Accepted Manuscript Ultrasonic-promoted rapid preparation of PVC/TiO2-BSA nanocomposites: Characterization and photocatalytic degradation of methylene blue Shadpour Mallakpour, Sima Shamsaddinimotlagh PII: DOI: Reference:
S1350-4177(17)30460-1 https://doi.org/10.1016/j.ultsonch.2017.09.052 ULTSON 3900
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Received Date: Revised Date: Accepted Date:
6 September 2017 27 September 2017 29 September 2017
Please cite this article as: S. Mallakpour, S. Shamsaddinimotlagh, Ultrasonic-promoted rapid preparation of PVC/ TiO2-BSA nanocomposites: Characterization and photocatalytic degradation of methylene blue, Ultrasonics Sonochemistry (2017), doi: https://doi.org/10.1016/j.ultsonch.2017.09.052
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Revised Ultrasonic-promoted rapid preparation of PVC/TiO 2-BSA nanocomposites: Characterization and photocatalytic degradation of methylene blue
Shadpour Mallakpour *, 1,2 and Sima Shamsaddinimotlagh 1
Organic Polymer Chemistry Research Laboratory, Department of Chemistry, Isfahan
University of Technology, Isfahan, 84156-83111, Islamic Republic of Iran 2
Research Institute for Nanotechnology and Advanced Materials, Isfahan University of
Technology, Isfahan, 84156–83111, Islamic Republic of Iran
Corresponding author at. Organic Polymer Chemistry Research Laboratory, Department of Chemistry, Isfahan University of Technology, Isfahan, 84156-83111, Islamic Republic of Iran ∗
Tel.; +98-311-3391-3267; FAX: +98-311-3391-2350. E-mail address: [email protected]
, [email protected]
, [email protected]
(Shadpour Mallakpour). 1
ABSTRACT In the present project in order to prevent agglomeration and better dispersion of TiO2 nanoparticles (NPs) in the poly(vinyl chloride) (PVC) matrix, initially, the surface of TiO2 NPs was covered by bovine serum albumin protein (BSA) via sonication method. Then, the TiO2-BSA powders were embedded into the PVC matrix using ultrasonic irradiations. With mechanical and magnetic stirring homogenous mixture was not obtained. So sonication process was very essential and vital. Physical, chemical and structural properties of the samples were investigated with various tools. Morphology studies showed the well distribution of spherical TiO2 NPs in the PVC matrix. TGA analysis showed that nanocomposites (NCs) have higher thermal stability than the pristine polymer. The photocatalytic activity tests by destroying the methylene blue dye on the pristine TiO2 NPs, TiO2-BSA NPs and PVC/TiO2-BSA NC 6 wt% were examined. The results showed that the photocatalytic activity of TiO2 NPs was reduced in the presence of BSA and PVC. It can be concluded that the TiO2-BSA NPs and PVC/TiO2-BSA NC 6 wt% have UV shielding properties and can protect film from degradation by UV.
Keywords: Poly(vinyl chloride) TiO2 nanoparticles Ultrasonic technique Photocatalytic activity Bovine serum albumin
1. Introduction Nanocomposites (NCs) consist of dispersed nanofillers in the matrix, if the type of matrix is a polymer, the obtained NCs called polymer NCs. Metal oxide nanoparticles (NPs) are used as fillers which their incorporation in the polymer matrix is one of the most effective method for producing macromolecule/inorganic NCs. However, these NPs have some limitations as follows: They show hydrophilic properties because of the existence of OH groups on their surface. Also, the small size and high surface area of these NPs increase their activity and subsequently decrease their stability. This two drawbacks lead to considerable agglomeration of metal oxide NPs. Surface modification of metal oxide NPs is one of the most effective methods to overcome these limitations. The functional groups of modifier can be linked to OH groups of metal oxide NPs and reduce their agglomeration [1-6]. The major of the proteins in blood plasma is composed of Bovine Serum Albumin (BSA) which has significant role in the biological system. BSA is a large globular and biocompatible protein with molecular weight of 66.5 kD taken from cow serum. This protein has many amino acid functional groups that can be used as a chelating factor for sorption of metal ions and able to interact with organic compounds via powerful hydrophobic interaction [7-10]. Poly(vinyl chloride) (PVC) is one of the greatest generally thermoplastics and is the second major produced resins in the world with many applications. It has valuable properties, for example, good processability, low production price, excellent chemical and mechanical resistance (to oxidants, halogens or acids). However, it has limitations such as low thermal stability and fragility, and it is non-biodegradable in nature [6, 11-13]. Ultrasonic irradiation is a modern technology, which extensively employed in chemical reactions. Ultrasonic is used to clean water from algae and other contaminants. Also, it was used to disperse nanofiller in various matrixes and it is a good alternative for great-speed
