Stepwise Debromination Research Articles

A Cascade Reaction Triggered by H‐H Steric Hindrance: Dimeric Covalent Organic Frameworks on Au(111) and Dimeric Nanoribbons on Ag(111)

Comprehensive SummaryIn on‐surface synthesis, dimers are typically utilized to explore reaction mechanisms or as intermediates in the formation of final products. However, constructing the innovative nanostructures with dimers as building blocks remains challenging. Here, using non‐planar 2,2′,7,7′‐tetrabromo‐9,9′‐biflurenyliden molecules, we have successfully synthesized dimeric covalent organic frameworks (COFs) on the Au(111) surface through a temperature‐controlled cascade reaction. Notably, the H‐H steric hindrance within precursors caused by double bonds leads to selective stepwise debromination during the thermal annealing, which promotes the dimerization through intermolecular Ullmann coupling and cyclodehydrogenation reaction to form COFs primarily constituted by dimer building blocks. Combining scanning tunneling microscopy/spectroscopy and density functional theory calculations, we have precisely confirmed the structural evolution and reaction mechanism. Furthermore, by introducing Ag adatoms to form C−Ag−C intermediates, we have successfully regulated the reaction path and synthesized one‐dimensional nanoribbons with dimers as building blocks. This work not only validates the strategy of synthesizing dimeric nanostructures on different surfaces through cascade reactions induced by precursor design, but also enriches the research field of surface synthesis of COFs and nanoribbons.

Computational study of mechanistic pathway and effect of zero valent metals on reductive debromination of some polybrominated biphenyls

Complete debromination of three polybrominated biphenyls (PBBs), namely 2,2′,3,3′,4,4′-hexabromobiphenyl (PBB-128), 2,2′,3,3′,4,5- hexabromobiphenyl (PBB-129) and 2,2′,3,3′,4,5′- hexabromobiphenyl (PBB-130) aided by zero valent magnesium (Mg0) andzinc (Zn0) in the presence of methanol was studied computationally using dispersion corrected ωB97XD functional with cc-pVTZ basis set. All possible debromination pathways were explored for each parent PBB and the most energetically favoured pathway was identified. Mono-debromination of each PBB afforded a two-step mechanism, viz, formation of a highly charged covalent intermediate that involves a phenyl-metal-bromine connectivity and protonation by methanol molecule.Total activation energy for the step-wise removal of one bromine substituent increased along the debromination pathway. Using substituent positions, favourable sequence of stepwise debromination was found to follow the order 3 or 3′2 or 2′ 4 or 4′, while Mg0catalyzed the debromination reaction better than Zn0. The order of ease of debromination was found to be PBB-128PBB-130PBB-129.

Different Stepwise Growth Mechanism of AIE-Active Tetraphenylethylene-Functionalized Metal-Organic Frameworks on Au(111) and Cu(111) Surfaces.

Fabricating tetraphenylethylene (TPE)-functionalized metal-organic frameworks (MOFs) with aggregation- induced emission on surfaces and understanding the growth mechanism have not yet been pursued. Herein, MOFs constructed via the Ullmann-type reaction of a C2-symmetry TPE derivative (p-BrTBE) on Au(111) and Cu(111) surfaces were thoroughly investigated using scanning tunneling microscopy. On a Au(111) surface, p-BrTBE molecules formed the self-assembled pattern at 298 K. Stepwise annealing led to a progressive evolution process, in which the stepwise debromination reaction led to organometallic intermediates, and surface-stabilized radicals and metal-organic networks were formed. By contrast, the relatively ordered MOFs were obtained by replacing the underlying substrate with the more catalytically active Cu(111) at 298 K. Density functional theory calculations demonstrated that the formation of different networks on Au(111) and Cu(111) was determined by the different conformations of the TBE unit on the different substrates due to the different adsorption energy.

