Hierarchically porous carbonaceous sponges and their magnetic nanocomposites were fabricated by a combined approach of hydrothermal carbonization and freeze drying. The resulting carbonaceous sponges have hierarchically porous structure and a large number of oxygen-containing functional groups. The unique structure enables carbonaceous sponges candidate materials for rapid and efficient organic molecules removal from water. Display omitted •The CS is sustainable, inexpensive and hierarchically porous.•The CS exhibits excellent adsorption capacities toward organic molecules.•Convenient solid–liquid separation after removal of organic molecules is achieved by introducing Fe3O4 NPs into CS network. This work describes the preparation, characterization and removal capability of a novel biomass derived carbonaceous sponges (CS) and their nanocomposites. The CS has hierarchically porous structure which is composed of lamellar structures and secondary porous structures. The pore size is on a scale from 1nm to 200μm. Utilizing the CS as adsorbents, rapid removal of model organic molecules, including methylene blue (MB), methyl orange (MO) and crystal violet (CV), from their aqueous solutions can be completed within 1min with the assistance of pressure and the removal efficiency reaches up to 100%, 81% and 98%, respectively. The removal capabilities for CS towards MB, MO and CV are 0.0769g/g, 0.2218g/g and 1.0384g/g, respectively and 0.0635g/g, 0.0977g/g and 0.8634g/g, respectively for CS nanocomposites.