Tóm tắt luận án Tổng hợp Nano kẽm Oxít có kiểm soát hình thái và một số ứng dụng

2 > NH3; Đối với trường hợp cảm biến khí ethanol, độ hồi đáp như là một hàm số tuyến tính theo nồng độ ban đầu. 4. Hệ xúc tác nâng cao ZnO/H2O2 kết hợp với sóng siêu âm rất có hiệu quả đối với quá trình làm mất màu và phân huỷ khoáng hoá MB. Phương pháp nồng độ đầu tiên cho kết quả lặp lại và thuận lợi cho nghiên cứu động học. Bậc phản ứng cho kết quả lặp lại tốt, nhưng hằng số tốc độ thay đổi tuỳ thuộc vào thời điểm tính toán nồng độ ban đầu. Phương trình 24 động học mất màu MB bằng H2O2 trên xúc tác nano ZnO có sự hỗ trợ của sóng siêu âm đã được đưa ra trong nghiên cứu. 5. Cả hai chất xúc tác ZnO và La-ZnO đều có hoạt tính xúc tác quang hoá trong vùng tử ngoại và khả kiến, nhưng hoạt tính quang hoá của nó trong vùng khả kiến yếu hơn nhiều so với vùng tử ngoại. Phương pháp nồng độ đầu rất hiệu quả trong việc nghiên cứu động học hình thức, kết quả cho thấy bậc phản ứng mất màu quang hoá là phản ứng bậc nhất. Hằng số tốc độ tính theo mô hình phản ứng đơn phân tử Langmuir - Hinshellwood cho thấy rằng, hằng số tốc độ thay đổi phụ thuộc nhiều vào thời điểm tính toán tốc độ đầu và hằng số tốc độ phản ứng có khuynh hướng giảm, tỉ số kT:Ka đặc trưng cho mức độ phản ứng quang hoá và hấp phụ rất lớn đến vài ngàn lần cho thấy sự hấp phụ có thể được bỏ qua và sự mất màu ở đây do phản ứng quang hoá quyết định. 6. Kiểu điện cực biến tính GC/P(BCP)/ZnO cũng đã tiến hành khảo sát được các điều kiện thực nghiệm cho phương pháp von – ampe hòa tan anot xác định acid uric, phương pháp này có độ lặp lại cao, khoảng tuyến tính tốt với độ nhạy thấp, độ đúng cao. Vì vậy, dùng nano ZnO dạng đĩa để biến tính điện cực áp dụng trong phân tích điện hóa, với mục đích xác định nồng độ acid uric trong nước tiểu và huyết thanh như đã nghiên cứu. DANH MỤC CÁC CÔNG TRÌNH KHOA HỌC 1. Võ Triều Khải, Trần Thái Hòa, Nguyễn Văn Ly, Đinh Quang Khiếu (2012), “Ảnh hưởng của dung môi hữu cơ đến hình thái vật liệu nano/micro ZnO”, Tạp chí Khoa học và công nghệ, Tập 50 (số 3B), Tr. 61 – 67. 2. Vo Trieu Khai, Mai Thi Thanh, Nguyen Hai Phong, Tran Thai Hoa, Dinh Quang Khieu (2013), “A kinetic study of ultrasound-assisted catalytic wet peroxide oxidation of methyl blue”, Tạp chí Hóa học, Tập 51 (Số 2AB), Tr. 317 – 321. 3. Võ Triều Khải, Trần Xuân Mậu, Nguyễn Hải Phong, Trần Thái Hoà, Đinh Quang Khiếu (2013), “Tổng hợp và đặc trưng ZnO, La-ZnO dạng que bằng phương pháp thủy nhiệt”, Tạp chí xúc tác và hấp phụ, Tập 3, 2014, Tr. 27 – 34. 4. Võ Triều Khải, Nguyễn Hải Phong, Trần Thái Hoà, Đinh Quang Khiếu (2013), “Nghiên cứu động học phản ứng mất màu phẩm nhuộm xanh methyl bằng xúc tác quang hóa La-ZnO”, Tạp chí xúc tác và hấp phụ, Tập 3, 2014, Tr. 35 – 40. 5. Võ Triều Khải, Trần Xuân Mậu, Nguyễn Hải Phong, Trần Thái Hoà, Đinh Quang Khiếu (2013), “Nghiên cứu hoạt tính cảm biến ethanol của ZnO và La-ZnO”, Tạp chí xúc tác và hấp phụ, Tập 3, 2014, Tr. 67 – 73. 6. Võ Triều Khải, Trần Xuân Mậu, Nguyễn Hải Phong, Trần Thái Hoà, Đinh Quang Khiếu (2013), “Nghiên cứu hoạt tính cảm biến khí H2 và NH3”, Tạp chí xúc tác và hấp phụ, Tập 3, 2014, Tr. 74 – 79. MINISTRY OF EDUCATION AND TRAINING HUE UNIVERSITY COLLEGE OF SCIENCES PhD candidate: VO TRIEU KHAI Dissertation title: SYNTHESIS OF NANO ZnO WITH CONTROLLED MORPHOLOGIES AND THEIR APPLICATION Major: Theoretical Chemistry and Physical Chemistry Code: 62.44.01.19 PHD DISSERTATION ABSTRACT Hue, 2014 The work was fullfilled at the Department of Chemistry, College of Sciences, Hue University 1. The primary academic supervisor: Prof. PhD. Tran Thai Hoa 2. The secondary academic supervisor: PhD. Dinh Quang Khieu The 1st examiner: The 2nd examiner: The oral defense will be taken place at... The dissertation can be found at: -National Library of Vietnam -Centre of Information-Library, National University of Hanoi 1 INTRODUCTION Zinc oxide (ZnO) is a direct wide band gap (3.37 eV) II–VI semiconductor with a large exciton binding energy (60 meV). ZnO micro- and nanoparticles have been extensively studied over the past few years because of their size-dependent electronic and optical properties. Particle size and morphology have a strong effect on their properties and application. Thus, various ZnO structures including nanostructures, nanowires, nanobowls, and nanopellets have been produced. They are widely used in many important areas, such as solar cells , pigments , gas sensors, electronics and photocatalysts . Different methods have been used to prepare ZnO nanostructures, such as hydrothermal, sol–gel, mechanical milling, and chemical vapor deposition. Heterogeneous photocatalysis with ZnO has been successfully applied to degrade organic pollutants. But the efficiency of photocatalytic degradation by ZnO should be further improved in order to meet the requirements of environmental protection. The main factor influencing the photocatalytic activity of ZnO is the quick recombination of charge carriers. In order to improve the photo catalytic activity, different kinds of ions were doped into Zone to inhibit the recombination of photo-induced electrons and holes, modification of Zone by doping with metal ions is an effective method to promote photo catalytic activity. According to my best knowledge, there are no works which study systematically the synthesis of ZnO to form various morphologies as well as their application in Vietnam. With the requirements of industrial development, the study on semiconductors such as ZnO and Me doped ZnO has significance in the views of sciences and practice. This motivates us to research “ Synthesis of nano ZnO with controlled morphologies and their application” Chapter 1 LITRATURE REVIEW Zinc oxide is one of the most promising materials for optoelectronic applications because of its wide direct band gap (3.37 eV) and large excitation binding energy of 60 meV. Its wide band-gap is suitable for short-wavelength optoelectronic applications. The high exciton binding energy larger than the thermal energy at room temperature promises an efficient excitonic emission at room temperature under low excitation intensity. Hence, ZnO is a promising photonic material for UV/blue devices such as short wavelength light emitting diodes and laser diodes in optoelectronics, but also is a promising material for spintronics 2 applications, if doped with magnetic impurities. ZnO exists in both wurtzite and blende crystals. 