Fabrication and characterization of tin oxide-silver composite nanomaterials synthesized by horizontal vapor phase growth (HVPG) technique for UV blocking property and antimicrobial application

Tin oxide and silver composite nanomaterials were successfully synthesized using the vapor phase crystal growth technique. Silver and tin oxide powders of high purity (99.99%) were weighed at approximately 35 mg with stoichiometric mixtures of 1:4, 2:3, 3:2, and 4:1 respectively and were poured into the quartz tube. Each quartz tube was attached to the Thermionic High Vacuum System with a pressure of 10-6 Torr which was fully sealed in one end. The sealed quartz tube was placed in a Thermolyne Horizontal Tube Furnace and baked at 800 0C growth temperature and 6 hours dwell time. The collected samples from the different zones of the tube were characterized using the scanning electron microscope (SEM), and energy dispersive x-ray spectroscopy (EDX). The nanomaterials were mixed with the laminating fluid and the solutions were coated to a glass slide. UV/Vis Spectrophotometer was used to measure the absorbance and transmittance values of the said coated glass to evaluate the materials UV blocking property. To confirm the materials antimicrobial property, alamar blue assay and absorbance measurement were used. Geometric and electronic property of the materials was also computed using Density Functional Theory. The SEM photomicrographs revealed the presence of nanoparticles, wires, rods and cotton-like structures grown in random directions. Most of the nanomaterials were observed at zone 3 of the quartz tube. Micromaterials like wires, rods, sphere, and cotton like structures were observed at zone 2. Zone 1 displays structures in nanometer and micrometer size. Energy dispersive X-ray analyses confirmed the presence of Ag, Sn, and O in the composite nanomaterials with a minimal presence of impurities. DFT analysis verified the growth of tin oxide on the surface of silver. Using largest unit cells of SnO2 (110) and Ag (111), nanorods can be formed which is supported by the SEM micrographs. Analysis on the different surface termination showed that tin oxide and silver composites are UV blockers with computed band gap energies of 2.72 to 4.84 eV. Absorbance peaks of the glass coated with nanomaterials solution showed that the materials are classified as UV absorbers. The findings revealed that the wavelength of the light absorbed by the glass slide ranges from 200 to 400 nm. Highest absorbance of UV was observed in the glass coated with nanoSnO2 solutions followed by 4:1 SnO2-Ag stoichiometric ratio. As the amount of tin oxide over silver increases, the absorbance values also increases. Highest transmittance of UVB and visible light was observed in the glass coated with nanomaterials solutions from zone 3 of the quartz tube. Alamar blue reduction was observed at the medium containing powder materials for both E. coli and S. aureus bacteria. Its pink color exhibits the viability of bacteria. SnO2 nanomaterials are more toxic to E. coli than S. aureus. Absorbance values depicted that the toxicity to E. coli and S. aureus increases as the amount of silver over tin oxide increases. Antimicrobial property was enhanced by reducing the materials to nanosize. The highest toxicity was observed at 1:4 SnO2-Ag stoichiometric ratios collected at zone 3