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Electrochemical impedance spectroscopy of electrodes modified with thin films of NiAlCl layered double hydroxides

Abstract The impedance spectra of NiAlCl LDH-modified electrodes after oxidation at different dc potentials were recorded. The data were fitted to a simple Randles type cell by replacing the Warburg impedance with a mass transfer resistance in parallel with a constant phase element. The film charge transfer resistance decreased dramatically at the onset of nickel oxidation, from more than 10 6 Ω for the unoxidized films, to a minimum of about 60 Ω in a film oxidized to Ni 2.5+ , before increasing slightly for more extensively oxidized films. For the partially oxidized films, the Nyquist plots consisted of depressed semicircles at high frequency, followed by larger capacitive loops at lower frequency where the impedance was dominated by mass transport. Effective diffusion coefficients estimated from the low frequency impedance varied between 1 and 5×10 −9 cm 2 s −1 , in agreement with previous reports for proton diffusion in nickel hydroxide films. The resistive component of the mass transport impedance decreased with increase in the nickel oxidation state. The addition of [Mo(CN) 8 ] 4− caused an increase of 140 mV in the dc potential required to affect the changes in the NiAlCl film impedance spectra associated with oxidation of the nickel sites. The impedance of a redox inactive ZnAlCl film was unaffected by the use of dc conditioning potentials.

In vitro hemocompatibility of PVA-alginate ester as a candidate for hemodialysis membrane.

Alginate based biopolymer with improved physical and chemical properties after esterification using polyvinyl alcohol (PVA) has been studied for possible application as a hemodialysis membrane. The alginic acid to vinyl alcohol molar ratio was predetermined at 0, 0.1, 0.5 and 1. Mechanical strength, hydrophilicity and Ca(2+) adsorption of the membrane before and after modification were evaluated. The obtained PVA-alginate (PVA-Alg) ester membrane was also confirmed using FTIR and SEM. It shows that the PVA-Alg membrane tensile strength is higher than that of native alginate. The water contact angle of the membrane was found to be around 33-50°. The Ca(2+) adsorption capacity tends to decrease with the increase in molar ratio. Furthermore, the modified PVA-Alg ester membrane achieves better protein adsorption and platelet adhesion than the unmodified one. It also exhibits a dialysis performance of 47.1-50.0% for clearance of urea and 42.2-44.6% for clearance of creatinine, respectively. It is expected that this PVA-Alg ester may challenge cellulose acetate for potential application as hemodialysis membranes.

Polyacrylonitrile Nanofiber-Based Quartz Crystal Microbalance for Sensitive Detection of Safrole

Safrole is the main precursor for producing the amphetamine-type stimulant (ATS) drug, N-methyl-3,4-methylenedioxyamphetamine (MDMA), also known as ecstasy. We devise a polyacrylonitrile (PAN) nanofiber-based quartz crystal microbalance (QCM) for detecting safrole. The PAN nanofibers were fabricated by direct electrospinning to modify the QCM chips. The PAN nanofiber on the QCM chips has a diameter of 240 ± 10 nm. The sensing of safrole by QCM modified with PAN nanofiber shows good reversibility and an apparent sensitivity of 4.6 Hz·L/mg. The proposed method is simple, inexpensive, and convenient for detecting safrole, and can be an alternative to conventional instrumental analytical methods for general volatile compounds.

