Name: Millifluidics for Chemical Synthesis and Time-resolved Mechanistic Studies (Video) | JoVE Journal
Uploaded: 2013-11-27T20:00:00.000+00:00
Duration: 12 min 55 s
Description: Learn millifluidic synthesis of copper and gold nanoparticles for time-resolved mechanistic studies. This method enables continuous flow catalysis and real-time observation of reaction intermediates using X-ray spectroscopy.

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This research work is supported as part of the Center for Atomic Level Catalyst Design, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001058 and also supported by Board of Regents under grants award number LEQSF (2009-14)-EFRC-MATCH and LEDSF-EPS(2012)-OPT-IN-15. MRCAT operations are supported by the Department of Energy and the MRCAT member institutions. The use of the Advanced Photon Source at ANL is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. Financial support for JTM was provided as part of the Institute for Atom-efficient Chemical Transformations (IACT), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.

Millifluidics set-up: Purchase a millifluidic chip (made of polyester terephthalate polymer) from Microplumbers Microsciences LLC, which has serpentine channels with dimensions of 2 mm (W) x 0.15 mm (H) x 220 mm (L). Use FEP Tubing &#160;with dimensions of 0.25 mm I.D., 1/16 in&#160;O.D., for connecting the chip to the pump. Use two different pumps for the two different experiments. Use P-Pump&#160;for the first experiment (copper nanoparticles) and the millifluidic device&#160;for the second experiment (gold nanoparticles). To minimize the problem of gas bubbles within the channels, freshly prepared NaBH4 solution was left open to stand for ~10-15 min before pumping into the chip so that the gas bubbles escape from the solution. This step was followed for all of our experiments.
1. Synthesis of Ultra-small Copper Nano Clusters (UCNCs)
<ol>
	<li>Chemicals required: Obtain copper(II) nitrate hydrate, sodium borohydride, sodium hydroxide pellets and O-[2-(3-mercaptopropionylamino)ethyl]-O&#39;-methylpolyethylene glycol (MW=5,000) [MPEG] and use all chemicals without further purification. Use nanopure water (18.2 M&#937;-cm) for the experiment.</li>
	<li>Use P-Pump regulated under nitrogen pressure for the experiment. Test the pumps with water as solvent at different pressures prior to the experiment to correlate with the corresponding flow-rates (ml/hr). Rinse the millifluidic reactor and tubing with deionized water before initiation of the experiment.</li>
	<li>Dissolve 174 mg (0.95 mmol) of copper(II) nitrate and 610 mg (0.122 mmol) of O-[2-(3-mercaptopropionylamino)ethyl]-O&#39;-methylpolyethylene glycol in 28 ml of nanopure water and keep them in a vial to be connected with one input channel</li>
	<li>Keep another solution of 111 mg (2.93 mmol) of sodium borohydride and 102 mg (2.78 mmol) sodium hydroxide in 28 ml (pH ~13) in a different vial and connect it with the other input channel.</li>
	<li>Flow both the solutions simultaneously within the millifluidic reactor at different flow-rates (given below) and collect the resulting UCNCs at the outlet in glass vial. Purge the solution with nitrogen and store it under nitrogen.</li>
	<li>Operate the pumps under different constant pressures of 50 mbar (6.81 ml/hr), 100 mbar (14.31 ml/hr), 200 mbar (32.7 ml/hr) and 300 mbar (51.4 ml/hr) at room temperature for the synthesis of UCNCs at different flow-rates.</li>
</ol>
While the synthesis procedure was demonstrated using the millifluidic set-up with P-Pump, it can also be carried out using the hand-held millifluidic device from Millifluidica.
