Synthesis and photocatalytic activities of cuo-Tio2 nanocomposites - Thi Ngoc Tu Le

Journal of Science and Technology 54 (4B) (2016) 35-41 SYNTHESIS AND PHOTOCATALYTIC ACTIVITIES OF CuO-TiO2 NANOCOMPOSITES Thi Ngoc Tu Le1, 2,*, Nu Quynh Trang Ton2, Thi Thu Ha Hoang2, Son D. N. Luu2, Thi Hanh Thu Vu2 1Dong Thap University, 783 Pham Huu Lau, Ward 6, Dong Thap Province, Vietnam 2Faculty of Physics and Engineering Physics, University of Science, Vietnam National University in Ho Chi Minh City, 227 Nguyen Van Cu, Ho Chi Minh City, Vietnam *Email: ltntu@dthu.edu.vn Received: 15 August 2016; Accepted for publication: 10 November 2016 ABSTRACT TiO2 nanotubes were prepared by hydrothermal method and then modified by CuO by two different methods: adsorption – calcination (A-C) method and photo-reduction method. The obtained solid product (CuO-TNTs) was investigated of: morphology, crystal structure and absorbance spectroscopy by transmission electron microscopy (SEM), X-ray diffractometry (XRD), UV-vis spectroscopy; respectively. The photocatalytic ability of CuO-TNTs was determined by absorbance spectroscopy of methylene blue (MB) solution under various irradiation conditions. Results showed that the photocatalytic activity of CuO-TNTs is lower than that of the original TNTs in UV irradiation. In contrast, it shows the better performance in visible light and sunlight than that of the TNTs. Keywords: CuO-TiO2, TiO2 nanotubes, hydrothermal synthesis, photo-reduction, A-C, photocatalysis. 1. INTRODUCTION Among the photocatalytic material such as TiO2 [1], ZnO [2], SnO2 [3]. TiO2 has attracted an excellent attention due to its chemical stability, high catalytic efficiency, low cost and environmentally friendly impact [4]. The photocatalytic performance of these materials is enhanced by the effect of quantum confinement of charge carriers [5]. Previous studies reported that CuO-TiO2 shows higher photocatalytic activity than that of TiO2 [4, 6]. In addition, CuO- TiO2 shows the ability to create hydrogen gas by photocatalytic water splitting [4,7]. CuO is one of the promising materials due to its low cost and high-performance applications [8]. However, the valence band edge of CuO is more negative than the oxidation potential necessary to generate *OH radicals (Figure 1a). Therefore, CuO cannot generate *OH free radicals under sunlight, causing its low photocatalytic performance [9]. Miyauchi et al. [12] indicated that the photocatalytic activity of CuO is not effective for water treatment because CuO cannot create a significant amount of high oxidative potential *OH radicals and cause the oxidation reaction of Sy 36 org con In ou me ph me 2.1 wa 2.2 Na pre C m 2.3 ch (T me (C spe at nthesis and anic polluta duction ban Figure this paper, T r previous s thod [13] otocatalytic thylene blue . Materials The comm ter and Cu(N . Synthesis TNTs are OH aqueous vious studie ethod and . Character The cryst aracterized b EM, JEM-1 The phot thylene blue ompact Lam ctrophotom a wavelength photocatalyt nts. The cha d (CB) and (a) 1. (a) Band ga energy band p iO2 nanotub tudies [15,1 and photo- activity of (MB) unde ercial TiO O3).3H20 w of CuO-TN fabricated b solution. T s [16]. The photo-reduct ization met al structure y X-ray dif 400), and U ocatalytic a (MB) unde p- CFL 3UT eter (JASCO of 664.6 nm ic activities o rge transpor valence band p (eV) and re ositions of T e structures 6]. The mod reduction m CuO-TNT r different ir 2 powder (T ere used. Ts y the hydro he detail of t modified Cu ion method hods , morpholog fraction (Br