Surface Modification of TiO2 and ZrO2 Nanoparticles with Organic Acids and Ultrasound to Enhance Antibacterial Activity

Metal oxide nanoparticles (NPs) are known to have biological activity against various microorganisms; thus, they have been widely used as microbicidal agents, and their use poses potential solutions to problems such as biofouling. This study focuses on the surface modification of TiO₂ and ZrO₂ nanoparticles with lactic acid (LA) and stearic acid (SA) to enhance their antibacterial activity (AA). The surface modification of TiO₂ and ZrO₂ nanoparticles was performed using continuous frequency ultrasound. Sonication was performed at different reaction times. Characterization of the modified nanoparticles by TGA, DSC, XRD, FTIR, and XPS techniques demonstrated the presence of the organic ligand on the surface of the nanoparticles. The surface modification results in a reduction in the crystal size of the nanoparticles. Regarding the antibacterial properties of modified TiO₂ and ZrO₂ nanoparticles, their minimum bactericidal concentration (MBC) against Gram-negative and Gram-positive bacteria of the bacterial strains <i>Escherichia coli</i> and <i>Staphylococcus aureus</i> was evaluated. The results obtained from the AA of the modified and unmodified nanoparticles demonstrated greater efficacy of the modified nanoparticles, in the particular case of TiO₂ and TiO₂-LA, evaluated at concentrations of 200, 500, 800, 1100, and 1400 ppm, TiO₂-LA nanoparticles showed better results at most of the concentrations studied and a bacterial inhibition percentage of 99.0% was achieved at a concentration of 500 ppm against the <i>Escherichia coli</i> bacteria, while TiO₂ NPs only reached 55.0%, this shows that ligands with more than one functional group play an important role in improving AA.