Influence of different cyanobacterial treatment methods on phosphorus cycle in shallow lake microcosms.

Cyanobacterial bloom is a pressing issue affecting water supply security and ecosystem health. Phosphorus (P) released from cyanobacterial bloom during recession is one of the most important components involved in the lake P cycle. However, little is known about the consequences and mechanisms of the P cycle in overlying water and sediment due to the anthropogenic treatments of cyanobacterial blooms. In this study, treatment methods using hydrogen peroxide (H2O2), polyaluminum chloride (PAC), and the feces of silver carp were investigated for their influence on the P cycle using microcosm experiments. Results showed that H2O2 treatment significantly increased the internal cycle of sediment-related P, while PAC treatment showed minor effects. H2O2 and PAC treatment suppressed the release of P from sediment before day 10 but promoted the release of P on day 20, while silver carp treatment suppressed the release of P during the whole experiment. The reductive dissolution of iron oxide-hydroxide was the major factor affects the desorption of P. Path analyses further suggested that overlying water properties such as dissolved oxygen (DO) and oxidation-reduction potential (ORP) play critical roles in the treatment-induced sediment P release. Our results quantify the endogenous P diffusion fluxes across the sediment-water interface attributed to cyanobacterial treatments and provide useful guidance for the selection of controlling methods, with silver carp being the most recommended of the three methods studied.

The effect of graphitized carbon on the adsorption and photocatalytic degradation of methylene blue over TiO2/C composites.

The TiO2/C composites with approximately 40 wt% of carbon were prepared by calcination of precursors, formed from a one-pot liquid phase reaction between Ti(SO4)2 and flour. All TiO2/C composites displayed mesoporous structures with high BET surface areas (117-138 m2 g-1) and small crystal sizes of TiO2 (8-27 nm). The contents of graphitic carbon and rutile TiO2 increased, while the surface area and TiO2 crystal size decreased for the TiO2/C composite on increasing the calcination temperature from 650 to 800 °C; when calcinated at 800 °C, the anatase TiO2 completely changed into rutile TiO2 in the TiO2/C composite. The TiO2/C composite calcinated at higher temperatures exhibited better adsorptive and photocatalytic degradation performance in the removal of methylene blue (MB). For the entire rutile TiO2/C-800 composite, the adsorption process of MB can be well described by the pseudo-second-order kinetic model and is governed by chemical adsorption with the maximum adsorption capacity value equal to about 15 mg g-1. Under continuous illumination with a 254 nm UV lamp (15 W) for 3 h, the percentage of MB (14 mg l-1) photocatalytic degradation on 50 mg of TiO2/C-800 was 25.1% higher than that of the maximum adsorption removal. These results suggest that the graphitized carbon has a significant effect on the adsorptivity and photocatalytic activity of the TiO2/C composite.

Photocatalytic TiO2 Nanoparticles Activated by Dielectric Barrier Discharge Plasma Assisted Ball Milling.

Developing defects on the surface of TiO2 nanoparticles by mechanical treatment is a fascinating approach to enhance photocatalytic efficiency. However, it poses risks to producing bulk defects and phase transformation, which seriously deteriorates photocatalytic performance. Here, activating TiO2 nanoparticles was elaborately fulfilled by using dielectric barrier discharge plasma assisted ball milling (DBDP-milling) as it imposes plasma to nano-scaled particles along with soft mechanical impact. The evolution of surface properties of TiO2 nanoparticles with DBDP-milling durations was inspected using a Fourier transform infrared (FTIR) and an X-ray photoelectron spectrometer (XPS), while the morphology and structure were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. Results showed that DBDP-milling developed a considerable number of oxygen vacancies in TiO2 nanoparticles as well as bulk defects free. These TiO2 nanoparticles formed agglomerates with BET surface area of 37.40 m2/g and exhibited enhanced photocatalytic efficiency.

Separation and preconcentration system based on ultrasonic probe-assisted ionic liquid dispersive liquid-liquid microextraction for determination trace amount of chromium(VI) by electrothermal atomic absorption spectrometry.

A novel method of ultrasonic probe-assisted ionic liquid dispersive liquid-liquid microextraction combined with electrothermal atomic absorption spectrometry (ETAAS) was developed for the determination of chromium(VI) species in water samples. In this procedure, the hydrophobic chelate of chromium(VI) with ammonium pyrrolidinedithiocarbamate (APDC) was extracted into the fine droplets of 1-hexyl-3-methylimidazolium hexafluorophosphate ([Hmim][PF(6)]), which was dispersed into the aqueous sample solution by ultrasonication using an ultrasonic probe. Several variables such as the volume of [Hmim][PF(6)], sample pH, concentration of APDC, and extraction time were investigated in detail. Under the optimum conditions, the limit of detection of the proposed method was 0.07 ng mL(-1) for Cr(VI) and the relative standard deviation for five-replicated determination of 2.0 ng mL(-1) Cr(VI) was 9.2%. The proposed method has been also successfully applied to the determination of chromium(VI) species in lake and tap water samples.

Angeli's salt (Na2N2O3) is a precursor of HNO and NO: a voltammetric study of the reactive intermediates released by Angeli's salt decomposition.

Under physiological conditions, it is usually accepted that the aerobic decomposition of Angeli's salt produces nitrite (NO(2)(-)) and nitroxyl (HNO), which dimerizes and leads to N(2)O. No consensus has yet been established on the formation of nitric oxide (NO) and/or peroxynitrite (ONOO(-)) by Angeli's salt. Because this salt has recently been shown to have pharmacological properties for the treatment of cardiovascular diseases, identification of its follow-up reactive intermediates is of increasing importance. In this work, we investigated the decomposition mechanism of Angeli's salt by voltammetry performed at platinized carbon fiber microelectrodes. By following the decomposition process of Angeli's salt, we showed that the mechanism depends on the experimental conditions. Under aerobic neutral and slightly alkaline conditions, the formation of HNO, NO(2)(-), but also of nitric oxide NO was demonstrated. In strongly alkaline buffer (pH>10), we observed the formation of peroxynitrite ONOO(-) in the presence of oxygen. These electrochemical results are supported by comparison with UV spectrophotometry data.