The photocatalytic reduction of U(VI) by Ag-doped SnS2 materials under visible light.

Efficient degradation of uranium(VI) (U(VI)) in wastewater is an urgent problem because of the chemical toxicity and radiotoxicity. In this study, the Agx-SnS2 photocatalysts were compounded by a simple hydrothermal method, effectively removing U(VI) under visible light in water. Compared with SnS2, the results indicated that Agx-SnS2 would decrease the crystallinity without destroying the crystal structure. Moreover, it has excellent photocatalytic performance on the degradation rate of U(VI). Ag0.5-SnS2 exhibited a prominent photocatalytic reduction efficiency of UO22+ of about 86.4% under optical light for 75 min. This was attributed to Ag-doped catalysts, which can narrow the band gap and enhance absorption in visible light. Meanwhile, the doping of Ag promoted the separation of photoinduced carriers, so that more photogenerated charges participated in the photocatalytic reaction. The stability and reusability were verified by the cycle test and the potential photocatalytic mechanism was analyzed based on the experiment.

Analysis of the process and factors influencing microbial phosphine production.

The process of phosphine production by phosphate-reducing bacteria Pseudescherichia sp. SFM4 has been well studied. Phosphine originates from the biochemical stage of functional bacteria that synthesize pyruvate. Stirring the aggregated bacterial mass and supplying pure hydrogen could lead to an increase of 40 and 44% phosphine production, respectively. Phosphine was produced when bacterial cells agglomerated in the reactor. Extracellular polymeric substances secreted on microbial aggregates promoted the formation of phosphine due to the presence of groups containing phosphorus element. Phosphorus metabolism gene and phosphorus source analysis implied that functional bacteria used anabolic organic phosphorus, especially containing carbon-phosphorus bonds, as a source with [H] as electron donor to produce phosphine.

Analysis of the characteristics of phosphine production by anaerobic digestion based on microbial community dynamics, metabolic pathways, and isolation of the phosphate-reducing strain.

Although phosphine is ubiquitously present in anaerobic environments, little is known regarding the microbial community dynamics and metabolic pathways associated with phosphine formation in an anaerobic digestion system. This study investigated the production of phosphine in anaerobic digestion, with results indicating that phosphine production mainly occurred during logarithmic microbial growth. Dehydrogenase and hydrogen promoted the production of phosphine, with a maximum phosphine concentration of 300 mg/m3. The abundance of Ruminococcaceae and Escherichia was observed to promote phosphine generation. The analysis of metabolic pathways based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) and the MetaCyc pathway database revealed the highest relative abundance of replication and repair in genetic information processing; further, the cofactor, prosthetic group, electron carrier, and vitamin biosynthesis were observed to be closely related to phosphine formation. A phylogenetic tree was reconstructed based on the neighbor-joining method. The results indicated the clear evolutionary position of the isolated Pseudescherichia sp. SFM4 strain, adjacent to Escherichia, with a stable phosphate-reducing ability for a maximum phosphine concentration of 26 mg/m3. The response surface experiment indicated that the initial optimal conditions for phosphine production by SFM4 could be achieved with nitrogen, carbon, and phosphorus loads of 6.17, 300, and 10 mg/L, respectively, at pH 7.47. These results provide comprehensive insights into the dynamic changes in the microbial structure, isolated single bacterial strain, and metabolic pathways associated with phosphine formation. They also provide information on the molecular biology associated with phosphorus recycling.

Fabrication of the novel Ag-doped SnS2@InVO4 composite with high adsorption-photocatalysis for the removal of uranium (VI).

A novel Ag-doped SnS2@InVO4 composite was successfully synthesized for efficient uranium removal from wastewater through a facile hydrothermal method. The structure, morphology and optical property of materials were characterized using various instruments. The results proved that Ag-doped SnS2@InVO4 composite presented as hexangular nanosheets with about 4.87 nm pore size and 101.58 m2/g specific surface area. Further characterization demonstrated that photo-adsorption ability of visible light was enhanced and band gap was narrowed. The adsorption kinetics and isotherm of U(VI) on Ag-doped SnS2@InVO4 composite could be depicted via the Langmuir model and pseudo-second-order mode, and the maximum adsorption capacity of U(VI) reached 167.79 mg/g. The elimination of U(VI) of as-synthesized composites was studied by a synergy of adsorption and visible-light photocatalysis, and the optimal content of InVO4 was found to be 2 wt% with the highest removal efficiency of 97.6%. In addition, compared with pure SnS2 and Ag-doped SnS2, the Ag-doped SnS2@InVO4 composites exhibited superior photocatalytic performance for the conversion of soluble U(VI) to insoluble U(IV) under visible light. The excellent photocatalytic performance was mainly attributed to numerous surface-active sites, strong optical adsorption ability and narrow band gap. Simultaneously, the heterojunction between Ag-doped SnS2 and InVO4 promoted the separation and transfer of photoexcited charges. The cyclic experiments indicated the Ag-doped SnS2@InVO4 composite remained good structural stability and reusability. Finally, the possible mechanism was discussed based on the experimental analysis.

