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Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright Author's personal copy Progress in Organic Coatings 72 (2011) 453–460 Contents lists available at ScienceDirect Progress in Organic Coatings journal homepage: www.elsevier.com/locate/porgcoat Synthesis, characterization and enhanced photocatalytic activity of TiO2 /SiO2 nanocomposite in an aqueous solution and acrylic-based coatings A. Mirabedini a , S.M. Mirabedini b,∗ , A.A. Babalou a , S. Pazokifard b a b Chemical Engineering Department, Sahand University of Technology, P.O. Box 51335-1996, Tabriz, Iran Iran Polymer & Petrochemical Institute, Colour & Surface Coatings Department, P.O. Box 14965-115, Tehran, Iran a r t i c l e i n f o Article history: Received 9 January 2011 Received in revised form 23 May 2011 Accepted 6 June 2011 Keywords: Photocatalytic TiO2 nanoparticles Sol–gel treatment Self-clean Organic coatings a b s t r a c t In this study, TiO2 /SiO2 nanocomposites were synthesized via a sol–gel route by adding tetraethylorthosilicate (TEOS) to a solution containing different molar ratios of Degussa P25 TiO2 nanoparticles. FTIR, TGA, EDAX and XRD techniques were used to characterize the modified nanoparticles. Photocatalytic activity of the nanoparticles in an aqueous solution and into the acrylic based coating was evaluated using colour coordinate data measurements, SEM analysis, gloss measurements and FTIR spectroscopy, in the presence of Rhodamine B (Rh.B) dyestuff, as a pollutant model, before and after exposure to the UVA (340 nm) irradiation and compared to their unmodified counterparts. The results showed that silica grafting effectively reduced the photocatalytic activity of the TiO2 nanoparticles as evidenced by absorption spectra and colour changes of Rh.B aqueous solutions during the UVA irradiation. The results revealed the effectiveness of sol–gel route for preparation of TiO2 /SiO2 nanocomposites. The optimum result was obtained with 1% molar ratio of TiO2 :TEOS. Addition of TiO2 /SiO2 nanocomposites into the acrylic based coating revealed reduction of photo-degradation of Rh.B compared to untreated nanoparticles. Finally, inclusion of TEOS treated TiO2 nanoparticles into the aqueous organic coatings, provides photocatalytic property and as a result, it can possibly be considered for self-cleaning coatings. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Titanium dioxide has been widely used as a white pigment in a broad variety of applications, such as coatings, cosmetics, foodstuffs and extensive potential applications, due to its unique physical and chemical properties. It is well known that TiO2 in anatase crystalline form, which is biologically and chemically inert, can be used as an excellent photo-catalyst material in the hydrophilic self-cleaning coatings and widespread photocatalytic purposes under UV/Visible light irradiation [1–4]. When a photocatalytic anatase TiO2 having a band gap of 3.26 eV is exposed to an UV light source with a wavelength less than 380 nm, the pairs of electron–holes are created. The electrons are promoted from the filled valence band to an equal or higher energy level conduction band, which can move freely. The pairs of electron–holes are very reactive and might adsorbed species (reactants) on the particle surface, thus photo-oxidation reactions happen [5–7]. The activation of photocatalytic TiO2 by UV light can be written as Eq. (1) [6]: TiO2 + h → h+ + e− ∗ Corresponding author. Tel.: +98 21 4458 0040; fax: +98 21 4458 0023. E-mail address: sm.mirabedini@ippi.ac.ir (S.M. Mirabedini). 