Name: exfoliation of egyptian blue and han blue, two alkali earth copper silicate-based pigments
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Description: Watch this Scientific Journal Video about Exfoliation of Egyptian Blue and Han Blue, Two Alkali Earth Copper Silicate-based Pigments at JoVE.com

We thank Prof. Mark Abbe (UGA) for providing the NIR imaging equipment and Dr. Rasik Raythatha (Solvay Performance Chemicals) for the barium carbonate used in this work. We acknowledge the efforts of Isaiah Norris (UGA undergraduate) and Terra Blevins (North Oconee High School), who helped test the synthetic methods.

1. Preparation of CaCuSi4O10
<ol>
	<li>Melt Flux Synthesis of CaCuSi4O10
	<ol>
		<li>Weigh out CaCO3, SiO2, and Cu2CO3(OH)2 in a 2:8:1 molar ratio: 0.1331 g (1.330 mmol) of CaCO3, 0.3196 g (5.319 mmol) of SiO2, 0.1470 g (0.6648 mmol) of Cu2CO3(OH)2. In addition, weigh out the flux components (12.5% by weight): 0.0375 g of Na2CO3, 0.0125 g of NaCl, and 0.0250 g of Na2B4O7.10H2O. Add these materials to a clean agate mortar.</li>
		<li>Hand grind for ~5 min with an agate pestle until the mixture becomes a homogeneous light green powder (Figures 1a and 2a). Transfer this mixture to a clean, dry platinum crucible.</li>
		<li>Heat the crucible in a furnace to 875 &#176;C (ramp rate of 2 &#176;C/min), hold at 875 &#176;C for 16 hr, and then cool down to room temperature (rate of 0.8 &#176;C/min).</li>
		<li>Remove the crystals from the crucible and gently crush them using a pestle.</li>
		<li>Allow the crystals to soak in 50 ml of 1 M aqueous HCl overnight to remove the melt flux.</li>
		<li>Filter the crystals and wash with deionized water to fully remove any remaining melt flux. 
		Note: This material should be ground into a finer powder for powder X-ray diffraction (PXRD) analysis (Figure 5). It also can be characterized by optical microscopy (Figure 3), scanning electron microscopy (SEM) (Figure 4), and NIR photography (Figure 8).</li>
	</ol>
	</li>
	<li>Solid State Synthesis of CaCuSi4O10
	<ol>
		<li>Weigh out CaCO3, SiO2, and CuO in a 1:4:1 molar ratio: 0.1331 g (1.330 mmol) of CaCO3, 0.3196 g (5.319 mmol) of SiO2, and 0.1058 g CuO (1.330 mmol) and add to a clean agate mortar.</li>
		<li>Dampen the powder mixture with 1-2 ml acetone and hand grind with an agate pestle for ~5 min. Transfer the resulting light gray powder (Figures 1b and 2b) into a platinum crucible.</li>
		<li>Heat the crucible in a box furnace to 1,020 &#176;C at a ramp rate of 5 &#176;C/min, hold for 16 hr, and then cool down to room temperature</li>
		<li>Scrape out the loose, light blue-gray powder using a polytetrafluoroethylene (PTFE) spatula. 
		Note: The product can be characterized by optical microscopy (Figure 3), SEM (Figure 4), PXRD (Figure 5), and NIR photography (Figure 8).</li>
	</ol>
	</li>
</ol>
2. Synthesis of BaCuSi4O10
<ol>
	<li>Melt Flux Synthesis of BaCuSi4O10 
	<ol>
		<li>Weigh out BaCO3, SiO2, and CuO in a 1:4:1 molar ratio: 0.2085 g BaCO3 (1.057 mmol), 0.2539 g SiO2 (4.226 mmol), and 0.0840 g CuO (1.056 mmol). In addition, weigh out the flux component (12.5% by weight): 0.0765 g of PbO. Add these materials to a clean agate mortar.</li>
		<li>Hand grind for ~5 min with an agate pestle until the mixture becomes a homogeneous light gray powder (Figures 1c and 2c). Transfer this mixture to a clean, dry platinum crucible.</li>
		<li>Heat the crucible in a furnace to 950 &#176;C (ramp rate of 2 &#176;C/min), hold at 950 &#176;C for 24 hr, then slowly cool down to 700 &#176;C (rate of 0.1 &#176;C/min), and finally cool to room temperature.</li>
		<li>Remove the crystals from the crucible and gently crush them using a pestle.</li>
		<li>Allow the crystals to soak in 50 ml of 1 M aqueous HNO3 overnight to remove the melt flux.</li>
		<li>Filter the crystals and wash with deionized water to fully remove the remainder of the melt flux. Note: This material should be ground into a finer powder for PXRD analysis (Figure 6). It also can be characterized by optical microscopy (Figure 3) and NIR photography (Figure 8).</li>
	</ol>
	</li>
	<li>Solid State Synthesis of BaCuSi4O10
	<ol>
		<li>Weigh out BaCO3, SiO2, and CuO in a 1:4:1 molar ratio: 0.2085 g BaCO3 (1.057 mmol), 0.2539 g SiO2 (4.226 mmol), and 0.0840 g CuO (1.056 mmol) and add to a clean agate mortar.</li>
		<li>Dampen the powder mixture with 1-2 ml acetone and hand grind with an agate pestle for ~5 min. Transfer the resulting light gray powder (Figures 1d and 2d) into a platinum crucible.</li>
		<li>Heat the crucible in a box furnace to 960 &#176;C at a ramp rate of 5 &#176;C/min and hold for 16 hr, then cool to room temperature.</li>
		<li>Scrape out the loose blue powder using a polytetrafluoroethylene (PTFE) spatula. Note: The product can be characterized by optical microscopy (Figure 3), PXRD (Figure 6), and NIR photography (Figure 8).</li>
	</ol>
	</li>
</ol>
3. Exfoliation of CaCuSi4O10
<ol>
	<li>Charge a 50 ml round bottom flask with 0.50 g of CaCuSi4O10, 40 ml of deionized water, and a glass-coated magnetic stir bar.</li>
	<li>Attach a water-cooled condenser to the flask. Heat the reaction to 85 &#176;C with magnetic stirring at 400 rpm for two weeks.</li>
	<li>Remove from the heat source, allow the solution to settle undisturbed overnight, and then filter the supernatant through a 0.4 &#181;m membrane filter. Vacuum dry the solids. Note: The product is a light blue powder that can be characterized by optical microscopy (Figure 3), PXRD (Figure 5), transmission electron microscopy (TEM) (Figure 7), and NIR photography (Figure 8).</li>
</ol>
4. Exfoliation of BaCuSi4O10
<ol>
	<li>Charge a 50 ml plastic centrifuge tube with 0.14 g of BaCuSi4O10 and 20 ml of N-vinyl pyrrolidone.</li>
	<li>With the centrifuge tube immersed in an ice/water bath, sonicate with a probe ultrasonicator at 40% amplitude (17 W) for 1 hr.</li>
	<li>Let the dispersion settle undisturbed overnight, and then decant the supernatant into a new centrifuge tube.</li>
	<li>Spin down at 10,286 x g using a centrifuge. Decant the supernatant, leaving the nanosheets at the bottom of the centrifuge tube.</li>
	<li>Resuspend this material in 20 ml of water with a few minutes of bath sonication. To isolate a powder, filter through a 0.4 &#181;m membrane filter and vacuum dry the solids. Note: The product is a light blue powder that can be characterized by optical microscopy (Figure 3), PXRD (Figure 6), TEM (Figure 7), and NIR photography (Figure 8).</li>
</ol>
5. Ink Preparation
<ol>
	<li>Disperse ~0.10 g of CaCuSi4O10 nanosheets in 5 ml&#160;of deionized water using bath sonication for ~10 min. Note: This ink (Figure 9) can be used for painting, printing, etc. See Figure 10 for a representative example where the ink was applied to paper with a brush.</li>
</ol>
6. Near Infrared Photographic Imaging
<ol>
	<li>Irradiate the samples using red light (e.g.&#160;with a red light-emitting diode array), taking care to eliminate any other sources of light.</li>
	<li>Photograph using a camera modified to image in the near infrared region. Use f stop setting f/22 and an exposure time of 0.5 sec.</li>
</ol>

