Efficient and selective adsorption of uranium by diamide-pyridine-functionalized hierarchically porous boron nitride

Uranium (U) released by nuclear accident raises concerns about human health owing to its long half-life and toxicity. Diamide-pyridine-modified hierarchically porous boron nitride (HPBN-DAPy) was prepared for efficient removal of U. HPBN, which could hardly adsorb U, gained the ability to uptake U only after functionalization with diamide pyridine (DAPy) groups. The hierarchically mesoporous structure with bimodal mesopores around 20 and 3 nm endowed HPBN-DAPy with unique adsorption kinetic. Uranyl ions (UO22+) easily approached the adsorption sites in those large mesopores and thus the adsorption rapidly reached temporary equilibrium within 0.5 min with a relatively high adsorption of amounts (qe) of 87.5 mg g-1 (adsorbent dosage = 0.4 g L-1, [U]0 = 100 mg L-1, pH = 4.0 +/- 0.1, T = 298 +/- 1 K), which was beneficial for rapid decontamination. Small mesopores and the inner large mesopores, which were connected through small mesopores, provided extra adsorption sites, leading to a further increased qe of 115.7 mg g- 1 after achieving final equilibrium. Investigation of adsorption mechanism showed that UO22+ were chemically adsorbed in monolayer at a low initial concentration while they were physically adsorbed in the form of polynuclear complexes at a high initial concentration. Benefited from the strong affinity between UO22+ and DAPy, HPBN-DAPy performed excellent selectivity for UO22+ toward other most concerned radionuclide ions. Furthermore, HPBN-DAPy also exhibited adequate salt tolerance and outstanding reusability, which should be promising in removal of U from contaminated water.