Recyclable hydrogel-MOFs composite beads for selective removal of Pb(II) from water

Lead ions (Pb2+) as a typical toxic contaminant in the water resources cause health risk. In order to selectively remove Pb2+ from water, a novel adsorptive composite bead was prepared via introducing different functional metal-organic frameworks (MOFs) into alginate (Alg) hydrogel. The hydrogel-MOFs composite beads possessed the excellent adsorption towards Pb2+. The sulfonic-functionalized A-U6S composite beads showed the best adsorption performance of Pb2+ with the adoption capacity of 400.5 mg g-1 among three tested hydrogel-MOFs composite beads due to the specific affinity between Pb2+ and -SO3H. The Langmuir adsorption and pseudo-second-order kinetic models validated that Pb2+ was adsorbed by A-U6S in the manner of monolayer chemisorption on the surface of A-U6S composite beads. The thermodynamics study indicated that the interaction between A-U6S and Pb2+ was spontaneous and endothermic. Meanwhile, A-U6S showed higher adsorption capacity of Pb2+ in the coexistence of Cu2+, Cd2+, Zn2+ and Ca2+, exhibiting excellent selective adsorption towards Pb2+. The selectivity factors of Pb2+ versus Cu2+, Cd2+, Zn2+, and Ca2+ were 5.4, 5.7, 6.1 and 9.1. A-U6S composite beads can be reused five times with stable adsorption ability towards Pb2+ and till reached 94.2% of pristine adsorption capacity. Moreover, UiO-66(SO3H) powder can be collected and recycled after degradation of Alg by H2O2 solution. The functionalized hydrogel-MOFs composite beads and the strategy for reuse and recycle of composite materials by the present study have great potential for practical applications in water purification treatment.