Inhibition of Fungal Growth Using Modified TiO₂ with Core@Shell Structure of Ag@CuO Clusters

Abstract

The photocatalytic disinfection (PCD) properties of TiO2 have attracted attention in the research communities because the produced reactive oxygen species (ROS) allow destruction of different types of microbes, such as fungi, bacteria, viruses, algae, unicellular organisms, etc. on surfaces, in water, and in air. However, TiO2 requires UV irradiation to produce the ROS, which limits its photoactivity in indoor environments. Surface-modified TiO2 with small Ag and CuO nanoclusters in a core–shell structure exhibits antifungal properties under dark and visible conditions, possibly because of the interaction between Ag–CuO nanoclusters in the fungi membrane and their penetration, and the co-presence of Cu2+ and Ag+ ions. Therefore, a synergetic effect is obtained with co-modification of TiO2 with silver and copper, and the sample Ag@CuO/TiO2 (core–shell structure of Ag–Cu in a ratio of 1:3) exhibits the highest antifungal activity; that is, fungi growth inhibition is observed for Aspergillus melleus and Penicillium chrysogenum. Moreover, significant inhibitions of the sporulation and generation of droplets, possibly containing mycotoxins and sclerotia under dark and visible exposure, are also obtained.

Heterojunction of CuO nanoclusters with TiO2 for photo-oxidation of organic compounds and for hydrogen production

“…These composite nanomaterials might find other applications, e.g., in gas phase for air treatment, self-cleaning surfaces or CO2 reduction. 16 Indeed, CuO has highly negative CB capable of reduce CO2 to methanol or formaldehyde. 52…”

“…14 Less expensive materials like copper-based nanomaterials have attracted attention in the field of photocatalysis. 10,15,16,17 It has been proposed that coupling of TiO2 (n-type semiconductor) with copper oxide (p-type semiconductor) of a narrow band gap (1.7 eV) 18 could overcome limitations of TiO2 in terms of visible light absorption and charge-carrier recombinations, enhancing the photoactivity under UV irradiation, and principally under visible irradiation.…”

“…However, it should be pointed out that titania modification with Cu-based bimetallic nanoparticles (NPs), e.g., Cu-Ag, Cu-Au, and Cu-Pt 10,15,16,17 does not always lead to an improvement in the photocatalytic activity. For example, it has been proposed that the deposition of two metals close to each other (e.g., core-shell nanostructures) can result in charge carriers' recombination (electron transfer between metallic deposits) instead of "hot" electron transfer from plasmonic metal nanoparticles (Ag-Cu and Ag-Au NPs) to the conduction band (CB) of titania.…”

Plasmonic Photocatalysts for Microbiological Applications

“…Interestingly, although mono Ag or Cu-modified titania does not show enhanced activity under visible light, bi-metallic titania (Ag/Pt and Cu/Ag) promote vis activity, due to the oxidation of organic compounds by superoxide anions [126]. Similarly, a synergistic effect has been observed for titania modified with Ag@CuO in respect to mono-modified titania (Ag/TiO2 and CuO/TiO2) against mold fungi (A. melleus and P. chrysogenum) [127]. Interestingly, only the sample with molar ratio of Ag to CuO of 1:3 shows synergism, and only bi-modified samples exhibit higher activity in the dark than that under vis irradiation.…”

Morphology-Governed Performance of Plasmonic Photocatalysts

“…Accordingly, various strategies for charge carriers' separation have been proposed, as already discussed in this review. In the case of efficient light harvesting, the preparation of highly polydisperse NPs of noble metals (broad LSPR [38,56]) and co-modifications with other metals [98], metal oxides [96,122] and metal complexes [105][106][107] have been investigated. Recently, another strategy has been proposed, i.e., using semiconductors in the form of photonic crystals with photonic bandgap and slow photon effect.…”