Vis-Responsive Copper-Modified Titania for Decomposition of Organic Compounds and Microorganisms

Abstract

Seven commercial titania (titanium(IV) oxide; TiO2) powders with different structural properties and crystalline compositions (anatase/rutile) were modified with copper by two variants of a photodeposition method, i.e., methanol dehydrogenation and water oxidation. The samples were characterized by diffuse reflectance spectroscopy (DRS), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Although zero-valent copper was deposited on the surface of titania, oxidized forms of copper, post-formed in ambient conditions, were also detected in dried samples. All samples could absorb visible light (vis), due to localized surface plasmon resonance (LSPR) of zero-valent copper and by other copper species, including Cu2O, CuO and CuxO (x:1-2). The photocatalytic activities of samples were investigated under both ultraviolet (UV) and visible light irradiation (>450 nm) for oxidative decomposition of acetic acid. It was found that titania modification with copper significantly enhanced the photocatalytic activity, especially for anatase samples. The prolonged irradiation (from 1 to 5 h) during samples’ preparation resulted in aggregation of copper deposits, thus being detrimental for vis activity. It is proposed that oxidized forms of copper are more active under vis irradiation than plasmonic one. Antimicrobial properties against bacteria (Escherichia coli) and fungi (Aspergillus niger) under vis irradiation and in the dark confirmed that Cu/TiO2 exhibits a high antibacterial effect, mainly due to the intrinsic activity of copper species.

Enhanced Photocatalytic Activity of Hierarchical Bi2WO6 Microballs by Modification with Noble Metals

“…Here, the zero-valent form of gold is the most predominant, reaching 92%. In the case of copper, only its oxidized forms could be detected, i.e., Cu + (932.16 eV [68]; 58%) and Cu 2+ (932.28 eV [68]; 42%), confirming the instability of zero-valent copper under ambient conditions [69][70][71]. As expected, palladium and platinum exist mainly in the zero-valent form, reaching 80% and 79%, respectively, making up the minority of the oxidized forms of metals (probably PdO [72] and Pt(δ+) [68]).…”

Fabrication of Antibacterial Metal Surfaces Using Magnetron-Sputtering Method

“…It was shown that copper is not genotoxic and does not cause DNA mutations or affect the enzymatic reactions inside the cells. On the other hand, this concept raises a lot of controversy, particularly with regard to photocatalytic materials (e.g., CuO 2 , CuxO@TiO 2 ) that present their antimicrobial effect when exposed to light [ 9 , 27 , 33 , 38 ]. It is possible that extended ROS generation by induced Fenton-like reactions could lead to an imbalance between the production and accumulation of reactive oxygen species (ROS) in cells (defined as oxidative stress), cell respiration arrest, or even DNA breakdowns.…”

“…Ag, Cu, and Au nanoparticles have also been used as germ-destroying agents [ 6 ]. They were investigated before the ongoing pandemic, but over the past two years there has been growing interest in this topic [ 7 , 8 , 9 ]. The scientific rationales for addressing this issue are: (i) metals can efficiently prevent virus and bacteria transmission [ 10 ]; (ii) bacterial/SARS-CoV-2 coinfections and secondary bacterial “super-infection” after SARS-CoV-2 play a significant role during COVID-19 infection [ 11 , 12 ]; (iii) the SARS-CoV-2 pandemic is superimposed on the ongoing pandemic of antibiotic-resistant bacteria (ARB); (iv) the common use of sanitizers and antibacterial agents as personal measures can enhance the transmission of antibiotic-resistance genes (ARG) [ 13 ]; and (v) microbial resistance to metal NPs is almost impossible [ 6 , 14 , 15 ].…”

Morphology-Governed Performance of Multi-Dimensional Photocatalysts for Hydrogen Generation

“…Zero-valent copper has been proposed as a promising co-catalytic material for photocatalysis, since copper has similar electronic properties to silver and gold, and is much cheaper. However, copper is easily oxidized when kept under ambient conditions (as discussed above) [42,43,49,50]. Therefore, formed, less active copper species (though Zero-valent copper has been proposed as a promising co-catalytic material for photocatalysis, since copper has similar electronic properties to silver and gold, and is much cheaper.…”

“…Therefore, formed, less active copper species (though Zero-valent copper has been proposed as a promising co-catalytic material for photocatalysis, since copper has similar electronic properties to silver and gold, and is much cheaper. However, copper is easily oxidized when kept under ambient conditions (as discussed above) [42,43,49,50]. Therefore, formed, less active copper species (though probably re-reduced under reductive conditions during hydrogen generation [43]) could seriously limit the practical application of copper-based photocatalysts [51].…”