Research on the synthesis and characterization of structure and properties of Tio2 - Based nanocomposite for the treatment of some pollutants in air enviroment

MINISTRY OF EDUCATION AND TRAINING VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY --------------------------- MA THI ANH THU RESEARCH ON THE SYNTHESIS AND CHARACTERIZATION OF STRUCTURE AND PROPERTIES OF TiO2-BASED NANOCOMPOSITE FOR THE TREATMENT OF SOME POLLUTANTS IN AIR ENVIROMENT Major: Theoretical Chemistry - Physical Chemistry Code: 62.44.01.19 ABSTRACT OF DOCTORAL THESIS Hanoi - 2017 The thesis was completed at Graduate University of Science and Technology, Vietnam Academy of Science and Technology Supervisor: Assoc. Prof. Dr. Nguyen Thi Hue Reviewer 1: Reviewer 2: Reviewer 3: The doctoral thesis will be defended with the Evaluation Committee at Graduate University of Science and Technology, Vietnam Academy of Science and Technology. Time: Date. month . 2018 This thesis can be found at: - The library of Graduate University of Science and Technology; - National Library of Vietnam. 1 INTRODUCTION 1. The rationale of the thesis Nowadays, the transportation, the industry activities, craft villages, etc. has emitted many high-toxic compounds and harmful bacteria harmful to human health into the air. Therefore, the polluted air is an urgent issue that needs to be studied and solved. A variety of methods has been employed to treat the polluting substances in the air such as membrane filtration, adsorption by activated carbon, thermophilization, ionization, ozone, photocatalyst, irradiation ultraviolet etc. In particular, the titanium dioxide (TiO2) photocatalyst possesses many outstanding advantages such as complete conversion of toxic compounds into carbon dioxide, water, and salts but no by-products, the ambient operation conditions, easy- to-look and low cost. However, TiO2 has some disadvantages as follows: the large band gap (Eg 3,2eV), the reaction occurring only when the radiation is in the ultraviolet area, the high rate of the combination of high electron-hole pair leads to the low efficiency of photochemical quantification and photocatalysis. Thus, doping of metals or nonmetals is often utilized on the crystal structure of TiO2 to obtain a catalyst that is operable in the visible light region. In all of the used elements, nitrogen is the most frequently employed because the process is very simple but effective. TiO2 is able to strongly oxidized – reduce, but has low capability of adsorption absorption, while hydroxyl apatite (HA) is a good adsorbent but has a poor oxidation – reduction feature. There has been a lot of studies on HA/TiO2 composite from HA with TiO2 that is highly photo-catalytic and has good adsorption properties. In addition, the HA coated on the TiO2 surface creates a space that allows TiO2 to perform the photo-catalytic properties without 2 destroying other materials. In particular, the HA/TiO2 composite is dispersed as a suspension in water and as a result, it is environmentally friendly. However, TiO2 is a dense but not a micro- porous structure and it is necessary to investigate the stability of suspended solid. TiO2 coated on metal aluminum oxide (TiO2/Al2O3) and HA coated on titanium dioxide nanoparticles (HA/TiO2) are promising materials for the treatment of some pollutants such as VOCs, CxHy, NOx, CO, bacteria in the air. If being doped with nitrogen, these two materials are able to effectively treat the airborne contaminants in the visible light, thereby increasing the applicability in the practical cases. The nano N-TiO2 rod has a larger specific surface area than that of the granular one, therefore the HA/N-TiO2 nanocomposite from N-TiO2 rod is more efficient and easier to have the stability in the suspension than that from the granular N-TiO2. For the above reasons, the thesis is proposes as "Research on the synthesis and characterization of structure and properties of TiO2-based nano- composite for the treatment of some pollutants in air environment ". The topic has practical significance, contributing to the reduction of the air pollution caused by chemicals and bacteria. 