Physiological and biochemical responses of Microcystis aeruginosa to phosphine.

The frequent outbreaks of cyanobacteria bloom are often accompanied by the generation and release of reduced phosphorus species (e.g., phosphine), which raises interesting questions regarding their potential algae-related effects. To clarify the physiological and biochemical responses of cyanobacteria to phosphine, Microcystis aeruginosa was treated with different concentrations of phosphine. Net photosynthetic rate, total antioxidant capacity (T-AOC), catalase (CAT) activity, and the concentrations of chlorophyll a, carotenoid and total protein were investigated and scanning electron microscopy (SEM) was conducted to elucidate the physiological and biochemical responses of M. aeruginosa to phosphine. The results showed that phosphine was beneficial to the growth of algal cells after M. aeruginosa acclimatized to the treatment of phosphine, and treatment with 2.48 × 10-2 mg/L phosphine had a greater positive effect on the growth and reproduction of M. aeruginosa than 7.51 × 10-3 mg/L phosphine, in which most algal cells were smooth and flat on day 16. Treatment with the high concentration of phosphine (7.51 × 10-2 mg/L) for 16 d reduced T-AOC, CAT activity, net photosynthetic rate, and the concentrations of chlorophyll a, carotenoid and total protein of M. aeruginosa to the minimums, resulting in the lysis and death of M. aeruginosa cells, which indicates phosphine has a toxic effect on the growth of algal cells. However, the high concentration of phosphine (7.51 × 10-2 mg/L) had a greater positive effect on the growth of M. aeruginosa cells than the lower two (7.51 × 10-3 mg/L and 2.48 × 10-2 mg/L) from 3 d to 12 d. Our findings provide insight into how phosphine potentially affects the growth of M. aeruginosa cells and the important roles of elevated phosphine on the outbreak of cyanobacteria bloom.

Photocatalytic reduction of Uranium(VI) under visible light with Sn-doped In2S3 microspheres.

Visible light-driven conversion of soluble U(VI) to slightly soluble U(IV) has been regarded as a efficient and environmentally friendly technology to deal with uranium containing wastewater. In this paper, we attempted to use photocatalytic technology to reduction U(VI) from aqueous solution by constructing a highly efficient photocatalysts. The novel Sn-doped In2S3 microspheres photocatalyst were synthesized for the first time by a simple hydrothermal method, and characterized with various analytical and spectroscopic techniques to determine their structural, morphological, compositional, optical and photocatalytic properties. In determination of photocatalytic activity, the results showed that all Sn-doped In2S3 samples exhibited greater photocatalytic performance in reduction of U(VI) under visible light than the pure In2S3. The optimum SnIn2S3 photocatalyst with Sn:In molar ratio of 1:4.8 (SnIn2S3) had the highest photocatalytic performance (95% reduction efficiency within 40 min irradiation time), which was approximately 15.60 times faster than that of pure In2S3. The enhanced photocatalytic activity of the optimum SnIn2S3 was largely ascribed to the higher specific surface area, red-shift in the absorption band, the efficient separation of photogenerated electron-hole pairs (e-/h+) and the narrowed band gap with an up shifting of valence band, conduction band potentials. In addition the optimum SnIn2S3 photocatalyst exhibited a good recyclability and stability during the repetitive experiments. Finally, the possible active species and the possible mechanism on basis of the experimental results were discussed in detail.

Phosphine production in anaerobic wastewater treatment under tetracycline antibiotic pressure.

The influence of tetracycline (TC) antibiotics on phosphine (PH3) production in the anaerobic wastewater treatment was studied. A lab-scale anaerobic baffled reactor with three compartments was employed to simulate this process. The reactor was operated in a TC-absence wastewater and 250µg/L TC-presence wastewater for three months after a start-up period, respectively. The responses of pH, oxidation-reduction potential (ORP), chemical oxygen demand (COD), total phosphorus (TP), enzymes activity (dehydrogenase and acid phosphatase), and microbial community were investigated to reveal the effect of TC on PH3 production. Results suggested that the dehydrogenase (DH) activity, acid phosphatase (ACP) activity and COD have positive relationship with PH3 production, while pH, ORP level and the TP in liquid phase have negative relationship with PH3 production. With prolonged TC exposure, decrease in pH and increase in DH activity are beneficial to PH3 production, while decrease in COD and ACP activity are not the limiting factors for PH3 production.

