We describe a novel method to produce monolithic, oriented, crystalline and highly porous coatings on solid substrates. By adopting the recently described liquid‐phase epitaxy (LPE) process developed ...to grow metal‐organic framework coatings (MOFs) on modified Au‐substrates to the spray method, we have prepared thick (μm) layers of several MOF types on modified Au‐substrates, including HKUST‐I and layer‐pillar MOFs. The spray method not only allows such SURMOFs to be grown much faster than with the LPE‐process but the dependence of layer thickness on the number of immersion cycles also provides valuable insights into the mechanism governing the layer‐by‐layer MOF formation process.
Crystalline, homogenous films of MOFs with well‐defined thicknesses are deposited on a modified Au substrate employing a high‐throughput spray‐method. The spray method not only allows such SURMOFs to be grown much faster than with the LPE‐process but the dependence of layer thickness on the number of immersion cycles also provides valuable insights into the mechanism governing the layer‐by‐layer MOF formation process
Dynamic crossflow filtration (DCF) is the state-of-the-art technology for solid-liquid separation from viscous and sensitive feed streams in the food and biopharma industry. Up to now, the potential ...of industrial processes is often not fully exploited, because fixed recipes are usually applied to run the processes. In order to take the varying properties of biological feed materials into account, we aim to develop a digital twin of an industrial brownfield DCF plant, allowing to optimize setpoint decisions in almost real time. The core of the digital twin is a mechanistic-empirical process model combining fundamental filtration laws with process expert knowledge. The effect of variation in the selected process and model parameters on plant productivity has been assessed using a model-based design-of-experiments approach, and a regression metamodel has been trained with the data. A cyclic program that bidirectionally communicates with the DCF asset serves as frame of the digital twin. It monitors the process dynamics membrane torque and transmembrane pressure and feeds back the optimum permeate flow rate setpoint to the physical asset in almost real-time during process runs. We considered a total of 24 industrial production batches from the filtration of grape juice from the years 2022 and 2023 in the study. After implementation of the digital twin on site, the campaign mean productivity increased by 15% over the course of the year 2023. The presented digital twin framework is a simple example how an industrial established process can be controlled by a hybrid model-based algorithm. With a digital process dynamics model at hand, the presented metamodel optimization approach can be easily transferred to other (bio)chemical processes.
Magnetic properties of superparamagnetic iron oxide nanoparticles are controlled mainly by their particle size and by their particle size distribution. Magnetic properties of multi-core iron oxide ...nanoparticles, often called iron oxide nanoflowers (IONFs), are additionally affected by the interaction of magnetic moments between neighboring cores. The knowledge about the hierarchical structure of IONFs is therefore essential for understanding the magnetic properties of IONFs. In this contribution, the architecture of multi-core IONFs was investigated using correlative multiscale transmission electron microscopy (TEM), X-ray diffraction and dynamic light scattering. The multiscale TEM measurements comprised low-resolution and high-resolution imaging as well as geometric phase analysis. The IONFs contained maghemite with the average chemical composition Formula: see text-FeFormula: see textOFormula: see text. The metallic vacancies located on the octahedral lattice sites of the spinel ferrite structure were partially ordered. Individual IONFs consisted of several cores showing frequently a specific crystallographic orientation relationship between direct neighbors. This oriented attachment may facilitate the magnetic alignment within the cores. Individual cores were composed of partially coherent nanocrystals having almost the same crystallographic orientation. The sizes of individual constituents revealed by the microstructure analysis were correlated with the magnetic particle sizes that were obtained from fitting the measured magnetization curve by the Langevin function.
One of the main steps in the biotechnological production of chemical building blocks, such as, e.g. bio‐based succinic acid which is used for lubricants, cosmetics, food, and pharmaceuticals, is the ...isolation and purification of the target molecule. A new approach to isolate charged, bio‐based chemicals is by electrosorption onto carbon surfaces. In contrast to ion exchange, electrosorption does not require additional chemicals for elution and regeneration. However, while the electrosorption of inorganic salts is well understood and in commercial use, the knowledge about electrosorption of weak organic acids including the strong implications of the pH‐dependent dissociation and their affinity towards physical adsorption must be expanded. Here, we show a detailed discussion of the main pH‐dependent effects determining the achievable charge efficiencies and capacities. An explicit set of equations allows the fast prediction of the named key figures for constant voltage and constant current operation. The calculated and experimental results obtained for the electrosorption of maleic acid show that the potential‐free adsorption of differently protonated forms of the organic acid play a dominating role in the process. At pH 8 and a voltage threshold of 1.3 V, charge efficiencies of 25% and capacities around 40 mmol/kg could be reached for a constant current experiment. While this capacity is clearly below that of ion exchange resins, the required carbon materials are inexpensive and energy costs are only about 0.013 €/mol. Therefore, we anticipate that electrosorption has the potential to become an interesting alternative to conventional unit operations for the isolation of charged target molecules.
