3D interconnected polymer/mesoporous silica nanoparticle hybrid materials with hierarchical macro/meso-structures for heavy metal adsorption

Polyethyleneimine (PEI)/mesoporous silica hybrid materials with hierarchical macro/mesostructures were synthesized using amine-coated mesoporous silica nanoparticles (MSN-NH₂), PEI, and 4,4′-methylenebis(phenyl isocyanate) (MPI) linkers. The isocyanate groups of MPI at both ends of the molecule act as linkers to three-dimensionally interconnect the amine groups of MSN-NH₂ and PEI to form polyurea bonds. Since the synthesized PEI/MSN composite has a large amount of amine groups, it adsorbs Pb²⁺, Cd²⁺, and Hg²⁺ ions by forming a metal chelate complex. Transmission electron microscopy (TEM) analysis showed that MPI is a good linker to form a hierarchical macro/meso network structure. Infrared analysis showed that the isocyanate (-N = C O) peak (∼2270 cm⁻¹) disappeared and a C O peak from the urea groups (1640-1670 cm⁻¹) appeared, further confirming that polyurea was successfully formed. Elemental analysis through ICP-OES validated the adsorption capabilities of the PEI/MSN composite, revealing its effectiveness in adsorbing Pb²⁺, Cd²⁺, and Hg²⁺ ions during heavy metal adsorption experiments, with adsorption rates reaching 74%, 86%, and 60%, respectively. Selectivity tests for Pb²⁺, Cd²⁺, and Hg²⁺ ions at the same concentration showed 9.6, 10.1, and 77.0% efficiency, representing a high absorption preference for mercury ions. This three-dimensionally interconnected PEI/MSN composite with hierarchical macro/meso-structures effectively removes heavy metal ions and can potentially be used as a good heavy metal adsorbent.