mixers [3, 14-17]. In order to achieve the goals of green chemistry, ultrasonic is an important technique which has a great influence on the speed of chemical processes. In an ultrasonic technique, with the passes alternately of the high and low-pressure waves through the fluid generate small bubbles from the fluid. This phenomenon is known as cavitation which reduces the accumulation of NPs due to its high cutting power. Dyes are one of the main pollutants which are generally aromatic and stable and their decomposition speed under biological process is low. Recently, numerous studies have been conducted for removal of these dyes from water and environment. Methylene blue (MB) known as thiazine cationic dye which is not very toxic but its high concentration has created problems for living organisms. The presence of this dye in the water prevents penetrating sunlight from the water that causes water pollution. One of the chemical processes for destruction of dyes is using photocatalysts process [19, 20]. When the semiconductor photocatalysts absorb light, the term of heterogeneous photocatalysis is used. Today, much attention has been associated with the photocatalytic semiconductors. The photocatalysis method has been studied in a number of metal oxides, for example, SiO2, Al2O3, WO3, V2O5, ZnO, and TiO2 [21, 22]. TiO2 NPs due to its unique properties such as cheap price, easy preparation, readily accessibility, safety toward environment and humans, chemical stability, non-toxicity, and better photodegradation are distinct from other particles. Furthermore, they have abundant applications in solar cells, sensors, and lasers. In nature, TiO2 exists in three forms: anatase, rutile, and brookite, therefore it is multi-crystal structure. The band gap values of anatase and rutile are 3.2 and 3.0 eV which are low for UV absorption. In fact, UV/Vis light and photons with high energy can be absorbed by TiO2. An easy way to reduce the band gap of TiO2 and prevent this limitation is the use of additives [23-26]. Simi et al. modified the TiO2 NPs with BSA by sodium aluminum silicate and glutaraldehyde. Transmission electron microscopy
(TEM) images showed that the size of TiO2 NPs after modification increased and found to be 0.4-0.6 micron . Cho et al. investigated the photocatalytic degradation of PVC–TiO2 composites and the results showed that the PVC–TiO2 composites have high photodegradation property . In 2014, Mudassir Hasan and coworker synthesized the PVC/TiO2 NC films and observed that the strain-induced band gap reduced and thermomechanical properties increased . Yang et al. investigated the solid phase photocatalytic degradation of PVC/vitamin C/TiO2 under UV/Vis light. They demonstrated that PVC–VC– TiO2 NC has a high photocatalytic activity; the photocatalytic degradation rate of it is 2 times greater than that of PVC–TiO2 film and 15 times greater than that of neat PVC film. . In 2016, Deng et al. studied the photocatalytic antibacterial activity of modified PVC/TiO2 film with iodine under visible light. They concluded that the fabricated I-TiO2/PVC-11d shows outstanding photocatalytic activity for the deactivation and killing of Escherichia coli bacteria under visible light irradiation.. Reddy et al. reported that the Ag-TiO2 composite showed higher photocatalytic activity than pure TiO2 nanofiber, which related to the efficient interaction between Ag NPs and TiO2 nanofiber support.. Size, morphology, and surface area of TiO2 NPs have a significant impact on physicochemical properties of NCs, so the aggregation of TiO2 NPs in polymer matrix prohibit to receive better properties and suitable applications [33, 34]. So, to improve different features of PVC matrix, first, the surface of TiO2 NPs was modified with BSA as a green molecule using of ultrasonic irradiation as a green and facile process for better dispersity of TiO2 NPs in the polymer matrix. PVC/TiO2-BSA NC films containing different weight percentages of TiO2-BSA were fabricated and the structure and properties of the fabricated NCs were investigated by different techniques. Finally, the photocatalytic activity of pristine TiO2, TiO2-BSA NPs and PVC/TiO2-BSA NC films under UV/Vis radiation via degradation of MB dye was investigated.