1.1. SYNHESIS OF ZnO IN NANO SCALES The physical chemistry properties of nano materials depend on scales, morphologies and compositions of its surfaces. Then, synthesized processes play a critical role on the nanotechnologies. Generally, the synthesized processes could be classified in two groups: The first is based on solution/wet chemical and the second is based on physical techniques. The physic technique such as vapour liquid-solid, vapour solid, chemical vapour deposition often operate at high temperature and pressure. These process provide ZnO with excellent quality. However, their backward are low yield, large energy consuming and high cost. Then, .. we don’t review these process. The wet chemistry processes, particular hydrothermal process, were studied widely. In this dissertation, with development of idea using hexamethylenetetramine to synthesize at low temperature, we will study on the effect of solvent onto its morphologies of ZnO by solvothermal method) and study on the synthesis of ZnO spherical /wire in nanoscale. The obtained ZnO with various morphologies will applied as gas sensing and catalytic materials. 1.2. Synthesis of La doped ZnO At present, gas sensors of semiconductors are one of the most popular sensor. There are three kinds of gas semiconductor sensors, e.g. Tin oxide, zinc oxide and iron oxide. ZnO and ZnO based materials have been studied widely in gas semiconductor sensors. Pt, Pd doped ZnO used as catalysts for improving selectivity, sensitivity and stability. Generally, they can enhance physial-chemistry properties of materials as well as reaction rates. In addition, TiO2, CuO, Fe2O3 and NiO have been investigated to enhance selectivity and sensitivity of sensors. These metal oxide acts as dopants to modify the band gap energy structures and form more active sites at grain boundary. However, most these dopants exhibit gas sensing properties at rather high temperature (>300oC). Then, a interesting challenges are to find the materials gas sensing at lower temperature. Rare earth elements are very important in modern industries such as photocatalyst, energy batteries, photoluminacents. They are excellent dopants into superconductors because electronic transitions of 4f-5d and 4f-4f vary from element to elements. Generally, rare earth elements used in catalysts in form of oxide or salts for enhancing the stability, selectivity and improving catalytic properties . 3 The reviews showed that La-ZnO materials possess various morphologies as well as physical properties. Based the conditions of Laboratory of Hue College of Sciences, we have motivated hydrothermal processes to synthesis the La-ZnO with various morphologies. The synthesized conditions influence on the morphologies as well as the surface properties will be discussed. 1.3. APPLICATION OF ZnO AND La-ZnO MATERIALS INTO PHOTOCATALYTIC DEGRADATION OF DYE Ultrasound being different from other energy sources such as heat, light or ion radiation become popular in the degradation of organic stuffs with frequencies of 20-1000 kHz. Environmental sonochemistry has been developed remarkably based on ultrasound application. In principle, most dyes could be decoloured and mineralized by ultrasound but the rates of decomposition might be too slow to practice. So many researches devote to improve this process. One of popular processes is the addition of catalysts to solutions under ultrasonic radiation. Some semiconductors such as TiO2 or ZnO, Au/TiO2, MnO2, with UV have been reported. The present of catalysts enhances the formation of ultrasonic cativation resulted in OH. Recently, in order to increase OH sources, one adds H2O2 together with ultrasonic radiation and catalysts, then these is called ultrasonically assisted catalytic hydroperoxide oxidation process) (denoted as UAHC). Apostolos et al used UAHC to oxidize phenol over Al-Fe/clay. The results of kinetic study showed that ultrasound increase the intradiffusion. The diffusion coefficient increases the second orders compared with the process without ultrasound. A kinetic comparison of phenol oxidation by UAHC with ReI3 catalyst with catalytic process without ultrasound has been reported. The comparison showed that the activation energy of this process around 13 kJ.mol-1 is equal one fourth of process without ultrasonic (57 kJ.mol-1) indicating that ultrasound enhances significantly the phenol oxidation. Most of cases, photocatalysts are semiconductors. When the light shines to semiconductors, the valance electrons can be moved to conductivity bands to form photo- induced electron-hole pairs. Materials exhibited the more photocatalytic ability as recombination of photo-induced electron-hole pairs takes place slowly. The aims of photocatalytic reactions is the formation of reactions between photo-induced electrons with oxidants to form products or photo-induced holes with reductants to form products. Due to the formation of photo-induced electron-hole pairs, the reduction-oxidation reaction takes 4 place at the surface of semiconductor. In oxidation reaction, the holes react with water to form OH free radicals. Some papers reported that zinc oxide exhibits photocatalytic effect higher than that of titanium oxide under some conditions. ZnO based catalysts have been attracted by many researchers because of uniquite properties such as high chemistry stability, nontoxic and low cost. According to my best knowledge, few papers report the organic stuff degradation using La-ZnO as photocatalyst materials. In the present dissertation, I will study the kinetics of green methyl degradation using zinc oxide catalyst with ultrasound assistance and the green methyl degradation using ZnO and La-ZnO as photocatalysts. 