135 American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) ISSN (Print) 2313-4410, ISSN (Online) 2313-4402 © Global Society of Scientific Research and Researchers http://asrjetsjournal.org/ The Photocatalytic Applications of TiO2-WO3 Heterostructure in Methylene Blue Guangyuan Hai a , Haiming Zhang b * a,b Tiangong University,School of Physical Science and Technology, TianJin,300387,CHN a Email: haiguangyuan@foxmail.com b Email: zhmtjwl@163.com Abstract In this work, TiO2-WO3 composite materials were forged by sol-gel method and the forged samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and UV-vis diffuse reflectance spectroscopy. The tough interaction in the interface of TiO2-WO3 heterostructures and the solar spectral response of TiO2 and WO3 reduce the electron-hole pair recombination rate and enhance the photoelectrochemical activity. The TiO2-WO3 heterostructures also show good adsorption ability for organic pollutants. This study testified that the fabricated TiO2-WO3 heterostructures are expectation materials for efficient water splitting as well as adsorption and photocatalytic wipe off organic pollutants. Keywords: titania dioxide; tungsten trioxide; photocatalytic; methylene blue. 1. Introduction In recent years, photocatalysis technology has received widespread attention on account of its applications in organic synthesis and the abatement of pollutants in water and air [1]. It is applied to wipe off the organic pollutant which includes detergent,dyes,pesticides and herbicides under UV-light irradiation.The heterogeneous photocatalyst attracted a crucial attention due to elimination of organic pollutants in water[2-5] and semiconductor photocatalysts drew attention because of inexpensive and environmental friendliness. ------------------------------------------------------------------------ * Corresponding author American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2019) Volume 61, No 1, pp 135-142 136 Photocatalysis is used to eliminate pollutants by conversion of optical energy into the electrochemical energy required for photo-oxidation by a catalyst[6].Titanium dioxide (TiO2) is demonstrably the most promising material for applications to air and water purification from various pollutants [7]. However, TiO2 only works in conjunction with irradiation of limited wavelength: TiO2 band gap (Eg≈3.2 eV) requires λ<385 nm, which rules out 95% of the solar spectrum.Moreover, the rapid recombination of the photocatalytically produced charge carriers competes with the electron transfer of the reactants adsorbed on the catalyst surface,which makes it not fit for efficient utilization[8].A arge number of methods have been used to increase the photocatalytic property of TiO2 for instance doping with metal or metal oxides, noble metal deposition and anion doping etc. Among semiconductor oxides, crystalline tungsten oxide (WO3) has some advantages including: induction of surface acidity to promote adsorption of OH − ; water and pollutant molecules ;its band gap is short (2.6-2.8 eV), thus requiring longer wavelengths for the excitation [9]. The lower conduction band (CB) position of WO3 than that of TiO2 accelerates the electron transfer from TiO2 to WO3 and the holes transfer in opposite direction. The idea of coupling TiO2 with another metal oxide with appropriate band gap and edge positions can be used as a feasible channel to promote photoproduced charge separation. Pandi and Gopinathan[10]fabricated TiO2/WO3 synthetic material by hydrothermal synthesis and surface modification. The enhanced decomposition of aqueous eosin-Y with TiO2/WO3 was because of visible light absorption and decreased carrier recombination rate. Ke etal.[11]fabricated TiO2/WO3 synthetic material hydrothermally with CTAB as a surfactant.The TiO2/WO3 disintegrated 100% of RhB in 50 min. Riboni and his colleagues [12]prepared WO3-TiO2 mixed oxide by a sol- gel method. The photocatalyst with the optimum tungsten content of 3% had higher activity than TiO2 P25 and degraded 31% acetaldehyde in2 h in the gas phase under mainly visible irradiation. Similarly, Eibl and his colleagues [13]state that WO3 is formed in tungstated titania when the tungsten loading exceeds a mass fraction of 20% and the powders are calcined above 923 K. In summary, the literature has inadequately characterized the TiO2/WO3 semiconductor catalyst. In this work,we fabricated WO3 by hydrothermal method and fabricated TiO2、 TiO2-WO3.The fabricated samples were characterized by various techniques for example X-ray diffraction(XRD), X-ray photoelectron spectroscopy (XPS),scanning electron microscope (FESEM) and UV-vis diffuse reflectance (UV-Vis-DRS) spectroscopy.The prepared TiO2-WO3 heterostructures have predominant interfacial interactions with tunable electrical property and show better photocatalytic activity. The TiO2-WO3 hetero structures also show good degradation competence towards the organic pollutant,methylene blue (MB). 