2. Experimental 2.1. Applied Materials PVC (Mw =78000 g. mol-1 ) and tetrahydrofuran (THF) (Mw = 72.11 g. mol-1 ) were purchased from LG Chem and JEONG Wang (Korea), respectively. Nanosized TiO2 powder (78.8% anatase and 21.2% rutile) with average particle sizes of 10-15 nm was purchased from Neutrino Co (Iran). BSA (Mw: 66,463 Da) was supplied from the company of SigmaAldrich. MB (Mw = 319.85 g. mol-1) was obtained from Merck Chemical Co. Germany. (Germany). 2.2 Apparatus The preparation of TiO2-BSA NPs and PVC/TiO2-BSA NCs was carried out on TOPSONIC ultrasonic liquid processors (Tehran, Iran). The ultrasound was used with a frequency wave of 20 kHz and a power of 100 W. Fourier transform infrared (FT-IR) spectra were collected by a Jasco-680 spectrophotometer (Tokyo, Japan). All spectra were recorded in the range of 4000-400 cm-1. Field-emission scanning electron microscopy (FE-SEM) images were obtained by HITACHI (S-4160). TEM was conducted at 150 kV with a Philips CM 120 (Netherlands) microscope. The X-ray diffraction (XRD) patterns of the samples were surveyed by Philips X′Pert MPD (Germany) diffractometer with Cu Kα of radiating of wavelength 1.540 Å. The 2θ scanning range was varied from 10 to 80º, worked at 40 kV and 35 mA tube current. The energy dispersive X-ray spectroscopy (EDX Analysis) was performed by TESCAN MIRA II (Czechoslovakia) spectrometer. Thermal gravimetric analysis (TGA) was accomplished by STA503 TA instrument to evaluate the thermal degradation behavior of the samples. To achieve the real results, samples were dried at 4050ºC for 4 h under vacuum before doing the TGA analysis The TGA analysis was performed from 100 to 800 ºC at a heating rate of 20 ºC min-1 under argon flow. Tensile tests were carried out on a Testometric Universal Testing Machine M350/500(UK). The tests were
performed at room temperature at a crosshead speed of 5 mm/min with dimensions of 10 mm×35 mm and average thickness of them is 0.043 mm. The UV–Vis spectra of the samples were measured with a Jasco 570 UV-Vis spectrometer in the wavelength range from 200-800 nm. For the measurement of the surface area of TiO2-BSA NPs and PVC/TiO2-BSA NC 6 wt%, the Brunauer-Emmet-Teller (BET) analysis via NANOSORD (Iran) was performed. 2.3 Surface modification of TiO2 NPs At first, the phosphate buffer solution with pH = 4.1 was prepared by adding 6.8 g of KH2PO4 in 100 mL of distilled water. Then, 0.015 g of BSA was added to 1 mL of buffer solution for wetting (beaker 1). In another small beaker, 0.1 g of TiO2 NPs were also added to 20 mL of buffer solution and sonicated for 7 min at power of 50 W and frequency of 20 kHz (beaker 2). Finally, the soaked BSA was added to beaker 2 and stirred magnetically for 24 h at room temperature. After that, the suspension was exposed to ultrasonic waves for 5 min. Then, the mixture was centrifuged for 9 min and washed with buffer solution and distilled water several times. The resulting powder was dried at room temperature (Scheme 1). 2.4 Fabrication of PVC/TiO2-BSA NCs 0.3 g PVC was completely dissolved in 10 mL of THF. Then, 0.009 g of TiO2-BSA NPs was added in prepared solution. The mixture was stirred at room temperature for 24 h and ultrasonicated for 7 min. Finally, the casting was done in a proper petri dish for the fabrication of PVC/TiO2-BSA NC 3 wt%. The same steps were performed for the preparation of PVC/TiO2-BSA NC films 6 and 9 wt%. At all stages of ultrasonic, the temperature of the samples goes up due to the mechanical motivation, which is why the samples were placed in the ice bath . 2.5 Photocatalytic test procedure
The photocatalytic activity of different samples like pristine PVC (0.1 g), TiO2-BSA NPs (0.04 g), bare TiO2 NPs (0.04 g), and PVC/TiO2-BSA NC 6 wt% (0.1 g) was tested in the beaker with 100 mL of solution MB (as the model of pollutant dye) (10 ppm) in wooden box (homemade) under UV/Vis source which contains 4 lamps TUV 8W (PHILIPS (made in Poland) G8 T5). The samples were placed at 15 cm away from the lamps. At first, all samples before irradiations were agitated for 30 min in a dark environment to arrive steady state between solution and solid catalyst and then, they were exposed to UV irradiation. During the irradiations, 2.5 mL of dye solution was taken from the beaker at different time intervals and centrifuged to remove remaining catalyst and obtain UV/Vis spectra at the specific wavelength (664 nm). After that, the taken dye solution was transferred to the beaker in the photocatalyst box. All these steps were repeated for twice. Blank test was also directed by using dye solutions without sorbent. 3.
