Hold on tight and let go : Electrically-responsive adsorption and desorption on polypyrrole

Separation processes play a key role in food production. This includes the extraction and purification of fractions from agricultural starting materials, recovery of valuable components, and removal of undesirable components, ultimately contributing to the production of safe food ingredients and products. The selection of an appropriate separation strategy depends on what needs to be separated, what else is present in the mixture, and how pure the final product must be. When high purity is desired, a precise technique like chromatography is often employed. This method usually relies on chemical changes, such as variations in the acidity or salt concentration, to release the target molecule, which can be costly and environmentally harmful. This thesis explores a more sustainable alternative: capturing and releasing molecules through electrical stimulation. To achieve this, new materials need to be designed. We focused on a material called polypyrrole, which can change its surface properties when an electrical signal is applied. The goal was to develop a material that can capture and release both charged molecules, like proteins, and uncharged molecules, like flavor compounds.Polypyrrole can switch between two electrical states, oxidized and reduced, which alters its surface properties. These properties, in turn, determine whether and how strongly the surface interacts with a target molecule, resulting in either adsorption (capture) or desorption (release). By adjusting how the material is produced, such as the preparation method or the starting solution, its properties could be tuned. The polypyrrole material was subsequently tested by exposing it to electrical signals and observing whether it could capture and release different molecules. For proteins, the extent of adsorption could be related to the electrical state of the material. This made it possible to capture proteins and (partially) release them over multiple cycles. For flavor molecules, capture depended strongly on the type of flavor, but releasing them using electrical signals proved to be difficult. However, the selectivity of the material could be improved using a technique called molecular imprinting, in which cavities were formed in the material that matched the shape of a specific flavor molecule.In addition, the research investigated the underlying switching mechanism upon electrical stimulation, including changes in the surface structure and composition. This showed that the reversibility and stability of the switching behaviour could be tuned by how the material was made. Overall, this work provides insights and future directions for developing more sustainable electrically-driven separation technologies.