The authors extend their appreciation to Dr. Thomas J. Emge and Wei Liu of Rutgers University for their analysis and expertise in small-angle X-ray diffraction and powder X-ray diffraction. Furthermore, the authors acknowledge Hao Wang for his support with the N2 adsorption experiments.

1. Al(OH)3 Nanoparticle Synthesis
<ol>
	<li>Dissolve 1.40 g of aluminum chloride hexahydrate in 5.822 g of deionized water.</li>
	<li>Add 2.778 g of L-arginine to the aqueous aluminum chloride solution while under magnetic stirring. Add the L-arginine slowly, so that the added arginine dissolves and does not form large clumps or chunks; furthermore, a slow addition reduces local concentrations of alkalinity and provides conditions for a more controllable hydrolysis.</li>
	<li>Once all the arginine dissolves into the solution, heat the solution for 72 h at 50 &#176;C; at this point, the solution may appear as a cloudy suspension.</li>
</ol>
2. Precipitating Al(OH)3 with NaCl
<ol>
	<li>Prepare a GPC column that is 49 in long and 1.125 in diameter. Pack the gel in successive steps of adding gel and allowing water to flow through the column to ensure proper packing, with minimal space between the gel beads. Pack the gel to about 80% of the column; the amount of gel packed varies every time and only affects the retention time of the separated species.</li>
	<li>Introduce 10 mL of as-synthesized Al(OH)3 nanoparticle suspension (prepared in step 1.3) into the column using an HPLC pump with a 10 mL injector loop. Custom-make the injector loop using tubing with an external diameter of approximately 0.125 in and a length that is calibrated to deliver 10 mL of injected sample.</li>
	<li>Collect the column elution in intervals correlating with the dRI peak location. Connect the GPC output to the input of a differential refractive index (dRI) detector. 
	NOTE: As separated species come out of the GPC, they appear on the dRI detector as a peak and are then collected in 125 mL bottles. The GPC column produces two well-resolved peaks, which are both collected and analyzed with size-exclusion chromatography (SEC) and elemental analysis (EA) to discern arginine from aluminum species. The total volume collected will depend on size of the GPC column, the total amount of packing material used, and the flow rate of the deionized water used to elute the column.
	<ol>
		<li>Collect the majority of the peak 1 fraction over 100 min at a 0.2 mL/min flow rate.</li>
		<li>Collect the eluent in 30 min intervals once a peak emerges on the RI detector of the GPC column. 
		NOTE: Changing the interval range will change the concentration and purity of the resulting purified peak 1 material. It is better to collect small intervals of the peak at first to determine which portion contains the highest concentration and purity of peak 1 species for a specific column.</li>
	</ol>
	</li>
	<li>Prepare 1 wt% of NaCl.</li>
	<li>Add the prepared NaCl solution dropwise to 10 mL of purified Al(OH)3 nanoparticles; the material prepared using NaCl precipitation is not used for further experiments.</li>
</ol>
3. Preparation of Al-MCM-41
<ol>
	<li>Activate approximately 1.0 g of MCM-41 at 120 &#176;C under vacuum for 3 h in a vacuum oven.</li>
	<li>Prepare 50.0 g of aluminum chloride solution by combining 9.6926 g of AlCl3&#183;6H2O with 40.3074 g of deionized water.</li>
	<li>Add 0.7 g of activated MCM-41 to 50.0 g of aluminum chloride solution (prepared in step 3.2).</li>
	<li>Allow adequate mixing time (1 h) to ensure homogeneity of the AlCl3 diffused throughout the MCM-41 channels.</li>
	<li>Add L-arginine to the heterogeneous mixture to an Arg/Al molar ratio of 2.75 under magnetic stirring. Similarly to step 1.2, add the arginine slowly enough so as to allow the instantaneously formed flocculates to redissolve and reduce the clumping of the arginine before continuing the addition.</li>
	<li>Once homogeneous, heat the mixture at 50 &#176;C for 72 h.</li>
	<li>Filter the obtained heterogeneous solution using a Buchner funnel, under vacuum and equipped with qualitative 90 mm filter paper circles (or any other appropriate filter papers).</li>
	<li>Wash the filtered white powder with excess deionized water to ensure the removal of unreacted aluminum chloride, arginine, or water-soluble byproducts from the produced Al-MCM-41 material.</li>
</ol>