V-vis spectr ctivities of r different i 4 30W H8) –V670) was . f CuO-TiO2 t mechanism (VB) edge dox potential iO2, CuO and were fabric ified CuO- ethod [14] s through t radiation con 2. EXPER iO2-Merck, thermal me he paramete O-TiO2 (wh (Figure 2). y and abso uker D8-AD ophotomete TNTs wer rradiation c and sunlig then used f nanocompo of CuO-TiO s are shown s of several se the electron t ated by the h TiO2 was sy . The stru he absorpti ditions are p IMENTS 99,9 %), 1 thod from c r of the hydr ite powder) rbance spe VANCE), t r (JASCO – e evaluated onditions: U ht (between or monitorin sites 2 and the di in Figure 1b (b) miconductor ransfer direct ydrotherma nthesized by ctural chara on of an a resented. 0M NaOH, ommercial T othermal pro is fabricated ctroscopy o ransmission V670), resp by the p VA (Philips 11h30 ÷13h g the absorp fference bet . s [10,11] and ion [4]. l method, re two metho cterization queous sol 2M HNO3, iO2 powder cess is show by two met f CuO-TN electron mi ectively. hoto-degrad , 25W), vis 30 noon). A tion of MB ween the (b) the ported in ds: A-C and the ution of distilled in 10M n in our hods: A- Ts were croscopy ation of ible light UV-Vis solutions 3.1 Re the tub str tub irr eas app A Figure . The morp Figure 3a sults showe length of th e was brok ucture of Cu es are simil adiation in p ily deposit o According ear at the 2 (204) of TiO Chemi preparat Magne Washi Dried Annea CuO-TN (a 2. The prepa hological an Figure and b show d that CuO- e CuO-TNT en. It can b O-TNTs-B ar to the initi hoto-reducti n the surfac to the XRD θ = 25.08 °, 2, respective cal ions tic ng led Ts-A ) ration process reducti 3..RE d crystal st (a) 3. TEM imag s the TEM TNTs-A and s-A (Figure e explained (Figure 3b) al tubular st on method in e TNTs with analysis o 37 °, 48.05 ° ly. In additi - TNTs - Cu(NO3) Magnetic sti 20 hou Washed w distilled w Dried at 60 overnig Annealed at for 2 ho of CuO-TNT on method (C SULTS AN ructure cha es of (a) CuO image of C CuO-TNTs 3a) was no by the the is not broke ructure. This creased the out making f TNTs and and 64 ° co on, the refle .3H20 rred for rs ith ater °C for ht 300 ºC urs 50 nm s: (a) A-C m uO-TNTs-B) D DISCUSS racteristics (b -TNTs-A and uO-TNTs-A -B remained t retaining i rmal shock n. The leng indicates th thermal mo TNTs broke CuO-TNTs rresponding ctions appea Cu(NO3)2.3H Irradiated Magneti with C Dried a (b) ethod (CuO-T . ION of CuO-TN ) (b) CuO-TN and CuO-T the tubular nitial length during the th and diam at magnetic tion of atom n. (Figure 4), to A (101), red at the 2θ 2O for 2 hours und c stirred for 2 h distilled water uO-TNTs-B t 80 °C for 4 ho Washing 50 n Thi Ngoc Tu NTs-A) and p Ts Ts-B. NTs-B, resp structure. H . The major heating. Th eter of CuO stirring and s and Cu2+ io the diffracti A (004), A ( of 35.3 ° an TNTs er UV ours urs m Le, et al 37 hoto- ectively. owever, ity of the e tubular -TNTs-B UV light ns could on peaks 200) and d 53.3 °, Synthesis and photocatalytic activities of CuO-TiO2 nanocomposites 38 representing the C (001) and C (020) planes of CuO in both CuO-TNTs-A and CuO-TNTs-B samples. On the other hand, the impurity peaks of Na2Ti3O7, NaCl, NaNO3 and H2Ti3O7 crystals are not detected in synthesized products, contrasting to the report of the previous work [17]. Furthermore, the phase transition is not observed in CuO-TNTs samples whilst the peak of Cu2O and Cu have not appeared in the XRD pattern which was consistent with another report [18]. CuO peaks appeared in these two synthetic methods, but the intensity of the characteristic TiO2 and CuO peaks of CuO-TNTs-A (Figure 4.a) was higher than those of CuO-TNTs-B (figure 4.b). 