Haizhu Wang

Distribution Patterns of Brominated, Chlorinated, and Phosphorus Flame Retardants with Particle Size in Indoor and Outdoor Dust and Implications for Human Exposure

Dust samples were collected in Beijing, China, from four different indoor microenvironments (office, hotel, kindergarten, and student dormitory) and one outdoor (road dust) microenvironment. These five composite samples were fractionated into 13 sequential size fractions and an individual fraction of <50 μm for further analysis. In the fractions of <50 μm, nine phosphorus flame retardants (∑PFRs), four novel brominated flame retardants (∑NBFRs), and two Dechlorane Plus isomers (DPs) showed the highest concentrations in hotel dust (124,000 ng g(-1)), dormitory dust (14,200 ng g(-1)), and kindergarten dust (231 ng g(-1)), respectively. Nevertheless, nine polybrominated diphenyl ethers (∑PBDEs) were the dominant flame retardants (FRs) (96% of total FRs) in road dust, with the maximum concentration of 23,700 ng g(-1), higher than in any indoor dust. The FR contamination varied strongly among different types of microenvironments, leading to high human exposure to various FRs. Concentrations of FRs did not increase constantly with a particle size decrease. Fractions with a particle size around 900, 100, and 10 μm could represent peak values, while valley values were commonly detected around fractions with a particle size around 40 μm. Large differences were found between indoor dust and road dust. In road dust, FRs were mainly enriched in fractions of <50 μm. The organic content of dust, FR application, and consequent abrasion processes of FR-containing materials might be the determinants of the FR concentrations. Volatilization and abrasion were considered to be important migration pathways for FRs. DPs and BDE-209 were sought to be mainly applied in abrasion-proof materials, while most phosphorus flame retardants (PFRs) were probably added in a large proportion in materials easy to wear.

Ball milling synthesized MnOx as highly active catalyst for gaseous POPs removal: significance of mechanochemically induced oxygen vacancies.

A rapid (1.5 h) one-step ball milling (BM) method was developed not only to modify commercial MnO2 via top-down approaches (BM0), but also to bottom-up synthesize MnO(x) by cogrinding of KMnO4 and MnC4H6O4 (BM1) or KMnO4 and MnSO4 (BM2). Catalysts activity on gaseous POPs removal was tested using hexachlorobenzene (HCBz) as surrogate. Catalytic performance decreases in the order of BM2 ≈ BM1 (T90% = 180-200 °C) > BM0 (260 °C) > CMO ≈ cryptomelane MnO2 (>300 °C). Both adsorption and destruction contribute to HCBz removal at 180 °C while destruction prevails at 200-300 °C. Mechanism studies show that destruction activity is lineally correlated with the amount of surface reactive oxygen species (Oads); stability is determined by the removal of surface chloride, which is associated with the mobility of bulk lattice oxygen (Olat); adsorption capacities are linearly correlated with surface area and pore structure. With the aid of extensive characterizations the excellent performance of BM prepared samples can be explained as (1) abundant surface vacancies enhance the generation of Oads; (2) massive bulk vacancies promote the mobility of bulk Olat; (3) large surface area and uniform pore size distribution facilitate the physisorption of HCBz.

Effect of geometry on the magnetic properties of CoFe2O4–PbTiO3 multiferroic composites

In this study, X-ray absorption near-edge structure (XANES), extended X-ray absorption fine structure (EXAFS), X-ray magnetic circular dichroism (XMCD) and element- and site-specific magnetic hysteresis (ESMH) are used to elucidate the effect of geometry (0-3- and 2-2-type) on the magnetic properties of CoFe2O4–PbTiO3 (CFO–PTO) multiferroic composites by comparison with those of the reference CFO and PTO powders. Magnetic Co ions in CFO have been confirmed to be located at both the tetrahedral (A)- and octahedral (B)-sites. CFO retains its mixed-spinel structure as verified by the EXAFS, XMCD and ESMH measurements. ESMH measurements further demonstrate that the magnetic moments of Co2+ and Fe3+/Fe2+ cations at both the A- and B-sites in the composites are smaller than those of the CFO powder. The reduction of the magnetic moments in the 2-2-type composite was larger than that in the 0-3-type composite. The reduction of the magnetic moments in the composites was attributable to the formation of anti-phase boundaries owing to the compressive strain in CFO, which is the largest strain in the 2-2-type composite. Based on the Ti L3,2-edge XMCD measurements of the CFO–PTO composites, no induced magnetic moment was observed at the Ti sites in the PTO matrix, excluding the possibility that the Ti ions in the PTO matrix affect the magnetic properties of these CFO–PTO composites.