Results and discussion In recent years, ultrasonic irradiation as a green and bio-safe method has many interest in
the green chemistry. For example, it was applied for modification of NPs and also for synthesis of polymer NCs. The probable mechanism of ultrasonic irradiation is based on creation of acoustic cavitation which causes high pressure (500 atmospheres) and temperature (5000 K) in the reaction environment. By applying ultrasound through the liquid, the process such as creation, gradual growth and ultimately the explosion of series of bubbles happened. The produced energy by this shock wave is used to break the covalent bonds, homogenize, and carry out some chemical reaction, especially the fabrication of NPs, synthesis of organic matter and etc . In this work because of high energy and pressure of ultrasonic tools, the BSA molecules were coated on the surface of TiO2 NPs. And also due to the high pressure and energy of the ultrasonic irradiations, the modified TiO2 NPs were homogenously dispersed in the matrix of polymer. The advantage of this method in comparison with the
conventional methods such as phase separation method and solvent casting method is its lowcost and simplicity which leads to reduction of the reaction time and also this method is green and environmentally friendly. Moreover, due to the high energy related to ultrasonic treatment, this method increases the homogenous dispersion of NPs in the matrix of polymer in comparison with the conventional methods . Surface modification is a vital issue for the better dispersion of NPs in the polymer matrix and avoiding aggregation. In this work, the surface of TiO2 NPs was modified by BSA as a coupling agent. The hydrogen bonds can be formed between surface hydroxyl groups of TiO2 NPs and carboxylic acid and amino groups of BSA. In a total of the process, a short period of ultrasonication was considered (7min) based on reported research by Jing et al. They explained that ultrasonic can change the secondary structure of BSA . The TiO2-BSA surface reacts with Cl atoms in the PVC chain (scheme 2). The visual images of NC films (3, 6, and 9 wt%) are shown in Fig. 1. As can be seen, the transparency is reduced by increasing the concentration of TiO2 NPs. Fig. 1e shows the flexibility of the prepared PVC/TiO2-BSA NC 6 wt% film.
3.1. FT-IR Fig. 2 depicts the FT-IR spectra of bare BSA, unmodified TiO2, and TiO2-BSA NPs. The FT-IR spectrum of bare BSA shows three important peaks at 1535, 1656 and 3329 cm-1 which are attributed to the amide type II (the combination of stretching vibrations of C–N and bending vibrations of N–H), amide type I (mostly C=O stretching vibrations) and stretching vibrations (–OH), respectively . The FT-IR spectrum of unmodified TiO2 represents the distinctive band at 3483 and 1630 cm-1 which are attributed to stretching and bending hydroxyl groups (adsorbed of water molecules), on the surface of TiO2 NPs. Stretching vibrations of Ti-O-Ti are located in the region of 450-1028 cm-1[40, 41]. Characteristics
peaks of both TiO2 and BSA could be seen in the spectrum of TiO2-BSA which shows successful surface treatment. FT-IR spectra of pristine PVC and PVC/TiO2-BSA NC films (3, 6, and 9 wt%) are illustrated in Fig. 3. In the spectrum of pristine PVC, the peaks placed in 616 and 692 cm-1 are related to the C-Cl band. The observed peaks in wavelength at 1097, 2912 and 2971 cm-1 are defined to C–C and C-H stretching vibrations, respectively . Furthermore, peaks related to pristine PVC and the corresponding peak of TiO2 were also observed in PVC/TiO2-BSA NC films.
3.2. XRD XRD profile was used to identify the crystallographic of the samples. Fig. 4, depicts a comparison of XRD profiles of the samples. In XRD profile of BSA, no characteristic peak was observed which indicates the composition of BSA is amorphous. In the pattern of pristine TiO2 NPs, the peaks of (101), (004), (200), (105), (211), and (204) at 2θ= 25-63º are related to anatase phase. Also, two characteristic peaks of (220) and (110) at 2θ=58.9 and 27.4 º are indexed to the rutile phase, which indicated that the percentage of anatase phase is more than of rutile phase [40, 41, 43]. In the XRD profile of TiO2-BSA NPs, all peaks of pristine TiO2 were observed which confirmed that modification of TiO2 has no effect on the crystallinity of particles. The broad peak of PVC indicated that it has poor crystallinity . But in obtained PVC/TiO2-BSA NC films, due to the presence of BSA-TiO2 NPs into the PVC, some crystalline phase was found.