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The authors have no competing financial interests.

The preparation of Egyptian blue pigment, a mixture of mostly CaCuSi4O10 and SiO2, is a well-studied process4,13-21. The numerous reported procedures may be categorized as either melt flux or solid-state reactions. Two major advantages of the melt flux approach are that it permits lower reaction temperatures (&#60;900 &#176;C) and allows CaCuSi4O10 crystals to nucleate and grow from a molten glass phase20. The flux component is typically an alkali salt (e.g.&#160;Na2CO3) or borate compound (e.g.&#160;borax). In comparison, the solid-state syntheses omit the flux but require higher temperatures (~1,000 &#176;C) for the reaction between Ca, CuO, and SiO2 sources to reach completion.
Although the synthesis of Han blue pigment is not as well studied as that of Egyptian blue4,22-25, the preparation of BaCuSi4O10 follows similar melt flux and solid-state routes with two differences: (1) a PbO flux should be used, and (2) the reaction temperatures must be more closely controlled because of alternative Ba-Cu-Si-O phases that can form (e.g.&#160;BaCuSi2O6).
These points are illustrated by the detailed procedures and results described in this paper. First, for all methods, the starting materials should be ground to a smooth powder (Figures 1a-d) consisting of 5-20 &#181;m particles (characterized by SEM; Figures 2a-d). Next, the use of a significant amount of flux (12.5% by weight) in the preparation of CaCuSi4O10 and BaCuSi4O10 leads to highly crystalline products, which are characterized by intense blue coloration (Figures 3a and&#160;3c), relatively large particle sizes (Figure 4a), and strong PXRD patterns (Figures 5a and 6a). The diminished isolated yields (~70%) from these preparations are caused by adhesion of the melted reaction mixtures to the crucible. In comparison, CaCuSi4O10 and BaCuSi4O10 prepared by the solid-state route exhibit less intense coloration (Figures 3b and 3d) and smaller particle sizes (Figure 4b). As synthesized, these products are powders that can be isolated in near-quantitative yields. Thus, for both CaCuSi4O10 and BaCuSi4O10, the advantages of flux and the importance of reaction temperature cannot be overstated.
Remarkably, the exfoliation of CaCuSi4O10 and BaCuSi4O10 occurs under simple aqueous conditions. In the case of CaCuSi4O10, this reaction is quite slow at room temperature (&#8805;6 weeks to see any appreciable exfoliation), but it becomes synthetically useful at 80 &#176;C (substantial exfoliation after 2 weeks). In comparison, the exfoliation of BaCuSi4O10 is sluggish even at 80 &#176;C, and so we apply an even greater energy input in the form of ultrasonication. These reactions are highly reliable with two caveats. For CaCuSi4O10, it is important to use a glass-coated stir bar; if a standard PTFE-coated stir bar is used, we find that PTFE byproducts contaminate the CaCuSi4O10 nanosheet product. For BaCuSi4O10, it is important to control the ultrasonication power and time so that the reaction is stopped before the nanosheets become degraded.
Transmission electron microscopy (TEM) of the nanosheet products shows that these very thin materials have lateral dimensions ranging from hundreds of nanometers to several microns. In general these lateral dimensions correlate with the crystallite size of the three-dimensional starting material. In prior work, atomic force microscopy provided topographic mapping that demonstrated the single-layer thicknesses (~1.2 nm) of these nanosheets12. Photographs of powder CaCuSi4O10 and BaCuSi4O10 nanosheet samples (Figures 3e-h) show that their color is less intense than that of the starting materials, a direct result of nanostructuring.
Additional information is provided by PXRD (Figures 5 and 6), which reveals basal cleavage along the (001) plane and preferred orientation along the {00l} series for all nanosheet samples. These features reflect the stacked alignment of these highly anisotropic nanomaterials when drop-cast onto a substrate. Furthermore, the characteristic NIR emission of CaCuSi4O10 at ~910 nm and BaCuSi4O10 at ~950 nm is illustrated in a NIR photograph of all eight samples (Figure 8).
The solution processing of CaCuSi4O10 can be accomplished by simply preparing a colloidal dispersion of CaCuSi4O10 nanosheets (Figure 9) to use as an ink. This ink then can be applied to a substrate via spin coating, spray coating, ink jet printing12, or simply brushing (Figure 10). Importantly, the NIR emission properties of CaCuSi4O10 are retained at all stages of this process. These new possibilities highlight the contrast between CaCuSi4O10 nanosheets and the traditional use of Egyptian blue pigment, a highly granular material that is challenging to incorporate into a smooth paint.

