One-pot synthesis of gold nanoparticles and aluminum hydroxide hydrogels-based composites with modulated optical properties

In this work, the one-pot synthesis of composites constituted by gold nanoparticles (AuNPs) and aluminum hydroxide hydrogels (AlHG) using the Epoxide Route as homogenous alkalization strategy is presented. To modulate the optical properties of the final composites, halides (X = Cl^-, Br^- and I^-) and SCN^- as a pseudo-halide, were used as growth directing agents of the AuNPs. In addition, the concentration of the reactants, e.g., the X:Cl ratio, was set in such a way to preserve the alkalization rate, the transparency of the hydrogels supporting the AuNPs, and the stability of the final composites. Consequently, the composites exhibit different plasmonic properties, resulting from the AuNPs with different sizes and morphologies, as confirmed through transmission electron microscopy. Furthermore, this versatile one-pot synthesis strategy was employed to design new composites with different I:Cl ratio and synthesize stable colloidal AuNPs within an aluminum hydroxide sol (AuNP@Alsol) without adding any conventional capping agent. This AuNP@Alsol composite was used as seed to accelerate the extremely slow AuNPs formation kinetics in AuNP@AlHG(SCN), demonstrating the potential of this synthesis method to create composites susceptible to be applied in the photonic and catalysis areas.