Effects of reaction temperatures and reactant concentrations on the antimicrobial characteristics of copper precipitates synthesized using L-ascorbic acid as reducing agent

Abstract

Copper-based precipitates were synthesized using a straightforward wet chemical reduction method with copper sulfate salts as precursor and L-ascorbic acid as reducing agent. Scanning electron micrographs of the precipitates reveal particle-like structures with edges. The percent age yield was observed to increase with the reaction temperature and the reductant-to-precursor concentration ratio. Comparison of samples prepared at different times showed that the bulk of the precipitates was formed during the first 24 hours. New yield added to the bulk decreased over time. Here, the ascorbic acid served as a capping agent, which impeded the oxidation. This capping was not visible in the electron micrographs but may be inferred from the infrared spectra. Faster capping reduced the amount of oxides in the precipitates. This was seen in samples prepared at a higher temperature and with a lower reductant-to-precursor concentration ratio. Antimicrobial testing under dynamic contact conditions showed that the copper-based precipitates were more effective against Staphylococcus aureus (a gram-positive bacteria) than Escherichia coli (a gram-negative bacteria). Copper-based precipitates collected after the first 24 hours were more potent than those collected after eight days. Furthermore, samples prepared at room temperature and lower reductant-to-precursor concentration ratios were found to be more effective in reducing the number of S. aureus after one hour of contact. The synthesized copper-based precipitates was observed to reduce the population of S. aureus (CFU/mL) by up to 98% after one hour of contact. Keywords: Wet-chemical method, Capping, Antimicrobial, Staphylococcus aureus, Escherichia coli