2. Time Resolved In situ Kinetic Studies on Gold Nanoparticle Formation
<ol>
	<li>Chemicals required: Obtain chloroauric acid (HAuCl4.3H2O) meso-2,3-dimercaptosuccinic acid (DMSA) and sodium borohydride&#160;and use all chemicals without further purification. Use nanopure water (18.2 M&#937;-cm) for the experiment.</li>
	<li>Use high precision, fully automated, pulsation free syringe pumps&#160;to flow the liquids within the chip. Test the pumps with water as solvent at different flow-rates prior to the experiment to optimize the required flow-rate.</li>
	<li>Prepare standard solutions of (i) HAuCl4.3H2O (10 mmol, 118.2 mg/30 ml) and (ii) DMSA (20 mmol, 109.2 mg/30 ml) with 50 mg of sodium hydroxide (pH 12) in nanopure water.</li>
	<li>Feed the two solutions through two separate syringes into the millifluidic chip at a constant flow-rate of 10 ml/hr using the automated pump.</li>
	<li>Couple the millifluidic chip to the synchrotron beam line using a metal stage that has access to movement in XYZ directions and collect the XAS data at different zones on the chip as the solutions were pumped through the chip.</li>
</ol>
While the in situ analysis procedure was demonstrated using the millifluidic set-up with P-Pump, it can also be carried out using a hand-held millifluidic device.
3. Continuous Flow Gold Catalysis
This procedure was demonstrated using a hand-held millifluidic device.
<ol>
	<li>Chemicals required: Obtain chloroauric acid (HAuCl4.3H2O), meso-2,3-dimercaptosuccinic acid (DMSA), sodium borohydride, 4-nitrophenol, 4-aminophenol&#160;and use all the chemicals without further purification. Use nanopure water (18.2 M&#937;-cm) for the experiment.</li>
	<li>Catalyst preparation: Prepare standard solutions of HAuCl4.3H2O (10 mmol, 118.2 mg/30 ml), DMSA (20 mmol, 109.2 mg/30 ml) and NaBH4 (10 mmol, 11.34 mg/30 ml) in Nanopure water.</li>
	<li>Take 10 ml each of HAuCl4 and DMSA solutions into two separate vials and flow them within the chip using the hand-held millifluidic device with a uniform flow-rate of 12 ml/hr for 45 min.</li>
	<li>Flow 10 mmol NaBH4 within the chip at 12 ml/hr flow-rate for 15 min to reduce the Au(I) to Au(0).</li>
	<li>Finally, wash the chip with nanopure water for 30 min at the same flow-rate before conducting the catalysis experiments.</li>
	<li>Catalysis reaction: Perform the chemical conversion reaction (reduction) of 4-nitrophenol (4-NP) into 4-aminophenol (4-AP) within the gold catalyst (prepared above) coated millifluidic channel as given below.</li>
	<li>Mix 15 ml of 9 x&#160;10-5 mol solution of 4-NP with 3.3 ml of 0.65 mol NaBH4 solution to form 4-nitrophenolate ion (4-NPI).</li>
	<li>Pass the resultant solution over the gold catalyst deposited within chip at a constant flow-rate of 5 ml/hr to evaluate the catalytic activity. Analyze the UV-Vis spectra&#160;of the collected products within the wavelength range of 250-500 nm to confirm the conversion of 4-NP.</li>
	<li>Estimate the catalytic activity of the reaction by obtaining the calibration curve of 4-NPI. Calibration curve can be acquired by plotting the experimentally observed absorption intensity (I) of 4-NPI at different standard concentrations. The peak heights (at 399 nm) for the UV-Vis absorption curves represent the absorption intensity (I) values and according to the Beer Lambert&#39;s law, any change in the peak height value would show corresponding change in its concentration. Therefore, estimate the catalytic activity by finding the difference in initial and final concentrations of the reactant from the calibration curve. For example, if the peak height is 1 unit (Figure 6) it corresponds to a catalytic conversion of 90% (based on the calibration plot).</li>
</ol>

