Novel ZIF-8/CNC Nanohybrid with an Interconnected Structure: Toward a Sustainable Adsorbent for Efficient Removal of Cd(II) Ions

Water pollution, especially by heavy metals, continues to pose significant challenges, emphasizing the urgency to develop sustainable processes to remove pollutants while developing sustainable materials derived from renewable sources. In the present research, a nanoscale adsorbent was prepared to remove cadmium (Cd(II)) ions from wastewater by hybridizing zeolitic imidazolate framework-8 (ZIF-8) with a cellulose nanocrystal (CNC). The prepared nanohybrid exhibited an interconnected structure in which the ZIF-8 particles were connected to each other via CNC nanoneedles. The hybridization of ZIF-8 with CNC caused a significant enhancement in the adsorption performance of the fabricated nanohybrid compared to pure ZIF-8, increasing its adsorption capacity by nearly 36%. The adsorption of ZIF/CNC followed the Langmuir isotherm model and pseudo-second-order kinetics models, remarking homogeneous adsorption onto the surface of ZIF/CNC, where chemisorption controlled the rate of adsorption. The thermodynamic study uncovered that the adsorption is spontaneous, endothermic, and entropy-governed as the randomness was increased at the solid-liquid interface. Additionally, the influence of operating variables, such as temperature, adsorbent dosage, pH, and ionic strength, was studied to mimic the adsorption capabilities of the adsorbent in real conditions. Accordingly, the optimum conditions were found to be at 45 °C and pH = 7 with a dosage of 0.4 g/L for the adsorbent. Moreover, the adsorption in a multimetal solution showed that the ZIF/CNC nanohybrid can remove various heavy metals, including Cd(II), Fe(III), Cu(II), and Pb(II) ions simultaneously. Finally, the regeneration study confirmed the great potential of the ZIF/CNC nanohybrid, which retained 94% of its initial adsorption capacity after 5 consecutive adsorption/desorption cycles.