The objectives of the thesis: Study on materials fabrication technology; structural - photocatalytic properties of TiO2 material, and TiO2 as the nanostructured variant. On the basis of such material system, the systematic and quantitative study on hydrophilicity or, in other words, the study of surface energy of material systems under Exciation of UV light radiation. Further clarification of the correlation between photocatalytic activity, self-cleaning and hydrophobicity of TiO2 nanostructured materials.
BỘ MINISTRY OF EDUCATION AND TRAINING VIETNAM ÂCDEMY OF SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY …… ….***………… NGUYEN THI MAI HUONG Study the fabrication and photocatalytic, hydrophilic properties of TiO2/SiO2 and TiO2/PEG thin films by sol-gel method Major: Solid State Physics Code: 44 01 04 SUMMARY OF THE THESIS Hà Nội – 2018 The thesis is completed at: Graduate University of Sciences and Technology, Vietnam Academy of Science and Technology Supervisors: 1) Dr Nguyen Trong Tinh 2) Dr Nghiem Thi Ha Lien Reviewer 1: … Reviewer 2: … Reviewer 3: … -1- A INTRODUCTION TiO2 is known as a photocatalytic and hydrophilic semiconductor material when excited by light That is why TiO2 is considered to be a functional material that has the potential to create self-cleaning materials for practical applications The hydrophilic nature of the material surface under optical excitiation is closely related to the material properties, surface configuration and stimulus For this reason, the study on the hydrophilicity of the material is a very academically attractive subject in studying the properties as well as physical processes on the surface In the world, recent studies show the relationship between the hydrophilicity of the solid surface and surface energy Exciation by light produces a change in surface energy, leading to a change in hydrophilicity The systematic and quantitative study of the changes in surface energy under the differentiation of TiO2 with different nano-structures promises to bring further information to the photocatalytic mechanism and super-hydrophilic effects of TiO2 material In Vietnam, there are a few studies related to hydrophilicity or surface energy of materials, especially hydrophilicity under the Exciation of the light Therefore, the objectives of the thesis are presented as follows: The objectives of the thesis: Study on materials fabrication technology; structural photocatalytic properties of TiO2 material, and TiO2 as the nanostructured variant On the basis of such material system, the systematic and quantitative study on hydrophilicity or, in other words, the study of surface energy of material systems under Exciation of UV light radiation Further clarification of the correlation between photocatalytic activity, self-cleaning and hydrophobicity of TiO2 nanostructured materials Research subjects: The thesis focuses on two structural systems on the basis of nanostructured and anatse-shaped TiO2: The complex nano-structure TiO2/SiO2 and Nano-porous TiO2/PEG -2- Main study contents: Fabrication of TiO2/SiO2, TiO2/PEG material systems and experimental study on the structural properties as well as the photocatalytic properties of the two material systems The hydrophilicity or surface energy of TiO2/SiO2, TiO2/PEG nanostructured films is studied by contact angle measurement and semi-quantitative techniques based on micro-theoretical models of solid surface under the presence of the stimulus The practical and theoretical significance of the thesis The technology of fabrication of nanostructured TiO2 material is controlled by sol-gel method The nanostructures of TiO2 thin films are controlled The phase transition is inhibited from the anatase configure with high photocatalytic activity of Anatase to Rutile phase into Rutile phase with low photocatalytic activity at high temperature A new methodology is developed for calculation and quantification of solid phase surface energy quantification based on micro theory of solid-state physics Based on this methodology, it is possible to calculate and quantify the solid surface energy based on experimental data of measuring the liquid-solid phase contact angle by contact angle measurement technique Quantitative