In situ generated Ligand-Free gold nanoparticles in polyvinylpyrrolidone solution assisted laser in liquid method for green oxidation of cyclohexane to adipic acid with high yield

• The simple, green and fast PLAL method was implemented for free-ligand Au nanoparticles synthesis. • Gold nanoparticles coated-double silica shells was developed for aerobic oxidation of cyclohexane. • The Au@SiO 2 @SiO 2 nanocatalyst exhibited the good activity and excellent selectivity to adipic acid. Here in we report a very simple method to create gold nanoparticles coated-double silica shells by using a three step process containing pulse laser ablation (PLAL) of metallic gold target in aqueous solution of polyvinylpyrrolidone, well-known stober process and calcination at high temperature respectively for achieving of Au@SiO 2 @SiO 2 nanoparticles with narrow size distribution. Final structure was characterized by techniques such STEM, FESEM, BET, XPS, XRD, TGA, ICP-OES and FT-IR and shows the activity of 26 % conversion in aerobic oxidation of cyclohexane to adipic acid with the 92 % selectivity in mild conditions. More over the catalyst has saved its activity until 6 cycles without any dominant losing.