PVA Polymer

Article pubs.acs.org/JPCA

Photogeneration of H2O2 in Water-Swollen SPEEK/PVA Polymer Films PaviElle Lockhart,† Brian K. Little,†,§ B. L. Slaten,‡ and G. Mills*,† †

Department of Chemistry and Biochemistry, ‡Department of Consumer and Design Sciences, Auburn University, Alabama 36849, United States S Supporting Information *

ABSTRACT: Efficient reduction of O2 took place via illumination with 350 nm photons of cross-linked films containing a blend of sulfonated poly(ether etherketone) and poly(vinyl alcohol) in contact with air-saturated aqueous solutions. Swelling of the solid macromolecular matrices in H2O enabled O2 diffusion into the films and also continuous extraction of the photogenerated H2O2, which was the basis for a method that allowed quantification of the product. Peroxide formed with similar efficiencies in films containing sulfonated polyketones prepared from different precursors and the initial photochemical process was found to be the rate-determining step. Generation of H2O2 was most proficient in the range of 4.9 ≤ pH ≤ 8 with a quantum yield of 0.2, which was 10 times higher than the efficiencies determined for solutions of the polymer blend. Increases in temperature as well as [O2] in solution were factors that enhanced the H2O2 generation. H2O2 quantum yields as high as 0.6 were achieved in H2O/CH3CN mixtures with low water concentrations, but peroxide no longer formed when film swelling was suppressed. A mechanism involving reduction of O2 by photogenerated α-hydroxy radicals from the polyketone in competition with second-order radical decay processes explains the kinetic features. Higher yields result from the films because cross-links present in them hinder diffusion of the radicals, limiting their decay and enhancing the oxygen reduction pathway.

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INTRODUCTION Photosensitive polymers remain a subject of investigation in view of their capacity to employ light as an energy source for initiating reactions. Much of the available knowledge pertains to the ability of these polymers to transform themselves via photoprocesses, which have resulted in important scientific and technological advances.1−3 Macromolecules able to initiate transformations of other compounds are also attractive because polymeric sensitizers can, in principle, be made compatible with both fluid and solid matrices. For instance, polymers containing benzophenone (BP) as a sensitizer can generate singlet oxygen, 1 O2, and incorporate oxygen-containing functionalities into organic compounds in solution.4,5 Solid-state initiators of various photoreactions including oxidation have been obtained through the binding of BP to polystyrene beads.6,7 Polymeric sensitizers that generate 1O2 have been used to induce oxidation of toxic chemicals.8,9 Macromolecular systems containing unstable, high energy species are envisioned to function as protective barriers, for instance in reactive clothing that chemically inactivates toxins and pathogens.10 Protective barriers based on polymeric sensitizers that photogenerate reactive intermediates constitute an attractive approach to realize “self-cleaning fabrics” as they can regenerate the active species via exposure to light. Examples of such systems are macromolecules containing sensitizers that exhibit antibacterial capabilities due to photogeneration of reactive 1O2;11 fabrics and fibers containing bonded BP have also been reported to inactivate pathogens upon irradiation.12 © XXXX American Chemical Society

Utilization of H2O2 as a reactive species seems worth considering since this chemical is the active ingredient in methodologies that degrade several chemical warfare agents,13,14 and also because the peroxide exhibits an effective biocidal activity against a wide spectrum of organisms and spores.15 O2 photoreduction was performed with swollen methacrylate gels that contained anthraquinone (AQ) as a sensitizer but peroxide generation occurred via a slow postirradiation process with a quantum yield of formation, ϕ(H2O2), equal to 0.08.16 Illumination of fibers containing bonded AQ also yielded H2O2 but the sensitizer was hydroxylated by reaction with the peroxide.17 This is not unusual given that numerous photosensitive polymers undergo self-induced photoreactions leading to irreversible transformations.3 Obviously, a desirable characteristic of macromolecular sensitizers suitable for protective barriers is stability under photolysis. Incorporation of the sensitizer tris(2,2′bipyridine)ruthenium(II) into water-swollen iminodiacetic acid-type chelate resins yielded a robust system for the photogeneration of H2O2.18 Stable systems were also achieved via deposition of porphyrins on polymer films, which generated peroxide with ϕ(H2O2) = 0.01 upon photolysis in contact with aqueous solutions containing oxygen.19 Received: January 14, 2016 Revised: April 18, 2016

