Enhanced hydrogen evolution from CuOx-C/TiO2 with multiple electron transport pathways.

Titanium dioxide nanoparticles co-modified with CuOx (0≤x≤2) and carbonaceous materials were prepared with a simple hydrolysis and photo-reduction method for photocatalytic hydrogen generation. SEM/TEM and XPS analysis indicated that the carbonaceous materials were mostly coated on the TiO2 surface and clearly revealed that the Cu species exhibited multivalence states, existing as CuOx (0≤x≤2). The optimal catalyst showed a 56-fold enhanced hydrogen evolution rate compared with that of the pure C/TiO2 catalyst. Further, an intensive multiple electron transfer effect originating from CuOx and the carbonaceous materials is proposed to be responsible for the elevated photoactivity. CuOx species serve as electron donors facilitating charge carrier transfer and proton reduction sites. The carbonaceous materials function as the "bridge" that transfers the electrons of TiO2 to the CuOx species, which provides a new route for electron transfer and reinforces the effect of CuOx as a co-catalyst. In this study, the CuOx and C co-modified TiO2 catalyst was prepared with multiple electron transport pathways and enhanced hydrogen production evolution, which provides a deep understanding for the design of co-catalyst-based photocatalysts.

Formation of 1,3,8-tribromodibenzo-p-dioxin and 2,4,6,8-tetrabromodibenzofuran in the oxidation of synthetic hydroxylated polybrominated diphenyl ethers by iron and manganese oxides under dry conditions.

Hydroxylated polybrominated diphenyl ethers (OH-PBDEs) are ubiquitous and highly toxic emerging endocrine disruptors found in surface and subsurface soils and clay deposits. Seriously, they could be easily transformed to the more toxic dioxins (PBDD/Fs) in photochemical processes and incineration, but the spontaneous formation of PBDD/Fs has rarely been reported. This study focused on the formation of 1,3,8-tribromodibenzo-p-dioxin (1,3,8-TrBDD) and 2,4,6,8-tetrabromodibenzofuran (2,4,6,8-TeBDF) from 2'-OH-BDE-68 and 2,2'-diOH-BB-80 under the oxidization of iron and manganese oxides (goethite and MnOx). Approximately 0.09 µmol/kg (2.33%) and 0.17 µmol/kg (4.15%) were transformed to 1,3,8-TrBDD and 2,4,6,8-TeBDF by goethite in 8 days and a higher conversion 0.15 µmol/kg (3.77%) and 0.23 µmol/kg (5.74%) were observed for MnOx in 4 days. However, the formation of PBDD/Fs, probably proceeding via Smiles rearrangements and bromine elimination processes, was greatly inhibited by the presence of water. Transformation of OH-PBDEs by goethite and MnOx was accompanied by release of Fe and Mn ions and the possible pathways for the formation of reaction products were proposed. In view of the ubiquity of OH-PBDEs and metal oxides in the environment, oxidation of OH-PBDEs mediated by goethite and MnOx is likely an abiotic route for the formation of PBDD/Fs.

Photocatalytic reductive dechlorination of 2-chlorodibenzo-p-dioxin by Pd modified g-C3N4 photocatalysts under UV-vis irradiation: Efficacy, kinetics and mechanism.

Polychlorinated dibenzo-p-dioxins (PCDDs), as a group of notorious anthropogenic environmental toxicants, are arguably ubiquitous in nature. In this study, we investigated the photocatalytic reductive dechlorination of 2-chlorodibenzo-p-dioxin (2-CDD) over Pd/g-C3N4 catalysts under UV-vis irradiation. The g-C3N4 and a series of Pd/g-C3N4 catalysts were prepared by thermal polymerization and mechanical mixing-illumination method and characterized by XRD, TEM, BET, SEM and UV-vis DRS analyses. Among all the samples, the Pd/g-C3N4 (5 wt%) yielded the optimal dechlorination activity with a total 2-CDD conversion of 54% within 4 h, and 76% of those converted 2-CDD were evolved to dibenzo-p-dioxin (DD). The kinetics of dechlorination could be described as pseudo-first-order decay model (R2 > 0.84). Corresponding rate constants (k) increased from 0.052 to 0.17 h-1 with Pd contents up to 5 wt% and decreased to 0.13 h-1 with a 10 wt% of Pd. The enhanced activities originated from the surface plasmonic resonance (SPR) effect of Pd nanoparticles and the formation of Schottky barrier between Pd and g-C3N4, which extend the spectrum responsive range and suppress the charge recombination of g-C3N4. This is the first report on the photocatalytic reductive removal of PCDDs and may provide a new approach for PCDDs pollution control.

Concentration and size distribution of total airborne microbes in hazy and foggy weather.

Atmospheric bioaerosol particles were collected using a bioaerosol sampler from Oct. 2013 to Aug. 2014 in the coastal region of Qingdao. The total microbes were measured using an epifluorescence microscope after staining with DAPI (4',6-diamidino-2-phenylindole). The concentration of total airborne microbes showed seasonal variation, with the highest value in winter and the lowest in summer. The mean concentration of total microbes was 6.55 × 10(5)Cells/m(3) on non-hazy days. The total microbe concentration increased to 7.09 × 10(5) and 9.00 × 10(5)Cells/m(3) on hazy and foggy days, respectively. The particle sizes of the total microbes presented a bimodal distribution on sunny days, with one peak at 1.1-2.1 µm and another at 4.7-7.0 µm. The size distribution of total microbes showed an increase in the fine fraction on hazy days and an increase in the coarse fraction on foggy days. However, the size distribution became unimodal during a heating period. Spearman correlation analysis showed that temperature and O3 had a significant negative correlation with the airborne microbe concentration, while PM2.5, SO2, NO2, CO and the air quality index (AQI) had significant positive correlations with the airborne microbe concentration during hazy days. The increased number of airborne microbes will affect the air quality on hazy days.