1.4. La – ZnO as gas sensing materials 1.4.1. Basic theory Materials that change their properties depending on the ambient gas can be utilized as gas sensing materials. Usually changes in the electrical conductance in response to environmental gases are monitored. When a molecule adsorbs at the surface electrons can be transferred to this molecule if the lowest lying unoccupied molecular orbitals of the adsorbate complex lie below the Fermi level (acceptor levels) of the solid and vice versa electrons are donated to the solid if the highest occupied orbitals lie above the Fermi-level of the solid (donor levels). Thus molecular adsorption may result in a net charge at the surface causing an electric field. This electrostatic field causes a bending of the energy bands in the solid. A negative surface charge bends the bands upward, i.e. pushes the Fermi level into the band gap of the solid, effectively reducing the charge carrier concentration and resulting in an electron depletion zone. Depleting electrons causes a positive space charge region that compensates for the negative surface charge. As a consequence of the charge carrier depletion zone in the presence of surface charges the sheet conductivity r of the surface is altered. This change in conductivity is commonly used as the signal in gas sensing devices. 1.4.3. Current review of hydrogen, ammoniac and ethanol sensing materials The hydrogen detection at low concentration is the critical requirement of a device for detecting hydrogen. Although the detection and concentration measurement of hydrogen has a history of over 100 years beginning with hydrogen measurements at filling stations for airships. However, there is a continued need for faster, more accurate and more selective detection of hydrogen gas in various areas of industry for monitoring and controlling hydrogen concentration. 5 Alternative hydrogen detection methods employ instruments such as gas chromatographs, mass spectrometers or specific ionization gas pressure sensors. Gas chromatographs use columns to separate the individual gas components in a mixture and different types of detector to identify each component. Mass spectrometers identify gas molecules based on their characteristic deflections from a magnetic field. Traditionally, these instruments are relatively large, expensive, high maintenance and slow in terms of their sampling and reaction times. I don’t review in this dissertation. ZnO is one of the most gas sensing materials, especially hydrogen. The gas sensitivity of zinc bulk is not enough high to apply in practice. The gas sensing properties of zinc oxide depends critically on its morphologies. ZnO with 0 dimension has high gas sensibility but is easy to agglomerate to form larger particles. In order to overcome these disadvantages, ZnO with hierarchical structure are favoured. Controlling and monitoring ethanol is important in some fields, such as testing alcohol levels of drivers, monitoring chemical synthesis, etc. SnO2, ZnO, Fe2O3, and other oxides are being investigated widely because of their high sensitivity to ethanol. However, many works needs to be done to improve the sensitivity of those materials to ethanol and further to explore new ethanol-sensitive materials. As the present research results on all kinds of semiconductor metal oxides have shown, ZnO may be one of the most hopeful candidates due to its mature fabrication technology, which can produce all kinds of ZnO nanostructures, such as nanowires, nanorods, nanobelts, nanoribbons, etc. Ammonia is produced and utilized extensively in many chemical industries, fertilizer factories, refrigeration systems, food processing, medical diagnosis, fire power plants, etc. A leak in the system can result the health hazards. Ammonia is harmful and toxic in nature. The exposure of ammonia causes chronic lung disease, irritating and even burning the respiratory track, etc. Therefore, all industries working on and for ammonia should have an alarm system detecting and warning for dangerous ammonia concentration levels. Detection of low concentration of ammonia is not only important from the points discussed above, but also it is very important from the view of chemical pollution in the production of silicon devices in clean rooms. It is therefore necessary to monitor ammonia gas and to develop the ammonia gas sensors. Efforts are made to develop the ZnO-based gas sensors which should detect ammonia at low temperature. In this dissertation we will focus on gas sensing activities of H2, C2H5OH and NH3 for ZnO and La-ZnO nimrods 6 1.5. ELECTRODE MODIFIED WITH NANO ZINC OXIDE Uric acid(2,4,6-trihydroxypurine) is an end product from urine derivatives in human metabolism. Uric acid undergoes no further metabolism in humans and is excreted by kidneys and intestinal tract. Serum concentration of uric acid is controlled by the balance of production and excretion. The normal level of uric acid in serum is between 240 and 520 mM and1.4 and 4.4Mm in urinary excretion. Abnormal uric acid level in biological fluids is a marker of several disorders such as gout, renal disease and Lesch–Nyhansyn- drome. Excessive amounts of uric acid in serum is known as hyper-uricemia and this has been found to be associated with hypertension, metabolics yndrome [11] and cardiovascular disease. Consequently, fast and reliable determination of uric acid in biological fluids is routinely required for diagnosis and treatment. The first method developed for uric acid analysis was introduced by Offer in 1894. This method is based on the chemical oxidation of uric acid to allantoin, which reduces phosphotungstic acid to a tungsten blue chromophoric compound. However, this method suffers from several problems especially the problem of interferences due to other species capable of producing the same reaction. A more selective approach is theuseofuricase enzyme (UOX),which catalyzes the oxidation of uric acid to allantoin, H2O2 and CO2. Alternative methods for uric acid determination