Spectroscopic studies of plasma-modified silver-exchanged zeolite and chitosan composites

Journal Pre-proof Spectroscopic studies of plasma-modified silver-exchanged zeolite and chitosan composites Kathrina Lois M. Taaca, Hideki Nakajima, Kanjana Thumanu, Pattanaphong Janphuang, Narong Chanlek, Magdaleno R. Vasquez, Jr. PII:

S0254-0584(20)30356-4

DOI:

https://doi.org/10.1016/j.matchemphys.2020.122980

Reference:

MAC 122980

To appear in:

Materials Chemistry and Physics

Received Date: 9 December 2019 Revised Date:

23 February 2020

Accepted Date: 27 March 2020

Please cite this article as: K.L.M. Taaca, H. Nakajima, K. Thumanu, P. Janphuang, N. Chanlek, M.R. Vasquez Jr., Spectroscopic studies of plasma-modified silver-exchanged zeolite and chitosan composites, Materials Chemistry and Physics (2020), doi: https://doi.org/10.1016/ j.matchemphys.2020.122980. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.

Credit Author Statement: Spectroscopic studies of plasma-modified silver-exchanged zeolite and chitosan composites Kathrina Lois M. Taaca: Conceptualization, Methodology, Writing - Original Draft. Hideki Nakajima: Data curation, Validation, Formal Analysis, Investigation. Kanjana Thumanu: Data curation, Validation, Software. Pattanaphong Janphuang: Data curation, Resources. Narong Chanlek: Data curation, Supervision. Magdaleno R. Vasquez, Jr.: Supervision, Resources, Writing- Reviewing and Editing.

Manuscript Template (A4 size) Spectroscopic studies of plasma-modified silver-exchanged zeolite and chitosan composites Kathrina Lois M. TAACA1, Hideki NAKAJIMA2, Kanjana THUMANU2, Pattanaphong JANPHUANG2, Narong CHANLEK2 AND Magdaleno R. VASQUEZ, Jr.1,* 1

Department of Mining, Metallurgical, and Materials Engineering, College of Engineering, University of the Philippines, Diliman, Quezon City, 1101 Philippines 2

Synchrotron Light Research Institute, Nakhon Ratchasima, 3000 Thailand *

Corresponding author e-mail: [email protected]

Abstract Composite biomaterials can be formed by combining natural or synthetic, organic or inorganic materials which are exactly or partially compatible when in contact with a living organism. To greatly improve the utilization of these biomaterials, understanding its interaction with its environment or host is essential. In this work, naturally-occurring and locally-abundant materials such as zeolite (Z) and chitosan (Ch), were fabricated as a silverexchanged zeolite/chitosan (AgZ-Ch) composite using a solvent casting approach. The composites were subsequently exposed to argon (Ar) plasma excited by a 13.56 MHz radio frequency (RF) power source. Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS) techniques were utilized to investigate the surface and subsurface properties of the AgZ-Ch composites. Results revealed different interactions within the bulk and on surface of the composite. The interactions for the composite formation are dominated by the attraction of the AgZ species with the -OH and -NH2 functional groups of Ch. On the other hand, the surface composition of Ch was influenced by the etching effect of Ar with the -COCH3 termination from the Ch. This study showed that the surface layer prefers to be terminated with amine and hydroxyl 1

Manuscript Template (A4 size) groups instead of amide functional groups. The present work also demonstrated the use of plasma irradiation to tune AgZ-Ch composite surface and tailor the reactivity of the functional groups on the surface.

Keywords:

plasma modification; chitosan; zeolite; silver; spectroscopy

1. Introduction Biomaterials are described as those materials combined with substances originating from natural, inorganic or organic materials. They are produced either as a standalone device which can perform or replace any physiological part of a living organism, or as a nonviable substance interacting with a biological system (Yoruç & Şener, 2012) (Boretos & Eden, 1984) (Williams & McNamara, 1987). These devices are routinely used in the medicinal and surgical fields, in various forms ranging from short term dressings to long term implants, where they play a critical role in the treatment of diseases and improvement of health care (Xu & J. Bauer, 2014). Despite the wide use of these biomaterials, the biocompatibility property remains to be one of the major concerns since this determines the ability of the material to perform with an appropriate host response for a specific application (Patel & Gohil, 2012) (Czernuszka, 1996). Biomaterials, when utilized, may still induce adverse reactions such as inflammation, fibrosis, infection, and thrombosis (Xu & J. Bauer, 2014). The biocompatibility and successful application of biomaterials depend largely on the interactions occurring at the surface. Understanding the mechanisms of biocompatibility as well as probing the specific and direct interactions between biomaterials and biological components, such as the tissue, will markedly improve the utilization of biomaterials. Prior to analyzing the interactions, it is crucial to investigate the surface property of the material. This property plays an important role in the subsequent biocompatibility of the materials, such as

