Nanocomposite beads with engineered pore architecture for improved removal of emerging contaminants from water

Abstract

The rapid crosslinking process for the formation of biopolymeric beads typically limits their adsorption rates and capacities due to suboptimal pore structures and morphology. In conventional beads, the highly porous core is enclosed by a semi-permeable shell, restricting mass transfer. To address this, we engineered the pore architecture of the beads using an internal gelation (IG) process. This approach overcomes diffusion resistance barriers, and improves the environmental performance of the beads. By controlling the gelation process with CaCO₃ (IGC), which is a gas forming agent, and CaSO₄ (IGS), which controls the rate of cross-linking from within the beads, we tailored the pore architecture. We characterized the beads in terms of elemental composition, morphology, mechanical properties, and stability. The IG beads, containing only 3.5 wt% graphene oxide (GO), showed significantly faster adsorption rates—up to two orders of magnitude higher for diclofenac and twice as fast for tetracycline removal compared to externally gelled (EG) beads. IGS beads demonstrated superior adsorption capacities, with multiple-fold increases for both diclofenac and tetracycline, due to enhanced intraparticle diffusion enabled by the IG process. The exceptional performance of IGS beads is attributed to the creation of a highly porous outer shell with hierarchical linkage to the inner core, reducing diffusion resistance and maximizing the adsorption potential of GO’s sp² hybridized domains, without the need for chemical reduction of the nanosheets. IGC beads, with improved mechanical properties, also showed remarkable adsorption capacities comparable to IGS beads, and surpassing that of EG beads. Our technique, not material specific, can be used in any hydrogel that is made by ionic cross-linking for a broad range of applications.