48th International Conference on Environmental Systems ICES-2018-284 8-12 July 2018, Albuquerque, New Mexico

UV Chemistry and Mitigation of

Lance Delzeit1. NASA Ames Research Center, Moffett Field, CA, 94035

and

ChaKaria J. Hunter2 KBR Wyle, Moffett Field, CA, 94035

The presence of dimethylsilanediol (DMSD) within the water supply of the International Space Station (ISS) causes issues with the Water Processing Assembly (WPA). It can degrade the WPA catalytic reactor’s effectiveness and cause the early replacement of Multifiltration Beds. The DMSD is believed to be a decomposition product of which are condensed into the water system with the humidity condensate. This paper presents the ultraviolet (UV) gas phase photochemistry of siloxanes under both long and short wavelength UV radiation, and high energy electron bombardment. The results of this study showed that the siloxanes reacted into progressively larger and more complex moieties which eventually formed large non-volatile components which included their attachment to various accessible surfaces.

Nomenclature Ar = Argon m = meter C = Carbon MF = Multi-filtration ca. = calculated MMST = monomethylsilanetriol Cd = Cadmium nm = nanometer DMSD = dimethylsilanediol O = Oxygen Dn = A cyclic Siloxane with n Si atoms OH = Hydroxyl group GCMS = Gas Chromatograph Mass Spectrometry ppb = parts per billion (by mass) H = Hydrogen atom ppm = parts per million (by mass) Hg = Mercury psi = pounds per square inch HS = Head Space SEM = Scanning Electron Microscopy ID = Inner diameter Si = Silicon ISS = International Space Station TMS = IUPAC = International Union of Pure and TOC = Total Organic Carbon Applied Chemistry ul = microliter J = Joules UV = Ultraviolet radiation kJ = kilojoules WPA = Water Processing Assembly Kr = Krypton Xe = Xenon Ln = A linear Siloxane with n Si atoms Zn = Zinc

1 Physical Scientist, Bioengineering Branch, and Mail Stop 239-15. 2 Research Engineer, Bioengineering Branch, and Mail Stop 239-15. I. Introduction HE International Space Station (ISS) has previously had issues with a shorter-than-expected life for its multi- T filtration (MF) beds, as well as it can degrade the Water Processing Assembly (WPA) catalytic reactor’s effectiveness.1 Both of these issues have been traced back to the presence of dimethylsilanediol (DMSD) and more recently monomethylsilanetriol (MMST) within the recycled water. Both DMSD and MMST are degradation products of siloxanes. DMSD can be formed directly from the cleavage of a monomeric unit of a cyclic siloxane or from the hydroxyl-dimethyl-silyl ends of a linear siloxane (Dn or Ln, respectively, where n is the number of Si atoms). MMST is the further decomposition of DMSD where an additional methyl group has been removed and replaced by a hydroxyl group.1,2 Plenty of literature exists describing the behavior of siloxanes. It can be best summarized as an equilibrium chemistry which will produce whichever product is not the dominant species; i.e., experiments starting with large siloxanes will produce smaller siloxanes, and experiments starting with small siloxanes will produce larger siloxanes. The reaction also requires the presence of water; although, in higher concentrations the water itself acts as an inhibitor.3,4,5 This research will look at the effects of short and long wavelength UV on the mitigation of siloxanes. It is believed that UV in the 300-400nm will probably not drive any photo chemistry since the energy of those photons are less than the energy required to break the molecular bonds. Photons around 250 nm would have enough energy to break most of the bonds present in a siloxane, and mercury lamps produce a strong band at 254 nm. Mercury (Hg) lamps also produce a line at 185 nm, which may or may not be blocked depending upon the quality of the emission window. The 185 nm line of a Hg lamp is generally only 3-9% of the intensity of the 254 nm line.