20 30 40 50 60 70 80 TNTs A(204)C(020) A(200) A(004) ∇ ∇ ∇ ∇ ∇ In te ns ity (a .u ) 2 (degree) A: Anatase R: Rutile C: CuO ∇ A(101) C(002) CuO-TNTs-A 20 30 40 50 60 70 80 ∇ C(113) C(002) C(020) A(200) A(004) ∇ ∇ ∇∇ ∇ ∇ In te ns ity (a .u ) 2θ (degree) ∇ A(101) A(204) C(110) CuO-TNTs-B TNTs A: Anatase R: Rutile C: CuO (a) (b) Figure 4. XRD patterns of (a) CuO-TNTs-A and (b) CuO-TNTs-B. From the results presented above, the photo-reduction method was chosen to synthesize the CuO-TNTs in different experimental parameters. The fabrication conditions are shown in Table 1. Table 1. The fabricated conditions of CuO-TNTs with with different Cu(NO3)2.3H2O:TiO2 ratio. Samples Materials Cu(NO3)2.3H2O: TNTs (wt%) Magnetic stirring time (hour) Hydrothermal temperature and time (°C,hour) CuO-TNTs-B1 TNTs, Cu(NO3)2.3H2O 10:1 3 130, 22 CuO-TNTs-B2 TNTs, Cu(NO3)2.3H2O 30:1 3 130, 22 CuO-TNTs-B3 TNTs, Cu(NO3)2.3H2O 40:1 3 130, 22 300 400 500 600 700 800 0.5 1.0 1.5 2.0 2.5 3.0 A bs or ba nc e (a .u ) Wavelength (nm) CuO-TNTs-B2 TNTs CuO-TNTs-B3 CuO-TNTs-B1 Figure 5. UV−vis absorption spectra of (a) TNTs and CuO-TNTs with different Cu(NO3)2.3H2O:TiO2. Thi Ngoc Tu Le, et al 39 The UV–vis absorption spectra of TNTs, and CuO-TNTs with different Cu(NO3)2.3H2O:TiO2 ratio is displayed in Figure 5. Results show that the absorbance of CuO-TNTs-B samples are significantly shifted from the UV light to the longer wavelength of, indicating that the band gap energy (Eg) of CuO-TNTs-B samples decrease. The absorbance of CuO-TNTs-B3 shifts from the UV light to the visible range with a wavelength of about 443 nm whilst the absorbance of CuO- TNTs-B2 had a wider shift to the light visible with a wavelength of about 517 nm. For the CuO- TNTs-B1, its absorbance shifts to the light visible with a wavelength of about 591 nm. It revealed that the CuO concentration was a significant effective on the Eg and absorbance of CuO-TNTs samples. This result was entirely consistent with the report of Yu et al. [19]. 3.2. Photocatalytic activity of CuO-TNTs 400 500 600 700 800 0.0 0.2 0.4 0.6 0.8 1.0 c) d) e) b) A bs or ba nc e (a .u ) Under UV light for 90 min a) a) CuO-TNTs-B1 b) TNTs c) CuO-TNTs-B2 d) CuO-TNTs-B3 e) MB Wavelength (nm) 400 500 600 700 800 0.0 0.2 0.4 0.6 0.8 1.0 d) c) e) b) A bs or bt an ce (a .u ) Wavelength(nm) Under visible light for 2 hours a) CuO-TNTs-B1 b) CuO-TNTs-B2 c) CuO-TNTs-B3 d) TNTs e) MB a) 400 500 600 700 800 0.0 0.2 0.4 0.6 0.8 1.0 e) d) c) b) A bs or ba nc e (a .u ) Wavelength (nm) a) a) CuO-TNTs-B1 b) CuO-TNTs-B2 c) CuO-TNTs-B3 d) TNTs e) MB Under sunlight for 90 min (a) (b) (c) Figure 6. Absorption spectra of MB under (a) UV irradiation, (b) visible light and (c) sunlight in the presence of different catalysts, respectively. The photocatalytic ability of TNTs and CuO-TNTs-B samples are evaluated by the absorption of MB in the presence of samples under the UV light, visible light and sunlight irradiation are presented in Figure 6. The peak absorption of MB appeared at 664.6 nm wavelength whilst the MB absorption efficiency varied with the structural properties of the catalysts. Figure 6a shows the absorption spectra of MB solution of TNTs and CuO-TNTs-B with various Cu(NO3)2.3H2O:TiO2 ratio under UVB irradiation for 90 min. The absorption spectra of TNTs sample showed the largest change under UVB irradiation condition. Calculating from the absorption spectra in Figure 6a, the degradation efficiency of MB solution of CuO-TNTs-B1, CuO-TNTs-B2, CuO-TNTs−B3 and TNTs is 92 %, 85 %, 77 % and 99.92 % within 90 min. Results indicate that TNTs showed better photocatalytic activity than that of CuO-TNTs-B samples under UV irradiation. In contrast, under visible light and sunlight condition, CuO−TNTs- B samples exhibit better photocatalytic activity than that of TNTs (Figure. 