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Manuscript Template (A4 size) implants, where the surface can influence the extent of protein adsorption, denaturation and functional activity. In addition, it should be noted that the surface composition or the biocomponent selective adsorption of a substrate is not always within the size scale analyzed by conventional microscopic techniques such as atomic force microscopy (AFM) and transmission electron microscopy (TEM) (Leung, Brash, & Hitchcock, 2010). Thus, the use of synchrotron-based X-ray spectroscopic techniques as tools for evaluating the biocompatibility response of materials is now being considered (Leung, Brash, & Hitchcock, 2010). Zeolite-chitosan composites are among the most recent chitosan-based systems being studied as a biomaterial. Chitosan (Ch) is a widely known deacetylated derivative of chitin due to its innate biological properties which are non-toxic, renewable, and biodegradable (Tantiplapol, et al., 2015) (Taaca & M.R. Vasquez, 2017). It has a (1-4)-2-amino-2-deoxy- βD-glucopyranose structure where the amino and hydroxyl functional groups determine some of its properties such as viscosity, hydrophilicity, and degree of deacetylation (Tantiplapol, et al., 2015) (Taaca & M.R. Vasquez, 2017) (Crofton, et al., 2016) (Vo, Guillon, Dupont, Kowandy, & Coqueret, 2014). Zeolites (Z), like Ch, can be a naturally-occurring material composed of aluminosilicates arranged in tetrahedron structures (Taaca, Olegario, & Vasquez Jr., 2017). These inorganic minerals continuously receive attention as catalysts, adsorbents, or ion exchangers due to its admirable properties such as high cation exchange capacity, high porosity, chemical stability, thermal stability, and molecular sieving capability (Taaca & M.R. Vasquez, 2017) (Zhang, et al., 2017) (Barbosa, Debone, Severino, Souto, & Silva, 2016) (Barbosa, Debone, Severino, Souto, & Silva, 2016) (Wang, et al., 2008). When these two naturally abundant resources are combined as a composite, its interesting properties find applications in adsorption (Muzzarelli, 1973) (Ngah, Teong, Toh, & Hanafiah, 2013)

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Manuscript Template (A4 size) (Habiba, et al., 2017) (Samadi, Yazd, Abdoli, Jafari, & Aliabadi, 2017) and energy-related applications (Wang, et al., 2008) (Fereidooni & Mehrpooya, 2017). Our previous works have successfully fabricated the composite using a solvent casting approach as well as tailoring its wettability and surface roughness properties through plasma treatment (Taaca & M.R. Vasquez, 2017). The potential of the composite for biomedical application was also investigated by assessing its antibacterial, hemocompatibility and cytocompatibility properties (Taaca & Vasquez Jr., 2018). However, the interaction of the three parameters; namely, Ch, silver-exchanged zeolite (AgZ), and plasma were not yet fully investigated. Therefore, it is essential to consider the surface properties of the composite as this is the first layer to be exposed to physiological environments when implanted or applied topically. In this study, we focused our work on understanding the influence of Z and plasma on the properties of Ch using synchrotron-based spectroscopic characterization. From the results, we may further determine how these three parameters interact and in turn, may provide correlation on the observed properties of the composite that can be used in tailoring the material characteristics for specific biomedical applications.

2. Experimental

2.1 Preparation of AgZ-Ch composites Composites of AgZ-Ch were fabricated using the solvent casting approach. The AgZ powders were prepared from natural zeolites (mixture of clinoptilolite and mordenite zeolite type mined from SAILE Industries, Inc., Pangasinan, Philippines) and silver nitrate (AgNO3) (99.99% purity, locally sourced) using the method of Osonio and Vasquez (Osonio & Vasquez, 2018). The samples were calcined at 400°C for 5 h. 2 wt% Ch (Sigma-Aldrich, 50494-100G-F) was mixed in a 90% solution of an ACS reagent grade glacial acetic acid

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Manuscript Template (A4 size) (Pharmco-Aaper, 281000ACS). After 1 h, 1wt% AgZ was added to each Ch mixture. 1 mL of glycerine (locally-sourced) was also added as a plasticizer to the AgZ-Ch mixture. The solution was stirred for 2 h and casted on a precleaned polystyrene dish. The mixture was airdried for 1 week. Post-treatment was done by soaking the film in an isopropanol solution then dried in a dark container, with desiccant, prior to plasma treatment. Pristine AgZ-Ch composites (0wt% and 1wt%) were labeled as samples A1 and A2, respectively.

2.2 Plasma Treatment Plasma treatment using 99.99% argon (Ar) as the working gas was conducted using the same system utilized in previous works (Cagomoc & Vasquez, 2016) (Osonio & Vasquez, 2018) (Taaca & M.R. Vasquez, 2017). Base pressure was set to below 10 Pa and the samples were exposed to Ar plasma under a working pressure of 30 Pa. Prior to treatments, plasma cleaning of the chamber was done to ensure that the presence of impurities is at minimum to nil. This cleaning step was done at a working pressure of 100 Pa at 100 W incident RF power for 10 min. Dried 1 cm x 1 cm sheets of AgZ-Ch samples were exposed to Ar plasma treatment for 2 min at 50 W incident RF power. The 0% and 1% AgZCh samples treated with Ar plasma were labeled as B1 and B2, respectively.

2.3 Characterization

2.3.1 Fourier Transform Infrared Spectroscopy The bulk chemical structure of the composite samples was probed using Fouriertransform infrared (FTIR) spectroscopy in attenuated total reflectance (ATR) mode. Specifically, the synchrotron radiation-based Fourier-transform infrared (SR-FTIR) in BL 4.1 infrared spectroscopy and imaging beamline at the Synchrotron Light Research Institute

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Manuscript Template (A4 size) (SLRI) in Nakhon Ratchasima, Thailand was used to acquire the spectra of each sample. The SR-FTIR equipment is composed of a Bruker Tensor 27 spectrometer (Globar source), coupled with an infrared microscopy (Hyperion 2000, Bruker Optick GmbH, Ettlin-Gen, Germany) and an ATR objective lens of 20x magnification with a mercury-cadmiumtelluride (MCT) detector cooled using liquid nitrogen (N2). Spectral analysis was measured from a range of 4000 to 800 cm-1, an aperture size of 20 x 20 µm2, spectral resolution of 4 cm-1 with 64 scans co-added (Pasela, et al., 2019). The spectral data were extracted using OPUS 7.5 (Bruker Optik GmbH) software (Pasela, et al., 2019) (Dunkhunthod, Thumanu, & Eumkeb, 2017). Preprocessing of the spectral data were also done in the OPUS 7.5 software prior to data analysis.

