Emerging contaminants including drugs, additives, pesticides, microplastics have been found in drinking water. Currently available standard treatments are not effective enough and new materials/device and purification technologies are required.
Graphene materials -composites, membranes- have shown high potential for both adsorption and filtration purposes with removal performance competitive and even higher than those of standard systems (e.g. activated carbon).
Graphene hydrogels can be also considered as a sustainable option for water treatment by a cleaning step that uses the sunlight.
CNR and Chalmers University, in collaboration with Medica, an Italian SME commercializing water filters, have developed polysulfone based composites showing enhanced performance in removing several classes of emerging organic contaminants such as antibiotics and dyes. In an article published on Nanoscale (2019), CNR demonstrated how graphene oxide (GO) can be used to recycle industrial plastic waste into filters able to outperform activated carbon materials.
This approach allows to obtain a new eco-sustainable sorbent and also reduce the amount of plastic scraps wasted by the membrane industry (3 tons/year, 10% of the yearly production).
In an article published on Faraday Discussions in January of 2020, the versatility of this technique was further demonstrated with a new technique to fix GO directly on the pores of conventional polymer filters, allowing to filter microscopic particles and mesoscopic molecules at the same time.
The filtering capacity of the new GO-PSU material has been tested by samples of water contaminated with substances such as rhodamine, a dye widely used in the textile and pharmaceutical fields, the antibiotic ofloxacin and the anti-inflammatory diclofenac, principles present in dozens of eye drops, tablets, ointments.
"These molecules are part of the so-called emerging pollutants - drugs, pesticides, detergents and various fragrances - recently identified in drinking water and subject to attention for the potential risks to health and the environment, so much so as to consider the revision of the European directive on drinking water currently being examined by the EU. The measurements confirmed that the filtering performance of the polysulfone membranes was added with graphene oxide more than three times that of the material containing only polysulfone "
explains Vincenzo Palermo of Cnr-Isof and Deputy Director of Graphene Flagship. "The excellent performance is due to the unique properties of two-dimensional materials, in particular to the structure of graphene oxide: the layered arrangement of these sheets, separated from each other by nanometric distances that guarantee, is ideal for trapping contaminating molecules and more efficient than that of classic three-dimensional filters.
Thinking more in a sustainable way what if we can clean the water by using sunlight? It seams impossible, however this is enabled by Photocatalytic process that uses eco-friendly materials to promote the degradation of water pollutants into harmless compounds.
Therefore the use of Solar light-activated photocatalyst nanoparticles (NPs) based on graphene can enable the use of the energy coming from the sunlight as a way to regenerate the filters, by destroying bacteria, and pollutants. In case these particles are embedded in a transparent hydrogel we can couple the retention effect of the filter, with the cleaning effect of the graphene NPs.