A sustainable multi-function biomorphic material for pollution remediation or UV absorption: Aerosol assisted preparation of highly porous ZnO-based materials from cork templates

Abstract

For the first time, highly porous ZnO-based biomorphic materials were synthesised using cork as a natural sustainable template. In the first step, waste cork powder was pyrolysed and converted into inorganic carbon. This template was then infiltrated using a novel approach employing an aerosol of zinc-containing solutions. The infiltrated powders were calcined to convert the precursors into zinc oxide. Depending on temperature, these could form either a ZnO-graphite composite material, or pure ZnO. Their morphology, porosity, microstructure and composition were characterised; their optical band gap energies, ability to adsorb and photodegrade organic pollutants and UV absorption were also assessed. When heated to 350 o C they maintained the 3D porous cork structure, producing a graphite-containing composite material, with both physical adsorption and photocatalytic activity (Eg = 3.19 eV), suitable for environmental remediation. When heated to 700 ºC, the powders were pure ZnO (no graphite), and they absorbed in the UV region, hence suitable for use as sunscreen. Doped ZnO ecoceramics were also produced, using silver and aluminium. An addition of 1 mol% Ag 3 improved photocatalysis under solar light. Conversely, adding 2 mol% Al and calcining at 700 ºC deactivated photocatalysis, but maintained strong UV absorption, producing a safer sunscreen material (no generation of free radicals). This is the first time that photocatalytic or UV absorption properties of any wood-derived biomorphic material or ecoceramic have been reported.

Biomimetic calcium carbonate with hierarchical porosity produced using cork as a sustainable template agent

“…These results showing the differences of samples prepared with different salts are in good agreement with previous work carried out on zinc precursors [24], that showed the effect of counter ions on the infiltration, and on the final crystalline structure. The experiments with zinc-based compounds also showed the loss of the cork structure caused by thermal treatment, primarily attributable to the released latent heat, which led to complete combustion and/or damage of the cells' walls.…”

“…Reasonably, high vacuum conditions ensure the effective removal of air entrapped in the pyrolysed powder, promoting the infiltration of the solution into both the microsized pores of the cells and nanosized ones of the cell walls. Three infiltration cycles were performed, to ensure a significant weight gain [24]. Finally, as summarized in Table 1, each sample was alternately exposed to further thermal treatment, that is calcination in air or a nitrogen atmosphere-based pyrolysis, both at 700 °C.…”

“…Some investigations were recently performed on the preparation of cork-derived ecoceramics; indeed, various biomorphic ceramics including ferrites, silicon carbide, ceria (CeO 2 ) and zinc oxide were prepared using cork as template agent [21][22][23][24][25]. These studies led to interesting results, showing the potential of cork as an effective template agent to obtain materials with high porosity and an ordered microstructure.…”

Cork-derived hierarchically porous hydroxyapatite with different stoichiometries for biomedical and environmental applications

“…N 2 ). 20 If the process is performed with a slow heating ramp, the 3D structure of the cork can be preserved, leading to a porous carbon skeleton, which can be infiltrated with precursor solutions and successively converted into different ceramic materials upon subsequent heating. Literature reports several cork-derived ceramics, such as silicon carbide, hexagonal ferrites, zinc oxide and cerium oxide.…”

Fabrication of Highly Porous and Pure Zinc Oxide Films Using Modified DC Magnetron Sputtering and Post-Oxidation

“…Alternatively, dry fabrication methods can also be considered, including the gas evaporation/condensation, aerosol [ 22 ], and sputtering routes [ 23 ]. However, the first two methods are not applicable for metals with high melting points and are particularly costly, while the aerosol method involves a higher safety risk and greater maintenance costs due to the high pressures required during its operation.…”