Synthesis of Co ₃ O ₄ Nanoparticles Using <i>Ananas Comosus</i> Peel Extract for Cr ⁶⁺ Ion Adsorption and Antibacterial Applications

Abstract 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 (Co 3 O 4 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 Cr 6+ from aqueous solution and antibacterial activity against drug‐resistant bacterial strains applications. The TGA–DTA analysis confirms that Co 3 O 4 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 Co 3 O 4 NPs were spherical‐shaped without impurities. The band gap energy and the specific surface area of the 1:1, 1:2, and 2:1 Co 3 O 4 NPs were calculated as 3.33, 2.95, and 2.70 eV and 24.7, 23.7, and 22.5 m 2 /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 Co 3 O 4 . The Co 3 O 4 (1:1) NPs exhibited higher adsorption efficiency (95%) toward Cr 6+ 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 Co 3 O 4 (1:2) NPs.