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E., 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=On+a+Theory+of+the+van+der+Waals+adsorption+of+gases.">On a Theory of the van der Waals adsorption of gases.</a> J. Am. Chem. Soc. 62 (7), 1723-1732 (1940).</li><li>Kresge, C. T., Leonowicz, M. E., Roth, W. J., Vartuli, J. C., Beck, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ordered+mesoporous+molecular+sieves+synthesized+by+a+liquid-crystal+template+mechanism.">Ordered mesoporous molecular sieves synthesized by a liquid-crystal template mechanism.</a> Nature. 359 (6397), 710-712 (1992).</li><li>Zeng, Q., Nekvasil, H., Grey, C. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Proton+Environments+in+Hydrous+Aluminosilicate+Glasses:+A+1H+MAS,+1H/27Al,+and+1H/23Na+TRAPDOR+NMR+Study.">Proton Environments in Hydrous Aluminosilicate Glasses: A 1H MAS, 1H/27Al, and 1H/23Na TRAPDOR NMR Study.</a> J. Phys. Chem. B. 103 (35), 7406-7415 (1999).</li><li>Kao, H. M., Grey, C. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Probing+the+Bronsted+and+Lewis+acidity+of+zeolite+HY:+A+1H/27Al+and+15N/27Al+TRAPDOOR+NMR+study+of+mono-methylamine+adsorbed+on+HY.">Probing the Bronsted and Lewis acidity of zeolite HY: A 1H/27Al and 15N/27Al TRAPDOOR NMR study of mono-methylamine adsorbed on HY.</a> J. Phys. Chem. 100 (12), 5105-5117 (1996).</li><li>DeCanio, E. C., Edwards, J. C., Bruno, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Solid-state+1H+MAS+NMR+characterization+of+&#947;-alumina+and+modified+&#947;-aluminas.">Solid-state 1H MAS NMR characterization of &#947;-alumina and modified &#947;-aluminas.</a> J. Catal. 148 (1), 76-83 (1994).</li><li>Shafran, K. L., Deschaume, O., Perry, C. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+static+anion+exchange+method+for+generation+of+high+purity+aluminium+polyoxocations+and+monodisperse+aluminum+hydroxide+nanoparticles.">The static anion exchange method for generation of high purity aluminium polyoxocations and monodisperse aluminum hydroxide nanoparticles.</a> J. Mater. Chem. 15 (33), 3415-3423 (2005).</li><li>Vogels, R. J. M. J., Kloprogge, J. T., Geus, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Homogeneous+forced+hydrolysis+of+aluminum+through+the+thermal+decomposition+of+urea.">Homogeneous forced hydrolysis of aluminum through the thermal decomposition of urea.</a> J. Colloid Interface Sci. 285 (1), 86-93 (2005).</li></ol>

The authors have nothing to disclose.

The preparation of an aqueous aluminum chloride solution entailed the use of a crystalline hexahydrate salt of aluminum chloride. Although the anhydrous form can also be used, it is not preferred due to its significant hygroscopic properties, which make it difficult to work with and to control the concentration of aluminum. It is noteworthy that aluminum chloride solution should be used within several days of preparation because over time, the [Al(H2O)6]3+ aqua acid hydrolyzes to yield undesired byproducts that can ultimately reduce the overall yield and purity of the final product. The synthetic methodology described here was conducted with a range of aluminum concentrations (~0.8-3.1 wt% Al). At the higher Al concentrations, the limitation of arginine solubility was reached; therefore, the synthesis could not proceed as intended. On the other hand, the lower concentrations of Al yielded smaller concentrations of nano-Al(OH)3. Previous methodologies incorporated strong bases (e.g., NaOH), the decomposition of molecules to yield a base source (e.g., urea), and ion exchange resin as a mild hydroxide source for hydrolysis.1,18,19 To the best of our knowledge, the use of organic molecules such as amino acids has not been previously incorporated to hydrolyze aluminum chloride. Furthermore, the synthesis of high-purity Al(OH)3 nanoparticles has not been reported using the hydrolysis of an aluminum chloride pathway.
Purification of the prepared nanogibbsite suspension was successfully conducted using a variety of gel packing amounts, packing morphologies, and flow rates. Due to the fragile plastic connectors on our column, the flow rate limitation was approximately 0.5 mL/min, with a majority of the purifications conducted at 0.2 mL/min. The retention time of nanogibbsite particles ranged based on the flow rate and amount of packing material. It is imperative that the column packing material is allowed to pack slowly, which means adding about 1 in of packing material at a time and flowing water at 0.2 mL/min for approximately 30 min to allow the gel to pack well. Moreover, after adding about half a column-worth of packing material, we allowed 24 h of water to flow through the column, which significantly enhanced the packing efficiency of the column. An initial run was conducted to measure the retention time of the two refractive peaks observed (i.e., nanogibbsite and arginine) on the column. Subsequently, the as-synthesized solution was separated on the column, and the two peaks were collected in 10 or 30 min intervals within the time span of the peaks. It was then necessary to analyze the various vials for aluminum and arginine concentrations to understand the species eluting under the specific peak. Due to the large amount of water flowing through the column, the obtained purified solution was significantly diluted.
For the loading of Al into mesoporous silica material, it is important to activate the material prior to the experiment to remove surface-adsorbed gas and liquid impurities, ensuring maximum loading within the pores. A wide variety of solid porous materials besides silica can be used as supports for the guest nanogibbsite molecules (e.g., mesoporous carbon, mesoporous transitional metal oxides, etc.), which can significantly increase the impact of the current synthetic methodology. During the heating process, it is ideal to maintain the temperature and duration to below 80 &#176;C and less than 3-5 days, respectively. Increasing the heating temperature or time can cause the aggregation of nanogibbsite particles and can block pores or coat the surface with aluminum. The developed method achieves a relatively high loading of Al and a concentration of octahedral Al as compared to other methods.

