Antibacterial activity of core-shell CuxO@TiO2 photocatalyst under UV, vis and dark

Abstract

The concept of a porous core@shell photocatalytic structure with less stable component as a core (CuxO) and a firm one (TiO2) as a shell having unique antimicrobial properties has been introduced in this study. The CuxO@TiO2 photocatalysts with different compositions (CuxO content from 1 to 50 wt.%), and thus various morphologies (a broad shell of titania composed of fine nanoparticles or incomplete coverage of CuxO core) and properties (oxidation states of elements, crystallite size, photoabsorption properties), have been prepared by water-in-oil microemulsion method. The materials have been characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS) and scanning transmission electron microscopy (STEM). The antibacterial tests have been performed via suspension method for Escherichia coli (E. coli) K12 in the dark and under UV (300–420 nm) or vis (> 420 nm) irradiation. It has been found that the morphology, which influences also other properties, e.g., surface charge and composition (being responsible for an efficient photocatalyst adsorption on the bacteria surface), is decisive for the overall antibacterial performance. The photocatalyst with the lowest content of copper (1%), and thus with a broad titania shell, exhibits the highest activity in the dark, probably due to the largest content of Cu2O. Interestingly, irradiation of this sample with any photons (UV or vis) is detrimental for antibacterial effect, probably due to the change of oxidation state of copper. In contrast, the irradiation significantly enhances the bactericidal activity of samples with larger content of CuxO (10 and 50%), and thus being not completely covered with titania, probably due to enhanced photocatalytic activity (Z-scheme mechanism) under UV irradiation, and electrostatic attractions between positively and negatively charged copper and bacteria, respectively, under vis light.