Luận văn thạc sĩ fabrication of photocatalytic thin films containing tio2 nanoparticles and poly(l dopa) by layer by layer self assembly

THAI NGUYEN UNIVERSITY UNIVERSITY OF AGRICULTURE AND FORESTRY DUONG CUONG THINH FABRICATION OF PHOTOCATALYTIC THIN FILMS CONTAINING TIO2 NANOPARTICLES AND POLY(L-DOPA) BY LAYER-BY-LAYER SELF-ASSEMBLY BACHELOR THESIS Study Mode : Full- time Major Faculty : Bachelor in Environmental Science and Management : International Training and Development Center Batch : 2011-1016 Thai Nguyen, 15/09/2016 n DOCUMENTATION PAGE WITH ABSTRACT Thai Nguyen University of Agriculture and Forestry Degree Program Bachelor in Environmental Science and Management Student Name Duong Cuong Thinh Student ID DTN1153180221 Supervisor Assoc Prof Wu Chien-Hou PhD Nguyen HuuTho Abstract: The photocatalytic thin films containing TiO2 nanoparticles and poly(LDopa) were fabricated by layer-by-layer self-assembly The thin films were characterized by dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and atomic force microscopy (AFM) The photocatalytic activity was evaluated through the degradation of sulforhodamine B (SRB) in aqueous solution Nano-structured thin films under different conditions and their photocatalytic activities were investigated and studied Poly(acrylic acid) (PAA) was used to verify the role of poly(L-Dopa).The results show that layer-by-layer self-assembly was a simple and useful method to fabricate Nanostructured thin films with low cost and high reusability High transparency films using Degussa P25 was attributed to suitable particle size and colloidal stability Poly(LDopa) with negatively charge at wide range of pH values made it a good substitute among commercially available polyelectrolytes P25 and poly(L-Dopa) were recorded as an optimal charge with high zeta-potential and small particle size, contributing for high colloidal stability and low sedimentation at pH The obtained multilayer films i n retained the band gap of bare P25 at 3.2 eV and the properties of functional groups of poly(L-Dopa) The optimal number of P25/Poly(L-Dopa) bilayers was 20.5.The photocatalytic thin films containing P25 and poly(L-Dopa) are promising materials for environmental remediation Keywords:Titanium dioxide, layer-by-layer self-assembly, P25, poly(L-Dopa) Number of page 51 Date of Submission 15/09/2016 Supervisor’s signature ii n ACKNOWLEDGEMENT To have completed this thesis, in addition to the ongoing efforts of myself, I would like to thank for teachers in faculty of International Training and Development as well as teachers in Thai Nguyen University of Agriculture and Forestry, who have dedicated teaching to me the valuable knowledge during study time in the university and given me a chance to my thesis oversea I had a precious opportunity to take part in the internship in Department of Biomedical Engineering and Environmental Sciences in National Tsing Hua University (NTHU), Taiwan First of all, I want to thank my supervisors Assoc Prof Wu Chien-Hou from Biomedical Engineering & Environmental Science Department, National Tsing Hua University and PhD Nguyen Huu Tho from Thai Nguyen University of Agriculture and Forestry Their priceless advices are not only valuable to my research in order to gain successful results, but also contribute to my future career orientation Secondly, I am grateful to Mr Weichang Yuan, MS student and my friends in the laboratory, who facilitated and provided the information and data necessary for my implementation process and helped me finish this thesis Last but not least, thanks to my parents and good friends who always encourage me and offer support and love Sincerely, Duong CuongThinh iii n TABLE OF CONTENT ACKNOWLEDGEMENT iii TABLE OF CONTENT iv LIST OF FIGURES LIST OF TABLES LIST OF ABBREVIATIONS PART I INTRODUCTION 1.1 Research rationale 1.2 Research’s objectives 1.3 Research questions and hypotheses 1.4 Limitations PART II LITERATURE REVIEW 2.1 Overview of Titanium dioxide 2.1.1 Titanium oxidation structures and properties 2.1.2 The photocatalytic activity of TiO2 2.2 Layer-by-layer self-assembly 10 2.3 Overview of Poly(L-Dopa) 12 PART III METHODS 13 3.1 Material 13 iv n 3.1.1 Chemicals .13 3.1.2 Equipment 