Materials made of aluminum hydroxide are promising candidates for a variety of industrial applications, including catalysis, pharmaceuticals, water treatment, and cosmetics.1,2,3,4 At elevated temperatures, aluminum hydroxide absorbs a substantial amount of heat during decomposition to yield alumina (Al2O3), making it a useful flame-retarding agent.5 The four known polymorphs of aluminum hydroxide (i.e., gibbsite, bayerite, nordstrandite, and doyleite) have been investigated using computational and experimental techniques to improve our understanding of the formation and structures thereof6. The preparation of nanoscale particles is of particular interest due to their potential to exhibit quantum effects and properties differing from those of their bulk counterparts. Nanogibbsite particles with dimensions on the order of 100 nm are easily prepared under various conditions7,8,9,10,11,12,13,14.
Overcoming inherent challenges associated with reducing the particle sizes further is difficult; therefore, only a few cases exist where nanogibbsite particles have dimensions on the order of 50 nm.14,15,16,17 To the best of our knowledge, there have been no reports of nanogibbsite particles smaller than 50 nm. In part, this is attributed to the fact that nanoparticles tend to agglomerate due to electrostatic instability and the high probability for the formation of hydrogen bonds between the colloidal particles, especially in polar protic solvents. Our objective was to synthesize small Al(OH)3 nanoparticles by using exclusively safe ingredients and precursors. In the current work, aqueous particle aggregation was inhibited by incorporating an amino acid (i.e., L-arginine) as a buffer and stabilizer. Moreover, it is reported that the guanidinium-containing arginine prevented aluminum hydroxide particle growth and aggregation to yield an aqueous colloidal suspension with average particle sizes of 10-30 nm. It is proposed here that the amphoteric and zwitterionic properties of arginine mitigated the surface charge of aluminum hydroxide nanoparticles during the mild hydrolysis to disfavor particle growth beyond 30 nm. Although arginine was not capable of reducing the particle size below 10 nm, such particles were achieved by taking advantage of the &#34;cage&#34; confinement effect within the mesopores of MCM-41. Characterization of the Al-MCM-41 composite material revealed ultrafine aluminum hydroxide nanoparticles within the mesoporous silica, which has an average pore size of 2.7 nm.

<table><tbody><tr><td>aluminum chloride hexahydrate</td><td>Alfa Aesar</td><td>12297</td><td></td></tr><tr><td>L-arginine</td><td>BioKyowa</td><td>N/A</td><td></td></tr><tr><td>aluminum hydroxide</td><td>Sigma Aldrich</td><td>239186</td><td></td></tr><tr><td>Bio-Gel P-4 Gel</td><td>Bio-Rad</td><td>150-4128</td><td></td></tr><tr><td>Mesoporous siica (MCM-41 type)</td><td>Sigma Aldrich</td><td>643645</td><td></td></tr></tbody></table>

facile preparation of ultrafine aluminum hydroxide particles with or without mesoporous mcm-41 in ambient environments

An aqueous suspension of nanogibbsite was synthesized via the titration of aluminum aqua acid [Al(H2O)6]3+ with L-arginine to pH 4.6. Since the hydrolysis of aqueous aluminum salts is known to produce a wide array of products with a wide range of size distributions, a variety of state-of-the-art instruments (i.e., 27Al/1H NMR, FTIR, ICP-OES, TEM-EDX, XPS, XRD, and BET) were used to characterize the synthesis products and identification of byproducts. The product, which was comprised of nanoparticles (10-30 nm), was isolated using gel permeation chromatography (GPC) column technique. Fourier transform infrared (FTIR) spectroscopy and powder X-ray diffraction (PXRD) identified the purified material as the gibbsite polymorph of aluminum hydroxide. The addition of inorganic salts (e.g., NaCl) induced electrostatic destabilization of the suspension, thereby agglomerating the nanoparticles to yield Al(OH)3 precipitate with large particle sizes. By utilizing the novel synthetic method described here, Al(OH)3 was partially loaded inside the highly ordered mesoporous framework of MCM-41, with average pore dimensions of 2.7 nm, producing an aluminosilicate material with both octahedral and tetrahedral Al (Oh/Td = 1.4). The total Al content, measured using energy-dispersive X-ray spectrometry (EDX), was 11% w/w with a Si/Al molar ratio of 2.9. A comparison of bulk EDX with surface X-ray photoelectron spectroscopy (XPS) elemental analysis provided insight into the distribution of Al within the aluminosilicate material. Furthermore, a higher ratio of Si/Al was observed on the external surface (3.6) as compared to the bulk (2.9). Approximations of O/Al ratios suggest a higher concentration of Al(O)3 and Al(O)4 groups near the core and external surface, respectively. The newly developed synthesis of Al-MCM-41 yields a relatively high Al content while maintaining the integrity of the ordered silica framework and can be used for applications where hydrated or anhydrous Al2O3 nanoparticles are advantageous.