2. The objectives of the thesis The objective of the thesis is to produce two types of materials: Nano N-TiO2 coated on metal oxide aluminum (N-TiO2/Al2O3) used as membrane for air purification and hydroxyl apatite nano-composite coating on TiO2 doped Nitrogen (HA/N-TiO2) coated on the wall for the treatment of toluene, bacteria and fungal contamination in the air. 3. The main research activities - The synthesis of two nanostructured TiO2 photocatalyst materials (N-TiO2/Al2O3 and HA/N-TiO2). 3 - Characterization of the structure, properties and composition of N-TiO2/Al2O3 and HA/N-TiO2. - Investigate the catalytic activity of the material through toluene treatment, B.cereus, S. areus, E. coli, B. cepacia and Candida albicans. 4. The content The thesis is composed of 117 pages, 28 tables, 77 figures, 117 references and 3 appendixes. There are following chapters: Introduction (2 pages); chapter 1: Literature review (39 pages); chapter 2: Methodology (22 pages); chapter 3: Resutl and discussion (52 pages); Conclusion (2 pages). CHAPTER 1: LITERATURE REVIEW 1.1 Introduction of some air pollutants and treatment methods 1.2 TiO2 nanomaterial 1.3 TiO2 nanoparticles coated on aluminum oxide 1.4 HA/TiO2 nanocomposite 1.5 Evaluation of the photo-catalyst activity of the material CHAPTER 2: METHODOLOGY 2.1 Chemicals, apparatus and equipment 2.2 Synthesis of materials 2.2.1 Synthesis of N- TiO2/Al2O3 N- TiO2/Al2O3 material was synthesized by sol-gel method from 2-phase metal alkoxide, including: N-TiO2 solubilization stage and N-TiO2 nanofiltration stage on aluminum fiber oxide. 2.2.2 Synthesis of HA/N-TiO2 nanocomposite HA/N-TiO2 materials were synthesized in two phases, including N-TiO2 powder phase and HA/N-TiO2 powder phase. 2.3 Characterization of materials 4 The state-of-the-art technique and equipment such as: thermal analysis (TGA), X-ray diffraction (XRD), IR spectroscopy, energy- dispersive X-ray spectroscopy (EDX), ICP-MS mass spectrometry were employed to determine the structure, the nature and composition of N- TiO2/Al2O3 and HA/N-TiO2. Morphology and specific surface area of the samples were determined by SEM and BET method. The critical absorption wavelength of the material is determined by UV-Vis absorption spectrometry. 2.4 Catalyst activity testing 2.4.1 Test of N-TiO2/Al2O3 on toluene treatment The 1m³ test chamber performs the experiments to evaluate the efficiency of the toluene treatment corresponding to the actual room but at a small scale. N-TiO2/Al2O3 material is used as a filter membrane in the air purifier, dimension: 370×100×6mm/membrane, the comparison sample is unmodified TiO2/Al2O3. The thesis investigated the effect of light source, the weight of material, initial toluene concentration, photo-catalyst activity, kinetics of toluene oxidation and the adsorption capacity of the material via the toluene degradation. 2.4.2 Test of HA/N-TiO2 on toluene treatment The HA/N-TiO2 material is coated on a brick surface of 40cm 40cm, using 4brick/1experiment/1m3 chamber. TiO2-P25 and HA/TiO2-P25 were used to compare. The investigated parameters are: the role of HA in HA/N-TiO2 material, the effect of HA/N-TiO2 content in suspension solution, HA/N-TiO2 content, light, initial toluene concentration, kinetics of toluene oxidation and catalytic stability of the material. 2.4.3 Toluene concentration analysis method 5 Toluene concentration was analyzed on the gas chromatograph GC-FID Shimadzu 2010, Japan. The quantitative limit of the toluene determination method is 3.33 μg/m3. 