II. Experimental Setup and Methodologies

A. Gas Phase Experimental Setup

The primary gas phase research, and the data presented in Appendix A and B, was conducted within the setup shown in Figure 1. The setup consisted of a GCMS headspace (HS) vial cap modified to hold a UVP Pen- Ray lamp. The HS vial cap was affixed to a fixture which had an ultra-torr fitting welded to it. The ultra-torr/cap fixture was then machined to accept and seal the Pen-Ray lamp. A HS vial screwed into this fixture, producing a sealed reaction chamber. A 1 ul sample of a siloxane (Table 1) was placed into the reaction chamber and processed for 5, 15, or 60 minutes. After processing, the Pen- Ray fixture was removed and a normal HS vial cap was placed on the vial. The sample was then analyzed using HS GCMS. The HS GCMS was performed by heating the vial to 200oC to ensure vaporization of the volatile and semi-volatile siloxanes. A 10 ul sample was then removed from the vial and injected directly onto the GCMS column. The column was a 60 m long, 0.320 ID, PerkinElmer Elite 5 (95% methyl 5% phenyl) column. The GC method was programmed to hold 30oC for 3 minutes, ramp to 300oC at 20oC per minute, and then soak at 300oC for 5 min to ensure removal of all siloxanes from the GC column. The analysis of the GCMS chromatograms are discussed below and presented in Appendix A. The vials were not specially treated, and as such, were filled with room Figure 1. Gas Phase Reaction air which contains oxygen and water vapor. If this process was used to Vial mitigate siloxanes within a space application, oxygen and water would be present within that application. The Pen-Ray Hg lamp reportedly heats to 100oC during operations. Additionally, the GCMS HS sampler heats the HS vial to 200oC to ensure vaporization. To check the possibility of thermal processing, a siloxane sample was place within a HS vial and allowed to thermally process at 200oC for 1 hour. No degradation products were detected due to the thermal processing in the HS vial at 200oC. The GCMS and Headspace methods used are presented in Appendix C.

2 International Conference on Environmental Systems B. Shorthand Nomenclature for Naming the Siloxane A general shorthand for naming linear and cyclic siloxanes already exists. They are described as Ln and Table 1. Siloxanes (shorthand) and Boiling Points Dn, respectively, where n is the number of Si atoms within the molecule. The Si atoms are all tetrahedrally Chemical (Shorthand) Boiling bonded, the backbone Si atoms are connected through an Point oxygen bridge, i.e., Si-O-Si, and any “missing” Tetramethylsilane (4-0) 26 6 coordination to the Si is a methyl group. Trimethylsilanol (3-1) 99 However, for this work, this nomenclature is DMSD (2-2) 122 inadequate to name the plethora of molecules observed MMST (1-3) 200 and the full IUPAC (International Union of Pure and Applied Chemistry) names are too long and tedious. (0-4)) ? Thus, this paper will use the naming convention of replacing long, tedious parts of the IUPAC name with the Tetraethoxysilane (TEOS) 168 Ln and Dn nomenclature, where Ln and Dn are n Si atoms in a linear or cyclic configuration, respectively. For (L2) 101 example, a Dn with two Ln siloxyl groups coming off of Octamethyltrisiloxane (L3) 152 it would be named x,y-Ln-Dn, where x and y will describe the position where the Ln is attached. Additionally, if an Decamethyltetrasiloxane (L4) 195 L2 had two hydroxyl groups attached to it, it would be Dodecamethylpentasiloxane (L5) ? named 1,1-OH-L2 or 1,2-OH-L2 depending on if the hydroxyl groups are both on the same or different Si Hexamethylcyclotrisiloxane (D3) 134 atoms, respectively. This molecule could otherwise be Octamethylcyclotetrasiloxane (D4) 175 named as L2(OH)2 if the number, but not the position, of Decamethylcyclopentasiloxane (D5) 210 the hydroxyls are known. The bi-, tri-, tetra-, as well as Dodecamethylcyclohexasiloxane (D6) 245 bis, tris, and tetrakis nomenclature is dropped. This is because, for example, since the x,y-Ln- and 1,1-OH- nomenclature used in the above examples makes it Methyl-tris(trimethylsiloxy)silane (B4) 60-70 obvious that there are two branches present, bis- or bi- is Tetrakis(trimethylsiloxy)silane (B5) 105 not strictly required.