Nanogibbsite Synthesis
Nanogibbsite was prepared by titrating AlCl3&#183;6H2O (14 wt%) with L-arginine to a final Arg/Al molar ratio of 2.75. The synthesis of nanogibbsite particles was monitored via SEC, which is a widely used analysis technique for partially hydrolyzed aluminum chloride solutions, capable of discerning five domains arbitrarily designated as peaks 1, 2, 3, 4, and 51. Here, we report that nanogibbsite particles with particle sizes of 10-30 nm are components of various potential structures that elute under the peak 1 domain of typical SEC analysis. To the best of our knowledge, the identification of molecules that elute within SEC peak 1 has not been described in the literature thus far. Powder X-ray diffraction (PXRD) and Fourier transform infrared spectroscopy (FTIR) experiments were able to unambiguously identify the Al(OH)3 structure. Elution from the GPC column yielded a translucent Al(OH)3 suspension with 99% purity (based on Al content), a pH of 6.7, +8.9 mV zeta potential (electrophoretic mobility and conductivity of 0.7 &#181;m&#183;cm/V&#183;s and 0.7 mS/cm, respectively), and undetectable amounts of nitrogen. Non-stoichiometric amounts of chloride (Al:Cl ratio of 35:1) anions were detected after purification with GPC, which suggests the presence of partially hydrolyzed cationic impurities with the stoichiometry [Al(OH)xCl3-x] (where x is the molar hydrolysis ratio typically in the range of 0-3), which are likely responsible for the positive zeta potential. The powder obtained by freeze-drying the purified solution was not soluble in water. The oxygen to aluminum ratio (3.3:1) was in good agreement with Al(OH)3 stoichiometry. SEC analysis indicates that the nanogibbsite particles can be synthesized at a conversion rate of 82%. Subsequent characterization was conducted on the GPC-purified material.
Characterization
FTIR analysis confirmed the gibbsite polymorph structure by the presence of a characteristic OH stretch at 3,620 cm-1, which can be discerned from that of bayerite (3,650 cm-1)2,3. Furthermore, other gibbsite vibration modes were evident from the absorptions at 3,617, 3,523, 3,453, 1,023, 970, and 918 cm-1 4,5,6. Arginine was not detected by the FTIR method. Static light scattering analysis of the sample with an Arg/Al molar ratio of 2.75 indicated that the average particle size was in the range of 10-30 nm. The calculated crystallite size, calculated from the XRD pattern using the Scherrer equation7,8, was ~8 nm, which is in decent agreement with light scattering data. Discrete particles with diameters in the range of 5-15 nm were observed in TEM images (Figure 1).
27Al NMR was measured for samples with Arg/Al molar ratios of 0, 2.25, and 2.75 (Figure 2). The results indicate that Al monomer (i.e., AlCl3), which has a characteristic sharp signal at 0 ppm, hydrolyzed to yield Keggin clusters (i.e., Al13-mer and Al30-mer) at an Arg/Al ratio of 2.25, as evidenced by their characteristic 63- and 70-ppm signals. The maximum concentration of Keggin clusters was measured at an Arg/Al of 2.25, which is in good agreement with the SEC data. At an Arg/Al ratio of 2.75, the 27Al NMR spectra exhibited a single Oh signal at 8 ppm.
Al-MCM-41 Synthesis and Characterization
Since its discovery in 1992, MCM-41 has been of great scientific and industrial interest for various applications, such as catalysis, drug delivery, and separations. Unlike zeolites, the structure of MCM-41-type materials can be tailored to exhibit uniform pore sizes between 1.6-10 nm in diameter and generally have surface areas on the order of 1,000 m2g-1. Here, MCM-41, with an average pore size of 2.7 nm, was used as a support &#34;cage&#34; for the confined growth of nanogibbsite particles. Prior to Al loading, MCM-41 was activated at 120 &#176;C to remove any adsorbed contaminants (e.g., water, atmospheric gasses, etc.) from the silica surface. Subsequently, aluminum chloride solution was added to the purely siliceous MCM-41 solid and allowed to equilibrate with Al3+ adsorption within the pores of MCM-41 for 1 h. The slow addition of arginine powder under magnetic stirring caused local flocculation, which was allowed to dissipate prior to further arginine addition. Product formation in the bulk solution was monitored using SEC analysis and 27Al NMR, which indicated that the aluminum chloride was effectively converted into predominantly peak 1 and nanogibbsite species, respectively. The resulting Al-MCM-41 material was filtered and washed with copious amounts of water prior to characterization.
The 27Al MAS NMR (Figure 3) of the prepared Al-MCM-41 material demonstrates the presence of both octahedral (~2 ppm) and tetrahedral (~57 ppm) Al environments, which are commonly observed in mesoporous silica modified with Al species12. The Oh/Td ratio was measured at 1.4. The bulk (EDX) elemental composition was 8.02% Al, 23.26% Si, and 68.70% O. The surface (XPS) elemental composition consisted of 6.13% Al, 21.75% Si, and 66.36% O, which suggests that there is a smaller content of Al on the surface of the particles as compared to the bulk counterpart. The Si/Al ratio was 2.9 and 3.6, as measured by EDX and XPS, respectively. The higher ratio of Si/Al observed in XPS versus EDX analysis indicates that a larger fraction of Al penetrated into the pores as opposed to building up on the surface. Chloride was not detected in stoichiometric concentrations using either method.
