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If you are a seller for this product, would you like to suggest updates through seller support? Read more Read less. Save Extra with 4 offers. From the Back Cover For the second edition of 'Microreactors in Organic Chemistry and Catalysis' all chapters have been revised and updated to reflect the latest developments in this rapidly developing field. To get the free app, enter mobile phone number. See all free Kindle reading apps. Don't have a Kindle? No customer reviews. Share your thoughts with other customers. Write a product review.

Pictorial representation of the micro-fixed bed reactor and the four positions of catalyst segments. Recently, in addition to microfluidic devices, the concept of applying millifluidic devices has been introduced in order to synthesize nanoparticles [62—66]. In general, millifluidic devices are referred to as devices which have an internal, transversal scale larger than one millimeter. Millifluidics are easier to fabricate compared with microfluidics and are therefore cheaper. Besides, millifluidic devices can better resist fouling and are easier to interface with typical laboratory devices.

Investigating the benefits of applying millifluidics in nanoparticle synthesis, researchers have begun to focus more and more attention to them [62—66]. Lately, metal nanoparticles such as gold, silver, and copper have been synthesized, applying millifluidics. Li et al. According to the results, they found that particle size can be better controlled compared with batch reactors. However, the synthesized nanoparticles within the millifluidic channels demonstrated a broad size distribution even at the shortest measured residence time 3.

Moreover, Krishna et al. Those gold nanoparticles were catalytically active and in order to provide a good application of them, they were applied for the reaction of 4-nitrophenol to 4-aminophenol. Pictorial representation of time-resolved growth of gold nanostructures within the millifluidic channel. Reprinted, with permission, from [68].

Jun et al. Using a millifluidic setup enabled them to control the mixing step between a gold salt solution and an ascorbic acid solution at different initial pH, which allows controlling the final gold nanoparticle sizes from 3 to 25 nm with a low polydispersity formed in an aqueous surfactant-free solution [69]. Pictorial representation scheme of the millifluidic mixer. Reprinted, with permission, from [69].

Gottesman et al. Besides, they compared their results with the corresponding standard batch reaction. Scanning electron microscope SEM images of silver nanowires synthesized in A millifluidics and B batch process. Reproduced, with permission, from The Royal Society of Chemistry [70]. Biswas et al. Accordingly, by using the millifluid setup, they could achieve low residence time. They also applied numerical simulation and according to those simulation results they demonstrated that high flow rates can be produced within the millifluidic reactor owing to the possibility of creating low pressure drops which leads to a decrease in residence times.

The low residence times coupled with the use of an effective stabilizing agent such as a bidentate PEGylated surfactant, MPEG, results in a highly stable colloid stable for more than 3 months composed of ultra-small Cu nanoclusters. They also showed that by increasing the flow rate lowering the residence time , smaller nanoparticles could be produced, due to better control of the growth process at higher flow rates [71] Figure The analysis of size and size distribution of Cu nanoclusters with mean residence times within the millifluidic reactor.

During the past 2 years, millifluidic devices have become attractive for the synthesis of nanomaterials because they present a growing potential and the possibility of future applications in the field. Nevertheless, there is still much room open for thorough investigations for applications in nanomaterial synthesis.

The application of flow chemistry techniques can offer the possibility for the in situ generation of nanomaterials. Owing to the short residence time scales of microfluidics, the unstable intermediates can be generated in flow. In this context, Yoshida applied the flash chemistry concept [72], which utilizes in-flow generated high-energy intermediates for ultrafast reaction, towards the making of new generations of unstable catalysts.

These unstable reactive catalysts are generated fast and consumed in a later reaction before they decompose. With such an approach, Nagaki et al. As there are hardly any available examples of in situ generated heterogeneous nanocatalysts in microfluidics, the work of Nagaki et al.

The outcoming flow mixture is then directly injected into a reaction section in which the Suzuki-Miyaura reaction mixture flows residence time: 0. This processing, named the flash method, is compared with three alternative injection schemes methods A—C which introduce the two catalyst precursors separately, either in serial or parallel fashion, directly into the reaction mixture. Accordingly, such injected catalysts exhibit a much slower reaction performance than the unstable, highly active flash catalyst.

