Getting the most out of waste water Phosphate is essential to life on earth, yet there are not limitless supplies, leading researchers to look at methods of recovering it. Researchers in the E-motion project are developing a method which combines modified polymers with an electrical field to recover key nutrients from waste water, as Dr Louis de Smet explains The majority of waste water treatment techniques are focused on improving the quality of the water, yet high-value nutrients like phosphate ions are often present in waste streams, and there is a great deal of interest in recovering them efficiently. Researchers in the E-motion project are developing a novel, highly specific method to separate key nutrients from waste water and recover them. “I want to combine modified polymers with an electrical field, to steer the separation,” outlines Dr Louis de Smet, the project’s Principal Investigator. As an organic chemist with a strong focus on surface chemistry, Dr de Smet has long experience of designing and characterising materials, in particular polymers, and now he aims to introduce specific properties to these polymers. “These properties will help these polymers to perform the specific role of separating certain ions from the aqueous environment,” he explains.
aspects of this process. “Is the ion that we are targetting indeed the only one going through the filter?” he asks.
The properties of these polymer coatings should be at least two-fold – they should be selective towards the target ion, which in my case is phosphate, but at the same time they should also have the ability to release it again, enabling recovery Organic materials This work centres around combining organic materials with an electrical field, with the goal of attracting negatively charged phosphate ions to a positively charged electrode. Water essentially flows through two parallel porous electrodes, one positive and the other negative, which will then attract those species that have the counter charge. “Phosphates are negatively charged ions – so these negatively charged ions will be attracted by a positively charged electrode,” says Dr de Smet. Researchers aim to use the tailor-modified polymers to generate a very thin coating on top of a porous electrode, that ideally will only allow phosphate ions to pass through, acting as a kind of filter; Dr de Smet and his colleagues are studying fundamental
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The porous nature of the electrodes means they have a very high surface area, and ions can then be electro-adsorbed. As explained, a polymer coating on top of such a porous electrode acts as a filter; Dr de Smet and his group are investigating different approaches to modifying the electrode surface with the polymer coating. “The properties of these polymer coatings should be at least two-fold – they should be selective towards the target ion, for example phosphate, but at the same time they should also have the ability to release it again, enabling recovery,” he outlines. Researchers now aim to find the right balance between the selectivity of binding, which typically goes hand in hand with a high binding strength, but at the same time ensuring that the binding process is reversible. “That’s one of the most important challenges from a chemistry point of view,” says Dr de Smet.
The goal is to design, synthesise and characterise ion-selective coatings, yet there are many technical challenges to deal with before selective ion transport can be achieved. At this stage, Dr de Smet and his colleagues are focusing on preparing macromolecules that can be used in very thin membrane films. “We are immobilising these tailored-macromolecules, then coating them onto model substrates. The next step would be to do the same with a porous electrode, and also implement electrical fields, to see whether we can achieve the desired transport properties,” he outlines. This research could also lead to new insights into the recovery of other ions, including lithium ions, potentially opening up other applications in battery design, solar fuel devices and fuel cells. “For example, there are a lot of lithium ions in certain salt-lakes, but here selectivity is also an important issue,” says Dr de Smet. “Currently, the main focus is on phosphate though.” Electro-motion for the sustainable recovery of high-value nutrients from waste water (E-motion) ERC-CoG-2015 - ERC Consolidator Grant Fe3O4 Nanoparticles Coated with a Guanidiniumfunctionalized Polyelectrolyte Extend the pH Range for Phosphate Binding, Paltrinieri, L.; Wang, M.; Sachdeva, S.; Besseling N.A.M.; Sudhölter, E.J.R.; de Smet, L.C.P.M. J. Mater. Chem. A, 2017, in press. DOI: 10.1039/ C7TA04054G (Front Cover Article) Dr Louis de Smet Laboratory of Organic Chemistry Wageningen University Stippeneng 4 6708WE WAGENINGEN T: + 31-15-2782636 E: louis.desmet@wur.nl W: www.louisdesmet.nl Dr Louis de Smet is an Associate Professor in Organic Analytical Chemistry at Wageningen University in the Netherlands. He is also a Senior Advisor to Wetsus, European centre of excellence for sustainable water technology in the Netherlands. His research work focuses on the molecular design of selective materials, mostly to recover high-value materials from waste water.
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