Synthesis of Co3O4 Nanoparticles Using Ananas Comosus Peel Extract for Cr6+ Ion Adsorption and Antibacterial Applications

Water contamination, caused by both point and nonpoint sources, alongside the prevalence of diseases caused by bacteria, represents a significant global challenge. In this work, cobalt oxide nanoparticles (Co₃O₄ NPs) were synthesized using various volume ratios such as 1:1, 1:2, and 2:1 of cobalt nitrate hexahydrate as salt precursor solution and Ananas comosus peel extract. The synthesized NPs were used as a high surface area nanoadsorbent for removal of Cr⁶⁺ from aqueous solution and antibacterial activity against drug-resistant bacterial strains applications. The TGA–DTA analysis confirms that Co₃O₄ NPs were thermally stable above 500 °C. The calculated average sizes were found to be 12.58, 13.40, and 22.05 nm for the 1:1, 1:2, and 2:1 ratios, respectively. The SEM–EDS analysis with TEM–HRTEM and SAED validated that Co₃O₄ NPs were spherical-shaped without impurities. The band gap energy and the specific surface area of the 1:1, 1:2, and 2:1 Co₃O₄ NPs were calculated as 3.33, 2.95, and 2.70 eV and 24.7, 23.7, and 22.5 m²/g, respectively. Functional group analysis confirms the presence of numerous secondary metabolites within the peel extract. Cyclic voltammetry coupled with EIS proves the enhanced electrochemical properties of synthesized Co₃O₄. The Co₃O₄ (1:1) NPs exhibited higher adsorption efficiency (95%) toward Cr⁶⁺ removal and were found to be fit with pseudo-second-order kinetics and also with both the Langmuir and Freundlich adsorption isotherm. The maximum (13 mm) zone of inhibition was achieved against Staphylococcus aureus and Streptococcus pyogenes by Co₃O₄ (1:2) NPs.