2.3.2 X-ray Absorption Spectroscopy The X-ray absorption spectroscopy (XAS) was used to investigate possible changes in the Ch-based composites in terms of their electronic structure. Specifically, the near-edge xray absorption fine structure (NEXAFS) spectroscopy was performed in this study. NEXAFS is located at the soft X-ray undulator beamline BL3.2Ua in SLRI. Carbon (C) and nitrogen (N) K edge absorption spectra were measured in the total electron yield (TEY) and total fluorescence yield (TFY) modes on the multi-channel plate detector by scanning photon energy with tuning undulator gap and angle of grating simultaneously. The photon energy of the beamline is calibrated in the C1s→π* transition in the graphite. The base pressure of analysis chamber is 2x10-8 Pa and the energy resolution is about 0.2 eV on C K edge and 0.4 eV on N K edge. The soft X-ray is emitted on the sample at 70° angle of incidence in the spolarized configuration. The samples were attached on a stainless sample holder using a conductive carbon tape and loaded into the load-lock chamber for vacuum pumping prior to the measurements.

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2.3.3 X-ray Photoelectron Spectroscopy X-ray photoelectron spectroscopy (XPS) was used to determine the surface chemistry of pristine and plasma-treated samples. This technique was performed in the SUTNANOTEC-SLRI joint research beamline facility in SLRI. XPS is equipped with Scanning XPS Microprobe (PHI5000 Versa Probe II, ULVAC-PHI) which generates X-rays from an aluminum (Al) Kα radiation at 1486 eV. The X-rays are monochromatized and focused on a 100 μm spot size of the sample surface using a quartz crystal. The energy of electrons emitted from the sample are analyzed by a concentric hemispherical analyzer, tilted 45° from the surface normal. The charging effect on the sample is neutralized by the low-energy electron and Ar ion irradiations on the sample surface. The binding energy is calibrated at the C-C peak of C1s at 284.6 eV. The total energy resolution is typically about 0.6 eV and the base pressure is 4x10-7 Pa in the analysis chamber.

3. Results and Discussion 3.1 FTIR Analysis

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Figure 1 Full IR spectra of pristine (A1 and A2) and plasma-treated (B1 and B2) AgZ-Ch composites. FTIR spectroscopy was used to investigate the effects of AgZ particles and plasma treatment on the bulk chemical structure of Ch. Figure 1 shows the full IR spectra of the AgZ-Ch composites. Various absorption bands within the 4000-800 cm-1 were recorded for the composites (Negrea, Caunii, Sarac, & Butnariu, 2015) (Rumengan, et al., 2014) (Yanming, et al., 2001) (Ahing & Wid, 2016). The spectra of pure Ch (A1) sample showed overlapping stretching vibrations of symmetric -OH and -NH2 groups at 3295 cm-1. The -CH bond of CH2 bending and the symmetric CH3 deformation of Ch is observed at 2935 cm-1 and 1493 cm-1, with the former having the major contribution (Yanming, et al., 2001) (Puvvada, Vankayalapati, & Sukhavasi, 2012). The absorption band observed at 1728 cm-1 represents the C=O stretching of the ester carbonyl bond due to the reaction of the hydroxyl and amino groups in the Ch sample (Saly, 1998) while the vibrations of protonated amine (NH3+) groups is at 1564 cm-1 (Negrea, Caunii, Sarac, & Butnariu, 2015) (Silva, et al., 2012). The symmetric 8

Manuscript Template (A4 size) -CH3 deformation and -CH bending were also observed at 1349 cm-1. The small peak measured at 1257 cm-1 and the strong peak at 1037 cm-1 are attributed to the complex amide III groups and the C-OH, C-O-C and CH2OH vibrations in the Ch ring, respectively (Zvezdova, 2010) (Negrea, Caunii, Sarac, & Butnariu, 2015).

The characteristic peaks

observed in Figure 1 are summarized in Table 1. In Figure 1, the distinct characteristic peaks of Ch were present in the spectra of A2, B1, and B2 with slight shifts with respect to positions assigned in A1. With its aluminosilicate structure, Z is known to have a net negative surface charge (Taaca & Vasquez Jr., 2018) (Pourshahrestani, Zeiimaran, Djordjevic, Kadri, & Towler, 2016). This induced an electrostatic interaction with Ch, causing a shift in the NH3+ vibration to a lower frequency from 1564 cm-1 to 1561 cm-1 (Silva, et al., 2012). The increased peak intensities within the 1200 cm-1 and 1650 cm-1 region of the A2 sample are attributed to the characteristic Z peaks assigned to the T-O asymmetric internal stretching (1210 cm-1) and H-O-H angular deformation (1630 cm-1) (Gligor, Maicaneanu, & Walcarius, 2010). Moreover, the presence of Ag on the surface of the Z particles exhibited few changes in the IR spectra of A2 and B2, with respect to that of A1. The characteristic bands of Ch at 3295 cm-1, corresponding to the OH and -NH stretching of the hydroxyl and primary amino groups of Ch, shifted to 3288 cm1

, suggesting the chelation of Ag with both the hydroxyl and amino groups of Ch (Chen,

Jiang, Ye, Li, & Huang, 2014). Plasma treatment, on the other hand, involves a different interaction with Ch and the Z-Ch composite. The -OH and -NH stretching characteristic band of Ch was observed to increase slightly in the intensity values compared to their pristine counterparts, and the peak for this band shifted to a higher frequency from 3309 cm-1 to 3323 cm-1. This increase in the absorbance intensities of the -OH and -NH stretching characteristic band may have contributed to the significant increase in the polar surface free energy (SFE) components of the composites observed in the previous studies (Taaca & M.R. Vasquez,

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Manuscript Template (A4 size) 2017) (Taaca & Vasquez Jr., 2018). This may have greatly influenced the increase in the hydrophilicity of the composites. Other effects of plasma treatment may be elucidated using synchrotron-based spectroscopic techniques.

