Name: preparation of expanded chitin foams and their use in the removal of aqueous copper
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The research was sponsored by the Combat Capabilities Development Command Army Research Laboratory (Cooperative Agreement Number W911NF-15-2-0020). Any opinions, findings and conclusions, or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the Army Research Lab.
We thank the Center for Advanced Materials Processing (CAMP) at Montana Technological University for the use of some of the specialized equipment required in this study. We also thank Gary Wyss, Nancy Oyer, Rick LaDouceur, John Kirtley, and Katherine Zodrow for the technical assistance and helpful discussions.

1. Preparation of expanded chitin
<ol>
	<li>Prepare a 250 mL solution of 5 wt% LiCl in dimethylacetamide (DMAc) 
	CAUTION: The solvent DMAc is a combustible irritant that may damage fertility and cause birth defects. Handle DMAc in a fume hood using chemical resistant gloves and goggles to avoid contact with skin and eyes.
	<ol>
		<li>Add 15 g of LiCl and 285 g (268 mL) of DMAc into a 500 mL Erlenmeyer flask with, then place a 50 mm Polytetrafluoroethylene (PTFE)-lined magnetic stir bar.</li>
		<li>Cap the flask w...

<ol>
	<li>Rinaudo, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chitin+and+chitosan:+Properties+and+applications.">Chitin and chitosan: Properties and applications.</a> Progress in Polymer Science. 31 (7), 603-632 (2006).</li><li>Percot, A., Viton, C., Domard, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optimization+of+chitin+extraction+from+shrimp+shells.">Optimization of chitin extraction from shrimp shells.</a> Biomacromolecules. 4 (1), 12-18 (2003).</li><li>Austin, P. 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L., Cunha, J. M., Calgaro, C. O., Tanabe, E. H., Bertuol, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface+modification+of+chitin+using+ultrasound-assisted+and+supercritical+CO2+technologies+for+cobalt+adsorption.">Surface modification of chitin using ultrasound-assisted and supercritical CO2 technologies for cobalt adsorption.</a> Journal of Hazardous Materials. 295, 29-36 (2015).</li><li>Phongying, S., Aiba, S., Chirachanchai, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+chitosan+nanoscaffold+formation+via+chitin+whiskers.">Direct chitosan nanoscaffold formation via chitin whiskers.</a> Polymer. 48 (1), 393-400 (2007).</li><li>Tan, T. S., Chin, H. Y., Tsai, M. L., Liu, C. 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Reaction kinetics and structure modifications.</a> Carbohydrate Polymers. 12 (4), 405-418 (1990).</li><li>Scherrer, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+the+size+and+the+internal+structure+of+colloidal+particles+by+means+of+X-rays.">Determination of the size and the internal structure of colloidal particles by means of X-rays.</a> News from the Society of Sciences in G&#246;ttingen, Mathematical- Physical Class. 2, 98-100 (1918).</li><li>Brunauer, S., Emmett, P. H., Teller, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adsorption+of+gases+in+multimolecular+layers.">Adsorption of gases in multimolecular layers.</a> Journal of the American Chemical Society. 60 (2), 309-319 (1938).</li><li>Sing, K. S. 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The proposed method for chitin foam fabrication allows for the production of such foams without the need for specialized equipment or techniques. Production of the chitin foam relies on the suspension of sodium hydride within a chitin sol-gel. Contact with water from the atmosphere induces gelling of the chitin matrix and evolution of hydrogen gas by decomposition of the sodium hydride. Therefore, the critical steps of the preparation are (1) formation of the sol-gel, (2) introduction of the sodium hydride in anhydrous c...

