a white colloidal solution. Subsequently, the color of the colloidal
solution turned to yellow with the addition of 100 mL H2O2 (30%).
The as-formed yellow solution was transferred into a Teflon-lined
autoclave of 25 mL capacity and heated for 6 h at 150 C. After the
autoclave was cooled to room temperature naturally, light brown
products were collected and washed with deionized water 4 times.
Finally, the products were washed with absolute ethanol, and
dried in an electric oven for 10 h at 70 C.