14 3.2 Methods 14 3.2.1 General principle 14 3.2.2 Fabrication of photocatalytic thin [TiO2/ Polymer]n films by the layer-bylayer self-assembly 15 3.2.2 Characterization .17 3.2.3 Photodegradation performance 19 PART IV RESULT .20 4.1 Optical Photo 20 4.1.1 Optical photos of P25/PDopa films .20 4.1.2 Optical photos of multiple films 20 4.2 Characterization of P25/Pdopa 21 4.2.1 Dynamic Light Scattering (DLS) 21 4.2.2 FTIR .23 4.2.3 SEM images of P25/Pdopa 24 4.2.4 AFM .26 4.3 Photodegradation performance 30 4.3.1 Calibration .30 4.3.2 Photodegradation activities of PDopa films 31 v n 4.3.2 Photodegradation performance of TiO2 34 4.4 P25/PDoPa films band gap 36 PART V DISCUSSION AND CONCLUSION 38 5.1 Discussion 38 5.2 Conclusion .40 REFERENCES 41 vi n LIST OF FIGURES Figure 1Crystal structures of rutile, anatase and brookite titanium dioxide Figure Schematic diagram illustrating the principle of TiO2 photocatalysis with the presence of water pollutant (RH) .10 Figure The principle of Layer-by-layer self-assembling method .11 Figure Poly(L-DOPA) 12 Figure Chemicals: a) PDopa, b) SRB 10 uM, DIW c) pH=3, d) PAA 13 Figure Equipment: a) UV-Visible Spectrophotometer, b) Photochemical reactor, c) pH adjustment, d) Magnetic stirrer, e) Ultrasonic, f) DLS 14 Figure Experimental process 15 Figure Photos of P25/PDopa film .20 Figure 5.5 bilayer thin films' images: a) St-01, b) St-21, c) P25 20 Figure 10 TiO2 size and zeta-potential at (pH=3, concentration = 1g/l) .21 Figure 11 PDopa zeta-potential and P25 zeta-potential varied from pH 22 Figure 12 P25 size varied from pH 22 Figure 13 FT-IR spectra of Degussa P25, L-Dopa, PDopa, P25/PDopa, PAA, P25/PAA .23 Figure 14 SEM images of (a) 0.5 bilayers, (b) 1.5 bilayers, (c) 2.5 bilayers, (d) 5.5 bilayers, (e) 10.5 bilayers, (f) 15.5 bilayers, (g) 20.5 bilayers 26 Figure 15 AFM images of thin films prepared with the coating sequence of (P25/PDopa)n: a) 0.5 bilayers, b) 2.5 bilayers, c) 5.5 bilayers before photodegradation n in UV light d) 5.5 bilayers after photodegradation in UV light, e) 5.5 bilayers after photodegradation 28 Figure 16 Absorbance of SRB: a) in range from 400nm to 750nm, b) at 562nm 30 Figure 17 (a) SRB photodegradation profiles of (P25/PAA)n thin films at wavelength 562 nm, (b) the first-order kinetic plot of ln(C/C0) and time(minutes) for photodegradation of SRB using (P25/PAA)n thin films at wavelength 562 nm 31 Figure 18 (a) SRB degradation profiles of (P25/PDopa)n thin films at wavelength 562 nm, (b) the first-order kinetic plot of ln(C/C0) and time(minutes) for photodegradation of SRB using (P25/PDopa)n thin films at wavelength 562 nm, 33 Figure 19 (a) SRB degradation profiles of (TiO2/PDopa)n thin films at wavelength 562 nm, (b) the first-order kinetic plot of ln(C/C0) and time(minutes) for photodegradation of SRB using diffirent kinds of TiO2 .34 Figure 20 (a) Absorbance of P25/PDoPa films, (b) Absorbance at 300 nm of P25/PDoPa, (c) band gap of P25/PDopa .36 n LIST OF TABLES Table Numbers of layers 17 Table Roughness of P25/PDopa films with different numbers of bilayer 29 n 4.3 Photodegradation performance 4.3.1 Calibration 2.0 0.5 uM uM uM uM 10 uM 20 uM Absorbance 1.5 1.0 0.5 0.0 400 450 500 550 600 650 700 750 Wavelength (nm) a) 2.0 Absorbance at 562nm 1.5 1.0 y = 0.0928x - 0.005 R² = 0.9999 0.5 0.0 10 15 20 Concentration (uM) b) Figure 16 Absorbance of SRB: a) in range from 400nm to 750nm, b) at 562nm The upper figure exhibits a straight-line calibration data set where X = concentration and Y = Absorbance at 562 nm (Y = 0.0928x -0.005) The black dots are data points For this set of data, the measured slope is 0.928 and the intercept is 0.005 The true value of the slope is exactly 7, which included blank The quality of fit 30 n (standard deviation) is 0.9999, which shows high quality of this method in concentration range from 0.5 uM to 20 uM 4.3.2 Photodegradation activities of PDopa films a) 2.5 Bilayers 5.5 Bilayers 10.5 Bilayers 15.5 Bilayers 20.5 Bilayers 1.0 0.8 C/C0 0.6 0.4 0.2 0.0 10 20 30 40 50 60 Time (min) b) 0.5 2.5 Bilayers 5.5 Bilayers 10.5 Bilayers 15.5 Bilayers 20.5 Bilayers 0.0 -0.5 -1.0 ln(C/C0) -1.5 y = -0.0316x + 0.0495 -2.0 R² = 0.996 y = -0.037x + 0.0602 -2.5 R² = 0.9957 