Economical Synthesis of Vanadia Aerogels Via Epoxide-Assisted Gelation of Vocl3

Economical Synthesis of Vanadia Aerogels via Epoxide-Assisted Gelation of VOCl3

Tyler M. Fears*, Chariklia Sotiriou-Leventis, Jeffrey G. Winiarz, Nicholas Leventis

Department of Chemistry, Missouri University of Science and Technology, 400 W. 11th St., Rolla, MO 65409, USA

*Email address: [email protected]

Electronic Supplementary Material

Contents: Page

Table of Contents S.1

Figure S.1 UV-Vis absorption spectra of VOCl3 solutions S.2

Figure S.2 UV-Vis absorption spectra collected during gel aging S.3

Figure S.3 Concentration study from time-resolved 13C NMR collected during gel aging S.4

Figure S.4 XRD and electron diffraction patterns of aerogel powders S.6

Figure S.5 Concentric cylinder model used to calculate crosslinking polymer density S.7

Figure S.6 Quasi-static compression of X-VOx aerogels S.8

Figure S.7 Full mass spectrometry data from tandem TGA-MS S.9

References S.11

S.1 EtOH VOCl H O ECH Spectrum 3 2 Apparent Color [mL] [mmol] [mmol] [mmol]

Neat VOCl3 - Neat - - Orange

VOCl3 in EtOH 6.0 5.70 - - Red

VOCl3 + 3 H2O in EtOH 6.0 5.70 17.1 - Red

VOCl3 + 5 ECH in EtOH 6.0 5.70 - 28.5 Yellow

Gel at t = 0 6.0 5.70 51.3 28.5 Red

Figure S.1. UV-Vis absorption spectra comparing several VOCl3 solutions and a wet gel, assuming a 25 μm path length. The major absorption in the visible spectrum is due to a metal-to-ligand charge-transfer transition.

S.2 S.3 Figure S.2. UV-Vis absorption spectra of standard epoxide gel during aging, assuming a 25 μm path length. No significant changes to absorption were detected after ~16 h. Strong absorption in the near UV gives rise to the initial red gel color. The onset of intense absorption across the entire visible spectrum causes gels to lose transparency.

S.4 -1 k [h-1] k [h ] Initial Relative Final Relative (Independently (Constrained Concentration Concentration Fit) Fit) (A +A0) (A0)

ECH 0.400 0.977 0.022

MCPDH2 0.364 0.003 0.329 0.406 MCEPH 0.433 0.021 0.649

Sum 2.83×10-30 1.001 1.000

Figure S.3. Concentration (C) of ECH (red), MCPDH2 (orange), MCEPH (blue) and their Sum (black) as a function of time (t) as monitored by 13C NMR. Individual peak intensities (open circles) were averaged (solid

S.5 squares) to determine the concentration of each species. All intensities were normalized to the time-averaged Sum to determine relative concentration. Data for each species was initially fit independently to an exponential decay. Noting that each of the rate constants (k) was similar―excepting the Sum series, for which k ≈ 0―this parameter was constrained to be identical for each species and the data was refit. The fits (solid line) are excellent (R2 = 0.994) and physically consistent, i.e., the sum of the fitted concentrations matches the fit of Sum, which has negligible (A = 8.81566×10-4) exponential character. This result indicates that ECH ring- opening is first-order with respect to ECH concentration. As both H2O and EtOH are present in large excess, changes in their concentration by consumption during ring-opening would have little effect on the observed kinetics.

This demonstrates that concentration curves can be determined via in-situ mesophase 13C NMR for analysis of slow gelation kinetics, even in the presence of poor signal to noise caused by low concentrations and anisotropic susceptibility broadening.

S.6 Figure S.4. X-ray (Cu-Kα) diffraction pattern of a ground vanadia aerogel monolith. Stick patterns for a series of potential VOx·nH2O species are included for comparison: V2O5·H2O (PDF# 01-074-3093), V3O7·H2O (01-

085-2401), V3O7 (01-71-0454), H3.78V6O13 (01-088-1753 38-8). Electron diffraction pattern inset.

The peaks in the X-ray diffraction pattern are in locations similar to several known VO x materials, but the broad low-intensity peaks are more consistent with an amorphous material. (A detailed analysis of the diffuse scattering and determination of a model pair distribution function (PDF) is beyond the scope of this study.) The electron diffraction pattern and TEM image (Fig. 4B) suggest that some intermittent nanocrystalline domains are present. A good single-crystal electron diffraction pattern was not obtainable, due in part to multiple scattering from the amorphous matrix. The scarcity of the nanocrystals also precludes the collection of a quality powder electron diffraction pattern.

S.7 Figure S.5. Conformally coated cylindrical VOx nanoworm approximation used to calculate polymer coating density, where r1 and r2 are the radii of the nanoworms and before and after isocyanate crosslinking, respectively and L is the length of the nanoworms. Since conformal crosslinking only adds onto existing nanoworms, the ratio of the radii can be determined from the ratio of the volumetric surface area, σv:

The skeletal density of the composite nanoworm, ρs,T, is the average of the skeletal density of the composite parts, ρs,1 and ρs,2, weighted by their respective volumes, V1 and V2:

S.8 Figure S.6. Representative quasi-static compression tests of X-VOx aerogels with different densities, as controlled by isocyanate concentration in crosslinking solutions. Elastic region expanded in inset. Protocols were followed as previously reported [17,18].

S.9 Figure S.7. MS signals between m/z = 15 and m/z = 300 above the detection limit (~10-10 A) for (a) vanadia aerogels and (b) vanadia xerogels. All identified signals are listed and identified in order of intensity at right, with isotopes labeled where more than one is observed. The ratios of the species are consistent with both

S.10 typical concentrations in air and natural isotopic abundancies. For TGA-MS analysis, signals due to air were removed by subtracting the m/z = 36 signal multiplied by the final measured ratio between each species. Only m/z = 18, H2O, (blue) and m/z = 44, CO2, (red) show a statistically significant deviation from the background.

These signals were normalized by sample mass and N2 carrier gas (m/z = 28) ion current, to account for variations in carrier gas flow. Latency between TGA and MS signals was determined to be 6 min by matching maxima in the mass-loss derivatives to maxima in the H2O and CO2 ion currents.

S.11 References: 1. Leventis N, Sotiriou-Leventis C, Mulik S, Dass A, Schnobrich J, Hobbs A, Fabrizio EF, Luo H, Churu G, Zhang Y, Lu H (2008) Polymer nanoencapsulated mesoporous vanadia with unusual ductility at cryogenic temperatures. Journal of Materials Chemistry 18:2475-2482.

2. Luo H, Churu G, Fabrizio EF, Schnobrich J, Hobbs A, Dass A, Mulik S, Zhang Y, Grady BP, Capecelatro A, Sotiriou-Leventis C, Lu H, Leventis N (2008) Synthesis and characterization of the physical, chemical and mechanical properties of isocyanate-crosslinked vanadia aerogels. Journal of Sol-Gel Science and Technology 48:113-134.