Table 1 Corresponding functional groups to characteristic peaks of each sample Assigned Functional Groups Overlapping symmetric -OH and -NH stretching -CH bond of CH2 bending and the symmetric CH3 deformation C=O stretching of ester NH3+ vibrations -CH bond of CH2 bending and the symmetric CH3 deformation symmetric -CH3 deformation and CH bending Amide III C-OH, C-O-C and CH2OH

A1

Wavenumbers (cm-1) A2 B1

B2

32945

3288

3309

3323

2935

2933

2929

2933

1728

1724

1729

1729

1564

1561

1569

1562

1493

1410

1446

1445

1349

1380

1377

1377

1257

1265

1256

1259

1037

1039

1037

1036

3.2 NEXAFS Results

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Figure 2 NEXAFS N K edge spectra of pristine (A) and Ar-treated (B) AgZ-Ch composites.

The NEXAFS technique is considered to be a powerful tool where information such as the local chemical and electronic structure in a condensed matter can be obtained (Secchi, et al., 2019). The NEXAFS N K-edge spectra of the pristine and Ar plasma-treated AgZ-Ch composites are shown in Figure 2. The spectrum of the pristine Ch (A1) is dominated by two small peaks and a shoulder. The small peak at 400.7 eV corresponds to the σ* (N-H) resonance while the shoulder detected at 405.4 eV is attributed to the σ* (N-H) and π* (NHC=O) of the amino functional group of Ch (Graf, et al., 2009) (Shard, et al., 2004) (Beck, et al., 2005). NEXAFS is sensitive to unsaturated bonds (Graf, et al., 2009). Thus, the NEXAFS spectra of the samples showed a small peak at 398.2 which is due to the formation of unsaturated imine (C=N) species possibly originated from the radiation damage of the interaction of the X-ray induced secondary electrons with the surface of the composite samples (Cody, et al., 2011). 11

Manuscript Template (A4 size) From Figure 2, there are no significant changes on the intensities of the Ch characteristic peaks for samples A2, B1 and B2. However, the peak intensities of the imine species are higher and more defined upon the addition of AgZ particles and plasma treatment. This increase may mean that these modified samples, subjected to either AgZ particle incorporation and/or plasma treatment, are more susceptible to radiation damage leading to the formation of imine species (Graf, et al., 2009). The C K edge of the AgZ-Ch composites was also measured to provide supplementary information on the complex molecular signature of Ch.

Figure 3 NEXAFS (a) TFY and (b) C K edges of pristine and Ar-treated AgZ-Ch composites.

The experimental NEXAFS C K edge spectra of the pristine and Ar plasma-treated AgZ-Ch composites are shown in Figure 3. The NEXAFS C K edge spectra measured by 12

Manuscript Template (A4 size) total fluorescence yield (TFY) is illustrated in Figure 3(a) while spectra obtained by total electron yield (TEY) is shown in Figure 3(b). The C 1s absorption edge peaks were utilized to determine the various features and identify the peak positions of the different AgZ-Ch samples (Cody, et al., 2011). The small broad peak at 285.1-285.7 eV corresponds to the 1sπ* transition of C=C and C=N species (Graf, et al., 2009) (Shard, et al., 2004) (GirardLauriault, Desjardins, Unger, Lippitz, & Wertheimer, 2008). The peak at 287.8 eV may not be excluded as this is attributed to the 1s-σ* of C-H in the Ch structure. The 1s-π* transition of amide carbonyl (C=O) is measured at 288.2 eV while the 1s-3p/σ* transition of C-OH is at 289.8 eV (Graf, et al., 2009) (Solomon, et al., 2009). From Figure 3, the NEXAFS spectra of all samples did not exhibit significant difference from each other. The appearance of the resonances at 285.1-285.7 eV in the NEXAFS spectra of the composites can be due to the radiation damage as depicted also in the N K edge case. The intensity of the peaks of 287.8 eV, 288.2 eV and 289.2 eV is considerably different from each composite, suggesting the possible increase in the functional groups of amide (-RCONH2) and alcohol (-RCOH) species of Ch after adding AgZ particles and plasma treatment. One of the advantages of utilizing the NEXAFS technique for characterization is that it can measure TEY and TFY modes simultaneously. The TFY mode is used in measuring non-conductive samples. However, it is less efficient on low Z materials such as carbon. The TEY mode of AgZ-Ch composites was also obtained since this mode has the advantage of being more surface-sensitive with an analytical depth of about 5- 10 nm compared to the several micrometer-depth of analysis of TFY (Anselmo, Dzwilewski, Svensson, & Moons, 2012). Figure 3(b) shows the C-NEXAFS spectra of the AgZ-Ch composites in the TEY mode. The presence of C=C-NH2, observed at 286.5 eV, is more defined than the other unsaturated species (C=C and C=N). The π* resonance of C=O, σ* resonance of C-H and the presence of the σ* resonance C-C and C-N species at 292.1 eV have more intense peaks

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Manuscript Template (A4 size) compared to the σ* resonance of C-OH. The result from the C K edge TEY mode indicated that the surface layer of the composites is terminated with amine or amide functional groups.