3.3. EDX analysis EDX analysis is an identification technique which can qualitatively prove the presence of elements in the BSA-TiO2 NPs and PVC/TiO2-BSA NC 6 wt%. EDX analysis results of BSA-TiO2 NPs are shown in Fig. 6 and Table 1. According to it, the elementals such as Ti,
O, C, N, S, P, and K were observed. The presence of S and N is the best sign for the existence of BSA molecules on the surface of TiO2 NPs. Also, the existence of Cl group in EDX analysis of PVC/TiO2-BSA NC 6 wt% (Fig. 7 and Table 2) confirmed the presence of PVC in NC film.
3.4. TGA The TGA graphs of pristine TiO2 and TiO2-BSA are drawn in Fig. 8. As it is clear from TGA graph of pristine TiO2, losing weight was about 3.5 % which is attributed to evaporation of water on the surface of NPs and the dehydroxylation on the surface of NPs . However, TiO2-BSA NPs have a weight loss in the range of 100 to 800 ºC which is related to the degradation of the BSA. According to the TGA graph, it can be inferred that the thermal stability of TiO2-BSA is less than pristine TiO2 and based on the graph, the amount of BSA on the surface of TiO2 NPs was about 16 wt%. The TGA thermograms of pristine PVC and different PVC/TiO2-BSA NC films are shown in Fig. 9. All of the thermograms have two stages of degradation. The first step of degradation occurs in the range of 200-350 ºC due to loss of additives in PVC and HCl and the second step of weight loss in the range of 400-500 º
C corresponded to the formation of aromatic compounds as a result of the serial loss of H-Cl
with polyene sequences [45, 46]. In contrast to the pristine PVC, PVC/TiO2-BSA NC films showed higher onset degradation temperatures. PVC/TiO2-BSA NC films showed high thermal stability than pristine PVC but by increasing of TiO2-BSA NPs content, the thermal stability decreased for PVC/TiO2-BSA NCs 6 and 9 wt%. As it is clear from the table 3 the onset decomposition temperature of PVC/TiO2-BSA NCs increased remarkably about 4653ºC and 38-43 ºC, respectively, by TiO2-BSA loading compared to the pristine PVC.
3.5. FE-SEM and TEM analyses
High-energy electrons which are produced by FE-SEM tool have a potential to produce variegation of signals on the surface of the materials. The generated signals from the interaction of beam electrons to samples give information about the morphology and inner structure of the samples . So, the surface morphology of TiO2-BSA NPs and PVC/TiO2BSA NC films was investigated and their images are shown in Figs 10 and 11, respectively. TiO2-BSA NPs showed spherical shape with uniform size (Fig. 10). As it can be observed from Fig. 11, after incorporation of TiO2-BSA into PVC matrix, the morphology of PVC did not change. For visualizing and determination of the arrangement template of NPs in TiO2BSA NPs and in the PVC/TiO2-BSA NCs, TEM analysis was applied. The TEM images of three nanoscopic magnifications of samples are displayed in Figs. 12 and 13, respectively. According to TEM images of TiO2-BSA NPs, NPs showed the mean diameter of 44 nm with the spherical shape and uniform distribution without noticeable aggregation. The mean size of TiO2-BSA NPs in the PVC matrix is calculated to be about 49 nm and the spherical morphology is retained by transferring to the polymer matrix. It is noteworthy to mention that the surface modification of TiO2 NPs and use of ultrasonic method were main keys for the adequate and homogeneous distribution of TiO2-BSA NPs in the PVC matrix.
3.6. UV/Vis The electron transfer among the special energy levels such as n, σ, and π from the ground state to the excited state is responsible for light absorption in the region of UV/Vis by polymeric materials. The UV/Vis spectra of pristine PVC and fabricated PVC/TiO2-BSA NC films in the wavelength range of 200-800 nm were collected in Fig. 14. The light absorption of the samples occurred in the UV region. The first absorption peak observed in the vicinity of 210 nm was due to electron transfer from π → π*and the second peak at around of 280 nm corresponded to electron transfer from n → π*. According to the Fig. 14, it can be
concluded that prepared PVC/TiO2-BSA NC films have higher absorbance than the pristine PVC. With the increase of the TiO2 NPs concentration, the peaks moved toward higher wavelengths and a redshift occurs which can be attributed to the interaction of the TiO2 NPs with polymer chains [48, 49]. Two methods have been used to calculate ban gap energy of samples. In the first method by equation 1, which λmax is the maximum wavelength  the values of energy gap for the pure TiO2, TiO2-BSA NPs, and PVC/TiO2-BSA NC 6 wt% are 6.1, 6.1, and 5.6, respectively. In the second method by equation 2 which called Tauc's relationship (α0 is absorption coefficient which is a constant value and h is Planck's constant hν is the energy of the photon, and n is exponent to the sort of electronic transition) [50, 51]. The band gap energy of pure TiO2, TiO2-BSA NPs, and PVC/TiO2-BSA NC 6 wt% showed in Fig. 15 and were estimated as 6.1, 6.1, and 5.2, respectively. The obtained results from both methods are matched well and the energy gap of TiO2 NPs does not change except in the case of PVC/TiO2-BSA NC 6 wt% which shows reduction in the bandgap.