Enhanced reductive debromination of decabromodiphenyl ether by organic-attapulgite supported Fe/Pd nanoparticles: Synergetic effect and mechanism

Effective removal of polybrominated diphenyl ethers (PBDEs) from the environment is essential for the ecosystem and human health. Reductive debromination of PBDEs by nanoscale zerovalent iron (nZVI) has become an important technology. However, the agglomeration and low persistence catalytic activity of nZVI particles have become urgent problems to be improved. Herein, we report the first application of a new organo-attapulgite (OA) supported Fe/Pd nanoparticles (OA-Fe/Pd) composite for decabromodiphenyl ether (BDE209) removal. BDE209 was efficiently removed using OA-Fe/Pd with a reaction rate that was 9.97 times greater than that of the nZVI due to the synergetic effect of support material OA and Pd loading. OA could prevent nZVI particles from agglomeration and adsorb BDE209 molecules to its surface. Pd could supply atomic hydrogen and also prevent the oxidation of nZVI particles. The degradation of BDE209 by OA-Fe/Pd was affected by many factors and followed pseudo first-order kinetics. The degradation of BDE209 by OA-Fe/Pd underwent a stepwise debromination manner with the H-transfer dominant mechanism. BDE209 (25 mg∙L-1) could be degraded to penta-BDEs to diphenyl ether (DE) by 3.0 g∙L-1 OA-Fe/Pd within 240 min under neutral condition. This study provides some inspiration for improving the removal efficiency of PBDEs with nZVI-based materials.

Application of dual carbon-bromine stable isotope analysis to characterize anaerobic micro-degradation mechanisms of PBDEs in wetland bottom-water

Polybrominated diphenyl ethers (PBDEs), one kind of persistent organic pollutants, were widely detected in coastal wetlands. Microbial reductive debromination is one of the most important attenuation processes for PBDEs in anaerobic environment, whereas the underlying reaction mechanisms remain elusive. Dual-element stable isotope analysis was recently recognized to distinguish different reaction mechanism for degradation of organic pollutants. In this study, the dual carbon-bromine isotope effects associated with the anaerobic microbial degradation were first investigated to characterize the reaction mechanisms for BDE-47 and BDE-153. Presence of lower brominated congeners indicated stepwise debromination as the main degradation pathway, with the preferential removal of bromine in para position > meta/ortho position. The pronounced isotope fractionation was observed for both carbon and bromine, with similar carbon (εC) and bromine isotope enrichment factor (εBr) between BDE-47 (εC = -5.98‰, εBr = -2.44‰) and BDE-153 (εC = -5.57‰, εBr = -2.06‰) during the microbial degradation. Compared to εC and εBr, the correlation of carbon and isotope effects (ΛC/Br = Δδ81Br/Δδ13C) was almost the same between BDE-47 (0.436) and BDE-153 (0.435), indicating the similar reaction mechanism. The calculated carbon and bromine apparent kinetic isotope effects (AKIEC and AKIEBr) were 1.0773 and 1.0098 for BDE-47 and 1.0716 and 1.0125 for BDE-153, within range reported for degradation of halogenated compounds following nucleophilic substitution. Combination analysis of degradation products, ΛC/Br and AKIE, all the results pointed to that the anaerobic reductive debromination of BDE-47 and BDE-153 followed the nucleophilic aromatic substitution, with the addition of cofactor to the benzene ring concomitant with dissociation of carbon-bromine bond via the inner-sphere electron transfer, and the cleavage of C-Br bond was the rate-determining step. This study contributed to the development of dual carbon-bromine isotope analysis as a robust approach to probe the fate of PBDEs in contaminated sites.

Highly efficient debromination of 4,4'-dibrominated diphenyl ether by organic palygorskite-supported Pd/Fe nanoparticles.

Organic palygorskite (OP)-supported Pd/Fe nanoparticles composite (OP-Pd/Fe) was prepared by stepwise reduction method. The removal capacity of 4,4'-dibrominated diphenyl ether (BDE15) by OP-Pd/Fe was compared with other various materials. For better understanding the possible mechanism, the synthesized and reacted OP-Pd/Fe materials were characterized by TEM, SEM, XRD, and XPS, respectively. The effects of major influencing parameters on the degradation of BDE15 were also studied. Benefit from the synergistic effect of the carrier and bimetallic nanoparticles, BDE15 could be completely debrominated into diphenyl ether (DE) under suitable conditions. A two-stage adsorption/debromination removal mechanism was proposed. The degradation of BDE15 with OP-Pd/Fe was mainly stepwise debromination reaction, and hydrogen transfer mode was assumed as the dominated debromination mechanism. The removal process fitted well to the pseudo first-order kinetic equation. The observed rate constants increased with increasing Pd loading and OP-Pd/Fe dosage while decreased with increasing initial BDE15 concentration, the tetrahydrofuran/water ratio, and the initial pH of the solution. The work provides a new approach for the treatment of PBDEs pollution.