3.2 XPS Analysis The XPS characterization was employed in this study to further analyze the detected variations in the surface chemistry of the AgZ-Ch samples. It is more surface sensitive than the NEXAFS TEY since the mean free path of the former has a depth of at most 1 nm below the surface while the latter collects electrons, including photoelectrons and secondary electrons, up to 2-10 nm below the surface (Anselmo, Dzwilewski, Svensson, & Moons, 2012) (Chua, et al., 2006). Relevant XPS C 1s, N 1s, and O 1s regions of pristine and plasmatreated AgZ-Ch samples are shown in Figure 4. The C 1s region of the pristine AgZ-Ch samples yields several peaks attributed to the glucosamine and N-acetylglucosamine units of the Ch structure (Cody, Brandes, Jacobsen, & Wirick, 2009). This region was fitted with different components typically found in pure Ch: aliphatic C-C, C-H, C-O, C-N and C=O groups (Carapeto, Ferraria, & Rego, 2017) (PinChieh, et al., 2016). These features are measured at peaks positioned at 284.5 eV, 286.4 eV, and 287.9.0 eV, respectively. The N 1s region of the pristine AgZ-Ch samples, on the other hand, shows a distinct peak which can be attributed to the different states of N, as supported by the NEXAFS N K edge spectra. The peak centered at 399.2 eV is assigned to the NH2 chemical bindings of Ch (Yap, Yunus, Talib, & Yusof, 2011) (Pin-Chieh, et al., 2016). Other N species, NHC=O and NH3+, were present and attributed to binding energy values at 400.4 eV and 401.3 eV, respectively (Yap, Yunus, Talib, & Yusof, 2011) (Carapeto, Ferraria, & Rego, 2017). The O 1s spectra were also fitted using 3 peaks centered at 531.3 eV (C=O), 532.6 eV (C-O and C-OH) and 533.5 (O-C=O and O-C-O) (Yap, Yunus, Talib, & Yusof, 2011) (Huang, et al., 2017). For both A1 and A2 samples, the distinct characteristic XPS

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Manuscript Template (A4 size) peaks in the C 1s, N 1s and O 1s regions are not significantly different even with the addition of AgZ particles. The XPS measurements were also carried out to investigate the surface chemistry of the polymeric surfaces modified by Ar plasma. The C 1s, O 1s, and N 1s spectra regions of B1 and B2 samples are also shown in Figure 4. The characteristic peaks for each region are still observed in B1 and B2 samples. In the C 1s region, for plasma-treated samples in general, there is a decrease in the intensity of C-C and C-H peaks and an increase in the intensity peaks of C-O, C-N and C=O species. Moreover, the peak of NH2 is more defined in the N 1s region of the samples after plasma treatment. A shift towards a higher binding energy was then detected in the O 1s region of the plasma-treated samples, indicating possible etching of C=O species.

Figure 4 XPS C 1s, N 1s, and O 1s regions of pristine and Ar-treated AgZ-Ch composites.

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3.3 Interaction Mechanisms in the AgZ-Ch Composites This study investigated the effects of the interaction of AgZ particles and plasma exposure to the chemical structure of Ch. Spectroscopic techniques such as FTIR, NEXAFS and XPS were utilized to investigate these effects among the 3 parameters. Based from the results, possible interactions of AgZ, Ch, and Ar were formulated. It is emphasized, however, that the mechanisms explained in this study are reactions that may be possible to occur in the composite. Atomic level modeling may be done to complement the results of this study. FTIR results revealed that the Ch film was produced by converting the NH2 group in the glucosamine unit of Ch to protonated amine (NH3+), shown in Figure 5, when CH3COOH solution was used as the solvent (Qin, et al., 2006). The hydrogen bonding interaction of Ch with glycerine (plasticizer) completed the film formation in this study, as shown in Figure 6.

Figure 5 Protonation of the amine functional group in the CH structure.

Figure 6 Proposed Film Formation of pristine 0% AgZ-Ch composite (A1). 16

Manuscript Template (A4 size) The proposed interaction for the formation of AgZ-Ch composites is illustrated in Figure 7. The state of the Ag clusters adsorbed in the pores of Z contain Ag0 and Ag+ species (Taaca, Olegario, & Vasquez Jr, 2019). These Ag species interact with Ch by electrostatic attraction in the -OH, NH2 or NH3+ terminal ends of the polymer (Godoi, RodriguezCastellon, Guibal, & Beppu, 2013). The negative net charge of the Z structure also influenced electrostatic attraction and hydrogen bonding with the -OH and -NH2 groups of Ch. The presence of AgZ particles in the Ch matrix may induce an electrostatic interaction between the particle filler and the polymer matrix. But the amount of AgZ particles are too low to trigger an electrostatic interaction which can produce a significant effect on the surface chemistry of Ch. This is supported by previous studies (Taaca & M.R. Vasquez, 2017) (Taaca & Vasquez Jr., 2018) where the total surface energy (SFE) of the composite is significantly affected by the increase in the polar groups of the composites after plasma treatment. Hence, the interaction from AgZ particles does not greatly affect the surface composition of Ch.

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Figure 7 Proposed interaction of AgZ and Ch for AgZ-Ch composite formation. Plasma treatment employed in this study utilized Ar as the working gas. Functionalization or etching processes may take place when a polymer is exposed to plasma (Silva, et al., 2008). The NEXAFS TEY C K edge results showed an increase in the intensity of the C=O peaks as compared to the TFY C K edge of all samples. Relating to the NEXAFS N K edge spectra, this increase in the C=O species can be attributed to the amide species which may be one of the N functional groups dominating the surface layer of the composites. After plasma treatment, it can be observed in the C 1s and O 1s XPS spectra of the samples 18

Manuscript Template (A4 size) that the presence of C-O, C-N and O-H species are more favored than C=O. This result may imply that some of the -COCH3 groups in the amide moieties of Ch were removed by an etching process caused by Ar plasma treatment. This further suggests that the topmost layer of the composite surface may prefer to be terminated with amines than amides, demonstrated in Figure 8, and with hydroxyl group as observed with the shifting to higher BE values in the O 1s XPS spectra.

Figure 8 Schematic representation of the removal of the acetyl group -COCH3 in the AgZCh composites.

