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 with a rubber septum and place it on a heating stir plate. Place a temperature probe through the septum into the mixture. Stir the mixture at 400 rpm and 80 &#176;C until all LiCl is dissolved (~ 4 h)</li>
	</ol>
	</li>
	<li>Dissolve 1.0 g of oven-dried chitin flakes in the LiCl/DMAc solution to form a sol-gel
	<ol>
		<li>Dry at least 1.2 g of chitin flakes in an oven at 80&#176;C for 24 h.</li>
		<li>Add 1.0 g of oven-dried chitin flakes and 250 mL of 5 wt% LiCl/DMAc solution into a 500 mL round bottom flask. Place a 50 mm PTFE-lined magnetic stir bar.</li>
		<li>Cap the flask with a rubber septum and place it on a stirring heat block. Pierce the septum with a needle and leave it to allow the flask to vent. Heat the block to 80 &#176;C and stir the mixture at 400 rpm until all the chitin is dissolved (24-48 h).</li>
		<li>Allow the resultant chitin sol-gel to cool down to room temperature slowly while continuing to stir (~ 1 h).</li>
		<li>Once at room temperature, place the flask containing the chitin sol-gel in an ice bath and continue stirring until its temperature stabilizes (~ 20 min).</li>
	</ol>
	</li>
	<li>Prepare a 100 mL slurry of NaH in DMAc. 
	CAUTION: NaH in contact with water releases flammable gases which may ignite spontaneously. To limit contact with moist air, NaH is stored in mineral oil which must be washed off before use. Handle with caution in a fume hood using chemical resistant gloves and goggles.
	<ol>
		<li>Remove approximately 1 g of NaH from its mineral oil storage and wash three times with 10 mL of hexanes.</li>
		<li>Add 100 mL of DMAC into a 250 mL Erlenmeyer flask, then add 0.82 g of the washed NaH and place a PTFE-lined magnetic stir bar.</li>
		<li>Swirl the mixture to produce a NaH/DMAc slurry. 
		NOTE: NaH will not completely dissolve.</li>
	</ol>
	</li>
	<li>Form the chitin gel by adding all the NaH/DMAc slurry to the chitin sol-gel.
	<ol>
		<li>Uncap the cooled sol-gel and add all the NaH slurry while stirring vigorously. Replace the cap and continue to stir the mixture at 400 rpm for 72 h or until a gel forms in the flask.</li>
	</ol>
	</li>
	<li>Form the chitin foam by adding water to the chitin gel.
	<ol>
		<li>After the formation of the gel, uncap the flask and add 100 mL of Deionized (DI) water. 
		NOTE: It is critical to perform this step in a fume hood as the process will evolve H2 gas.</li>
	</ol>
	</li>
	<li>Isolate, and wash the chitin foam in water and methanol to remove DMAc and salts.
	<ol>
		<li>Remove the expanded chitin foam from the flask and place in a crystallization dish or beaker sufficiently large to hold it and 1000 mL of DI water. 
		&#8203;NOTE: The chitin foam will not come out in one piece and may have to be broken up.</li>
		<li>Rinse the isolated gel three times with 500 mL of DI water. Soak the gel in 1000 mL of DI water for 24 h, then in 500 mL of methanol for 24 h, and finally in 1000 mL of DI water for 24 h again.</li>
		<li>Remove the expanded chitin foam from the water wash and allow to air dry for 24-48 h.</li>
	</ol>
	</li>
	<li>Dry the washed chitin gel to form a solid foam and then grind to a powder.
	<ol>
		<li>Dry the gel in the oven at 85 &#176;C for 48 h under ambient air, or in a lyophilizer at -43 &#176;C and 0.024 mbar for 48 h.</li>
		<li>Using a mortar and pestle, grind the dry chitin foam into a fine powder.</li>
	</ol>
	</li>
</ol>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/62301/62301fig02.jpg" /> 