have appeared since then and various techniques such as chemiluminescence, fluorescence, spectrophotometry, HPLC–mass spectrometry, ion chromatography, high- performance liquid chromatography (HPLC)/isotope dilution mass spectrometry (ID-MS), capillary electrophoresis– amperometry, capillary electrophoresis with chemiluminescence detection, colorimetry and enzymatic test-kits have been reported. However, these methods are usually laborious, expensive, time-consuming and/or complex to perform. Therefore, there is great interest in developing inexpensive, simple and rapid methods for uric acid determination as a routine analysis. Among these techniques, the enzymatic-colorimetric method using Uri case and peroxidase together is widely used in routine analysis due to its simplicity, sensitivity and specificity. Although test kits of this method are commercially available, the cost of uricase and peroxidase used in the kit is a factor that limits widespread use of the method for large number of samples. In the present dissertation, we will study on the making nano zinc oxide modified electrodes and its application to analyze uric acid by stripping voltametry anodes. 7 Chapter 2 AIMS, CONTENTS AND EXPERIMETAL METHOD 2.1. AIMS Synthesis of nano/micro zinc oxide with various morphologies and their application 2.2. CONTENTS 2.2.1. Study on the synthesis of ZnO using zinc acetate-ethanol and hexamethylenetetramine (HM) 2.2.2. Study on the synthesis of ZnO using zinc acetate-ethanol and KOH/NaOH 2.2.3. Study on the synthesis of La-ZnO 2.2.4. Study on the green methyl degradation by hydroperoxide-ZnO catalytic oxidation process with ultrasonic assistance 2.2.5. Photocatalytic degradation of green methyl using La-ZnO 2.2.6. Study on La-ZnO as gas sensing materials 2.2.7. Electroanalysis of uric acid using nano ZnO modified electrodes. 2.3. ANALATICAL TECHIQUES OF PHYSICALCHEMISTRY 2.3.1. X-ray diffraction 2.3.2. Scanning electron microscope 2.3.3. Transmission Electron Microscopy 2.3.4. Energy Dispersive X – ray Spectrometry 2.3.5. Raman spectroscopy 2.3.6. UV-Visible Diffuse Reflectance Spectroscopy 2.3.7. UV-Vis Absorption Spectroscopy 2.3.8. Nitrogen adsorption/desorption isotherms 2.3.10. Temperature-Programmed Desorption). 2.3.11. High Performance Liquid Chromatography 2.3.12. Electroanalysis 2.3.13. Statistics 2.4. Experimental 2.4.1. Chemicals 2.4.2. Experimental methods 2.4.2.1. Synthesis of ZnO using zinc acetate-ethanol- hexamethylenetetramine 2.4.2.2. Synthesis of La doped ZnO 8 2.4.2.3. Synthesis of ZnO using zinc acetate-ethanol -KOH/NaOH 2.4.2.4. Determination of catalytic activities 2.4.2.5. Measurement of chemical oxygen demand 2.4.2.6. Measurement of isoelectric point 2.4.2.7. Measurement of gas sensing 2.4.2.8. Modification GC by nano ZnO 9 Chapter 3 RESULTS AND DISSCUSSION 3.1. SYNTHESIS WITH CONTROLLED MORPHOLOGIES OF MICRO/NANO ZnO FROM DISK TO ROD FORM USING ZINCK ACETATE-ETHANOL- HEXAMETHYLENETETRAMINE In order to obtain desired physical chemistry properties of ZnO, its controlled morphologies are favoured. The processes to control the morphologies have developed quickly recently. Most proposed processes have conducted in high temperature or using surfactants such as polyvinylpyrrolidone (PVP), poly (acrylic - acid) (PAA). In the present part, we will present the results of synthesis with controlled morphologies by using friendly solvents to provide ZnO with various morphologies. ZnO synthesized in ethanol solvent provided ordered hexagonal disks while that synthesized in alcohols such as ethanol, propanol and buthanol tend to produce hexagonal disks in different extent. The effect of solvent on ZnO morphologies is different due to the different nature of boiling temperature, chemistry, polarization of solvents. In the scope of dissertation, we only focus on the solvent system of ethanol-water Fig 3.2. TEM images with various resolution of ZnO prepared at ratio of 75 : 25 ethanol - water Fig 3.1. TEM images with various resolution of ZnO prepared at ratio of 90 : 1 ethanol - water 10 XRD analysis showed the ratio of I(101)/I(002) increases with an increase in the ratio of ethanol/water. I(101)/I(002) = 2,405 for Theo JCPDS No. 01 - 089 - 1397. The sample with ratio of 75 : 25(ethanol – water) had the ratio of 0,965 but the water increase in (25 : 75) the the ratio increases to t 3,314 indicating the structure of ZnO changes while solvent ratio changes. The morphologies of the obtained samples were observed by TEM as shown in Fig. 3.1-3.5 As discussed above, the morphologies of ZnO depend significantly on the ratio of water in the mixture of water and ethanol. When the low water ratio, the sample with 90:10 Fig 3.3. TEM images with various resolution of ZnO prepared at ratio of 50 : 50 ethanol - water Fig 3.4. TEM images with various resolution of ZnO prepared at ratio of 25 : 75 ethanol - water Fig 3.5. TEM images with various resolution of ZnO prepared at ratio of 0 : 100 ethanol - water 11 ethanol:water exhibited the live buoy like shape, and hexagonal disk with the defects in center. With the higher water ratio, the sample with 75:25 showed only hexagonal disks. The sample with 50:50 ethanol:water consists of hexagonal disks and rods. Further increasing the water ratio, the only rod shapes were obtained. It is concluded that when the solvent polarization increases, the morphologies of ZnO tent to decrease in dimension e.g. Live buoy like shape (multiple dimensions)  hexagonal disks (6D)  rods (2) The question rises is why the peak of (0002) exhibits high intensity in hexagonal structure or the ratio of I(101)/I(002) in hexagonal disk is lower than those of JCPDS with wurtzite structure or rode ZnO. Fig. 3.6 represents hexagonal structure of ZnO. The ratio of c/a for ideal packed hexagonal structure is 1,663. The plan of (0002) plane go throught the centre of c-axis and perpercular to [0001] direction. In hexagonal disk the c-axis tents to is shrink so the atom density increasing significantly in (0002) plane the reason why the