Influence of synthesis parameters on the growth of CdS nanoparticles in colloidal solution and determination of growth kinetics using Karhunen–Loeve decomposition

Kinetic study on bonding reaction of gelatin with CdS nanopaticles by UV-visible spectroscopy

The chemical kinetics on gelatin-CdS direct conjugates has been systematically investigated as a function of different temperature and reactant concentration (i.e. Cd(2+), S(2-) and gelatin) by UV-visible spectroscopy, for the first time. The nonlinear fitting and the differential method were used to calculate the initial rate based on the absorbance-time data. A double logarithmic linear equation for calculating the rate constant (k) and the reaction order (n) was introduced. The reaction kinetic parameters (n, k, Ea, and Z) and activation thermodynamic parameters (ΔG(≠), ΔH(≠), and ΔS(≠)) were obtained from variable temperature kinetic studies. The overall rate equation allowing evaluation of conditions that provide required reaction rate could be expressed as: r = 1.11 × 10(8) exp(-4971/T)[Cd(2+)][gelatin](0.6)[S(2-)](0.6) (M/S) The calculated values of the reaction rate are well coincide with the experimental results. A suitable kinetic model is also proposed. This work will provide guidance for the rational design of gelatin-directed syntheses of metal sulfide materials, and help to understand the biological effects of nanoparticles at the molecular level.

Pseudomonas fluorescens JH 70-4 promotes pb stabilization and early seedling growth of sudan grass in contaminated mining site soil

A bacterial strain (JH 70-4) exhibiting plant growth promoting characteristics (indoleacetic acid production and 1-aminocyclopropane-1-carboxylate deaminase activity), as well as heavy metal(loid) (HM) tolerance and Pb precipitation, was isolated from HM-contaminated soil at an abandoned mine site. The bacterium was identified as Pseudomonas fluorescens based on 16S rDNA sequencing. The JH 70-4 strain induced precipitation of Pb as PbS nanoparticles, confirmed by X-ray diffraction. Solution pH, incubation time, and Pb concentration influenced removal and PbS formation. Inoculating contaminated soil with JH 70-4 decreased Pb availability; exchangeable Pb decreased while organic- and sulphide-bound Pb increased. The toxicity characteristic leaching procedure showed a 65% decrease in Pb in leachate 60 d after inoculating soil with JH 70-4. Shoot and root lengths of Sudan grass grown in the inoculated soil were greater than in the uninoculated soil. Findings suggest that microbial Pb fixation is a viable strategy for remediating soil and promoting plant growth for phytostabilization of contaminated sites.

Growth Kinetics of ZnO Nanocrystals: A Few Surprises

Using extensive state-of-the-art experiments over a wide range of synthesis parameters, such as the temperature and concentrations of different reactants, we establish qualitatively different growth kinetics for ZnO nanocrystals compared to all growth kinetics of semiconductor nanocrystals, including ZnO, discussed so far in the literature. The growth rate is shown to be strongly dependent on the concentration of (OH)- in an intriguing nonmonotonic manner as well as on temperature and is almost invariably much slower than well-known and generally accepted growth mechanisms based on a diffusion-controlled Ostwald ripening process or that expected in the surface reaction controlled regime. We show that these qualitatively different results arise from the unexpected role played by a part of the reactants by inhibiting rather than facilitating the reaction; we explain this extraordinary result in terms of an effective passivating layer around the growing nanocrystals formed by a virtual capping shell of Na+ ions.