Nanocomposite Films Prepared from Differently Modified ZSM-5 Zeolite and Cellulose Nanofibrils for Cationic and Anionic Dyes Removal

Ecologically-friendly and water-stable composite films were prepared by solvent casting process using variable concentrations (20 and 80 wt %) of de-aluminated (D-ZSM) and Cu (Cu-ZSM) or Fe (Fe-ZSM) ion-exchanged ZSM-5 (ZSM) zeolite as adsorbents and 0.6 wt% of cellulose nanofibrils (CNFs) as a matrix, to be used in removal of both cationic and anionic dyes. The films were characterized by spectroscopic (FTIR and XRD), microscopic (SEM), potentiometric titration, and CO2-adsorption (BET) analysis, and tested for cationic and anionic dyes removal capacity and kinetic via the batch adsorption process in aqueous buffer solutions. The influence of contact time, initial dye concentration, and pH is investigated and evaluated using various isotherm and kinetic models. The Langmuir isotherm is recognized as better fitting model for relevant study conditions, and the process follows pseudo-second order kinetic, yielding a monolayer adsorption capacity of about 34 mg/g and 16 mg/g for cationic and anionic dyes using D-ZSM/CNF and Fe-ZSM/CNF based films, respectively. Maximum dye removal is observed for a higher (80 wt %) amount of ZSM containing films and pH ≥ 7 vs. pH ≤ 7, influencing on electrostatic, physical, and hydrophobic adsorption mechanism. A higher adsorption efficiency of D-ZSM/CNF film with surface area of 194 m2/g is also related to unevenly distributed and globule-like structures of 40 nm sized D-ZSM, compared to more densely-packed and 72 nm sized platelet/flake-like structures of Cu-ZSM and Fe-ZSM covering the CNFs surface (7.5 m2/g). The films show potential in removal of differently charged contaminants, thus acting within a broader pH range, by being prepared with a combination of suitably modified ZSMs.