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<li>Abahmane, L., Köhler, J. M., Groß, G. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Gold-nanoparticle-catalyzed+synthesis+of+propargylamines%3A+the+traditional+A3-multicomponent+reaction+performed+as+a+two-step+flow+process%5BTitle%5D)+AND+%22Chem.+Eur.+J%22%5BJournal%5D)">Gold-nanoparticle-catalyzed synthesis of propargylamines: the traditional A3-multicomponent reaction performed as a two-step flow process.</a> Chem. Eur. J. 17, 3005-3010 (2011).</li>
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<li>Abou-Hassan, A., Sandre, O., Cabuil, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Microfluidics+in+Inorganic+Chemistry%5BTitle%5D)+AND+%22Angew.+Chem.+Int.+Ed%22%5BJournal%5D)">Microfluidics in Inorganic Chemistry.</a> Angew. Chem. Int. Ed. 49, 6268-6286 (2010).</li>
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All authors except C.S.S.R. Kumar declare that they have no competing financial interests. C .S.S.R. Kumar is the founder of the company Millifluidica LLC.

The UCNCs were formed by the reduction reaction of copper nitrate with sodium borohydride in the presence of the polymeric capping agent O-[2-(3-Mercaptopropionylamino)ethyl]-O&#39;-methylpolyethylene glycol (MW=5,000) [MPEG]. The reaction was performed within the millifluidic chip reactor at different flow-rates such as 6.8 ml/hr, 14.3 ml/hr, 32.7 ml/hr, and 51.4 ml/hr to study the effect of flow-rates on the UCNCs formed. The respective residence times for the above flow-rates are 47.49, 24.44, 16.56, and 9.02 sec. The...

Lab-on-a-chip (LOC) devices for chemical synthesis have demonstrated significant advantage in terms of increased mass and heat transfer, superior reaction control, high throughput and safer operation environment1. These devices can be broadly classified into chip based fluidics and nonchip based fluidic devices. Among the chip-based fluidics, microfluidics is well investigated and a topic well-covered in the literature2-5. Nonchip based LOC systems use tubular reactors6. Conventionally, microfluidic systems are used for precise control and manipulation of fluids that are geometrically constrained to submillimeter scale. We have recently introduced the concept of chip-based millifluidics, which can be used for manipulation of fluids in channels in millimeter scale (either width or depth or both of the channels are at least a millimeter in size)7-9. Furthermore, the millifluidic chips are relatively easy to fabricate while offering similar control over flow-rates and manipulation of reagents. These chips could also be operated at higher flow-rates, creating smaller residence times, thereby, offering the possibility for scale-up of controlled synthesis of nanoparticles with narrower size distribution. As an example, we have recently demonstrated the synthesis of ultra-small copper nanoclusters and characterized them using in situ X-ray absorption spectroscopy as well as TEM. Ability to obtain small residence times within millifluidic channels in combination with the use of MPEG, which is very efficient bidentate PEGylated stabilizing agent for the formation of stable colloids of copper nanoclusters7 .
In addition to the synthesis of chemicals and nanomaterials, the millifluidics could offer, due to higher volume and concentration at the probe area, a synthetic platform that is more generalized and efficient for time-resolved kinetic studies and also achieves better signal to noise ratio than microfluidic systems7,10. We show the use of millifluidic chip as an example for time resolved analysis of the growth of gold nanostructures from solution using in situ XAS with a time resolution as small as 5 msec11.
Also, majority of the micro reactors developed to date for catalysis applications are based on silicon12,13. Their expensive fabrication in addition to small volumes generated makes them unsuitable for large scale manufacturing. The two general methods for coating the channels with nanocatalysts - chemical and physical, often referred to as silicon coating procedures, are currently in vogue14,15 . In addition to expensive micro fabrication, clogging of the channels makes micro reactor catalysis may be unsuitable for large-scale manufacturing. Although microreactors have been used for heterogeneous catalysis in micro continuous flow-through processes earlier16-18 , the ability to control the dimension, and morphology of the embedded gold nanostructured catalysts within continuous flow channels was never explored before. We have recently developed a technology for coating the millifluidic channels with Au catalysts, having controlled nano morphology and dimensions (Figure 5)11, for carrying out catalysis of industrially important chemical reactions. As an example we have demonstrated conversion of 4-nitrophenol into 4-aminophenol catalyzed by nanostructured gold coated within the millifluidic channels. Considering that a single millifluidic reactor chip can produce flow-rates of 50-60 ml/hr,7 high-throughput and controlled synthesis of chemicals is possible either through continuous flow operation or parallel processing.
In order to capitalize on the possibilities the millifluidics offer, with few examples described as above, we also demonstrate a user-friendly millifluidic device that is portable and has the all the required components such as millifluidic chips, manifolds, flow controllers, pumps and electrical connections integrated. Such a millifluidic device, as shown in the Figure 7, is now available from the company Millifluidica LLC (<a href="http://www.millifluidica.com" target="_blank">www.millifluidica.com</a>). The manuscript also provides protocols using the hand-held millifluidic device, as described below, for controlled synthesis of nanomaterials, time-resolved analysis of reaction mechanisms and continuous flow catalysis.

