Alginate/graphene double network hydrogel has recently been demonstrated as a promising adsorbent for water pollutants. To improve the adsorption capacity of the double network hydrogel, physical and chemical modifications are made to obtain an excellent porous structure and more functional groups. As-modified alginate/graphene double network hydrogel has a higher hydroxyl group content under a higher polyvinyl alcohol content and a higher carboxyl group content with a higher oxidation degree. Moreover, the CO2 produced by CaCO3 is used as pore formation agent avoiding the use of toxic organic matters. The modified alginate/graphene double network hydrogel shows a higher specific surface area, a larger mean pore diameter, and a higher pore volume with a higher initial CaCO3. In antibiotics adsorption, the mechanistic understanding shows that hydrogen bonds have greater influence on adsorption than carboxyl groups. The results reported here pave the way for the use of the alginate/graphene double network hydrogel for water treatment. (C) 2017 Elsevier Inc. All rights reserved.