European centre of excellence
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Interview with Associate Prof. Louis de Smet on organic chemistry and water technology

Published: 7 april 2017
Interview with Associate Prof. Louis de Smet on organic chemistry and water technology

Louis de Smet, an associate professor at Wageningen University, specializes in organic chemistry, and one of the many areas that he is applying this knowledge to is water technology. Since receiving the ERC Consolidator Grant a little over a year ago, de Smet has been expanding his research team, and together they are cooperating closely with Wetsus to bring their research to the front of advanced desalination and wastewater treatment methods.

In this interview, de Smet describes some of his latest research on chemical sensors, including a nanoscale device that can detect TNT explosives and a chemical attachment system for phosphate removal, as well as ongoing research on polymer coatings for the detection of volatile water pollutants.

Question: What are some of the research projects you’re working on right now?

Louis de Smet: My expertise is on the modification of surfaces with molecules to control and tune their properties. Often, we first synthesize or functionalize molecules before subjecting them to physisorption or chemisorption strategies. Over the past decade, I have been mainly working on sensor projects where the resulting molecular coatings, sometimes composites, act as a so-called affinity layer. These layers are prepared onto a transducer platform and, upon their interaction with an analyte, this input signal is converted into, for instance, an electrical or optical signal. For many applications it is crucial to have an affinity layer that interacts with specifically one analyte. To facilitate or even tune the process of recognition, a molecular receptor is added. Organic chemists have a toolbox of synthetic approaches available to change the structure of (receptor) molecules and hence also the way they interact with other molecules or ions, the targets.

Since a few years, we also have been applying our surface modification engineering strategies to membrane-related applications. After all, in the case of separation processes, recognition plays an important role.

Q: Can you describe the research in your recent papers in the journals of Nano Letters and Soft Matter?

LDS: Together with researchers from the University of Twente, Philips Research and the University of Melbourne, we made an electrical nanodevice that can detect TNT, an explosive molecule. In this case, the affinity layers consist of molecular cages, the receptors, that each can host one TNT molecule. This work was featured on the cover of the first 2017 issue of Nano Letters. Apart from the progress we made in terms of selectivity, I am particularly happy with this paper as it shows the importance of cross-interdisciplinary collaborations: we could only achieve this by combing experimental and computational chemistry, electrical engineering and nanofabrication.

In our Soft Matter paper we describe the chemical attachment of a phosphate receptor to a polymer. Although not 100% selective yet, coatings containing this functionalized polymer did show a preference for phosphate. Early March I presented a follow-up study on this work at the 5th International Conference on Multifunctional, Hybrid and Nanomaterials in Lisbon. In this work we have put the functionalized polymer onto iron oxide nanoparticles to study the uptake of phosphate at a pH value that met those of typical wastewater.

Polymer phosphate formula
Polymer phosphate formula

Where TNT is detected and phosphate absorbed or collected, I now also work on using molecular systems like these to specifically remove, harvest and recover certain ions from (waste) water. Apart from adding and tuning the selectivity of the coating, another benefit of the surface chemistries we work on is related to the level of control when it comes to the coating thickness. This can range from several nanometers to hundreds of micrometers. The required thickness depends on the application.

Q: When did you receive the ERC grant, and how are you using it (or how do you plan to use it)?

LDS: I’ve obtained an ERC Consolidator Grant in late 2015 to work on the design and preparation of materials that can be used to remove and, ultimately, recover high-value nutrients from (waste) water. The main focus is on phosphate, but other targets like heavy metals, lithium or sodium are very interesting as well. Building further on our Soft Matter study, we not only aim to improve the selectivity for phosphate, but we also wish to tune the binding reversibility: after all, the selective removal should be followed by a release. In this research program we combine organic chemistry, surface chemistry and advanced water treatment methods to meet this challenge.

Phosphate can be removed, recovered, and recycled from wastewater

From an organizational point of view, this five-year program allows me to hire four PhD students and a part-time technician. Additionally, the grant covers investments for the purchase of new equipment, including a so-called Quartz Crystal Microbalance. With this technique we measure the change in frequency of a quartz crystal resonator when materials adsorb on it. From this shift we can obtain the change in mass at a sensitivity of ng/cm2. The equipment has been installed in our labs last month and we plan to use it to study the coating preparation as well as the uptake or release of nutrients to/from these coatings.

Q: When and why did you begin collaborating with Wetsus? How are you connected to Wetsus now? And how do you think this connection to Wetsus has helped you in your research?

LDS: My first contacts with Wetsus date from 2008 when I worked at TU Delft. Within the theme of Sensoring, we started a project on using polymer coatings for the detection of volatile water pollutants. Most technologies for the detection of volatile organic compounds (VOCs) in water make use of the principle that VOCs distribute themselves between the aqueous phase and the gas phase just above it. By analyzing the gas phase, something can be said about the presence of certain VOCs in the water. We worked on a capacitive sensor device to detect VOCs directly in the water. We prepared a hydrophobic polymer coating onto the device, and tested its affinity to a series of VOCs. An ongoing project aims to integrate this type of layer with a coax sensor, a platform with low noise levels and high sensitivities.

Several years ago I also become active within the theme of Desalination and we currently work on phosphate-selective membranes and sodium-selective materials. As of this year, I work at Wetsus one day per week as an advisor on materials for sustainable water technology. This does not only enable me to combine studying fundamental interface issues with applied research, aiming to improve existing water treatment technologies, but I strongly believe this multidisciplinary approach is also a good recipe for breeding new strategies for tackling some of the most important global challenges along the themes of water scarcity and the depletion of natural resources.

Q: What is your perspective of the current research going on in the field of water science and technology? And what areas of water research do you think will be most exciting in the future?

LDS: I believe material science and materials engineering will become of increasing importance for various water treatment technologies. What I mean is that new organic materials, molecules, whether or not combined with inorganic matter, will be designed, made and integrated into these technologies, to meet several of the big challenges in the field: increasing selectivity and stability and reduction or even prevention of fouling. Clearly, within my research program the focus is on membranes and separation, related to desalination techniques, but on a more fundamental level: more knowledge on controlling and tuning interfacial properties may also boost some other water-related technologies, like blue energy and sensor systems, given the importance of the transport of charges (ions and/or electrons).

Also, I realize I still talk about water treatment technologies, but it is broader than that: the focus is not only on water. Wastewater is resource water and more and more attention will be given to closing the loops of water and its often high-value impurities as well as to increase the use of sustainable energy in the related technologies.

Cabrera-Rodríguez, Carlos I.; Laura Paltrinieri, Louis C.P.M. de Smet; Luuk A. M. van der Wielen; Adrie J. J. Straathof. “Recovery and esterification of aqueous carboxylates by using CO2-expanded alcohols with anion exchange.” Green Chemistry (2017) 19, 729-738

Cao, Zh.; P.I. Gordiichuk, K. Loos, E.J.R. Sudhölter and L.C.P.M. de Smet. “The effect of guanidinium functionalization on the structural properties and anion affinity of polyelectrolyte multilayers.” Soft Matter (2016) vol. 12, 1496-1505

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