The difference in reaching reaction completion ranges from approximately 3 min flash to approximately 15 min method A to approximately 30 min method B. This homogeneous catalytic reaction example with an unstable catalytic intermediate has a heterogeneous counterpart. Jamal et al. Such produced gold nanoparticles have very narrow size distribution 1—3 nm and are immobilized into the inner volume of functionalized silica microcapillaries, which then constitutes the catalytic microreactor Figure This example can be considered as an outlook of a promising process that combines the advantages of microfluidic devices to synthesize nanoparticles and using them in situ as catalysts in organic reactions.

A SEM image of the non-functionalized microreactor. B SEM image of the gold nanoparticle functionalized microreactor. Reproduced, with permission, from Springer [75]. This review aims to cover recent achievements on metal nanoparticles, which are produced in continuous flow micro and millifluidics devices and their catalytic application in organic synthesis. The significantly reduced diffusion distance in microfluidic systems provides strongly improved mixing and heat transfer.

In combination with reduced and kinetically matched residence times and decoupling of elementary processes each under optimal conditions by serial injection of reactants, this allows metal nanoparticles to be synthesized with controlled size, shape, and size distribution. In the field of organic chemistry, metal nanoparticles can be applied as catalysts. The joined benefits of the microflow and the catalytic nanoparticles can remarkably enhance the reaction performance, for example, in terms of minimizing the reaction time and improving the yield.

Nanoengineering of inorganic and hybrid hollow spheres by colloidal templating. Science , , — Nanoparticles, nanotechnology and pulmonary nanotoxicology. Port Pneumol. Salata OV. Applications of nanoparticles in biology and medicine. Electroluminescence from single monolayers of nanocrystals in molecular organic devices. Nature , , — Semiconductor nanocrystals as fluorescent biological labels. Gold nanoparticle-assembled capsules and their application as hydrogen peroxide biosensor based on hemoglobin. Bioelectrochemistry , 84, 32— Recent advances in the liquid-phase syntheses of inorganic nanoparticles.

Synthesis and functionalization of a mesoporous silica nanoparticle based on the sol-gel process and applications in controlled release. Recent advances in nanoparticle synthesis with reversed micelles. Colloid Interf. Onion phases as biomimetic confined media for silica nanoparticle growth.


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Langmuir , 21, — Marre S, Jensen K. Synthesis of micro and nanostructures in microfluidic systems. Nanoparticle synthesis in microreactors. Controllable preparation of particles with microfluidics. Particuology , 9, — Hung L, Lee A. Microfluidic devices for the synthesis of nanoparticles and biomaterials. DeMello A. Control and detection of chemical reactions in microfluidic systems. Jensen K. Microreaction engineering — is small better?

On-line analysis of CdSe nanoparticle formation in a continuous flow chip-based microreactor. Spatially-resolved analysis of nanoparticle nucleation and growth in a microfluidic reactor. Lab Chip , 7, — Microfluidics in inorganic chemistry. Optical and MRI multifunctional nanoprobe for targeting gliomas. Nano Lett. Microfluidic synthesis of polymer and inorganic particulate materials. Accelerated synthesis of titanium oxide nanostructures using microfluidic chips. Direct synthesis of dextran-coated superparamagnetic iron oxide nanoparticles in a capillary-based droplet reactor.


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  6. A novel continuous microfluidic reactor design for the controlled production of high-quality semiconductor nanocrystals. Nanoparticle Res. Continuous synthesis of gold nanoparticles in a microreactor. Synthesis of silver nanoparticles in a continuous flow tubular microreactor. Gold nanoparticles formation via gold III chloride complex ions reduction with glucose in the batch and in the flow microreactor systems. Colloids Surf. A Physicochem.

    Aspects , , — Continuous synthesis of CdSe-ZnS composite nanoparticles in a microfluidic reactor. Microfluidic generation of metal nanoparticles by borohydride reduction. Multi-step synthesis of nanoparticles performed on millisecond time scale in a microfluidic droplet-based system. Lab Chip , 4, — Continuous sonocrystallization of acetylsalicylic acid ASA : control of crystal size. Crystal Growth Des. Microscale reactors: nanoscale products. Lab Chip , 4, 11N—15N. Daniel M, Astruc D. Gold nanoparticles: assembly, supramolecular chemistry, quantum-size-related properties, and applications toward biology, catalysis, and nanotechnology.

    Formation of isolated and clustered Au nanoparticles in the presence of polyelectrolyte molecules using a flow-through Si chip reactor. Synthesis of gold nanoparticles in an interdigital micromixer using ascorbic acid and sodium borohydride as reducers. Nightingale A, DeMello J.