Figure 2. Preparation of expanded chitin foam. (A) The initial chitin in LiCl/DMAc solution. (B) The addition of the NaH/DMAc slurry. (C) The chitin foam after addition of water. (D) The chitin foam as extracted from the reaction flask. (E) The chitin foam during washing with water. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62301/62301fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
2. Development of the adsorption isotherms
<ol>
	<li>Prepare 500 mL stock solutions of aq. Cu2+ (MW 63.5 g/mol) at concentrations 50 mg/L, 100 mg/L, 200 mg/L, 300 mg/L, 400 mg/L, and 450 mg/L. To do this, add 90 mg, 180 mg, 360 mg, 540 mg, 720 mg, and 810 mg of Cu(NO3)2&#903; 2.5 H2O (MW 232.6 g/mol) to six containers, respectively. Add 500 mL of 18 M&#937; water, cap the container, and shake to dissolve the solids.</li>
	<li>Add 50 mg of chitin to 100 mL of each stock solution, adjust the pH to 7, and allow to equilibrate for 48 h.
	<ol>
		<li>Transfer 100 mL of each stock solution to a 100 mL container so the headspace is minimal. Add 50 mg of ground chitin to each container and then cap them.</li>
		<li>Place containers on an orbital shaker and shake at 60 rpm for 30 min. Then take containers off the orbital shaker and adjust the pH to 7 using NH4HCO3 or HNO3.</li>
		<li>Replace containers back on the orbital shaker and shake at 60 rpm and at a constant temperature for 48 h. Maintain the laboratory at 18 &#177; 2 &#176;C throughout.</li>
	</ol>
	</li>
	<li>Measure the Cu concentration of the initial stock solutions and of those to which chitin was added. Use the colorimetric bicinchoninate method, a colorimeter, and pre-measured reagent packets27.
	<ol>
		<li>Remove containers from the orbital shaker, allow the mixtures to settle for a minimum of 30 min, and then take a 1 mL aliquot with a syringe fitted with a 0.3 &#181;m glass microfiber filter.</li>
		<li>Transfer the aliquot to a 250 mL container and dilute to 100 mL with 18 M&#937; water. 
		&#8203;NOTE: This step is necessary due to the low ceiling of detection of Cu (5 mg/L) by the bicinchoninate method using the colorimeter.</li>
		<li>Transfer 10 mL of the diluted sample to a cuvette. Place the cuvette in the colorimeter and zero the instrument.</li>
		<li>Add one packet of premeasured Cu reagent (bicinchoninate method) to the diluted sample in the cuvette and wait 45 s for the chelation reaction to complete. Allow the solution to become purple. The intensity of the color formed is proportional to the Cu concentration.</li>
		<li>Place the cuvette back in the colorimeter and measure the Cu concentration of the diluted sample. Multiply the concentration of the diluted sample by 100 to obtain that of the original sample.</li>
	</ol>
	</li>
	<li>Extract the maximum Cu uptake from the adsorption isotherm data.
	<ol>
		<li>Calculate the uptake of each sample for each equilibrium Cu concentration using the equation28: 
		<img alt="Equation 1" src="/files/ftp_upload/62301/62301eq01.jpg" /></li>
		<li>Plot the adsorption uptake versus equilibrium concentration of the samples to produce a standard Cu adsorption isotherm.</li>
		<li>Plot the ratio of equilibrium concentration to uptake versus the equilibrium concentration to produce the linearized Cu adsorption isotherm. 
		NOTE: The plot should be linear, and the inverse of the slope represents the maximum Cu uptake.</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

