With the rapid development of industry, air and water pollution has become a critical topic to the public and scientific community since the quality of air and water is essential for the prosperity of life. In this study, two novel adsorbents, Fe3O4@polydopamine (PDA)-Ag microspheres and SBA-15-Ag composites, have been synthesized by facile wet chemical methods. Monodisperse Ag nanoparticles (NPs) are densely deposited on the surface of PDA layers and within the mesopores of SBA-15, respectively. High catalytic activity of Fe3O4@PDA-Ag on the reduction of methylene blue (MB) and effective removal of Hg0 by SBA-15-Ag have been achieved mainly due to the presence of monosized Ag NPs. The capture of Hg0 by Ag NPs is due to the amalgamation mechanism of Ag-Hg alloy. Fe3O4@PDA-Ag microspheres also exhibit high adsorption rate on MB because of the electrostatic interaction between PDA layer and MB molecules. More importantly, the as-prepared Fe3O4@PDA-Ag microspheres demonstrate excellent reusability and cyclic stability (>27 cycles), and the regeneration process could be completed within several minutes by using NaBH4 as the desorption agent via a unique catalytic desorption process. The Fe3O4@PDA-Ag microspheres can be easily recycled from the solution by an external magnetic field, thanks to the good magnetic performance of Fe3O4 cores. In addition, the Fe3O4@PDA-Ag microspheres show good aqueous and acid stability in aqueous solution without significant change in morphology and performance for over half a year. The new adsorbents developed in this work show important potentials in practical applications for adsorption and catalysis.