Magnetic adsorbents enable alternative process modes of selective separations, such as the use of batch or continuous stirred-tank reactors followed by magnetic separators but also more sophisticated ...systems such as magnetic extractors or so-called magnetically stabilized fluidized beds. In small scale, the use of magnetic adsorbents for clinical diagnostics and bioanalytical assays is common practice and well established; however, despite several decades of research and pilot-scale campaigns, there are only few industrial applications of magnetic adsorbents. Therefore, we highlight recent equipment and process developments having the potential to overcome limitations regarding continuous operation, processable particle sizes, and cleanability. Afterward, we review the state of the art of selective separations exploiting magnetic adsorbents in the most promising fields of application, such as algae harvesting, phosphate recycling, and protein purification.
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For a comparative study of the gas sensing performance to dissolved volatile organic compounds (VOCs), the SnO2-powders have been prepared using two different fabrication routes; the ...flame-spray-pyrolysis (FSP) and the sol-gel (SG) route; and were admixed with the same additive-powders (alumina, YSZ, and NASICON). The morphology of the two different SnO2/additive families were investigated by ESEM analysis and Energy-dispersive X-Ray Spectroscopy (EDS). Both SnO2/additive material families were separately deposited as thick-film-layers on two four-fold sensor-chips which were simultaneously thermo-cyclically operated in a measurement cell combined with a carrier gas probe, which enables sensing tests with evaporated VOCs (acetic acid, propionic acid, ethanol, acetone) dissolved in water. The resulting Conductance-over-Time-Profiles (CTPs) highlight better sensitivities of most of the FSP-layers to all the analytes compared to the SG-prepared layers. Furthermore, the CTP shapes of the FSP layers show clearly enhanced specificity representing the individual analyte components. This was interpreted to be the consequence of the extremely fine, scarcely agglomerated grain morphology of FSP-prepared powders and their very narrow grain size distribution which provide better conditions for enhanced gas specific surface reactions. Results promise a better chemical analysis capability of dissolved VOCs by numerical analysis of the CTP of FSP-prepared gas sensitive layers.
Capacitive deionization (CDI) has become an important research topic in terms of water purification as it is a cost- and energy efficient approach for the desalination of brackish water. Carbon- ...based materials are often used as electrodes in this process due to a variety of morphologies and their suitable performance in this field. In recent studies it has been already shown that a conscientiously chosen set of electrode properties has an enormous effect on the performance behavior of CDI cells. However, most of the studies focus on the optimization of the electrosorption capacity, while the question on how material properties influence the kinetic behavior of a CDI setup has been less intensively studied so far. Here we show that the kinetic effects of electrode materials can be studied in great detail by using electrochemical impedance spectroscopy (EIS). EIS studies of CDI electrodes have been reported before, however, in contrast to these we introduce a method of presenting and analyzing EIS results. This is especially suitable for extracting the frequency ranges in which different rate limiting mechanisms dominate. The new Nyquist Incline Frequency plot (NIF) shows the local slope of the Nyquist plot in dependency of the applied frequency. By this, electron transfer and mass transfer mechanisms which show a characteristic slope in the classical Nyquist plot can be directly visualized together with the information in which time domain they occur. The data derived from the new EIS plot show a clear correlation to pore size distributions from BET measurements, as well as effective capacities and electrosorption kinetics, extracted from CDI experiments. Therefore, we think that by using the NIF plot electrode materials for CDI processes can be conveniently characterized and compared within a single diagram, helping to standardize CDI material development.