2. Materials and Methods 2.1. Chemicals Ammonium tungsten partial, Ammonium metatungstate hydrate (AMT); Tetrabutyl titanate(TBOT);ethyl alcohol absolute(C2H6O);hydrochloric acid(HCl); AceticAcid(CH3COOH) ; methylene blue(MB);All chemicals and reagents were of analytical grade and were used as such without further purification, and double distilled water was used throughout this work. 2.2. Catalyst preparation Tungsten trioxide (WO3) powder was prepared by hydrothermal method.Weigh ammonium metatungstate file:///C:/Users/MI/AppData/Local/youdao/dict/Application/8.6.2.0/resultui/html/index.html%23/javascript:; file:///C:/Users/MI/AppData/Local/youdao/dict/Application/8.6.2.0/resultui/html/index.html%23/javascript:; American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2019) Volume 61, No 1, pp 135-142 137 (AMT) and add it to 20mL of deionized water, stirring constantly until dissolved.Then add hydrochloric acid to the resulting solution to adjust the pH to 2.After stirring the solution for half an hour, transfer the solution to a 100 mL high-pressure reactor, put the high-pressure reactor into a drying oven, and keep the oven at 180℃ for 24 hours. After cooling the reactor to room temperature, take out the product and centrifuge and wash the product.First wash with deionized water for three times and then wash with anhydrous ethanol for three times. Then dry at 80℃, grind the dried products to obtain pale yellow powder products. TiO2 powder was prepared by sol-gel method.Tetrabutyl titanate was added into anhydrous ethanol and stirred for 20 min to obtain yellow clarification solution A.Deionized water and glacial acetic acid were added into anhydrous ethanol, and proper amount of nitric acid was added after full stirring. PH value was adjusted to 2 to obtain solution B.Then under the intense mixing, mixing solution A and solution B, fully mixing stand for 24 hours, after get the gel after place into the oven, drying under 80℃ temperature, then put the samples in under 550 ℃ heat treatment resistance furnace, heating speed 2℃ per minute, after the heat treatment of samples of grinding end up with white powder. 2.3. Photocatalytic activity Photocatalytic activity test was performed as follows. 0.3g WO3/TiO2/WO3-TiO2 composites were added to 300 mL MB (300 mg/L) aqueous solution and the suspension solution was stirred in the dark for 30 min until the adsorption/desorption process reached equilibrium. Xe lamp was employed as the UV-visible light source, and it was placed 14 cm away from the solution. In every 20 min, 5 mL of the solution was taken away and the suspension was removed by using centrifugation. Then measuring the maximum absorbance at 665 nm of the MB by the spectrophotometry.The degradation rate was calculated using E=(1-C/C0), where C0 and C are the MB concentrations before and after photodegradation with UV-visible light. 3. Results and discussion Control TiO2 phase (Figure.1a) is pure anatase with a tetragonal structure (JCPDS＃01-083-0950). Control WO3 (Figure.1b) exhibits main peaks indexed as monoclinic crystalline structure (JCPDS＃01-083-0950). In the TiO2 sample the diffraction peak of [101] at2θ = 25.28° and the peak of [200] of WO3 at 2θ = 24.36° are the highest intense, show that [101,200] are the most growth orientations.As evident from the XRD patterns (Figure.1c) the main anatase peaks [101,103,200,105,213] at 2θ = 25.3° ,37.9° ,48.4° ,53.9° ,62.7° and the monoclinic form peaks [200,220,222,400,420,422] at 2θ =23.6°，33.6°，41.5°，48.4°，54.6°，60.3°.Besides, no phase transformation of TiO2 or of WO3 occurred during the compound of the hybrid powders: in all the samples TiO2 maintained the anatase structure, while WO3 kept the monoclinic form. American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2019) Volume 61, No 1, pp 135-142 138 Figure 1: (a) XRD patterns of WO3 (b) XRD patterns of TiO2, (c) XRD patterns of TiO2-WO3 heterostructures. We report the field emission scanning electron microscope (SEM) micrographs of control TiO2 and WO3 and hybrid TiO2-WO3 powders calcined at 550 °C Figure. 