0300-9440/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.porgcoat.2011.06.002 (1) where h, h+ and e− are absorbed photon energy, hole and electron, respectively. The schematic of the photocatalytic oxidation process using TiO2 particles as a catalyst is illustrated in Fig. 1 [6]. However, photocatalytic TiO2 particles cannot be incorporated or deposited on the organic coatings, as they may oxidize the polymeric matrix. Therefore, surface modification of TiO2 particles is recommended to adjust their photocatalytic activity [8], dimensional stability [9] and wet-out between resin and particles [5]. Among the various techniques that are used to adjust photocatalytic activity of TiO2 particles, the silane treatment method offers definite advantages such as simplicity and low cost and also low processing temperature [9,10]. As this regard, a large number of reports deal with the application of titania–silica materials as catalysts in photocatalytic processes [10–13]. It is well known that TiO2 reveals outstanding photocatalytic activity for oxidative degradation of environmental pollutants [13–18]. The photocatalytic performance of TiO2 depends on; crystalline phases, specific surface area, particle size, morphology or heat treatment conditions [14]. The main application of photocatalytic activity in organic coatings is in decomposition of organic contaminants of water and air [13,19]. Illuminated anatase TiO2 also exhibited super hydrophilic properties, which were exploited for various applications such as self-cleaning, anti-fogging and antimicrobial effects in coatings [16,17]. Author's personal copy 454 A. Mirabedini et al. / Progress in Organic Coatings 72 (2011) 453–460 nanoparticles were washed several times with distilled water and finally dried in a low pressure oven at 100 ◦ C. 2.3. TiO2 /SiO2 nanocomposite characterization Fig. 1. The schematic of TiO2 UV photo-excitation process (R = reduction; O = oxidation) [6]. Despite the large number of works in this field, up to date, only some articles have been published on the usage of photocatalytic TiO2 particles in the organic coatings with the aim of achieving self-cleaning property [18–20]. The presence of photocatalytic TiO2 in a binder which contains mainly C–C bonds, leads to the binder structure degradation. Ultraviolet radiation that causes photo-catalysis supplies the energy needed for breaking C–C bonds [12]. The replacement of untreated TiO2 by surface-treated ones in binders will inhibit photo-reduction of the particle by ultraviolet radiation, therefore reduces its activity against radiation and as a result, it can inhibit binder destruction. In this study, TiO2 /SiO2 nanocomposites were prepared via a two-stage, sol–gel route using different molar ratios of TiO2 nanoparticles and tetraethoxysilane as precursors. The treated nanoparticles were characterized using conventional techniques. Photocatalytic activity of TiO2 nanoparticles in distilled water and into a water based acrylic coating was evaluated, in the presence of Rh.B dyestuff as a model. FTIR spectroscopy was performed in KBr pellet on a Bruker EQUINOX 55 LSI01 FTIR spectrometer, collecting 16 scans in the 400–4000 cm−1 range with 4 cm−1 resolution. The thermal behaviour of the nanoparticles (after drying in 100 ◦ C for 3 h) was evaluated using a TGA-PL-1500 under O2 atmosphere from room temperature to 700 ◦ C with 10 ◦ C min−1 heating rate. Energy dispersive X-ray spectroscopy (EDAX) was taken from the compressed nanoparticles and with Dot-mapping method by INCA250 instrument; Oxford Co. Samples were prepared with the same method that was used for EDAX analysis with a LSI01-3 SPECAC press instrument under 12 bar pressure. X-ray diffraction (XRD) patterns of the nanoparticles were recorded on a Shimadzu XRD-6000 with flow intensity and voltage of 50 mA and 30 kV, in the range 20–70◦ . 2.4. Preparation of acrylic nanocomposite coatings 2. Experimental 0.5 g of P25 or treated TiO2 nanoparticles (1 mol.