6b, 6c). Calculating from the absorption spectra in Figure 6b, the degradation efficiency of MB solutions in CuO- TNTs-B1 is 85 % whilst Cu-TNTs-B2, CuO-TNTs-B3, and TNTs turn in 62 %, 38 %, and 30 % within 2 hours. Similarly, under sunlight irradiation, the degradation efficiency of the MB solution in CuO-TNTs-B1 is 98 % whilst Cu-TNTs-B2, CuO-TNTs-B3 and TNTs are 96 %, 84 %, 74 % within 90 min. It indicated that CuO concentration was effective on the photocatalytic ability of CuO-TNTs-B, and 10 wt.% CuO (CuO-TNTs-B1) was the optimized value to achieve the highest degradation efficiency of MB solution. According to the Figure 6b, 6c under the visible light and sunlight irradiation conditions, the CuO deposition on TNTs showed the better photocatalytic activity than that of TNTs. This can be explained by following hypothesis: CuO molecules exist on TNTs surface, forming the Ti-O-Cu bonds on the surface of TNTs. Cu2+ ions acted as an electron acceptor and play the role of electron trap in CB of TNTs. The recombination rate of Synthesis and photocatalytic activities of CuO-TiO2 nanocomposites 40 electron-hole pairs is limited, thus enhancing the photocatalytic activity. However, when the amount of CuO increased 30 wt.% and 40 wt.%, the light absorption of TNTs is prevented because all active sites on the TNTs would be covered by CuO deposition, reducing the efficiency of charge separation [14,20]. Moreover, results also showed that the absorption efficiency of MB in visible light (2 hours) was slower than in sunlight condition (90 min). This can be explained according to the sunlight region was largely an optical radiation source (mostly visible light and only 5 % of UV light the light absorption of TiO2) and led to the rate of photocatalytic degradation of MB in sunlight was faster than the rate photocatalytic degradation of MB in visible light region. 4. CONCLUSION CuO has been successfully deposited to TNTs by two different methods (A-C and photo- reduction). Compared to the A-C method, the photo-reduction method was more suitable because it remains the stability of morphology and the initial structure of TNTs. The appearance of CuO results in the gradually shifted absorption spectrum of TNTs to the longer wavelengths, in other words, contributing to narrowing the Eg of CuO-TNTs. Photocatalytic property of the synthesized CuO-TiO2 nanocomposite is significantly improved under visible light and sunlight. Composite with 10 wt.% CuO (CuO-TNTs-B1) possessed the highest photocatalytic performance. The results of the efficient photocatalytic activity of CuO-TNTs under visible light and sunlight in this study indicate that CuO-TNTs nanocomposite has great promising applications in clean energy production. Acknowledgment. This research is funded by Vietnam National University Ho Chi Minh City (VNU- HCM) under grant number C2016-18-02. REFERENCES 1. Ge M., Cao C., Huang J., Li S., Chen Z., Zhang K.Q., Al-Deyab S.S., and Lai Y. - A review of one-dimensional TiO2 nanostructured materials for environmental and energy applications, J. Mater. Chem. A4 (18) (2016) 6772-6801. 2. Lee K.M., Lai C.W., Ngai K.S. and Juan J.C. - Recent developments of zinc oxide based photocatalyst in water treatment technology: a review, Water Res. 88 (2016) 428-448. 