2.4.4 Testing the bactericidal capability of HA / N-TiO2 material HA/N-TiO2 material is coated on 10×10cm bricks. The experiments were performed with four bacteria strains: B.cereus, S. areus, E.coli, B. cefalacia and a fungal strain of Candida. CHAPTER 3: RESULTS AND DISCUSSION 3.1 N-TiO2/Al2O3 material 3.1.1 Synthesis of N-TiO2/Al2O3 material The sol solutions and the materials N-TiO2/Al2O3 are denoted as Sa-b. Where (a) is the mole of TTIP, (b) is the mole of DEA. Table 3.1 Composition of sol N-TiO2 Composition (mole) Number Notation TTIP DEA EtOH 1 S1-1 1 1 34 2 S1-2 1 2 34 3 S2-1 2 1 34 4 S2-2 2 2 34 5 S3-1 3 1 34 6 S3-2 3 2 34 Table 3.2 N-TiO2/Al2O3 - The effect of time Num ber Notation Immersio n time Turn of immersion Calcination time (hour) Calcination temprature (ºC) 1 S1-1-30’ 30 min 1- 10 3 470 2 S1-1-60’ 60 min 1- 10 3 470 3 S1-1-90’ 90 min 1- 10 3 470 4 S1-1-120’ 120 min 1- 10 3 470 5 S1-1-24h 24 hour 1- 10 3 470 6 Table 3.3 N-TiO2/Al2O3 - The effect of concentration Number Notation Immersion time Turn of immersion Calcination time (hour) Calcination temprature (ºC) 1 S1-2 60 5 3 470 2 S2-1 60 5 3 470 3 S2-2 60 5 3 470 4 S3-1 60 5 3 470 5 S3-2 60 5 3 470 3.1.2 Structure and properties of N-TiO2/Al2O3 3.1.2.1 Effect of time and turn of dip coatings Fig 3.2 XRD patterns of N-TiO2/Al2O3 samples 30 min - 24 hour. Fig 3.3 SEM of Al2O3 before coating and after coating with N-TiO2 Cps 0 500 1000 1500 2000 20 25 30 35 40 45 50 55 60 A(101) Al(200) Al(202) A(004) A(200) A(105) A(211) S 1-1-30' S 1-1-60' S 1-1-90' S 1-1-120' S 1-1-24h 2 –Theta-Scale 7 Figure 3.2 shows that there are two large peaks: Al (200) and Al (202) of the carrier material. The diffraction peaks occurring at 2θ  25.3°(101); 37.8°(004); 48°(200), 54º(105); 55°(211) are the anatase phase of TiO2, and the peak A (101) at 2θ25.3° has the strongest intensity. The small peaks indicate that the pattern of the 60-minute immersed sample is very strong, suggesting that the 60-minute samples are more crystallized than the other ones. Thus, the optimized dipping time of Al2O3 fiber in N-TiO2 sol is 60 minutes. The surface of the Al2O3 fiber is initially rough like fish scales. After 5 turns of dip-coating and incubation, the surface of the Al2O3 fiber has become almost flat with the N-TiO2 layer formed and there are some indications of the N-TiO2 cracking (Fig 3.3). Thus, the optimized turn of dipping is 5 times. 3.1.2.2 Effect of composition of N-TiO2 solutions N-TiO2 crystals are granular in all samples (Fig. 3.5). The particle size of N-TiO2 increases when the mole of TTIP is higher (in the column from top to bottom). When the samples had the same TTIP ratio (in left to right row), the particle size of 2mol-DEA sample is more uniformed than that of 1mol-DEA sample. This conclusion is proved from the XRD spectrum (Fig. 3.6). The intensity of the X-ray diffraction peak of the samples increases with the increase of TTIP concentration from 1 to 3 mol. From the width of the diffraction peak at 2θ25.3° on the face (101) described in Figure 3.6A, the average N-TiO2 particle size of samples is calculated in the range 12-33 nm from the Scherrer's formulation. The N-TiO2 particle size increased rapidly (8-12nm) by increasing the amount of TTIP mole per unit and decreasing slowly (1-2nm) by increasing DEA from 1 mole to 2 moles (Fig 3.6B). The sharpness of peaks also differed between the samples, especially with the small peak such as A(004) at 2θ 37.8° which is easily observed in sample S1-2 but are difficult to recognize in the remaining samples. Thus, the S1-2 has the highest crystallinity. 