Efficient mineralization of TBBPA via an integrated photocatalytic reduction/oxidation process mediated by MoS2/SnIn4S8 photocatalyst

Currently, Tetrabromobisphenol A (TBBPA) has been regarded as an emerging organic pollutant and efficient TBBPA elimination technology has been attracting increasing attention. In this work, a novel photocatalyst, MoS2/SnIn4S8, was synthesized through hydrothermal method by introducing few-layer MoS2 nanosheets and then employed to establish an integrated photocatalytic reduction/oxidation system for the remediation of TBBPA under visible light. The characterization results demonstrated that the few-layer MoS2 nanosheets were well combined with SnIn4S8 and significantly lowered the recombination rate of the photo-induced electron and holes, leading to outstanding photocatalytic performance of MoS2/SnIn4S8 composite. Besides, the MoS2/SnIn4S8 composite also exhibited excellent reusability (over 10 runs) and stability. The TBBPA degradation experiments showed that the integrated photocatalytic reduction/oxidation system was able to completely degrade TBBPA and mineralize its byproducts (60.2 ± 2.9%). In the photocatalytic reduction, due to the cleavage of C–Br bonds by photo-induced electrons, TBBPA underwent stepwise debromination and finally transferred into BPA in 6 h. In the following photocatalytic oxidation, under the attack of reactive oxygen species (1O2, h+,OH and O2−), BPA was first decomposed into aromatic products (such as phenol, benzoic acid, p-hydroxybenzyl alcohol and so on) via C–C bond cracking and hydroxylation, and then further oxidized into organic acids like maleic acid and muconic acid through ring-opening, and finally mineralized into CO2 and H2O. What was noteworthy was that the final effluent from the photocatalytic reduction/oxidation system showed no toxicity to the luminescent bacteria.

Photodegradation of novel brominated flame retardants (NBFRs) in a liquid system: Kinetics and photoproducts

The photolysis of four typical NBFRs decabromodiphenyl ethane (DBDPE), bis(2-ethylhexyl) tetrabromophthalate (TBPH), pentabromotoluene (PBT) and hexabromobenzene (HBB) were first explored under different sources of light, two temperatures, organic solvents and the presence of humic substance (HS). Degradation could be described by pseudo-first-order kinetic model. Under different irradiation sources, the degradation rates were in order of UVC (0.0616–0.137 min−1) > UVB (0.0348–0.0810 min−1) > sunlight (0.0102–0.0370 min−1) > UVA (almost no degradation). Under UVB irradiation, the half-life of NBFRs was the lowest in tetrahydrofuran (6.16–22.77 min), and the longest (93.42–>120 min) in acetone, indicating that organic solvents greatly affected the degradation kinetics. HS could influence the degradation, and DBDPE or TBPH respectively declined 13.92–30.68% and 12.17–59.41% at 240 min, while the degradation of PBT and HBB were highly inhibited. TBPH photolysis was affected by humic acid (HA) or fulvic acid (FA) concentration, but DBDPE degradation barely showed significant difference (p < 0.05) in the presence of 1 and 10 mg L−1 of HA. Photolytic products of the four NBFRs were identified by GC-NCI/EI-MS, indicating that the photodegradation process was mainly stepwise debromination from high- down to low-bromine-substituted NBFRs. 2,4,6-triBT and 2,4,5-triBT were identified as products of PBT. PBB, 1,2,4,5-tetraBB, 1,2,4-triBB, 1,3,5-triBB and 1,3/1,2-diBB were identified as products of HBB. Our observations could provide a few insights into the removal of NBFRs in a liquid environment.