3.7. Mechanical behavior The mechanical performance of the pristine PVC and PVC/TiO2-BSA NC films was shown in Fig. 16. The mechanical properties data were tabulated in Table 4. Not only the type and amount of fillers, can affect the mechanical properties of the NCs, but also the
amount of interaction of NPs with the matrix and uniform distribution are the other effective factors on the mechanical properties . Based on results, elongation at breaking, strain, and stress of all PVC/TiO2-BSA NC films were lower than the pristine PVC. However, iiitwiaincrease in the content of TiO2-BSA NPs, these characteristics were increased. But Young’s modulus values of all PVC/TiO2-BSA NC films was higher than the pristine PVC and indicated that the TiO2-BSA NPs has a positive effect on the stiffness of PVC/TiO2-BSA NC films. The increment in the modulus might be ascribed to the resistance to the segmental motion of the polymer chains identified by the presence of TiO2-BSA NPs within the PVC matrix.
3.8. Contact angle The wettability properties of materials can be studied by measuring the contact angle and it plays a significant role to reject salt solutions, corrosive and can influence on anti-corrosion behavior. When the contact angle is smaller than 90 degrees, wettability properties is high [53, 54]. Contact angle measurements were conducted by placing three drops with a same color and volume using a syringe (Fig. 17). The photos of drops were taken by a digital camera after 30 s. The results were listed in Table 5. According to the data, all the PVC/TiO2BSA NCs showed lower contact angles and higher hydrophilicity compared to the pristine PVC. Also with increasing of NPs loading, the hydrophilicity was increased for NCs. Hydroxyl functional groups on the surface of TiO2 NPs as well as polar and hydrophilic groups of the BSA can enhance the wettability and hydrophilicity properties of the substrates .
3.9. BET test
Via the BET analysis, the specific surface area (SSA) of the TiO2-BSA NPs and PVC/TiO2-BSA NC 6 wt% film was estimated to be about 32.82 m2 g-1 and 26.64 m2 g-1, respectively. The results showed that with modification of the TiO2 NPs and embedding them in the PVC matrix, the surface area was decreased compared to the pure TiO2, which can be attributed to the presence of the PVC matrix around the TiO2 NPs .
3.10. Study of photocatalytic activity of the samples TiO2 NPs have the ability to absorb UV/Vis light. Among the different forms of TiO2, anatase form is a highly UV/Vis absorbent. When TiO2 is irradiated by UV/Vis, electrons and holes are created which lead to the production of hydroxyl radical and superoxide groups via reaction of the hole in the valance band (vb) and electron in conduction band (cb) . The produced radicals with strong oxidation capability react with MB dye as an electron acceptor and change it to carbon dioxide and water (Fig. 18). Reaction steps for MB degradation in the PVC/TiO2-BSA NC film are shown as follows :
TiO2 + hυ → TiO2* → e- (cb) + h+ (vb) .e (cb) + O2 → O2 h+ (vb) + OH surface or H2O → OH .-
O2 and OH + Organic pollutant (MB) → H2O + CO2 . In this study, TiO2 NPs which are in the PVC matrix play key role in photodegradation process. UV/Vis spectra of pure TiO2 during irradiation time were shown in Fig. 19. As can be seen, MB was degraded after 300 min totally and the blue color of the sample was changed to colorless. Whereas, this phenomena happened after 660 min for the TiO2-BSA sample (Fig. 20). This is because of the surface coating of NPs by BSA, which causes decreasing in SSA of TiO2 NPs as was shown by BET analysis.
