A novel ultralight 3D-Mn(OH)₄ porous material for heavy metal ions removal from water

Three-dimensional (3D) metal oxides, consisting of a simple nanostructure, have become the key to numerous environmental remediation technologies owing to their unique properties. Herein, a novel ultralight (0.0834 g/cm³) 3D manganese(IV) hydroxide (Mn(OH)₄) material without volume shrinkage was exploited for the first time. The 3D-Mn(OH)₄, with a porous structure composed of cross-linked ultra-long nanowires was fabricated through a mild and cost-effective hydrothermal treatment followed by a freeze-drying process. The excellent removal performance for low concentration toxic metal ions of 3D-Mn(OH)₄ was ascribed to its high specific surface area, 3D porous structure, and abundant hydroxyl groups on the surface. Experimental data show that the maximum Cd(II), Co(II), and Cu(II) ions adsorption capacities have been demonstrated to be 107.75, 85.48, and 102.45 mg/g, respectively. Importantly, the used 3D-Mn(OH)₄ demonstrated an excellent regeneration performance. To account for the mechanisms that affect the adsorption properties, a systematic study was carried out. These findings provide the possibility to expand the use of a novel ultralight 3D-Mn(OH)₄ nanomaterial for application in the environmental sciences. It is believed that our research strategy could be extended to fabricate other three-dimensional porous manganese oxides with great promise for various applications.