Vibrant colors were prized throughout the ancient world. Even today, we can still see the remains of pigments and dyes created by every major culture. Remarkably, two of the most famous synthetic blue pigments share a similar chemical composition and structure, despite having been developed at widely different times and places. The colored components of both Egyptian blue, CaCuSi4O10, and Han blue, BaCuSi4O10, belong to the alkali earth copper tetrasilicate series, ACuSi4O10 (A = Ca, Sr, Ba)1, as well as the larger gillespite group, ABSi4O10 (B = Fe, Cu, Cr)2,3.
Beyond traditional pigment applications, current scientific interest in these materials centers on their strong near infrared (NIR) emission properties. This emission originates from the Cu2+ in square planar coordination; these ions are linked by tetrahedral silicate moieties within the three-dimensional crystal structure, and the resulting layers alternate with alkali earth ions4-6. Recent technical highlights include NIR imaging to identify Egyptian and Han blue pigments on cultural heritage artifacts7,8, lanthanide doping of ACuSi4O10 to enhance NIR reflectance properties and open new energy transfer pathways9,10, the use of ACuSi4O10 as the active material for optical sensors11, and the exfoliation of CaCuSi4O10 into monolayer nanosheets12.
In particular, this last example provides a way to nanostructure CaCuSi4O10 so that it can be handled as a colloidal dispersion rather than as a particulate solid12. Because colloidal dispersions are compatible with solution-processing techniques (e.g.&#160;spin coating, ink jet printing, layer-by-layer deposition), this advance opens new application areas that range from security inks to biomedical imaging. The experimental protocols illustrated in this contribution will enable researchers from diverse backgrounds to prepare, characterize, and use CaCuSi4O10 and BaCuSi4O10 nanosheets in their work.

