Development of Metal Ion Absorbing Filter Using Cellulose Nanofibrils

Many studies have shown that CNFs are useful for the production of sheet-type materials, including film, filters, and so on. There are many advantages to the use of CNFs in the filter industry, however, filters made from only CNFs cannot be widely used as water treatment filters, due to their hydrophilic behavior. As a result, a new design of CNF water treatment filters must be developed. In this study, we made a metal ion adsorbing filter made from two types of CNFs: chemically untreated CNF and carboxymethylated CNF. The new CNF filter was composed of two layers; the top layer was made from CNF with PAE, and the bottom layer was made from carboxymethylated CNF. The role of the top layer of the CNF filter was to improve the wet strength of the CNF filter and the bottom layer was designed to adsorb metal ions due to the high negative zeta-potential of carboxymethylation. The CNF filter was produced by vacuum filtration and the use of two types of CNF slurries. Also, the capacity to remove Fe ions from water was analyzed by high pressure filtration experiments with a 1,000 ppm concentration of the Fe standard solution. The CNF filter removed Fe ions in the water by adsorbing them, and it did not break during the high pressure filtration experiments. Therefore, we concluded that the new CNF filter can be used as a filter for the removal of heavy metal ions in water.