Reductive Degradation of Tetrabromobisphenol Using Iron-Silver and Iron-Nickel Bimetallic Nanoparticles with Microwave Energy

Reductive transformation of tetrabromobisphenol A by sulfidated nano zerovalent iron

Recent studies showed that sulfidated nano zerovalent iron (S-nZVI) is a better alternative to non-sulfidated nano zerovalent iron (NS-nZVI) commonly used for contaminated site remediation. However, its reactivity with different halogenated pollutants such as tetrabromobisphenol A (TBBPA) remains unclear. In this study, we explored the reductive transformation of TBBPA by S-nZVI and compared it with that by NS-nZVI. The results showed that over 90% of the initial TBBPA (20 mg L(-1)) was transformed by S-nZVI within 24 h of reaction, which was 1.65 times as high as that for NS-nZVI. The TBBPA transformation by S-nZVI was well described by a pseudo-first-order kinetic model, whilst that by NS-nZVI was well fitted by a three-parameter single exponential decay model. After 11 weeks of aging, S-nZVI was still able to transform up to 56% of the initial TBBPA within 24 h of reaction; by contrast, the two-week aged NS-nZVI lost more than 95% of its original capacity to transform TBBPA. Moreover, S-nZVI showed only an approximately 20% decrease in its capacity to transform TBBPA in the seventh cycle, while NS-nZVI was no longer able to transform TBBPA in the fourth cycle. XPS analysis suggested the formation of FeS layer on S-nZVI surface and electrochemical analysis revealed an elevated electron transfer capacity of S-nZVI, which were likely responsible for the superior performances of S-nZVI in TBBPA transformation. While the transformation rate of TBBPA by S-nZVI decreased with increasing initial concentration of TBBPA, it showed an increasing trend with increasing S/Fe ratio and initial concentration of S-nZVI. The study indicated that S-nZVI has the potential to be a promising alternative to NS-nZVI for remediation of TBBPA-contaminated aquatic environments.

Decontaminating soil organic pollutants with manufactured nanoparticles

Organic pollutants in soils might threaten the environmental and human health. Manufactured nanoparticles are capable to reduce this risk efficiently due to their relatively large capacity of sorption and degradation of organic pollutants. Stability, mobility, and reactivity of nanoparticles are prerequisites for their efficacy in soil remediation. On the basis of a brief introduction of these issues, this review provides a comprehensive summary of the application and effectiveness of various types of manufactured nanoparticles for removing organic pollutants from soil. The main categories of nanoparticles include iron (oxides), titanium dioxide, carbonaceous, palladium, and amphiphilic polymeric nanoparticles. Their advantages (e.g., unique properties and high sorption capacity) and disadvantages (e.g., high cost and low recovery) for soil remediation are discussed with respect to the characteristics of organic pollutants. The factors that influence the decontamination effects, such as properties, surfactants, solution chemistry, and soil organic matter, are addressed.

Mechanistic and kinetic investigation on OH-initiated oxidation of tetrabromobisphenol A

Detailed mechanism of the OH-initiated transformation of tetrabromobisphenol A (TBBPA) has been investigated by quantum chemical methods in this paper. Abstraction reactions of hydrogen atoms from the OH groups and CH3 groups of TBBPA are the dominant pathways of the initial reactions. The produced phenolic-type radical and alkyl-type radical may transfer to 4,4'-(ethene-1,1-diyl)bis(2,6-dibromophenol), 4-acetyl-2,6-dibromophenol and 2,6-dibromobenzoquinone at high temperature. In water, major products are 2,6-dibromo-p-hydroquinone, 4-isopropylene-2,6-dibromophenol and 4-(2-hydroxyisopropyl)-2,6-dibromophenol resulting from the addition reactions. Total rate constants of the initial reaction are 1.02 × 10(-12) cm(3) molecule(-1) s(-1) in gas phase and 1.93 × 10(-12) cm(3) molecule(-1) s(-1) in water at 298 K.

Preparation and characterization of Pd/Fe bimetallic nanoparticles immobilized on Al2O3/PVDF membrane: Parameter optimization and dechlorination of dichloroacetic acid

Using a liquid-solid phase inversion method, a hybrid matrix poly(vinylidene fluoride) (PVDF) membrane was prepared with alumina (Al2O3) nanoparticle addition. Pd/Fe nanoparticles (NPs) were successfully immobilized on the Al2O3/PVDF membrane, which was characterized by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The micrographs showed that the Pd/Fe NPs were dispersed homogeneously. Several important experimental parameters were optimized, including the mechanical properties, contact angle and surface area of Al2O3/PVDF composite membranes with different Al2O3 contents. At the same time, the ferrous ion concentration and the effect of hydrophilization were studied. The results showed that the modified Al2O3/PVDF membrane functioned well as a support. The Al2O3/PVDF membrane with immobilized Pd/Fe NPs exhibited high efficiency in terms of dichloroacetic acid (DCAA) dechlorination. Additionally, a reaction pathway for DCAA dechlorination by Pd/Fe NPs immobilized on the Al2O3/PVDF membrane system was proposed.

Reductive debromination of tetrabromobisphenol A by Pd/Fe bimetallic catalysts

The bimetallic catalysts of micron sizes were synthesized and the rates of tetrabromobisphenol A (TBBPA) transformation were measured under various conditions using a batch reactor system. The results showed that TBBPA was rapidly debrominated to tri-, di- and mono-bromobisphenol A and to bisphenol A (BPA). The pseudo-first-order rate constants normalized to the specific surface area of the catalysts were found to increase as functions of the Pd coverage on the Fe particles and the dosages of the catalysts and the mass of Pd within the reactors. The rate constants were also decreasing as the solution pH increased. At pH 4.2, Pd coverage of 0.022wt% and catalyst dosage of 4gL(-1), 99% of TBBPA was transformed within 2min, and tri-, di-, and mono-bromobisphenol A were detected as the major intermediate products. After reaction for 45min, BPA was the only compound found in this specific system. Meanwhile, the rate constants measured at constant solution pH correlated linearly with the Pd mass introduced to the reactors, regardless of Pd/Fe catalyst dosage or Pd surface coverage. The study suggested that Pd/Fe catalysts could be used for efficiently treating brominated flame retardants extracted from e-wastes.