<table><tbody><tr><td>Sodium carbonate (Na&lt;sub&gt;2&lt;/sub&gt;CO&lt;sub&gt;3&lt;/sub&gt;)</td><td>Sigma Aldrich</td><td>S7795</td><td>bioXtra, &amp;ge;99.0%</td></tr><tr><td>Calcium carbonate (CaCO&lt;sub&gt;3&lt;/sub&gt;)</td><td>Sigma Aldrich</td><td>C4830</td><td>bioXtra, &amp;ge;99.0%</td></tr><tr><td>Barium carbonate (BaCO&lt;sub&gt;3&lt;/sub&gt;)</td><td>Solvay Performance Chemicals</td><td></td><td>Research sample: Electronic-grade purity, nanocrystalline</td></tr><tr><td>Copper (II) carbonate basic [Cu&lt;sub&gt;2&lt;/sub&gt;CO&lt;sub&gt;3&lt;/sub&gt;(OH)&lt;sub&gt;2&lt;/sub&gt;]</td><td>Sigma Aldrich</td><td>207896</td><td>Reagent grade</td></tr><tr><td>Copper(II) oxide (CuO)&amp;nbsp;</td><td>Sigma Aldrich</td><td>450812</td><td>99.99% trace metals base</td></tr><tr><td>Silicon dioxide (SiO&lt;sub&gt;2&lt;/sub&gt;)</td><td>Sigma Aldrich</td><td>S5631</td><td>~99%, particle size 0.5-10 &amp;mu;m (approximately 80% between 1-5 &amp;mu;m)</td></tr><tr><td>Sodium tetraborate decahydrate (Na&lt;sub&gt;4&lt;/sub&gt;B&lt;sub&gt;4&lt;/sub&gt;O&lt;sub&gt;7&lt;/sub&gt;&lt;sup&gt;.&lt;/sup&gt;10H&lt;sub&gt;2&lt;/sub&gt;O)</td><td>Sigma Aldrich</td><td>S9640</td><td>ACS &amp;ge; 99.5%</td></tr><tr><td>Sodium chloride (NaCl)&amp;nbsp;</td><td>Sigma Aldrich</td><td>S9888</td><td>ACS &amp;ge; 99.0%</td></tr><tr><td>Lead(II) oxide (PbO)&amp;nbsp;</td><td>Sigma Aldrich</td><td>402982</td><td>ACS &amp;ge; 99.0%</td></tr><tr><td>N-Vinylpyrrolidinone (C&lt;sub&gt;6&lt;/sub&gt;H&lt;sub&gt;9&lt;/sub&gt;NO)</td><td>Sigma Aldrich</td><td>V3409</td><td>contains sodium hydroxide as inhibitor, ACS &amp;ge; 99.0%</td></tr><tr><td>Box Furnace</td><td>Thermo Scientific</td><td></td><td>Lindberg Blue M</td></tr><tr><td>Box Furnace</td><td>Carbolite</td><td>CWF 12/5 1200C</td><td></td></tr><tr><td>Bath Sonicator</td><td>Branson</td><td></td><td></td></tr><tr><td>Ultrasonicator</td><td>Qsonica</td><td></td><td>Misonix S-4000</td></tr><tr><td>Camera</td><td>custom modification of Nikon D3000 camera by LDP LLC MaxMax.com</td><td>n/a</td><td>Xnite Nikon D3000 camera with a Nikkor 18-200 mm lens and a Xnite 830 filter&amp;nbsp;</td></tr><tr><td>Light Source</td><td>Excled Ltd.</td><td>PAR64</td><td>LED Colour Beamer</td></tr><tr><td>Light Microscope</td><td>Leica</td><td></td><td>mz6 Stereomicroscope with Spot Idea camera and Software</td></tr><tr><td>Powder X-Ray Diffractometer</td><td>Bruker</td><td></td><td>D8-Advance diffractometer (Co-K&amp;alpha; radiation source)</td></tr><tr><td>Transmission Electron Microscope</td><td>FEI</td><td></td><td>Technai 20</td></tr><tr><td>Scanning Electron Microscope</td><td>FEI</td><td></td><td>Inspect F</td></tr><tr><td>Membrane filters</td><td>Millipore</td><td>HTTP04700</td><td>Isopore Membrane filter with 0.4 &amp;micro;m pore size</td></tr></tbody></table>

exfoliation of egyptian blue and han blue, two alkali earth copper silicate-based pigments

In a visualized example of the ancient past connecting with modern times, we describe the preparation and exfoliation of CaCuSi4O10 and BaCuSi4O10, the colored components of the historic Egyptian blue and Han blue pigments. The bulk forms of these materials are synthesized by both melt flux and solid-state routes, which provide some control over the crystallite size of the product. The melt flux process is time intensive, but it produces relatively large crystals at lower reaction temperatures. In comparison, the solid-state method is quicker yet requires higher reaction temperatures and yields smaller crystallites. Upon stirring in hot water, CaCuSi4O10 spontaneously exfoliates into monolayer nanosheets, which are characterized by TEM and PXRD. BaCuSi4O10 on the other hand requires ultrasonication in organic solvents to achieve exfoliation. Near infrared imaging illustrates that both the bulk and nanosheet forms of CaCuSi4O10 and BaCuSi4O10 are strong near infrared emitters. Aqueous CaCuSi4O10 and BaCuSi4O10 nanosheet dispersions are useful because they provide a new way to handle, characterize, and process these materials in colloidal form.

