Membrane operations are important tools to tackle water contamination enabling supply of potable water for a growing number of people living on this planet. Conventional membranes for this task are usually produced from synthetic polymers, derived from fossil resources, or ceramics requiring significant amounts of energy, chemicals and solvents during their production. Therefore, utilization of membranes based on a renewable resource, such as nanocellulose papers, could be an alternative. Cellulose papers have a long tradition as filter and membrane material dating back to ancient times. However, conventional filter papers, produced from cellulose microfibrils, exhibit certain limitations when pollutants in the nanometer range are to be removed. Recently, we demonstrated the utility of nanocellulose papers, so-called nanopapers, as tight aqueous UF membranes by application of a simple papermaking process. Unfortunately, removal of contaminants smaller than 5 nm or ions was not feasible. Here we present an approach to improve the performance of nanopapers, derived from paper industry residues, via the introduction of certain functional groups, such as phosphate (PO43−) or ammonium (NH4+) groups. Nanopapers equipped with these groups are expected to perform adsorption operations for nitrates or heavy metal ions not in static media only but also while permeated. Modification of CNF, derived from fibre sludge, an industrial side-stream, with NH4+ or PO43− groups was successfully performed via the reaction with glycidyltrimethylammonium chloride or H3PO4, respectively. Nanopapers were produced from various grades of CNF by filtering nanocellulose suspensions and consolidating the filter cake in a hot-press. Filtration experiments were performed in a dead-end cell, resulting in values for the permeance and the rejection of nitrates and heavy metal ions, respectively. Nanopapers equipped with phosphate groups were able to adsorb copper in dynamic filtration experiments up to 20 mg per g phosphorylated CNF, whereas ammonium-modified CNF captured nitrates up to 12 mg per g cationic CNF, which is in the range of adsorbent materials derived from industrial or agricultural waste-streams for batch-wise adsorption, with the advantage of contact times of seconds rather than hours. Acknowledgement: Financial support from the European Commission under EU FP7 project “NanoSelect” (NMP4-SL-2012-280519) is gratefully acknowledged.

Cellulose nanopapers as ion-exchangers for nitrate and heavy metal removal

251st National Meeting (2016)

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