Chitin is a mechanically robust and chemically inert biopolymer, second only to cellulose in natural abundance1. It is the major component in the exoskeleton of arthropods and in the cell walls of fungi and yeast2. Chitin is similar to cellulose, but with one hydroxyl group of each monomer replaced with an acetyl amine group (Figure 1A,B). This difference increases the strength of hydrogen bonding between adjacent polymer chains and gives chitin its characteristic structural resilience and chemical inertness2,3. Due to its properties and abundance, chitin has attracted significant industrial and academic interest. It has been studied as a scaffold for tissue growth4,5,6, as a component in composite materials7,8,9,10,11, and as a support for adsorbents and catalysts11,12,13,14. Its chemical stability, in particular, makes chitin attractive for adsorption applications that involve conditions inhospitable to common adsorbents14. In addition, the abundance of amine groups make chitin an effective adsorbent for metal ions15. However, the protonation of the amine groups under acidic conditions reduces the metal adsorption capacity of chitin16. A successful strategy is to introduce adsorption sites more resistant to protonation17,18. Instead, herein is described a simple method to increase the specific surface area and, therefore, the number of adsorption sites in chitin.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/62301/62301fig01.jpg" /> 
Figure 1. Chemical structure. (A) cellulose, (B) chitin, (C) chitosan. <a href="https://www.jove.com/files/ftp_upload/62301/62301fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
In spite of its many potential uses, chitin is underutilized. Chitin processing is challenging due to its low solubility in most solvents. A key limitation to its use in catalysis and adsorption is its low specific surface area. While typical carbon and metal oxide supports have specific surface areas in the order 102-103 m2/g, commercial chitin flakes have surface areas in the order of 10 m2/g19,20,21. Methods to expand chitin into foams exist, but they invariably rely on high temperature and pressure, strong acids and bases, or specialized equipment that represent a significant entry barrier5,21,22,23,24,25. In addition, these methods tend to deacetylate chitin to form chitosan (Figure 1C)-a more soluble and reactive biopolymer5,25,26.
Herein, a method is described to expand chitin into solid foams, increase its specific surface area and adsorption capacity, and maintain its chemical integrity. The method relies on the rapid evolution of gas from within a chitin gel and requires no specialized equipment. The increased adsorption capacity of the expanded chitin is demonstrated with aqueous Cu2+-a common contaminant in the local groundwater26.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td></td>
			<td>Unit</td>
			<td>Neat Flake</td>
			<td>Baked Foam</td>
			<td>Lyophilised Foam</td>
		</tr>
		<tr>
			<td>Crystallinity</td>
			<td>%</td>
			<td>88</td>
			<td>74</td>
			<td>58</td>
		</tr>
		<tr>
			<td>Crystal size</td>
			<td>nm</td>
			<td>6.5</td>
			<td>4.4</td>
			<td>4.4</td>
		</tr>
		<tr>
			<td>Surface Area</td>
			<td>m2/g</td>
			<td>12.6 &#177; 2.1</td>
			<td>43.1 &#177; 0.2</td>
			<td>73.9 &#177; 0.2</td>
		</tr>
		<tr>
			<td>Cu Uptake</td>
			<td>mg/g</td>
			<td>13.8 &#177; 2.9</td>
			<td>48.6 &#177; 1.9</td>
			<td>73.1 &#177; 2.0</td>
		</tr>
		<tr>
			<td>Cu Uptake</td>
			<td>atom/nm2</td>
			<td>10.5 &#177; 2.8</td>
			<td>10.7 &#177; 0.4</td>
			<td>9.4 &#177; 0.3</td>
		</tr>
	</tbody>
</table>
Table 1. Summary of material properties. Chitin foams have lower crystallinity and crystal size relative to neat chitin flakes. However, the specific surface area and Cu uptake of the chitin foams are proportionally higher than that of the neat chitin flakes.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Ammonium bicarbonate</td>
			<td>Sigma-Aldrich</td>
			<td>9830</td>
			<td>NH4HCO3, &#8805;99.5 %</td>
		</tr>
		<tr>
			<td>Chitin</td>
			<td>Sigma-Aldrich</td>
			<td>C7170</td>
			<td>Pandalus borealis, practical grade</td>
		</tr>
		<tr>
			<td>Colorimeter</td>
			<td>Hanna Instruments</td>
			<td>HI83399-01</td>
			<td>Photometer for wastewater analysis</td>
		</tr>
		<tr>
			<td>Copper High Range Checker</td>
			<td>Hanna Instruments</td>
			<td>HI702</td>
			<td>Bicinchoninate colorimetric titration</td>
		</tr>
		<tr>
			<td>Copper nitrate hydrate&#160;</td>
			<td>Sigma-Aldrich</td>
			<td>223395</td>
			<td>Cu(NO3)2 &#183; 2.5 H2O, 98 %</td>
		</tr>
		<tr>
			<td>Dimethylacetamide (DMAc)</td>
			<td>Sigma-Aldrich</td>
			<td>271012</td>
			<td>Anhydrous, 99.8 %</td>
		</tr>
		<tr>
			<td>IR Spectrophotometer</td>
			<td>Thermo Nicolet</td>
			<td>Nexus 670</td>
			<td>Fitted with an ATR cell</td>
		</tr>
		<tr>
			<td>Lithium chloride</td>
			<td>Sigma-Aldrich</td>
			<td>310468</td>
			<td>LiCl, &#8805;99 %</td>
		</tr>
		<tr>
			<td>N2 Physisorption Apparatus</td>
			<td>Micromeritics</td>
			<td>Tristar II</td>
			<td></td>
		</tr>
		<tr>
			<td>Nitric acid</td>
			<td>BDH</td>
			<td>BDH7208-1</td>
			<td>HNO3, 0.1 N</td>
		</tr>
		<tr>
			<td>Scanning electron microscope</td>
			<td>Zeiss LEO</td>
			<td>1430 VP</td>
			<td>15 kV, secondary electron detector, 29-31 mm working distance</td>
		</tr>
		<tr>
			<td>Sodium hydride</td>
			<td>Sigma-Aldrich</td>
			<td>223441</td>
			<td>NaH, packed in mineral oil, 90 %</td>
		</tr>
		<tr>
			<td>Thermogravimetric analyzer</td>
			<td>TA Instruments</td>
			<td>Q500</td>
			<td>100 ml/min N2, 10 &#176;C/min to 800 &#176;C</td>
		</tr>
		<tr>
			<td>Water Purification System</td>
			<td>Millipore</td>
			<td>Milli-Q</td>
			<td>Type A water (18 M&#937;)</td>
		</tr>
		<tr>
			<td>X-Ray Diffractometer</td>
			<td>Rigaku</td>
			<td>Ultima IV</td>
			<td>Cu K-&#945; radiation, 8.04 keV</td>
		</tr>
	</tbody>
</table>