4. Conclusions In this study, AgZ-Ch composites were fabricated with varying AgZ content and modified with plasma treatment. Interactions of the AgZ particles and plasma with Ch was observed using spectroscopic techniques, namely, FTIR, NEXAFS and XPS. Results revealed that electrostatic attraction and hydrogen bonding predominated the interactions of AgZ, glycerine, and Ch to form the pure film as well as the composite samples. The limited amount of AgZ particles in the Ch matrix did not induce significant changes in the surface structure of chitosan Thus, the interactions on the surface were dominated by plasma treatment where active species from the discharge etched the -COCH3 group in the N-acetylglucosamine unit of the polymer to favor the termination of the composites with amine and hydroxyl groups. Based from these results, the attraction of AgZ and Ch is due to electrostatic attraction while plasma treatment with Ar gas favors etching of the acetyl (-COCH3) groups and termination with NH2 and OH in the surface of Ch. This study suggests to consider the reactivity of NH2 especially when surface modifications are done on AgZ-Ch composites. In addition, further

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Manuscript Template (A4 size) studies involving electrostatic/electronic modeling may be done to further understand the interactions proposed in this study.

5. Acknowledgements K. Taaca would like to express her gratitude to Dr. Chanan Eauruksakul of SLRI for a guide to the plasma treatment facility in SLRI, to Ms. Eleanor Olegario and SAILE Industries Inc. for the zeolites, 2017 DARETO (Discovery-Applied Research and Extension for Trans/Inter-disciplinary Opportunities) Cycle 2 Program of the Commission on Higher Education (CHED) Philippines, University of the Philippines Office of the Vice Chancellor for Research and Development Outright Research Grant (191933-ORG) and to the Marithé Girbaud Professorial Chair. M. Vasquez acknowledges the University of the Philippines Office of the Vice President for Academic Affairs BALIK-PhD Research Grant (OVPAABPhD-2014-01) and the Jardiolin Family Professorial Chair.

References Ahing, F., & Wid, N. (2016). Extraction and Characterization of Chitosan from Shrimp Shell Waste in Sabah. Transactions on Science and Technology, 227-237. Anselmo, A., Dzwilewski, A., Svensson, K., & Moons, E. (2012). Molecular Orientation and Composition at the Surface of Spin-Coated Polyfluorene: Fullerene Blend Films. Journal of Polymer Science, 176-182. Barbosa, G., Debone, H., Severino, P., Souto, E., & Silva, C. d. (2016). Design and characterization of chitosan/zeolite composite films- Effect of zeolite type and zeolite dose on the film properties. Materials Science and Engineering: C, 246-254. Beck, A., Whittle, J., Bullett, N., Eves, P., Neil, S. M., McArthur, S., & Shard, A. (2005). Plasma Processes and Polymers 2, 641. Boretos, J., & Eden, M. (1984). Contemporary Biomaterials, Material and HOst Response, Clinical Applications, New Technology and Legal Aspects. Park Ridge, New Jersey: Noyes Publications. Cagomoc, C., & Vasquez, M. (2016). Enhanced chromium adsorption capacity via plasma modification of natural zeolites. Japanese Journal of Applied Physics, 01AF02.

20

Manuscript Template (A4 size) Carapeto, A., Ferraria, A., & Rego, A. B. (2017). Unraveling the reaction mechanism of silver ions reduction by chitosan from so far neglected spectroscopic features. Carbohydrate Polymers, 601-609. Chen, Q., Jiang, H., Ye, H., Li, J., & Huang, J. (2014). Preparation, Antibacterial, and Antioxidant Activities of Silver/Chitosan Composites. Journal of Carbohydrate Chemistry, 1-15. Chua, L., Dipankar, M., Sivaramakrishnan, S., Gao, X., Qi, D., Wee, A., & Ho, P. (2006). Large Damage Threshold and Small Electron Escape Depth in X-ray Absortpion Spectroscopy of a Conjugated Polymer Thin Film. Langmuir, 8587-8594. Cody, G., Brandes, J., Jacobsen, C., & Wirick, S. (2009). Soft x-ray induced chemical modification of polysaccharides in vascular plant cell walls. Journal of Electron Spectroscopy and Related Phenomena, 57-64. Cody, G., Gupta, N., Briggs, D., Kilcoyne, A., Summons, R., Kenig, F., . . . Scott, A. (2011). Molecular signature of chitin-protein complex in Paleozoic arthropods. Geology, 255-258. Crofton, A., Hudson, S., Howard, K., Pender, T., Abdelgawad, A., Wolski, D., & Kirsch, W. (2016). Formulation and characterization of a plasma sterilized, pharmaceutical grade chitosan powder. Carbohydrate Polymers, 420-426. Czernuszka, J. (1996). Biomaterials under the microscope. Materials World, 452-453. Dunkhunthod, B., Thumanu, K., & Eumkeb, G. (2017). Application of FTIR microspectroscopy for monitoring and discrimination of the anti-adipogenesis activity of baicalein in 3T3-L1 adipocytes. Vibrational Spectroscopy, 92-101. Fereidooni, L., & Mehrpooya, M. (2017). Experimental assessment of electrolysis method in production of biodiesel from waste cooking oil using zeolite/chitosan catalyst with a focus on waste biorefinery. Energy Conversion and Management, 145-154. Girard-Lauriault, P.-L., Desjardins, P., Unger, W., Lippitz, A., & Wertheimer, M. (2008). Plasma Processes and Polymers 5, 631. Gligor, D., Maicaneanu, A., & Walcarius, A. (2010). Iron-enriched natural zeolite modified carbon paste electrode for H2O2 detection. Electrochimica Acta, 4050-4056. Godoi, F. d., Rodriguez-Castellon, E., Guibal, E., & Beppu, M. (2013). An XPS study of chromate and vanadate sorption mechanism by chitosan membrane containing copper nanoparticles. Chemical Engineering Journal, 423-429. Graf, N., Yegen, E., Gross, T., Lippitz, A., Weigel, W., Krakert, S., . . . Unger, W. (2009). XPS and NEXAFS studies of aliphatic and aromatic amine species on functionalized surfaces. Surface Science, 2849-2860. Habiba, U., Siddique, T., Joo, T., Salleh, A., Ang, B., & Afifi, A. (2017). Synthesis of chitosan/polyvinyl alcohol/zeolite composite for removal of methyl orange, Congo red and chromium (VI) by flocculation/adsorption. Carbohydrate Polymers, 1568-1576.

