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.

“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

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.

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.