Synthesis of TiO2 nanoparticles on mesoporous aluminosilicate Al-SBA-15 in supercritical CO2 for photocatalytic decolorization of methylene blue

In the present study, titania nanoparticles were first constructed on mesoporous aluminosilicate Al-SBA-15 in supercritical carbon dioxide (Sc-CO₂) and the resultant samples were characterized by a combination of various techniques, such as X-ray diffraction (XRD), nitrogen physisorption, ²⁷Al MAS NMR, UV–vis diffuse reflectance spectroscopy, and transmission electron microscopy (TEM). It was identified that the Al species incorporated samples retained structures similar to that of the parent SBA-15. In addition, the content of titania loading varied with reaction temperature and time in Sc-CO₂. As-synthesized TiO₂/Al-SBA-15 samples were evaluated in terms of photocatalytic decolorization of methylene blue in aqueous solutions. It was observed that all TiO₂/Al-SBA-15 samples showed satisfactory decolorization efficiency that was much higher than those of TiO₂/SBA-15 and commercial TiO₂ under identical conditions, which could be mainly attributed to the effective adsorption capability, resulting from the extension of specific surface area after substitution of Si species with Al species.     

An All-solid-state Cd-selective electrode with a low detection limit

A new all-solid-state Cd²⁺-selective electrode with a low detection limit was prepared by using conjugated thiophene oligomer α-sexithiophene (α-6T) as solid contact deposited between an ionophore-doped poly(vinyl chloride) membrane and a gold disc substrate. The electrode exhibited a Nernstian response for Cd²⁺ ions over a wide concentration range of 10⁻³-10⁻⁷ M with a detection limit as low as 1.3 × 10⁻⁸ M. Results showed that the fabricated potentiometric sensor was suitable for use within the pH range of 2.0-9.0 and exhibited good reproducibility for long-term measurements.     

Assessing and forecasting atmospheric outflow of α-HCH from China on intra-, inter-, and decadal time scales

Atmospheric outflow of α-HCH from China from 1952 to 2009 was investigated using Chinese Gridded Pesticide Emission and Residue Model (ChnGPERM). The model results show that the outflows via the northeast boundary (NEB, longitude 115-135 °E along 55 °N and latitude 37-55 °N along 135 °E) and the mid-south boundary (MSB, longitude 100-120 °E along 17 °N) of China account for 47% and 35% of the total outflow, respectively. Two climate indices based on the statistical association between the time series of modeled α-HCH outflow and atmospheric sea-level pressure were developed to predict the outflow on different time scales. The first index explains 70/83% and 10/46% of the intra-annual variability of the outflow via the NEB and MSB during the periods of 1952-1984 and 1985-2009, respectively. The second index explains 16% and 19% of the interannual and longer time scale variability in the outflow through the NEB during June-August and via the MSB during October-December for 1991-2009, respectively. Results also revealed that climate warming may potentially result in stronger outflow via the NEB than the MSB. The linkage between the outflow with large scale atmospheric circulation patterns and climate warming trend over China was also discussed.     

Colorimetric detection of trace copper ions based on catalytic leaching of silver-coated gold nanoparticles

A colorimetric, label-free, and nonaggregation-based silver coated gold nanoparticles (Ag/Au NPs) probe has been developed for detection of trace Cu(2+) in aqueous solution, based on the fact that Cu(2+) can accelerate the leaching rate of Ag/Au NPs by thiosulfate (S(2)O(3)(2-)). The leaching of Ag/Au NPs would lead to dramatic decrease in the surface plasmon resonance (SPR) absorption as the size of Ag/Au NPs decreased. This colorimetric strategy based on size-dependence of nanoparticles during their leaching process provided a highly sensitive (1.0 nM) and selective detection toward Cu(2+), with a wide linear detection range (5-800 nM) over nearly 3 orders of magnitude. The cost-effective probe allows rapid and sensitive detection of trace Cu(2+) ions in water samples, indicating its potential applicability for the determination of copper in real samples.     

Blue-to-red colorimetric sensing strategy for Hg²⁺ and Ag⁺ via redox-regulated surface chemistry of gold nanoparticles

Here we report a "blue-to-red" colorimetric method for determination of mercury ions (Hg2?) and silver ions (Ag?) based on stabilization of gold nanoparticles (AuNPs) by redox formed metal coating in the presence of ascorbic acid (AA). AuNPs were first stabilized by Tween 20 in phosphate buffer solution with high ionic strength. In a target ion-free system, the addition of N-acetyl-L-cysteine resulted in the aggregation of Tween 20 stabilized AuNPs for mercapto ligand self-assembled on the surface of AuNPs, which induced the AuNPs to be unstable. This would lead to a color change from red to blue. By contrast, in an aqueous solution with Hg2? or Ag?, the ions could be reduced with the aid of AA to form Hg-Au alloy or Ag coating on the surface of AuNPs. This metal coating blocked mercapto ligand assembly and AuNPs kept monodispersed after addition of N-acetyl-L-cysteine, exhibiting a red color. Therefore, taking advantage of this mechanism, a "blue-to-red" colorimetric sensing strategy could be established for Hg2? and Ag? detection. Compare with the commonly reported aggregation-based method ('red-to-blue'), the color change from blue to red seems more eye-sensitive, especial in low concentration of target. Moreover, selective analysis of Hg2? and Ag? was simply achieved by the redox nature of target ions and the application of classic ion masking agents, avoiding the design and selection of ion chelating moieties and complicated gold surface modification procedure. This method could selectively detect Hg2? and Ag? as low as 5 nM and 10 nM in pure water with a linear range of 5 × 10?? to 1 × 10?? M for Hg2? and 1 × 10?? to 8 × 10?? M for Ag?, respectively. It was successfully applied to determination of Hg2? and Ag? in tap water and drinking water.