    Flow Technology for Organometallic-Mediated Synthesis

    Segmented flow reactors for nanocrystal synthesis. Size-controlled flow synthesis of gold nanoparticles using a segmented flow microfluidic platform. Langmuir , 28, — Microfluidic continuous flow synthesis of rod-shaped gold and silver nanocrystals. A seedless approach to continuous flow synthesis of gold nanorods. Duraiswamy S, Khan S. Droplet-based microfluidic synthesis of anisotropic metal nanocrystals. Small , 5, — Gold-nanoparticle-catalyzed synthesis of propargylamines: the traditional A3-multicomponent reaction performed as a two-step flow process.

    Control of selectivity in heterogeneous catalysis by tuning nanoparticle properties and reactor residence time. Effects of interior wall on continuous fabrication of silver nanoparticles in microcapillary reactor. Segmented flow synthesis of Ag nanoparticles in spiral microreactor: role of continuous and dispersed phase. Preparation of Au-Ag, Ag-Au core-shell bimetallic nanoparticles for surface-enhanced Raman scattering. Scripta Mater. Multishell bimetallic AuAg nanoparticles: synthesis, structure and optical properties. Microfluidic biosynthesis of silver nanoparticles: effect of process parameters on size distribution.

    On-chip fabrication of silver microflower arrays as a catalytic microreactor for allowing in situ SERS monitoring. Synthesis of palladium nanoparticles using a continuous flow polymeric micro reactor. Microflow reactor synthesis of palladium nanoparticles stabilized with poly benzyl ether dendron ligands. Cross-coupling in flow. Inductive heating for organic synthesis by using functionalized magnetic nanoparticles inside microreactors. Inductive heating with magnetic materials inside flow reactors. Synthesis, assembly and reaction of a nanocatalyst in microfluidic systems: a general platform.

    Lab Chip , 12, — Microreactor containing platinum nanoparticles for nitrobenzene hydrogenation. A Gen. Investigation into sulfobetaine-stabilized Cu nanoparticle formation: toward development of a microfluidic synthesis. B , , — Microfluidic synthesis of copper nanofluids. Microfluidics Nanofluidics , 9, — Monnier F, Taillefer M. ChemSusChem , 6, — Generation of porous solids with well-controlled morphologies by combining foaming and flow chemistry on a Lab-on-a-Chip.

    Aspects , , 17— Millifluidic production of metallic microparticles. Soft Matter. Geometric optimization of liquid-liquid slug flow in a flow-focusing millifluidic device for synthesis of nanomaterials. A simple millifluidic benchtop reactor system for the high-throughput synthesis and functionalization of gold nanoparticles with different sizes and shapes.

    ACS Nano , 7, — Size evolution of gold nanoparticles in a millifluidic reactor. In this way, gold nuclei are obtained, which grow by agglomeration, and it is controlled by the interaction of the nuclei with local flow. Therefore, the difference in the physical properties of the two phases, such as density, viscosity, and surface tension, and the inlet flow rates finally control the particle growth. Hence, a careful choice of continuous and dispersed phases is necessary to control the nanoparticle size and size distribution.

    Reprinted, with permission, from [38]. Copyright American Chemical Society. By increasing the residence time, the particle size distribution widened independent of the inert fluid dispersed in the aqueous phase. For instance, with toluene as the inert fluid, particle sizes of 3. In addition to spherical nanoparticles, anisotropic metal nanocrystals such as nanorods have been synthesized using microfluidics [39—41]. As one of the early works, Boleininger et al. They used small, spherical gold seeds in a growth solution containing the gold salt HAuCl 4 in millimolar concentrations, a mild reducing agent ascorbic acid , and a high concentration of a surfactant molecule cetyltrimethylammonium bromide, CTAB , which produces a rod-shaped anisotropic particle growth solution.

    The seeds and growth solution are injected to a microreactor. The effects of the concentration in the mixture of growth-to-seeds solution and of the growth temperature on particle shape were tested. Fewer seeds generate particles of higher aspect ratio and also a higher growth temperature produced smaller aspect ratio fatter rods Figure 6.

