process in the combined bioelectrode-UASB reactor. This study may provide a new strategy to improve the performance of microbial electrolysis cells and enhance the pollutant removal efficiency.