Behind the PhD degree: Zexin Qian

Midnight calls, electric walls, and water shawls – discover how Chinese PhD student Zexin Qian found a way to distinguish between invisibly small particles that are the spitting image of one another. While encountering unexpected turns throughout.

On September 16th, 12.30hrs, at Delft University of Technology, Zexin Qian will defend her thesis ”Selective ion separation by supported liquid membranes under electrodialysis conditions”.

The science behind the person, and the person behind the science.

Sudden start

“I still remember the moment I signed up for a PhD at Wetsus. An unsure decision – not knowing how to continue from my master’s degree on. I was busy at the time, not giving it a second thought,’ says Zexin Qian.

“After what felt like a month, I suddenly got a reply – congratulations, please join us for an online interview. Living in the States at the time, the meeting was scheduled for three in the morning with the time zone difference. And, as I had bad internet in my house, I had to rush to the office at midnight. It was a good call, though, as later I was invited for an in-person meeting. Rushing across the US to get my Visa. I made it, and a day after the interview I got an email asking whether I would like to accept the offer. ‘Could you reply before the end of the week, as I leave for the holiday?’ Just like that I started my PhD.” Certainly, a memorable experience

Liquid layers

It was an excellent match for Zexin. At least on paper. “We were going to explore the separation of two very similar charged particles – sodium and potassium. It’s important to filter out sodium if we want to reuse water for plant growth, as too much of it is toxic to the plant.” Getting to a solution would be immensely valuable, as sodium accumulation is one of the main issues preventing the horticulture sector from recycling repeatedly.

“We would do it with a ‘charged’ liquid membrane – a non-water-mixing liquid sandwiched between layers of water separating ions under electric field. Within the membrane, crown ether will do the trick on selectivity. I liked both the organic synthesis and electro-chemistry part, so it sounded like great research.” The crown ether molecules were supposed to act as a carrier, helping target ion transporting through the membrane. But with the complicated interactions between ions and the carrier, other solutions had to be found.

“So, we removed the crown ether. And much to our surprise, we still had a selective membrane!” says Zexin. It – in a way – changed the direction of the PhD research. “But I didn’t mind,” says the scientist, “I was struggling with the synthesis for a long time anyway”.

Instead, the investigation was now on understanding how it worked and how to improve the method. Fitting with the Wetsus theme, water turned out to be the solution. “In order to get into the membrane, water-surrounded ions first need to get rid of the H2O shell, or at least part of the water shell. The higher required dehydration energy makes sodium losing the competition with potassium from moving through the membrane.” The same basic principle goes for the double-charged ions; however, the mechanism is a little different in the details.

A proof of concept

It’s great progress, but the system is still quite demanding. “It takes a lot of energy, and the membrane stability needs further improvement. But as a first step to future application, I did some modelling with the performance of the membrane system in treating greenhouse drainage water, and the experiments seem to line up with the theory. So, the proof of concept is there, ready for use.”

And Zexin? She now works in industry, at CCIC EUROPE Food Test B.V. “I like working at the R&D department here. It’s a change of pace and pressure. I don’t mind being less in the lab, but it is important for me to feel the connection.”

“It is also still a bit of an experiment for me. See what I like best. All my life I have been checking of the list of things I don’t like, to get to the ones I do like.” In a sense, her dabble into academia is no different. Sometimes a PhD is – more than in one way – a proof of concept.

Towards an economy of value preservation | By Niels Faber


The realisation of a circular economy has thus far unfolded under the assumption that it would fit within existing economic arrangements. In practice, we witness many circular initiatives struggling to give shape to their ambitions, let alone develop to maturity. These past months, various material recycling organisations terminated their activities, seeing virgin alternatives from other parts of the world flooding the market at prices against they cannot compete. If the transition towards a circular economy (i.e. an economy of value preservation) is to be taken seriously, a new perspective on value in our economic system seems unavoidable, as the rewriting of the rules of the economic game. At this moment, current perceptions of value stand in the way of this transition both at micro as well as macro levels. Several contours for a collective exploration of new directions of value and economic configuration that foster circular transition will be addressed.

Searching Innovation for the Common Good | By Cees Buisman


In his key note he will conclude after a life of innovations that it is impossible that humanity will stay within the save planetary boundaries with innovation only. We should be more critical about the behaviour of the rich population in the world and more critical about new innovations that prove to be dangerous, like the PFAS crisis shows at this moment. In his keynote he will investigate how to look at the world that can stay within the save planetary boundaries, how should we change ourselves? It is clear if we only talk about the words of science and systems we miss the essential words of how we should cooperate and change ourselves. And his search for coherent save innovations. Which innovations will be save and will lead to a fair and sustainable world? And will lead to a world we want to live in.

Future-fit economic models: What do they have in common – how can they join forces? | By Christian Felber


There is a growing number of new sustainable, inclusive, cohesive, participatory, just and humane economic models. A possible next step in the discourse about them is the comparative analysis in order to find out key commonalities, potential synergies, and “requirements” for a future-fit economic model. The author and initiator of the Economy for the Common Good provides an overview of these „new sustainable economic models“ and compares them according to underlying values, principles, and practical ways of implementation. The keynote addresses the cooperative spirit of the conference and prepares the ground for its public highlight on the eve of June 3rd, the round table with representatives of diverse future-fit economic models.

The era of postgrowth economics | By Matthias Olthaar


The scientific debate on whether economies should always continue to grow increasingly becomes a political and societal debate. On the one hand further growth for the most affluent countries seems neither possible nor valuable, but on the other hand there is still lack of understanding and knowledge what a non-growing economy should look like and could best be governed. In this lecture we discuss various policy measures that can be realistically implemented, take into account government finances and aim at a higher quality of life despite a non-growing economy.

Democratic principles for a sustainable economy | By Lisa Herzog


Democracy is under pressure, and less and less able to stir the economy into a sustainable direction. Therefore, to stabilize democracy and to make possible the socio-ecological transformation of the economy, democratic principles need to be implemented directly in the economy. This is not only a matter of morality, but also has practical advantages. Democratizing the economy can increase legitimacy and take advantage of the “knowledge of the many” to accelerate the transformation. Democratic practices, especially deliberation, allow bringing together different forms of knowledge, which is crucial for the local implementation of principles of social and ecological sustainability. This talk explores what this idea means in more concrete terms, from democratic participation in the workplace to the democratization of time.

Market, state, association, and well-being. An historical approach | By Bas van Bavel


Over the past decades, markets have conventionally been seen as the best instrument to stimulate economic growth and enhance prosperity and well-being. The automatic link between markets and economic growth is increasingly questioned, however, as well as the automatic link between economic growth and enhancement of well-being. This has led to attempts to capture well-being development more directly than through GDP per capita figures and has produced a more variegated picture of well-being growth. Also, this has led to a shift of focus to other coordination systems than the market, as primarily the state but increasingly also the association. Analyses of the historical record suggest that especially the latter could be a vital component in future well-being.