Photocatalyst composites of zinc oxide-doped titanium dioxide modified with sodium silicate for antibacterial applications

Abstract

Superbugs have troubled and challenged mankind since the development of antibiotics could not keep up with the rate of bacterial evolution. To avoid cross-contamination, the emphasis should be placed on effective protection beginning with the surroundings. This study concentrated on the rapid sonochemical synthesis of photocatalyst sodium silicate loaded titanium dioxide and zinc oxide (TiO2@ZnO_Na2SiO3) composites as an antibacterial agent using short synthesis time and less hazardous solvents. Anatase was obtained as evidenced by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) analyses. Meanwhile, bonding present between the main element of the synthesized sample were confirmed by Fourier transform infrared spectroscopy (FTIR). Visible range was obtained for TiO2@ZnO samples while near ultraviolet range was obtained for TiO2@ZnO_Na2SiO3 samples as depicted by diffused reflectance ultraviolet-visible spectroscopy (DR UV-Vis). All TiO2@ZnO have lower recombination rate compared to ZnO whereas all TiO2@ZnO_Na2SiO3 samples have lower recombination rate compared to TiO2@ZnO (TiO2:ZnO = 1:0.1) composite as observed under fluorescence spectroscopy. All composites have irregular shape as noticed under scanning electron microscopy (SEM). Variation of ratios in TiO2:xZnO (x = 0.1, 0.2, 0.3, 0.4, and 0.5) and TiO2@ZnO_yNa2SiO3 volume percent (y = 2, 4, 6, 8, and 10) were made to obtain the best ratio for highest antibacterial activity. TiO2@0.1ZnO was determined to be the optimal ratio by evaluating both physiochemical properties and antibacterial performance. TiO2@0.1ZnO had a bacteria killing efficiency (BKE) of 78.68% against S. aureus and 99.99% against E. coli, due to its smallest crystallite size (55 nm), lowest band gap energy (2.68 eV), and lower recombination rate. The optimal ratio of TiO2@ZnO_10Na2SiO3 was obtained after further modification of previous ratio of TiO2@0.1ZnO with Na2SiO3, which achieved a lower band gap energy (3.10 eV) and the lowest rate of recombination amongst other variants, with a BKE of 81.36% against S. aureus and 99.99% against E. coli. As seen under HRTEM image and amorphous XRD pattern, the loading of Na2SiO3 outside of TiO2@ZnO was successful. Therefore, this study has successfully synthesised a new antibacterial agent TiO2@ZnO_Na2SiO3.