2. Figure 2: (a) SEM images of WO3 (b) SEM images of TiO2 (c) SEM images of TiO2-WO3 heterostructures. X-ray photoelectron spectroscopy (XPS) was applied to further research the chemical and bonding environment of the composite powders.Figure.3 a presents a low-resolution full range XPS spectrum of the TiO2-WO3 composite powders. The XPS survey spectrum showed that the distinctive as well as the Auger peaks of Ti, O, W and the combined material confirmed the presence of titanium, oxygen, tungsten . The Ti2p high resolution XPS spectra are analyzed in Figure.3 b. The binding energies of 459.6 and 465.25 eV are state that Ti2p3/2 and Ti2p1/2 separately. The splitting of the 2p doublet was 5.65 eV, reveal a normal state of Ti 4+ in the TiO2-WO3 composite powders.The high-resolution W4f XPS (Figure.3 c) shows the peaks at 38.4 and 36.3 eV corresponding to the characteristic W4f5/2 and W4f7/2 components respectively in WO3. The energy gap between these two peaks is 2.1 eV which suggested the W 6+ oxidation state in WO3.The XPS results confirm the superior interaction between TiO2 and WO3 through the formation of Ti-O-W bonds in TiO2-WO3 heterostructures.With respect to the XPS spectra of O1s in Figure.3 d,the O1s peak at 530.95 eV is attributed to O 2− . American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2019) Volume 61, No 1, pp 135-142 139 Figure 3: XPS spectra of the TiO2-WO3 heterostructures: (a) fully scanned spectra; (b) XPS spectra of Ti2p; (c) XPS spectra of W4f (d) XPS spectra of O1s. The UV-Vis-DRS spectrum was recorded to understand the light absorption property of the samples and shown in Figure.4 a.The re-flectance of TiO2-WO3 heterostructures reduced with the addition of WO3 content which revealed the enhanced absorption of the incident light. We used Tauc diagram to calculate the band gap of the prepared samples.The transformed Kubelka-Munk function, [F(R)hν] 1/2 (F(R) = (1-R) 2 /2R and R is the reflectance) was plotted against the energy of light, hν. The intercepts of the tangent drawn at absorption function to the energy axis at zero absorption are evaluated to get the band gap values[15]. The band gap of TiO2 and WO3 was 3.12 eV(Figure.4 c) and 2.52 eV(Figure.4 b),and the TiO2-WO3 heterostructures band gap was 2.36 eV(Figure.4 d). The fractionally reduced band gap values in TiO2-WO3 heterostructures compared to pure TiO2 shows the hard interaction between TiO2 and WO3. The strong mutual effect can availably hinder the recombination of e - -h + through the TiO2-WO3 heterojunction. American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2019) Volume 61, No 1, pp 135-142 140 Figure 4: (a) UV-Vis-DRS spectra of TiO2、WO3and TiO2-WO3 (b) (c) (d)Tauc plot of TiO2、WO3and TiO2-WO3 heterostructure. Figure.5 shows photocatalytic activity of as-prepared TiO2、WO3 and TiO2-WO3. It can be observed that TiO2- WO3 possesses the highest photocatalytic degradation rate (99% within 100 min), which is higher than that of WO3 (57%) and TiO2 (25%) at the same condition. Figure 5: Photodegradation of Methylene blue in the presence of TiO2、WO3 and TiO2-WO3 composites. American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2019) Volume 61, No 1, pp 135-142 141 4. Conclusions A simple sol-gel method followed by calcination process was used to synthesize TiO2-WO3 heterostructures with superior interfacial interactions. The TiO2-WO3 showed almost complete removal of MB in 100 min under visible light by photocatalytic and adsorption processes suggesting the higher adsorption of MB on the surface of TiO2-WO3 heterostructures.The band gap of TiO2 reduced from 3.12 eV to 2.36 eV in the TiO2-WO3 heterostructures which show the formation of heterojunction, and resulted in the reduction of recombination of e - -h + pair.TiO2 and WO3 act in synergy: due to the difference in band possible of the semiconductors, electrons shift from the conduction band of TiO2 to that of WO3 upon UV light irradiation. This research projects TiO2- WO3 heterostructures with great promise solar and visible light active materials for efficient water splitting as well as adsorption and photocatalytic reduce of organic pollutants. 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