An extraordinary metal–organic framework FJI-H9 with high adsorption and selectivity for the reversible uptake of Cd(II) has been developed. Further research indicates that such high absorption results from an unusual synergy from active sites and the confined cavity. In addition, fast detection of Cd(II) at low concentrations down to 10 ppm and in situ reconstruction of the used framework into a fresh one have also been successfully achieved.