Fresh leaves of Anacardium occidentale were procured from the
rural areas of Thiruvananthapuram, India. The auric acid, NaBH4
and p-nitro phenol were obtained from Sigma–Aldrich.
Extraction of essential oil
About 360 g of homogenized fresh leaves of A. occidentale were
hydro distilled using Clevenger type apparatus to yield 0.0639% of
oil yield. The oil was dissolved in 2 ml acetone to form the reducer
as well as stabilizer for the synthesis of gold NPs.
Phytosynthesis of gold NPs
In a typical synthesis of gold NPs, about 2 ml of oil was added to
30 ml of aqueous 2.5 104 M HAuCl4 solution at 100 C with continuous stirring and boiled for one minute (sample A). Rapid reduction of Au3+ ions to Au0 occurred and the color of the solution
became pink. The experiment was repeated with 5 ml and 8 ml
of diluted oil to get purple and violet colored solutions, respectively (sample B & C). The reduction was also successful at room
temperature but slightly slowly (sample D).
Catalysis of gold NPs
The stock solutions of 5 103 M 4-nitrophenol and 0.25 M
NaBH4 solution were prepared. About 1 ml of 4-nitrophenol was
mixed with 23 ml of de-ionized water followed by the addition
of 1 ml of NaBH4 solution [28] and stirred for ten minutes to get