study of surface energy of nanostructured TiO2 photocatalytic film under the Exciation of UV radiation This provides empirical evidence about a physical effect: optical Exciation can change the surface energy of the photocatalyst The correlation between the photocatalytic mechanism and the super-hydrophilic mechanism of the nano-structured TiO2 material system is demonstrated Quantitative empirical data is provided, contributing to consolidate the hypothesis of the origin of the mechanism of super-hydrophilic effect of the TiO2 material system Layout of the thesis: The thesis consists of the introduction, chapters and the conclusion The results are published in five journals including 03 international publications and 02 national publications -3- B CONTENTS OF THE THESIS Chapter OVERVIEW OF TITANIUM DIOXIDE NANOMATERIALS (TIO2) 1.1 Titanium Dioxide Nanomaterials 1.1.1 Introduction In recent years, Nano TiO2 powder in the rutile, anatase, or mixture of rutile and anatase and brookite mixtures have been studied for use in the fields of solar cells, manufacturing electronic device, sensing head, etc With high photocatalytic activity, TiO2 nano-material are applied in the fields of environmental treatment such as: decomposition of toxic organic compounds, water treatment, bactericidal, mildew-proof Especially, in combination with hydrophobicity when exposed to light, TiO2 is developed as a self-cleaning material With durable and non-toxic structure, TiO2 material is considered to be the most promising material to address many serious environmental problems and challenges of pollution Phase-pure TiO2 nanoparticles: TiO2 has four forms of formation In addition to amorphous form, it has three crystalline forms, including: anatase, rutile and brookite (Figure 1.1) Anatase Rutile Brookite Figure 1.1: The Crystal structure of TiO2 Differences in network structure lead to differences in electronic density between the two rutile and anatase forms of TiO2 and this is the cause of difference in nature between them The nature and application of TiO2 is highly dependent on the crystalline structure of the forms and particle size of such forms Among the forms of TiO2, the anatase exhibits higher photocatalytic activity than the rest -4- Transformation of TiO2 forms: amorphous → anatase → rutile is significantly affected by synthetic conditions and the process of form transformation of modified TiO2 material is different from that of of pure TiO2 1.1.2.Photocatalytic property of the TiO2 nano-material Photocatalytic mechanism of the TiO2 nano-material TiO2 has an anatase band gap of 3.2eV Therefore, under the effect of the photon energy that is greater than 3.2eV, the following process will occur: TiO h eCB hVB When positive holes (h+VB) appear in the water environment, the *OH radical formation reaction will occur: hVB H 2O *OH H hVB OH *OH Figure 1.2: Mechanism of semiconductor photocatalysis On the other hand, when electrons appear on the conducting zone (e-CB) if O2 is present in the water, the *OH radical formation reaction will occur Factors affecting photocatalytic properties There are many factors affecting the photocatalytic activity of the film such as manufacturing method, crystal crystallinity, heating temperature, effective surface area, catalytic mass, illumination intensity However, the two major determinants of photocatalytic activity of TiO2 films are the effective surface area -5- and the crystallinity of the film In addition, for photocatalytic reactions to occur in the visible light, it is important to pay attention to the important factor known as the absorption edge of the right membrane located within this light zone 1.1.3 Modified TiO2 nano-material TiO2 crystals have a big band gap (3.0-3.2eV), therefore, photocatalytic sensitivity is located only in ultraviolet light with wavelengths of less than 380nm, i.e only 5% of solar energy in the ultraviolet zone is capable of activating photocatalytic activity In order to transfer the photocatalytic reaction into visible light, where there is 45% of solar energy, the methods are applied such as TiO2 doping with transitional metal elements to form intermediate states in the band gap of TiO2; attaching semiconducting photoresist