preparation of expanded chitin foams and their use in the removal of aqueous copper

Chitin is an underexploited, naturally abundant, mechanically robust, and chemically resistant biopolymer. These qualities are desirable in an adsorbent, but chitin lacks the necessary specific surface area, and its modification involves specialized techniques and equipment. Herein is described a novel chemical procedure for expanding chitin flakes, derived from shrimp shell waste, into foams with higher surface area. The process relies on the evolution of H2 gas from the reaction of water with NaH trapped in a chitin gel. The preparation method requires no specialized equipment. Powder X-ray diffraction and N2-physisorption indicate that the crystallite size decreases from 6.6 nm to 4.4 nm and the specific surface area increases from 12.6 &#177; 2.1 m2/g to 73.9 &#177; 0.2 m2/g. However, infrared spectroscopy and thermogravimetric analysis indicate that the process does not change the chemical identity of the chitin. The specific Cu adsorption capacity of the expanded chitin increases in proportion to specific surface area from 13.8 &#177; 2.9 mg/g to 73.1 &#177; 2.0 mg/g. However, the Cu adsorption capacity as a surface density remains relatively constant at an average of 10.1 &#177; 0.8 atom/nm2, which again suggests no change in the chemical identity of the chitin. This method offers the means to transform chitin into a higher surface area material without sacrificing its desirable properties. Although the chitin foam is described here as an adsorbent, it can be envisioned as a catalyst support, thermal insulator, and structural material.

Expanded chitin shows the same morphology regardless of the drying method. Figure 3 shows images of neat chitin flakes (Figure 3A1), oven-dried expanded chitin (Figure 3B1), and lyophilized expanded chitin (Figure&#160;3C3). While the neat flakes have the appearance of coarse sand, the expanded chitin foam has the appearance of a kernel of popped corn. Scanning electron micrographs show a similar ch...

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Preparation of Expanded Chitin Foams and their Use in the Removal of Aqueous Copper

This study describes a method to expand chitin into a foam by chemical techniques that require no specialized equipment.

Chitin is an underexploited, naturally abundant, mechanically robust, and chemically resistant biopolymer. These qualities are desirable in an adsorbent, ...