C. GCMS Identification Standards for L2, L3, L4, L5, D3, D4, and D5 can be purchased, but those are only 7 of the ~100 peaks that are produced. For the other 90+ peaks which do not have reference standards, the following conventions were used. The largest peak of the mass spectrum is assumed to be the –CH3 peak, and thus the parent molecule is assumed to be 15 mass units heavier. This assumption is made because it was observed with the siloxane reference compounds. Since siloxanes are made from a limited number of atoms (Si, O, C, and H) with given coordination Si (4), O (2), C (4), and H (1), there is a limited number of combinations which can produce a given mass (parent molecule). For example, masses 15 and 17 could only be CH3 and OH, respectively. The mass of the parent molecule will identify the general class of the molecule, linear or cyclic, but not its exact structure. For example, both the linear and the branched variants of the L4 class contain 4 Si atoms and will have the same mass. Additionally, they will also have very similar mass spectra just as butane and iso-butane have the same mass and very similar mass spectra. However, they will have different retention times within the GCMS, and thus can be individually identified by their retention times; a similar effect happens with siloxanes. D5, L1-D4, L2-D3, L3-D2, 1,1-L1-D3, and 1,2-L1-D3 will all have the same mass and similar GCMS mass spectra, but different GCMS retention times. All of these D5 variants will be referred to as the D5 class and the linear and branched L4, mentioned above, will be referred to as the L4 class. The branched variants of L4 and L5 with the structures 2-L1-L3 and 2,2- L1-L3 were available commercially and will be specifically referred to as B4 and B5, respectively.6,7,8 Some classes of molecules have the same mass, but different structures. For example, Ln and Bis(Disilane)-D(n+1) have the same mass. Ln will elute first because it is a small molecule in terms of the number of Si and O atoms. The L3 has a shorter retention time than the Bis(Disilane)-D4. Methyl groups increase the vapor pressure of a molecule because they don’t interact with their surroundings as strongly as other moieties. Unfortunately, a few classes do have the same mass. For example, the Dicyclic-Dn and Disilane-Ln(OH) both have the same mass, and it is unclear which would have the shorter retention time. Additionally, Dn, Dn Class, and Disilane-Ln(O) all have the same mass. The Dn is identifiable due to its reference standard; however, the Dn Class and Disilane-Ln(O) are more difficult to specifically identify.

3 International Conference on Environmental Systems D. General Gas Phase Photochemistry of Siloxanes Table 2 shows the energy and photon wavelength required to break the various Table 2. Photon Energy and Photochemistry bonds found within a siloxane. As shown in Table 2, the gas phase photochemistry of Bond Energy Energy Energy Wavelength siloxanes is expected to be driven by kJ/mol kJ/bond J nm photons shorter than 260 nm. As such, the 254 nm line of a low-pressure Hg lamp O=O 494 8.20E-22 8.20E-19 242 could be used to drive the photochemistry. 9 O-H 459 7.62E-22 7.62E-19 261 A low-pressure Hg lamp produces O-Si 452 7.51E-22 7.51E-19 265 major spectral lines at 365 nm, 254 nm, and C-H 411 6.82E-22 6.82E-19 291 185 nm with relative intensities of nominally 10%, 100%, and 10%, C-Si 318 5.28E-22 5.28E-19 376 respectively. Two variants of the Hg lamp H-Si 318 5.28E-22 5.28E-19 376 are available. The first uses a lower quality quartz (non-ozone producing), which blocks shorter wavelengths, eliminating the 185 nm line. Table 3. Lamps and Wavelengths The second uses a higher quality quartz (ozone Lamp Wavelength Intensity producing), which allows the 185 nm line through with a relative intensity of 3-9%. Wavelengths less than 240 nm nm % will begin to produce ozone. Low Pressure Hg Lamp 365 3 - 10 There are other types of lamps that are also able to 254 100 produce wavelengths less than 260 nm and are 185 3 - 10 summarized in Table 3. Table 3 lists various lamps capable of producing UV less than 260 nm and presents the wavelength and relative intensity of those lines. In Zinc Lamp 307 100 addition to the low-pressure Hg lamps, a Zn lamp and a 214 100 Cd lamp were also investigated. The findings from the Zn 206 1 and Cd lamps are presented in a following section. From here on, the lamps will be described either by 202 1 their dominant photochemistry line as presented in Table 3, or by the element used. Cadmium Lamp 326 100

228 100 III. Results and Discussion 214 2

A. Hg Lamp UV Treatment of Siloxanes Two low-pressure Hg lamps have been studied. Both Ar2* Eximer 126 100 lamps produce the 254 nm line, but only one produces the 185 nm line as explained above, and will be described as the 254 nm and the 185 nm lamp, respectively. Kr2* Eximer 146 100

