Enhanced Mechanical Properties and Water Contaminant Adsorption Performance of Nanocomposite Beads via Cellulose Nanocrystal Encapsulation

The poor mechanical properties of hierarchically porous biopolymeric beads synthesized via the internal gelation process have hindered their practical application in point-of-use and centralized water treatment systems. To overcome this limitation, we improved the mechanical properties of nanoengineered alginate-graphene oxide (AL-GO) nanocomposite beads by incorporating cellulose nanocrystals (CNCs). The enhanced properties of the resulting ternary beads were confirmed through various characterization techniques. CNCs provided structural support between the pores and reinforced the nanocomposites, producing more compact and rigid beads with over a 500% increase in their storage modulus. The robust multifunctional beads demonstrated excellent reusability, successfully undergoing four cycles of regeneration and reuse. These ternary beads exhibited exceptional adsorption capacities for methylene blue (MB, 962 mg/g), diclofenac (DCF, 384 mg/g), and tetracycline (TC, 95 mg/g), with at least a 49% improvement in contaminant adsorption capacity compared to beads without CNCs. This superior performance is attributed to the synergistic effects of the negatively charged functional groups of AL, GO, and CNC at neutral pH, which enhanced electrostatic attraction for MB adsorption and hydrogen bonding for TC adsorption. Kinetic modeling revealed that surface adsorption was the primary rate-limiting step for DCF, whereas intraparticle diffusion dominated the adsorption of MB and TC. Using the Mathews–Weber external mass transfer model, we optimized the CNC content in the nanocomposite to 10 wt %, achieving a balance between mechanical properties and adsorption efficiency without compromising the faster adsorption rate of the beads for water treatment.