Fabrication and catalytic performance of Au-AAo composites for the reduction of p-nitrophenol

Highly ordered anodic aluminium oxide (AAO) can be fabricated via electrochemical anodization, either in membrane or wire form. Due to its excellent thermal stability and tunable surface properties, AAO is a promising support material for noble metal catalysts such as gold (Au). This study focuses on the synthesis of gold on AAO (Au/wAAO) composites in wire form using deposition precipitation (DP) and reduction deposition (RD) methods. The DP method is widely used for producing uniformly dispersed supported Au catalysts. In contrast, the RD method uses reducing agents such as sodium borohydride (RD1) and sodium citrate (RD2) remains relatively underexplored for this application. Therefore, this work aims to synthesize Au/wAAO using DP, RD1, and RD2, and to compare their catalytic activity and reusability in p-nitrphenol (p-NP) reduction. Fourier Transform Infrared (FTIR) spectroscopy confirmed successful surface functionalization and gold incorporation, as evidenced by shifts in the characteristic FTIR peak. The peak at 3400 cm⁻¹ for functionalized AAO shifted to 3272 cm⁻¹ for DP, 3275 cm⁻¹ for RD1, and 3286 cm⁻¹ for RD2. The rate constants (k) for p-NP reduction using Au/wAAO prepared by DP and RD2 were 4.3 х 10-3 s-1 and 7.0 х 10-4 s-1, respectively, while the RD1 based catalyst exhibited negligible activity. Notably, the Au/wAAO RD2 catalyst demonstrated excellent reusability across three consecutive cycles without the need for regeneration. Meanwhile, the regeneration through calcination of both DP- and RD2-derived catalysts restored their activity to levels comparable with the fresh catalysts. Field Emission Scanning Electron Microscopy (FE-SEM) and Energy Dispersive X-ray (EDX) analyses confirmed the structural integrity of the AAO support and uniform dispersion of Au nanoparticles within the AAO pores (~125.15 ± 5.2 nm) in the DP and RD2 sample. Overall, this study reveals a clear structure–activity relationship and highlights the RD2 method as a highly effective strategy for developing reusable Au–AAO catalysts.