This work was supported by the National Basic Research Program of China (2014CB932400), National Natural Science Foundation of China (Nos. 51525204 and U1607206) and Shenzhen Basic Research Project (No. JCYJ20150529164918735). Also, we would like to thank Daicel-Allnex Ltd. and JSR Co. for kindly supplying polyurethanes and styrene butadiene rubber, respectively.

1. Preparation of 1 wt% 2,2,6,6-Tetramethylpiperidin-1-oxyl (TEMPO)-mediated Oxidized Cellulose Nanofiber (TOCN) Sol
NOTE: The sol is defined as a colloidal suspension of very small solid particles in a continuous liquid medium.
<ol>
	<li>Suspend 66.7 g of Nadelholz Bleached Kraft Pulp (NBKP, containing 12 g of cellulose) in 700 mL of deionized (DI) water with a mechanical agitator at 300 rpm for 20 min.</li>
	<li>Add 20 mL of aqueous TEMPO solution (containing 0.15 g of TEMPO) and 20 mL of ...

<ol>
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Rep. 3, 2975 (2013).</li></ol>

The most critical step for achieving the MHMs is the unidirectional freezing step, during which water solidifies to form columnar ice crystals and push the dispersoid aside to form the framework. The unidirectional freezing process basically involves thermal transfer between the precursor sol and the coolant. In our setup, a dipping machine was used to insert a PP tube containing a precursor sol into the coolant (liquid nitrogen) with a constant velocity. Since liquid nitrogen keeps evaporating all the time, a fluctuant ...

As a brand-new material, microhoneycomb monolith (denoted MHM) has recently attracted tremendous attention from multidisciplinary fields1,2,3,4,5,6,7,8. The MHM was first prepared by S. Mukai et al. through a modified unidirectional freeze-drying (UDF) approach as a monolith with an array of straight microchannels with honeycomb-like cross sections9. MHM possesses the general advantages of honeycomb structures, i.e., efficient tessellation, high strength-to-weight ratio, and low pressure drop. Moreover, compared with the honeycomb monolith with a larger channel size, the MHM has a much larger specific surface area. The UDF method involves the unidirectional growth of ice crystals and simultaneous phase separation upon freezing. After the removal of the ice crystals, a solid component molded by the ice crystal is obtained. The morphology formed upon the phase separation depends on the intrinsic nature of the precursor (sol or gel), and in most of cases, lamella10, fiber11, and fishbone12 structures are likely to form rather than the MHMs. As a result, the formation of MHMs has been reported only in limited precursors, and this has significantly hampered the diversity of their chemical property. We have recently found that cellulose nanofibers have a strong structure-directing function toward forming the MHM structure through the UDF process13. Simply by mixing the cellulose nanofibers with other water-dispersible components, it is possible to prepare a variety of MHMs with different chemical properties. Moreover, their exterior shapes and channel sizes are flexibly and easily controlled13. Thus, MHMs are expected to be used as filters, catalyst supports, flow-type electrodes, sensors and scaffolds for biomaterials.
In this paper, we first explain the basic preparation technique of MHMs from the aqueous dispersion of cellulose nanofibers through the UDF process in detail. Moreover, we demonstrate the preparation of several different types of composite MHMs.

<table border="0" cellpadding="0" cellspacing="0" width="572">
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Nadelholz Bleached Kraft Pulp</td>
			<td style="width:100px;">Seioko PMC company</td>
			<td style="width:89px;">CSF=600</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">TEMPO</td>
			<td style="width:100px;">Macklin Inc.</td>
			<td style="width:89px;">T819129</td>
			<td style="width:167px;">98%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">NaBr</td>
			<td style="width:100px;">Macklin Inc.</td>
			<td style="width:89px;">S818075</td>
			<td style="width:167px;">AR, 99%</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">NaClO</td>
			<td style="width:100px;">Aladin Inc.</td>
			<td style="width:89px;">S101636</td>
			<td style="width:167px;">6-14 wt% active chlorine basis</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">SBR colloid</td>
			<td style="width:100px;">JSR corp.</td>
			<td style="width:89px;">TRD102A</td>
			<td style="width:167px;">48.5 wt%</td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:216px;">TiO2</td>
			<td style="width:100px;">Sinopharm Chemical Reagent Co., Ltd.</td>
			<td style="width:89px;">A63725402</td>
			<td style="width:167px;">crystalline anatase phase</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">carbon fiber</td>
			<td style="width:100px;">Shenzhen Xian&#8217;gu Ltd.</td>
			<td style="width:89px;">XGCP-300</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Nitric acid</td>
			<td style="width:100px;">Huada Reagent Ltd.</td>
			<td style="width:89px;">7697-37-2</td>
			<td style="width:167px;">65-68 wt%</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Mixer</td>
			<td style="width:100px;">Scientific Industries, Inc</td>
			<td style="width:89px;">G-560</td>
			<td style="width:167px;">the mixer&#160;</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Mechanical blender</td>
			<td style="width:100px;">Waring Lab Ltd.</td>
			<td style="width:89px;">MX1000XTX</td>
			<td style="width:167px;">For disintegrating cellulose bundles into nanofibers.</td>
		</tr>
		<tr height="46">
			<td height="46" style="height:46px;width:216px;">Homogenizer</td>
			<td style="width:100px;">Scientz Ltd.</td>
			<td style="width:89px;">HXF-DY</td>
			<td style="width:167px;">For dispersing TiO2 nanoparticles</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">pH meter&#160;</td>
			<td style="width:100px;">Horiba Ltd.</td>
			<td style="width:89px;">F-74BW</td>
			<td></td>
		</tr>
	</tbody>
</table>

