A one-pot synthesis of multibranched Au/TiO2 hybrid nanoparticles under flow conditions: exploiting the plasmonic features for catalytic purposes

Plasmonic nanoarchitectures built by metal/semiconductor hybrid pairs had showed promising application as efficient visible light photocatalyst. Among them, gold nanoparticles (AuNPs) coated with TiO2 (AuNPs@TiO2) are ideal candidates, since they could efficiently harvest toward solar light spectra by promoting the e-/h+ pairs separation, reducing the recombination and enhancing the photocatalytic activity. Recentely, anisotropic AuNPs gain increasing interests for their unique optical properties and their tunable localized surface plasmon resonance band (LSPR). However, the reliable development of anisotropic AuNPs decorated with TiO2 by direct wet chemistry approaches is still challenging. Herein, we report a novel synthetic protocol for the preparation of star-shaped AuNPs (AuNStar) functionalized with nanostructured thin TiO2 layers, by exploiting a designed bench-top microfluidic reactor. This one-pot seedless procedure is based on the accurate mixture of gold and titania precursors that allows the direct and continuous production of AuNStar@TiO2. The hybrid composites exhibit a stable red-shift LSPR band and an astonishing dispersibility in water and alcohols. By properly tuning the reagents ratio (see Figure 1), we synthesized sample batches with different Au/Ti loadings and we successfully tested their catalytic photoactivity toward the Rhodamine-B degradation, under simulated solar light. Before the photocatalytic tests, any eventual residual ligand on the NP surface has been cleaned-off by treating NPs with H2O2, affording purified hybrid nanosystems highly active and water dispersible. AuNStar@TiO2 were fully characterized by UV/vis, ICP-OES, HRTEM, STEM, EELS map to disclose the Ti distribution. This original procedure is reproducible and scalable, allowing the production of high amount of shape-controlled AuNStar@TiO2 hybrid nanoparticles.