%) were directly added to the 25 ml distilled water (containing 0.25 g L−1 Rh.B) and dispersed using ultrasonic irradiating for 20 min. The dispersions were then added to the 50 g emulsion resins and 0.5 g coalescing agent, mixed for further 60 min at a constant rate of 1000 rpm. Coating samples with a wet thickness of 200 ± 5 ␮m were applied on the degreased glass substrate using a film applicator (Model 352, Erichsen Co.). The applied films were then allowed to dry at 23 ± 2 ◦ C for about a week. The freestanding films were also prepared by application of the coating samples on the PTFE sheets with a wet film thickness of 200 ± 1 ␮m. The films were then left to dry at room temperature (23 ± 2 ◦ C) for about one week and detached from the sheets easily. 2.1. Materials 2.5. TiO2 /SiO2 nanocomposite photocatalytic activity TiO2 nanoparticles (P-25, with an average particle size of 30 nm) and tetraethylorthosilicate, TEOS, 98 wt.% were obtained from Evonik Degussa GmbH and Fluka, respectively. Acrylic emulsion resin, Mowilith® LDM 7729, 48 wt.% solid content, was obtained from Celanese Emulsions Co. Rhodamine B (Rh.B) and texanol was purchased from Ciba Gigy and Eastman Chemical Co., respectively. All other chemicals were of reagent grade and used without further purification. The aqueous dispersions were prepared by adding 0.65 g L−1 untreated or treated TiO2 nanoparticles, 0.025 g L−1 Rh.B and 0.12 mol L−1 sodium dodecyl sulfate, in distilled water. The dispersions were then exposed to the UVA irradiation (340 nm, 0.89 W m−2 ) in a QUV chamber at 60 ◦ C for various time intervals up to 8 h. The photocatalytic degradation of Rh.B in the dispersions was monitored using UV–Visible spectrophotometer, CECIL CE9200 in wavelengths 200–700 nm, via measuring the intensity of the typical absorbance peak at wavelength of 543 nm. Photocatalytic activity of TiO2 nanoparticles into the coating films was studied using colour coordinate data measurements, before and during exposure to the UVA irradiation. Photocatalytic performance of the paint films containing 1 wt.% of P25 and treated TiO2 (1 mol.%) was studied, in the presence of Rh.B dyestuff as a model. The sample’s films were exposed to the UVA light (340 nm, 0.89 W m−2 ) in a Q-Panel, QUV/Spray chamber, at 60 ◦ C for different time intervals up to 240 min. The colour coordinates were measured in accordance with ASTM D 65 standard practice using a Miniscan XE Plus colourimeter, from Hunter lab Co., illuminant D65, in angle 10◦ . Total colour difference, E, as a function of the UVA exposure time was calculated from CIE (Commission International de l’é clairage) L* a* b* 1976 formula (Eq. (2)) [21]: 2.2. Surface modification of TiO2 nanoparticles The synthesis procedure was based on a two-stage sol–gel method of acid hydrolysis and basic condensation at ambient temperature [8,10]. Three various levels of TiO2 nanoparticles (0.5, 1.0 and 2.0 mol.%) were dispersed in 40 ml isopropanol by the aid of sonication (Bandelin, HD3200, KE-76 probe) for 15 min under power of 70 W, 0.7 s pulse on and 0.3 s pulse off, and were then stirred for a further 1 h. 2.5 ml distilled water, 2.5 ml HCl and 35 ml isopropanol were then added to the mixtures, and stirred at 1000 rpm for a further 1 h. pH of the mixture was measured between 2 and 3. Proper amount of TEOS (molar ratio isopropanol/TEOS = 2 and molar ratio H2 O/TEOS = 1.2) was added dropwise to the mixture under stirring within 15 min and were stirred for a further 16 h at a dark place. Equivalent amount of TEOS for surface treatment of nanoparticles was obtained by means of elemental analysis (CHN). Treated nanoparticles were then filtered under suction and physically adsorbed TEOS compounds on the modified surface of ∗ Eab =  2 2 (L∗ ) + (a∗ ) + (b∗ ) 2 (2) where L* is on the black–white (L* = 0 for black, L* = 100 for white) axis, a* is on the red–green axis, and b* is on the yellow–blue axis. SEM analysis (Cambridge Stereo scan S360 SEM, with Au coating), gloss measurements (Nova gloss at 20◦ ) and FTIR-ATR Author's personal copy A. Mirabedini et al. / Progress in Organic Coatings 72 (2011) 453–460 455 Table 1 Characteristic absorption peaks achieved from FTIR spectra of P25 and TEOS treated TiO2 nanoparticles. Fig. 2. FTIR spectra of (a) neat TiO2 , TEOS treated with; (b) 0.5 mol.