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 conditions, and (3) the reaction of atmospheric water with the chitin sol-gel and sodium hydride suspension.
Two important limitations arise from the third step. First, the process scales up poorly. The chitin sol-gel is a highly hygroscopic and readily absorbs moisture, but as the reaction volume increases, water diffusion limitations may prevent gelling. In fact, we observed that doubling the reaction volume increased the gelling time from days to weeks. Second, the process relies on atmospheric moisture. Local climate and seasonal weather will cause variations in the gelling time. A possible modification to the procedure is to use Schlenk techniques to maintain the reaction atmosphere air and moisture free, and then gradually add water to the chitin sol-gel and sodium hydride suspension. However, such a change requires resources and skills that would limit applicability.
Both the crystallinity index and crystal size reported above are only semi-quantitative estimates. The crystallinity index was calculated as described by Focher, et al.29, and is therefore not a true crystallinity fraction. It was not obtained by comparing peak areas to those of standards of known purity. Similarly, use of the Scherrer equation to obtain crystallite size from the line broadening only provides estimates. Other phenomena, such as non-uniform strain, can also contribute to line broadening34. For this reason, it is more appropriate to focus on trends rather than the absolute values of crystallinity index and crystallite size. As recommended elsewhere, those values are reported without associated errors or variances34.
Calculating specific surface areas by applying the BET equation to N2 physisorption isotherms requires thorough drying and degassing of samples prior to the analysis. The presence of moisture and adsorbates on the sample will alter specific area measurements in two ways: (1) by blocking and lowering the effective number of vacant adsorption sites, and (2) by desorbing volatiles, increasing the measured pressure above the sample, and lowering its apparent adsorption. To prevent these errors, carbon and oxide samples are typically degassed at temperatures near 300 &#176;C under flowing N2 or vacuum for at least 1 h. Although structurally robust, chitin will thermally decompose under such conditions (Figure 6). Instead, specific surface area measurements of expanded chitin foams were most reliable for samples degassed at 50 &#176;C under flowing N2 for 1 week immediately after oven drying or lyophilizing.
Conducting adsorption isothermal experiments is routine, but the specific protocols vary greatly based on the adsorbent, solution, mixing method, available instruments, and convenience. For that reason, this study includes a detailed protocol based on a procedure for waste water analysis28. The adsorption of Cu on chitin is low relative to other adsorbents, such as carbons. Chitin requires high Cu concentrations in the range of 100-500 mg/L in order to reach saturation35. However, the colorimetric bicinchoninate method has a Cu detection ceiling of only 5 mg/L27. This means that aliquots had to be diluted 100 times for their Cu concentration to be measurable by the instrument. Dilutions can introduce significant experimental error into measurements, so the dilution and measurements were repeated three times per sample. Using a graduated cylinder to perform the dilutions, the observed variance in the measured concentrations were low-less than 3.7 % for low Cu concentrations and less than 0.35% for high Cu concentrations. The variance could be decreased by using volumetric flasks to perform the dilution. In addition, it is important to minimize the headspace during the adsorption experiments. Any adsorbent that adheres to the container walls above the liquid line will not equilibrate with the solution and will induce error in the experiment. This can be prevented by placing the containers at a 15&#176; angle relative to the orbital plane of the shaker, and routinely shaking the containers by hand to dislodge any adsorbent adhered to the inner walls.
The Langmuir model for isothermal, non-dissociative adsorption assumes that (1) the analyte adsorbs in a single layer, (2) adsorption sites are energetically equivalent and can contain a single analyte molecule or ion, and (3) adsorbed molecules or ions do not interact with one another. The collected Cu adsorption data fits the Langmuir model and validates these assumptions. However, we used refined chitin harvested from a single species as the starting material. Using lower purity chitin, or chemically modifying the surface17,36, can result in greater morphological and energetic variation between adsorption sites, which would call for a different adsorption model.

