Mesoporous alpha-manganese dioxide (alpha-MnO2) were synthesized from manganese(II)-based deep eutectic solvent (DES) of MnCl2 center dot 4H(2)O and acetamide in a 1:7 molar ratio. The DES can act as solvent and reducing reagent. As-prepared samples were characterized and used as absorbents for the removal of Congo red (CR) from aqueous solutions. Results show that the sample prepared at 70 degrees C (M-70) could remove 93% CR from aqueous solutions in 30 min. The maximum adsorption capacity of the M-70 was estimated to be 54.85 mg/g. Finally, the exhausted M-70 can be regenerated by thermal desorption.