Efficient photocatalytic debromination of 2,2ʹ,4,4ʹ-tetrabromodiphenyl ether by Ag-loaded CdS particles under visible light

Highly active and visible light-driven Ag-loaded CdS photocatalysts were prepared via a hydrothermal synthesis and photodeposition method. The removal and debromination of 2,2ʹ,4,4ʹ-tetrabromodiphenyl ether was achieved efficiently using this Ag-loaded CdS under visible light, with a removal efficiency of 100% and a debromination ratio of 44.3% being achieved within 30 min. Both the reaction solvent and the water content were found to have a strong influence on the removal efficiency and the debromination ratio. In addition, the stepwise debromination preference was ortho ≫ para, thereby indicating that the main debromination pathway was electron reduction. The stability and efficiency of these Ag-loaded CdS photocatalysts for the removal of BDE47 were satisfactory, and so our results confirmed the development of a promising visible light-driven catalyst for the removal of polybrominated diphenyl ethers.

Reductive degradation of 2,2′,4,4′-tretrabromodiphenyl ether with PAC-Pd/Fe nanoparticles: Effects of Pd loading, initial pH and HA, and degradation pathway

As a typical congener of Polybrominated diphenyl ethers (PBDEs), 2,2′,4,4′-tetrabromodiphenyl ether (BDE47) has attracted more and more attention due to its high biological toxicity and environmental abundance. In this study, a novel polyanionic cellulose stabilized Pd/Fe (PAC-Pd/Fe) nanoparticle was successfully synthesized for BDE47 degradation under ambient condition. Batch experiments showed that BDE47 degradation followed pseudo first-order kinetic model. Pd loading played a crucial role as it affected the formation of activated hydrogen species H∗ and accelerated electron transfer. At Pd loading of 0.3 wt%, nearly 100% BDE47 was degraded completely within 10 min by 0.4 g L−1PAC-Pd/Fe nanoparticles. When compared with strong acidic (pH 3) and alkaline (pH 9 and 11) conditions, weak acidic condition (pH 5) was more favorable for BDE47 degradation, with nearly 100% BDE47 was removed within 7.5 min. In the presence of HA inhibited the degradation of BDE47, and the degradation efficiencies within 15 min decreased from 100%, 88.6%, 79.5% to 73.1% as HA concentration increased from 0, 10, 40 to 70 mg L−1. The degradation of BDE47 by PAC-Pd/Fe nanoparticles was a reductive debromination process, and a stepwise debromination from n-Br to (n-1)-Br BDEs was the dominant reaction, in which the para-Br was more susceptible to remove than ortho-Br. This study suggests PAC-Pd/Fe nanoparticle can be utilized as a promising remediation technology for PBDEs contaminated wastewater.

Enhanced debromination of decabrominated diphenyl ether in aqueous solution by attapulgite supported Fe/Ni bimetallic nanoparticles: kinetics and pathways

In this study, Fe/Ni bimetallic nanoparticles were supported on the attapulgite (A-Fe/Ni) to enhance the degradation reactivity of decabrominated diphenyl ether (BDE209) in aqueous solution. The Fe/Ni nanoparticles were well distributed on the attapulgite surface with an average diameter of 20–40 nm. The removal percentage of BDE209 by A-Fe/Ni was 1.59 times higher than Fe/Ni nanoparticles alone because attapulgite could act as supporting material to disperse Fe/Ni nanoparticles and prevent Fe/Ni nanoparticles from aggregation. The degradation kinetics for BDE209 debromination by A-Fe/Ni could be well described by a pseudo-first-order model, and the debromination rate constant of BDE209 increased with increasing the dosage of A-Fe/Ni, water/THF ratio, and decreasing the initial BDE209 concentration and solution pH. The degradation products were identified using a third-order polynomial regression equation between the experimental and reference gas chromatography relative retention times. Stepwise debromination from n-bromo-DE to (n − 1)-bromo-DE was a possible pathway with bromines being substituted sequentially by hydrogen. The preferred elimination of bromines of BDE209 by A-Fe/Ni followed the debromination preference of para-Br > meta-Br > ortho-Br. The results provide evidences for understanding the debromination mechanism of polybrominated diphenyl ether by clay-supported Fe/Ni nanoparticles.

