Three organic acid ammoniums (ammonium succinate (AS), ammonium tartrate (AT) and ammonium citrate (AC)) were employed to modify Phragmites australis (PA)-based activated carbons during phosphoric acid activation via microwave irradiation to improve acid red 18 (AR 18) removals from aqueous solutions. The physicochemical properties of the modified (PAC-AS, PAC-AT and PAC-AC) and unmodified carbons (PAC) were systematically characterized. The nitrogen content, pH(iep) and basic foundational groups of the modified carbons increased however their surface areas decreased after modification. FTIR and XPS analyses revealed that N-containing groups such as -NH, -CONH and -NH2 were effectively introduced on modified carbons' surfaces. Although PAC-AS and PAC-AT had lower surface area than PAC, their adsorption capacity were higher due to larger amount of N-containing groups. The adsorption kinetic data were simulated well by the Elovich equation and the equilibrium data were best fit to the Freundlich model for all PACs. The adsorption of AR 18 on PACs decreased with increasing pH values. The maximum AR 18 adsorption capacity followed an order of PAC-AS (115.93 mg/g) > PAC-AT (104.23 mg/g) > PAC (90.52 mg/g) > PAC-AC (57.99 mg/g), indicating that AS and AT are promising activating agents for activated carbons to improve their AR18 adsorption performances. (C) 2017 Elsevier B.V. All rights reserved.