Mechanochemical destruction of decabromodiphenyl ether into visible light photocatalyst BiOBr

In the present study, mechanochemical (MC) treatment of polybrominated diphenyl ethers (PBDEs), a kind of emerging persistent organic pollutant (POPs), was performed using a high energy ball mill. With Bi2O3 as co-milling reagent, deca-BDE was effectively destroyed and no hazardous intermediates or organic products were observed in the MC reaction. Meanwhile, BiOBr, a promising visible light photocatalyst, was proved to be the final product which could be utilized in further steps. Neither excessive Bi2O3 nor unreacted deca-BDE was left after the reaction as they were originally added at stoichiometric ratio for BiOBr formation. FITR and Raman analyses demonstrate the collapse of deca-BDE skeleton and the cleavage of C–Br bonds with the generation of inorganic carbon, revealing the mechanism of carbonization and debromination. The gaseous products at different reaction atmosphere were also analyzed, showing that mostly CO2 with a fraction of CO were released during the MC process. The reaction formula of deca-BDE and Bi2O3 was then proposed based on the identified final products. Besides, the photocatalytic activity of the generated BiOBr was evaluated using methyl orange as the model pollutant. A good degradation performance from BiOBr was achieved under both simulated sunlight and visible light irradiation, indicating the possibility for its further utilization.

Mechanochemical degradation of hexabromocyclododecane and approaches for the remediation of its contaminated soil.

Hexabromocyclododecane (HBCD) has been listed in the Stockholm Convention for elimination due to its persistent and accumulative properties. In consideration of its sound disposal, mechanochemical (MC) method was employed using different co-milling reagents. Fe-Quartz was proven to a good reagent for HBCD destruction achieving both good degradation efficiency and high yield of bromide. The absence of organic matters after MC treatment was demonstrated by thermogravimetry and GC-MS analysis, indicating the complete degradation of HCBD and its conversion into inorganic compounds. No obvious intermediates could be detected due to the swift and spontaneous reaction between HBCD and Fe-Quartz. FTIR and Raman spectra further showed that the organic structures in HBCD were broken down while amorphous and graphite carbon were obtained as another final product besides bromide. After the successful destruction of HBCD, approaches to remediate its contaminated soil were also carried out. Fe-Quartz was also proven to be the best reagent for HBCD degradation in Kaolin, while CaO showed better performance for the remediation of HBCD contaminated Krasnozem. For practical application, preliminary experiments are necessary in order to select a suitable co-milling reagent and a proper milling time depending on the differences in soil properties and HBCD concentration.

Effects of zero-valent metals together with quartz sand on the mechanochemical destruction of dechlorane plus coground in a planetary ball mill.

Mechanochemical destruction by grinding with additives in high energy ball milling has been identified as a good alternative to traditional incineration for the disposal of wastes containing halogenated organic pollutants. Despite CaO normally used as an additive, recently Fe+SiO2 has been used to replace CaO for a faster destruction. In the present study, zero-valent metals (Al, Zn, besides Fe) together with SiO2 were investigated for their efficiencies of prompting the destruction of dechlorane plus (DP). Aluminum was found of be the best with a destruction percentage of nearly 99% for either syn- or anti-DP after 2.5h milling. In comparison, only 88/85% and 37/32% of syn-/anti-DP were destroyed when using zinc and iron after the same time, respectively. The detected water soluble chloride was lower than the stoichiometric amount containing in the original DP samples, due to the Si-Cl bond formed during the process. The potential fate of C and Cl present in DP is in the form of inorganic carbon, inorganic Cl and formation of Si-Cl bonds, respectively. The results suggested that Al+SiO2 is promising in the mechanochemical destruction of chlorinated organic pollutants like DP.

Magnetic anisotropic properties of Pd/Co/Pd trilayer films studied by X-ray absorption spectroscopy and magnetic circular dichroism

We study the magnetic anisotropic properties of as-grown and annealed Pd/Co/Pd trilayer films based on their atomic and electronic structures using extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES) spectroscopy and magnetic circular dichroism (XMCD) measurements. The annealed film exhibits interesting perpendicular magnetic anisotropy (PMA) whereas the as-grown film exhibits in-plane anisotropy. Cross-sectional transmission electron microscopic analysis together with the Co K-edge EXAFS results confirm the formation of an ordered-alloy CoPd phase in the annealed film, whereas the as-grown film has an hcp Co-like phase. Co L3,2-edge XMCD measurements reveal an enhanced ratio of the Co 3d orbital to spin moments of the annealed film providing evidence of the observed PMA upon annealing.