<table><tbody><tr><td>Copper (II) nitrate hydrate</td><td>Sigma-Aldrich</td><td>13778-31-9</td><td>99.999% pure</td></tr><tr><td>O-[2-(3-mercaptopropionylamino)ethyl]-O&amp;prime;-methylpolyethylene glycol</td><td>Sigma-Aldrich</td><td>401916-61-8</td><td>MW=5,000</td></tr><tr><td>HAuCl&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;.&lt;/sup&gt;3H&lt;sub&gt;2&lt;/sub&gt;O (Chloroauric acid)</td><td>Sigma-Aldrich</td><td>27988-77-8</td><td>99.999% pure</td></tr><tr><td>meso-2,3-dimercaptosuccinic acid (DMSA)</td><td>Sigma-Aldrich</td><td>304-55-2</td><td>~98% pure</td></tr><tr><td>4-Nitrophenol</td><td>Sigma-Aldrich</td><td>100-02-7</td><td>spectrophotometric grade</td></tr><tr><td>4-Aminophenol</td><td>Sigma-Aldrich</td><td>123-30-8</td><td>&gt;99% pure (HPLC grade)</td></tr><tr><td>Sodium borohydride</td><td>Sigma-Aldrich</td><td>16940-66-2</td><td>98% pure</td></tr><tr><td>Sodium hydroxide pellets</td><td>Sigma-Aldrich</td><td>1310-73-2</td><td>99.99% pure</td></tr><tr><td colspan="4">&lt;strong&gt;EQUIPMENT&lt;/strong&gt;</td></tr><tr><td>Millifluidic Chips</td><td>Microplumbers Microsciences LLC</td><td>SDC-01</td><td>Made from polyester terephthalate polymer</td></tr><tr><td>Pressure Pump</td><td>Mitos P-Pump, Dolomite</td><td>3200016</td><td></td></tr><tr><td>Automated Syringe Pump</td><td>Cetoni Automation and Microsystems, GmbH</td><td></td><td>Syringe pump neMESYS</td></tr><tr><td>UV-3600 UV-VIS-NIR Spectrophotometer</td><td>Shimadzu</td><td></td><td></td></tr><tr><td>Hand-held Millifluidic Device</td><td>Millifluidica</td><td>SCMD-1008</td><td>&lt;strong&gt;Figure 7&lt;/strong&gt;</td></tr></tbody></table>

millifluidics for chemical synthesis and time-resolved mechanistic studies

Millifluidics for Chemical Synthesis and Time-resolved Mechanistic Studies

Procedures utilizing millifluidic devices for chemical synthesis and time-resolved mechanistic studies are described by taking three examples. In the first, synthesis of ultra-small copper nanoclusters is described. The second example provides their utility for investigating time resolved kinetics of chemical reactions by analyzing gold nanoparticle formation using in situ X-ray absorption spectroscopy. The final example demonstrates continuous flow catalysis of reactions inside millifluidic channel coated with nanostructured catalyst.