Fig. 21 shows the UV/Vis spectra of MB in the presence of pure PVC at different irradiation times. As can be observed there is no significant change in the peak positions of UV/Vis during irradiations. So, it can be said that the pure PVC cannot degrade MB under UV irradiations, lonely. While, PVC/TiO2-BSA NC 6 wt % could degrade MB more than pure PVC, but less than pure TiO2 and TiO2-BSA (Fig. 22), respectively. It can be due to good dispersion of NPs and their surrounding by PVC which lead to increasing in size of NPs and decreasing SSA as well as photocatalytic activity. The degradation rate of MB solution with TiO2, TiO2-BSA, pure PVC and PVC/TiO2-BSA NC 6 wt% is shown in Fig. 23. According to the following formula, the percentages of dye removal for TiO2-BSA NPs and PVC/TiO2-BSA NC 6 wt % were 97% and 44%, respectively after 600 min. It was 97% for pure TiO2 after 300 min. R%=
It was observed that with an increase in irradiation time, the intensities of the peak at 650700 nm were reduced which showed MB degradation. The degradation rate of MB was faster for the pure TiO2, TiO2-BSA, and PVC/TiO2-BSA NC, respectively. As a conclusion, it can be mentioned that TiO2 NPs in prepared samples of modified TiO2 and NC can absorb UV less than the pure TiO2, so they can play a role as UV protector and shield film from degradation by UV.
Conclusions In this research, TiO2 NPs were modified by BSA as a bio-coupling agent and then incorporated into the PVC matrix by ultrasonic irradiation for uniform dispersion of NPs in the PVC matrix. Homogenous NCs were provided by an ultrasonic technique which this extraordinary feature was not achieved with mechanical stirring as well as magnetic stirring procedure. Various analyses such as TEM, EDX, and photocatalytic activity were applied 16
on PVC/TiO2-BSA NC 6 wt%. Studies showed an increase in optical and thermal properties of the obtained NCs compared with the pristine polymer. FT-IR analysis of modified NPs was done and showed a successful modification of NPs. Contact angle measurement demonstrated which fabricated PVC/TiO2-BSA NC films are more hydrophilic than the pure polymer. Spherical morphology and nanometer size of TiO2 NPs were detected by FESEM and TEM analyses. From the data of photocatalytic test it can be understood that the photocatalytic activity of TiO2-BSA NPs was reduced by embedding into the PVC matrix. This phenomenon could be due to an increase in the size of TiO2 NPs, a decrease of the surface area of the particles after modification, a decrease also to its content and effect of the modification on the band gap energy.
Acknowledgments The authors would like to thank the Research Affairs Division Isfahan University of Technology (IUT), Isfahan, Iran. This project was supported by a grant from Iran Nanotechnology Initiative Council (INIC), Tehran, Iran, National Elite Foundation (NEF), Tehran, Iran and Center of Excellence in Sensors and Green Chemistry Research (IUT), Isfahan, Iran is mercifully acknowledged.
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Legends for the Schemes: Scheme 1. Surface modification of TiO2 NPs with BSA by ultrasonic irradiation. Scheme 2. Schematic of the suggested attractions among BSA/TiO2 NPs in the PVC matrix.
Legends for the Figures:
FIG. 1. Visual images of (a): pristine PVC, (b): PVC/TiO2-BSA NC 3 wt%, (c): PVC/TiO2BSA NC 6 wt%, (d): PVC/TiO2-BSA NC 9 wt%, and (e): flexibility of PVC/TiO2-BSA NC 6 wt%
FIG. 2. FT-IR spectra of (a): BSA, (b): bare TiO2, and (c) TiO2-BSA NPs. FIG. 3. FT-IR spectra of (a): pristine PVC, (b): PVC/TiO2-BSA NC 3 wt%, (c): PVC/TiO2BSA NC 6 wt%, and (d): PVC/TiO2-BSA NC 9 wt%. FIG. 4. XRD profiles of (a): BSA, (b): bare TiO2, and (c): TiO2-BSA NPs. FIG. 5. XRD profiles of a) Pristine PVC, b) PVC/TiO2-BSA-NC 3 wt%, c) PVC/TiO2-BSANC 6 wt%, and d) PVC/TiO2-BSA-NC 9 wt%. FIG. 6. EDX analysis of TiO2-BSA NPs. 21