%, (c) 1.0 mol.% and (d) 2.0 mol.% TiO2 , respectively. spectroscopy were used to examine the effect of UVA irradiation on the surface properties of the acrylic based coatings containing untreated and treated TiO2 nanoparticles. 3. Results and discussion 3.1. Characterization of TiO2 /SiO2 nanocomposites Fig. 2 shows the FTIR spectra of neat and differently treated TiO2 nanoparticles. The assignments for the main FTIR bands of the untreated and treated nanoparticles are listed in Table 1. A broad absorption peak of molecular water at around 3400 cm−1 and a sharp band at around 1625 cm−1 , observed in both untreated and treated TiO2 nanoparticles, are significantly intense [26,28]. The No. Wavenumber (cm−1 ) Functionality (group) 1 2 3 4 5 6 7 400–800 450, 780 and 1080 955 1079 1570 1625 3400 Crystalline TiO2 [22] Bending vibrations of Si–O or SiOH [22,23] Vibration modes (Ti–O–Si) [24] Asymmetric stretching vibration (Si–O–Si) [24] Main characteristic peaks of Si–O bonds [24,25] Vibration band of –OH [26,27] Vibration band of –OH [26,27] intensities of absorption peaks due to O–H group near 1620 and 3400 cm−1 increased with an increase of the silica amount and it shows similar tendency with the results reported in the literature [27,29]. The absorption peak at around 1079 cm−1 is considerably broad toward larger wavelength regions and getting broad and greater, respectively, with increasing of TiO2 mol.%. This peak can be assigned to Si–O–Si asymmetric stretching vibration and confirms the silica grafting of TiO2 nanoparticles [30]. FTIR analysis indicates that the SiO2 is chemically bonded with the TiO2 nanoparticles, because of the absorption peak assigned to Ti–O–Si vibration modes at around 955 cm−1 [31]. Neat TiO2 have broad bands in the range of 400–800 cm−1 which can be apparent in crystalline TiO2 [22]. Moreover, the peaks common for all silicate structures at around 1080, 780, and 450 cm−1 , due to one of the stretching and bending vibrations of Si–O or SiOH, were observed [22]. TGA technique was used to evaluate variations in the weight of a sample as a function of increasing temperature. Fig. 3 shows the TGA thermographs of untreated and differently treated TiO2 nanoparticles. TGA thermographs reveal that the weight% of neat TiO2 slightly decreases from 50 up to about 100 ◦ C, and then sharply decreases from 310 to 550 ◦ C. As can be seen from Fig. 3(b–d), the Fig. 3. TGA thermographs of nanoparticles after 3 h drying at 100 ◦ C; (a) neat TiO2 , TEOS treated with; (b) 0.5 mol.%, (c) 1.0 mol.% and (d) 2.0 mol.% TiO2 . Author's personal copy 456 A. Mirabedini et al. / Progress in Organic Coatings 72 (2011) 453–460 (110) 300 Count Ti O C Ti Ti (a) Si (200) (101) (211) (112) (301) O (202) a) Ti C Ti (b) Ti Si O b) c) C Ti Ti (c) Ti Si d) 10 0 C Ti 1 2 3 4 Ti Ti 5 6 (d) 7 Energy (keV) Fig. 4. EDAX spectra of TiO2 nanoparticles; (a) P25, (b) 0.5 mol.% TiO2 , (c) 1 mol.% TiO2 and (d) 2 mol.% TiO2 . various mol.% of TiO2 grafted nanoparticles show sharp weight loss, beginning at around 270 ◦ C, continued till 650 ◦ C. By decreasing TiO2 mol.%, more weight loss can be observed due to more SiO2 grafting on the TiO2 nanoparticles. TGA thermographs are separated in three zones: the first zone (from 50 ◦ C to about 210 ◦ C) corresponds mainly to the removal of physically adsorbed water and isopropanol [32]. For untreated sample, the weight loss is about 0.5 wt.% and for differently treated samples are up to 2.7 wt.