or organic matter that is capable of absorbing visible light; forming the TiOx and doping nitrogen, carbon to replace oxides in TiO2 anatase crystals; forming TiO2 composites with different compounds The complex nano-material TiO2/SiO2 In order to increase the hydrophilicity and self-cleaningability of TiO2 material, SiO2 is doped with TiO2 to increase the acidity of the surface, which results in stronger water absorption and reduction in surface contamination According to Guan et al., when SiO2 is added into TiO2, meaning that silicon can enter the titanium network and replace the position of Ti4+ cations, the number of oxygenatoms associated with Si and Ti varies, creating an electrical imbalance The result is that the acidic center (Lewis center) with a positive charge is formed on the TiO2/SiO2 complex surface The acidity of the surface makes the TiO2/SiO2 absorb more OH-radicals Specifically, silicon cations or saying more precisely, Ti-Si bonds can take OH- of the adsorbed H2O molecules and O2- of the complex can bind to H+ of the adsorbed water Therefore, there is a competition of absorption of compounds in the environment and water on TiO2/SiO2 complex surface As the acidity of the surface increases, the water (OH groups) is more strongly adsorbed and surface contamination decreases Hydrophilicactivity causes the -6- water to flow all over the surface, absorb into dirt and push it away from the surface Nano porous material TiO2/PEG PEG (PolyEthylene Glycol) is an organic polymer with a chain circuit and when being dissolved in the TiO2 sol, these chains alternate between TiO2 particles After the fabrication, the film undergoes thermal treatment, as a result, the PEG burns and porous holes are left between the TiO2 particles Therefore, the addition of PEG increases the volume and diameter of the porous holes of the material, leading to the increase in the surface area of the catalyst It is hoped that this will increase the hydrophilicity of the material 1.2 Hydrophilic effects of TiO2 1.2.1 Hydrophilic mechanism under the light Exciation for the TiO2 nano-material Fingre.1.3: Schematic representation of photo-induced hydrophilicity In the presence of UV light, some electrons and holes participating in redox reactions with oxygen molecules and water adsorbed on the TiO2 surface to produce the free oxygen radicals with strong oxidation and destruction of organic impurities Other electrons involved in deoxidizing the Ti4+ catrions into Ti3+ catrions and the hole oxidizes the anions to release the atomic oxygen and produce oxygen-free locations on the TiO2 surface Water in the air will occupy this position and create an OHabsorption group on the TiO2 surface The OH- absorption groups form hydrogen bonds with water, therefore, the surface is hydrophilic (Figure 1.3) -7- The hydrophilicity of the material is measured by the contact angle value of the water drop with the material surface; the smaller the contact angle is, the greater the hydrophilicity is Chapter FABRICATION TECHNOLOGY, EXPERIMENTAL PROCESSES AND RESEARCH METHODS 2.1 Fabrivation technology The thesis selects sol - gel method and centrifugal spin – coating method for fabrication of materials and thin films on nanostructured TiO2 base Fabrication technology is based on two processes: Hydrolysis process: Condensation process: 2.2 Study methods of photocatalytic properties for TiO2 nano-material Methods of measuring decomposition of organic pigments which determine the speed of the photocatalytic reaction -8- The Methylene Blue (MB) solution has an initial concentration of C0 decomposed on contact with the optically catalytic active surface due to the UV radiation, resulting in a discoloration of the solution The Ct concentration of the solution is determined at equal intervals during the measurement from the UV-VIS absorption spectra Ln (C0/Ct) = kt, in which k: constant of reaction speed, t: Reaction time Measurement method of bactericidal of photocatalytic effect Photocatalytic materials can destroy biological materials such as bacteria, viruses and mildew The germicidal mechanism is mainly formed by photobiological holes; photobiological electrons on the catalytic surface will destroy or deform the cell