In biorefinery processes often the downstream processing is the technological bottleneck for an overall high efficiency. On the basis of recent developments, the selective liquid phase adsorption applying highly hydrophobic porous materials opened up new opportunities for process development. In this contribution, the efficiency of selective liquid phase adsorption is demonstrated for the separation and purification of itaconic acid from aqueous solutions for the first time. A wide range of different adsorbents was screened, revealing the surface polarity as well as textural properties as critical parameters for their performance. Adsorption from mixed solutions of itaconic acid and glucose exhibited extraordinary high selectivities for adsorbents with highly hydrophobic surfaces, especially certain activated carbons and hyper-cross-linked polymers. Evaluation of the pH dependence showed that the respective molecular species of itaconic acid/itaconate has a major impact on the adsorption performance. Additionally, experiments on a continuously operated fixedbed adsorber were carried out, and the desorption behavior was evaluated. Overall, the technical feasibility of the selective adsorptive removal of itaconic acid from aqueous solutions with hydrophobic adsorbents is demonstrated as a model system for an alternative technology to conventional separation strategies in biorefinery concepts.

Complementary to the quickly advancing understanding of the swimming of microorganisms, we demonstrate rather simple design principles for systems that can mimic swimming by body shape deformation. For this purpose, we developed a microswimmer that could be actuated and controlled by fast temperature changes through pulsed infrared light irradiation. The construction of the microswimmer has the following features: (i) it is a bilayer ribbon with a length of 80 or 120 $$\upmu $$ μ m, consisting of a thermo-responsive hydrogel of poly-N-isopropylamide coated with a 2-nm layer of gold and equipped with homogeneously dispersed gold nanorods; (ii) the width of the ribbon is linearly tapered with a wider end of 5 $$\upmu $$ μ m and a tip of 0.5 $$\upmu $$ μ m; (iii) a thickness of only 1 and 2 $$\upmu $$ μ m that ensures a maximum variation of the cross section of the ribbon along its length from square to rectangular. These wedge-shaped ribbons form conical helices when the hydrogel is swollen in cold water and extend to a filament-like object when the temperature is raised above the volume phase transition of the hydrogel at $$32\,^{\circ } \hbox {C}$$ 32 ∘ C . The two ends of these ribbons undergo different but coupled modes of motion upon fast temperature cycling through plasmonic heating of the gel-objects from inside. Proper choice of the IR-light pulse sequence caused the ribbons to move at a rate of 6 body length/s (500 $$\upmu $$ μ m/s) with the wider end ahead. Within the confinement of rectangular container of 30 $$\upmu $$ μ m height and 300 $$\upmu $$ μ m width, the different modes can be actuated in a way that the movement is directed by the energy input between spinning on the spot and fast forward locomotion. Graphic abstract

In this work, the concentration polarization layer (CPL) of sulphate in a cross-flow membrane system was measured in-situ using Raman microspectroscopy (RM). The focus of this work is to introduce RM as a new tool for the study of mass transfer inside membrane channels in reverse osmosis (RO) and nanofiltration (NF) generally. Specifically, this work demonstrates how to use RM for locally resolved measurement of sulphate concentration in a cross-flow flat-sheet NF membrane flow cell with channel dimensions similar to commonly applied RO/NF spiral wound modules (channel height about 0.7 mm). Concentration polarization profiles of an aqueous magnesium sulphate solution of 10 gsulphate·L−1 were obtained at operating pressure of 10 bar and cross-flow velocities of 0.04 and 0.2 m·s−1. The ability of RM to provide accurate concentration profiles is discussed thoroughly. Optical effects due to refraction present one of the main challenges of the method by substantially affecting signal intensity and depth resolution. The concentration profiles obtained in this concept study are consistent with theory and show reduced CPL thickness and membrane wall concentration with increasing cross-flow velocity. The severity of CP was quantified to reach almost double the bulk concentration at the lower velocity.

We consider the dynamics of micro-sized, asymmetrically coated thermoresponsive hydrogel ribbons (microgels) under periodic heating and cooling in the confined space between two planar surfaces. As the result of the temperature changes, the volume and, thus, the shape of the slender microgel change, which leads to repeated cycles of bending and elastic relaxation, and to net locomotion. Small devices designed for biomimetic locomotion need to exploit flows that are not symmetric in time (non-reciprocal) to escape the constraints of the scallop theorem and undergo net motion. Unlike other biological slender swimmers, the non-reciprocal bending of the gel centerline is not sufficient here to explain for the overall swimming motion. We show instead that the swimming of the gel results from the flux of water periodically emanating from (or entering) the gel itself due to its shrinking (or swelling). The associated flows induce viscous stresses that lead to a net propulsive force on the gel. We derive a theoretical model for this hypothesis of jet-driven propulsion, which leads to excellent agreement with our experiments.