Flow Chemistry: A Sustainable Voyage Through the Chemical Universe en Route to Smart Manufacturing

Photo-Induced Bandgap Engineering of Metal Halide Perovskite Quantum Dots In Flow

Over the past decade, lead halide perovskite (LHP) nanocrystals (NCs) have attracted significant attention due to their tunable optoelectronic properties for next-generation printed photonic and electronic devices. High-energy photons in the presence of haloalkanes provide a scalable and sustainable pathway for precise bandgap engineering of LHP NCs via photo-induced anion exchange reaction (PIAER) facilitated by in situ generated halide anions. However, the mechanisms driving photo-induced bandgap engineering in LHP NCs remain not fully understood. This study elucidates the underlying PIAER mechanisms of LHP NCs through an advanced microfluidic platform. Additionally, the first instance of a PIAER, transforming CsPbBr3 NCs into high-performing CsPbI3 NCs, with the assistance of a thiol-based additive is reported. Utilizing an intensified photo-flow microreactor accelerates the anion exchange rate 3.5-fold, reducing material consumption 100-fold compared to conventional batch processes. It is demonstrated that CsPbBr3 NCs act as photocatalysts, driving oxidative bond cleavage in dichloromethane and promoting the photodissociation of 1-iodopropane using high-energy photons. Furthermore, it is demonstrated that a thiol-based additive plays a dual role: surface passivation, which enhances the photoluminescence quantum yield, and facilitates the PIAER. These findings pave the way for the tailored design of perovskite-based optoelectronic materials.

Bimetallic Nickel-Palladium Nanoparticles Supported on Multiwalled Carbon Nanotubes for Suzuki Cross-Coupling Reactions in Continuous Flow

An efficient Suzuki cross-coupling reaction under continuous flow conditions was developed utilizing an immobilized solid supported catalyst consisting of bimetallic nickel-palladium nanoparticles (Ni-Pd/MWCNTs). In this process, the reactants can be continuously pumped into a catalyst bed at a high flow rate of 0.6 mL/min and the temperature of 130 °C while the Suzuki products are recovered in high steady-state yields for prolonged continuous processing. The catalyst was prepared by mechanical shaking of the appropriate nickel and palladium salts using ball-mill energy without the requirement of any solvent or reducing agent. This straightforward, facile, and simple method allows for bulk production of Ni-Pd/MWCNTs nanoparticles with a small particle size ideal for application in continuous flow cross-coupling catalysis. The as-prepared catalyst mostly contains nickel (7.9%) with a very small amount of palladium (0.81%) according to ICP-OES analysis. This remarkable immobilized catalyst can be used several times for different Suzuki reactions with a minimum loss of reactivity and no detectable leaching of the metal nanoparticles. Notably, by modifying the groups on both aryl halides and phenylboronic acids, the method provides access to a diverse array of the Suzuki products in flow with high steady-state yield, making it suitable for applications in industrial and pharmaceutical scales. Moreover, several spectroscopic techniques were employed to identify the structure and composition of the as-prepared Ni-Pd/MWCNTs nanoparticles before and after the reaction in flow such as transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), BET surface area (physisorption), and FTIR spectroscopy.

Autonomous nanomanufacturing of lead-free metal halide perovskite nanocrystals using a self-driving fluidic lab

Lead-based metal halide perovskite (MHP) nanocrystals (NCs) have emerged as a promising class of semiconducting nanomaterials for a wide range of optoelectronic and photoelectronic applications. However, the intrinsic lead toxicity of MHP NCs has significantly hampered their large-scale device applications. Copper-base MHP NCs with composition-tunable optical properties have emerged as a prominent lead-free MHP NC candidate. However, comprehensive synthesis space exploration, development, and synthesis science studies of copper-based MHP NCs have been limited by the manual nature of flask-based synthesis and characterization methods. In this study, we present an autonomous approach for the development of lead-free MHP NCs via seamless integration of a modular microfluidic platform with machine learning-assisted NC synthesis modeling and experiment selection to establish a self-driving fluidic lab for accelerated NC synthesis science studies. For the first time, a successful and reproducible in-flow synthesis of Cs3Cu2I5 NCs is presented. Autonomous experimentation is then employed for rapid in-flow synthesis science studies of Cs3Cu2I5 NCs. The autonomously generated experimental NC synthesis dataset is then utilized for fast-tracked synthetic route optimization of high-performing Cs3Cu2I5 NCs.