Small-angle X-ray diffraction (SAXRD) patterns were measured before and after Al loading and were indexed based on hexagonal symmetry (Figure 4). The presence of 100 (2.2&#176;), 110 (3.9&#176;), 200 (4.4&#176;), and 210 (5.8&#176;) lattice reflections were observed in both samples, indicating that significant changes in the highly ordered porosity did not occur as a result of Al insertion. Brunauer-Emmett-Teller (BET) analysis of the original MCM-41 material yielded a BET surface area of 997 m2/g, a pore volume of 0.932 cm3/g, and a pore width of 2.7 nm. BET data after grafting Al demonstrated a BET surface area of 742 m2/g (20.4% reduction), a pore volume of 0.649 cm3/g (30.4% reduction), and a pore width of 2.1 nm (22.2% reduction). Moreover, the incorporation of Al within the pores reduced the overall N2 adsorbed from 602 to 419 cc/g. The N2 desorption curve (not shown) exhibited a hysteresis loop typical of uniform mesoporosity. 1H MAS NMR was also measured before and after Al particle growth within the mesopores. The introduction of Al caused a downfield shift (~1 ppm) for the predominant 3.1-ppm signal observed in MCM-41. A new, isolated signal emerged at 0.9 ppm, which was assigned to hydroxyl protons coordinating with aluminum atoms, since it experiences relatively stronger shielding and is commonly observed in acidic zeolite materials made of aluminum15,16,17.
27Al nuclear magnetic resonance (27Al NMR) and pH measurements were obtained for samples with varied Arg/Al ratios (Figures 2 and 5). FTIR-ATR and transmission electron microscope (TEM) experiments were conducted for nanogibbsite prepared with an Arg/Al molar ratio of 2.75 (Figures 1 and 6). After loading Al into MCM-41 void space, 27Al MAS NMR, N2 adsorption, SAXRD, 1H MAS NMR, and TEM analyses were carried out to characterize the prepared Al-MCM-41 material (Figures 3, 4, and 7-10).
<img alt="Figure 1" src="/files/ftp_upload/55423/55423fig1.jpg" /> 
Figure 1: TEM micrograph of purified nano-Al(OH)3 with a scale bar of 100 nm. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55423/55423fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/55423/55423fig2.jpg" /> 
Figure 2: Liquid 27Al NMR of samples with Arg/Al rations of 0 (a), 2.25 (b), and 2.75 (c). The main peaks at 0, 8, 63, and 70 ppm are noted above the respective peak positions. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55423/55423fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/55423/55423fig3.jpg" /> 
Figure 3: 27Al MAS NMR spectrum of prepared nanogibbsite (a) and prepared Al-MCM-41 (b). The major peaks at 7.6, 2.4, and 56.9 ppm are labeled above the respective peak positions. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55423/55423fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" src="/files/ftp_upload/55423/55423fig4.jpg" /> 
Figure 4: SAXRD diffraction pattern of MCM-41 (a) and Al-MCM-41 (b), with their tabulated lattice reflections and corresponding d-spacing. The 110 and 200 reflections are magnified 10X in the Al-MCM-41 diffraction pattern. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55423/55423fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" src="/files/ftp_upload/55423/55423fig5.jpg" /> 
Figure 5: Measured pH values at various Arg/Al molar ratios. The arrows point to the samples comprised of Arg/Al ratios of 2.75 and 3.00, which show a drastic increase in pH after the further addition of arginine past the nanogibbsite-containing Arg/Al 2.75 sample. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55423/55423fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" src="/files/ftp_upload/55423/55423fig6.jpg" /> 
Figure 6: FTIR-ATR absorption spectrum of purified Al(OH)3 powder, with characteristic gibbsite vibrations labeled with their wavenumber values. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55423/55423fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" src="/files/ftp_upload/55423/55423fig7.jpg" /> 
Figure 7: N2 sorption isotherms of MCM-41 and Al-MCM-41 obtained via BET method at 77 K. The inset is the corresponding BJH pore size distribution. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55423/55423fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" src="/files/ftp_upload/55423/55423fig8.jpg" /> 
Figure 8: 1H MAS NMR spectra of Al-MCM-41 (a) and MCM-41 (b). The dominant peaks at 0.9, 3.1, and 4.2 ppm are labeled above the respective peak positions. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55423/55423fig8large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 9" src="/files/ftp_upload/55423/55423fig9.jpg" /> 
Figure 9: TEM micrograph of MCM-41. Scale bar = 100 nm. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55423/55423fig9large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 10" src="/files/ftp_upload/55423/55423fig10.jpg" /> 
Figure 10: TEM micrograph of Al-MCM-41. Scale bar = 100 nm. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55423/55423fig10large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Facile Preparation of Ultrafine Aluminum Hydroxide Particles with or without Mesoporous MCM-41 in Ambient Environments at JoVE.com

