Dongyun Du

Synergistic effects of hollow structure and surface fluorination on the photocatalytic activity of titania

To study the synergistic effects of hollow structure and surface fluorination on the photoactivity of TiO(2), TiO(2) hollow microspheres were synthesized by a hydrolysis-precipitate method using sulfonated polystyrene (PS) as templates and tetrabutylorthotitanate (TBOT) as precursor, and then calcined at 500 degrees C for 2h. The calcined samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and N(2) sorption. Photocatalytic activity was evaluated using reactive brilliant red X3B, an anionic organic dye, as a model pollutant in water. The results show that the photocatalytic activity of TiO(2) hollow microspheres is significantly higher than that of TiO(2) nanoparticles prepared in the same experimental conditions. At pH 7 and 3, the apparent rate constants of the former exceed that of the latter by a factor of 3.38 and 3.15, respectively. After surface fluorination at pH 3, the photoactivity of hollow microspheres and nanoparticles further increases for another 1.61 and 2.19 times, respectively. The synergistic effect of surface fluorination and hollow structure can also be used to prepare other highly efficient photocatalyst.

Toxic effects of cadmium on tall fescue and different responses of the photosynthetic activities in the photosystem electron donor and acceptor sides

Tall fescue (Festuca arundinacea Schreb) is a turf grass species which is widely used for rhizoremediation of organic contaminants and shows notable prospects in heavy metal phytoremediation. In this study, different concentrations of cadmium ion (Cd2+) were applied to study toxic effects of Cd2+ and responses of tall fescue by soilless culture. Tall fescue showed comparable high tolerance to Cd2+ as Indian mustard (Brassica juncea L.). Additionally, the treatment with high concentration of Cd2+ leaded to decreased chlorophyll contents, production of reactive oxygen species (ROS) and lipid peroxidation, as well as damage of cell membrane, necrosis and apoptosis in tall fescue roots, and toxicity of Cd2+ on physiologic properties of tall fescue has been well discussed. Moreover, in photosystem II electron donor side, electron transport from oxygen evolution complex (OEC) to Yz residue of D1 protein was inhibited under high Cd2+ treatments, which may be due to the Cd2+ induced ROS production and the replacement of Ca2+ in the core of OEC. In electron acceptor side, electron transport efficiency from quinone B to photosystem I acceptors increased under high Cd2+ treatments, which may be an important response for plants against Cd2+ toxicity and its mechanism needs our further study.

In-situ transformation of Bi 2 WO 6 to highly photoreactive Bi 2 WO 6 @Bi 2 S 3 nanoplate via ion exchange

As a two dimensional (2D) visible-light-responsive semiconductor photocatalyst, the photoreactivity of Bi 2 WO 6 is not high enough for practical application owing to its limited response to visible light and rapid recombination of photogenerated electron-hole pairs. In this paper, 2D core-shell structured Bi 2 WO 6 @Bi 2 S 3 nanoplates were prepared by calcination of a mixture of Bi 2 WO 6 (1.3 g) and a certain amount of Na 2 S·9H 2 O (0–3.0 g) at 350 °C for 2 h. The reactivity of the resulting photocatalyst materials was evaluated by photocatalytic degradation of Brilliant Red X-3B (X3B), an anionic dye, under visible light irradiation ( λ > 420 nm). As the amount of Na 2 S·9H 2 O was increased from 0 to 1.5 g, the degradation rate constant of X3B sharply increased from 0.40 × 10 −3 to 6.6 × 10 −3 min −1 . The enhanced photocatalytic activity of Bi 2 WO 6 @Bi 2 S 3 was attributed to the photosensitization of Bi 2 S 3 , which greatly extended the light-responsive range from the visible to the NIR, and the formation of a heterojunction, which retarded the recombination rate of photogenerated electron-hole pairs. However, further increases in the amount of Na 2 S·9H 2 O (from 1.5 to 3.0 g) resulted in a decrease of the photocatalytic activity of the Bi 2 WO 6 @Bi 2 S 3 nanoplates owing to the formation of a photo-inactive NaBiS 2 layer covering the Bi 2 WO 6 surface.

Sediment biomarker, bacterial community characterization of high arsenic aquifers in Jianghan Plain, China

Representative biomarkers (e.g., n-alkanes), diversity and microbial community in the aquifers contaminated by high concentration of arsenic (As) in different sediment depth (0–30 m) in Jianghan Plain, Hubei, China, were analyzed to investigate the potential mechanism of As enrichment in groundwater. The concentration of As was abundant in top soil and sand, but not in clay. The analysis of the distribution of n-alkanes, CPI values, and wax to total n-alkane ratio (Wax(n)%) indicated that the organic matter (OM) from fresh terrestrial plants were abundant in the shallow sediment. However, n-alkanes have suffered from significant biodegradation from the depth of 16 m to 30 m. The deposition of fresh terrestrial derived organic matters may facilitate the release of As from sediment to groundwater in the sediment of 0–16 m. However, the petroleum derived organic matters may do the favor to the release of As in the deeper section of borehole (16 m to 30 m). The 16S rRNA gene sequences identification indicated that Acidobacteria, Actinomycetes and Hydrogenophaga are abundant in the sediments with high arsenic. Therefore, microbes and organic matters from different sources may play important roles in arsenic mobilization in the aquifers of the study area.

Nitric oxide alleviates toxicity of hexavalent chromium on tall fescue and improves performance of photosystem II

Tall fescue (Festuca arundinacea Schreb) was widely studied for phytoremediation of organic or heavy metal contaminated soils. However, there is still little information concerning toxicity of chromium (Cr) to tall fescue and roles of nitric oxide (NO) in plants against Cr(VI) stress. In this study, different Cr(VI) treatments (0, 1, 5 and 10 mg/L Cr(VI)) and NO treatments were applied with different combinations in hydroponics culture and their interactions to tall fescue were studied. Specifically, 100 µM sodium nitroprusside (SNP) and 100 µM NG-nitro-L-arginine-methyl ester (L-NAME) treatments were used to apply exogenous NO or inhibit synthesis of NO respectively. Our results showed that tall fescue exhibits comparable Cr(VI) tolerance as wheat (Triticum aestivum L.). Additionally, Cr(VI) accumulation in tall fescue leaves were carefully studied and discussed. Moreover, we observed the significantly increased reactive oxygen species (ROS) contents of tall fescue when subjected to Cr(VI) stress, as well as decreased photosynthetic activities induced by Cr(VI) stress by methods of chlorophyll a fluorescence transient, slow chlorophyll fluorescence kinetics and rapid light response curves. Decreased behaviors of photosynthetic activities may due to destruction of antennae pigments by Cr(VI), ROS burst induced by Cr(VI), and down regulation of photosystem II (PSII) by non-photochemical quenching to avoid over reduction of quinone A, which could be considered as an important strategy to cope with Cr(VI) stress. Meanwhile, exogenous NO treatment improves overall physiological and photosynthetic behaviors of tall fescue against Cr(VI) stress. Moreover, increased translocation factors and improved Cr(VI) tolerance of plants under exogenous NO treatment suggest that SNP treatment could be a useful application for Cr phytoremediation.