%. In the second weight loss degreasing zone, in temperature ranging from 210 to 450 ◦ C, weight loss is caused mainly by degradation of Si-compounds on TiO2 surface, and other organic intermediates. For untreated nanoparticles, relatively slight weight loss after 340 ◦ C can be attributed to water molecules formed from condensation of hydroxyl groups on the particle’s surface (TiOH) [27]. In the last zone (about 550 ◦ C), the samples are almost stable and free of any organic composition since slightly weight change is observed due to de-hydroxylated at high temperatures [28]. Fig. 4 illustrates EDAX spectra of untreated and treated TiO2 nanoparticles, which indicates different graftings of Si element on TiO2 nanoparticles in different sol–gel processing conditions. The relative nanoparticle compositions, as derived from EDAX spectra, are listed in Table 2. EDAX analysis of TEOS treated nanoparticles clearly revealed the presence of Si element, suggesting the silica grafting on the TiO2 nanoparticles. It is also shown that the Si content of the treated nanoparticles was increased with increasing the ratio of TEOS/TiO2 nanoparticles. XRD patterns of untreated and silica-coated titanium dioxide with different mole ratios of TEOS/TiO2 nanoparticles are shown in Fig. 5. In the P25 XRD spectrum, three primary diffraction signals can be observed at 2 of 25.2◦ , 37.8◦ and 48.0◦ , which are Table 2 Elemental composition of P25 and TiO2 nanoparticles treated with different amounts of TEOS obtained from EDAX analysis. Sample code P25 0.5 mol.% TiO2 1.0 mol.% TiO2 2.0 mol.% TiO2 20 30 40 50 60 70 2 Theta O Component concentration (wt.%) Ti Si O C 52.10 8.88 10.32 15.62 – 25.34 19.97 14.61 45.17 55.53 63.85 56.41 2.73 9.21 10.89 8.01 Fig. 5. X-ray diffraction patterns of the samples; (a) untreated TiO2 , TEOS treated with; (b) 0.5 mol.%, (c) 1.0 mol.% and (d) 2.0 mol.% of TiO2 . assigned to diffraction from (1 0 1), (0 0 4) and (2 0 0) planes of anatase crystalline form, respectively. It is reported that P25 is a totally crystalline material with an anatase/rutile ratio 81/19 [25]. As it can be seen, by decreasing mole ratio of TiO2 /TEOS, the diffraction signal of anatase TiO2 (1 0 1) decreased, which is related to a decrease in the ratio of the crystalline anatase phase to the entire composition of the particle. XRD analysis indicates the silica compound layer absorbed (either physically and/or chemically) on the surface of TiO2 nanoparticles and by decreasing ratio of TiO2 /TEOS, the intensity of amorphous silica layer on the surface of TiO2 nanoparticles increased. 3.2. Photocatalytic activity of TiO2 nanoparticles Visual appearance of Rh.B dyestuff in isopropanol dispersions during 2 h UVA irradiation in presence of untreated and treated nanoparticles is illustrated in Fig. 6. Obviously, the discolouration efficiency of P25 is slightly higher than that of treated nanoparticle counterparts, during UVA irradiation. UV–Vis nanoparticle spectra of prepared suspensions of Rh.B in the presence of modified and unmodified TiO2 nanoparticles are shown in Fig. 7(a and b), respectively. As it can be seen from the Fig. 7a, the maximum absorption peak (at 543 nm) regularly reduces during the UVA irradiation time as a result of lower concentration of Rh.B. Since there are no additional peaks emerging in the UV–Vis spectra in the course of the experiment either using P25 or treated nanoparticles, throughout the UVA irradiation, Rh.B can be changed in products that do not reveal any absorption in the UV–Vis wavelength, therefore, photobleaching and de-colourization, can be the main mechanisms of photodegradation [33]. The colour difference (E) results of acrylic films containing modified and unmodified TiO2 nanoparticles prior to and during 8 h exposure to the UVA irradiation are shown in Fig. 8. It is evident that surface treatment TiO2 nanoparticles with TEOS coupling agent, reduces E values of the films; therefore, photocatalytic activity of TiO2 is reduced. From the Fig. 8, it is clear that in the presence of P25, the degradation of Rh.B is faster than that of its silane treated counterpart. The Rh.B dyestuff was completely degraded after 8 h exposure to the UVA irradiation and a colourless solution was obtained, while this was extended to more than 16 h for treated nanoparticles. Clearly, surface treatment of nanoparticles reduces the effective surface area of TiO2 available to Rh.B by which Rh.B is degraded. Untreated TiO2 nanoparticles provide a higher degradation rate of Rh.B than untreated counterpart because of the higher Author's personal copy A. Mirabedini et al. / Progress in Organic Coatings 72 (2011) 453–460 457 30 Delta E 25 20 15 P25 & Acrylic 10 Tr.P25 & Acrylic 5 0 0 60 120 180 240 300 360 420 480 UVA Exposure Time (min) Fig. 8. Colour difference (E) of coating films containing 1 wt.