Hierarchical petaloid-array structure of carbon dots/Mg(OH)2 (marked as CDs/Mg(OH)2) composite was prepared via a facile method. The synergistic effect of Mg(OH)2 and CDs enable composite o recover Cd(II) ions at a controllable rate and produce Cd(OH)2 1D nanowires. Display omitted •Petaloid-array carbon dots/Mg(OH)2 was prepared by a facile method.•DFT study recognized the composite structure and explored interfacial property.•Cd(II) was removed at a controllablerate by synergistic effect of composite.•Cd(OH)2 was recovered as 1D nanowires.•The removal capacity of composite reaches 1015.4 mg g−1. The ever-growing contamination of water resources generated by heavy metals is posing significant threat to sustainable development, and urging the necessity of safe disposal. In this work, we designed a facile method to prepare carbon dots/Mg(OH)2 (marked as CDs/Mg(OH)2) composite, which enables to remove and recover potentially toxic metal of Cd2+ from water. The newly-prepared CDs/Mg(OH)2 features a hierarchical petaloid-array structure and has large specific surface area of 96.2 m2 g−1. It is evident that the composite is composed of Mg(OH)2 slices, to which CDs are attached. Density functional theory calculation recognized the composite microstructure at the atomic level. Weak chemical coupling between sub-units were borne out by optimized structures, energetics, infrared vibrations, and electronic structures. The CDs/Mg(OH)2 composite shows high removal capacity and long durability while treating Cd(II)-contaminated water. The incorporation of CDs could regulate and control the up-taking rate of Cd2+ ions and consequently fabricate well-dispersed 1D nanowires of Cd(OH)2. The corresponding mechanism was proposed. Specifically, the sample CDs/Mg(OH)2-60 reaches 1015.4 mg g−1 removal capacity; it can be used for 12 cycles and still keep removal efficiency as high as 98.6%.