y = -0.0488x + 0.1525 -3.0 R² = 0.9864 y = -0.0523x + 0.1732 -3.5 R² = 0.9845 y = -0.0643x + 0.2285 R² = 0.9823 -4.0 10 20 30 40 50 60 70 80 Time (min) Figure 17 (a) SRB photodegradation profiles of (P25/PAA)nthin films at wavelength 562 nm, (b) the first-order kinetic plot of ln(C/C0) and time(minutes) for photodegradation of SRB using (P25/PAA)n thin films at wavelength 562 nm 31 n Figure 17(a) shows the efficiencies of the photocatalytic degradation under UVvis irradiation, C is the concentration of SRB at the irradiation time t and C0 is the concentration in the absorption equilibrium of photocatalysts before irradiation As shown in this figure, in term of P25/PAA bilayers films, about 98% of SRB solutions were degraded after h irradiation for 20.5 bilayers films whereas 85% for 2.5 bilayers films made by dip-coating, which reveals that the photocatalytic activity has been extremely improved due to the layer by layer structure Figure 17(b) shows the relationship of time versus ln(C/C0) for all photocatalysts According to the results, it is of great importance to note that the photocatalytic efficiency of P25/PAA layer by layer composite 20.5 bilayers is two times that of 2.5 bilayers film 32 n a) 2.5 Bilayers 5.5 Bilayers 10.5 Bilayers 15.5 Bilayers 20.5 Bilayers 1.0 0.8 C/C0 0.6 0.4 0.2 0.0 10 20 30 40 50 60 Time (min) b) 0.5 0.0 -0.5 -1.0 ln (C/C0) -1.5 -2.0 y = -0.0364x + 0.0551 -2.5 y = -0.0427x + 0.11 R² = 0.9963 R² = 0.9913 y = -0.0541x + 0.1605 2.5 Bilayers 5.5 Bilayers 10.5 Bilayers 15.5 Bilayers 20.5 Bilayers -3.0 -3.5 -4.0 R² = 0.9896 y = -0.0599x + 0.2305 R² = 0.9802 y = -0.0749x + 0.2933 -4.5 -5.0 R² = 0.9786 Time (min) Figure 18 (a) SRB degradation profiles of (P25/PDopa)n thin films at wavelength 562 nm, (b) the first-order kinetic plot of ln(C/C0) and time(minutes) for photodegradation of SRB using (P25/PDopa)n thin films at wavelength 562 nm, 33 n By comparison, the multilayer films containing Poly(L-Dopa) were recorded at higher of photodegradation efficiency It is about almost 99% of SRB solutions were degraded after h irradiation for 20.5 bilayers films whereas 89% for 2.5 bilayers films made by dip-coating 4.3.3 Photodegradation performance of TiO2 a) P25 St-01 St-21 1.0 0.8 C/C0 0.6 0.4 0.2 0.0 10 20 30 40 50 60 Time (minutes) b) 0.0 y = -0.0061x - 0.0055 -0.5 R² = 0.9993 y = -0.0144x + 0.0055 ln(C/C0) -1.0 R² = 0.9997 -1.5 -2.0 P25 St-01 St-21 -2.5 -3.0 10 y = -0.0427x + 0.11 R² = 0.9913 20 30 40 50 60 70 80 Time (minutes) Figure 19 (a) SRB degradation profiles of (TiO2/PDopa)n thin films at wavelength 562 nm, (b) the first-order kinetic plot of ln(C/C0) and time(minutes) for photodegradation of SRB using diffirent kinds of TiO2 34 n SRB degradation profiles of the multilayer films containing different kinds of TiO2 and the first-order kinetic plot of ln(C/C0) and time (minutes) for photodegradation of SRB using diffirent kinds of TiO2 were graphed as in figure 19 The photodegradation efficiency of the multilayer films containing P25 was recorded as three times as that of St-21 and six times as that of St-01 35 n 4.4 P25/PDoPa films band gap a) 2.5 Bilayers 5.5 Bilayers 10.5 Bilayers 15.5 Bilayers 20.5 Bilayer Absorbance 200 300 400 500 600 Wavelength (nm) b) 3.0 Absorbance at 300 nm 2.5 2.0 1.5 1.0 0.5 10 12 14 16 18 20 22 No P25/PDopa bilayers c) 3.5 3.0 2.0 1.5 1/2 (ahv) /(eV.m) 1/2 2.5 1.0 0.5 0.0 -0.5 Photo energy/(eV) Figure 20 (a) Absorbance of P25/PDoPa films, (b) Absorbance at 300 nm of P25/PDoPa, (c) band gap of P25/PDopa 36 n It is quite obvious in figure 20(a) that the P25/Pdopa bilayer films cannot absorb any visible light due to the fact that its absorption edge is 400 nm As the data shown in figure 20 (b), at 300 nm wavelength, as the increase of bilayers, the absorbance of the films is increasing According to the Kubelka-Munkequation : αhυ=const(hυ−Eg)2 where α=(1−R)2/2R, R=10−A, and A is an optical absorption Band gap of photocatalyst can be calculated from the equation Figure 20(c) plots the relationship of (αhυ)1/2 versus photon energy, showing that the band gap of P25/PDoPa films is around 3.2 eV 37 n PART V DISCUSSION AND CONCLUSION 5.1 Discussion In general, based on photodegradation data, fabrication