wall, break down the DNA chain of such biological materials, making them inoperable or dead The principle of the method is to evaluate the number of live bacteria over time as it comes into contact with the material and then to evaluate the photocatalytic activity of the material Method of measurement of hydrophilic properties by contact angle technique The device includes functional blocks as shown in the figure Figure 2.1: Schematic diagram of the contact angle device - 16 - 4.2 Nano porous TiO2/PEG 4.2.1.Results of material fabrication Figure 4.4: TiO2/PEG fabrication process 4.2.2.Crystalline phase structure of TiO2/PEG material (a) (b) (c) Hình 4.5: X-ray diffraction spectra of TiO2/PEG (0÷50%) sintered at 5000C (a), 6500C (b) 8000C (c) Thus, the percentage of introduced PEG affects the phase transition from anatase to rutile when the sample is sintered at high - 17 - temperature (6500C) However, when the sintering temperature is raised to 8000C for TiO2/PEG samples (0%, 30% and 50%) (Figure 4.5), the whole crystalline phase structure has been transformed into a rutile form This is an undesirable phase for TiO2 photocatalyst 4.2.3 Structure of TiO2 / PEG film surface form 0% 10% 20% 30% 40% 50% Hình 4.6: SEM image of TiO2/PEG (0÷50%) thin films Surface area of nano porous material TiO2/PEG Sample TiO2 - 0%PEG TiO2- 10%PEG TiO2- 20%PEG TiO2- 30%PEG TiO2- 40%PEG TiO2 - 50%PEG Surface area(m2/g) 41,5 47,1 63,2 68,5 86,7 54,3 Table4.1: Surface area of TiO2/PEG (0÷50%) According to the result of the surface form structure and surface area measurement, when PEG is added to TiO2 solution, - 18 - resulting in a change in film porosity and the optimum level at the percentage of PEG in the sol of about 40% 4.2.4 The findings on photocatalytic properties of nano porous material TiO2/PEG Figure 4.7: MB concentration Figure 4.8: The MB decay rate by time of illumination constant depends on the PEG Figure 4.8 demonstrated the decomposition rate of TiO2/PEG film samples (0 ÷ 50%), showing the effect of PEG percentage on the decomposition rate Of which, the TiO2/PEG sample (40%) has the fastest MB decomposition rate Chapter FINDINGS ON HYDROPHIBILITY AND SURFACE ENERGY OF TWO PHOTOCATALYTIC MATERIAL SYSTEMS TIO2/SIO2, TIO2/PEG There are many applications in life directly related to wetting such as the industries of printing, painting, detergents, weaving, dyeing, self-cleaning materials, textiles and so on The biomedical sector also has applications related to the wetting such as ability of absorption of protein, interaction on the cell surface, etc Therefore, the study on the wetting (hydrophilicity, hydrophobicity) or, in other words, the study on surface energy is very useful and of big concern - 19 - In a normal way, surface energy is denoted by γ, but there is rarely an absolutely ideal surface, in fact the contact surface is always between two different phases or two different substances It is very important to determine the interface energy of two solid-vapor (γsv) phases and two solid-liquid (γsl) phases in pure science and in application Direct measurement of energy among phases is very difficult At present, there is a series of indirect approaches to obtain these values Determination of the surface energy through the contact angle from the Young’s equation ( sl sv lv cos ) is one of the simplest methods since the contact angle is a value that can be easily determined by experiment In order to change the surface energy, physicochemical agents have been used such as changing the coating with surfactants or mechanical-physical-thermal effects, as well as fabrication technology, changing the position of atoms, molecules in structure, etc However, recently, there are other methods In this thesis, we use experiment to prove that it is possible to use light Exciation to change surface energy of TiO2 photocatalyst And we have also started to study the properties and rules of photocatalytic effects that affect surface energy This is a kind of physically pure agent, which is different from known physicochemical agents 5.1 Hydrophilicity and surface energy of complex nanomaterial TiO2/SiO2 5.1.1 Hydrophilicity of of complex nano-material TiO2/SiO2 TiO2/SiO2 thin films (0 ÷ 50%) are applied