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potassium hydrogen phthalate, KH2PO4, Na2B4O710·H2O, NaOH, HPLC grade CH3OH, and CH3CN, H2SO4, HClO4, and H2O2 (30% v/v) were purchased from Fisher Scientific. Samples of poly(ether etherketone), PEEK, were provided as gifts by Victrex (APTIV 1000-075, average molar mass of Mn = 4.5 × 104 g/mol) and Evonik (VESTAKEEP L4000G, Mn = 5 × 104 g/mol). PEEK served as a precursor of the sodium salt of SPEEK, and the samples consisted of sheets that were cut into strips, followed by grinding into a powder and then drying under vacuum at 100 °C for 6 h. All solutions were prepared with water purified by a Milli-Q Biocel system. Unless otherwise stated, all experiments were conducted at room temperature, 23 °C. Large batches (∼150 g) of PEEK from Victrex were sulfonated using the method described in detail previously.22 Sulfonation of PEEK from Evonik was accomplished using smaller batches (∼10 g) dispersed in H2SO4 at a concentration of 30% w/v of the dried powders. The dispersions were heated at 50−55 °C under constant stirring for up to 10 days; isolation of the resulting sodium salt of sulfonated PEEK was performed as indicated previously.22 Owing to the smaller amount of PEEK treated, complete dissolution (indicating substantial sulfonation) was achieved after a few days of reaction. Characterization of the SPEEK samples followed standard procedures,26 including 1H and 13C NMR determinations in DMSO-d6 solutions, FTIR measurements in the transmission mode with KBr pellets, and elementary analysis performed by Atlantic Microlab, Atlanta, Georgia. SPEEK/PVA films cross-linked with GA were made according to a slightly modified version of the previous casting procedure.21 Films with compositions of 30/70 SPEEK/PVA wt % (neglecting the small amount of glutaraldehyde incorporated) were obtained from mixtures of SPEEK and PVA aqueous solutions with concentrations of 1.5 and 3.6% w/ v, respectively, that also contained 1% (0.1 M) GA and 0.1 M HCl. The lower SPEEK and PVA concentrations used in the present study enabled the preparation of films with a wider range of thicknesses that were reproducible and uniform. Films containing only PVA were made via an analogous procedure excluding SPEEK. Determinations of film thickness used a digital micrometer Mitutoyo model 1″ SFB; unless otherwise stated, the dimensions (when dry) of films employed for irradiations were 50 (±6) μm in thickness, 2.5 cm in width, and a surface area of between 11 and 16 cm2. The masses of dry and also of swollen films were determined gravimetrically. Swelling experiments were performed in the absence of light via immersion of individual cross-linked films in Petri dishes containing H2O at the natural pH (∼5.4). The procedures to conduct illuminations and measurements of light intensity (I0) by means of the Amberchrome 540 actinometer were described in detail previously.20 Every photochemical experiment was performed at least twice and under constant stirring. Swollen SPEEK/PVA films were susceptible to rolling on themselves and also to rupturing under mechanical stress. To avoid such problems, special irradiation vessels made from borosilicate glass served as photoreactors. The vessels featured a vertically located glass tube that enabled fixing the films in a fully extended position throughout the experiments. Provided in the Supporting Information (SI) section are the dimensions as well as an image of a photoreactor (Figure S1), together with a diagram specifying the film location in the irradiation vessel (Figure S2). Prior to illumination the films were swollen for 1 h inside the