The described syntheses of CaCuSi4O10 and BaCuSi4O10 provide approximately 0.5 g of product per batch. Isolated yields of CaCuSi4O10 from the melt flux and solid-state syntheses typically range from 70-75% and 90-95%, respectively. For BaCuSi4O10, the isolated yields from the melt flux and solid-state syntheses typically range from 65-70% and 95-99%, respectively.
The textures of all of the prepared materials, as well as differences in the intensity of their blue color due to varying crystallite sizes, are visible by low magnification optical microscopy (Figures 3a-h). Scanning electron microscopy (SEM) images confirm that the solid-state method of synthesizing CaCuSi4O10 produces ~1-15 &#181;m primary crystallites (Figure 4b) whereas melt flux conditions lead to ~5-50 &#181;m crystallites (Figure 4a). Powder X-ray diffraction (PXRD) patterns for CaCuSi4O10 (Figures 5a and 5c) and BaCuSi4O10 (Figures 6a and 6c) showcase the composition and phase purity of these products.
Representative transmission electron microscopy (TEM) images show the nanosheet morphology of the exfoliated products (Figure 7). In addition, NIR photographic imaging shows the strong luminescence of both the bulk and exfoliated materials (Figure 8). A simple way to illustrate the solution processability of CaCuSi4O10 nanosheets is to prepare an aqueous ink (Figure 9) suitable for painting (Figure 10).
<img alt="Figure 1" fo:content-width="5in" fo:src="/files/ftp_upload/51686/51686fig1highres.jpg" src="/files/ftp_upload/51686/51686fig1.jpg" /> 
Figure 1.&#160;Photographs of the hand-ground starting materials.&#160;(a) CaCuSi4O10 melt flux, (b) CaCuSi4O10 solid-state, (c) BaCuSi4O10 melt flux, and (d) BaCuSi4O10 solid-state syntheses. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/51686/51686fig1highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" fo:content-width="5in" fo:src="/files/ftp_upload/51686/51686fig2highres.jpg" src="/files/ftp_upload/51686/51686fig2.jpg" /> 
Figure 2.&#160;Scanning Electron Microscopy. Images of the hand-ground starting materials for the (a) CaCuSi4O10 melt flux, (b) CaCuSi4O10 solid-state, (c) BaCuSi4O10 melt flux, and (d) BaCuSi4O10 solid-state syntheses. All samples were coated with gold prior to imaging. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/51686/51686fig2highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" fo:content-width="5in" fo:src="/files/ftp_upload/51686/51686fig3highres.jpg" src="/files/ftp_upload/51686/51686fig3.jpg" /> 
Figure 3.&#160;Optical Microscopy. Bulk CaCuSi4O10 prepared by melt flux (a) and solid state (b) procedures. Bulk BaCuSi4O10 prepared by melt flux (c) and solid state (d) procedures. Exfoliated products (e-h) of (a-d), respectively. All images share the 1 mm scale bar show in panel (a). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/51686/51686fig3highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" fo:content-width="5in" fo:src="/files/ftp_upload/51686/51686fig4highres.jpg" src="/files/ftp_upload/51686/51686fig4.jpg" /> 
Figure 4.&#160;Scanning Electron Microscopy. Images of bulk CaCuSi4O10 made by melt flux (a) and solid state (b) methods. Samples were coated with gold prior to imaging. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/51686/51686fig4highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" fo:content-width="5in" src="/files/ftp_upload/51686/51686fig5highres.jpg" width="500" /> 
Figure 5.&#160;Powder X-Ray Diffraction: CaCuSi4O10. Patterns for bulk CaCuSi4O10 prepared by melt flux (a) and solid state (c) methods. Asterisks denote a silica impurity. Patterns for exfoliated CaCuSi4O10, (b) and (d), prepared from (a) and (c), respectively. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/51686/51686fig5highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" fo:content-width="5in" src="/files/ftp_upload/51686/51686fig6highres.jpg" width="500" /> 
Figure 6.&#160;Powder X-Ray Diffraction: BaCuSi4O10. Patterns for bulk BaCuSi4O10 prepared by melt flux (a) and solid state (c) methods. Asterisk denotes a silica impurity. Patterns for exfoliated BaCuSi4O10, (b) and (d), prepared from (a) and (c), respectively. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/51686/51686fig6highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" fo:content-width="5in" fo:src="/files/ftp_upload/51686/51686fig7highres.jpg" src="/files/ftp_upload/51686/51686fig7.jpg" /> 
Figure 7. Transmission Electron Microscopy. Representative images of exfoliated CaCuSi4O10 derived from bulk CaCuSi4O10 made by melt flux (a) or solid state (b) methods. Representative images of exfoliated BaCuSi4O10 derived from bulk BaCuSi4O10 made by melt flux (c) or solid state (d) methods. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/51686/51686fig7highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" fo:content-width="5in" fo:src="/files/ftp_upload/51686/51686fig8highres.jpg" src="/files/ftp_upload/51686/51686fig8.jpg" /> 
Figure 8.&#160;Near Infrared Imaging. Luminescence of bulk CaCuSi4O10 prepared by melt flux (a) and solid state (b) procedures. Luminescence of bulk BaCuSi4O10 prepared by melt flux (c) and solid state (d) procedures. Luminescence of the exfoliated products (e-h) of (a-d), respectively. Powder samples are contained within glass vials, and the entire set of samples was imaged at once. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/51686/51686fig8highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 9" fo:content-width="5in" fo:src="/files/ftp_upload/51686/51686fig9highres.jpg" src="/files/ftp_upload/51686/51686fig9.jpg" /> 
Figure 9.&#160;Photograph of a CaCuSi4O10 nanosheet ink in a vial.
<img alt="Figure 10" fo:content-width="5in" fo:src="/files/ftp_upload/51686/51686fig10highres.jpg" src="/files/ftp_upload/51686/51686fig10.jpg" /> 
Figure 10.&#160;Near Infrared Imaging. A rudimentary painting with the CaCuSi4O10 nanosheet ink that illustrates both its simple application and its luminescence properties.

Watch this Scientific Journal Video about Exfoliation of Egyptian Blue and Han Blue, Two Alkali Earth Copper Silicate-based Pigments at JoVE.com

Exfoliation of Egyptian Blue and Han Blue, Two Alkali Earth Copper Silicate-based Pigments

The preparation and exfoliation of CaCuSi4O10&#160;and BaCuSi4O10 are described. Upon stirring in hot water, CaCuSi4O10 spontaneously exfoliates into monolayers, whereas BaCuSi4O10&#160;requires ultrasonication in organic solvents. Near infrared (NIR) imaging illustrates the NIR emission properties of these materials, and aqueous dispersions of these nanomaterials are useful for solution processing.