This protocol allows the novel physical transformation of chitin, a high volume waste material, that is notoriously difficult to work with. The main advantage of this technique is the simplicity of the processing methodology. As it does not require specialized materials.Only the basic equipment commonly found in chemistry laboratories. We demonstrated this method with chitin, but this technique can be modified to create expanded versions of other polymers and bio polymers that form gels. In the simplest version of this technique, performed as demonstrated.Patience is important. The jelling rate will change with daily and seasonal changes to humidity. One day before preparing the expanded chitin, dry at least 1.2 grams of chitin flakes for 24 hours in an 80 degrees Celsius oven.The next morning in a fume hood and wearing chemical resistant gloves and goggles, add 15 grams of lithium chloride to 285 grams of D-MAc, In a 500 milliliter Erlenmeyer flask, containing a 50 milliliter PTFE line magnetic stir bar. Cap the flask with a rubber septum and place it on a heating stir plate. Place, a temperature probe into the mixture through the septum and stir the mixture at 400 rotations per minute at 80 degrees Celsius, for about 4 hours.When all of the lithium chloride has dissolved, add 1 gram of the oven dried chitin flakes to the 5%lithium chloride D-MAc solution. And transfer the resulting solution into a 500 milliliter round bottom flask, containing a 50 milliliter PTFE lined magnetic stir bar. Place the flask cap with the rubber septum on a stirring heat block.Pierce to septum with a needle to allow the flask to vent and heat the solution at 80 degrees Celsius, with stirring at 400 rotations per minute for 24 to 48 hours. When all of the chitin has dissolved, allow the resultant chitin sol-gel to cool to room temperature for about one hour, with stirring. Once the solution reaches room temperature, place the flask in an ice bath, with continued stirring for approximately 20 minutes, until the temperature stabilizes.To prepare a 100 milliliter slurry of sodium hydride and D-MAc. In a fume hood, wearing chemical resistant gloves and goggles, wash approximately 1 gram of sodium hydride removed from mineral oil storage. 3 times with 10 milliliters of hexane per wash.Add 0.82 grams of the wash sodium hydride to a fresh 250 milliliter Erlenmeyer flask, containing 100 milliliters of D-MAc at a PTFE line magnetic stir bar, and swirl the mixture, to produce a sodium hydride D-MAc slurry. To form the chitin gel, add the entire volume of sodium hydride slurry to the cooled sol-gel, while vigorously stirring the gel solution. Then replace the cap and continue to stir the mixture at 400 rotations per minute, until a gel forms.After the gel is formed, add 100 milliliters of deionized water to the flask in a fume hood, and remove the expanded chitin foam from the flask, breaking the foam into pieces, if necessary. Place the foam in a crystallization dish sufficiently large enough to hold the foam, along with 1000 milliliters of deionized water. Rinse the isolated gel 3 times, with 500 milliliters of deionized water per wash, before soaking the gel in 1000 milliliters of deionized water, 500 milliliters of methanol, and 1000 milliliters of fresh deionized water for 24 per immersion.After the last deionized water wash, allow the gel to air dry for 24 to 48 hours. The gel can then be dried in the oven for 48 hours at 85 degrees Celsius under ambient air or an lyophilizer, at minus 43 degrees Celsius and 0.024 millibars of pressure, for 48 hours. When a solid chitin foam is formed, use a mortar and pestle to grind the foam into a fine powder.Before drying, the knead chitin flakes, exhibit a core sand appearance. After drying, the expanded chitin morphology resembles a kernel of popcorn, regardless of the method. Scanning electron micrographs revealed that knead chitin is a compact dense structure, while the expanded chitin, resembles crinkled paper or wrinkled sheets.In x-ray diffraction studies, knead chitin displays a strong peak at 19.3 degrees corresponding to its crystal plane. Which decreases in intensity after baking, or lyophilizing. Suggesting, that drying changes the crystallinity index of the chitin.Measurement of the specific surface area obtained from nitrogen physisorption isotherms, shows the greatest uptake volume, for the expanded foams. Confirming the more open and porous structure of these samples. Despite these changes in morphology, the expansion process does not appear to affect the chemical structure of the chitin.As observed in these representative IR spectrograms. Similar observations are noted, after thermogravimetric analysis. With the onset of thermal decomposition of all three samples occurring at 260 degrees Celsius, and the maximum decomposition rate occurring at a higher temperature for chitin flakes, due to its more compact morphology.The increase in specific surface area is accompanied by an expected increase in the maximum copper uptake by chitin. However, these differences in uptake disappear, when the copper uptake is normalized by the surface area. It's important to remember that D-MAc and NAH are dangerous chemicals, that must be handled carefully.Always work in a fume hood, and wear the appropriate personal protective equipment. The limited nitrogen adsorption isotherms we collected, can only provide specific surface area. Full nitrogen absorption isotherms, can give porosity information that is critical to determining the usefulness in size-selective applications.

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