In the last decade, the fabrication of microfluidic chips was revolutionized by 3D printing. It is not only used for rapid prototyping of molds, but also for manufacturing of complex chips and even ...integrated active parts like pumps and valves, which are essential for many microfluidic applications. The manufacturing of multiport injection valves is of special interest for analytical microfluidic systems, as they can reduce the injection to detection dead volume and thus enhance the resolution and decrease the detection limit. Designs reported so far use radial compression of rotor and stator. However, commercially available nonprinted valves usually feature axial compression, as this allows for adjustable compression and the possibility to integrate additional sealing elements. In this paper, we transfer the axial approach to 3D-printed valves and compare two different printing techniques, as well as six different sealing configurations. The tightness of the system is evaluated with optical examination, weighing, and flow measurements. The developed system shows similar performance to commercial or other 3D-printed valves with no measurable leakage for the static case and leakages below 0.5% in the dynamic case, can be turned automatically with a stepper motor, is easy to scale up, and is transferable to other printing methods and materials without design changes.
The development of process steps catalyzed by immobilized enzymes usually encompasses the screening of enzyme variants, as well as the optimization of immobilization protocols and process parameters. ...Direct immobilization of biocatalysts by physical entrapment into hydrogels can be applied to reduce the effort required for immobilization, as the enzyme-specific optimization of the immobilization procedure is omitted. Physical entrapment is applicable for purified enzymes as well as crude cell extracts. Therefore, it can be used to quickly assess and compare activities of immobilized enzymes. For the application in flow reactors, we developed 3D-printed hydrogel lattices for enzyme entrapment as well as matching housings, also manufactured by 3D-printing. Testing the resulting enzyme reactors for three different enzymes, namely alcohol dehydrogenase from
, benzoylformate decarboxylase from
and β-galactosidase from
, and four different enzymatic reactions showed the broad applicability of the approach but also its limitations. The activity of the immobilized biocatalysts was measured in batch experiments and compared to the kinetics of the respective free enzymes in solution. This comparison yields an effectiveness factor, which is a key figure to describe the extent the immobilized catalyst is effectively utilized. For the examined systems the effectiveness factor ranged between 6 and 14% and decreased with increasing absolute activity of the entrapped enzymes due to mass transfer limitations. To test the suitability of the hydrogel lattices for continuous operation, they were inserted into 3D-printed reactor housings and operated at constant flow. Stable product formation could be monitored over a period of 72 h for all four enzymatic systems, including two reactions with redox cofactor regeneration. Comparing calculated and experimental conversion in the continuous setup, higher values of the effectiveness factor in batch experiments also hint at good performance in continuous flow. This can be used to optimize complex biocatalytic reactions on a small scale.
In biotechnology, immobilization of functional reactants is often done as a surface immobilization on small particles. Examples are chromatography columns and fixed-bed reactors. However, the ...available surface for immobilization is directly linked to particle diameter and bed porosity for these systems, leading to high backpressure for small particle sizes. When larger molecules, such as enzymes are immobilized, physical entrapment within porous materials like hydrogels is an alternative. An emerging technique for the production of geometrically structured, three-dimensional and scalable hollow bodies is 3D-printing. Different bioprinting methods are available to produce structures of the desired size, resolution and solids content. However, in case of entrapped enzymes mass transfer limitations often determine the achievable reactivities. With increasing complexity of the system, for example a fixed-bed reactor, 3D-simulation is indispensable to understand the local reaction conditions to be able to highlight the optimization potential. Based on experimental data, this manuscript shows the application of the dimensionless numbers effectiveness factor and Thiele modulus for the design of a 3D-printed flow-through reactor. Within the reactor, enzymes are physically entrapped in 3D-printed hydrogel lattices. The local reaction rate of the enzymes is directly dependent on the provided substrate amount at the site of reaction which is limited by the diffusion properties of the hydrogel matrix and the diffusion distance. All three parameters can be summed up by one key figure, the Thiele modulus, which, in short, quantifies mass transfer limitations of a catalytic system. Depending on the rate of the enzymatic reaction in correlation to the diffusional transport, mass transfer limitations will shift the optimum of the system, favoring slow enzyme kinetics and small diffusion distances. Comparison with the enzymatic reaction rate in solution yields the effectiveness factor of the system. As a result, the optimization potential of varying the 3D-printed geometries or the reaction rate within the experimentally available design space can be estimated.
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