diffraction at (0002) is higher in compared with other structure. Then, the ratio of I(101)/I(002) could be used as indicator to evaluate the hexagonal disk extent of ZnO crystals When this ratio is lower 2,405 (the ratio of JCPDS), ZnO tent to form live-buoy-like shape or hexagonal disk. The cell parameters were calculated by the least-squared method using SPSS-19. The sample with ethanol-water (75:25) exhibits the expand of cell volume in compared with other sample. It is noted that, c-parameter tents to decrease as the development of c-direction increases. When [0001] direction develops for forming the rod shape the unit cell was less pushed. The ratios of c/a for all obtained sample are less than that of ideal structure of 1.666 b a c 1010   1100   0110   1010   1100   0110   (a) c a c y x z (b) Fig. 3.6. a. Direction index of plane for hexagonal structure; b. Structure of hexagonal crystal 12 due to control impurities or defects during synthesized processes. However, these values are closed to that of JCPDS – 01 – 089 - 1397 (1.603). 3.2. SYNTHESIS OF ZnO USING ZINC ACETATE – ETHANOL – NAOH/KOH 3.2.1. Synthesis of nano rod ZnO by zinc acetate-ethanol-NaOH Fig. 3.7 shows images of ZnO synthesized by different NaOH concentration. The results showed ethanol effected lightly on the morphologies of ZnO. The NA8 was used as gas sensing sample for following experiments. 3.2.2. Synthesis of ZnO spherical particles in zinc aceate – KOH – ethanol-water system In this case, morphologies tent to form spherical particles. Effect of ethanol on morphologies was investigated by varying ethanol amount of 100 mL/1,122 gam KOH to 350 mL/1,122 KOH. As the KOH amount is low (0,2 gam KOH/300 mL ethanol) the spherical particles of around 60 nm were formed6. KOH amount was increased (0,5 gam/300 mL). The size of particles reduced remarkably however, further increasing KOH provided significantly agglomerates. có sự xuất hiện các kết tụ agglomerates with some hundrous nanometer in size were formed as KOH amount around 1,5 - 2 gam/300 mL. Nano rode ZnO NA8 possessed the diffraction of (002) stronger than that of spherical particles KO3 indicating the uu tien developing c-axis direction. The porous properties was studied by nitrogen adsorption/desorption isotherms. Both was characteristic of V type. Hình 3.7. TEM images of ZnO with various ethanol composition NA5 NA6 NA7 NA8 KO5 KO6 KO7 KO8 Hình 3.8. Ảnh SEM của ZnO với lượng KOH khác nhau 13 However, the specific surface area of NA8 calculated by BET around 27,65 m2/g was significantly higher than that of KO3 (12,2 m2/g) indicating the nano rode ZnO with hierarchical structure exhibits a high order assemble to minimize “scarifying” surface area. Whereas, ZnO with spherical particles is easy to agglomerate. The role of KOH and NaOH effecting onto the rod or spherical morphologies is not clear. We thought that hydroxyl ion plays important role in controlling crystal surface through different direction to form Zn(OH)n direction. The different adsorption interaction of K+ and Na+ on crystal surface resulted in NaOH being favored in [002] direction. Whereas NaOH is favored in spherical particles. 3.3. STUDY ON SYNTHESIS OF La-ZnO There are many way to dope rare metals into semiconductors in which hydrothermal process is one of popular processes because its procedure is simple and easy to control the morphologies of materials by adjusting the parameters of process. In this study, we will introduce La into ZnO by hydrothermal process (denoted as La-ZnO). The synthesis of nano rod ZnO was mentioned in the part of 3.1.1 and the sample of NA8 was used to study later. The factors including gel concentration, hydrothermal temperature, NaOH concentration, La concentration effecting into the morphologies, size as well as the crystalline will discussed. 3.3.1. The effect of gel concentration The gel composition effected significantly on the morphologies of obtained materials. It is clear that when gel concentration was low the morphology changed from rod to nano particles. All obtained ZnO possessed wurtzite structure. Diffraction peaks tents to shift to larger angle corresponding to reduce cell volume, particularly, the parameter of cell shrinking as gel concentration increased. The intensity of diffraction increases with increase in hydrothermal temperature indicating the increase in crystallinity 0,01M0,02M Fig. 3.9. SEM observation of samples synthesized by different gel concentration 0,07M 14 As molar ratio of La/Zn is 0.047, NaOH concentration 0.414 M, gel concentration 0.07 and hydrothermal temperature 180oC the obtained La-ZnO consist of nanoparticles around 20-30 nm and nano-rods with 20-30 nm. The nanoparticle fraction decreases and size of nano-rods increase as hydrothermal temperature increases from 100oC to 200oC. However, the temperature is beyond 200oC, irregular shapes consisting of rods and fine particles appear. The hydrothermal temperature of 150oC is favored for forming rod shape The synthesized condition of LZ1 was fixed and NaOH concentration varied from 0.138 to 0.829 M. EDX analysis showed only two elements of La and Zn is in sample. The molar ratio of La/Zn presented in Table 3.10. NaOH concentration effects slightly on the molar ratio of La/Zn. The molar ratio of obtained samples are very closed to the initial molar ratio (0.047). XRD analysis of samples synthesized in various NaOH concentration showed that obtained ZnO possessed wurtzite structure with JCPDS No. 00 - 005 – 0664. The ration of I(101)/I(002) decreases with an increase in NaOH concentration indicating that I(101)/I(002) is related to the morphologies as the smaller I(101)/I(002) is morphologies tent to spherical shape whereas the larger I(101)/I(002) is morphologies tent to spherical rod. Fixing the synthesized condition of LZ1, the molar ratio of La/Zn varied from 0 to 0.09. The molar ratios of obtained samples are closed to initial one indicating that La is completely introduced into ZnO. The ratio of La/Zn effects on size of rods in which diameter