    Pictorial representation of the measured extinction, which is color-coded as a function of time. A The ratio of growth-to-seed solution was varied from to Reproduced, with permission, from The Royal Society of Chemistry [39]. Bullen et al. The rotating tube processing provides a good mixing of two solutions and therefore with the aid of centrifugal force gold nanocrystals were formed. Thereafter, the gold nanocrystal solution continuously entered the narrow channel processor for growth of the gold nanorods Figure 7. Reproduced, with permission, from The Royal Society of Chemistry [40].

    In addition to single-phase flow, droplet-based flow has been used to synthesize anisotropic gold nanocrystals. Duraiswamy and Khan [41] used presynthesized gold nanoparticle seeds and growth reagents. These are dispensed into monodisperse picoliter droplets which are produced by a microfluidic T-junction Figure 8. From the other arm of the T-junction silicon oil was continuously introduced into the microchannel.

    Creating the mixtures in a droplet prevents the contact between the growing nanocrystals and the microchannel walls. Pictorial representation of the droplet-based microfluidic synthesis of anisotropic gold nanocrystals. A gold nanoparticle seed suspension S and aqueous reagent solutions R 1 and R 2 are separately introduced into one arm of a microfluidic T-junction, and silicone oil is introduced into the other arm.

    The effects of the reagent concentrations and of the flow rate ratio of the oil to aqueous reagent streams. By varying those critical factors, nanocrystals with desired shape and size with tunable optical resonances are achieved Figure 9. One of the recent applications of gold nanoparticles in flow chemistry is catalyzing the aminoalkylation reaction [42]. Abahmane et al. The A 3 reaction mechanism includes two reaction steps that require different catalytic supports.

    Montmorillonite K MM K is applied to promote the initial condensation reaction and Au nanoparticles on an alumina support are used to catalyze the second aminoalkylation step.

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    Three different reaction regimes A—C were realized by operating at one temperature or using a two-temperature ramp, as well as having a different reactant insertion scheme along the reaction pathway Figure The flow chemistry approach considerably improved the reaction performance of the A 3 -coupling reaction in terms of shortened reaction time and higher yields compared with conventional batch reactors. Homogeneous and heterogeneous catalysis have their own advantages and a combination of those advantages could develop sustainable catalysts with novel reactivity and selectivity.

    Heterogeneous catalysts are recycled more easily than homogeneous ones, but it is difficult to apply them in traditional organic reactions. As a solution out of this dilemma, Gross et al. The diastereoselectivity of Au-catalyzed cyclopropanation reactions can be considerably improved Scheme 1. The same heterogeneous catalyst was also applied in a fixed-bed flow reactor. By adjusting the residence time of reactants, the catalytic reactivity and product selectivity of secondary reactions can be well controlled in a way that is not easily available for homogeneous catalysts Scheme 2.

    Comparison of homogeneous and heterogeneous gold catalysts for the formation of a substituted cyclopropane [43]. Comparison of the total conversion of gold-catalyzed cyclopropanation reaction for different flow rates in batch and flow [43].

    Flow Chemistry Publications | Chemtrix BV

    One of the earlier methods to synthesize silver nanoparticles in a microflow reactor was based on thermal reduction [27]. Lin et al. A narrow particle size dispersion is obtained. The reaction mixture is introduced into a tubular coil made of a stainless steel needle 0.

    The flow rate has a major influence on the size of the nanoparticles and their polydispersity. At a flow rate of 0. As the flow rate is increased to 0. In contrast to this, a change in the TOA concentration did not make any substantial difference in either the size or size distribution of the nanoparticles.

    TEM image of the particle size distribution analysis of the Ag nanoparticles made in the tubular microreactor at a flow rate of 0. Reprinted, with permission, from [27]. He et al. A relation between the particles and the interior wall of the tube results in a broader size distribution and a lower yield. To observe the effect of segmented flow on the nanoparticle size distribution, Ravi Kumar et al. Whereas in one case the reactant phase is in the form of dispersed phase slugs, in the other case it is in the form of continuous phase.

    The particle sizes were much smaller when generated by gas-liquid flow than by liquid-liquid flow Figure This effect is strengthened by the unidirectionally expanding spiral geometry of the channel, inducing transverse flows. Reproduced, with permission, from Elsevier BV [45]. The effect of segmentation, which is determined by the slug sizes and the slip velocity, controlled the nanoparticle size distribution.