microhoneycomb monoliths prepared by the unidirectional freeze-drying of cellulose nanofiber based sols: method and extensions

Monolithic honeycomb structures have been attractive to multidisciplinary fields due to their high strength-to-weight ratio. Particularly, microhoneycomb monoliths (MHMs) with micrometer-scale channels are expected as efficient platforms for reactions and separations because of their large surface areas. Up to now, MHMs have been prepared by a unidirectional freeze-drying (UDF) method only from very limited precursors. Herein, we report a protocol from which a series of MHMs consisting of different components can be obtained. Recently, we found that cellulose nanofibers function as a distinct structure-directing agent towards the formation of MHMs through the UDF process. By mixing the cellulose nanofibers with water soluble substances which do not yield MHMs, a variety of composite MHMs can be prepared. This significantly enriches the chemical constitution of MHMs towards versatile applications.

The morphologies for different positions of the MHM-TOCN along the direction of unidirectional freezing are investigated and shown in Figure 2. With the position being further away from the bottom part of the MHM-TOCN, a gradual morphology change was revealed (Figure 2, Discussion). By introducing a second component into the TOCN sol to form a homogeneous mixture sol, it is possible to prepare various kinds of co...

Watch this Scientific Journal Video about Microhoneycomb Monoliths Prepared by the Unidirectional Freeze-drying of Cellulose Nanofiber Based Sols: Method and Extensions at JoVE.com

Microhoneycomb Monoliths Prepared by the Unidirectional Freeze-drying of Cellulose Nanofiber Based Sols: Method and Extensions

Here, we present a general protocol to prepare a variety of microhoneycomb monoliths (MHMs) in which fluid can pass through with an extremely low pressure drop. MHMs obtained are expected to be used as filters, catalyst supports, flow-type electrodes, sensors and scaffolds for biomaterials.

Monolithic honeycomb structures have been attractive to multidisciplinary fields due to their high strength-to-weight ratio. Particularly, microhoneycomb ...