FIG. 7. EDX analysis of PVC/TiO2-BSA NC film 6 wt%. FIG. 8. TGA graphs of (a): bare TiO2, (b): TiO2-BSA NPs. FIG. 9. TGA graphs of (a): pristine PVC, (b): PVC/TiO2-BSA NC 3 wt%,(c): PVC/TiO2BSA NC 6 wt%, and (d): PVC/TiO2-BSA NC 9 wt%. FIG. 10. The FE-SEM image of TiO2-BSA NPs in two diverse magnifications. FIG. 11. FE-SEM pictures of (a): Pure PVC, (b): PVC/TiO2-BSA NC 3 wt%, (c); PVC/TiO2BSA NC 6 wt%, and (d): PVC/TiO2-BSA NC 9 wt% at different magnifications. FIG. 12. TEM images of TiO2-BSA NPs at three dissimilar magnifications with related histogram. FIG. 13. TEM images of PVC/TiO2-BSA NC 6 wt% with related histogram. FIG. 14. UV/VIS spectra of (a): pristine PVC, (b): PVC/TiO2-BSA NC 3 wt%, (c): PVC/TiO2-BSA NC 6 wt%, and (d): PVC/TiO2-BSA NC 9 wt%. FIG. 15. UV-Vis spectra of (Ahν)0.5 versus energy (hν) of (a): pure TiO2, (b):TiO2-BSA NPs and (c):PVC/TiO2-BSA NC 6 wt%. FIG. 16. The stress-strain curves of the pristine PVC and PVC/TiO2-BSA NC films. FIG. 17. Contact angle pictures of a) Pristine PVC, b) PVC/TiO2-BSA NC 3 wt%, c) PVC/TiO2-BSA NC 6 wt%, and d) PVC/TiO2-BSA NC 9 wt%. FIG. 18. Degradation mechanism of MB by OH and super oxide radical. FIG. 19. A: Variation of the absorption intensity of the pure PVC solution at λmax=664 nm under UV/Vis light for 600 min time and B: Zoom in the wavelength range 595 to 665 nm (a: Initial concentration of MB, b: 30 min at dark, c: after 20 min, d: after 60 min, e: after 120 min, f: 240 min, g: after 300 min, h: after 480 min, i: after 540 min, and j: after 600min). FIG. 20. Variation of the absorption intensity of the MB solution at λmax=664 nm for pure TiO2 NPs under UV/Vis light for 300 min time. (a : Initial concentration of MB, b: 20 min, c: after 90 min, d: after 180 min, e: after 240 min, f: after 300 min).
FIG. 21. Variation of the absorption intensity of the MB solution at λmax=664 nm for TiO2BSA NPs under UV/Vis light for 660 min time.(a: Initial concentration of MB, b: 30 min at dark, c: after 20 min, d: after 90 min, e: after 180 min, f:240 min, g: after 300 min, h: after 360 min, i: after 480 min, j: after 540 min, k: after 600 min, and l: after 660 min). FIG. 22. A: Variation of the absorption intensity of the MB solution at λmax=664 nm for PVC/TiO2-BSA NC 6 wt% under UV/Vis light for 540 min time and B: Zoom in the wavelength range 595 to 665 nm. (a: Initial concentration of MB, b: 30 min at dark, c: after 20 min, d: after 60 min, e: after 120 min, f:180 min, g: after 300 min, h: after 360 min, and i: after 540 min). FIG. 23. Photodegradation performance of MB solution for different samples (a: pure MB, b: PVC/TiO2-BSA NC 6 wt%, b': TiO2-BSA NPs, c: pure PVC and c': pure TiO2) under UV/Vis light irradiation.
Caption for Table: Table 1: Percentages and types of elements in the TiO2-BSA NPs. Table 2: Percentages and types of elements in the PVC/TiO2-BSA NC 6 wt%. Table 3: Thermal performance of the pristine PVC and PVC/TiO2-BSA NC films. Table 4: Mechanical performance of the pristine PVC and PVC/TiO2-BSA NC films. Table 5: The contact angle measurement of the pristine and NC films of the PVC.
Table 1 Intensity
Table 2 Intensity
Table 3 T10(ºC)b
PVC/TiO2-BSA NC 293 3 wt% PVC/TiO2-BSA NC 286 6 wt% PVC/TiO2-BSA NC 287 9 wt%
Temperature at which 5% of the samples was destroyed with the speed of 20 °C/min under an argon flow b Temperature at which 10% of the samples was decomposed with the speed of 20 °C/min under an argon flow c weight loss of samples under argon flow at temperature 800 °C
Table 4 Stress
PVC/TiO2-BSA NC 3 wt% PVC/TiO2-BSA NC 6 wt% PVC/TiO2-BSA NC 9 wt%
Table 5 Samples
PVC/TiO2-BSA NC 3 wt%
PVC/TiO2-BSA NC 6 wt%
PVC/TiO2-BSA NC 9 wt%
TiO2 NPs were modified with BSA and embedded into the PVC matrix to prepare NCs.
The above novel and essential materials were synthesized by ultrasonication method.
EDX, FT-IR and XRD analyses confirmed successful modification of TiO2 NPs.
Enhancement in optical and thermal performance of NCs films was observed.
The photocatalytic results showed degradation ability of the obtained nanomaterials.