3. Pan J., Shen H. and Mathur S. - One-dimensional SnO2 nanostructures: synthesis and applications, J. Nanotechnol. 2012 (2011) 1-12. 4. Bandara J., Udawatta C.P.K. and Rajapakse C.S.K. - Highly stable CuO incorporated TiO2 catalyst for photocatalytic hydrogen production from H2O, Photoch. Photobio. Sci. 4 (11) (2005) 857-861. 5. Huỳnh Duy Nhân, Trương Văn Chương, Lê Quang Tiến Dũng - Nghiên cứu và chế tạo vật liệu TiO2 nano bằng phương pháp siêu âm thủy nhiệt, Tạp chí Đại học Thủ Dầu Một 2 (2012) 20-27. 6. Jung M., Ng Y.H., Jiang Y., Scott J. and Amal R. - Active Cu species in Cu/TiO2 for photocatalytic hydrogen evolution, Chemeca 2013: Challenging Tomorrow (2013) 214 - 217. Thi Ngoc Tu Le, et al 41 7. Kumar D.P., Reddy N.L., Kumari M.M., Srinivas B., Kumari V.D. and Shankar M.V., - CuO/TiO2 nanocomposites: effect of calcination on photocatalytic hydrogen production, J. Catal. Catal. 1 (2014) 13-20. 8. Debart A., Dupont L., Poizot P., Leriche J. B., Tarascon J. M. - A transmission electron microscopy study of the reactivity mechanism of tailor-made CuO particles toward lithium, J. Electrochem. Soc. 148 (2001) A1266−A1274. 9. Yu J., Hai Y. and Jaroniec M. - Photocatalytic hydrogen production over CuO-modified titania, J. Colloid. Interf. Sci. 357 (2011) 223-228. 10. Nah Y. C., Paramasivam I., Schmuki P. - Doped TiO2 and TiO2 nanotubes: synthesis and applications, ChemPhysChem 11 (2010) 2698-2713. 11. Rehman S., Mumtaz A. and Hasanain S.K. - Size effects on the magnetic and optical properties of CuO nanoparticles, J. Nanopart. Res. 13 (2011) 2497-2507. 12. Miyauchi M., Nakajima A., Watanabe T. and Hashimoto K. - Photocatalysis and photoinduced hydrophilicity of various metal oxide thin films, Chem. Mater. 14 (2002) 2812-2816. 13. Xu S., Du A.J., Liu J., Ng J. and Sun D.D. - Highly efficient CuO incorporated TiO2 nanotube photocatalyst for hydrogen production from water, Int. J. Hydrogen. Energ. 36 (2011) 6560- 6568. 14. Menon A.K. and Kalita S.J. - Efficient photocatalytic degradation of methylene blue with CuO loaded nanocrystalline TiO2, Ceram. Eng.Sci. Proc. (2010) 77-87. 15. Lê Thị Ngọc Tú, Vũ Thị Hạnh Thu - Nghiên cứu quy trình đánh giá tính năng quang xúc tác của vật liệu TiO2 bằng axit terephthalic và methylene blue, Tạp chí Khoa học và Công nghệ 52 (2014) 599-608. 16. Lê Thị Ngọc Tú, Vũ Thị Hạnh Thu - Nghiên cứu và chế tạo vật liệu quang xúc tác TiO2 cấu trúc nano ống bằng phương pháp thủy nhiệt. Tạp chí Khoa học và Công nghệ 52 (2014) 397-404. 17. Lê Thị Ngọc Tú, Bùi Thị Thu Hằng, Lại Thịnh Vượng, Vũ Thị Hạnh Thu - Ảnh hưởng của quá trình xử lí sau thuỷ nhiệt lên hình thái, thành phần và tính chất quang xúc tác của ống nano TiO2, Tạp chí Khoa học và Công nghệ 53 (2015) 96-103. 18. Clarizia L., Spasiano D., Di Somma I., Marotta R., Andreozzi R. and Dionysiou D.D. - Copper modified-TiO2 catalysts for hydrogen generation through photoreforming of organics. A short review, Int. J. Hydrogen. Energ. 39 (30) (2014) 16812-16831. 19. Yu L., Yuan S., Shi L., Zhao Y. and Fang J. - Synthesis of Cu2+ doped mesoporous titania and investigation of its photocatalytic ability under visible light, Micropor. Mesopor. Mat. 134 (2010) 108-114. 20. Lalitha K., Sadanandam G., Kumari V.D., Subrahmanyam M., Sreedhar B. and Hebalkar N.Y. - Highly stabilized and finely dispersed Cu2O/TiO2: a promising visible sensitive photocatalyst for continuous production of hydrogen from glycerol: water mixtures, The J. Phys. Chem. C 114 (2010) 22181-22189.