% untreated and silica treated TiO2 nanoparticles, during UVA exposure time, in the presence of Rh.B dyestuff. crystallinity and higher surface areas than silica treated nanoparticles. Higher surface areas of untreated TiO2 nanoparticles resulted in larger amounts of Rh.B adsorbed on the nanoparticle surface leading to the higher degradation rates of dyestuff as compared to the silica treated nanoparticles. That, in turn, reduces the electron and hole (e− /h+ ) recombination, as a result more electrons and holes are available, which diffuse to the nanoparticle surface to react with the dyestuff molecules adsorbed on the surface at the faster rate [27,34]. Fig. 6. Discolouration of Rh.B in the presence of P25 and SiO2 /TiO2 nanoparticles during 2 h UVA irradiation. a 1.75 207.8 nm 1.701 A 272.9 nm 1.493 A Absorbance (%) 1.5 1.25 207.5 nm 1.615 A 545.3 nm 1.478 A 345.2 nm 1.428 A 543.1 nm 1.125 A 323.3 nm 1.374 A 1 P25 TiO2 After 8 h UVA Exposure P25 TiO2, Before UVA Exposure P25 TiO2 After 3h UVA Exposure 0.75 200 300 400 500 600 700 Wavelength (nm) b 1.25 Absorbance (%) 1 Tr.TiO2, After 8 h UVA Exposure Tr. TiO2, Before UVA Exposure Tr.TiO2, After 3 h UVA Exposure 207.5 nm 1.154 A 542.3 nm 0.847 A 0.75 275.0 nm 0.443 A 542.3 nm 0.609 A 0.5 369.8 nm 0.125 A 0.25 0 200 300 400 500 600 700 Wavelength (nm) Fig. 7. Absorption spectra of; (a) P25 TiO2 and Rh.B, (b) TiO2 /SiO2 nanoparticles and Rh.B, during UVA irradiation. 3.3. Coating performance under UVA irradiation SEM micrographs of coating’s samples containing 1 wt.% of untreated and treated nanoparticles are shown in Fig. 9(a and b), before and after 8 h exposure to the UVA irradiation. As it can be observed, for sample containing untreated nanoparticles, relatively large particle aggregates with the size of 0.2–0.6 ␮m with a non-uniform distribution appeared on the surface of the samples. However, with TEOS treatment of nanoparticles, the size of particle aggregates on the surface of the coating film reduced to about 0.1 ␮m and less and more uniform distribution of nanoparticles was also achieved, as compared to its untreated counterparts. However, in order to evaluate the homogeneity and distribution of the nanoparticles to the entire volume of the film, further studies are needed. It is clear from the SEM analysis, that the sample having treated nanoparticles revealed a relatively appropriate performance during exposure to the UVA irradiation. After exposure to the UVA irradiation, rarely small holes are observed on the surface of the sample containing silica treated nanoparticles. However, coating sample containing untreated nanoparticles, the UVA irradiation performance was getting worse and chalking phenomenon is observed on the surface and the number and size of pores and defects are dramatically increased. These results revealed that TEOS grafting modifies the photocatalytic activity of TiO2 nanoparticles. It seems that silica layer on the TiO2 particles acts as a barrier and delay C–C bond on the polymeric matrix. This means, it is possible to use modified TiO2 nanoparticles in the organic coatings, with slight further polymer degradation. Gloss measurement results of coating samples containing 1 wt.% of nanoparticles are shown in Fig. 10, during 8 h exposure to the UVA irradiation. Gloss measurement results also indicate the relatively homogeneity of the distribution of the silica nanoparticles on the surface of coating film compared to its untreated counterparts, as gloss measurement values directly associated to the rough film’s surface. The results reveal that by inclusion of treated nanoparticles within the coating film, the gloss measurement value was Author's personal copy 458 A. Mirabedini et al. / Progress in Organic Coatings 72 (2011) 453–460 Fig. 9. SEM micrographs of coating samples containing 1 wt.