Environmentally Sustainable Solutions for Pollution Remediation and Self-Sterilising Antibacterial Surfaces

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Nano-dimensioned titania is attracting increasing interest, owing to its unique physio-chemical properties and the creation of electron-hole pairs under UV and/or visible light. This leads to a unique range of properties and widespread applications in solar energy conversion, sensors, photochromic devices, photocatalysis, antibacterial effects and environmental remediation of virtually all organic molecules. Surfaces containing such titania could be used to remove pollutants from waste waters and industrial effluents, as well as atmospheric pollutants from interior (“sick building syndrome”) or exterior surfaces. Titania can also become either super-hydrophobic or super-hydrophilic, depending upon the conditions, allowing for self-cleaning surfaces. Antibacterial or antimicrobial features could enable self-sterilising media for biomaterials, bio-implants, food packaging, kitchen surfaces, and construction materials for homes, hospitals and schools. Nanoparticles of materials such as metallic silver have also attracted a lot of attention for their well-known antibacterial properties, and we have shown that optical effects such as surface plasmon resonance (SPR) enable the tuning of the photochemistry of titania under visible light in Ag-doped TiO₂. We have also shown that other dopants can shift the photo-activity from UV to visible light wavelengths, and improve the degradation of pollutants. Furthermore, we have shown calcium phosphates and apatites (e.g., HAp - Ca₁₀(PO₄)₆ (OH)₂), biomaterials derived from agricultural and fisheries wastes, to be suitable for bio-implants, pollution remediation, and to be photocatalysts in their own right, with antibacterial properties.

            However, the present drive for such photocatalysts and biomaterials often ignores the requirement for a genuinely environmentally sustainable solution to these problems. Clearly the processes used should be as environmentally benign as possible, water-based and avoiding organic solvents if we can, and using readily available, non-toxic and preferably recycled waste-derived starting materials. To this end we have a programme of research at Aveiro focusing on three approaches to creating a new generation of environmental and biomaterials:

1. Nanosynthesis of photocatalyst NPs from environmentally benign aqueous routes.
2. Valorising agricultural, fisheries and industrial wastes to produce sustainable materials for pollution remediation, biomedical and antibacterial uses. We have focused on using typical/traditional products of Portugal, such as bacalhao (cod) and sardine bones, Ginja cherry stones, cork, natural Portuguese clays, wastes from industry and local micro-organisms.
3. The modification, tuning and optimisation of photocatalysts using dopants, nanoparticles, magnetic materials and composites.