Both the 254 nm and 185 nm lamps drive the photochemistry of siloxanes, however, the 185 nm lamp Xe2* Eximer 172 100 drives it to a greater extent. Figures 2 and 3 show the relative degree of degradation from the 254 nm and 185 nm lamps, respectively. It is seen that the 254 nm lamp will quickly degrade 75% of L2 from 5241 ppm to 1464 ppm in 5 min of processing, but not much more after that. The 185 nm lamp will degrade 99.6% of L2 from 5241 ppm to 22 ppm in the same 5 min, and an additional 2 orders of magnitude reduction (to less than 1 ppm) over the following hour. Additionally, it is noted that Figures 2 and 3 show that the 254 nm lamp produces very low initial concentrations of products and that those concentrations continue to increase over the next hour of processing. The 185 nm lamp, in comparison, produces higher concentrations of products initially, and those products generally decrease in concentration over the next hour of processing. Very similar effects are seen for the other Ln and Dn siloxanes. Thus, the 254 nm line drives only a limited degree of photochemistry. The 185 nm line, although far weaker in intensity, is much more efficient at driving siloxane photochemistry, mostly eliminating the siloxanes to only ppb trace quantities.

4 International Conference on Environmental Systems B. Solidification of Siloxanes into a Glassy Material: Siloxane UV Mitigation 10000.000 L2 Parent, w/o 185nm L2 Figure 4 shows a HS vial after 60 min of 1000.000 processing. The top image of Figure 4 shows what L3 appears to be “liquid droplets” on the inside of the 100.000 L4 vial. However, after treatment in a vacuum oven L5 at 200°C overnight, the “droplets” remain. Even 10.000 D3 with wiping from a cotton swab, the “droplets” are 1.000 D4 not removed. Thus, they are, in fact, some type of 0 10 20 30 40 50 60 ppm of of ppmSiloxane D5 a solidified glassy material formed from the 0.100 siloxanes. The bottom images in Figure 4 show a B4 second vial after 60 min of siloxane processing: 0.010 B5 the left image after overnight vacuum oven Time (min) treatment at 200°C, and the right image after Figure 2. Siloxane degradation from the 254nm lamp. additional vigorous rubbing with a cotton swab. The vacuum oven treatment did not remove the 10000.000 “foggy” material coating the inside of the vial. L2 Parent, w/ 185nm L2 Even light swabbing with a cotton swab did not 1000.000 L3 remove the “foggy” material (image not shown). 100.000 L4 It was only after vigorous brushing with the cotton L5 swab that some of the “foggy” material was finally 10.000 D3 scrubbed off. This, again, shows that the gas D4 phase siloxanes are being deposited on the inside 1.000 0 10 20 30 40 50 60 ppm of of ppmSiloxane D5 wall of the HS vial as some type of a highly cross- 0.100 linked glassy material. All of the Ln and Dn B4 siloxanes tested produced this effect. 0.010 B5 Time (min) Figure 3. Siloxane degradation from the 185nm lamp. C. Hg Lamp Gas Phase Degradation Products The UV treatment of siloxanes results in the degradation of the parent molecule and the formation and degradation of primary and secondary products.10 Figure 5 shows this effect for B5. The left panel of Figure 5 shows the degradation of B5 with progressively longer UV treatments (of fresh samples). The right panel shows the early formation of a primary product and its subsequent degradation, as well as a secondary product’s slow formation and eventual degradation. The 5 minute UV treatment of L2 shows a number of degradation products as shown in Figure 6. The initial intensity of L2 before UV treatment was 8x108 counts. After 5 minutes of UV treatment only 8x106 counts, or approx. 1%, Figure 4. Top image shows what appears to be “liquid” of the L2 remained. droplets on the inside of the HS vial. These “droplets” are The UV treatment of L2 can cause a number not removed by temperature or wiping; see text for of cascading reations. The L2 could be cleaved in details. The bottom left image shows the foggy material half by the hydration reaction forming two L1OH which is deposited on the inside of the HS vial during UV molecules, which can be seen in Figure 6 at 4.46 processing of the siloxanes. The bottom right image minutes. Alternatively, the methyl could be shows the same vial after vacuum oven treatment and cleaved and oxidized into methanol (2.84 min). vigorous scrubbing with a cotton swab failing to remove The methanol can undergo further oxidation into all of the foggy material. formaldehyde (2.53 min) and then formic acid (3.72 min).