tents to increase from 30 -80 nm. When La increases up to 0.03 its morphology seems to be unchangeable but further increase in La leads to form irregular shapes (see Fig. 3.10) Fig 3.10. SEM images of La-ZnO with various molar ratio of La/ZnO 0,01 0,090,07 0,050,03 0,00 15 The crystallite sizes calculated by Debye – Scherrer equation also showed in 3.12. It was noted that when lathanum is dopped in ZnO the diameters of rod shape increase significantly incompared with pure ZnO. Table 3.1. Some physical chemistry properties of La - ZnO ZnO is a n-type semiconductor with band energy from 3.1-3.3 eV. The band gap energy depends on crystal defects, morphologies, size etc…The UV-Vis spectra of La-ZnO with various molar La/Zn and plot of (E)2 vs. photon energy shows in Fig. 3.32. The results shows a blue shift with the increase in lanthanum concentration. This could be explained by Burstein-Moss effect in which the band gap energy of La-ZnO was expanded in comparison with that of pure ZnO. The fact that band gap energy of 5.5 eV is significantly higher than ZnO around 3.1-3.2 eV could be explained for a band gap energy increase of La-ZnO. In addition, the extension of band gap energy may be due to quantum confinement. When the molar ratio of La/Zn increases up to 0.03 the band gap energy tends to decrease due to the crystal size increase. The porous properties of La-ZnO were studied by nitrogen adsorption/desorption isotherms. There are a surface area decrease from pure ZnO (27.65 m2/g) to La-ZnO (12.2-12.5 m2/g) Acid sites of ZnO and La-ZnO were studied by TPD-NH3. Acid sites were calculated NH3 adsorption at different temperature. Both ZnO and La-ZnO exhibited two characteristic peaks for medium acid site at 300-400oC and strong acid site at 400-550oC. The NH3 adsorption amount at various temperatures shows in Table 3.2. Table 3.2. Amount f acid site at different temperatures measured by NH3-TPD LZ1 LZ14 LZ15 Temperature (oC) NH3 adsorption volume (cm3/g) Temperature (oC) NH3 adsorption volume (cm3/g) Temperature (oC) NH3 adsorption volume (cm3/g) Cell parameters Notation Wide size of wires (nm) Crystallinity size (nm) Molar ratio La/Zn (EDX) a (nm) c (nm) V (nm3) Eg (eV) LZ15 40,0 36,0 0,000 3,245 5,196 47,386 3,18 LZ11 36,0 31,9 0,010 3,248 5,198 47,492 3,23 LZ12 63,0 60,5 0,031 3,247 5,201 47,494 3,26 LZ1 90,0 88,9 0,047 3,247 5,205 47,540 3,21 LZ13 128,0 127,6 0,075 3,247 5,200 47,481 3,22 LZ14 130,0 129,5 0,093 3,247 5,200 47,488 3,21 16 199.02 0.40 426.30 0.21 379.44 1.16 397.54 4.23 232.97 0.97 485.85 0.25 436.80 0.32 546.00 0.17 548.59 1.34 546.48 0.13 384.69 2.94 522.77 2.09 - - - - 471.05 3.51 Total amount of acid sites decreases significantly as the lanthanum concentration increases. For pure ZnO, total NH3 adsorption amount is 8,37 cm3/g while La-ZnO (LZ1) and La-ZnO (LZ2) are 5,09 and 4,3 cm3/g, respectively. Pure ZnO has strong acid site amount larger than La-ZnO (LZ1 and LZ14). As La was introduced into ZnO, weak acid sites tend to increase in comparison with pure ZnO. The isoelectric points of LZ1 and LZ15 are around 7. 3.4. CATALYTIC ACTIVITIES OF ZnO AND La-ZnO Kinetic study is one of basic study in term of theory to apply to design the reactors and predict the reaction mechanisms. There are several method to conduct kinetic study. In this dissertation, we used the initial rate method to investigate kinetics of advanced oxidation reaction as well as photocatalytic reaction of green methyl degradation. 3.4.1. Decoloured kinetics of green methyl over ZnO/H2O2 catalyst with ultrasonic assistance The kinetics of the green methyl degradation by ZnO with nano spherical particle and H2O2 with ultrasonic assistance was performed. The advanced oxidation using ZnO/H2O2 with ultrasonic assistance exhibited efficiently the decoloured process and mineralized degradation of MB. The initial rate is favoured for kinetic study. The kinetic equation in this case is 31.0 22 ]].[.[ OHMBkr  (mol.L-1.s-1) at 21 - 26oC, and k = 0,0874 [s-1.L0.31.mol-0.31] for ri calculated at 20 s and 0,0438 [s-1.L0.31.mol-0.31] for ri calculated at 40 s. 3.4.2. MB degradation by photocatalytic La-ZnO The results shows that rate constant depended on how to calculate initial rate and rate constant tends to decrease and adsorption equilibrium constant increases with the increase in the time to calculate initial rate. The ratio of kT:Ka characteristic of photocatalytic reaction and adsorption is very large some thousand times indicating the adsorption could be ignored and decoloured process was mainly determined by photocatalytic reaction process. The recycle of La-ZnO for three times exhibits the same convections. The structure and composition of catalyst after three times of reuse seems to be unchangeable indicating the La-ZnO is stable. COD of initial solution is 60.3 mg/L but that is only 5.2 mg/L after 120 17 minutes suggesting that the oxidation reaction occurred deeply and the final product is carbon dioxide as schema as follows: 3.5. GAS SENSING PERFORMANCE OF ZnO AND La-ZnO In the present study, we will study on gas sensing performance of ZnO and La-ZnO synthesized with various molar ratio of La/Zn e.g. 0.00 (LZ15) 0.047 (LZ1); 0,07 (LZ13) and 0.09 (LZ14) for H2, C2H5OH and NH3. 3.5.1. Hydrogen gas sensing performance The response increases as lanthanum is introduced into ZnO, but decreases significantly as large lanthanum amount is introduced into ZnO. The response tends to increase as the temperature increases and decrease with further temperature increase. For example, at 250 ppm hydrogen, LZ15 possesses S = 2,4 ở 300 oC, S = 3,8 ở 400 oC và S = 2,5 ở 450 oC. While the response of LZ1 increases from 300oC to 450oC. This result was different from the results reported by Malyshev and Pislyakov. The response tends to increase with the increase in hydrogen concentration. Table 3.3. The hydrogen sensing response of ZnO and La - ZnO Temperature (oC) 300 400 450 Concentration (ppm) Concentration (ppm) Concentration (ppm) Notion 25 50 100 250 25 50 100 250 25 50 100 250 LZ15 1,4 1,6 2,0 2,4 1,5 1,7 2,6 3,8 1,1 1,3 1,8 2,5 LZ1 1,5 1,6 2,0 2,2 1,7 2,4 5,4 8,2 1,7 3,0 9,5 9,9 LZ13 1,1 1,4 1,4 1,8 1 1 1,3 2,0 1 1 1 1 LZ14 1 1 1 1 1 1 1 1 1 1 1 1 The hydrogen sensing response is higher n comparison with previous reports. The response of nano rod ZnO in the present study is higher than nano particle ZnO. However, nano rode ZnO dispersed on annotate Al2O3 exhibites very high hydrogen sensing performance. 