Continuous Stripping with Dense Carbon Dioxide

The integration of flow chemistry into continuous manufacturing requires efficient, controllable, and continuous methods for the concentration of diluted solutions on relatively small scales. The design and application examples of a new continuous solvent removal process are presented. The continuous stripping method employing dense carbon dioxide is based on the formation of homogeneous mixtures of dilute organic solutions of the target molecules with a large excess of carbon dioxide at temperatures as low as 35 °C and pressures around 10 MPa. Subsequent pressure reduction results in the quick release of carbon dioxide and vaporization of a significant fraction of the organic solvent. The concentration of the solute in the separated liquid phase can be up to 40 times higher than in the feed. Among the many controllable process parameters, the most significant ones are the mass-flow rate ratio of carbon dioxide to the feed and the temperature of the phase separator. By careful setting of the operational parameters, the degree of concentration enhancement may be accurately controlled. The new apparatus-despite consisting of laboratory equipment and being built in a fume hood-could easily support pilot-scale synthetic flow chemistry, being a continuous, efficient alternative to thermal concentration methods.

Continuous Ligand-Free Catalysis Using a Hybrid Polymer Network Support

Although the pharmaceutical and fine chemical industries primarily utilize batch homogeneous reactions to carry out chemical transformations, emerging platforms seek to improve existing shortcomings by designing effective heterogeneous catalysis systems in continuous flow reactors. In this work, we present a versatile network-supported palladium (Pd) catalyst using a hybrid polymer of poly(methylvinylether-alt-maleic anhydride) and branched polyethyleneimine for intensified continuous flow synthesis of complex organic compounds via heterogeneous Suzuki-Miyaura cross-coupling and nitroarene hydrogenation reactions. The hydrophilicity of the hybrid polymer network facilitates the reagent mass transfer throughout the bulk of the catalyst particles. Through rapid automated exploration of the continuous and discrete parameters, as well as substrate scope screening, we identified optimal hybrid network-supported Pd catalyst composition and process parameters for Suzuki-Miyaura cross-coupling reactions of aryl bromides with steady-state yields up to 92% with a nominal residence time of 20 min. The developed heterogeneous catalytic system exhibits high activity and mechanical stability with no detectable Pd leaching at reaction temperatures up to 95 °C. Additionally, the versatility of the hybrid network-supported Pd catalyst is demonstrated by successfully performing continuous nitroarene hydrogenation with short residence times (<5 min) at room temperature. Room temperature hydrogenation yields of >99% were achieved in under 2 min nominal residence times with no leaching and catalyst deactivation for more than 20 h continuous time on stream. This catalytic system shows its industrial utility with significantly improved reaction yields of challenging substrates and its utility of environmentally-friendly solvent mixtures, high reusability, scalable and cost-effective synthesis, and multi-reaction successes.

SpectIR-fluidics: completely customizable microfluidic cartridges for high sensitivity on-chip infrared spectroscopy with point-of-application studies on bacterial biofilms

We present a generalizable fabrication method for a new class of analytical devices that merges virtually any microfluidic design with high-sensitivity on-chip attenuated total reflection (ATR) sampling using any standard Fourier transform infrared (FTIR) spectrometer. Termed "spectIR-fluidics", a major design feature is the integration of a multi-groove silicon ATR crystal into a microfluidic device, compared with previous approaches in which the ATR surface served as a structural support for the entire device. This was accomplished by the design, fabrication, and aligned bonding of a highly engineered ATR sensing layer, which con```tains a seamlessly embedded ATR crystal on the channel side and an optical access port that matched the spectrometer light path characteristics at the device exterior. The refocused role of the ATR crystal as a dedicated analytical element, combined with optimized light coupling to the spectrometer, results in limits of detection as low as 540 nM for a D-glucose solution, arbitrarily complex channel features that are fully enclosed, and up to 18 world-to-chip connections. Three purpose-built spectIR-fluidic cartridges are used in a series of validation experiments followed by several point-of-application studies on biofilms from the gut microbiota of plastic-consuming insects using a small portable spectrometer.

Efficient degassing and ppm-level oxygen monitoring flow chemistry system

Low oxygen levels are critical for a long range of chemical transformations carried out in both flow and batch chemistry. Here, we present an inline continuous flow degassing system based on a gas-permeable membrane inside a vacuum chamber for achieving and monitoring ppm-level oxygen concentrations in solutions. The oxygen presence was monitored with a molecular oxygen probe and a continuously running UV-vis spectrometer. An automated setup for discovering optimal reaction conditions for minimal oxygen presence was devised. The parameters tested were: flow rate, vacuum pressure, solvent back-pressure, tube material, tube length and solvent oxygen solubility. The inline degassing system was proven to be effective in removing up to 99.9% of ambient oxygen from solvents at a flow rate of 300 μl min^-1 and 4 mbar vacuum pressure inside the degassing chamber. Reaching lower oxygen concentrations was limited by gas permeation in the tubing following the degassing unit, which could be addressed by purging large volume flow reactors with an inert gas after degassing or by using tubing with lower gas permeability, such as stainless steel tubing. Among all factors, oxygen solubility in solvents was found to play a significant role in achieving efficient degassing of solvents. The data presented here can be used to choose optimal experimental parameters for oxygen-sensitive reactions in flow chemistry reaction setups. The data were also fitted to an analytically derived model from simple differential equations in physical context of the experiment.