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Figure 5. Extracts from a GCMS Chromatogram of B5 showing the degradation of B5 (left) and the formation and degradation of primary and secondary products (right). The scale for the B5 is 100 times more intense than the products.

When a methyl group is cleaved from the L2, it converts the L2 into L2OH (Figure 6, 7.16 min). The L2OH may then, subsequently, react with an L1OH or another L2OH in a dehydration reaction forming L3 (3.19 min) and L4 (10.04 min), respectively. If the two ends of the L3 or L4 can undergo methyl cleavage into 1,3-OH-L3 or 1,4-OH- L4, respectively, the two ends of each molecule can undergo a self-dehydration reaction to form D3 (7.53 min) or D4 (9.34 min), respectively. The D3 and D4 molecules can undergo methyl removal to form D3OH (not observed in

Figure 6. Chromatogram showing the different products produced from L2 after 5 min of processing.

6 International Conference on Environmental Systems Figure 6) and D4OH (10.42 min), respectively. Alternatively, the L4 could form the 1,3-OH-L4 which could then undergo ring closure to form L1-D3 (9.58 min). Additionally, the L3 can undergo a single methyl removal forming either 1-OH-L3 or 2-OH-L3. The 1- and 2- OH-L3 can be identified because the trimethylsilyl (TMS) removal from B4 forms 2-OH-L3 (9.24 min) and thus the 1-OH-L3 peak is observed at 9.17 min in Figure 6. Figure 6 also shows that cyclic siloxanes are more stable to degradation than linear siloxanes. This isn’t because they are intrinsically less reactive, but rather, they just have a “built-in healing mechanism”. If an Ln gets hydrolyzed, the two halves will simple fly away from each other. However, in a Dn siloxane, when the ring gets hydrolyzed, the Dn is transformed into 1,n-OH-Ln which can then undergo a dehydration reaction to reform the Dn. Thus, to destroy the Dn, either methyl cleavage is required to form Dn-OH which can then subsequantly “grow” the Dn into a larger moiety, or the Dn has to be hydrolyzed a second time before the Ln(OH)2 can undergo dehydration and ring closure back into Dn. Finally, there are peaks which, as of yet, are still unidentified, such as the two peaks around 11 min in Figure 6. Peaks can remain unidentified because there are too many possibilities for their identification as with Dicyclic-Dn and Disilane-Ln(OH); the mass of the parent ion is unrecognized as a possible SinOxCyHz molecule, or the mass of the parent ion implies a violation of the assumed order of elution, i.e., n>n+1. Most of the early eluting siloxane products have been identified, however, larger, more complex siloxanes, which elute later in the GCMS chromatograph, have not been identified at this time. The general results of the processing of the various Ln and Dn samples at various processing times results in the following conclusions: 1) The removal of a methyl group produces methanol, formaldehyde and formic acid; as well as larger organics in trace quantities, such as ethanol and acetic acid. 2) The Ln siloxanes produce L1OH and L(n-1)OH from the cleavage of their end TMS groups, but generally results in only very weak or even no peaks being observed between the L1OH and L(n-1)OH peaks, i.e., the siloxanes only get larger due to processing. 3) The Dn siloxanes are more stable to UV treatment than Ln siloxanes. 4) Eventually all of the siloxanes, and their products, are removed from the gas phase by either: a. Increased size, reducing their vapor pressure. b. Condensation reaction between the siloxane and a surface, resulting in a glassy layer being deposited on that surface.