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.remotexs.ntu.edu.sg/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><tbody><tr><td>Ammonium bicarbonate</td><td>Sigma-Aldrich</td><td>9830</td><td>NH4HCO3, &amp;ge;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&amp;nbsp;</td><td>Sigma-Aldrich</td><td>223395</td><td>Cu(NO3)2 &amp;middot; 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, &amp;ge;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 &amp;deg;C/min to 800 &amp;deg;C</td></tr><tr><td>Water Purification System</td><td>Millipore</td><td>Milli-Q</td><td>Type A water (18 M&amp;Omega;)</td></tr><tr><td>X-Ray Diffractometer</td><td>Rigaku</td><td>Ultima IV</td><td>Cu K-&amp;alpha; 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 change at smaller scales. While the neat chitin flakes (Figure 3A2, 3A3) have a compact, dense structure, the oven dried (Figure 3B2, 3B3) and lyophilized (Figure 3C2, 3C3) expanded chitin resemble crinkled paper or wrinkled sheets. The samples were sputter coated with gold before imaging with a secondary electron detector, with a 15 kV accelerating voltage, and at a working distance in the range of 29-31 mm.
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/62301/62301fig03.jpg" /> 
Figure 3. Photographs and micrographs of neat flake and expanded chitin. The photographs correspond to chitin (A1) in its neat flake form and in its expanded foam form dried by (B1) baking at 80 &#176;C and (C1) lyophilizing. The scanning electron micrographs correspond to two magnifications of chitin (A2, A3) in its neat flake form and in its expanded foam form dried by (B2, B3) baking at 80 &#176;C and (C2,C3) lyophilizing. Note the more compact form of the neat flakes relative to the expanded foam.&#160;<a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62301/62301fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
These visual and microscopic observations agree with the powder X-ray Diffraction (XRD) and N2-physisorption analyses of the samples. Diffractograms show a widening of crystalline reflections and an increase in the intensity of the amorphous peak in the expanded foams relative to the neat flakes (Figure 4). This observation can be illustrated by comparing the semi-quantitative crystallinity index and the crystallite size estimates of the neat and expanded chitin. The crystallinity index is the normalized difference of crystalline to amorphous diffraction intensities29. It is given by the equation:
<img alt="Equation 2" src="/files/ftp_upload/62301/62301eq02.jpg" />
For chitin, the crystalline diffraction intensity typically used is that of crystal plane (110) at 19.3&#176; and the amorphous diffraction intensity is that at 16.0&#176;29. The crystallinity index drops from 88% in the neat flakes, to 74% in the oven-dried expanded foam, and to 58% in the lyophilized expanded foam (Table 1). The crystallite size can be estimated by the Scherrer equation30:
<img alt="Equation 3" src="/files/ftp_upload/62301/62301eq03.jpg" />
We assume a shape factor of 1 and the instrument used Cu K&#945; radiation (wavelength = 15.4 nm). Using the diffraction of the (110) plane at 19.3&#176;, the crystallite size drops from 6.6 nm in the neat chitin to 4.4 nm in the expanded chitin (Table 1).
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/62301/62301fig04.jpg" /> 
Figure 4. X-ray diffractograms of neat and expanded chitin. The figure shows the diffractograms of chitin in its neat flake form and in its expanded foam form dried by two different methods-baking at 800 &#176;C and lyophilizing. All three diffractograms are normalized to the maximum intensity of reflection at 19.3 &#176;, which corresponds to plane (110). Note the general widening of peaks in the expanded foams relative to the neat flakes. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62301/62301fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Measurements of specific surface area, obtained from N2-physisorption isotherms at 77 K using the Brunauer-Emmett-Teller (BET) equation31, lead to similar observations. For all the materials, the N2 adsorption isotherms show the uptake volume to increase linearly with partial pressure in the range p/po = 0.05-0.25 (Figure 5A), as is expected of N2 multilayer condensation32. However, the uptake volume is greatest for the expanded foams. The BET plot (Figure 5B,5C), show a positive linear correlation with partial pressure and positive intercept, indicating that the data is within the valid range of the BET equation33. As such, the specific surface area of the materials is proportional to the inverse of the sum of the slope and intercept of those lines31. While the specific surface area of the neat flakes is 12.6 &#177; 2.1 m2/g, that of oven dried foam is 43.1 &#177; 0.2 m2/g, and that of the lyophilized foam is 73.9 &#177; 0.2 m2/g. The changes in crystallinity index, crystallite size, and specific surface area indicate that the material either (1) forms a more open and porous structure, or (2) is degraded into smaller particles. The micrographs in Figure 3 suggest the former, but the latter cannot be ruled out without a thorough pore-size distribution analysis.
