Biochars produced by pyrolysis of corn cob(600℃) which is agricultural waste, and modified with hydrochloric acid, hydrogen peroxide and nitric acid separately. Elemental analysis, BET-N2 surface area(SA), scanning electron microscopy, Boehm titration and FTIR spectra were used to characterized their physicochemical properties. Batch experiments were conducted to investigate ammonium adsorption process of corn cob biochars. The results revealed that acid modification can significantly improve biochars' spec...