% of (a) untreated and (b) treated nanoparticles, before and after 8 h exposure to the UVA irradiation. Fig. 10. Gloss measurement results of coating samples containing 1 wt.% of nanoparticles, and neat coating, during 8 h exposure to the UVA irradiation. decreased only 1.5 compared with neat coating film, while gloss value reduction for coating film having untreated nanoparticles was about 5 units, showing relatively rough film’s surface as a result of nanoparticles aggregation. These results are confirmed by SEM analysis. During UVA irradiation, gloss levels were degreased due to light scattering diffusion as a result of polymer degradation. The total gloss reduction during the UVA irradiation usually is an apparent indication of coating performance against outdoor conditions [35]. Fig. 11 shows FTIR spectra of neat acrylic coating and coatings containing 1 wt.% untreated and treated TiO2 nanoparticles, before and after 8 h exposure to the UVA irradiation, respectively. Regarding the influence of nanoparticle type on the polymer structure stability, under UAV irradiation, negligible changes were observed in the FTIR spectra. However, for all spectra, after UVA irradiation, the intensity of absorption band in 1620–1700 cm−1 , was slightly increased due to the increasing intensity of carbonyl groups of polymeric matrix [11]. Nevertheless, for sample containing untreated nanoparticles, the intensity of absorption peak related to carbonyl groups is slightly higher than its counterpart containing untreated nanoparticles or neat coating films, possibly due to rather degradation of polymeric matrix. A broad absorption Author's personal copy A. Mirabedini et al. / Progress in Organic Coatings 72 (2011) 453–460 2.4 (a) 2 Transmittance (%) 1.6 (b) 1.2 0.8 (c) 0.4 0 4000 3500 3000 2500 2000 1500 1000 500 -1 Wavenumber (cm ) Fig. 11. FTIR-ATR spectra of; (a) neat acrylic coating, (b) coating containing 1 wt.%, and (c) coating having 1 wt.% silica treated TiO2 nanoparticles, before (solid line) and after (dashed line) 8 h exposure to the UVA irradiation. peak of molecular water due to O–H group at region 3400 cm−1 and a sharp band at around 1625 cm−1 are relatively intense, and these absorption peaks to some extent increased after UVA irradiation [26,27]. Fig. 11(d) shows relatively intense absorption bands in the range of 400–800 cm−1 , in FTIR spectrum of coating sample having untreated nanoparticles, which can be obvious in crystalline TiO2 particles on the surface of coating’s sample [22]. 4. Conclusion This work reports the preparation, characterization and photocatalytic activity of silica treated TiO2 nanoparticles. The results revealed the effectiveness of sol–gel route for preparation of TiO2 /SiO2 nanocomposites. The optimum result was obtained with 1% molar ratio of TiO2 :TEOS. Addition of TiO2 /SiO2 nanocomposites into the acrylic based coating revealed adjustment of photo-degradation of Rh.B compared with untreated counterparts. Inclusion of TEOS treated TiO2 nanoparticles into the aqueous organic coatings, provides photocatalytic property and due to the low polymer degradation, under UAV irradiation. Silica on the TiO2 particles acts as a barrier layer and delay C–C bond on the polymeric matrix. The potential application of these silica treated TiO2 nanoparticles into the self-clean coating materials seems warranted. Acknowledgement The authors wish to acknowledge support from the research work reports in this paper from Iran Polymer and Petrochemical Institute and University of Sahand, Tabriz. References [1] M.H. Habibi, S. Tangestaninejad, B. 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