Creating Combined Material Filters With Enhanced Effectiveness

Although there is always talk about how Earth may not have enough habitable space for whatever the future population may be, I have never been particularly worried about this. Over the last fifty years places on this planet that were only habitable to the occasional hunter-gatherer group have managed to support massive growing urbanisation. For instance the United Arab Emirates, despite being next to the Persian Gulf, is a desert biome in its natural state. Drinking water is obtained through massive desalination plants which use reverse osmosis to remove the salt from the sea water. Normally the filter which the water is forced through is thin film composite (a film made of multiple layers) which normally contains a polyamide (as an active component) and polysulphone (as a support) layer.

These thin film composites have advantages and disadvantages with the primary disadvantage being that as their salt removing ability increases, their lifetime before fouling makes them become ineffective decreases. One of the more common kinds is biofouling, where bacteria cling to the membrane and since polyamides are  iodegradable the microbes are able to chemically react with the film. The other main material used to make the thin films is graphene. Now graphene is quite antibacterial by nature and is certainly applicable in reverse osmosis but it is difficult to chemically alter graphene to give it beneficial qualities. Graphene oxide, when produced, avoids these problems by covering the graphene in many carboxyl and hydroxyl functional groups which other chemicals can then react with.

Attempts were made to combine the two technologies and infuse the polyamide layer within the thin film with a layer of graphene oxide. However it was found that these combined membranes had a crucial flaw where the salt separation could not be improved in tandem with the total volume of water passing through the filter. Recently work was done that involved producing one of these hybrid membranes. The graphene oxide was treated with tannic acid (C76H52O46) and polyethyleneimine (x of C2H5N) and then combined with the polyamide. The resulting material was treated to a variety of experimental tests in order to determine the range of its properties.

Paper links: A Novel Fabrication Approach for Multifunctional Graphene-based Thin Film Nano-composite Membranes with Enhanced Desalination and Antibacterial Characteristics

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