This method can help answer key questions about achieving functional MHM materials for applications such as filtration, catalyst supporting, flow type batteries, sensors and bio-scaffolds. The main advantage of this technique is that it utilizes the structure directing function of cellulose nanofibers and can realize constitutional control of the targeted MHMs. This method can help answer key questions about achieving functional MHM materials for applications such as filtration, catalyst supporting, flow type batteries, sensors and bio-scaffolds.Demonstrating the procedure with myself and Cong Wang, a grad student from our laboratory. To begin preparing the tempo-mediated oxidized cellulose nanofiber sol, first combine 66.7 grams of softwood bleached kraft pulp with 700 microliters of deionized water. Mechanically agitate the mixture for 20 minutes at 300 rpm.Over the course of one minute, slowly add to the stirring kraft pulp suspension 20 milliliters each of a 7.5 gram per liter aqueous tempo solution and 75 gram per liter aqueous sodium bromide solution. Begin continuously monitoring the pH of the mixture with a pH meter. Adjust the mixture pH to about 10.5 with a three molar sodium hydroxide solution.Then, over the course of several minutes, slowly pipette into the suspension 63.8 grams of aqueous sodium hypochlorite with 6 to 14%active chlorine. After addition is complete, continue adjusting the pH back to 10.5 whenever it drops to about 10. Once the pH decrease slows, time how long it takes for the pH to drop from 10.5 to 10 to determine how often to check on the mixture during the reaction.Allow the tempo mediated oxidation to proceed normally for a bout 2.5 hours from the start of the sodium hypochlorite addition. Afterwards, filtrate the reaction mixture through a filter. And collect the oxidized cellulose nanofiber.Then, agitate the oxidized cellulose fibers in 1.2 liters of deionized water. Rinse the fibers three times in this way. Dry a small portion of the washed fiber paste overnight in an oven at 60 degrees Celsius to determine the solid content of the paste.Calculate the quantity of water needed to make a 1%by weight sol from the paste. Then transfer the washed fiber paste to laboratory grade blender. Add an appropriate amount of DI water to adjust the concentration of the mixture to 2%by weight.Vigorously blend the paste to disintegrate the oxidized cellulose fibers into nanofibers. Begin with low power blending before vigorously blending the paste at high power. Add one fifth of the needed volume of deionized water to the paste, and blend thoroughly.Repeat this process four more times to obtain the 1%by weight tempo mediated oxidized cellulose nanofiber sol. Store the sol at four degrees Celsius. We hear extracting is constant of the resulting TOCN sol.If it is hot enough, the MHM is likely to be obtained through the newly added process. Normally, the viscosity must be greater than 20, 000 millipascal second. Prior to preparing the tempo mediated oxidized cellulose nanofiber surface oxidized carbon fiber mixed sol, reflux 1.7 grams of 300 mesh carbon fiber in 150 milliliters of concentrated nitric acid to obtain the surface oxidized carbon fibers.Then, place in a 20 milliliter glass vial, 01 grams of the prepared surface oxidized carbon fibers, and 10 grams of the 1%by weight tempo mediated oxidized cellulose nanofiber sol. Manually shake the mixture until the surface oxidized carbon fibers are evenly distributed throughout the sol. Sonicate the mixture for five minutes to obtain an evenly dispersed TOCN SOCF mixed sol.Store the sol at four degrees Celsius. To begin preparing a microhoneycomb monolith, fill the bottom five centimeters of the 13 by 150 millimeter or similarly sized polypropylene tube with glass beads as filler material. Slowly load at least 2.7 milliliters of the chosen sol into the tube, ensuring that the sol level is about 22 millimeters or more above the glass beads.Avoid disturbing the sol unnecessarily to minimize the formation of bubbles in the tube. Use a narrow tipped pipette to carefully remove from the sol any bubbles that were introduced during the loading process. Store the sol sample at four degrees Celsius overnight.Then connect the sample tube to a dipping instrument for a unidirectional freezing. Place a Dewar of liquid nitrogen under the tube. Freeze the sol at an emerging speed of either 50 centimeters per hour for the TOCN sol or 20 centimeters per hour for the mixed sols.Keep the sol frozen once unidirectional freezing is complete. We use our cool time to constantly cool the frozen TOCN sol side hook to prevent it from sleep which will lead to the deterioration of the micromorphology of the resulting monolith. Use a saw to cut open the polypropylene tube.Crack the frozen sol into several pieces using pliers. Freeze dry the frozen sol pieces at minus ten degrees Celsius, minus five degrees Celsius, and zero degrees Celsius for one day each sequentially to obtain the microhoneycomb monolith. Unidirectionally freezing 1%by weight TOCN sol at 50 centimeters per hour without glass beads resulted in a gradual change in orientation and channel size along the freezing direction.The microhoneycomb morphology was retained longitudinally throughout the monolith. The bottom centimeter of the monolith was oriented toward the center of the bulk. A well-aligned honeycomb morphology was obtained two centimeters from the bottom.The microhoneycomb channel size increased from 10 micrometers between the second and third centimeters of the monolith and then remained stable. Overall, the unidirectional freezing effect showed no influence on the morphology past three centimeters. The channel size could be tuned by altering the dipping speed and the temperature of the coolant.Tempo oxidized cellulose nanofibers strongly tended to form the microhoneycomb structure via the unidirectional freezing process even in the presence of a second component. A mixed sol with styrene butadiene rubber yielded a composited microhoneycomb monolith with smooth walls. Tempo oxidized cellulose nanofiber microhoneycomb monoliths also supported titanium oxide nanoparticles in a well-ordered microhoneycomb monolith with nanoparticles adhering to the microhoneycomb walls.A mixed sol with SOCF yielded a novel substructure in which the carbon fibers bridged the neighboring microhoneycomb walls. The unidirectional freeze-drying technique is a novel approach through which many regular microstructures can be obtained. We first had the idea for this method will be so well in random microhoneycomb morphology in a wood pattern.It seems the major component of the wood is cellulose. We began to try imbuing up a similar construction with cellulose. Once mastered, this technique can be used to construct many other functional composite MHMs for targeted applications.

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8.7K vistas.  Tsinghua University. This method can help answer key questions about achieving functional MHM materials for applications such as filtration, catalyst supporting, flow type batteries, sensors and bio-scaffolds. The main advantage of this technique is that it utilizes the structure directing function of cellulose nanofibers and can realize constitutional control of the targeted MHMs. This method can help answer key questions about achieving functional MHM materials for applications such as filtration, catalyst supp...