Well dispersed and uniform sized copper nanoclusters with a narrow size distribution were obtained using the millifluidic chip setup (Fig. 1a). The different flow-rates used for synthesis did not have a significant effect on the size of the clusters. Nevertheless, with increase in the flow-rate, there is an observable improvement in the narrowing of the size distribution. UCNCs with a best narrow size distribution were obtained at a flow-rate of 32.7 mL/hr. The size of UCNCs formed at 32.7 mL/hr flow-rate has an average ...

Millifluidic devices are utilized for controlled synthesis of nanomaterials, time-resolved analysis of reaction mechanisms and continuous flow catalysis.

Procedures utilizing millifluidic devices for chemical synthesis and time-resolved mechanistic studies are described by taking three examples. In the ...

The overall goal of this procedure is to demonstrate the utility of simple milli fluidic based lab on a chip devices for high throughput synthesis of nanomaterials time resolved investigation of their formation and demonstration of continuous flow catalysis. This is accomplished by first demonstrating the synthesis of copper nanoparticles using a milli fluidic reactor. Next, the formation of gold particles within the milli fluidic channel is visualized using time resolved in C two x-ray absorption spectroscopy in order to observe reaction intermediates.In the final part, continuous flow catalysis is demonstrated by the conversion of four nitro phenol to four amphenol as it is flowed over gold nano structures within the milli fluidic chip. Ultimately, these three experiments demonstrate that simple milli fluidic systems offer opportunities for high throughput synthesis in C two investigation of formation and carrying out continuous flow catalysis. The main advantage of this technique or existing methods like traditional microfluidics, is that they can accommodate higher flow rates due to wider channels without compromising on fluid properties.They also enable easier scale up of reacting volumes for larger scale synthesis, and they provide an effective platform for pro probing reactions in C two using different spectroscopy tools. This Method can help answer key questions in the field of flow-based devices, such as real time institute, monitoring of chemical reactions, mapping the growth of nanoparticles and kinetics of a catalytic reaction. For those researchers who are not familiar with lab on a chip devices, these experiments at first may seem a little complicated, but once they get familiarized, these are pretty easy to carry out and can be applied easily to their own unique investigations.While these experiments are relatively simple to carry out, it's important to look at them visually first in order to understand the intricacies of these experiments, especially when you're carrying out in C two analysis of both synthesis of nanomaterials as well as for in C two catalytic probing. These reactions need to be observed carefully, so that's why the visualization is extremely important and the need for us to provide these visual observations To begin fabricate or purchase a milli fluidic chip like the one shown here with serpentine channels that are two millimeters wide, 0.15 millimeters high and 220 millimeters in length. Then connect the milli fluidic chip to a Mitoses P pump using FEP tubing with an inner diameter of 0.25 millimeters and an outer diameter of one 16th of an inch.Regulate the P pump under nitrogen pressure for pulseless flow during the experiment. Next test the pumps using water as a solvent to correlate different pressures with their corresponding flow rates in milliliters per hour. Once calibrated, rinse the milli fluidic reactor and tubing with the ionized water before initiation of the experiment in a clean vial dissolve 174 milligrams of copper two nitrate and add 610 milligrams of 5, 000 molecular weight eg into 28 milliliters of nano pure water.In a separate vial mix a solution consisting of 111 milligrams of sodium or hydride, and 102 milligrams of sodium hydroxide into 28 milliliters of nano pure water. This will result in a solution with a pH of around 13. Next, connect both solutions through the P pump to the milli fluidic device using separate input channels.Flow both the solutions simultaneously within the milli fluidic reactor using 50 millibar of pressure. This will result in a combined flow rate of around 6.81 milliliters per hour. Collect two to three milliliters of the resulting ultra small copper nano