    The micromixer having a smaller orifice diameter yields smaller slugs and also a narrow particle size distribution. Knauer et al. Binary metal nanoparticles of silver and gold can have optically fine-tuned absorption in the visible spectrum, the so-called plasmonic absorption. The shift of the plasmonic band is influenced by the ratio between silver and gold, the shape and the size of the binary particles, and the distribution of the two metals inside the particle. For example, when forming silver or gold as a shell or core, a different plasmon absorption is found. The synthesis is based on the reduction of a gold salt, HAuCl 4 , and a silver salt, AgNO 3 , at the surface of seed particles by ascorbic acid [46].

    In order to improve mixing in the microfluidic system, the segmented flow principle was applied. The optical spectra of the particle solutions exhibited extreme changes with the deposition of each additional metal shell Figure Owing to the changes in their optical properties, the prepared particles are very useful for future sensing applications as well as for labeling in bioanalytics or as nonlinear optical devices. Reproduced, with permission, from Elsevier BV [46].

    As one spotlight of the increasing interest in biosynthesis of nanoparticles, the microfluidic biosynthesis of Ag nanoparticles in tubular microreactors in the presence of Cacumen Platycladi C. Platycladi extract was developed by Liu et al. The effect of technical parameters volumetric flow rate, the concentration of the C. Platycladi extract, the inlet mixing pattern and reactor parameters reactor materials and inner diameter on the size distribution of the silver nanoparticles were studied. To simulate the profile evolution of the velocity, biomass concentration and temperature within the microreactors, computational fluid dynamics was applied.

    It was found that, unlike in conventional batch reactors, the interfacial effect between the solid surface and bulk solutions cannot be ignored in microreactors and has an important influence on the particle size distribution. Reactor materials with more intense interfacial interaction coarser surface and larger friction coefficient with the bulk solutions yield silver nanoparticles with larger average size and wider size distribution. They stated that the relatively coarse surface of the reactor material can provide more sites for nucleation due to its larger superficial area.

    Nanoparticle deposition on the wall surface increases friction by improving the roughness of the surface. Therefore, materials with rough surface are capable of producing a stronger interfacial effect, which then leads to particle formation with larger average size and wider size distribution of the nanoparticles. In addition, Ag nanoparticles were synthesized with larger average size and wider size distribution.


    1. Microreactors in organic synthesis and catalysis -ORCA.
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    5. The research unraveled the influence of process parameters on the size distribution of Ag nanoparticles in the microfluidic biosynthesis. Xu et al. Silver nanostructures were produced by photoreduction using a femtosecond laser of upright nanoplates and attached nanoparticles and were fabricated inside the microfluidic channel as catalytic active sites for the reduction of 4-nitrophenol to 4-aminophenol. On-chip catalytic reduction achieved silver microstructures with high catalytic activity.

      This was monitored by in situ surface-enhanced Raman scattering. Pictorial representation of the laser fabrication of Ag microstructure arrays inside a microfluidic chip. Reproduced, with permission, from The Royal Society of Chemistry [50]. Palladium nanoparticles play a key role as a catalyst in many reactions such as the formation of C-C bonds. Song et al. Five parallel channels were fabricated to scale up the production yield and minimize the mixing volume and dead time. The Pd nanoparticles, when obtained from conventional batch process, had a mean diameter of 3.

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      The effects of the hydrodynamic parameter capillary diameter, velocity, volume flow rate, and reaction temperature and concentration precursor and stabilizer on the particle size were investigated. The particle size is not influenced by the volume flow rate but by the velocity. The reason is that the reaction time is defined by the latter. Unlike batch processes, smaller Pd particles are produced in the microreactor system at low ligand concentrations when the molar ratio of the ligand to metal precursor is kept in the range of 1—5.

      As another characteristic of the microreactor synthesis, the concentration of the Pd precursor can be increased up to 27 m m with keeping a constant particle size 3. Reproduced, with permission, from Springer [52]. One of the most important applications of palladium nanoparticles is catalyzing the cross-coupling reactions [53].

      Ceylan et al. Palladium particles obtained by reductive precipitation of ammonium-bound tetrachloropalladate salts give nanoparticles which can be used as good catalysts for different Pd-catalytic cross-coupling reactions. Only a slight amount of palladium leaching is observed 34 ppm for Suzuki-Miyaura reactions and ppm for Heck reactions. Pictorial representation of the preparation of magnetic nanoparticles doped with Pd. Lee et al. Applying a spiral silicon-Pyrex microreactor, platinum nanoparticles were produced continuously and coated onto the surface of the magnetic silica nanospheres.