to the sintered glass substrate at a temperature of 5000C The film is UV-irradiated (365 nm wavelength), the light intensity measured on the sample surface is 1mW/cm2 The graph demonstrates the contact angle of the TiO2/SiO2 samples at illumination time shown in Figure 5.1 In all samples, the contact angles of the water drop decrease with the illumination, reaching a saturation value - 20 - Hình 5.1: Contact angle by the time illumination of the TiO2/SiO2 (0÷50%) thin films Hình 5.2:Saturation angle of TiO2/SiO2(0÷50%) thin films It can be commented that the wetting increases (ie, the wetting angle decreases) when the ratio of SiO2 increases, however, when the ratio of SiO2 is up to 50%, the wetting decreases The optimum ratio of SiO2 is at about 40% This changing law is in line with the changing law of photocatalytic properties discussed in Chapter It can be deduced that photocatalytic activity and the wetting are created by the same origin Hình 5.3: contact angle is restored _ TiO2/SiO2 (0÷50%) Surface acidity produces surface hydroxyl groups Such stable hydroxyl groups are beneficial for maintaining hydrophilicity This explains why the contact angle of water slowly increases and remains at low value for a long time in the dark for complex films 5.1.2 Energy surface of TiO2/SiO2 thin films When a liquid drop is placed on the surface of a solid, it is easy to determine the contact angle through the measurement - 21 - However, the important thing is that the contact angle holds important information about the surface energy of the solid γsl and interface energy of the liquid γsl through the Young's equation: sv sl lv cos Surface energy (γsv) value of TiO2/SiO2 film The liquids are selected as in Table 5.1 Table5.1: Surface energy (γsv) value of liquids Liquids lv (mJ.m-2) Liquids lv (mJ.m-2) Ethanol TritonX PEG 600 22,39 33 44,5 Ethyleneglycol Glycerol Nước 47,3 63,4 72,29 From the results of the contact angle of different solutions on the TiO2/SiO2 film (0 ÷ 50%) according to the illumination time by UV light (365nm) The illumination intensity at the sample surface is 1mW/cm2 Apply the surface energy calculation model with TiO2 material presented in Chapter 3: cos sv ( e lv lv sv ) We can calculate the surface energy value γsv of TiO2/SiO2 films (0 ÷ 50%) Bảng 5.2: Surface energy value γsv of TiO2/SiO2 (0÷50%) thin films at times0, 30, 60, 90,120 minute TiO2/SiO2 (0÷50%) 0% 10% 20% 30% 40% 50% γsv(mJ.m-2) minute 30 minute 60 minute 90 minute 120 minute 43,5 51,0 59,9 60,7 60,8 42,6 59,8 60,6 60,8 60,9 46,5 60,3 61,1 61,3 61,6 44,8 60,2 61,5 61,4 61,6 48,6 61,2 62 62,1 62,1 45,7 59,3 60,2 60,9 61,5 - 22 - Illumination time (Minute) Hình 5.4: Surface energy γsvof TiO2/SiO2(0÷50%) thin films by time of illumination Figure 5.4 demonstrates the dependence of the surface energy γsv of the TiO2/SiO2 film (0 ÷ 50%) by the illumination time We have comment that the γsv of the samples increases according to the illumination time to the saturation value The magnitude of the change in energy value γsv from the moment of non- illumination to the saturation value is about 20% The saturated energy values among samples with different SiO2 ratios are different but insignificant Of which, the TiO2/SiO2 sample (40%) had the highest saturation value γsv Value of the interface energy (γsl) between water and TiO2/SiO2 film With the γsv of each kind of TiO2/SiO2 film (0 ÷ 50%), by substituting the value γsv in the Young’s equation sv sl lv cos , for each value of the contact angle θ - 23 - changing at the illumination time, it is possible to calculate the interface energy between water and thin films sl sv lv cos Table 5.3: Contact angle θ of the water, the surface energy γsv and the interface energy between water and TiO2/SiO2(0÷50%) thin films illumination time (minute) 30 60 90 120 illumination time (minute) 30 60 90 120 illumination time (minute) 30 60 90 120 TiO2/SiO2 (0%) TiO2/SiO2 (10%) θ γsv γsl θ γsv γsl 33,7 25,2 17,4 16,3 17,4 43,5 51 59,9 60,7 60,8 -16,7 -14,4 -9,1 -8,7 -8,2 29,3 22,3 13,8 13,1 14,6 42,6 59,8 60,6 60,8 60,9 -20,5 -7,1 -9,6 -9,6 -9,1 TiO2/SiO2 (20%) TiO2/SiO2 (30%) θ γsv γsl θ γsv γsl 28,3 20,6 12,1 11,2 13,2 46,5 60,3 61,1 61,3 61,6 -17,2 -7,4 -9,6 -9,6 -8,8 26,9 