clusters at the outlet in a glass vial.Purge this resulting solution with nitrogen and store it under nitrogen as well. Repeat this process under different constant pressures of 100 millibar, 200 millibar and 300 millibar at room temperature for the synthesis of ultra small copper nano clusters at different flow rates. First, prepare a 10 millimole solution of chloro ORIC acid by adding 118.2 milligrams of gold.Three chloride hydrate into 30 milliliters of nano pure water and a 20 millimoles solution of meso two three dimer CAPTO SIC acid or DMSA by adding 109.2 milligrams of it to 30 milliliters of nano pure water. Then add 50 milligrams of sodium hydroxide to the DMSA solution so that it reaches a pH of 12. Load the two solutions into separate syringes and place them into high precision, fully automated pulsation free pumps.Then connect the pumps to the milli fluidic chip using tubing. Next couple the milli fluidic chip to the synchrotron beam line for X-ray absorption spectroscopy using a metal stage that has access to movement in the X, Y, and C directions. Feed the two solutions through the two separate syringes and into the milli fluidic chip at a constant flow rate of 10 milliliters per hour.Using the automated pumps. Collect data at different zones shown here as zones one through five as the solutions are pumped through the chip. Prepare all gold catalyst solutions using nano pure water mix a 10 milli mole solution of chloro ORIC acid and a 20 milli mole solution of DMSA as previously shown.Additionally, prepare a 10 millimoles solution of sodium oral hydride by adding 11.34 milligrams of it into 30 milliliters of water. Then transfer 10 milliliters each of the chloral ORIC acid and DMSA solutions into two separate vials and flow them within the chip using a handheld milli fluidic device with a uniform flow rate of 12 milliliters per hour for 45 minutes. Next, flow the 10 milli ole solution of sodium boro hydride within the chip at a 12 milliliter per hour flow rate for 15 minutes.To reduce the gold one to gold zero, then wash the chip with nano pure water for 30 minutes at a flow rate of 12 milliliters per hour. Next, mix 15 milliliters of nine times 10 to the negative five molar solution of four nitro APH phenol with 3.3 milliliters of 0.65 molar sodium oral hydride. To form a solution of four nitro pholate ion connect this mixture to the Millie fluidic gold coated chamber via the input files.Flow the solution through the prepared gold catalyst chamber at five milliliters per hour to reduce the solution of four nitro phenol to four amphenol within the coated milli fluidic channel and collect the flow through in a vial. Place three milliliters of the collected product into a UV visible spectrophotometer and measure the wavelength range of 250 to 500 nanometers. Compare the resulting spectrum to the original mixture to confirm the conversion of four nitro pholate.Next, estimate the catalytic activity of the reaction by plotting the experimentally observed absorption intensity of four nitro pholate ion at different standard concentrations. The change in the 399 nanometer peak height represents a corresponding change in its concentration. Using a scanning electron microscope, the gold nanoparticle catalyst can be resolved from the surface of the milli fluidic channel.A high gold surface area can be achieved using this process. The x-ray absorption near edge structure spectra shown here is reflective of the gold L three edge at zone three, zone five, and zone five. After 12 hours, the peak shows the presence of the precursor chloro orric acid, which has a gold three oxidation state.As described earlier. The UV visible spectra can be used to determine the conversion of four nitro phenol to four amphenol. Shown here is a representative spectra of four nitro phenol, four nitro pholate ion, and four amphenol.The rate of conversion of four NPH pholate ion to four amphenol without the presence of the gold catalyst is very poor compared to the same reactant with the gold catalyst. While attempting these experiments, one has to remember that the nanoparticles formed within the redic channels can also get attached to the channel vault Following this procedure. Other methods like in city investigation of cataly reactions can be performed in order to answer additional questions like time solve kinetics of a catalytic reaction.

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Research

JoVE Journal

Bioengineering

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