21

Manuscript Template (A4 size) Hidalgo, T., Giménez-Marqués, M., E. Bellido, J. A., Asension, M., Salles, F., Lozano, M., . . . Horcajada, P. (2017). Chitosan-coated mesoporous MIL-100 (Fe) nanoparticles as improved bio-compatible oral nanocarriers. Scientific Reports. Huang, Z., Li, Z., Zheng, L., Zhou, L., Chai, Z., Wang, X., & Shi, W. (2017). Interaction mechanism of uranium (VI) with three-dimensional graphene oxide-chitosan composite: Insights from batch experiments, IR, XPS, and EXAFS spectroscopy. Chemical Engineering Journal, 10661074. Leung, B., Brash, J., & Hitchcock, A. (2010). Characterization of Biomaterials by Soft X-Ray Spectromicroscopy. Materials, 3911-3938. Muzzarelli, R. (1973). Natural chelating polymers; alginic acid, chitin, and chitosan. New York: Pergamon Press. Negrea, P., Caunii, A., Sarac, I., & Butnariu, M. (2015). The Study of Infrared Spectrum of Chitin and Chitosan Extract as Potential Sources of Biomass. Digest Journal of Nanomaterials and Biostructures, 1129-1138. Ngah, W., Teong, L., Toh, R., & Hanafiah, M. (2013). Comparative study on adsoprion and desorption of Cu (II) ions by three types of chitosan-zeolite composites. Chemical Engineering Journal, 231-238. Ninan, N., Muthiah, M., Yahaya, N., Park, I., Elain, A., Wong, T., . . . Grohens, Y. (2014). Antibacterial and wound healing analysis of gelatin/zeolite scaffolds. Colloids Surfaces B: Biointerfaces, 244-252. Osonio, A., & Vasquez, M. (2018). Plasma-assisted reduction of silver ions impregnated into a natural zeolite framework. Applied Surface Science, 156-162. Pasela, B. R., Castillo, A. P., Simon, R., Pulido, M. T., Mana-ay, H., Abiquibil, M. R., . . . Taaca, K. L. (2019). Synthesis and Characterization of Acetic Acid-Doped Polyaniline and PolyanilineChitosan Composite. Biomimetics, 1-16. Patel, N., & Gohil, P. (2012). A Review on Biomaterials: Scope, Applications & Human Anatomy Significance. Journal of Emerging Technology and Advanced Engineering, 91-101. Pin-Chieh, L., Guan-Ming, L., Kumar, S. R., Chao-Ming, S., Chun-Chen, Y., Da-Ming, W., & Lue, S. J. (2016). Fabrication and Characterization of Chitosan Nanoparticle-Incorporated Quaternized Poly (Vinyl Alcohol) Composite Membranes as a Solid Electrolytes for Direct Methanol Alkaline Fuel Cells. Electrochimica Acta, 616-628. Pourshahrestani, S., Zeiimaran, E., Djordjevic, I., Kadri, N., & Towler, M. (2016). Inorganic hemostats: the state-of-the-art and recent advances. Materials Science and Engineering C, 1255-1268. Puvvada, Y., Vankayalapati, S., & Sukhavasi, S. (2012). Extraction of chitin from chitosan from exosckeleton of shrimp for application in the pharmaceutical industry. International Current Pharmaceutical Journal, 258-263. Qin, C., Li, H., Xiao, Q., Liu, Y., Zhu, J., & Du, Y. (2006). Water-solubility of chitosan and its antimicrobial activity. Carbohydrate Polymers, 63.