19,2 7,6 8,2 44,8 60,2 61,5 61,4 61,6 -19,7 -8,1 -9,9 -10,3 -10,0 TiO2/SiO2 (40%) TiO2/SiO2 (50%) θ γsv γsl θ γsv γsl 24,7 15,6 5,1 4,8 3,9 48,6 61,2 62 62,1 62,1 -17,1 -8,4 -10,0 -9,9 -10,0 30,5 21,1 14,5 12 13,1 45,7 59,3 60,2 60,9 61,5 -16,6 -8,1 -9,8 -9,8 -8,9 Figure 5.5 demonstrates the dependence of the interface energy value between the TiO2/SiO2 film surface (0 ÷ 50%) and water γsl at the illumination time - 24 - Illumination time (Minute) Figure 5.5: Interface energy TiO2/SiO2(0÷50%) thin films – Water by time of illumination We have comments that the interface energy γsl of the film samples with water increases by the illumination time up to the saturation value The magnitude of the change in the value of γsl from the time of no illumination ~-18mJ.m2 to the saturation value ~ -9mJ.m-2 is about 50% The saturation magnitude γsl is not significantly different among samples with different SiO2 content The saturation setting time of samples is approximately the same, after about 30 minutes of illumination 5.2 Nano porous material TiO2/PEG Unlike the TiO2/SiO2 system that is a two-component complex, the TiO2/PEG system studied in this part has only one physical component, nanoTiO2, while the mixed PEG is burned out - 25 - after being sintered and holes are left on the film structure, resulting in a TiO2/PEG porous film The PEG ratio here corresponds to the porosity of the obained material as indicated in Chapter It means that feffective surface will be different for each percentage of PEG The following studies and measurements are performed in the same way as for TiO2/SiO2 samples 5.2.1 Findings on hydrophilic properties of nano porous material TiO2/PEG The contact angle of the water drop will be measured on the TiO2/PEG film samples (0 ÷ 50%) under UV light (365nm) at the same intensity of 1mW/cm2 by time and when the film sample is placed in the darkness Thereby, we will see the influences of factors such as film porosity and thickness through the percentage of PEG added into solution on the hydrophilic effect Effect of porosity and thickness on hydrophilicity of TiO2/PEG films Decrease the contact angle when illuminated film thickness ~0,042μm film thickness ~0,092μm film thickness ~0,14μm Recovery process of contact angle in dark Figure 5.6: Contact angle by the time illumination and the recovery of contact angle in dark of TiO2/PEG (0÷50%) thin films - 26 - In all the samples, the contact angle reduces by illumination time However, there is an influence of PEG percentage or porosity on the hydrophilicity Specifically, the increase in porosity increases the area of the internal surface, leading to better water absorption of the film and creating more OH groups The OH group will make hydrogen bonds; therefore, when reaching the film surface, the water will easily spread over the surface We also commented that the thinner the film, the smaller the amount of TiO2 particles on the film, meaning that the smaller the internal surface area When the film is lighted by light with a higher energy than that of band gap, the number of electron-hole pairs is produced in less and slower manner; On the other hand, due to the narrow internal surface area, the possibility of contact with the environmental factors is low, which makes the free OH group produced less than that of the film samples produced from strong fluid or spin-coating for more times Therefore, the hydrophobicity of the thinner film sample is poorer than that of the thicker film samples The influence of thickness is similar in the recovery process 5.2.2 Surface energy of TiO2/PEG thin films Surface energy value (γsv) of TiO2/PEG thin films The calculations will be similarly implemented to the TiO2/SiO2 film system Table 5.4: Surface energy value γsv of TiO2/PEG(0÷50%) thin films at 0, 30, 60, 90,12, 150 (minute) TiO2/PEG (0÷50%) 0% 10% 20% 30% 40% 50% γSV(mJ.m-2) minute 30 minute 60 minute 90 minute 120 minute 40,2 40,8 42,7 42,8 45,5 42,5 47,4 49,6 49,6 49,7 51,1 49,4 55,7 56,8 57,5 58,1 60,3 58 59,6 60,2 60,6 61 61,6 60,6 60,5 61 61,3 61,5 62,1 61,5 150 minute 60,7 61,1 61,4 61,6 61,9 61,3 - 27 - Illumination time (minute) Figure 5.7: Interface energy TiO2/PEG(0÷50%) thin films – Water by time of illumination Surface