Recently, formation of hydrogen peroxide was reported to occur with ϕ(H2O2) = 0.02 when poly(vinyl alcohol), PVA, together with the sodium salt of sulfonated poly(ether etherketone), SPEEK, was irradiated in air-saturated aqueous solutions.20 The polymer mixtures generate α-hydroxy radicals from SPEEK (or SPEEK·) upon photolysis with 350 nm photons,21,22 and H2O2 originates from the O2 reduction by the macromolecular radicals. SPEEK/PVA mixtures act as polymeric analogues of the BP/2-propanol system, known to undergo efficient photochemistry in solution.23 SPEEK· results from the light-induced formation of a triplet (n, π*) excited state of BP groups present in SPEEK. Such an excited state can then abstract an H atom from PVA forming a α-hydroxy radical of SPEEK. Concurrently formed is a PVA α-hydroxy radical that can reduce another BP group from SPEEK, yielding up to two SPEEK· per absorbed photon. Photogeneration of SPEEK· also takes place upon photolysis of films made by casting homogeneous mixtures, or blends, of SPEEK and PVA followed by cross-linking of the polyol.21 These photoreactive films operate for extended periods of time in the presence of chemicals that oxidize SPEEK·, thereby reforming the polyketone photosensitizer. The previous solution study on peroxide photogeneration by SPEEK/PVA mixtures yielded useful mechanistic information and avoided the problems associated with product quantification in solid samples such as films.20 However, realistic assessments on the ability of SPEEK/PVA films to serve as light-activated protective barriers require quantitative information about their capability to produce H2O2. Quantification of reactions involving polymer films has been demonstrated using a medium (fluid or gas) able to facilitate extraction of products from the solid matrix.24 Presented in this report are kinetic data from experiments using cross-linked SPEEK/PVA films that were immersed into air-saturated aqueous solutions during irradiations. Efficient transport of O2 into the films was anticipated as they swell significantly in water, which, in turn, was expected to enable fast O2 reduction by SPEEK· formed throughout the polymer matrix. In contrast, SPEEK radicals generated within dry films under air persist for several hours due to the low radical mobility and slow O2 diffusion in the solid blends.21 Several additional advantages existed when swollen SPEEK.PVA films were utilized, including a thermodynamic driving force for the O2 reduction similar to that of aqueous solutions. In water E0(O2/·O2−) corresponds to −0.33 V at pH = 7,25 whereas SPEEK· is a strong reducing agent exhibiting an oxidation potential of 1.2−1.4 V.22 Water-filled SPEEK/PVA films were anticipated to provide an environment somewhat akin to that of aqueous solutions, meaning that no drastic changes in the driving force of the O2 reduction were expected for such systems. Another benefit was the ability of continuously extracting hydrogen peroxide from the films, enabling the use of conventional analytical methods for [H2O2] quantification. Significantly higher quantum yields for H2O2 photogeneration were obtained in the present study as compared with those of homogeneous solutions,20 highlighting the efficiency of the O2 reduction in swollen SPEEK/PVA films.

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EXPERIMENTAL SECTION Poly(vinyl alcohol), 99% hydrolyzed with an average molar mass of 8.9−9.8 × 104 g/mol as well as ammonium molybdate (VI) tetrahydrate, glutaraldehyde (GA, 25 wt % solution), and dimethyl sulfoxide (d6) were obtained from Sigma-Aldrich. KI, B

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The Journal of Physical Chemistry A irradiation vessel to ensure that the equilibrium volume was reached. A side arm, located near the bottom of the photoreactor and sealed with a septum, served to retrieve aliquots of the photolyzed solution for analysis. Tests using methylene blue as an indicator of the flow of chemicals ensured that transport of H2O2 from the films into the solution took place immediately after peroxide generation; details of the procedure are provided in the SI section. Experiments at different temperatures employed a Fisher Isotemp 9500 bath circulator connected to a photoreactor equipped with a water jacket. Optical spectra were recorded on a Shimadzu UV−vis 2501PC spectrophotometer and NMR data were collected on a Bruker Avance 400 MHz instrument. FTIR spectra were acquired by means of a Shimadzu IR-Prestige-21 spectrometer, whereas differential scanning calorimetry (DSC) data were obtained using a Mettler Toledo FP90 instrument equipped with a FP84HT hot stage. Determinations of [H+] employed a Radiometer PHM95 pH/ion meter in conjunction with an Accumet electrode. Buffers containing ∼10−3 M of salts maintained desired pH values during photolysis as they were found to exhibit no adverse effects during the H2O2 generation in earlier experiments with SPEEK/PVA solutions.20 [H2O2] was quantified by means of the spectrophotometric molybdenum-triiodide method.27 Small aliquots of the illuminated solutions were mixed under stirring with 1 mL of a 0.1 M potassium biphthalate solution and 1 mL of a mixture containing 0.4 M KI, 2 × 10−4 M (NH4)2MoO4, and 0.06 M NaOH in a 1 cm quartz optical cell, followed by dilution to 3 mL. Because the aliquots were diluted extensively with H2O, no interferences in the peroxide detection due to CH3CN were noticed when films were photolyzed in H2O/CH3CN mixtures. The optically determined [H2O2] was then corrected for the decrease in solution volume due to sample withdrawal from the photochemical reactor. Evaluation of the rates of peroxide photogeneration inside the films used the factor Df = V(solution)/V(film) where V(solution) is the solution volume (33 mL) while V(film) represents the volume of the swollen film. Df corrects for the dilution resulting from H2O2 transport from the swollen polymer matrices into solution. The corrected rate of peroxide formation within the film, rc(H2O2), was then obtained from the equation: rc(H2O2) = Df r(H2O2), where r(H2O2) was evaluated from the changes in [H2O2] as a function of irradiation time. Quantifications of [H2 O 2 ] via the I3 − procedure exhibited a typical error of 1 for smaller films, but decreased to reach values smaller than 1 for the largest solid samples. Such change was most likely related to the smaller swell ratio ( 8 only partially originated from quenching of 3{R′RC O}z by OH−. Although the stability of H2O2 decreases at pH ≥ 9,48 the thermal decay of the peroxide is not fast enough to H