3.5.2. Ethanol sensing performance Ethanol sensing performance at several ethanol concentration and temperature for ZnO and La-ZnO is shown in Table 3.4. MB Aromatic compounds degradation of aromatic rings CO2 + H O 18 Table 3.4. Ethanol sensing response of ZnO and La - ZnO The ethanol response increases remarkably as temperature increases from 300 to 400oC, then decreases as temperature increase further. The linear regression of log(S-1) with logC with =0,05 shows that all linear models are stastiscally significant. In the confident interval of 95% the value of a and b are different from zero indicating that a and a have physical significance. For LZ15 (ZnO), b is equal 0,75 at low temperature of 300oC but the temperature increases the value of b is closed to unity. Then, a transformation from O2- adsorption to O- adsorption mechanism occurs with a temperature increase. This mechanism could be expressed as follows: O2  O2 (adsorption) (3.28) O2 (adsorption)  2O (adsorption) (3.29) O + 2e  O2- at low temperature (3.30) O + e  O- at high temperature (3.31) The adsorption process (3.28) and oxidation reaction (3.29), (3.30), (3.31), (3.32) are endothermic process. This explained the reason why the response increases with the increase in temperature. The adsorption rate increases with an increase in temperature because the process of (3.28) is chemistry adsorption. However, the temperature increases to certain extent then desorption occurs then adsorption of (3.28) reduces. In the case of ZnO and La- ZnO, oxygen exist mainly in O- species, the reaction of (3.31) is dominant. Temperature (oC) 300 350 400 450 Con. (ppm) Con. (ppm) Con. (ppm) Con. (ppm) Noti on 10 25 50 100 10 25 50 100 10 25 50 100 10 25 50 100 LZ15 1,9 3,6 4,9 6,2 3,1 6,1 8,8 15,1 3,9 14,5 27,5 42,4 2,4 6,1 11,2 13,5 LZ1 1,9 4,0 6,3 9,2 2,8 7,9 15,4 23,2 2,8 8,5 17,9 31,2 1,5 3,4 5,9 12,0 LZ13 1,1 1,2 1,6 1,9 1,3 1,9 3,0 3,7 1,6 2,8 4,8 6,3 1,5 2,8 4,5 6,4 LZ14 1,1 1,2 1,3 1,5 1,2 1,5 1,8 2,3 1,2 1,8 2,5 3,7 1,2 1,8 2,5 3,8 19 The comparison of ethanol sensing response of present study to previous reports shows that that of rode ZnO (1D) is higher than that of nano particle ZnO(0D). Rao reported that La or Pd-ZnO could provide gas sensor at low temperature of 210oC. Our device could not measure the such low temperature to compare. In general, the responses of the obtained ZnO and La-ZnO are rather higher than those in some reports. 3.5.3. Ammonia sensing performance The ammonia sensing responses at different ammonia concentration and temperature are shown in table 3.5. Table 3.5. The ammonia sensing response of ZnO and La - Zn Temperature (oC) 300 400 450 Con. (ppm) Con. (ppm) Con. (ppm) Notion 10 25 50 100 10 25 50 100 10 25 50 100 LZ15 1,2 1,3 1,4 1,6 1,4 2,0 2,7 4,0 1,3 1,9 2,7 4,2 LZ1 1,1 1,3 1,6 1,9 1,1 1,4 1,9 2,7 1 1 1,1 1,3 LZ13 - - - - - - - - - - - - LZ14 - - - - - - - - - - - - The tendency of temperature and ammonia concentration is similar to H2 and ethanol. The response increase with an increase in temperature. However, ammonia sensing properties of ZnO or La-ZnO are weaker than hydrogen or ethanol in the same concentration and temperature. The order is as follows: C2H5OH > H2 > NH3. As mentioned above, the study of hydrogen, ethanol or ammonia sensing performance for ZnO and La-ZnO is few, so there are no available data for comparison. But in comparison to other metal doped ZnO or SnO2, the responses of obtained ZnO and La-ZnO is rather high, particularly ethanol and hydrogen. 3.6. MODIFICATION OF GLASSY CARBON USING NANO ZINC OXIDE Differential pulse anodic stripping voltammetric method (DPASV) is one of electrode determination methods with high sensitivity, low limit of detection able to detect the trace of metals. However, the reports about organic species determination by DPASV is limited. The aim of this study is the development of modified electrode to detect uric acid (UA) in biological sample. Based on the references, two methods of DPASV and squared wave anodic stripping voltammetric method (SW-ASV) are used widely to determine UA. The experimental conditions of DPASV was fixed. ZnO with hexagonal disk in 3.1 was used in this study. 20 Some results of UA determination by DPASV with modified glassy carbon electrode (GC) using ZnO were obtained. - The modified GC by GC/P(BCP)/ZnO provide a highest background signal compared with that by pure GC and GC/ZnO Procedure of electrode modification: + electrode modified with 4 layer with the thickness of 2 µL in the suspension of ZnO + DMF + BCP concentration is 5.10-4 M at CV scanning to form polymer + CV scanning number is 50 cycles as poly(BCP) is formed. - Investigated the pH effect on dilute signals: + pH is 5.5 + The number exchangeable proton and electron are equal as 2. - Investigated experimental for DP-ASV to detect UA: + Deposition potential, Edep: -100 mV + Pulse Amplitude, ΔE : 80 mV; + The potential scan rate is 80 mV/s. + Simultaneous determined of the transfer coefficient () and the rate constant (ks) of the electrochemical reaction are 0.283 and 9.88 s–1. - Assessmented of the satisfactory of method: + The repeatability at 3 concentrations 10 µM, 80 µM and 150 µM, there are RSD (%) from 0.60 to 2.6 (%) with 9 measurement (n = 9). + Linear range from 0 đến 160 µM with sensity of 0.054 µA/µM. + Limit of detection is 5.4 µM and Limit of quality is 18.0 µM for UA. - The practical application of the fabricated nano-ZnO/P(BCP)/GCE has been examined by measuring the concentrations of UA in urine and serum samples: + Assessmented of repeatability of the concentration UA in real samples. + Assessmented of accuracy base on spiked sample. 