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Samuel de Lint (promotion date: 27 January 2003)

Ion-separation with charged mesoporous inorganic membranes

Interview: 27 January 2003

Samuel de Lint

I have been working on fluid (mainly salt solutions) transport through inorganic membranes. In our research group, inorganic materials science, people know a lot about making membranes that function very well, and after that they perform measurements on them. But how these membranes work is something a little more difficult. I worked in a bit different way.

What has your research been about?
I have been working on fluid (mainly salt solutions) transport through inorganic membranes. In our research group, inorganic materials science, people know a lot about making membranes that function very well, and after that they perform measurements on them. But how these membranes work is something a little more difficult. I worked in a bit different way. I used membranes that are being made in our group on a regular basis in and looked at how electrolyte solutions were transported through them. To do this, I needed to know how the membranes worked. Because of that, an important part of my assignment was to design a model that would describe the system.
Our membranes consist of two layers. The bottom layer, the support, provides mechanical strength. The support is formed by vacuum filtration of a particle suspension and subsequent calcination (baking) in an oven, producing a ceramic oxide. The second layer forms the contact layer with the solution that needs to be separated.
A point of interest in the research was the size of the pores in the material. It is difficult to measure this parameter directly but must be between 2 and 4 nanometers. In contrast to conventional membrane separation, the size of the pores of our ceramic membranes does not really play an important role in the separation of electrolyte solutions. The pores have a diameter of about 4 nanometers, while the size of the particles is in the order of 4 Ängstrøm, that is about 10 times smaller. The surface charge is the property of the membrane that is mainly responsible for the separation of the salt ions and the solvent. It also complicates the understanding of the system, since the interaction of the ions and the surface is different for differently charged ions and also changes as a function of electrolyte concentration and pH. I designed a predictive transport model for fluids through inorganic membranes, in which I inserted several important material and solution-material properties, and it turned out that values predicted with the model agreed well with experiments. I would have like to do some more experiments to put my model to the test, but maybe someone else can work on that.
This actually is the first predictive model for systems like these that exists. Earlier people used data from separation experiments, fitted them and were content with the result. With the development of this model I think I have contributed a lot to the understanding of inorganic membranes.

Have you had a collaboration of some kind with other research groups?
In this scientific area there seems to be quite some rivalry. There are some researchers who are thought very highly of, and the rest is mainly following their approach. One time when I was giving a talk at a conference someone asked me the following question: “Why are you doing this research, it has already been shown that your method does not work”. We have, however, proven that our method really works and the people who previously followed the same approach overlooked crucial things. To me this is a clear indication of how much people are thinking in standard ways, which leads to a lot of work being done twice, slowing down progress. During my Ph.D. I have really noted how much it pays off to work together with other people, especially interdisciplinary. I have always tried to get in contact with a lot of people. For example I visited a professor in this area in Wageningen a couple of times who is an expert on the charging of ceramic materials. It has been really helpful to be able to use his knowledge.

Did you have the opportunity to visit a lot of nice places for your work?
Not really. I only visited some conferences, in Toulouse, France for example, and in Leiden, in the Netherlands. I do not think that visiting conferences is the most successful way of acquiring knowledge or to get acquainted with someone. In Toulouse there were some 1000 visitors for the conference and I must say that in general the scientific level of the talks was not too high. In Leiden it was far better. We were about 40 people there so we really got to know one another.

What techniques in your research area do you think will boost new developments?
The most important thing will be to gain more control on the growing of your membrane. The most important technique that can provide that is probably templating. It would also be nice if in general we could perform more precise measurements on the surface properties (e.g., pore size, charging characteristics) of a membrane. It would allow us to characterise it better and localize constraints.

What are your plans for the nearby future?
I still remain interested in research and also in this particular area so I plan to stay in contact with it, but only sideways. First I am going to the University of South Australia, in Adelaide as a post-doc. Only for half a year, though. There I want to take a look at the charge properties of composite materials. This work bears a strong relation to my research on membranes.
On the other side I really enjoy to do many different things. I always had a broad range of interests, so after coming back from Australia I would like to work in a company. I am not sure whether I will like it or not, but I will always have the possibility of going back to do research in a university. I am already in the run for a job with Shell. They are quite enthusiastic about me but they do not have any vacancies at the moment. I will have to wait for at least half a year. That is why I am going to Australia in the mean time. Working within a company is much more applied than at a university, a client has a problem and some investigations have to be done to solve it. They will only get involved in projects if they expect results in the near future. The diversity of work at a company is exactly what I like.