8 Fig 3.5 SEM picture of N-TiO2/Al2O3 sample with different sol concentration. Fig 3.6 XRD patterns of N-TiO2/Al2O3 samples in different sol concentration. S1-1 S1-2 S2-1 S2-2 S3-1 S3-2 2 - Theta - Scale 20 25 30 35 40 45 50 55 60 Cps S 1-1 S 1-2 S 2-2 S 2-1 S 3-1 S 3-2 A(004) 0 10 20 30 40 0 1 2 3 Nồng độ TTIP (mol) Kí ch th ướ c h ạt (n m ) 1 DEA 2 DEA (B) 23 24 25 26 27 28 S 1 - 1 S 2 - 1 S 3 - 1 S 3 - 2 S 2 - 2 S 1 - 2 (A) 9 Fig 3.7 The UV-Vis spectra of N-TiO2 in N-TiO2/Al2O3 material. (a) TiO2 - P25, (b) N-TiO2 sample S1-2, (c) N-TiO2 sample S1-1. From the ICP-MS and UV-Vis result, the TiO2 content is approximately 6.1 - 6.8% of the total mass of N-TiO2/Al2O3 material, the light absorbing wavelength of N-TiO2 samples moves 40 nm towards the visible region, in compared with TiO2-P25 (Fig. 3.7). Thus, the photocatalyst reaction with N-TiO2/Al2O3 material can work effectively with the visible light. 3.1.3 Results of the photo-catalyst activity of N-TiO2/Al2O3 3.1.3.1 Investigate the adsorption capacity of N-TiO2/Al2O3 Light sources are used in two types of lamp: 10w fluorescent daylight and 8w UV365nm lamp. In each experiment, the initial concentration of toluene C° ≈ 400μg/m3, catalytic mcat ≈ 10g, testing time t = 8 hours. The test results show that the TiO2/Al2O3 materials with or without nitrogen express the weak adsorption of toluene. 3.1.3.2 Effect of the light source If being illuminated by the fluorescent lamp (Figure 3.8), N- TiO2/Al2O3 samples gave a relatively high yield, 68% with S1-1 and 72% with S1-2, while the very low yield (14%) was achieved with the non-doped sample (14%). In case with the 365nm UV lamp (Figure 3.9), the toluene treatment efficiency was 85.50% with the S1-1 and 86.29% with the S1-2. 10 Fluorescent lamp 0 10 20 30 40 50 60 70 80 2 4 6 8 Time, (hour) E ff ic ie n cy , (% ) S1-1 S1-2 TiO2/Al2O3 UV365nm lamp 0 20 40 60 80 100 2 4 6 8 Time, (hour) E ff ic ie n cy , (% ) S1-1 S1-2 TiO2/Al2O3 Fig 3.8 Performance of toluene treatment N-TiO2/Al2O3 and fluorescent light. Fig 3.9 Performance of toluene treatment N-TiO2/Al2O3 and the light UV365nm. 3.1.3.3 Effect of photo-catalyst weight The weight of N-TiO2/Al2O3 catalyst varied from 10-60g. The experiment conditions are: C° ≈ 400μg/m3, fluorescent, t = 8 hours. As can be seen from the Figure 3.10, the optimized weight of N- TiO2/Al2O3 is 40 g for both S1-1 and S1-2. 0 50 100 10 20 30 40 50 60 mcat , (gr) E ff ic ie n cy , ( % ) S1-1 S1-2 0 200 400 600 800 1000 0 2 4 6 8 Time, (hour) C , (µ g /m 3 ) 100µg/m3 300ug/m3 500µg/m3 700µg/m3 900µg/m3 Fig 3.10 Performance of toluene decomposition N-TiO2/Al2O3 in different catalyst weight Fig 3.11 The correlation between C0 and the photo- catalyst activity of N- TiO2/Al2O3 3.1.3.4 Effect of initial toluene concentration In the initial toluene concentration range of 100-500 μg/m3, when C0 increases, the frequency of collisions between free radicals and toluene molecules is high, thus the rate of toluene degradation increases (Figure 3.11). If the initial toluene concentration is in the range of 700-900μg/m3, the light can be absorbed by toluene in the 11 gas, reducing the light density on the surface of the TiO2 particles, resulting in a reduction in the efficiency of toluene decomposition. 3.1.3.5 Kinetics of toluene oxidation using N-TiO2/Al2O3 Table 3.11 The rate constant (kobs) initial speed (r0) of the toluene decomposition equals N- TiO2/Al2O3 C0 (µg/m3) kobs (minute-1) r0 (µg/m3minute-1) 100 0,0026 2,354118 300 0,0025 1,766800 500 0,0018 0,904428 700 0,0044 1,338744 900 0,0034 0,343808 y = 269,49x + 0,1972 R 2 = 0,9373 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 0 0,005 0,01 0,015 1/C0, µg/m 3 1 /r 0, ( m in .