21 CONCLUTIONS In the present dissertation we studied on the synthesis of ZnO and La doped ZnO nanostructures, their catalytic and gas sensing activities. 1. The results showed that nano/micro zinc oxides were synthesis by hydrothermal process using three component system of zinc acetate-alcohol-water with hexamethylentetramine at 90oC. Morphology as well as crystallization depend significantly in organic solvent composition. As the water proportion in solvent (polarity increase) the crystalline of zinc oxide decreases and the their morphology tents to transfer from hexagonal structure (6-D) to cubic structure (4-D), finally rode structure (2-D). The morphologies of ZnO including nano rods and nano particles were also synthesized by using zinc acetate-NaOH and zinc acetate-KOH, respectively. 2. La-doped ZnO photo catalysts with different molar ratio of La/Zn were prepared by a hydrothermal method. The obtained La3+-doped ZnO nanorods were homogenous with an average diameter of 25–40 nm. The doping La3+ into ZnO reduces the specific surface area. The XRD patterns of the La-doped ZnO calcined at 773 K show only the characteristic peaks of wurtzite-type. The doping La3+ into ZnO increases the band gap energy, structure cells but reduces acidic sites. 3. The ultrasound-assisted catalytic zinc oxide wet peroxide oxidation was used as a means to degrade methyl blue (MB). The methyl blue oxidation was conducted at ambient temperature in various conditions: (a) ultrasound irradiation, alone, (b) H2O2, alone, (c) ZnO, alone, (d) combination of H2O2 and ultrasound, (e) combination of ZnO and ultrasound, (f). combination of H2O2, ZnO and ultrasound. The ultrasound irradiation enhances significantly hydro peroxide activating of catalytic ZnO. The oxidation reaction under ultrasound condition occurred statistically faster in comparison with the conditions without ultrasound. A kinetic study using initial rate method was performed. The results showed the MB degradation with H2O2 over ZnO with ultrasound has the first order to MB and 0.31 orders to H2O2. However, the value of rate constant is changeable and depends significantly on time point, which the initial rate is made. 4. The kinetics of decoloured reaction of methyl blue using the La-ZnO photo catalyst were investigated. Both ZnO and La-ZnO exhibit the photocatalytic activity in region ultra violet and visible light. The initial concentration method is capable for studying the kinetics of this reaction. The results showed that the decoloured reaction of methyl blue is followed the first ordered. The rate constants based on Langmuir Hinshelwood reaction vary and depend on the 22 calculated time. The ratio of KT:KL being characteristic of reaction and adsorption, respectively is very large up to some thousands indicating that the decolourization is determined by photocatalyst reaction with the ignore of adsorption. 5. The ethanol-sensing properties of La doped ZnO with various mol ratios of La/Zn were tested. The addition of an appropriate amount of La results in an enhancement of the ethanol sensitivity at low temperature less than 350oC. The mechanism analysis of sensor revealed that the oxygen species on the surface was O- for La-ZnO while oxygen species on the space tends to transfer from O2- to O- form as temperature increases. The response S (= Ra/Rg) of single zinc oxide nanorod sensor reached 6.2 and 9.2 to 100 ppm ethanol at 300oC, which was rather high compared with that reported in literature, demonstrating the potential for developing stable and sensitive gas sensors. The gas sensitivity of ZnO and La doped ZnO, a semiconductor metal oxide, to hydrogen in air and to NH3 in air is presented. The addition of an appropriate amount of La results in an enhancement of the H2 sensitivity while this seems to reduce NH3 sensitivity due to reducing acid sites on the surface of La-ZnO in comparison with single ZnO. 6. Electrochemical sensors of ZnO poly(bromocresol purple) modified glassy carbon electrode (GC/poly(BCP)/nano-ZnO) has been developed for the determination of uric acid. Compared with a glassy carbon and ZnO-glassy carbon electrode the GC/poly(BCP)/nano- ZnO poly(BCP) film exhibited the highest background signal. Under the optimized conditions, the current increased linearly with the concentration of uric acid in the range of 0-160 mm with the detection limit of 5,4 µM in pH=5.5. The repeatability of GC/poly(BCP)/nano-ZnO for the uric acid determination was conducted at three concentrations 10 µM, 80 µM and 150 µM with RSD (%) corresponding 0,60-2,6 (%). The proposed method has been successfully applied to the determination of acid uric in urine and serum with satisfactory. 23 Lists of articles related to the dissertation 1. Võ Triều Khải, Trần Thái Hòa, Nguyễn Văn Ly, Đinh Quang Khiếu (2012), “Ảnh hưởng của dung môi hữu cơ đến hình thái vật liệu nano/micro ZnO”, Tạp chí Khoa học và công nghệ, Tập 50 (số 3B), Tr. 61 – 67. 2. Vo Trieu Khai, Mai Thi Thanh, Nguyen Hai Phong, Tran Thai Hoa, Dinh Quang Khieu (2013), “A kinetic study of ultrasound-assisted catalytic wet peroxide oxidation of methyl blue”, Tạp chí Hóa học, Tập 51 (Số 2AB), Tr. 317 – 321. 3. Võ Triều Khải, Trần Xuân Mậu, Nguyễn Hải Phong, Trần Thái Hoà, Đinh Quang Khiếu (2014), “Tổng hợp và đặc trưng ZnO, La-ZnO dạng thanh bằng phương pháp thủy nhiệt”, Tạp chí Xúc tác và hấp phụ. T3, No1, tr. 27-34. 4. Võ Triều Khải, Nguyễn Hải Phong, Trần Thái Hoà, Đinh Quang Khiếu (2014), “Nghiên cứu động học phản ứng mất màu phẩm nhuộm xanh methyl bằng xúc tác quang hóa La-ZnO”, Tạp chí Xúc tác và hấp phụ, T3, No1, tr. 35-40. 5. Võ Triều Khải, Trần Xuân Mậu, Nguyễn Hải Phong, Trần Thái Hoà, Đinh Quang Khiếu (2014), “Nghiên cứu hoạt tính cảm biến ethanol của ZnO và La-ZnO”, Tạp chí Xúc tác và hấp phụ, T3, No1, tr. 67-73. 6. Võ Triều Khải, Trần Xuân Mậu, Nguyễn Hải Phong, Trần Thái Hoà, Đinh Quang Khiếu (2014), “Nghiên cứu hoạt tính cảm biến khí H2 và NH3”, Tạp chí Xúc tác và hấp phụ, T3, No1, tr. 74-79.