Abstract
A solid-state Ultraviolet-photoreduction process of silver cations to produce Ag0 nanostructures on a mesoporous silica is presented as an innovative method for the preparation of efficient environmental anti-fouling agents. Mesoporous silica powder, contacted with AgNO3, is irradiated at 366 nm, where silica surface defects absorb. The detailed characterization of the materials enables us to document the silica assisted photo-reduction. The appearance of a Visible (Vis) band centered at 470 nm in the extinction spectra, due to the surface plasmon resonance of Ag0 nanostructures, and the morphology changes observed in transmission electron microscopy (TEM) images, associated with the increase of Ag/O ratio in energy dispersive X-ray (EDX) analysis, indicate the photo-induced formation of Ag0. The data demonstrate that the photo-induced reduction of silver cation occurs in the solid state and takes place through the activation of silica defects. The activation of the materials after UV-processing is then tested, evaluating their antimicrobial activity using an environmental filamentous fungus, Aspergillus niger. The treatment doubled inhibitory capacity in terms of minimal inhibitory concentration (MIC) and biofilm growth. The antimicrobial properties of silver–silica nanocomposites are investigated when dispersed in a commercial sealant; the nanocomposites show excellent dispersion in the silicon and improve its anti-fouling capacity.
Highlights
The search for an effective strategy to inhibit the growth of microorganisms on exposed surfaces is attracting increasing attention from the scientific community
Silica–silver nanocomposites were synthetized by using a sustainable photochemical process
The superficial charge variation after the irradiation process confirms the reduction of silver ions; energy dispersive X-ray (EDX) spectra evidenced the increased content of silver with respect to oxygen, suggesting the occurrence of photoreduction processes; transmission electron microscopy (TEM) images show the presence of monodisperse silver nanoparticles in the matrix pores with a smaller size in the case of the irradiated sample
Summary
The search for an effective strategy to inhibit the growth of microorganisms on exposed surfaces is attracting increasing attention from the scientific community. Materials and strategies to prevent the growth of environmental fungi, such as Aspergillus niger, are relevant due to respiratory diseases or complications caused by a fungi-contaminated environment [1,2]. Reducing or preventing surface contamination is an updated challenge since commercially available surface cleaning and disinfection procedures have modest effectiveness for medium- and long-term prevention [4]. Silver-based nanomaterials are among the most used additives to confer antimicrobial properties to materials for different applications, from biomedical devices and disinfectants [5] to food-packaging [6,7,8]. Many synthetic strategies have been proposed for the preparation of silver-based nanomaterials [9]. Synthetic processes based on microorganisms, such as bacteria, fungi and algae, are currently being explored [10], but with these methods, nanomaterial samples with
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