Classical wet chemical synthesis was used to fabricate a hybrid composite that contained copper nanoparticles (average size ∼1 nm), which were embedded into a silicon oxide carrier. The structural and chemical alternations in the copper-functionalized silica were investigated in systems that were sintered at 573 K, 873 K, 1173 K, and 1473 K. A general trend, which was associated with the transformation of metallic copper with a cubic structure into copper(II) oxide with a monoclinic structure in the heat-treated systems, was found. XPS and FTIR spectroscopies also revealed the presence of copper(I) oxide, which formed a shell around the CuO. SEM and TEM showed gradual densification of the hybrid system at ever higher sintering temperatures, which corresponded with the gradual copper agglomeration. A temperature of 873 K was determined to be the temperature at which amorphous silica was transformed into cristoballite and tridymite, as well as the formation of a bulk-like copper structure. In relation to the physicochemical and structural data, high antimicrobial features that had a relatively low toxicity effect on the normal human fibroblasts (NHDF) below 250 mg/L was found for the initial copper-silica composite and the samples that were sintered at 573 K. In turn, a significant decrease in the biological impact was observed in the samples that were sintered at temperatures above 573 K. As a result, the paper discusses the model of structural modifications in copper-silica nanocomposite concerning their biological impact that was developed.
Keywords: Annealing; Antimicrobial activity; Chemical composition; Chemical reduction; Copper-silica nanocomposite; Cytotoxicity; Morphology; Particle size and distribution; Physicochemical features.
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