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The Journal of Physical Chemistry A Nevertheless, the data indicated that modest changes in T induced no detrimental effect on the H2O2 photogeneration. While swelling of SPEEK/PVA films enabled extraction and detection of the peroxide, incorporation of H2O into the polymer matrices negatively affected their sturdiness. Additional tests using H2O/CH3CN mixtures were carried out to determine if the presence of water in the films was necessary for the formation of H2O2. CH3CN was selected as a suitable replacement of H2O since the O2 photoreduction in the aqueous BP/2-propanol system was not affected by acetonitrile.42 Figure 7 depicts the evolution of ϕ(H2O2) as a function of H2O content in water/acetonitrile mixtures for SPEEK/PVA films with a thickness of 40−50 μm. Efficiencies of peroxide generation of 0.067−0.064 were determined at water mole fractions of 0.964−0.9. These quantum yields were about 3 times lower than the value obtained in neutral solutions, see Figure 6. A higher and nearly constant ϕ(H2O2) of about 0.1 resulted upon further decreases of the water mole fraction to 0.392. While small amounts of CH3CN affected the O2 photoreduction, mole fractions of the organic solvent up to 0.608 induced no change in the swelling of SPEEK/PVA films. In contrast, mixtures with CH3CN mole fractions >0.608 inhibited film swelling completely, and no H2O2 was detected after photolysis. Efforts to extract any H2O2 possibly trapped in the films by swelling them in water after illumination were also unsuccessful. The trends depicted in Figure 7 for the thicker films can be explained in terms of two competing effects that result when CH3CN is added to H2O. Solvent mixtures with decreasing dielectric constant are obtained upon systematic incrementing the CH3CN concentration in water.50 However, altering the properties of the reaction medium can lead to important kinetic consequences, for instance, decreasing the solvent polarity negatively affects the rate of reactions involving polar compounds.51 Given that several polar intermediates participated in the H2O2 formation, the initial ϕ(H2O2) decrease noticed in Figure 7 was probably a consequence of lowering the solvent polarity. On the other hand, the O2 solubility also changes when the solvent composition is altered. Values of 1.7−2.4 mM have been reported for [O2] in CH3CN saturated with air.52,53 In contrast, the solubility of oxygen in air-saturated SPEEK/PVA solutions amounted to 0.26 mM.20 While the solubility of O2 in H2O/CH3CN mixtures of different compositions remains unavailable, this quantity is expected to rise with increasing CH3CN concentration. Hence, the larger ϕ(H2O2) value shown in Figure 7 for CH3CN mole fractions >0.254 reflected the increasing rates of step 8 due to the systematic [O2] increases when the H2O concentration decreased. The nearly constant ϕ(H2O2) value in the H2O concentration range of 0.746−0.392 most probably resulted because the two competing kinetic effects counterbalance each other. Included in Figure 7 are data gathered using 30−40 μm thick films, showing that similar quantum yields of H2O2 generation were obtained using SPEEK prepared from either Evonik or Victrex precursors. Utilization of thinner films was anticipated to enhance transport of O2 to the radical chains since swelling in water was more pronounced for thinner films (see Figure 1), a phenomenon also observed in the H2O/CH3CN mixtures. In analogy to the findings with the thicker films, a low ϕ(H2O2) value of 0.03 was determined at the highest water mole fraction (0.964). However, the quantum yields increased rapidly with decreasing H2O concentration to reach maxima of 0.5−0.58 at

