Synthesis and characterization of coffee husk extract (CHE)-capped Fe₃O₄/PU/ZnO nanocomposites with antimicrobial activity

Waterborne diseases pose a significant threat to global health, particularly in developing nations mainly attributed to disease-carrying microbes. This study aims to synthesize plant-mediated nanocomposite material with antimicrobial activity that can have applications for domestic water treatment. The study employed phytochemicals extracted from coffee husk (CH) as a capping agent to synthesize a novel coffee husk extract-capped magnetic pumice zinc oxide nanocomposite (CHE-capped Fe₃O₄/PU/ZnO-NC) for antibacterial material applications. The study was carried out to examine the effects of coffee husk extract (CHE) on biosynthesized nanocomposite characteristics and to compare the antibacterial activity of CHE-capped Fe₃O₄/PU/ZnO-NCs versus bare CHE-capped ZnO nanoparticles (ZnO-NPs). The biosynthesized CHE-capped Fe₃O₄/PU/ZnO-NC have high zeta potential (− 23.8 mV) proving that the synthesized nanocomposite material was more stable than bare ZnO-NPs (− 21 mv) as a colloidal dispersion. SEM was used to examine the shape and size of CHE-capped Fe₃O₄/PU/ZnO-NC particles and for comparison with bare ZnO-NPs. It was noted that the Fe₃O₄/PU/ZnO-NC has smaller particle size (11.2 nm) than ZnO-NPs (22.2 nm). The CHE Fe₃O₄/PU/ZnO-NC also demonstrated a better bacterial growth inhibition zone against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) than pure CHE-capped ZnO-NPs. The CHE Fe₃O₄/PU/ZnO-NC exhibited more potent antimicrobial activity against S. aureus than against E. coli. This confirmed that the developed biosynthesized CHE-capped nanocomposite could be a promising candidate for pathogen disinfection.