Highly efficient photocatalytic bismuth oxide coatings and their antimicrobial properties under visible light irradiation

The aim of the present paper is to assess the antimicrobial activity of novel narrow band gap semiconductor photocatalysts under visible light irradiation, compared to titanium dioxide, which is the conventionally used photocatalytic material. Bismuth oxide, bismuth tungstate and titanium dioxide coatings were prepared using pulsed DC reactive magnetron sputter deposition onto batches of 2 mm spherical glass beads that were agitated during the deposition process to ensure uniform coverage. Additional coatings were deposited onto flat glass substrates for specific analytical techniques. Following deposition, the coatings were annealed in air at 673 K for 30 min to enable crystal structure development. Annealed coatings were analysed with SEM, EDX, XRD, XPS, AFM, UV–vis spectroscopy and water contact angle measurements. The photocatalytic properties of the coatings were initially assessed via a Rhodamine B dye degradation test under visible light irradiation. Antimicrobial efficiency of the coatings was tested via inactivation of E. coli; additionally, bacterial adhesion experiments were performed for all types of the studied coatings. It was found that the performance of bismuth oxide for both dye degradation and bacterial inactivation experiments under visible light was superior to that observed for either bismuth tungstate or titanium dioxide. Moreover, bismuth oxide coatings (and to a lesser extent – bismuth tungstate), due to its hydrophobic nature was able to inhibit bacterial adhesion to the surface.