Highly efficient Au hollow nanosphere catalyzed chemo-selective oxidation of alcohols

• First report of hollow Au nanospheres of size 26 ± 2 nm by soft-templating method.
• Core–shell–corona type micelles of triblock co-polymer act as the template.
• Au hollow nanospheres exhibit excellent catalytic efficiency and chemoselectivity.
• Highly selective synthesis of carbonyl compounds under eco-friendly conditions.

Micelles of poly(styrene-b-2-vinyl pyridine-b-ethylene oxide) (PS-PVP-PEO) with core–shell–corona structures have been used as a scaffold for the fabrication of gold (Au) hollow nanospheres of particle size 26 ± 2 nm using HAuCl4 and NaBH4 as metal precursor and reducing agent, respectively. The PS core acts as a template for hollow void, the PVP shell serves as reaction sites for inorganic precursors, and PEO corona stabilizes the composite particles. Under acidic conditions, the PVP shell domain becomes positively charged pyridinum-species that electrostatically interacts with negatively charged AuCl4− ions. On reduction of these composite particles and subsequent solvent extraction leads to the formation of Au hollow nanospheres. Various analytical tools such as powder X-ray diffraction (XRD), transmission electron microscope (TEM), thermogravimetric analyses (TG/DTA), dynamic light scattering of (DLS) have been employed to characterize the polymeric micelles and hollow nanoparticles. The TEM and XRD studies confirmed the formation of highly crystalline Au hollow nanospheres. The Au hollow nanosphere/H2O2 system efficiently catalyzes the chemoselective oxidation of allylic-type unsaturated alcohols into aldehydes and ketones under mild liquid-phase conditions. The versatility of present catalytic system for the oxidation of other substrates like aliphatic-, acylic-, aromatic-, and heteroaromatic alcohols to their respective keto compounds has also been reported.

Hollow gold nanospheres of size less than 30 nm has been synthesized using triblock copolymer poly(styrene-b-2-vinyl pyridine-b-ethylene oxide) (PS-PVP-PEO) as a soft template and it showed excellent catalytic activity for the chemoselective oxidation of allylic unsaturated alcohols to the respective ketones in the presence of dilute aqueous H2O2 as an oxidant.Figure optionsDownload high-quality image (143 K)Download as PowerPoint slide