Jonas Wohlgemuth

Ultrasound-assisted synthesis of mesoporous β-Ni(OH)2 and NiO nano-sheets using ionic liquids

Via a facile ultrasound synthesis from nickel acetate and sodium hydroxide with ionic liquids as the solvent and template it is possible to obtain nano-β-Ni(OH)2 of various dimensionalities depending on the reaction conditions with the ionic liquid (IL) being the most important factor. Scanning electron microscopy (SEM) imaging showed β-Ni(OH)2 to form as nanosheets, nanorods and nanospheres depending on the IL. ILs with strong to moderate hydrogen bonding capability like [C3mimOH][Tf2N] (1-(3-hydroxypropyl)-3-methylimidazolium bis(trifluoromethanesulfonylamide)), [C4mim][Tf2N] (1-butyl-3-methylimidazolium bis(trifluoromethanesulfonylamide)) and [Edimim][Tf2N] (1-ethyl-2,3-diemethylimidazolium bis(trifluoromethanesulfonylamide)) lead to the formation of nanosheets whilst [Py4][Tf2N] (butyl-pyridinium bis(trifluoromethanesulfonylamide)) leads to nanoparticles and [N1888][Tf2N] (methyltrioctylammonium bis(trifluoromethanesulfonylamide)) to nanorods. Subsequent calcination of the materials at elevated temperatures (285–425 °C) leads to the conversion of β-Ni(OH)2 to NiO under preservation of the nanostructure. Scanning electron microscopy (SEM), X-ray diffraction (XRD), TG-DTA, X-ray photoelectron spectroscopy (XPS), and energy dispersive X-ray spectroscopy (EDX) were used to observe the morphology, crystallinity, and chemical composition in more detail. Mesoporous NiO nanosheets obtained in [C4mim][Tf2N] possess an exceptionally high surface area of 141.28 m2 g−1 and a pore volume of 0.2 cm3 g−1 at 285 °C. As a result of calcination at 425 °C the surface area decreased to 92.84 m2 g−1, but the pore volume increased to 0.48 cm3 g−1. In addition, the product has an extraordinarily high saturation magnetization of 1.38 emu g−1, a coercivity of 117 Oe and an excellent specific capacitance of 199.4 F g−1 which renders the material highly interesting for application in supercapacitors.

Sprayable, Large‐Area Metal–Organic Framework Films and Membranes of Varying Thickness

Despite their huge potential for efficient molecular separation, the fabrication of membranes from metal-organic frameworks (MOFs) remains a major challenge. The powders obtained by the conventional solvothermal MOF syntheses are difficult to process, and as a result the fabrication of well-performing, large-area MOF-based membranes is still awaiting success. The deposition of MOF thin films suited for membrane applications is demonstrated by employing a step-by-step spray method. This method can be scaled up to obtain industrially relevant membrane areas and a continuous process is also possible. The performance of sprayed HKUST-1-based membranes by the separation of a binary H2 /CO2 mixture is also demonstrated. Furthermore, this approach enables the control of the MOF film thickness, and thus controlling the permeance and the selectivity of the membrane.

Compartmented microfluidic bioreactor system using magnetic enzyme immobilisates for fast small-scale biotransformation studies

In the last decade, microfluidic bioreactor systems became increasingly important due to their high suitability for lab‐on‐a‐chip applications and resource‐saving experiments with small sample volumes. Here, a prototype of a microfluidic device for fast small‐scale investigations of enzymatic and biochemical reactions is introduced. Single or consecutive enzyme‐catalyzed reactions can be implemented within compartmented reaction environments separated by immiscible fluidic plugs. By immobilizing one of the reactants onto magnetic microcarriers, a fast and easy separation of the reaction products is possible allowing the realization of a sequence of different reaction steps with different enzymes and varying chemical environments. Besides permanent magnetic fields for separation processes, alternating electromagnetic fields can be applied to resuspend the carriers. This leads to an intense mixing as well as even microcarrier distribution within the compartment. In a proof of concept, kinetic studies of HRP immobilized onto polyvinyl alcohol‐magnetite composite microcarriers are presented. The results showed a specific enzyme activity of approximately 89 units per gram immobilized biocatalyst under the applied reaction conditions. In addition, results of recycling experiments point out the importance of the magnetically induced resuspension. While ten times reuse with immobilisate resuspension resulted in substrate conversion yields between 95 and 65%, the same experiment without the magnetically induced resuspension showed conversion yields below 10% over all cycles.

A 3D-printed modular reactor setup including temperature and pH control for the compartmentalized implementation of enzyme cascades

In recent years, 3D printers developed rapidly from an expensive niche product used mainly by architects and designers into a versatile tool for engineers helping them to quickly realize and test new ideas. While most of the reported examples still focus on the use of 3D‐printed parts as mechanical but chemically inert tools, we developed a 3D‐printed modular reactor system which allows the fast implementation and testing of enzyme cascades. 3D printing offers several advantages in this context, as complex fluidic structures that cannot be fabricated by other methods can be generated, and the printed reactors are easily scalable in order to adjust their size to specific reaction parameters. Using a so‐called PolyJet technique, highly porous monolithic enzyme carriers were printed and directly UV‐cured from acrylate monomers, allowing simple immobilization of enzymes in a subsequent step. The enzyme immobilisates were fixed in a 3D‐printed housing with integrated fluid distributors forming a compact module to conduct a biotransformation step. Several of such modules can be connected in series to a pumping and analyzing system. A model cascade connecting two enzyme transformation modules, the first containing Glucose Oxidase and the second containing Horseradish Peroxidase, was operated using a commercial FPLC system for flow control and UV–Vis detection of the generated product. In order to adjust the temperature, a Peltier‐based tempering jacket for the enzyme transformation modules was designed. In addition, a flow‐through pH regulation module was developed, based on an electrochemical principle which allows unidirectional pH changes without the need for membranes or discharge of partial fluid streams. Except for the electrodes, also the pH regulation module was fabricated by 3D printing.

Release of Nanoparticles from Ion Exchange Resins and Their Detection

Nanoparticles released from commercial ion exchange resins were analyzed by laser-induced breakdown detection (LIBD). It was shown that virgin resins release a considerable amount of nanoparticles which may harm sensitive production lines, if the resins are used without proper pretreatment. Particle release is reduced to below 1 ppb after regeneration and rinsing of the resins. However, the nanoparticle concentration can still be detected quantitatively by LIBD.