UV photoluminescence and antimicrobial properties of silver ion modified calcined and non calcined eggshell based substrates

In this study, raw and calcined eggshell-based biomaterials were modified with Ag⁺ ions, and their structural, surface, optical, and antimicrobial properties were systematically investigated. A sustainable approach was used to valorize eggshell waste, with AgNO₃ providing Ag-related species immobilized onto the material surface. X-ray diffraction confirmed the transformation of CaCO₃ to CaO upon calcination, while the absence of metallic silver peaks indicated incorporation of Ag⁺ within the nanocomposite. Zeta potential measurements showed increased positive surface charge after Ag⁺ modification, particularly in calcined samples, suggesting enhanced surface reactivity and colloidal stability. EDX analysis revealed localized Ag accumulation on non-calcined eggshells, whereas calcined composites exhibited more homogeneous Ag distribution. Photoluminescence studies showed green emission for ES@Ag⁺, while PL intensity was suppressed in C-ES@Ag⁺ due to Ag⁺-induced surface defects and charge transfer. Ag⁺ emission confirmed by UV-Vis. In addition, minimum inhibitory concentration (MIC) analysis revealed that ES@Ag⁺ exhibited superior antimicrobial efficiency at lower concentrations compared to C-ES@Ag⁺, demonstrating consistent performance across both liquid and solid media. Antimicrobial activity was tested against Candida albicans ATCC 10239 and Escherichia coli ATCC 8739 via the agar well diffusion method. ES@Ag⁺ exhibited inhibition zones of 17.00 ± 0.05 mm and 16.00 ± 0.07 mm, while C-ES@Ag⁺ showed 15.00 ± 0.02 mm and 9.00 ± 0.05 mm for C. albicans and E. coli, respectively. These results demonstrate the potential of Ag⁺-modified eggshell nanocomposites as sustainable materials for biomedical and environmental applications. While antimicrobial efficacy is promising, further cytotoxicity and biocompatibility studies are needed to assess safety and performance.