µ g /m 3 ) Fig 3.13 The dependence of 1/r0 in 1/C0 in toluene decomposition by N-TiO2/Al2O3. Figure 3.13 indicates that the kinetics of the toluene decomposition by N-TiO2/Al2O3 conforms to the Langmuir- Hinshelwood model. The value of k-1 is 0.1972 and the slope (269.49) is the value of k-1K-1L-H. Thus, the rate constant is k = 5.0710 (min-1μg/m3) and the adsorption constant is KL-H = 7.32 × 10 -4 (μg/m3). 3.1.3.5 The stability of photo-catalyst activity of N- TiO2/Al2O3 The investigation shown that after 2-6 months, the toluene treatment efficiency of N-TiO2/Al2O3 are relatively stable over 80% (sample S1-1) and over 90% (sample S1-2). After 12-24 months, the efficiency decreases to 60-70% and 70-80%, respectively with S1-1 and S1-2. 3.2 HA/N- TiO2 nanocomposite 3.2.1 Synthesis of HA/N- TiO2 nanocomposite 12 3.2.1.1. Production results of N- TiO2 powder Analysis of SEM and XRD shows that the commercial TiO2 powders are particle, larger than 100 nm, single-phase anatase TiO2. After the hydrothermal and calcination at 800ºC, TiO2 was obtained in the form of rods of 5×10nm, with a length of about 10-500nm, two phases: anatase and rutile with the anatase/rutile ratio of about 80/20. Faculty of Chemistry, HUS, VNU, D8 ADVANCE-Bruker - Sample B 01-078-2486 (C) - Anatase, syn - TiO2 - Y: 77.17 % - d x by: 1. - WL: 1.5406 - Tetragonal - a 3.78450 - b 3.78450 - c 9.51430 - alpha 90.000 - beta 90.000 - gamma 90.000 - Body-centered - I41/amd (141) - File: Thu MT mau B.raw - Type: 2Th/Th locked - Start: 10.000 ° - End: 70.000 ° - Step: 0.030 ° - Step time: 0.8 s - Temp.: 25 °C (Room) - Time Started: 14 s - 2-Theta: 10.000 ° - Theta: 5.000 ° - Chi: 0.00 ° - L in ( C p s) 0 100 200 300 400 500 600 700 800 2-Theta - Scale 10 20 30 40 50 60 70 d = 3 .5 0 5 d= 2 .4 2 5 d = 2. 3 7 2 d = 2 .3 2 7 d = 1 .8 89 d = 1 .6 9 8 d= 1 .6 6 4 d =1 .4 9 1 d= 1 .4 7 9 d = 1 .3 6 3 Fig 3.15 SEM picture of the commercial TiO2 Fig 3.16 XRD patterns of commercial TiO2 0 500 1000 1500 20 25 30 35 40 45 50 55 60 Cp s 2 - Theta - Scale A A A A A A A R R R R R TiO 2 0,25 0,5 1,0 2,0 Fig 3.20 SEM picture of TiO2 after the hydrothermal and calcination at 800ºC Fig 3.21 XRD patterns of TiO2 after the doping nitrogen There are two phases (anatase and rutile) in the TiO2 samples after being doped with nitrogen. The result of EDX and UV-Vis show that the N-ratio represents over 2% of the N-TiO2 weight, the critical wavelength of the N-TiO2 samples is 410-460nm, in which the sample with mTiO2: mure = 1: 1 absorbs the high quantity of visible light. 13 3.2.1.2. Synthesis of HA/N-TiO2 materials Table 3.12 The HA/N-TiO2 samples – Effect of time Number Notation Immersion time of N-TiO2 powder (hour) Concentration Ca2+ (mmol/L) Concentration PO4 3- (mmol/L) 1 HA/N-TiO2 1h 1 25 10 2 HA/N-TiO2 3h 3 25 10 3 HA/N-TiO2 6h 6 25 10 4 HA/N-TiO2 12h 12 25 10 5 HA/N-TiO2 24h 24 25 10 Table 3.13 The HA/N-TiO2 samples – Effect of concentration Number Notation Immersion time of N-TiO2 powder (hour) Concentration Ca2+ (mmol/L) Concentration PO4 3- (mmol/L) 1 S5 3 12,5 5 2 S7 3 17,5 7 3 S10 3 25 10 4 S15 3 37,5 15 3.2.2 Characteristics of HA/N-TiO2 materials 3.2.2.1 Effect of N-TiO2 immersion time in the stock solution Figure 3.24 shows the results of XRD analysis of HA/N-TiO2 samples at different HA formation times. Diffraction peaks of anatase and rutile phases of TiO2 appear in all samples. A small but clearly visible peak at 2θ31.6° is the face (211) of the HA crystals. This peak represents a small crystalline HA. The intensity of the HA peak increased sharply from 1h to 6h, then 12h and 24h showed no increase in intensity. 14 0 500 1000 1500 2000 20 25 30 35 40 45 50 55 60 C ps 2 - Theta - Scale N - TiO 2 1 h 3 h 6 h 12 h 24 h A A AA A A A R R R R R R HA Fig 3.24 XRD patterns of HA/N- TiO2 samples 1-24 hour. Fig 3.25 SEM picture of HA/N- TiO2 samples 1-24 hour. N-TiO2 HA/N-TiO2 – 1h HA/N-TiO2 – 3h HA/N-TiO2 – 6h HA/N-TiO2 – 12h HA/N-TiO2 – 24h 15 The original N-TiO2 powder (wi