Ultralong and Mesoporous ZnO and γ-Al₂O₃ Oriented NanowiresObtained by Template-assisted Hydrothermal Approach

Highly mesoporous ZnO and γ-Al₂O₃ nanowires (NWs) are both synthesized by a hydrothermal method using commercially available porous anodic aluminium oxide (AAO) as template. AAO membrane acts as template for ZnO NWs and both as template and precursor for γ-Al₂O₃ NWs. The formation of intermediate phases of porous Zn₆Al₂(OH)₁₆CO₃ and boehmite (γ-AlOOH) were observed, both occurring during the hydrothermal synthesis of porous ZnO and γ-Al₂O₃ NWs, respectively, and disappearing after annealing at 600°C. This novel template-assisted hydrothermal process leads to the formation of porous ZnO and γ-Al₂O₃ NWs (specific surface area of 192m²g^-1 and 263m²g^-1, respectively), showing pore sizes around 4nm in diameter. The influence of the reaction parameters on the nanostructure morphology was also investigated. A ZnO seed layer, deposited on the AAO channels prior to the hydrothermal synthesis, leads to more compact ZnO nanowires (99m²g^-1) protecting the AAO host from the chemical attack of the precursor solution.