Facile Preparation of Ultrafine Aluminum Hydroxide Particles with or without Mesoporous MCM-41 in Ambient Environments

An ultrafine aluminum hydroxide nanoparticle suspension was prepared via the controlled titration of [Al(H2O)]3+ with L-arginine to pH 4.6 with and without cage-effect confinement within mesoporous channels of MCM-41.

An aqueous suspension of nanogibbsite was synthesized via the titration of aluminum aqua acid [Al(H2O)6]3+ with L-arginine to pH 4.6. Since the hydrolysis ...

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Nanyang Technological University

Research

JoVE Journal

Chemistry

10.8K Views.  Colgate-Palmolive Company.  Een ultrafijne aluminiumhydroxide nanodeeltjesuspensie werd bereid via de gecontroleerde titratie van [Al (H20)] 3+ met L-arginine tot pH 4,6 met en zonder kooi-effectbevestiging binnen mesoporeuze kanalen van MCM-41. 

Video: Facile Preparation of Ultrafine Aluminum Hydroxide Particles with or without Mesoporous MCM-41 in Ambient Environments

Preparation of Silica Nanoparticles Through Microwave-assisted Acid-catalysis

Microwave-assisted synthetic techniques were used to quickly and reproducibly produce silica nanoparticle sols using an acid catalyst with nanoparticle diameters ranging from 30-250 nm by varying the reaction conditions. Through the selection of a microwave compatible solvent, silicic acid precursor, catalyst, and microwave irradiation time, these microwave-assisted methods were capable of overcoming the previously reported shortcomings associated with synthesis of silica nanoparticles using microwave reactors. The siloxane precursor was hydrolyzed using the acid catalyst, HCl. Acetone, a low-tan &#948; solvent, mediates the condensation reactions and has minimal interaction with the electromagnetic field. Condensation reactions begin when the silicic acid precursor couples with the microwave radiation, leading to silica nanoparticle sol formation. The silica nanoparticles were characterized by dynamic light scattering data and scanning electron microscopy, which show the materials&#39; morphology and size to be dependent on the reaction conditions. Microwave-assisted reactions produce silica nanoparticles with roughened textured surfaces that are atypical for silica sols produced by St&#246;ber&#39;s methods, which have smooth surfaces.

Silica nanoparticles were prepared using acid-catalysis of a siloxane precursor and microwave-assisted synthetic techniques resulting in the controlled growth of nanomaterials ranging from 30-250 nm in diameter. The growth dynamics can be controlled by varying the initial silicic acid concentration, time of the reaction, and temperature of reaction.

Microwave-assisted synthetic techniques were used to quickly and reproducibly produce silica nanoparticle sols using an acid catalyst with nanoparticle ...

Preparation of Hydrophobic Metal-Organic Frameworks via Plasma Enhanced Chemical Vapor Deposition of Perfluoroalkanes for the Removal of Ammonia

Plasma enhanced chemical vapor deposition (PECVD) of perfluoroalkanes has long been studied for tuning the wetting properties of surfaces. For high surface area microporous materials, such as metal-organic frameworks (MOFs), unique challenges present themselves for PECVD treatments. Herein the protocol for development of a MOF that was previously unstable to humid conditions is presented. The protocol describes the synthesis of Cu-BTC (also known as HKUST-1), the treatment of Cu-BTC with PECVD of perfluoroalkanes, the aging of materials under humid conditions, and the subsequent ammonia microbreakthrough experiments on milligram quantities of microporous materials. Cu-BTC has an extremely high surface area (~1,800 m2/g) when compared to most materials or surfaces that have been previously treated by PECVD methods. Parameters such as chamber pressure and treatment time are extremely important to ensure the perfluoroalkane plasma penetrates to and reacts with the inner MOF surfaces. Furthermore, the protocol for ammonia microbreakthrough experiments set forth here can be utilized for a variety of test gases and microporous materials.

Herein the procedures for plasma enhanced chemical vapor deposition of perfluoroalkanes on microporous materials such as metal-organic frameworks to enhance their stability and hydrophobicity are described. Furthermore, breakthrough testing of milligram quantities of samples is described in detail.

Plasma enhanced chemical vapor deposition (PECVD) of perfluoroalkanes has long been studied for tuning the wetting properties of surfaces. For high ...

Ultrahigh Density Array of Vertically Aligned Small-molecular Organic Nanowires on Arbitrary Substrates

In recent years &pi;-conjugated organic semiconductors have emerged as the active material in a number of diverse applications including large-area, low-cost displays, photovoltaics, printable and flexible electronics and organic spin valves. Organics allow (a) low-cost, low-temperature processing and (b) molecular-level design of electronic, optical and spin transport characteristics. Such features are not readily available for mainstream inorganic semiconductors, which have enabled organics to carve a niche in the silicon-dominated electronics market. The first generation of organic-based devices has focused on thin film geometries, grown by physical vapor deposition or solution processing. However, it has been realized that organic nanostructures can be used to enhance performance of above-mentioned applications and significant effort has been invested in exploring methods for organic nanostructure fabrication.	
A particularly interesting class of organic nanostructures is the one in which vertically oriented organic nanowires, nanorods or nanotubes are organized in a well-regimented, high-density array. Such structures are highly versatile and are ideal morphological architectures for various applications such as chemical sensors, split-dipole nanoantennas, photovoltaic devices with radially heterostructured "core-shell" nanowires, and memory devices with a cross-point geometry. Such architecture is generally realized by a template-directed approach. In the past this method has been used to grow metal and inorganic semiconductor nanowire arrays. More recently &pi;-conjugated polymer nanowires have been grown within nanoporous templates. However, these approaches have had limited success in growing nanowires of technologically important &pi;-conjugated small molecular weight organics, such as tris-8-hydroxyquinoline aluminum (Alq3), rubrene and methanofullerenes, which are commonly used in diverse areas including organic displays, photovoltaics, thin film transistors and spintronics.	
Recently we have been able to address the above-mentioned issue by employing a novel "centrifugation-assisted" approach. This method therefore broadens the spectrum of organic materials that can be patterned in a vertically ordered nanowire array. Due to the technological importance of Alq3, rubrene and methanofullerenes, our method can be used to explore how the nanostructuring of these materials affects the performance of aforementioned organic devices. The purpose of this article is to describe the technical details of the above-mentioned protocol, demonstrate how this process can be extended to grow small-molecular organic nanowires on arbitrary substrates and finally, to discuss the critical steps, limitations, possible modifications, trouble-shooting and future applications.