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/62301/62301fig05.jpg" /> 
Figure 5. N2 adsorption isotherms and BET plots. (A) N2 adsorption isotherms of chitin in its neat flake form and in its expanded foam form dried by two different methods-baking at 80 &#176;C and lyophilizing-for partial pressures in the BET range. (B, C) BET plot for the same materials and the range of partial pressures. The specific surface areas are proportional to the inverse of the sum of intercept and slope of the lines in the BET plots. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62301/62301fig05large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
In spite of the morphological changes described above, the expansion process does not appear to affect the chemical structure of chitin. The IR spectrum, obtained as attenuated total reflectance (ATR), of all chitin samples remain virtually unchanged regardless of processing (Figure 6). Note the similarity of the peaks at 1650 cm-1 and 1550 cm-1 which correspond to the amide functional group23.
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/62301/62301fig06.jpg" /> 
Figure 6. ATR IR spectrograms of neat and expanded chitin. The figure shows the IR spectra of chitin in its neat flake form and in its expanded foam form dried by two different methods-baking at 80 &#176;C and lyophilizing. The differences in the spectra are minimal and suggest no significant chemical changes between neat flakes and expanded foam chitin. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62301/62301fig06large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
The thermal decomposition behavior also indicates minimal chemical changes between the three samples (Figure 7). The shape of the thermogravimetric profile is identical for the expanded chitin regardless of drying method, but both differ from that of the neat flakes (Figure 7A). This is ascribed to mass and thermal diffusion limitations associated with the more compact flakes. The onset of thermal decomposition of all three samples occurs at 260 &#176;C (Figure 7B), but the maximum decomposition rate for chitin flakes occurs at higher temperatures due to its more compact morphology.
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/62301/62301fig07.jpg" /> 
Figure 7. Thermogravimetric profiles of neat and expanded chitin. The figure shows the integral (above) and differential (below) thermogravimetric profiles of chitin in its neat flake form and in its expanded foam form dried by two different methods-baking at 80 &#176;C and lyophilizing. The onset of thermal decomposition of all three materials is at 260 &#176;C, but flakes decompose over a longer temperature range relative to the foams. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62301/62301fig07large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
The increase in specific surface area is accompanied by an expected increase in the maximum uptake Cu by chitin. While the neat flakes uptake 13.8 &#177; 2.9 mg/g, the oven-dried foam uptakes 43.1 &#177; 1.9 mg/g and the lyophilized foam uptakes 73.1 &#177; 2.0 mg/g (Table 1). The increase in Cu uptake is more clearly illustrated by comparing the standard (Figure 8A) and linearized (Figure 8B) Langmuir adsorption isotherms. The maximum uptake is represented by the asymptotic limit in the standard isotherm and the inverse of the slope in the linearized isotherm. However, these differences in the uptake disappear when the Cu uptake is normalized by the surface area (Table 1). While the neat flakes uptake 10.5 &#177; 2.8 atoms/nm2, the oven-dried foam uptakes 10.7 &#177; 0.4 atoms/nm2, and the lyophilized foam uptakes 9.4 &#177; 0.3 atoms/nm2 (Table 1). This suggests that the surface of the expanded chitin is chemically similar to that of the initial chitin flakes, which agrees with spectroscopy and thermogravimetric observations.
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/62301/62301fig08.jpg" /> 
Figure 8. (A) Standard and linearized (B, C) Cu adsorption isotherm. The figure shows Cu adsorption isotherms of chitin in its neat flake form and in its expanded foam form dried by baking at 80 &#176;C and lyophilizing. Each data point is the average of three measurements and the error bars represent two standard deviations. Error bars for the expanded foams in the linearized isotherm are small and can only be seen in (C). The solid lines show the best fit Langmuir adsorption isotherms. The maximum uptake is the asymptotic value in the standard adsorption isotherm and the inverse slope in the linearized ones. Expanded chitin shows a higher Cu uptake than that of chitin flakes by at least a factor of 4.&#160;<a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62301/62301fig08large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Preparation of Expanded Chitin Foams and their Use in the Removal of Aqueous Copper at JoVE.com

