70 C. The dried samples were then ground and sieved to desired particle size of 500–710 lm and further dried in the oven. The sample was then soaked in orthophosphoric acid (H3PO4) with an impregnation ratio of 1:1 (w/w) according to the preliminary experiments for 24 h and dehydrated in an oven overnight at 105 C [33]. Afterwards, the sample was activated in an electric stainless steel tubular furnace at 500 C with constant heating rate of 10 C/min, under purified nitrogen (99.995%) flow rate of 150 cm3/min for 2 h. The AC produced was then cooled to room temperature and washed with 0.1 M HCl and successively with hot distilled water repeatedly until the pH of the filtrate reached
6–7. The final product was dried in an oven at 105 C for 24 h
and kept in an airtight container for further use.