energy γsv of the TiO2/PEG film (0 ÷ 50%) increases by the illumination time to the saturation value However, the change in saturated energy γsv by PEG percentage is insignificant (from the minimal value γSV of the TiO2/PEG (0%) sample = 60,70mJ.m-2 to the sample with the maximal value γsv of the TiO2/PEG sample (40%) = 62,1mJ.m-2) The saturated energy setting time of the post-illumination samples are similar, after about 60 minutes of illumination The results are consistent with the photocatalytic survey results and hydrophilicity studies - 28 - Value of the interface energy between water and TiO2/PEG film (γsl) Table 5.5: Contact angle θ of the water, the surface energy γsv and the interface energy between the water and TiO2/PEG(0÷50%) thin films illumination time (minute) 30 60 90 120 150 illumination time (minute) 30 60 90 120 150 illumination time (minute) 30 60 90 120 150 TiO2/PEG (0%) θ 41,2 34,2 22 18,1 16,2 14,1 γsv 40,2 47,4 55,7 59,6 60,5 60,7 γsl -14,2 -12,4 -11,3 -9,1 -8,9 -9,4 TiO2/PEG (10%) θ 39,5 31,3 21,8 14,3 12,1 12,2 TiO2/PEG (20%) θ 35,1 30,1 19,4 15,6 11,4 13,6 γsv 42,7 49,6 57,5 60,6 61,3 61,4 γsl -16,5 -13,0 -10,7 -9,0 -9,6 -8,9 35,7 29,1 16,2 10,5 8,5 7,4 γsv 45,5 51,1 60,3 61,6 62,1 61,9 γsl -13,2 -12,1 -9,1 -9,5 -9,4 -9,8 40,8 49,6 56,8 60,2 61 61,1 γsl -15,0 -12,2 -10,3 -9,9 -9,7 -9,6 TiO2/PEG (30%) θ 34,1 28,4 17,5 13,2 10,2 9,7 TiO2/PEG (40%) θ γsv γsv 42,8 49,7 58,1 61 61,5 61,6 γsl -17,1 -13,9 -10,8 -9,4 -9,6 -9,7 TiO2/PEG (50%) θ 37,2 33,4 21,3 17,3 12,4 14 γsv 42,5 49,4 58 60,6 61,2 61,3 γsl -15,1 -11,0 -9,4 -8,4 -9,4 -8,8 - 29 - Illumination time (minute) Figure 5.8: Interface energy TiO2/PEG(0÷50%) thin films – Water by time of illumination The interface energy of the film with water γsl increases by the illumination time to the saturation value The magnitude of the change in value γsl from the time of no illumination ~ -15mJ.m-2 to the saturation value ~ -9.5mJ.m-2 is about 35% The saturation magnitude of γsl is not significantly different among samples with different PEG percentage Saturation setting time γsl of samples is approximately the same after about 60 minutes of illumination - 30 - CONCLUSIONS The thesis has new contributions that can be mentioned as follows: - Titanium Dioxide Anantase phase and modified nanostructure materials were successfully fabricated by sol-gel method Nanostructures of the TiO2 thin films were wellcontrolled The undesired crystalline phases transition at high temperatures from Anatase (high photocatalytic activity phase) to Rutile (lower photocatalytic activity phase) has been inhibited - The methodology based on the micro theory of materials for quantitative calculation energy of the solid surface and solidliquid interface has been developed The implementation of this calculation methodology to experimental data from contact angle measurements has been applied It is possible to quantity calculate the energy of a solid surface and solid-liquid interface from experimental data - The quantitative data of surface and solid-liquid interface energy of the TiO2 nanostructured photocatalytic film under the excitation of UV radiation has been done The calculated data provides empirical evidence for an interesting effect: the light excitation can vary the surface energy of photocatalyst material such as Titanium dioxide - The relationship between photocatalytic and hydrophilic properties in the nanostructured TiO2 materials has been cleared Quantitative empirical data provided the contribution to hypothesis of the mechanism formation of super hydrophilic effect in Titanium dioxide nanostructure thin film system ... consolidate the hypothesis of the origin of the mechanism of super -hydrophilic effect of the TiO2 material system Layout of the thesis: The thesis consists of the introduction, chapters and the conclusion... techniques based on micro-theoretical models of solid surface under the presence of the stimulus The practical and theoretical significance of the thesis The technology of fabrication of nanostructured... hydrophilicity or surface energy of materials, especially hydrophilicity under the Exciation of the light Therefore, the objectives of the thesis are presented as follows: The objectives of the