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, ...

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3.5K Views.  Montana Technological University. This study describes a method to expand chitin into a foam by chemical techniques that require no specialized equipment.

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

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Protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms are presented. Three ...

Electrophoretic Crystallization of Ultrathin High-performance Metal-organic Framework Membranes

We report the synthesis of thin, highly intergrown, polycrystalline metal-organic framework (MOF) membranes on a wide range of unmodified porous and non-porous supports (polymer, ceramic, metal, carbon, and graphene). We developed a novel crystallization technique, which is termed the ENACT approach: the electrophoretic nuclei assembly for the crystallization of highly intergrown thin films (ENACT). This approach allows for a high density of heterogeneous nucleation of MOFs on a chosen substrate via the electrophoretic deposition (EPD) directly from the precursor sol. The growth of well-packed MOF nuclei leads to a highly intergrown polycrystalline MOF film. We show that this simple approach can be used for the synthesis of thin, intergrown zeolite imidazole framework (ZIF)-7 and ZIF-8 films. The resulting 500 nm-thick ZIF-8 membranes show a considerably high H2 permeance (8.3 x 10-6 mol m-2 s-1 Pa-1) and ideal gas selectivities (7.3 for H2/CO2, 15.5 for H2/N2, 16.2 for H2/CH4, and 2655 for H2/C3H8). An attractive performance for C3H6/C3H8 separation is also achieved (a C3H6 permeance of 9.9 x 10-8 mol m-2 s-1 Pa-1 and a C3H6/C3H8 ideal selectivity of 31.6 at 25 &#176;C). Overall, the ENACT process, owing to its simplicity, can be extended to synthesize intergrown thin films of a wide range of nanoporous crystalline materials.

A simple, reproducible, and versatile approach for the synthesis of intergrown, polycrystalline metal-organic framework membranes on a wide range of unmodified porous and non-porous supports is presented.

We report the synthesis of thin, highly intergrown, polycrystalline metal-organic framework (MOF) membranes on a wide range of unmodified porous and ...

Generation of Scalable, Metallic High-Aspect Ratio Nanocomposites in a Biological Liquid Medium

The goal of this protocol is to describe the synthesis of two novel biocomposites with high-aspect ratio structures. The biocomposites consist of copper and cystine, with either copper nanoparticles (CNPs) or copper sulfate contributing the metallic component. Synthesis is carried out in liquid under biological conditions (37 &#176;C) and the self-assembled composites form after 24 hr. Once formed, these composites are highly stable in both liquid media and in a dried form. The composites scale from the nano- to micro- range in length, and from a few microns to 25 nm in diameter. Field emission scanning electron microscopy with energy dispersive X-ray spectroscopy (EDX) demonstrated that sulfur was present in the NP-derived linear structures, while it was absent from the starting CNP material, thus confirming cystine as the source of sulfur in the final nanocomposites. During synthesis of these linear nano- and micro-composites, a diverse range of lengths of structures is formed in the synthesis vessel. Sonication of the liquid mixture after synthesis was demonstrated to assist in controlling average size of the structures by diminishing the average length with increased time of sonication. Since the formed structures are highly stable, do not agglomerate, and are formed in liquid phase, centrifugation may also be used to assist in concentrating and segregating formed composites.

Here we present a protocol to synthesize novel, high-aspect ratio biocomposites under biological conditions and in liquid media. The biocomposites scale from nanometers to micrometers in diameter and length, respectively. Copper nanoparticles (CNPs) and copper sulfate combined with cystine are the key components for the synthesis.

The goal of this protocol is to describe the synthesis of two novel biocomposites with high-aspect ratio structures. The biocomposites consist of copper ...

Bioengineering

Accumulation and Analysis of Cuprous Ions in a Copper Sulfate Plating Solution

Knowledge of the behavior of cuprous ions (monovalent copper ion: Cu(I)) in a copper sulfate plating bath is important for improving the plating process. We successfully developed a method to quantitatively and easily measure Cu(I) in a plating solution and used it for evaluation of the solution. In this paper, a quantitative absorption spectrum measurement and a time-resolved injection measurement of Cu(I) concentrations by a color reaction are described. This procedure is effective as a method to reproduce and elucidate the phenomenon occurring in the plating bath in the laboratory. First, the formation and accumulation process of Cu(I) in solution by electrolysis of a plating solution is shown. The amount of Cu(I) in the solution is increased by electrolysis at higher current values &#8203;&#8203;than the usual plating process. For the determination of Cu(I), BCS (bathocuproinedisulfonic acid, disodium salt), a reagent that selectively reacts with Cu(I), is used. The concentration of Cu(I) can be calculated from the absorbance of the Cu(I)-BCS complex. Next, the time measurement of the color reaction is described. The color reaction curve of Cu(I) and BCS measured by the injection method can be decomposed into an instantaneous component and a delay component. By analysis of these components, the holding structure of Cu(I) can be clarified, and this information is important when predicting the quality of the plating film to be produced. This method is used to facilitate the evaluation of the plating bath in the production line.

