Supporting Information

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Phillip Daniel
5 years ago
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1 Supporting Information Figure S1: NMR of the HCl in ether from Sigma Aldrich shows two peaks, other than those known for ether, corresponding to the acid (Supplementary Figure 1a). One peak at ~ 3 ppm is from associative combination of the HCl and ether and the other at ~7.5 is dissociative. In comparison to this, the HCl in OS-20 has only one peak downfield showing it is mostly associative. We verified what the spectra of some expected contaminants would look like (Supplementary Figure 1b), including water and silanol (Xiameter PMX-0156). In the silanol spectra (red), we see both a shift in the methyl protons as well as a small peak at ~3.5 ppm corresponding to the hydroxyl proton. In the siloxane doped with silanol (purple), these features are significantly reduced. However, if the siloxane is doped instead with water (light blue), we observe a peak corresponding to the acidified water at ~5.5 ppm. The chemical shift indicates the acidity, as the chemical shift for water is typically between 4-5 ppm 25 ). Comparing these potential byproducts to the spectra of our acidified siloxane (black), it is clear that not only has water been eliminated, but that the bulk of the oil remains unhydrolyzed.

2 Figure S2: The effects of varying aqueous acid exposure time (Supplementary Figure 2a) as well as acid composition (Supplementary Figure 2b) were explored, both with regards to byproducts as well as stability. Supplementary Figure 2a shows samples that were exposed to the 12 M HCl for 1 hour (light grey), overnight (grey), or 4 days (black). It is clear that minimal acid is retained in the siloxane after only 1 hour of exposure. Exposure for up to 4 days increases the volume (and therefore concentration) of the acid peak by 25% compared to the overnight exposure, however a third peak appears that we attribute to hydrolysis of the siloxane. We concluded that hours of exposure provides sufficient time to absorb HCl, but insufficient time for the siloxane to hydrolyze appreciably. We then tested whether we could acidify the siloxane using another acid (Supplementary Figure 2b). We chose HBr which has a higher boiling point and a slightly greater dissociation constant than HCl. Bromide ions also tend to be less reactive than chloride ions. We wanted to determine whether replacing HCl with HBr affected the electronic properties of the siloxane or its ability to remove metal oxides. The HBr siloxane appears identical to the virgin OS-20 and has no peak relating to the acid like the HCl siloxane does. We did observe a small peak in HBr siloxane after extended exposure (4 days) at ~2.5 ppm, indicating that the acid is incorporated in an associative manner. However, the peak volume indicates that even after 4 days of exposure the siloxane contains only approximately 50 µm HBr, compared to 1.5 M HCl after hours of exposure. We attribute this to the weaker dissociation constant of HCl, which would preserve a higher concentration of the associated HCl in the 12N aqueous solution.

No other difference was observed between the regular oil and the HCl oil (Supplementary Figure 3a).

3 Figure S3: FTIR was used to identify functional groups and to confirm that no substantial changes were occurring to the oil. A peak at ~2350 nm was attributed to HCl, but was very weak (Supplementary Figure 3b). No other difference was observed between the regular oil and the HCl oil (Supplementary Figure 3a). Comparison of the regular oil, HCl oil purposefully contaminated with water, and HCl oil exposed to GaLMA showed that the water produced by the oxide-acid reaction is taken up into the HCl oil and perturbs the functional groups minimally (Supplementary Figure 3b).

4 Figure S4: a) b) Proposed chemical reactions from NMR: a) gallium chloride adducts interfacing with the siloxane and b) hydrolysis of the siloxane.

5 Figure S5: Unique isotope pattern helped to identify gallium chloride adducts (60% M, 40% M+2). Upon closer inspection, indium chloride adducts were also identified (standard isotopic pattern).

(a) Calcium reacts with water to form calcium hydroxide, Ca(OH) 2. O(l) Ca(OH) 2

1 Magnesium and calcium are in group 2 of the periodic table. They are less reactive than the metals in group 1. (a) Calcium reacts with water to form calcium hydroxide, Ca(OH) 2, and hydrogen, H 2. Ca(s)