a water mole fraction of 0.392. As before, no changes in the swelling behavior of the SPEEK/PVA films occurred for CH3CN mole fractions ≤0.608. Film swelling or H2O2 photogeneration were not observed at higher acetonitrile concentrations, also in good agreement with the behavior of thicker films. The findings of experiments with H2O/CH3CN mixtures demonstrated that water needed to be present in the films for H2O2 to be produced by light. Indeed, no H2O2 was formed at CH3CN mole fractions >0.608, at which the swelling by H2O was completely inhibited irrespective of film thickness. O2 diffusion into solid PVA samples is possible only if they contained adsorbed water;35 a similar situation occurs for SPEEK/PVA films since they consist mainly of the polyol. In the absence of swelling the films contained only small amounts of H2O and, therefore, not enough O2 to sustain an efficient peroxide generation. Another significant observation was that for water mole fractions of 0.746−0.392 the thinner films outperformed their thicker counterparts by a factor of at least 5. Such a large increase in performance is hard to reconcile with the rather modest difference in swelling (20%, Figure 1) between the two types of films. However, increases in the amount of liquid diffusing into the films can also change the distance between functional groups of SPEEK chains. BP groups achieve close proximity via coiling of an SPEEK chain, or when two polyelectrolyte chains are next to each other. In both cases the photochemical efficiency of SPEEK is foreseen to decrease. The reason is that 3BP* is quenched efficiently by BP molecules, kq = 1.8 × 108 M−1 s−1,39 an analogous selfquenching of 3{R′RCO}z* is anticipated for SPEEK systems. Increases in swelling diminish the local concentration of BP groups from SPEEK, decreasing the probability of selfquenching. Thus, the higher photochemical activity of thinner films shown in Figure 7 originated from their more pronounced swelling, which increased the [O2] available for reduction and decreased the self-quenching experienced by excited SPEEK chains. Other significant findings of the experiments with H2O/ CH3CN mixtures were quantum yields closer to the theoretical maximum efficiency. According to the proposed reaction mechanism ϕ(H2O2) = ϕ(3{R′RCO}z*, meaning that formation of the triplet excited state of SPEEK occurred with efficiencies (0.5−0.58) approaching the quantum yield of 1 determined experimentally for BP and pVBP.23,40 Such ϕ(3{R′RCO}z* values are significantly higher than those derived from solution data.20,22 These findings support our earlier interpretation that the low quantum yields derived from solution systems reflected mainly the small amount of macromolecular radicals able to survive step 9.

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CONCLUSIONS The present study showed that H2O2 was produced upon illumination of cross-linked SPEEK/PVA films swollen by airsaturated aqueous solutions. A method based on continuous extraction of peroxide provided quantitative data on the heterogeneous reduction of O2 dissolved in H2O by polymer radicals bound to the solid network. The swollen SPEEK/PVA solid matrices exhibited much higher H2O2 quantum yields as compared with those reported earlier for several films and also aqueous polymer solutions.16,19,20 Even higher efficiencies that approached the theoretical maximum were obtained in solvent mixtures exhibiting an O2 solubility higher than that of H2O. These kinetic results are consistent with a modified mechanism I

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described here was supported by NTC through contract C06AC01.

involving competition between the O2 reduction step and radical−radical decay processes. Cross-links present in the solid macromolecular matrices restricted the diffusion of radicals and hindered second-order radical decay processes. The film findings support our hypothesis that the lower solution quantum yields originated from the fast radical−radical decay reactions occurring in homogeneous systems.20,22 H 2O 2 photogeneration is an important feature for potential uses of SPEEK-based films as reactive barriers since the peroxide can attack toxins and microorganisms in the absence of light. In this way the protective ability of such films can be extended to periods where no light is available to induce formation of reactive radicals. Furthermore, the presence of both H2O2 and SPEEK· in the films is attractive given that the simultaneous attack of reducing and oxidizing agents was shown to be particularly effective, possibly via a synergistic action, against toxic chemicals that are resistant to oxidative degradation.54 Another important finding was that only water-swollen films were able to photogenerate hydrogen peroxide. The most probable reason for such a behavior is the inability of O2 to permeate into the dry solid polymer blends as was found in the case of PVA films.35 Hence, SPEEK-based films suitable to function as reactive barriers will need to contain some polymeric component able to adsorb water from air. In this way partial swelling of the films will enable them to incorporate enough O2 to induce efficient H2O2 photogeneration. At the same time, further improvements in the mechanical properties of the films must be achieved via enhanced cross-linking.