Here, accumulation of cuprous ions in a copper sulfate plating solution in a model experiment and an analysis based on quantitative measurements are described. This experiment reproduces the accumulation process of cuprous ions in the plating bath.

Knowledge of the behavior of cuprous ions (monovalent copper ion: Cu(I)) in a copper sulfate plating bath is important for improving the plating process. ...

Synthesis of Biocompatible Liquid Crystal Elastomer Foams as Cell Scaffolds for 3D Spatial Cell Cultures

Here, we present a step-by-step preparation of a 3D, biodegradable, foam-like cell scaffold. These scaffolds were prepared by cross-linking star block co-polymers featuring cholesterol units as side-chain pendant groups, resulting in smectic-A (SmA) liquid crystal elastomers (LCEs). Foam-like scaffolds, prepared using metal templates, feature interconnected microchannels, making them suitable as 3D cell culture scaffolds. The combined properties of the regular structure of the metal foam and of the elastomer result in a 3D cell scaffold that promotes not only higher cell proliferation compared to conventional porous templated films, but also better management of mass transport (i.e., nutrients, gases, waste, etc.). The nature of the metal template allows for the easy manipulation of foam shapes (i.e., rolls or films) and for the preparation of scaffolds of different pore sizes for different cell studies while preserving the interconnected porous nature of the template. The etching process does not affect the chemistry of the elastomers, preserving their biocompatible and biodegradable nature. We show that these smectic LCEs, when grown for extensive time periods, enable the study of clinically relevant and complex tissue constructs while promoting the growth and proliferation of cells.

This study presents a methodology to prepare 3D, biodegradable, foam-like cell scaffolds based on biocompatible side-chain liquid crystal elastomers (LCEs). Confocal microscopy experiments show that foam-like LCEs allow for cell attachment, proliferation, and the spontaneous alignment of C2C12s myoblasts.

Here, we present a step-by-step preparation of a 3D, biodegradable, foam-like cell scaffold. These scaffolds were prepared by cross-linking star block ...

A Freeze-Thawing Method to Prepare Chitosan-Poly(vinyl alcohol) Hydrogels Without Crosslinking Agents and Diflunisal Release Studies

Chitosan-poly(vinyl alcohol) hydrogels can be produced by the freeze-thawing method without using toxic crosslinking agents. The applications of these systems are limited by their characteristics (e.g., porosity, flexibility, swelling capacity, drug loading and drug release capacity), which depend on the freezing conditions and the kind and ratio of polymers. This protocol describes how to prepare hydrogels from chitosan and poly(vinyl alcohol) at 50/50 w/w % of polymer composition and varying the freezing temperature (-4 &#176;C, -20 &#176;C, -80 &#176;C) and freeze-thawing cycles (4, 5, 6 freezing cycles). FT-IR spectra, SEM micrograph and porosimetry data of hydrogels were obtained. Also, the swelling capacity and drug loading and release of diflunisal were assessed. Results from SEM micrographs and porosimetry show that the pore size decreases, while the porosity increases at lower temperatures. The swelling percentage was higher at the minor freezing temperature. The release of diflunisal from the hydrogels has been studied. All the networks maintain the drug release for 30 h and it has been observed that a simple diffusion mechanism regulates the diflunisal release according to Korsmeyer-Peppas and Higuchi models.

A Freeze-Thawing Method to Prepare Chitosan-Polyvinyl alcohol Hydrogels Without Crosslinking Agents and Diflunisal Release Studies

The freezing-thawing method is used to produce chitosan-poly(vinyl alcohol) hydrogels without crosslinking agents. For this method, it is important to consider the freezing conditions (temperature, number of cycles) and polymer ratio, which can affect the properties and applications of the obtained hydrogels.

Chitosan-poly(vinyl alcohol) hydrogels can be produced by the freeze-thawing method without using toxic crosslinking agents. The applications of these ...