EXTRACTION AND SPECIATION OF CHROMIUM(VI) AND CHROMIUM(III) AS ION-ASSOCIATION COMPLEXES OF TETRAMETHYLAMMONIUM-CHROMATE

A specific, selective and simple method for speciation of chromium(VI) and chromium(III) has been developed. This method is based on the quantitative extraction of chromium(VI) and chromium(III) as an ion association of tetramethylammonium-chromate in methyl isobutyl ketone (MIBK), followed by back extraction and preconcentration with an acidic diphenylcarbazide (DPC) solution. Back extraction was applied to achieve further preconcentration by a final factor of 20. The chromium(VI)-DPC complex was determined by a UV-Visible spectrophotometer. The optimum conditions of this method are as follows, optimum wavelength at 545 nm, MIBK as organic solvent, 7.5 mL of nitric acid (65%) for each 100 mL sample, mole ratio of TMAC to Cr(VI) of 2x104:1, 5 min shaking time, mole ratio of DPC to chromium(VI) of 8:1, and immediate UV-Vis measurement after obtaining of backextract. The calibration curve was linear in the concentration range 0.00-0.40 g.mL of chromium(VI) with a regression equation of Abs=0.0038+1.7427x, in which x was the chromium species concentration (g.mL). The correlation coefficient (r) for the curve was 0.9991 and the detection limit was found to be 0.946 ng.mL -1 . The result of analysis and speciation of chromium in water samples from a river near a leather processing plant in Yogyakarta area showed that the total content of chromium was in the range of 0.04 0.05 g.mL consisting of 0.03 0.04 g.mL of chromium(VI) and 0.002 0.01 g.mL of chromium(III). This result indicates that the concentration of chromium in the river is still below the safety limit.

Structural characterization of LiCrxMn2−xO4 via a simple reflux technique

LiCrxMn2−xO4 (x=0; 0.02; 0.04; 0.06; 0.08, 0.10) have been successfully synthesized via a facile and simple reflux technique. The SEM-EDS data confirm the presence of Cr, Mn and O elements in the products, while the XRD pattern suggests that the materials have well-developed cubic crystals. Direct method was applied to extract structural parameters of LiCrxMn2−xO4 using the Fullprof and Oscail software in WinPlotr package program. Materials were refined in the crystal system, and space group of structures Fd3m phase were then identified. The lattice parameters decrease with the decrease in Cr content. The highest Li-O bond length was found for LiCr0.10Mn1.90O4. It was observed that there is no significant change in particle size as Cr content increased.

Conversion of Green House CO 2 Gas into Useful Hydrocarbon Gasses by Photoreduction Method over TiO 2 /SiO 2 from Volcanic Ash

In order to decrease CO2 level, converting the gas into hydrocarbon fuel gasses has been performed by using photoreduction method under TiO2/SiO2 photocatalysis. The silica (SiO2) for TiO2/SiO2 preparation was purified from volcanic ash, that mixed with TiO2 suspended in water. The photoreduction process of CO2 was carried out in a batch technique, by exposing CO2 and water vapor in the presence of TiO2/SiO2 photocatalyst with UV lamp for 24 h. The gasses produced from the photoreduction were determined by gas chromatography method. In the research, the effects of HCl and HNO3 as hydrogen ion supplier were also evaluated. The research results indicate that the photoreduction of CO2 with the water vapor over the photocatalyst of TiO2/SiO2-volcanic ash has successfully produced methane and ethylene as fuel gasses, while in the presence of TiO2 no ethylene was resulted. The methane produced by TiO2/SiO2 was observed to be larger than by TiO2 powder. The content of TiO2 in TiO2/SiO2 with low level strongly influenced the yield of the products. In contrast, the yield was independent on the TiO2 content in high level. The presence of the acids was found to increase the methane produced , and no ethylene was formed, but instead, methanol was resulted. The effect of HCl was higher than HNO3.

Synthesis of LiNixMn2-xO4 by low-temperature solid-state reaction and its microstructure

This study aims to synthesis the Ni-doped LiNixMn2-xO4 (x = 0; 0.02; 0.04; 0.06; 08; 0.1) by low temperature solid-state reaction. The microstructure of the product was evaluated based on the mole ratio of Ni/Mn of the precursors. The structural analysis of LiNixMn2-xO4 was analyzed by x-ray diffraction equipped with the Direct Method of win PLOTR package program and Diamond. It was found that doping with Ni could change the size, crystallinity and microstructure of LiNixMn2-xO4. The LiNixMn2-xO4 solids have a cubic structure with a space group of Fd3m. The increase in the doping content does not affect the structure. The particle size of the products is about 150-500 nm. The crystallinity of the solids tends to increase with the increase in Ni content. However, the increase of Ni content in the product causes the lattice parameters of the unit cell to decrease.