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(1) Ishimura, K. In Organic Photochromic and Thermochromic Compounds; Crano, J. A., Guglielmetti, R. J., Eds.; Kluwer/Plenum: New York, 1999; Vol. 2, Chapter 1. (2) Reiser, A. Photoreactive Polymers: The Science and Technology of Resists; Wiley-Interscience: New York, 1989. (3) Guillet, J. Polymer Photophysics and Photochemistry; Cambridge University Press: Cambridge, 1985; Chapters 9 and 10. (4) Koizumi, H.; Shiraishi, Y.; Hirai, T. Temperature-Controlled Photosensitization Properties of Benzophenone-Conjugated Thermoresponsive Copolymers. J. Phys. Chem. B 2008, 112, 13238−13244. (5) Koizumi, H.; Shiraishi, Y.; Fujitsuka, M.; Majima, T.; Tojo, S.; Hirai, T. Temperature-Driven Oxygenation Rate Control by Polymeric Photosensitizer. J. Am. Chem. Soc. 2006, 128, 8751−8753. (6) Nishikubo, T.; Kondo, T.; Inomata, K. Study of Polymeric Photosensitizers. 5. Synthesis of Multifunctional Photosensitizers Bonded on Cross-Linked Polymer Beads and Their Application for Photoisomerization of Potassium Sorbate. Macromolecules 1989, 22, 3827−3833. (7) Bourdelande, J. L.; Font, J.; Sánchez-Ferrando, F. The use of Insoluble Benzoylated Polystyrene Beads (Polymeric Benzophenone) in Photochemical Reactions. Can. J. Chem. 1983, 61, 1007−1016. (8) Nowakowska, M.; Kepczynski, M.; Szczubialka, K. New Polymeric Sensitizers. Pure Appl. Chem. 2001, 73, 491−495. (9) Nowakowska, M.; White, B.; Guillet, J. E. Studies of the Antenna Effect in Polymer Molecules. 12. Photochemical Reactions of Several Polynuclear Aromatic Compounds Solubilized in Aqueous Solutions of Poly(sodium styrenesulfonate-co-2-vinylnaphthlene). Macromolecules 1989, 22, 2317−2324. (10) Schreuder-Gibson, H.; Truong, Q.; Walker, J. E.; Owens, J. R.; Wander, J. D.; Jones, W. E., Jr. Chemical and Biological Protection and Detection in Fabrics for Protective Clothing. MRS Bull. 2003, 28, 574−578. (11) Ji, E.; Corbitt, T. S.; Parthasarathy, A.; Schanze, K. S.; Whitten, D. G. Light and Dark-Activated Biocidal Activity of Conjugated Polyelectrolytes. ACS Appl. Mater. Interfaces 2011, 3, 2820−2829. (12) Sun, G.; Hong, K. H. Photo-induced Antimicrobial and Decontaminating Agents: Recent Progress in Polymer and Textile Applications. Text. Res. J. 2013, 83, 532−542. (13) Wagner, G. W.; Sorrick, D. C.; Procell, L. R.; Brickhouse, M. D.; Mcvey, I. F.; Schwartz, L. I. Decontamination of VX, GD, and HD on a Surface Using Modified Vaporized Hydrogen Peroxide. Langmuir 2007, 23, 1178−1186. (14) Wagner, G. W.; Yang, Y.-C. Rapid Nucleophilic/Oxidative Decontamination of Chemical Warfare Agents. Ind. Eng. Chem. Res. 2002, 41, 1925−1928. (15) McDonnell, G.; Russell, D. Antiseptics and Disinfectants: Activity, Action and Resistance. Clinical Microbiol. Rev. 1999, 12, 147− 179. (16) Foyle, V. P.; Takahashi, Y.; Guillet, J. A. Photocatalytic Production of Hydrogen Peroxide Using Polymer Bound Anthraquinone. I. Photoproducts in 2-Hydroxyethyl Methacrylate Hydrogels Swollen with Water and 2-Propanol. J. Polym. Sci., Part A: Polym. Chem. 1992, 30, 257−269. (17) Liu, N.; Sun, G.; Zhu, J. Photo-induced Self-cleaning Functions on 2-Anthraquinone Carboxylic Acid Treated Cotton Fabrics. J. Mater. Chem. 2011, 21, 15383−15390. (18) Kurimura, Y.; Nagashima, M.; Takato, K.; Tsuchida, E.; Kaneko, M.; Yamada, A. Photoredox Reactions Using Ion-Exchange ResinAdsorbed Ru(bpy)32+. Photosensitized Reductions of Methyl Viologen and Molecular Oxygen Using Ion-Exchange Resin-Adsorbed Tris(2,2′bipyridine)ruthenium(II). J. Phys. Chem. 1982, 86, 2432−2437. (19) Schlettwein, D.; Kaneko, M.; Yamada, A.; Wöhrle, D.; Jaeger, N. I. Light-Induced Dioxygen Reduction at Thin Films Electrodes of Various Porphyrins. J. Phys. Chem. 1991, 95, 1748−1755.