In a visualized example of the ancient past connecting with modern times, we describe the preparation and exfoliation of CaCuSi4O10 and BaCuSi4O10, the ...

exfoliation-egyptian-blue-han-blue-two-alkali-earth-copper-silicate

Nanyang Technological University

Research

JoVE Journal

Chemistry

15.6K Views.  The University of Georgia. The preparation and exfoliation of CaCuSi4O10 and BaCuSi4O10 are described. Upon stirring in hot water, CaCuSi4O10 spontaneously exfoliates into monolayers, whereas BaCuSi4O10 requires ultrasonication in organic solvents. Near infrared (NIR) imaging illustrates the NIR emission properties of these materials, and aqueous dispersions of these nanomaterials are useful for soluti...

Video: Exfoliation of Egyptian Blue and Han Blue, Two Alkali Earth Copper Silicate-based Pigments

Improved Heterojunction Quality in Cu2O-based Solar Cells Through the Optimization of Atmospheric Pressure Spatial Atomic Layer Deposited Zn1-xMgxO

Atmospheric pressure spatial atomic layer deposition (AP-SALD) was used to deposit n-type ZnO and Zn1-xMgxO thin films onto p-type thermally oxidized Cu2O substrates outside vacuum at low temperature. The performance of photovoltaic devices featuring atmospherically fabricated ZnO/Cu2O heterojunction was dependent on the conditions of AP-SALD film deposition, namely, the substrate temperature and deposition time, as well as on the Cu2O substrate exposure to oxidizing agents prior to and during the ZnO deposition. Superficial Cu2O to CuO oxidation was identified as a limiting factor to heterojunction quality due to recombination at the ZnO/Cu2O interface. Optimization of AP-SALD conditions as well as keeping Cu2O away from air and moisture in order to minimize Cu2O surface oxidation led to improved device performance. A three-fold increase in the open-circuit voltage (up to 0.65 V) and a two-fold increase in the short-circuit current density produced solar cells with a record 2.2% power conversion efficiency (PCE). This PCE is the highest reported for a Zn1-xMgxO/Cu2O heterojunction formed outside vacuum, which highlights atmospheric pressure spatial ALD as a promising technique for inexpensive and scalable fabrication of Cu2O-based photovoltaics.

Improved Heterojunction Quality in Cu2O-based Solar Cells Through the Optimization of Atmospheric Pressure Spatial Atomic Layer Deposited Zn1-xMgxO

Here we present a protocol for synthesizing Zn1-xMgxO/Cu2O heterojunctions in open-air at low temperature via atmospheric pressure spatial atomic layer deposition (AP-SALD) of Zn1-xMgxO on cuprous oxide. Such high quality conformal metal oxides can be grown on a variety of substrates including plastics by this cheap and scalable method.

Atmospheric pressure spatial atomic layer deposition (AP-SALD) was used to deposit n-type ZnO and Zn1-xMgxO thin films onto p-type thermally oxidized Cu2O ...

Synthesis of Plant Phenol-derived Polymeric Dyes for Direct or Mordant-based Hair Dyeing

Effective hair dyeing through in situ incubation of keratin hair with the products of fungal laccase-catalyzed polymerization of plant phenols has been previously demonstrated. However, the dyeing process takes a long time to complete compared to commercial hair-dyeing products. To overcome this bottleneck, pre-synthesized polymeric products of the oxidative reaction of Trametes versicolor laccase on catechin and catechol, either with or without mordant agents (e.g., FeSO4), were here employed to achieve permanent keratin hair dyeing in various colors and shades. The laccase action in acidic sodium acetate buffer led to a deep black coloration after coupling reactions between the plant phenols. The colored dye products were then desalted and concentrated with ultrafiltration. The dyes, with or without mordant agents, caused a significant increase in &#916;E values (i.e., color difference value) in gray human hair within 2.5 hours. In addition, different keratin colors and shades were induced depending upon the mordanting and pH changes. The dyed hair also exhibited a strong resistance to detergent treatments, indicating that our methods can give rise to permanent hair dyeing.&#160;Overall, our work has provided novel insight into developing eco-friendly hair-dyeing methods as alternatives to commercial toxic diamine-based dyes.

Here, we present a protocol to use pre-synthesized polymeric products derived from fungal laccase-catalyzed polymerization of plant phenols, either with or without mordant agents (e.g., FeSO4), to induce detergent-resistant keratin hair dyeing within 2.5 hours.

Effective hair dyeing through in situ incubation of keratin hair with the products of fungal laccase-catalyzed polymerization of plant phenols has been ...

Fabrication and Testing of Catalytic Aerogels Prepared Via Rapid Supercritical Extraction

Protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms are presented. Three preparation methods are described: (a) the incorporation of metal salts into silica or alumina wet gels using an impregnation method; (b) the incorporation of metal salts into alumina wet gels using a co-precursor method; and (c) the addition of metal nanoparticles directly into a silica aerogel precursor mixture. The methods utilize a hydraulic hot press, which allows for rapid (&#60;6 h) supercritical extraction and results in aerogels of low density (0.10 g/mL) and high surface area (200-800 m2/g). While the work presented here focuses on the use of copper salts and copper nanoparticles, the approach can be implemented using other metal salts and nanoparticles. A protocol for testing the three-way catalytic ability of these aerogels for automotive pollution mitigation is also presented. This technique uses custom-built equipment, the Union Catalytic Testbed (UCAT), in which a simulated exhaust mixture is passed over an aerogel sample at a controlled temperature and flow rate. The system is capable of measuring the ability of the catalytic aerogels, under both oxidizing and reducing conditions, to convert CO, NO and unburned hydrocarbons (HCs) to less harmful species (CO2, H2O and N2). Example catalytic results are presented for the aerogels described.

