Acid-Base and Photocatalytic Properties of the CeO2-Ag Nanocomposites.

In this work, CeO2 nanoparticles, as well as CeO2 nanocomposites with plasmonic silver nanoparticles, were synthesized using a simple sol-gel process. The concentration of silver in the composites varied from 0.031-0.25 wt%. Cerium hydroxide dried gel was calcined at temperatures from 125 to 800 °C to obtain CeO2. It was shown that, at an annealing temperature of 650 °C, single-phase CeO2 nanopowders with an average particle size in the range of 10-20 nm can be obtained. The study of acid-base properties showed that with an increase in the calcination temperature from 500 to 650 °C, the concentration of active centers with pKa 9.4 and 6.4 sharply increases. An analysis of the acid-base properties of CeO2-Ag nanocomposites showed that with an increase in the silver concentration, the concentration of centers with pKa 4.1 decreases, and the number of active centers with pKa 7.4 increases. In a model experiment on dye photodegradation, it was shown that the resulting CeO2 and CeO2-Ag nanopowders have photocatalytic activity. CeO2-Ag nanocomposites, regardless of the silver concentration, demonstrated better photocatalytic activity than pure nanosized CeO2.

Synthesis and Characterization of Calcium Silicate Nanoparticles Stabilized with Amino Acids.

This work presents the development of a method for the synthesis of calcium silicate nanoparticles stabilized with essential amino acids. CaSiO3 nanoparticles were obtained through chemical precipitation. In the first stage, the optimal calcium-containing precursor was determined. The samples were examined using scanning electron microscopy. It was found that Ca(CH3COO)2 was the optimal calcium-containing precursor. Then, the phase composition of calcium silicate was studied using X-ray phase analysis. The results showed the presence of high-intensity bands in the diffractogram, which characterized the phase of the nanosized CaSiO3-wollastonite. In the next stage, the influence of the type of amino acid on the microstructure of calcium silicate was studied. The amnio acids studied were valine, L-leucine, L-isoleucine, L-methionine, L-threonine, L-lysine, L-phenylalanine, and L-tryptophan. The analysis of the SEM micrographs showed that the addition of amino acids did not significantly affect the morphology of the CaSiO3 samples. The surface of the CaSiO3 samples, both without a stabilizer and with amino acids, was represented by irregularly shaped aggregates consisting of nanoparticles with a diameter of 50-400 nm. Further, in order to determine the optimal amino acid to use to stabilize nanoparticles, computerized quantum chemical modeling was carried out. Analysis of the data obtained showed that the most energetically favorable interaction was the CaSiO3-L-methionine configuration, where the interaction occurs through the amino group of the amino acid; the energy value of which was -2058.497 kcal/mol. To confirm the simulation results, the samples were examined using IR spectroscopy. An analysis of the results showed that the interaction of calcium silicate with L-methionine occurs via the formation of a bond through the NH3+ group of the amino acid.