Titanium dioxide/silver nanoparticle bilayers prepared in self-assembly processes

A new method for the preparation of TiO2/Ag bilayers via colloid self-assembly process using well-characterized titanium dioxide and silver suspensions was developed. The titanium dioxide nanoparticles, forming a supporting layer, were 46 nm in diameter, exhibiting an isoelectric point at pH 6.4. The silver nanoparticles, forming an external layer of the diameter of 50 nm were prepared via a chemical reduction method with the presence inorganic phosphate salts. The electrophoretic mobility measurements revealed that the zeta potential of silver nanoparticles was highly negative for a broad range of pH and ionic strengths. By explaining this information, the optimum condition for the silver nanoparticle immobilization on TiO2 supporting layers were selected. The coverage of the first layer was adjusted by ionic strength of the suspensions and by the deposition time. Afterward, the silver nanoparticle monolayers of controlled coverage were deposited under the diffusion-controlled transport. Their coverage was determined by a direct enumeration of deposited nanoparticles from AFM images and SEM micrographs. The experimental results showed that for extended deposition times, the coverage of silver nanoparticle layers significantly increases with ionic strength. Therefore, it was proven that the formation of bilayers is mainly controlled by electrostatic interactions and that it is feasible to produce uniform TiO2/Ag materials of desired coverage and structure

Chemical Structure of Stabilizing Layers of Negatively Charged Silver Nanoparticles as an Effector of Shifts in Soil Bacterial Microbiome under Short-Term Exposure

In this work, we have assessed the exposure of soil bacteria from potato monoculture to three types of silver nanoparticles (AgNPs) as well as silver ions (Ag+ ions) delivered in the form of silver nitrate and a commercially available fungicide. The diversity of the soil microbial community, enzymatic activity, and carbon source utilization were evaluated. It was found that only the fungicide significantly limited the abundance and activity of soil bacteria. Silver ions significantly reduced bacterial metabolic activity. In turn, one type of AgNPs prepared with the use of tannic acid (TA) increased bacterial load and activity. There was found in all AgNPs treated soils (1) a greater proportion of all types of persistent bacteria, i.e., Bacillus, Paenibacillus, and Clostridium; (2) a visible decrease in the proportion of Nocardioides, Arthrobacter, and Candidatus Solibacter; (3) almost complete depletion of Pseudomonas; (4) increase in the number of low-frequency taxa and decrease in dominant taxa compared to the control soil. Despite the general trend of qualitative changes in the bacterial community, it was found that the differences in the chemical structure of the AgNP stabilizing layers had a significant impact on the specific metabolic activity resulting from qualitative changes in the microbiome