Here we present protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms. Methods for preparing materials using copper salts and copper-containing nanoparticles are featured. Catalytic testing protocols demonstrate the effectiveness of these aerogels for three-way catalysis applications.

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

Enhanced Electron Injection and Exciton Confinement for Pure Blue Quantum-Dot Light-Emitting Diodes by Introducing Partially Oxidized Aluminum Cathode

Stable and efficient red (R), green (G), and blue (B) light sources based on solution-processed quantum dots (QDs) play important roles in next-generation displays and solid-state lighting technologies. The brightness and efficiency of blue QDs-based light-emitting diodes (LEDs) remain inferior to their red and green counterparts, due to the inherently unfavorable energy levels of different colors of light. To solve these problems, a device structure should be designed to balance the injection holes and electrons into the emissive QD layer. Herein, through a simple autoxidation strategy, pure blue QD-LEDs which are highly bright and efficient are demonstrated, with a structure of ITO/PEDOT:PSS/Poly-TPD/QDs/Al:Al2O3. The autoxidized Al:Al2O3 cathode can effectively balance the injected charges and enhance radiative recombination without introducing an additional electron transport layer (ETL). As a result, high color-saturated blue QD-LEDs are achieved with a maximum luminance over 13,000 cd m-2, and a maximum current efficiency of 1.15 cd A-1. The easily controlled autoxidation procedure paves the way for achieving high-performance blue QD-LEDs.

A protocol is presented for fabricating high-performance, pure blue ZnCdS/ZnS-based quantum dots light-emitting diodes by employing an autoxidized aluminum cathode.

Stable and efficient red (R), green (G), and blue (B) light sources based on solution-processed quantum dots (QDs) play important roles in next-generation ...

Engineering

Exfoliation and Analysis of Large-area, Air-Sensitive Two-Dimensional Materials

We describe methods for producing and analyzing large, thin flakes of air-sensitive two-dimensional materials. Thin flakes of layered or van der Waals crystals are produced using mechanical exfoliation, in which layers are peeled off a bulk crystal using adhesive tape. This method produces high-quality flakes, but they are often small and can be hard to find, particularly for materials with relatively high cleavage energies such as black phosphorus. By heating the substrate and the tape, two-dimensional material adhesion to the substrate is promoted, and the flake yield can be increased by up to a factor of ten. After exfoliation, it is necessary to image or otherwise analyze these flakes but some two-dimensional materials are sensitive to oxygen or water and will degrade when exposed air. We have designed and tested a hermetic transfer cell to temporarily maintain the inert environment of a glovebox so that air-sensitive flakes can be imaged and analyzed with minimal degradation. The compact design of the transfer cell is such that optical analysis of sensitive materials can be performed outside of a glovebox without specialized equipment or modifications to existing equipment.

A method for exfoliating large thin flakes of air sensitive two-dimensional materials and safely transporting them for analysis outside of a glovebox is presented.

We describe methods for producing and analyzing large, thin flakes of air-sensitive two-dimensional materials. Thin flakes of layered or van der Waals ...

[(DPEPhos)(bcp)Cu]PF6: A General and Broadly Applicable Copper-Based Photoredox Catalyst

Our group recently reported the use of [(DPEPhos)(bcp)Cu]PF6 as a general copper-based photoredox catalyst which proved efficient to promote the activation of a broad variety of organic halides, including unactivated ones. These can then participate in various radical transformations such as reduction and cyclization reactions, as well as in the direct arylation of several (hetero)arenes. These transformations provide a straightforward access to a range of small molecules of interest in synthetic chemistry, as well as to biologically active natural products. Altogether, [(DPEPhos)(bcp)Cu]PF6 acts as a convenient photoredox catalyst which appears to be an attractive, cheap and complementary alternative to the state-of-the-art iridium- and ruthenium-based photoredox catalysts. Here, we report a detailed protocol for the synthesis of [(DPEPhos)(bcp)Cu]PF6, as well as NMR and spectroscopic characterizations, and we illustrate its use in synthetic chemistry for the direct arylation of (hetero)arenes and radical cyclization of organic halides. In particular, the direct arylation of N-methylpyrrole with 4-iodobenzonitrile to afford&#160;4-(1-methyl-1H-pyrrol-2-yl)benzonitrile and the radical cyclization of N-benzoyl-N-[(2-iodoquinolin-3-yl)methyl]cyanamide to afford natural product luotonin A are detailed. The scope and limitations of this copper-based photoredox catalyst are also briefly discussed.

[DPEPhosbcpCu]PF6: A General and Broadly Applicable Copper-Based Photoredox Catalyst

Detailed and general protocols are presented for the synthesis of [(DPEPhos)(bcp)Cu]PF6, a general copper-based photoredox catalyst, and for its use in synthetic chemistry for the direct arylation of C-H bonds in (hetero)arenes and radical cyclization of organic halides.

Our group recently reported the use of [(DPEPhos)(bcp)Cu]PF6 as a general copper-based photoredox catalyst which proved efficient to promote the ...