D. Hg Lamp UV Photochemistry products produced: Discussion of Appendix A Appendix A shows a compiled list of products produced from the UV photochemistry of the siloxanes studied. The smaller, earlier eluting products are generally identified with a high degree of certainty because of the limited number of possibilities. For example, L1OH (4.47 min), L1(OH)2 (5.9 min), L2OH (7.17 min), and L1-D2 (7.61 min) are all easily identified because there is only one reasonable possibility for the given mass spectrum produced. The second peak that appears to be L1OH at 4.63 min is believed to be an instrumental error. It was only observed for later experiments where many of the peaks have been identified as being 0.05 min late. Larger molecules, such as L3, can produce products such as L3OH (9.18 min and 9.22 min) which have multiple possible structures. The presence and absence of one or the other band from different parent molecules can be used to indicate which band is which structure. For example, a single hydrolysis of a TMS from B4 will produce 2-OH- L3. In the B4 chromatograph, only a single peak is observed for L3OH and thus, must be 2-OH-L3 (9.22 min). Therefore, the second L3OH peak observed has to be 1-OH-L3 (9.18 min). For larger molecules, the number of possible structures grows to the point where only a general class can be given for the molecule, i.e., the D4 class with its 5 different possible structures. For the largest molecules, even determining the general class is not usually feasible because multiple classes are possible, i.e., L4(O), Bis(Disilane)-L5OH, and Bis(Disilane)-D5(O) all have the same mass. From the observation made for the various siloxane parent molecules, the order of elution of the siloxanes from the GCMS follow these general rules (In the form: elutes first > elutes second > etc.): 1) n= 1 > 2 > 3 > etc. 2) Dn > Dn class > Ln class > Ln 3) (Silane) > (Silane)(OH) > (Silane)(OH)2 > (Silane)(OH)3 > etc 4) Addition of multiple OH groups can cause a violation of rules 1) and 2) 5) For larger n, Dn class > Ln class may be violated for highly linear Dn and highly branched Ln siloxanes 6) Dn > Ln(X) > D(n+1) where Ln(X) is an exotic structure 7) Dn > Dn(X) > D(n+1) where Dn(X) is an exotic structure

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E. Other Lamps Studied Because of the potential toxicity of a Hg lamp, alternative short wavelength UV lamps have been investigated. A Cd and a Zn lamp have been purchased and initially studied. However, due to time constrains, only an initial, very- quick investigation has been allowed. The Zn and Cd lamps could not be used in the gas phase setup described above. An alternative “quick and dirty” setup was constructed. The results are of a limited but hopeful nature. The new setup was first tested with the 185 nm Hg lamp as a point of reference. However, in the new setup, the Hg lamp only showed the production of L2OH from L2 with no evidence of any other products. The reason for this limited result is currently unknown. However, the Zn and Cd lamps also produced the L2OH in the same relative intensity and as such, it is believed that either the Zn or Cd lamp could potentially be a viable alternative to the Hg lamp.

F. Effect of radiation energy on Siloxane degradation The effect of radiation energy on the degradation of siloxanes has also been investigated. The use of the 254 nm and 185 nm Hg lamps and the MS gives the results of three different degradation energies. In electron volts, the 254 nm line is 4.9 eV, the 185 nm line is 6.7 eV, and the MS produces a 70 eV electron, which fragments the siloxane into the mass spectrum. Since only D3, D4, and D5 are observed on the ISS, this gives indirect evidence to the energy of the process which is producing them. For example, if the siloxanes were being produced directly from high energy radiation, then the results would be very similar to what is observed in the MS: the siloxane molecule would be completely blown apart into numerous small fragments. Additionally, if the siloxanes were being produced from the secondary radiation, such as x-rays, electrons, or other high energy particles resulting from the collision of galactic radiation with the ISS, this would also produce highly fragmented siloxanes. If, however, the energy of the radiation or particles driving the siloxane chemistry was on the order of 5 to 10 eV (short wavelength UV, or soft ionization), then, as observed in this study, the siloxanes could grow into larger moieties and the cyclic siloxanes, Dn, would be the dominant product.

IV. Conclusion The exposure of siloxanes to short wavelength UV results in the transformation of those siloxanes into progressively larger, more complex moieties which eventually become multi-cyclic with a reduced number of methyl groups. Eventually these moieties become “glassified” and attached to a surface, removing them from the gas phase. This process has the potential of being modified such that it could be used to remove the siloxanes from the cabin air of the ISS or other NASA missions.

8 International Conference on Environmental Systems Appendix A A list of the various known siloxanes produced from the UV treatment of the parent siloxane.