of photocatalytic thin films by the layer-by-layer self-assembling method containing P25 and poly(L-Dopa) contributed to be a promising method for efficiency improvement in contaminant degradation because of its advantage of it materials as well as the method Compared to St-01 and St-21, DLS shows that P25 has the highest zetapotential and the smallest particle size at pH 3.At pH 3, the highest zeta-potential contributes to a high colloidal stability rate in P25 (Greenwood & Kendall, 1999;Hanaor, Michelazzi, Leonelli, & Sorrell, 2012) whereas with smallest particle size, P25 has low sedimentation rate (Kammermeyer, K., Binder, J 1941) In addition to this, the photodegradation efficiency of the multilayer films containing P25 was recorded as much higher than that of St-21 and that of St-01 As a result, at pH 3, P25 solution is suitable for fabrication of multilayer films due to its high colloidal stability and low sedimentation rate Additionally, in case of pH values, Poly(L-Dopa) domains negative charge at wide range of pH values from to (Zeta-potential < -30 mV) while P25 gets high positive charge from pH to (Zeta-potential >40 mV) and small size from pH to According to “Zeta Potential for measurement of stability of nanoparticles “by Anirbandeep Bose, at range of Zeta-potential is around +-30 to +-60, stability behavior of the colloids is moderate and good stable Therefore, P25 and Poly(L-Dopa) solutions at pH to are good selection 38 n In comparison between Poly(L-Dopa) and PAA, the multilayer films containing Poly(L-Dopa) were recorded at higher of photodegradation efficiency This contributes to former researches by using Poly(L-Dopa) instead of PAA in fabrication of multilayer films Moreover, FTIR figure shows the inheritance of functional group as well as the properties of bare P25 and PDopa in the multilayer films It is clear that the multilayer films have similar peaks to P25 and PDopa, which means that they have the same functional groups Furthermore, SEM and AFM images present the growth of thickness of the multilayer films as results of increment of both P25 and PDopa layers This result shows that layer-by-layer self-assembly method works effectively in improvement of the thickness of the films The record indicated that the growth of films thickness is not an ideal one layer after another deposition.TiO2 nanoparticles fill into the pores and stack to achieve thickness growth simultaneously In addition, the photodegradation performance shows the effectiveness of P25 and PDopa in presence of themselves As the result of the increment of bilayers, the photodegradation rate increases Besides, the multilayer films were recorded with band gap 3.2 and the disability of visible light absorption It is the same with the band gap of bare P25 (Amtout & Leonelli, 1995; Asahi, Taga, Mannstadt, & Freeman, 2000; Koelsch, Cassaignon, Minh, Guillemoles, & Jolivet, 2004; Pelaez et al., 2012) However, there are various unanswered questions and limitations here Firstly, the highest number of bilayers in the study is 20.5, so what is the maximum number of 39 n bilayers in reality that is possible to fabricate for the most effective? Secondly, this study evaluated only the photodegradation performance of the multilayer films in SRB Thus, it is quite limited to conclude that P25/PDopa performs good result in pollution degradation This could be interesting to focus on for future researchers 5.2 Conclusion In this study, it is clear that particle size and colloidal stability of TiO2 aqueous suspension play an important part in achievement of high photocatalytic performance Poly(L-Dopa) was negatively charge at wide range of pH values, which contributes it a good substitution for the current commercially available polyelectrolyte At pH 3, P25 Degussa and Poly(L-Dopa) were recorded as an optimal charge with high zetapotential and low particle size, contributing for high colloidal stability and low sedimentation Furthermore, the results show that the layer-by-layer self-assembling method was simple and useful to fabricate the thin films of nano-structured thin film containing P25 nanoparticles and Poly(L-Dopa) with low 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