The key role of biochar in the rapid removal of decabromodiphenyl ether from aqueous solution by biochar-supported Ni/Fe bimetallic nanoparticles

Some problems exist in the current remediation of polybrominated diphenyl ethers (PBDEs) from aqueous solution by using iron-based nanoparticles. Our efforts have contributed to the synthesis of biochar-supported Ni/Fe bimetallic nanoparticle composites (BC@Ni/Fe). Under the optimum operating parameters of BC@Ni/Fe, the morphologic analysis revealed that biochar effectively solved the agglomeration of Ni/Fe nanoparticles and the removal efficiency of BDE209 obtained by BC@Ni/Fe (91.29%) was seven times higher than the sum of biochar (2.55%) and Ni/Fe (11.22%) in 10 min. The degradation products of BDE209 in the solution and absorbed on the BC@Ni/Fe were analyzed with gas chromatography-mass spectroscopy, which indicated that the degradation of BDE209 was mainly a process of stepwise debromination. Meanwhile, compared with Ni/Fe nanoparticles, the adsorption ability of the by-products of BDE209 by BC@Ni/Fe was greater, to a certain extent, which reduced the additional environmental burden. In addition, the concentration of nickle ion leaching from the Ni/Fe nanoparticles was 3.09 mg/L; conversely, the concentration of nickle leaching from BC@Ni/Fe was not detected. This excellent performance in our study indicates a possible means to enhance the reactivity and reduce the secondary risks of Ni/Fe nanoparticles.

Microbial bioavailability of 2,2′,4,4′-Tetrabromodiphenyl ether (BDE-47) in natural sediments from major rivers of China

Microbial degradation plays a crucial role in eliminating polybrominated diphenyl ethers (PBDEs) in environments. However, the microbial bioavailability of PBDEs in aquatic sediments is not well understood. In this work, the bioavailability of 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47), a typical PBDE congener, to PBDE-degrading microorganisms in natural sediments from six Chinese rivers under anaerobic conditions was investigated. The contents of black carbon (BC) and total organic carbon (TOC) in the six sediment samples were in the range of 0.025%–0.30% and 0.03%–3.38%, respectively. BDE-47 desorption from various sediments was fitted well with the first-order three-compartment desorption model. The desorbing fraction of sediment-associated BDE-47 at each desorption time interval exhibited a significant negative correlation with the BC content (p < 0.01). In the sediments, the anaerobic debromination of BDE-47 by microorganisms underwent a stepwise debromination pathway generating mainly three lower brominated congeners (BDE-28, -17 and −4). The microbial debromination ratio of BDE-47 ranged from 4.21% to 7.89% in various sediments after 120 d incubation anaerobically, and it negatively correlated with the content of sediment BC significantly (p < 0.01). However, the desorbing fraction and microbial debromination ratio of BDE-47 only showed weak correlations with the TOC content in sediments (p > 0.05). Furthermore, there was a significant positive correlation of desorbing fraction of BDE-47 from sediments with its microbial debromination ratio (p < 0.01) as well as with the level of its three lower brominated products (p < 0.05) after the first 20 d incubation. This study suggests that the BDE-47 bioavailability to microorganisms in anaerobic river sediments is mainly influenced by the content of sediment BC which controls the desorbing fraction of sediment-associated BDE-47.

Liquid phase catalytic hydrodebromination of tetrabromobisphenol A on supported Pd catalysts

Tetrabromobisphenol A (TBBPA) is a widely used brominated flame retardant and reductive debromination is an effective method for the abatement of TBBPA pollution. In this study, Pd catalysts supported on TiO2, CeO2, Al2O3 and SiO2 were prepared by the impregnation (the resulting catalyst denoted as im-Pd/support), deposition-precipitation (the resulting catalyst denoted as dp-Pd/support), and photo-deposition (the resulting catalyst denoted as pd-Pd/support) methods. The catalysts were characterized by N2 adsorption-desorption isotherm, X-ray diffraction, transmission electron microscopy, measurement of zeta potential, CO chemisorption, and X-ray photoelectron spectroscopy. The results showed that at an identical Pd loading amount (2.0wt.%) Pd particle size in dp-Pd/TiO2 was much smaller than those in im-Pd/TiO2 and pd-Pd/TiO2. Pd particle size of the dp-Pd/TiO2 catalyst increased with Pd loading amount. Additionally, Pd particles in the dp-Pd/TiO2 catalysts were positively charged due to the strong metal-support interaction, whereas the cationization effect was gradually attenuated with the increase of Pd loading amount. For the liquid phase catalytic hydrodebromination (HDB) of TBBPA, tri-bromobisphenol A (tri-BBPA), di-bromobisphenol A (di-BBPA), and mono-bromobisphenol A (mono-BBPA) were identified as the intermediate products, indicative of a stepwise debromination process. The catalytic HDB of TBBPA followed the Langmuir-Hinshelwood model, reflecting an adsorption enhanced catalysis mechanism. At an identical Pd loading amount, the Pd catalyst supported on TiO2 exhibited a much higher catalytic activity than those on other supports. Furthermore, dp-Pd/TiO2 was found to be more active than im-Pd/TiO2 and pd-Pd/TiO2.