ASSOCIATED CONTENT

* Supporting Information S

Presented in . The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/ acs.jpca.6b00442. Figure S1, image of the custom-built Pyrex photoreactor; a thorough description of the vessel parts; Figure S2, topview representation of the film positioning within the irradiation vessel; image of the photoreactor containing a dye solution to highlight the position of the SPEEK/PVA films; Table S1, characterization results concerning the degree of sulfonation achieved after reaction of Evonik PEEK with H2SO4 for different times (PDF)

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Present Address §

B.K.L.: University of Dayton Research Institute, U.S. Air Force Research Laboratory, Eglin AFB, Florida 32542−5910, United States. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are grateful to R. Leibfried (Victrex USA Inc.) and to J. Scherble (Evonik, Germany) for generous gifts of PEEK samples. We thank Md. S. Islam for his help during DSC determinations, R. Blumenthal for useful discussions, and D. Berry (Berry Industrial) for his continuous advice and support. Acquisition of the DSC instrumentation was made possible by an Auburn University OVPR&ED Intramural Grant. The work J

DOI: 10.1021/acs.jpca.6b00442 J. Phys. Chem. A XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry A (20) Little, B. K.; Lockhart, P.; Slaten, B. L.; Mills, G. Photogeneration of H2O2 in SPEEK/PVA Aqueous Polymer Solutions. J. Phys. Chem. A 2013, 117, 4148−4157. (21) Korchev, A. S.; Konovalova, T.; Cammarata, V.; Kispert, L.; Slaten, B. L.; Mills, G. Radical-Induced Generation of Small Silver Particles in SPEEK/PVA Polymer Films and Solutions: UV-Vis, EPR, and FT-IR Studies. Langmuir 2006, 22, 375−384. (22) Korchev, A. S.; Shulyak, T. S.; Slaten, B. L.; Gale, W. F.; Mills, G. Sulfonated Poly(Ether Ether Ketone)/Poly(Vinyl Alcohol) Sensitizing System for Solution Photogeneration of Small Ag, Au, and Cu Crystallites. J. Phys. Chem. B 2005, 109, 7733−7745. (23) Gilbert, A.; Baggott, J. Essentials of Molecular Photochemistry; CRC Press: Boca Raton, 1991; pp 287−353. (24) Henson, J. H. L.; Hybart, F. J. The Degradation of Poly(vinyl Chloride). I. Hydrogen Chloride Evolved from Solid Samples and from Solutions. J. Appl. Polym. Sci. 1972, 16, 1653−1662. (25) Bielski, B. H.; Cabelli, D. E.; Arudi, R. L.; Ross, A. B. Reactivity of HO2/O2− Radicals in Aqueous Solution. J. Phys. Chem. Ref. Data 1985, 14, 1041−1100. (26) Jin, X.; Bishop, T.; Ellis, T. S.; Karasz, F. E. A Sulphonated Poly(aryl ether ketone). Br. Polym. J. 1985, 17, 4−10. (27) Kormann, C.; Bahnemann, D. W.; Hoffmann, M. R. Photocatalytic Production of H2O2 and Organic Peroxides in Aqueous Suspensions of TiO, ZnO, and Desert Sand. Environ. Sci. Technol. 1988, 22, 798−806. (28) Muthu Lakshmi, R. T. S.; Choudhary, V.; Varma, I. K. Sulfonated Poly(ether ether ketone): Synthesis and Characterisation. J. Mater. Sci. 2005, 40, 629−636. (29) Xing, P.; Robertson, G. P.; Guiver, M. D.; Mikhailenko, S. D.; Wang, K.; Kaliaguine, S. Synthesis and Characterization of Sulfonated Poly(ether ether ketone) for Proton Exchange Membrane. J. Membr. Sci. 2004, 229, 95−106. (30) Daoust, D.; Godard, P.; Devaux, J.; Legras, R.; Strazielle, C. Chemical Modification of Poly(ether ether ketone) for Size Exclusion Chromatography at Room Temperature: 1. Absolute Molecular-mass Determination for Sulfonated PEEK. Polymer 1994, 35, 5491−5497. (31) Lee, P. I. Swelling Effect of Semicrystalline Poly(vinyl alcohol) in Hydrogen Peroxide. J. Appl. Polym. Sci. 1991, 42, 3077−3082. (32) Kim, K.-J.; Lee, S.-B.; Han, H.-W. Effects of the Degree of Crosslinking on Properties of Poly(vinyl alcohol) Membranes. Polym. J. 1993, 25, 1295−1302. (33) Gudeman, L. F.; Peppas, N. A. Preparation and Characterization of pH-Sensitive Interpenetrating Networks of Poly(vinyl alcohol) and Poly(acrylic acid). J. Appl. Polym. Sci. 1995, 55, 919−928. (34) Levine, I. N. Physical Chemistry, 6th ed.; McGraw-Hill: New York, 2009; pp 264−268. (35) Lien, L.; Fellows, C. M.; Copeland, L.; Hawkett, B. S.; Gilbert, R. G. Water Binding and Oxygen Permeability in Poly(vinyl alcohol) Films. Aust. J. Chem. 2002, 55, 507−512. (36) Stefanic, I.; Asmus, K.-D.; Bonifacic, M. Quantification of Iodide Oxidation by Trichloromethyl Peroxyl Radicals and I− + I2 D I3− Equilibrium in Alcohol/water Mixtures. Phys. Chem. Chem. Phys. 2003, 5, 2783−2789. (37) Ulanski, P.; Bothe, K.; Rosiak, J. M.; von Sonntag, C. OHInduced Crosslinking and Strand Breaking of Poly(vinyl alcohol) in Aqueous Solution in the Absence and Presence of Oxygen. A Pulse Radiolysis and Product Study. Macromol. Chem. Phys. 1994, 195, 1443−1461. (38) von Sonntag, C.; Bothe, E.; Ulanski, P.; Adhikary, A. Radical Transfer Reactions in Polymers. Radiat. Phys. Chem. 1999, 55, 599− 603. (39) Ledger, M. B.; Porter, G. Primary Photochemical Processes in Aromatic Molecules. Part 15.The Photochemistry of Aromatic Carbonyl Compounds in Aqueous Solution. J. Chem. Soc., Faraday Trans. 1 1972, 68, 539−553. (40) Knoesel, R.; Weill, G. Internal Photoreduction and Chain Scission in Polyvinylbenzophenone. Polym. Photochem. 1982, 2, 167− 173.

