Ammonia modified cotton-based activated carbon (AC-NH3) was prepared and utilized to investigate the effect of ammonia modification on the chemical properties of activated carbon in catalyzed peroxymonosulfate (PMS) oxidation of aqueous organic pollutant. Activated carbons with and without modification were characterized by N-2 adsorption/desorption, scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), Boehm titration, Fourier Transform Infrared Reflection (FTIR) and X-ray photoelectron spectroscopy (XPS), respectively. Results indicated that ammonia modification has a promoting effect on the catalytic ability of AC in our system. And as small amount as 0.04 AC-NH3 can efficiently activate PMS and subsequently degrade a model contaminant, Reactive Black 5 (RB5). Considering RB5 was barely removed by sole-AC-NH3 or sole-PMS, adsorption and catalytic oxidation have a significant synergistic effect in the combined AC-NH3/PMS system. With the XPS spectra deconvolution, we inferred that the pi-pi and pyrrolic functional groups resulted in the promoting catalytic ability of AC-NH3. However, the pyridine seems to play a nonsignificant role in our process. In addition, the parameters in the AC-NH3/PMS system, including the mole ratio of PMS to RB5, the dosage of AC-NH3, the initial concentration of RB5, initial pH, and the feeding method of PMS, were also discussed. (C) 2016 Elsevier B.V. All rights reserved.