Mechanism of matrix-bound phosphine production in response to atmospheric elevated CO2 in paddy soils.

To explore the effect of elevated CO2 concentrations ([CO2]) on phosphine formation in paddy fields, the matrix-bound phosphine (MBP) content, different phosphorus fractions and various carbon forms in soil samples from rice cultivation under varying CO2 concentrations of 400 ppm, 550 ppm and 700 ppm by indoor simulation experiment were determined. This study showed that MBP concentration did not increase significantly with elevated [CO2] over four-week cultivation periods of rice seedlings, regardless of soil layers. MBP had a significant positive correlation with total phosphorus (TP) and inorganic phosphorus (IP), and multiple stepwise linear regression analysis further indicated that MBP preservation in neutral paddy soils with depths of 0-20 cm may have been due to conversion from FeP and CaP. Based on redundancy analysis and forward selection analysis, speculated that the formation of MBP in the neutral paddy soils as the response to atmospheric elevated [CO2] was due to two processes: (i) FeP transformation affected by the changes of soil respiration (SCO2) and TOC was the main precursor for the production of MBP; and (ii) CaP transformation resulting from variation in HCO3- was the secondary MBP source. The complex combination of these two processes is simultaneously controlled by SCO2. In a word, the soil environment in the condition of elevated [CO2] was in favor of MBP storage in neutral paddy soils. The results of our study imply that atmospheric CO2 participates in and has a certain impact on the global biogeochemical cycle of phosphorus.

Phosphine in paddy fields and the effects of environmental factors.

Ambient levels of phosphine (PH3) in the air, phosphine emission fluxes from paddy fields and rice plants, and the distribution of matrix-bound phosphine (MBP) in paddy soils were investigated throughout the growing stages of rice. The relationships between MBP and environmental factors were analyzed to identify the principal factors determining the distribution of MBP. The phosphine ambient levels ranged from 2.368±0.6060 ng m(-3) to 24.83±6.529 ng m(-3) and averaged 14.25±4.547 ng m(-3). The highest phosphine emission flux was 22.54±3.897 ng (m(2)h)(-1), the lowest flux was 7.64±4.83 ng (m(2)h)(-1), and the average flux was 14.17±4.977 ng (m(2)h)(-1). Rice plants transport a significant portion of the phosphine emitted from the paddy fields. The highest contribution rate of rice plants to the phosphine emission fluxes reached 73.73% and the average contribution was 43.00%. The average MBP content of 111.6 ng kg(-1)fluctuated significantly in different stages of rice growth and initially increased then decreased with increasing depth. The peak MBP content in each growth stage occurred approximately 10 cm under the surface of paddy soils. Pearson correlation analyses and stepwise multiple regression analysis showed that soil temperature (Ts), acid phosphatase (ACP) and total phosphorus (TP) were the principal environmental factors, with correlative rankings of Ts>ACP>TP.

[Simulation study on behaviors of sediment phosphorus affected by iron ion].

A simulation study has been done that vertical transport of conduct of phosphorus in sediment affected by iron inorganic salt. The results showed: when 10 mL or 50 mL of 1 mol/L FeCl3 solution were added to the simulation system respectively, phosphorus content in sediments was reduced, however, 30 mL of 1 mol/L FeCl3 solution was added, phosphorus content of sediments increased. Appropriate quantum iron inorganic salt will prevent phosphorus in sediment released to the water, otherwise, iron ion quantum added is too high or too low, to a certain extent, will promote the release of phosphorus in the sediments. The results of the study will help further study on the release of the source of phosphorus and lake eutrophication.

Intracellular phosphorus metabolism of Microcystis aeruginosa under various redox potential in darkness.

Phosphorus metabolism of Microcystis aeruginosa was studied under gradient redox potential from 252 mV to -70 mV in darkness. The release of phosphorus occurred in all the treatments, and this process was accelerated in darkness when the redox potential was lowered. Low redox potential in darkness stimulated the accumulation of polyphosphate (PolyP) and the degradation of polyglucose. The synthesis of PolyP delayed the decrease of intracellular orthophosphate. The death of M. aeruginosa was slowered when the redox potential was low in darkness. The accumulation of PolyP under low redox potential in the dark was very important to M. aeruginosa for endurance through the unfavorable growth conditions for maintaining phosphorus concentration, energy storage, and other physiological functions. The ability to accumulate PolyP in the dark and negative redox potential may be of considerable advantage in the low-light, organically rich, and low-redox habitats.