We report a simple method for fabricating an ultrahigh density array of vertically ordered small-molecular organic nanowires. This method allows for synthesis of complex heterostructured hybrid nanowire geometries, which can be inexpensively grown on arbitrary substrates. These structures have potential applications in organic electronics, optoelectronics, chemical sensing, photovoltaics and spintronics.

In  recent years &pi;-conjugated  organic semiconductors have emerged as the active material in a number of  diverse applications including large-area, ...

Engineering

Reverse Microemulsion-mediated Synthesis of Monometallic and Bimetallic Early Transition Metal Carbide and Nitride Nanoparticles

A reverse microemulsion is used to encapsulate monometallic or bimetallic early transition metal oxide nanoparticles in microporous silica shells. The silica-encapsulated metal oxide nanoparticles are then carburized in a methane/hydrogen atmosphere at temperatures over 800 &#176;C to form silica-encapsulated early transition metal carbide nanoparticles. During the carburization process, the silica shells prevent the sintering of adjacent carbide nanoparticles while also preventing the deposition of excess surface carbon. Alternatively, the silica-encapsulated metal oxide nanoparticles can be nitridized in an ammonia atmosphere at temperatures over 800 &#176;C to form silica-encapsulated early transition metal nitride nanoparticles. By adjusting the reverse microemulsion parameters, the thickness of the silica shells, and the carburization/nitridation conditions, the transition metal carbide or nitride nanoparticles can be tuned to various sizes, compositions, and crystal phases. After carburization or nitridation, the silica shells are then removed using either a room-temperature aqueous ammonium bifluoride solution or a 0.1 to 0.5 M NaOH solution at 40-60 &#176;C. While the silica shells are dissolving, a high surface area support, such as carbon black, can be added to these solutions to obtain supported early transition metal carbide or nitride nanoparticles. If no high surface area support is added, then the nanoparticles can be stored as a nanodispersion or centrifuged to obtain a nanopowder.

A &#8220;removable ceramic coating method&#8221; is presented in visual format for the synthesis of non-sintered and metal-terminated monometallic and bimetallic early transition metal carbide and nitride nanoparticles with tunable sizes and crystal structures.

A reverse microemulsion is used to encapsulate monometallic or bimetallic early transition metal oxide nanoparticles in microporous silica shells. The ...

Experimental Protocol to Investigate Particle Aerosolization of a Product Under Abrasion and Under Environmental Weathering

The present article presents an experimental protocol to investigate particle aerosolization of a product under abrasion and under environmental weathering, which is a fundamental element to the approach of nanosafety-by-design of nanostructured products for their durable development. This approach is basically a preemptive one in which the focus is put on minimizing the emission of engineered nanomaterials' aerosols during the usage phase of the product's life cycle. This can be attained by altering its material properties during its design phase without compromising with any of its added benefits. In this article, an experimental protocol is presented to investigate the nanosafety-by-design of three commercial nanostructured products with respect to their mechanical solicitation and environmental weathering. The means chosen for applying the mechanical solicitation is an abrasion process and for the environmental weathering, it is an accelerated UV exposure in the presence of humidity and heat. The eventual emission of engineered nanomaterials is studied in terms of their number concentration, size distribution, morphology and chemical composition. The purpose of the protocol is to study the emission for test samples and experimental conditions which are corresponding to real life situations. It was found that the application of the mechanical stresses alone emits the engineered nanomaterials' aerosols in which the engineered nanomaterial is always embedded inside the product matrix, thus, a representative product element. In such a case, the emitted aerosols comprise of both nanoparticles as well as microparticles. But if the mechanical stresses are coupled with the environmental weathering, the experimental protocol reveals then the eventual deterioration of the product, after a certain weathering duration, may lead to the emission of the free engineered nanomaterial aerosols too.

In this article, an experimental protocol to investigate particle aerosolization of a product under abrasion and under environmental weathering is presented. Results on the emission of engineered nanomaterials, in the form of aerosols are presented. The specific experimental set-up is described in detail.

The present article presents an experimental protocol to investigate particle aerosolization of a product under abrasion and under environmental ...

Nanothermite with Meringue-like Morphology: From Loose Powder to Ultra-porous Objects

The goal of the protocol described in this article is to prepare aluminothermic compositions (nanothermites) in the form of porous, monolithic objects. Nanothermites are combustible materials made up of inorganic fuel and an oxidizer. In nanothermite foams, aluminum is the fuel and aluminum phosphate and tungsten trioxide are the oxidizing moieties. The highest flame propagation velocities (FPVs) in nanothermites are observed in loose powders and FPVs are strongly decreased by pelletizing nanothermite powders. From a physical standpoint, nanothermite loose powders are metastable systems. Their properties can be altered by unintentional compaction induced by shocks or vibrations or by the segregation of particles over time by settling phenomena, which originates from the density differences of their components. Moving from a powder to an object is the challenge that must be overcome to integrate nanothermites in pyrotechnic systems. Nanothermite objects must have both a high open porosity and good mechanical strength. Nanothermite foams meet both of these criteria, and they are prepared by dispersing a nano-sized aluminothermic mixture (Al/WO3) in orthophosphoric acid. The reaction of aluminum with the acid solution gives the AlPO4 &#34;cement&#34; in which Al and WO3 nanoparticles are embedded. In nanothermite foams, aluminum phosphate plays the dual role of binder and oxidizer. This method can be used with tungsten trioxide, which is not altered by the preparation process. It could probably be extended to some oxides, which are commonly used for the preparation of high performance nanothermites. The WO3-based nanothermite foams described in this article are particularly insensitive to impact and friction, which makes them far safer to handle than loose Al/WO3 powder. The fast combustion of these materials has interesting applications in pyrotechnic igniters. Their use in detonators as primers would require the incorporation of a secondary explosive in their composition.