      The reactants were: amine grafted magnetic core-shell silica suspension, Pt precursor [dipotassium tetrachloroplatinate II ] and the reducing agents.

      Microreactor with Integrated Mass Spectrometer for Catalysis Studies - The CATLAB - Hiden Analytical

      To ensure a single liquid phase reaction, the microreactor is kept at a high pressure of 10 bar and high temperature. These Pt-decorated silica nanospheres are assembled into micron-sized particles by using emulsion templates generated with a microfluidic drop generator. Lastly, in order to study the catalytic reactivity, the assembled particles are introduced into a packed-bed microreactor.

      Pictorial representation of the application of a microfluidic system for synthesis, self-assembly, and catalysis with Pt-decorated magnetic silica PMS supraballs. Reproduced, with permission, from The Royal Society of Chemistry [56]. One of the applications of Pt nanoparticles is to catalyze the hydrogenation of nitrobenzene to aniline. Kataoka et al. To improve the adsorption and catalytic activity of the nanoparticles, catalytic support layers are offered as a film on the inner wall of the microreactor. Applying an immobilization technique, Pt nanocatalysts demonstrated a good catalytic activity and can be easily regenerated.

      Table 2 presents a comparison of catalyst activity in microreactor and batch experiments. Comparison of catalyst activity in microreactor and batch experiments reproduced, with permission, from Elsevier BV [57]. The study and comparison of the copper nanoparticle formation between microfluidic and conventional batch processes was reported by Song et al. Compared with results from the conventional batch process, Cu nanoparticles synthesized from microfluidic devices are smaller 8.

      In addition, X-ray diffraction analysis and size distribution is given. Reprinted, with permission, from [58]. Zhang et al. The effects of the flow rate of reactants, reactants concentrations, and surfactant concentration on the copper particle size and size distribution were studied. Neither of them had much impact on the particle size and size distribution of copper nanoparticles synthesized in microfluidic reactors because of the fast mass diffusion in the microscale dimension.

      The copper nanoparticle average size was approximately 3. The synthesis time of copper nanofluids in the microreactor can be reduced as much as one order of magnitude, from approximately 10 min to approximately 28 s. TEM images of copper nanoparticles formed in A a flask and B a microreactor.

      Reproduced, with permission, from Springer [59]. Compared with Au and Pt, the application of heterogenized Cu catalysts is limited due to their oxidative instability and limited catalyst activity. Cu nanocatalysts were used in the Ullmann-type C-O coupling [60] of potassium phenolate and 4-chloropyridine in a combined microwave MW and microflow process. Benaskar et al.

      With the combination of microwave and microflow in one process, the Ullmann-type C-O coupling of potassium phenolate and 4-chloropyridine is performed Figure Pictorial representation of the micro-fixed bed reactor and the four positions of catalyst segments. Recently, in addition to microfluidic devices, the concept of applying millifluidic devices has been introduced in order to synthesize nanoparticles [62—66]. In general, millifluidic devices are referred to as devices which have an internal, transversal scale larger than one millimeter.

      Millifluidics are easier to fabricate compared with microfluidics and are therefore cheaper. Besides, millifluidic devices can better resist fouling and are easier to interface with typical laboratory devices. Investigating the benefits of applying millifluidics in nanoparticle synthesis, researchers have begun to focus more and more attention to them [62—66]. Lately, metal nanoparticles such as gold, silver, and copper have been synthesized, applying millifluidics.

      Li et al. According to the results, they found that particle size can be better controlled compared with batch reactors. However, the synthesized nanoparticles within the millifluidic channels demonstrated a broad size distribution even at the shortest measured residence time 3. Moreover, Krishna et al. Those gold nanoparticles were catalytically active and in order to provide a good application of them, they were applied for the reaction of 4-nitrophenol to 4-aminophenol.

      Pictorial representation of time-resolved growth of gold nanostructures within the millifluidic channel. Reprinted, with permission, from [68]. Jun et al. Using a millifluidic setup enabled them to control the mixing step between a gold salt solution and an ascorbic acid solution at different initial pH, which allows controlling the final gold nanoparticle sizes from 3 to 25 nm with a low polydispersity formed in an aqueous surfactant-free solution [69].

      Pictorial representation scheme of the millifluidic mixer.