Aesthetically Enhanced Silica Aerogel Via Incorporation of Laser Etching and Dyes

A procedure for aesthetically enhancing silica aerogel monoliths by laser etching and incorporation of dyes is described in this manuscript. Using a rapid supercritical extraction method, large silica aerogel monolith (10 cm x 11 cm x 1.5 cm) can be fabricated in about 10 h. Dyes incorporated into the precursor mixture result in yellow-, pink- and orange-tinged aerogels. Text, patterns, and images can be etched onto the surface (or surfaces) of the aerogel monolith without damaging the bulk structure. The laser engraver can be used to cut shapes from the aerogel and form colorful mosaics.

This protocol describes a method for etching text, patterns, and images onto the surface of silica aerogel monoliths in native and dyed form and assembling the aerogels into mosaic designs.

A procedure for aesthetically enhancing silica aerogel monoliths by laser etching and incorporation of dyes is described in this manuscript. Using a rapid ...

Quantitative Characterization of Bioink Properties for Continuous DLP Printing

Quantitative Characterization of Liquid Photosensitive Bioink Properties for Continuous Digital Light Processing Based Printing

Precise printing fabrication of bioinks is a prerequisite for tissue engineering; the Jacobs working curve is the tool to determine the precise printing parameters of digital light processing (DLP). However, the acquisition of working curves wastes materials and requires high formability of materials, which are not suitable for biomaterials. In addition, the reduction of cell activity due to multiple exposures and the failure of structural formation due to repeated positioning are both unavoidable problems in conventional DLP bioprinting. This work introduces a new method of obtaining the working curve and the improvement process of continuous DLP printing technology based on such a working curve. This method of obtaining the working curve is based on the absorbance and photorheological properties of the biomaterials, which do not depend on the formability of the biomaterials. The continuous DLP printing process, obtained from improving the printing process by analyzing the working curve, increases the printing efficiency more than tenfold and greatly improves the activity and functionality of cells, which is beneficial to the development of tissue engineering.

Author Spotlight: Quantitative Characterization of Liquid Photosensitive Bioink Properties for Continuous Digital Light Processing Based Printing  

This study uses temperature and material composition to control the yield stress properties of yield stress fluids. The solid-like state of the ink can protect the printing structure, and the liquid-like state can continuously fill the printing position, realizing the digital light processing 3D printing of extremely soft bioinks.

Precise printing fabrication of bioinks is a prerequisite for tissue engineering; the Jacobs working curve is the tool to determine the precise printing ...

Bioengineering

In Vitro Reconstitution of Light-harvesting Complexes of Plants and Green Algae

In plants and green algae, light is captured by the light-harvesting complexes (LHCs), a family of integral membrane proteins that coordinate chlorophylls and carotenoids. In vivo, these proteins are folded with pigments to form complexes which are inserted in the thylakoid membrane of the chloroplast. The high similarity in the chemical and physical properties of the members of the family, together with the fact that they can easily lose pigments during isolation, makes their purification in a native state challenging. An alternative approach to obtain homogeneous preparations of LHCs was developed by Plumley and Schmidt in 19871, who showed that it was possible to reconstitute these complexes in vitro starting from purified pigments and unfolded apoproteins, resulting in complexes with properties very similar to that of native complexes. This opened the way to the use of bacterial expressed recombinant proteins for in vitro reconstitution. The reconstitution method is powerful for various reasons: (1) pure preparations of individual complexes can be obtained, (2) pigment composition can be controlled to assess their contribution to structure and function, (3) recombinant proteins can be mutated to study the functional role of the individual residues (e.g., pigment binding sites) or protein domain (e.g., protein-protein interaction, folding). This method has been optimized in several laboratories and applied to most of the light-harvesting complexes. The protocol described here details the method of reconstituting light-harvesting complexes in vitro currently used in our laboratory, and examples describing applications of the method are provided.

In Vitro Reconstitution of Light-harvesting Complexes of Plants and Green Algae

This protocol details the reconstitution of light-harvesting complexes in vitro. These integral membrane proteins coordinate chlorophylls and carotenoids and are responsible for harvesting light in higher plants and green algae.

In plants and green algae, light is captured by the light-harvesting complexes (LHCs), a family of integral membrane proteins that coordinate chlorophylls ...

Biology

A Method for Extracting Pigments from Squid Doryteuthis pealeii

Cephalopods can undergo rapid and adaptive changes in dermal coloration for sensing, communication, defense, and reproduction purposes. These capabilities are supported in part by the areal expansion and retraction of pigmented organs known as chromatophores. While it is known that the chromatophores contain a tethered network of pigmented granules, their structure-function properties have not been fully detailed. We describe a method for isolating the nanostructured granules in squid Doryteuthis pealeii chromatophores and demonstrate how their associated pigments can be extracted in acidic solvents. To accomplish this, the chromatophore containing dermal layer is first manually isolated using a superficial dissection, and the pigment granules are removed using sonication, centrifugation, and washing cycles. Pigments confined within the purified granules are then extracted via acidic methanol solutions, leaving nanostructures with smaller diameters that are void of visible color. This extraction procedure produces a 58% yield of soluble pigments isolated from granules. Using this method, the composition of the chromatophore pigments can be determined and used to provide insight into the mechanism of adaptive coloration in cephalopods.

A Method for Extracting Pigments from Squid Doryteuthis pealeii

A protocol for the extraction of pigments from the nanostructured granules in squid Doryteuthis pealeii chromatophores is presented.

Cephalopods can undergo rapid and adaptive changes in dermal coloration for sensing, communication, defense, and reproduction purposes. These capabilities ...

Exfoliation of Egyptian Blue and Han Blue, Two Alkali Earth Copper Silicate-based Pigments

Summary

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