Removal of decabromodiphenyl ether (BDE-209) by sepiolite-supported nanoscale zerovalent iron

Nanoscale zerovalent iron (nZVI) synthesized using sepiolite as a supporter was used to investigate the removal kinetics and mechanisms of decabromodiphenyl ether (BDE-209). BDE-209 was rapidly removed by the prepared sepiolite-supported nZVI with a reaction rate that was 5 times greater than that of the conventionally prepared nZVI because of its high surface area and reactivity. The degradation of BDE-209 occurred in a stepwise debromination manner, which followed pseudo-first-order kinetics. The removal efficiency of BDE-209 increased with increasing dosage of sepiolite-supported nZVI particles and decreasing pH, and the efficiency decreased with increasing initial BDE-209 concentrations. The presence of tetrahydrofuran (THF) as a cosolvent at certain volume fractions in water influenced the degradation rate of sepiolite-supported nZVI. Debromination pathways of BDE-209 with sepiolite-supported nZVI were proposed based on the identified reaction intermediates, which ranged from nona- to mono-brominated diphenylethers (BDEs) under acidic conditions and nonato penta-BDEs under alkaline conditions. Adsorption on sepiolite-supported nZVI particles also played a role in the removal of BDE-209. Our findings indicate that the particles have potential applications in removing environmental pollutants, such as halogenated organic contaminants.

Debromination of polybrominated diphenyl ethers by attapulgite-supported Fe/Ni bimetallic nanoparticles: Influencing factors, kinetics and mechanism

To enhance the removal efficiency of 2,2′,4,4′-tetrabromodiphenylether (BDE47) in aqueous solutions, novel attapulgite-supported Fe/Ni bimetallic nanoparticles (A-Fe/Ni), which were characterized by a core–shell nanoparticle structure and with an average diameter of 20–40nm, were synthesized for use in BDE47 degradation. The presence of attapulgite in bimetallic systems could reduce Fe/Ni nanoparticle aggregation and enhance their reactivity. BDE47 was degraded with a significant improvement in removal efficiency of at least 96% by A-Fe/Ni that played a reductive role in the reaction. The degradation kinetics of BDE47 by A-Fe/Ni complied with pseudo-first-order characteristics. To better understand the removal mechanism, detailed analyses were performed for several influential parameters. The improved dosage of A-Fe/Ni was found to be beneficial, and higher values of initial concentration, pH, and methanol/water ratio hindered the degradation rate, which, for example, decreased significantly in mixtures with a methanol proportion higher than 50%. The identification of BDE47 degradation products revealed a stepwise debromination from n-bromo-DE to (n-1)-bromo-DE as a possible pathway, wherein the para-Br was more easily eliminated than ortho-Br. Our findings provide insight into the removal mechanism and evidence for polybrominated diphenyl ether debromination by clay–Fe/Ni bimetallic nanoparticles.

Uptake Kinetics, Bioconcentration and Debromination of BDE-47 in Juvenile Marine Fish Psetta maxima

Polybrominated diphenyl ethers (PBDEs) are a class of global flame retardants whose residues have markedly increased in fish and human tissues during the last decade. They belong to persistent and toxic contaminants which need more attention and toxicological study as their degradation in the environment is not well understood. This study characterizes 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) bioconcentration, elimination and biotransformation in juvenile turbot Psetta maxima, in order to evaluate the risk of its bioaccumulation in the marine environment. During this study, juvenile turbot were exposed to environmentally relevant BDE-47 concentrations from 0.001 to 1 μg/L for 16 days via aqueous exposure. This study found that juvenile turbot bioconcentrated and biotransformed BDE-47. There was no difference in standard length or weight between control and exposed fish. Uptake and elimination of BDE-47 by the turbot during exposure were examined in controlled laboratory experiments. Bioconcentration of BDE-47 was similar in fish from all treatment groups. Bioconcentration was rapid and increased with exposure time, since the bioconcentration factor (BCF) was higher. However, elimination was slower in comparison and low elimination was detected after 10 days in clean water. BDE-47 concentration in water influences the BCF. Half-life ranged between 37 and 108 days and theoretical times t 90 could range from 120 to 358 days. The present study demonstrates a stepwise debromination of BDE-47 to BDE-28.