(41) Neta, P.; Grodkowski, J.; Ross, A. B. Rate Constants for Reactions of Aliphatic Carbon-Centered Radicals in Aqueous Solution. J. Phys. Chem. Ref. Data 1996, 25, 709−1050. (42) Görner, H. Oxygen Uptake and Involvement of Superoxide Radicals upon Photolysis of Ketones in Air-Saturated Aqueous Alcohol, Formate, Amine or Ascorbic Acid Solutions. Photochem. Photobiol. 2006, 82, 801−808. (43) Sánchez, G.; Knoesel, R.; Weill, G. External and Internal Quenching in Photochemical Reactions of Vinylbenzophenone-Vinyl Ferrocene Copolymers. Eur. Polym. J. 1978, 14, 485−488. (44) Sedlák, M. In Physical Chemistry of Polyelectrolytes; Radeva, T., Ed.; Marcel Dekker: New York, 2001; pp 1−58. (45) Schuster, D. I.; Karp, P. B. Photochemistry of Ketones in Solution LVIII: Mechanism of Photoreduction of Benzophenone by Benzhydrol. J. Photochem. 1980, 12, 333−344. (46) Ramseier, M.; Senn, P.; Wirz, J. Photohydration of Benzophenone in Aqueous Acid. J. Phys. Chem. A 2003, 107, 3305− 3315. (47) Shizuka, H.; Obuchi, H. Anion-Induced Triplet Quenching of Aromatic Ketones by Nanosecond Laser Photolysis. J. Phys. Chem. 1982, 86, 1297−1302. (48) Galbács, Z. M.; Csányi, L. J. Alkali-Induced Decomposition of Hydrogen Peroxide. J. Chem. Soc., Dalton Trans. 1983, 2353−2357. (49) Peppas, N. A.; Merrill, E. W. Differential Scanning Calorimetry of Crystallized PVA Hydrogels. J. Appl. Polym. Sci. 1976, 20, 1457− 1465. (50) Gagliardi, L. G.; Castells, C. B.; Ràfols, C.; Rosés, M.; Bosch, E. Static Dielectric Constants of Acetonitrile/Water Mixtures at Different Temperatures and Debye-Hückel A and a0B Parameters for Activity Coefficients. J. Chem. Eng. Data 2007, 52, 1103−1107. (51) Moore, J. W.; Pearson, R. G. Kinetics and Mechanism; 3rd ed.; Wiley-Interscience: New York, 1981; pp 246−250. (52) (a) Franco, C.; Olmstead, J., III Photochemical Determination of the Solubility of Oxygen in Various Media. Talanta 1990, 37, 905− 909. (53) Hussey, C. L.; Achord, C. L. Determination of Dissolved Oxygen in Nonaqueous Electrochemical Solvents. Anal. Chem. 1980, 52, 601−602. (54) Gonzalez, M. C.; Le Roux, G. C.; Rosso, J. A.; Braun, A. M. Mineralization of CCl4 by the UVC-photolysis of hydrogen peroxide in the presence of methanol. Chemosphere 2007, 69, 1238−1244.

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DOI: 10.1021/acs.jpca.6b00442 J. Phys. Chem. A XXXX, XXX, XXX−XXX