Antimicrobial and Photocatalytic Properties of Bentonite/Titanium Dioxide Nanocomposites Doped with Silver

One of the main applications of titanium dioxide nanoparticles is killing the microorganisms spatially in drinking water and wastewater treatment.

  Pure bentonite/Titanium Dioxide nanocomposites and doped with 3, 5 and 10% w/w silver were prepared by molten salt method. In this study, the antibacterial activity of silver doped titanium dioxide/bentonite nanocomposites was studied against two important microorganisms in food industry i.e. Escherichia coli and Staphylococcus aureusunder visible or UV radiation. The photocatalytic activity of these composites against methyl orange was also investigated. The prepared nanocomposites were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDX), UV-Vis diffusive reflectance spectrometer (UV-Vis DRS).

The scanning electron microscope was showed, that agglomeration of spherical TiO2 nanoparticles formed on the bentonite surface. The XRD pattern revealed that all of the samples have only an anatase phase with crystalline size less than 50 nm. According to EDX analysis, the silver ions successfully doped to the TiO2 nanoparticles. According to UV-Vis DRS results, increasing amounts of doped Ag content in the silver-doped titanium dioxide results in a higher visible absorbance capability of the materials. Parent bentonite did not show antibacterial activity. Titanium dioxide/bentonite nanocomposites showed very weak antibacterial activity. The results showed that the antibacterial ability was significantly improved by doping silver content comparing with pure TiO2/bentonite nanocomposites. This study also showed that Gram-positive bacteria (S. aureus) were more readily disinfected by the photo catalysts than a Gram-negative bacterium (E. coli). According to photocatalytic activity findings, doping of nanocomposites with 5 % silver ions showed maximum photocatalytic activity. This is attributed to the increasing visible absorption capacity due to the presence of silver ions.

Antibacterial and photocatalytic activity of titanium dioxide/bentonite nanocomposites increases dramatically due to the addition of silver ions. This can be attributed to the release of silver ions from nanocomposites and the increase in the production of free radicals as a result of increased photocatalytic activity due to reducing the energy gap of titanium dioxide nanoparticles in nanocomposites.