Estimating stepwise debromination pathways of polybrominated diphenyl ethers with an analogue Markov Chain Monte Carlo algorithm

A stochastic process was developed to simulate the stepwise debromination pathways for polybrominated diphenyl ethers (PBDEs). The stochastic process uses an analogue Markov Chain Monte Carlo (AMCMC) algorithm to generate PBDE debromination profiles. The acceptance or rejection of the randomly drawn stepwise debromination reactions was determined by a maximum likelihood function. The experimental observations at certain time points were used as target profiles; therefore, the stochastic processes are capable of presenting the effects of reaction conditions on the selection of debromination pathways. The application of the model is illustrated by adopting the experimental results of decabromodiphenyl ether (BDE209) in hexane exposed to sunlight. Inferences that were not obvious from experimental data were suggested by model simulations. For example, BDE206 has much higher accumulation at the first 30min of sunlight exposure. By contrast, model simulation suggests that, BDE206 and BDE207 had comparable yields from BDE209. The reason for the higher BDE206 level is that BDE207 has the highest depletion in producing octa products. Compared to a previous version of the stochastic model based on stochastic reaction sequences (SRS), the AMCMC approach was determined to be more efficient and robust. Due to the feature of only requiring experimental observations as input, the AMCMC model is expected to be applicable to a wide range of PBDE debromination processes, e.g. microbial, photolytic, or joint effects in natural environments.

Remediation of polybrominated diphenyl ethers in soil using Ni/Fe bimetallic nanoparticles: Influencing factors, kinetics and mechanism

Polybrominated diphenyl ethers (PBDEs) are commonly used as additive flame retardants in all kinds of electronic products. PBDEs are now ubiquitous in the environment, with soil as a major sink, especially in e-waste recycling sites. This study investigated the degradation of decabromodiphenyl ether (BDE209) in a spiked soil using Ni/Fe bimetallic nanoparticles. The results indicated that Ni/Fe bimetallic nanoparticles are able to degrade BDE209 in soil at ambient temperature and the removal efficiency can reach 72% when an initial pH of 5.6 and at a Ni/Fe dosage of 0.03g/g. A declining trend in degradation was noticed with decreasing Ni loading and increasing of initial BDE209 concentration. The degradation products of BDE209 were analyzed by GC-MS, which showed that the degradation of BDE209 was a process of stepwise debromination from nBr to (n−1)Br. And a possible debromination pathway was proposed. At last, the degradation process was analyzed as two-step mechanism, mass transfer and reaction. This current study shows the potential ability of Ni/Fe nanoparticles to be used for removal of PBDEs in contaminated soil.

Carbon-catalyzed dye-sensitization for solar hydrogen production

The catalytic effects of four different carbon materials (graphite, multi-walled carbon nanotubes, carbon fibers, and activated carbon) on dye-sensitized solar hydrogen production were investigated under a simulated solar light (AM 1.5G, 100mW/cm2). Eosin-Y (EY) and triethanolamine (TEOA) were employed as a sensitizer and electron donor, respectively. All the tested carbon materials enhanced the sensitized H2 production, while multi-walled carbon nanotubes (CNT) exhibited the highest catalytic activity with 9- and 4-fold enhanced H2 production and photocurrent generation, respectively. This suggests that CNT is highly effective in catalyzing charge injection and thus sensitized H2 production. With Pt loading onto the carbon materials, the H2 production was further improved by a maximum of 10 times. With the bare carbon materials, EY underwent simultaneous spectral shifts and decreases in absorbance presumably due to stepwise de-bromination and cleavage of chromophoric groups. With CNT/Pt, however, only the former was observed despite far higher H2 production. This indicates that the regeneration of EY is significantly enhanced with CNT/Pt. A detailed comparison of carbon materials and the sensitized mechanism was discussed.