Known Identifications L4 D4 Class 9.63 Parent Identification Time L3 (1,2 or 1,3) 9.68 D3, D4, D5, Formaldehyde 2.53 D4-Bis(Disilane) B4, B5 L3 (1,2 or 1,3) D4-Disilane 9.76 D3, D4, D5 Methanol 2.84 L3 (1,2 or 1,3) 9.83 D3, D5, L2, Formic Acid 3.76 D4-Bis(Disilane) L3, D4, B5, L3 (1,2 or 1,3) D4-Disilane 9.83 L4, L5 L2, B5, L5, B4 (Standard) 9.89 L2, L3 Methoxy-L1 4.41 L3, D4, L4, B4, B5, L5, L1OH 4.48 B4 D4 B5, L5, L2, L4 (Standard) 10.04 D3, L4 Acetic Acid 4.53 L3 L2, L3 L1OH 4.63 L4 L4OH or 10.13 L3 L1-formate 5.39 BisDisilane-D5(OH) L2, B5 L2 (Standard) 5.85 L3 L4-Bis(Disilane) 10.31 D4, D5 L1(OH)2 5.90 L4 L4OH or 10.33 L2 Bis(L1) peroxide 6.99 BisDisilane-D5(OH) L2, L5, L4, L3, L2OH 7.17 D4 L4OH or 10.42 D4 BisDisilane-D5(OH) L2, B5, L5, D3 (Standard) 7.54 B5 D5-Dicyclic or 10.48 L3, D3, L4, L5-Disilane-OH D4 L2, L4, L3, D4OH 10.49 L4, L3, D3 D2-L1 7.61 D4, D5 L2 D3-Disilane 7.85 L4 L4OH or 10.57 B5, L3, L2 L3 (Standard) 8.18 BisDisilane-D5(OH) L3 1,1-OH-L2 8.34 L4 L5-Bis(Disilane)-OH 10.65 L3, L4 1,2-OH-L2 8.44 L3 1,1-L1-D2 10.65 L3, D3 L3OH 8.62 D4 L4OH or 10.66 L3 L3(OH)3 8.81 BisDisilane-D5(OH) L2, L4, D3, D3OH 8.93 B4 1,1-L1-D2 10.72 D4, D5 L2, L5, L4, D5-Dicyclic or 10.76 L3 L3-O 8.95 D3, D4 L5-Disilane-OH L3 L3-O 9.09 L2, D4 Bis(Disilane)-L5OH or 10.79 Bis(Disilane)-D5(O) or L2, L3, L4, D4 1-OH-L3 9.17 L4(O) L2, L4, L3 2-OH-L3 9.23 L2, L3, L5, L2, 1,2-L1-D2 10.83 L2, L5, L4, D4 (Standard) 9.33 B4 L3, D3, D4, L4 L4OH or 10.84 D5 BisDisilane-D5(OH) D4 Dicyclic-D4 9.49 L5, L4, D3, D5 (Standard) 10.88 B5, L2, L5, L4, L1-D3 9.58 D4, L2, D5, L3, B4, D4 L5, L3

