A novel template-activation method was used to create nanoporous carbon materials derived from core-shells@rGO sheets. The carbon materials were prepared through an acid etching and thermal activation procedure with three-dimensional Fe3O4@C@rGO composites as precursors and Fe3O4 nanoparticles as the structural template. The activation at different temperatures could provide materials with different specific surface areas. The unique nanoporous structures with large surface areas are ideal adsorbents. The nanoporous carbon materials were used as adsorbents for the removal of rhodamine B (Rh-B). C@rGO-650 illustrated better adsorption performance than the other synthesized adsorbents. It displayed good recyclability, and its highest adsorption capacity reached up to 14.8 L·g-1. The remarkable adsorption properties make nanoporous carbon a useful candidate for wastewater treatment. This template-activation method can also broaden the potential applications of core-shells@sheet structures for the construction of nanoporous carbon, which helps to resolve the related energy and environmental issues.