This manuscript describes the synthesis of combustible aluminophosphate matrices by the reaction of orthophosphoric acid (H3PO4) with aluminum nanopowder. When this reaction is carried out with excess aluminum in the presence of tungsten trioxide nanopowder, it leads to a solid, porous nanothermite foam.

The goal of the protocol described in this article is to prepare aluminothermic compositions (nanothermites) in the form of porous, monolithic objects. ...

Simultaneous Multi-surface Anodizations and Stair-like Reverse Biases Detachment of Anodic Aluminum Oxides in Sulfuric and Oxalic Acid Electrolyte

After reporting on the two-step anodization, nanoporous anodic aluminum oxides (AAOs) have been widely utilized in the versatile fields of fundamental sciences and industrial applications owing to their periodic arrangement of nanopores with relatively high aspect ratio. However, the techniques reported so far, which could be only valid for mono-surface anodization, show critical disadvantages, i.e., time-consuming as well as complicated procedures, requiring toxic chemicals, and wasting valuable natural resources. In this paper, we demonstrate a facile, efficient, and environmentally clean method to fabricate nanoporous AAOs in sulfuric and oxalic acid electrolytes, which can overcome the limitations that result from conventional AAO fabricating methods. First, plural AAOs are produced at one time through simultaneous multi-surfaces anodization (SMSA), indicating mass-producibility of the AAOs with comparable qualities. Second, those AAOs can be separated from the aluminum (Al) substrate by applying stair-like reverse biases (SRBs) in the same electrolyte used for the SMSAs, implying simplicity and green technological characteristics. Finally, a unit sequence consisting of the SMSAs sequentially combined with SRBs-based detachment can be applied repeatedly to the same Al substrate, which reinforces the advantages of this strategy and also guarantees the efficient usage of natural resources.

A protocol for fabricating nanoporous anodic aluminum oxides via simultaneous multi-surfaces anodization followed by stair-like reverse biases detachments is presented. It can be applied repeatedly to the same aluminum substrate, exhibiting a facile, high-yield, and environmentally clean strategy.

After reporting on the two-step anodization, nanoporous anodic aluminum oxides (AAOs) have been widely utilized in the versatile fields of fundamental ...

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 ...

Solvothermal Synthesis of MIL-96 and UiO-66-NH2 on Atomic Layer Deposited Metal Oxide Coatings on Fiber Mats

Metal-organic frameworks (MOFs), which contain reactive metal clusters and organic ligands allowing for large porosities and surface areas, have proven effective in gas adsorption, separations, and catalysis. MOFs are most commonly synthesized as bulk powder, requiring additional processes to adhere them to functional devices and fabrics that risk decreasing the powder porosity and adsorption capacity. Here, we demonstrate a method of first coating fabrics with metal oxide films using atomic layer deposition (ALD). This process creates conformal films of controllable thickness on each fiber, while providing a more reactive surface for MOF nucleation. By submerging the ALD coated fabric in solution during solvothermal MOF synthesis, the MOFs create a conformal, well-adhered coating on the fibers, resulting in a MOF-functionalized fabric, without additional adhesion materials that may block MOF pores and functional sites. Here we demonstrate two solvothermal synthesis methods. First, we form a MIL-96(Al) layer on polypropylene fibers using synthetic conditions that convert the metal oxide to MOF. Using initial inorganic films of varying thicknesses, diffusion of the organic linker into the inorganic allows us to control the extent of MOF loading on the fabric. Second, we perform a solvothermal synthesis of UiO-66-NH2 in which the MOF nucleates on the conformal metal oxide coating on polyamide-6 (PA-6) fibers, thereby producing a uniform and conformal thin film of MOF on the fabric. The resulting materials can be directly incorporated into filter devices or protective clothing and eliminate the maladroit qualities of loose powder.

Solvothermal Synthesis of MIL-96 and UiO-66-NH2 on Atomic Layer Deposited Metal Oxide Coatings on Fiber Mats

Metal-organic frameworks are effective in gas storage and heterogeneous catalysis, but typical synthesis methods result in loose powders that are difficult to incorporate into smart materials. We demonstrate a method of first coating fabrics with ALD metal oxides, resulting in conformal films of MOF on the fabrics during solvothermal synthesis.

Metal-organic frameworks (MOFs), which contain reactive metal clusters and organic ligands allowing for large porosities and surface areas, have proven ...

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 ...

Facile Preparation of Ultrafine Aluminum Hydroxide Particles with or without Mesoporous MCM-41 in Ambient Environments

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