22

Manuscript Template (A4 size) Regiel-Futyra, A., Kus-Liskiewicz, M., Sebastian, V., Irusta, S., Arruebo, M., Kyziol, A., & Stotchel, G. (2017). Development of noncytotoxic silver-chitosan nanocomposites for efficient control of biofilm forming microbes. Royal Society of Chemistry Advances, 52398-52413. Rumengan, I., Suryanto, E., Modaso, R., Wullur, S., Tallei, T., & Limbong, D. (2014). Structural Characteristics of Chitin and Chitosan Isolated from the Biomass of Cultivated Rotifer, Brachionus rotundiformis. International Journal of Fisheries and Aquatic Sciences, 12-18. Saly, A. (1998). Self-dissolving chitosan I: Preparation, characterization and evaluation for drug delivery system. Die Angewandte Makromolekulare Chemie, 13-18. Samadi, S., Yazd, S., Abdoli, H., Jafari, P., & Aliabadi, M. (2017). Fabrication of novel chitosan/PAN/magnetic ZSM-5 zeolite coated sponges for absorption of oil from water surfaces. International Jounral of Biological Macromolecule, 370-376. Scacchetti, F., Pinto, E., & Soares, G. (2017). Preparation and characterization of cotton fabrics with antimicrobial properties throught the application of chitosan/silver-zeolite film. Procedia Engineering, 276-282. Secchi, V., Franchi, S., Ciccarelli, D., Dettin, M., Zamuner, A., Serio, A., . . . Battochio, C. (2019). Biofunctionalization of TiO2 Surfaces with Self-Assembling Layers of Oligopeptides Covalently Grafted to Chitosan. ACS Biomaterials Science and Engineering. Shard, A., Whittle, J., Beck, A., Brookes, P., Bullett, N., Talib, R., . . . McArthur, S. (2004). A NEXAFS Examination of Unsaturation in Plasma Polymers of Allylamine and Propylamine. Journal of Physical Chemistry B, 12472-12480. Silva, S., Braga, C., Fook, M., Raposo, C., Carvalho, L., & Canedo, E. (2012). Application of Infrared Spectroscopy to Analysis of Chitosan/Clay Nanocomposites. In P. T. Theophile, Infrared Spectroscopy- Materials Science, Engineering and Technology (pp. 43-62). InTech. Silva, S., Luna, S., Gomes, M., Benesch, J., Pashkuleva, I., Mano, J., & Reis, R. (2008). Plasma Surface Modification of Chitosan Membranes: Characterization and Preliminary Cell Response Studies. Macromolecular Bioscience, 568-576. Solomon, D., Lehmann, J., Kinyangi, J., Liang, B., Heymann, K., Dathe, L., & Hanley, K. (2009). Carbon (1s) NEXAFS Spectroscopy of Biogeochemically Relevant Reference Organic Compounds. Soil Science Society of America Journal, 1817-1830. Taaca, K., & M.R. Vasquez, J. (2017). Fabrication of Ag-exchanged zeolite/chitosan composites and effects of plasma treatment. Microporous and Mesoporous Materials, 383-391. Taaca, K., & Vasquez Jr., M. (2018). Hemocompatibility and cytocompatibility of pristine and plasma-treated silver-zeolite-chitosan composites. Applied Surface Science, 324-331. Taaca, K., Olegario, E., & Vasquez Jr, ,. M. (2019). Impregnation of silver in zeolite-chitosan composite: thermal stability and sterility study. Clay Minerals, 145-151. Taaca, K., Olegario, E., & Vasquez Jr., M. (2017). Antibacterial Properties of Ag-exchanged Philippine Natural Zeolite-Chitosan Composites. AIP Conference Proceedings, (p. 030015).

23

Manuscript Template (A4 size) Tantiplapol, T., Singsawat, Y., Narongsil, N., Damrongsakkul, S., Saito, N., & Prasertsung, I. (2015). Influences of solution plasma conditions on degradation rate and properties of chitosan. Innovative Food Science & Emergng Technologies, 116-120. Vo, K. N., Guillon, E., Dupont, L., Kowandy, C., & Coqueret, X. (2014). Influence of Au (III) Interactions with Chitosan on Gold Nanoparticle Formation. The Journal of Physical Chemistry C, 4465-4474. Wang, J., Zheng, X., Wu, H., Zheng, B., Jiang, Z., Hao, X., & Wang, B. (2008). Effect of zeolites on chitosan/zeolite hybrid membranes for direct methanol fuel cell. Journal of Power Sources, 919. Williams, D., & McNamara, A. (1987). Potential of polyetheretherketone (PEEK) and carbon-fibrereinforced PEEK in medical applications. Journal of Materials Science Letters, 188-190. Xu, L., & J. Bauer, C. A. (2014). Proteins, Plateles, and Blood Coagulation at Biomaterial Interfaces. Colloids and Surfaces B: Biointerfaces, 49-68. Yanming, D., Congyi, X., Jianwei, W., Mian, W., Yusong, W., & Yonghong, R. (2001). Determination of degree of substitution for N-acylated chitosan using IR spectra. Science in China, 216-224. Yap, W., Yunus, W., Talib, Z., & Yusof, N. (2011). X-ray photoelectron spectroscopy and atomic force microscopy studies on crosslinked chitosan thin film. International Journal of Physical Sciences, 2744-2749. Yoruç, A. B., & Şener, B. C. (2012). Biomaterials, A Roadmap of Biomedical Engineers and Milestones. Retrieved from InTech: http://www.intechopen.com/books/a-roadmap-ofbiomedical-engineers-and-milestones/biomaterials Yu, L., Gong, J., Zeng, C., & Zhang, L. (2013). Preparation of zeolite-a/chitosan hybrid composites and their bioactivities and antimicrobial activities. Materials Science Engineering C, 36523660. Zhang, J., Chen, Z., Wang, Y., Zheng, G., Zheng, H., Cai, F., & Hong, M. (2017). Influence of the nature of amino acids on the formation of mesoporous LTA-type zeolite. Microporous and Mesoporous Materials, 79-89. Zhang, Y., Yan, W., Sun, Z., Pan, C., Mi, X., Zhao, G., & Gao, J. (2015). Fabrication of porous zeolite/chitosan monolliths and their applications for drug release and metal ions adsorption. Carbohydrate Polymers, 657-665. Zvezdova, D. (2010). Synthesis and characterization of chitosan from marine sources in Black Sea. НАУЧНИ ТРУДОВЕ НА РУСЕНСКИЯ УНИВЕРСИТЕТ, 65-69.

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Spectroscopic studies of plasma-modified silver-exchanged zeolite and chitosan composites

Highlights - Silver-zeolite is attracted to the -OH and -NH2 functional groups of chitosan - -COCH3 termination is induced by the argon plasma etching effect - surface prefers to be terminated with amine and hydroxyl groups

25 November 2019

Declaration of Interest Statement On behalf of the authors, we have no pecuniary or other personal interest, direct or indirect, in any matter that raises or may raise a conflict with the submission of the manuscript, Spectroscopic studies of plasma-modified silver-exchanged zeolite and chitosan composites.

Magdaleno R. Vasquez Jr. Corresponding Author [email protected]