9 International Conference on Environmental Systems L2 iso-B5 or 10.92 12.37, D6-Bis(Disilane) 12.45 B5 D5 Class (1,1-DiL1-D3 or 11.01 L3 D5-Dicyclic 12.04 1,1,1-TriL1-D2) L5, B5 L6-Bis(Disilane)-OH 12.06, L3 D4 w/267 11.04 12.09, D4 D4OH Class 11.07 12.23, 12.85 B5, L5, L2 D5 Class 11.10 L2 D5-Dicyclic or 12.07 D4 D4OH Class 11.16 L5-Disilane-OH L2, L5, L3 D5 Class 11.19 D3 Disilane-D5 12.08 B5 B5 (Standard) 11.19 D4 Dicyclic-D5-(OH)1 12.13 L3 D4-Disilane 11.32 D4 Bis(Disilane)-L5OH or 12.15 L4 D5-Disilane 11.35 Bis(Disilane)-D5(O) or D4 L4OH or 11.39 L4(O) Bis(Disilane)-D5OH L3 D5-Dicyclic 12.18 D4 Dicyclic-D4 or 11.40 L2 D6 Class 12.19 Disilane-L4OH or D5 Dicyclic-D5OH with 12.24 L4OH Class missing 343 w/ missing 297 D5 Disilane-D5(OH) 12.24 L5, L3 iso-L5 11.46 D5 Dicyclic-D5OH 12.40 L4, D4 D5-Disilane 11.49 B5, L5, L2, L3 D6-Disilane 12.40, L4 L5-Disilane 11.55 12.72, 12.90 L2, L4, L3, L5 (Standard) 11.59 L5 D5 Class 12.45 L5 L2 D6 Class 12.47 B5 L5OH 11.66 D5 Dicyclic-D5OH 12.48 D5 Disilane-D5(OH)2 11.67 D5 Dicyclic-D5OH with 12.51 B5 D5-Dicyclic or 11.70 missing 343 L5-Disilane-OH L5, L3 D5 Class or 12.54, B5 D5 Class 11.76 Disilane-L5(O) 12.71, B5 L5OH or 11.81 12.79, D6-Bis(Disilane)-OH 12.89, L4 L5-Bis(Disilane)-OH 11.81 13.10 B5 D5 Class 11.84 L5 D6-Disilane or 12.68 D5 Class D4 Disilane-D5-(OH)1 11.84 L4 D5-Disilane 12.72 L2, L5 L6-Bis(Disilane) 11.94 L2 D5-Dicyclic or 12.97 L3 D5-Dicyclic or 11.98 L5-Disilane-OH L5-Disilane-OH or D5 Disilane-D5(OH)2 13.01 (w/327 D5-Disilane-OH) D4 Disilane-D6(OH) 13.99 D4 Bis(Disilane)-L5OH or 14.02 Bis(Disilane)-D5(O) or L4, L5, L3, L5 D5-Dicyclic or 11.99, L4(O) L5-Disilane-OH 12.18, D4 Bis(Disilane)-L6(OH)2 14.28 12.23, D4 D5 Class or 14.62, 12.28, Disilane-L5(O) 15.05

10 International Conference on Environmental Systems B5 D6-Disilane or 15.71 B5 L5 (strong 369) 16.56 D5 Class

Appendix B A list of the various unknown siloxanes produced from the UV treatment of the parent siloxane.

Unknown B5 341 12.03 Identifications L3 D5-Dicyclic w/327 12.08 Parent Identification Time B5 384,369 12.17 D4 D4(OH)2 or 9.00 D5 385, 341, 325, 267, 252, 12.20 Disilane-L4(O)(OH)2 253, 223, 73, 75 L3 D4 Class or 9.17 B5 267, 207, 73, 281 12.48 L4-Disilane-O B4 281, 207, 73 12.64 L3 D4 Class or 9.24 B4 341, 327, 295,…, 73 14.96 L4-Disilane-O D3 Unidentified Bands 10.76, B4 L3OH 9.29 11.57, L3 236, 221, 193, 191, 177 9.31 11.64, L2 221, 207, 191 9.77 11.86, 11.99, L2 295, 267, 251, 207 10.67 12.37, B4 L4 Class 10.68 12.92 D5 341, 325, 311, 10.78 L2 Unidentified Bands 10.86 295,….,73 L3 Unidentified Bands 13.19, L3 310, 295, 267, 275, 251, 10.99 13.29, 249 13.39, L3 D4 w/251 11.14 13.57, L4 L4 Class 11.29 13.78, 13.95 D5 371, 283, 267, 89, 73 11.52 L4 Unidentified Bands 11.10, D5 341, 343, 325,327, …, 11.71 11.21 73,75 L5 Unidentified Bands 11.26 D5 341,327,325,329,73 12.02 B5 Unidentified Bands 12.10

11 International Conference on Environmental Systems Appendix C GCMS Method

The GCMS method used: a Perkin Elmer Elite-5ms, 60m x 0.25mm x 1um column; He carrier gas; a heating profile of a 1 min hold at 30oC, followed by a 20oC/min ramp to 300oC, followed by a 5.5 min soak at 300oC; the line, source, and A-CAP temperatures were all 250oC; and a 1:10 split.

Headspace Method

The Headspace Method used: 200oC oven temperature; a 5 minute oven soak at 200oC; a vial pressurization to 42 psi; a 1 minute soak at 42 psi; a 0.01mL ca. injection volume; and a 210oC transfer line temperature.

Acknowledgments The authors would like acknowledge the AES Water Program for financial support.

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