The CelloZIFPapers with the highest ZIF-8 content were evaluated for heavy metal adsorption capacity using aqueous solutions of Cd 2+ , Co 2+ , Cu 2+ , Fe 3+ , and Pb 2+ (Fig. ). The metal adsorption using ZIF-8 is usually fast . The adsorption equilibrium for Co 2+ ions can be achieved after 30 min (Fig. ). The fast adsorption can also be confirmed from the fast color change of the CelloZIFPaper from white to blue or purple after the soaking into Cu 2+ or Co 2+ ions solution, respectively, after 10 min. CelloZIFPaper_In Situ exhibited higher adsorption capacity than CelloZIFPaper_Ex Situ. The materials exhibited adsorption capacities of 143, 350, 354.0, 260.8, and 307.3 mg/g for Cd 2+ , Co 2+ , Cu 2+ , Fe 3+ , and Pb 2+ ions, respectively (Fig. ). On the other hand, CelloZIFPaper_Ex Situ showed adsorption capacities of 196.8, 300, 166.5, 66.2, and 87.2 mg/g for Cd 2+ , Co 2+ , Cu 2+ , Fe 3+ , and Pb 2+ , respectively (Fig. ). There is no significant Zn leaching during the adsorption (Fig. ). The adsorption of Pb 2+ using CelloZIFPaper_In Situ increased with the initial metal ion concentration (Fig. ). Several mechanisms for metal ion adsorption using ZIF8-based materials have been suggested . The metal can be adsorbed using ZIF-8/TOCNF/CP via ion exchange (e.g., with a metal node of ZIF crystals) or coordination to the functional groups of cellulose (i.e., -O.H. or -COOH). In this work, pH changes (Figure ), FT-IR (Figure ), DRS (Fig. ), Tauc's plot (Figure ) , XPS (Fig. ), CV (Fig. ), and LSV (Fig. ) analyses were performed to elucidate the mechanism that controls these interactions. The Pb 2+ solution is acidic, i.e., pH=4 (Figure ). There is an increase in pHduring the adsorption due to the removal of the metal ions (Figure ). It was reported that ZIF-8 crystals provide a variety of active adsorption sites, including O-H and N-H groups, low-coordinated Zn atoms, and free N -groups belonging to Hmim . Cellulose and TOCNF have functional groups such as O-H and COO -, adsorb metal ions . FT-IR spectra for CelloZIFPaper before and after adsorption of metal ions are reported (Figure ). Tetrahedrally coordinated atoms such as Co and Cu can replace Zn in the frameworks. FT-IR spectrum of CelloZIFPaper shows a peak at 421 cm -1 corresponding to Zn-N (Figure ). The FT-IR spectrum of Cu adsorbed CelloZIFPaper shows two peaks at 425 cm -1 and 430 cm -1 corresponding to Zn-N, and Cu-N, respectively (Figure ). DRS spectra of the papers before and after metal adsorption indicate the change in the intensity of the UV-Vis absorption (Fig. ). This change can be attributed to the strong interaction between the adsorbed metal ions and the functional groups of the membranes that can be determined from Tauc's plot (Figure ). The bandgap values of CelloZIFPaper before and after adsorption are tabulated in Table . The change in the bandgap of CelloZIFPaper reveals the presence of the adsorbed metal inside the crystal of ZIF-8. Thus, the white color of CelloZIFPaper turns purple and blue after the adsorption of Co 2+ and Cu 2+ , respectively (Figure ). Other metal ions, such as Pb 2+ or Cd 2+ , caused no dramatic change in the bandgap of CelloZIFPaper due to the low tendency for coordination inside ZIF-8 crystals (Table ). The elemental survey for CelloZIFPaper_In Situ confirms the presence of C, N, Zn, and adsorbed metal species (Fig. ). XPS analysis of Pb@CelloZIFPaper_In Situ shows two peaks at binding energies of 143.9 eV and 138.9 eV corresponding to Pb 4f5/2 and Pb 4f7/2, respectively (Fig. ). The Pb 4f7/2 peak reveals three peaks at binding energies of 137.8 eV and 140.4 eV, which are associated with Pb-O, and Pb-O-C, indicating the coordination to the carboxylic group of TOCNF (Fig. ). The analysis of the Cd adsorbed membrane shows two peaks at binding energies of 405.6 eV and 412.3 eV, corresponding to Cd 3d5/2 and Cd 3d3/2 (Fig. ). At the same time, the spectrum of the CelloZIFPaper used for the adsorption of Fe 3+ shows peaks at 711.0 eV, and 724.3 eV, corresponding to Fe 2p3/2 and Fe 2p1/2, respectively (Fig. ). The Cu ion adsorbed paper analysis shows peaks at binding energies of 934.7 eV and 954.7 eV, corresponding to Cu 2p3/2 and Cu 2p1/2, respectively, with two satellite peaks at 943.8 eV and 962.9 eV (Fig. ). The analysis confirms that the oxidation state of Cu is 2+ indicating no reduction of Cu 2+ after adsorption (Fig. ). This observation suggests that the adsorption mechanism is different from the previously reported mechanism using only TOCNF, which causes the reduction of Cu 2+ and formation of Cu2O . The ion-exchange mechanism for the adsorbed Cu 2+ can be investigated via the analysis of N 1s (Fig. ). The XPS spectrum of N 1s of ZIF-8/TOCNF/CP paper shows two peaks at binding energies of 399.4 eV and 400.7 eV corresponding to -C-N and -C=N in Hmim, respectively . After adsorption tests with the Cu 2+ solution, the two peaks of N 1s for Hmim still exist, and an extra peak at 398.9 eV is observed, indicating the coordination between the nitrogen atom and Cu 2+ (Fig. ). A previous study reported a new peak at a binding energy of 403.4 eV due to ion exchange and coordination between Cu 2+ and ZIF-8 crystals . This peak (at a binding energy of 403.4 eV) is not present in our case, indicating that the interactions are mainly electrostatic and coordination to N in Hmim. Both