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MINISTRY OF EDUCATION AND TRAINING VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY SCIENCE AND TECHNOLOGY ------- *** ------- NGUYEN THI LIEU STUDY ON FABRICATION NANO PLATINUM MODIFIED GLASSY CARBON ELECTRODE FOR APPLICATION TO ANALYZE LEAD, CADMIUM IN THE WATER ENVIRONMENT Major: Analytical chemistry Code: 9.44.01.18 SUMMARY OF CHEMICAL DOCTORAL THESIS HA NOI - 2020 This thesis is completed at Graduate University of Science and Technology - Vietnam Academy of Science and Technology Supervisor 1 : Assoc. Prof. Dr. Le Truong Giang Supervisor 2 : Assoc. Prof. Dr. Cao Van Hoang Thesis reviewer 1: …. Thesis reviewer 2: …. Thesis reviewer 3: ….. The thesis will be defended at the doctoral thesis committee at the Academy level, meeting at the Graduate University of Science and Technology - Vietnam Academy of Science and Technology at …..h, date ….., month ….., year 2020 The Thesis can be found in: - The library of Graduate University of Science and Technology - National Library of Viet Nam NEW CONTRIBUTIONS OF THE THESIS 1. Study on successfully fabricated to form a new electrode: nano flower-shaped platinum on glassy carbon electrode and evaluated the morphological, structure, composition, electrochemical properties, electrochemically active surface area of fabricated electrodes by modern analytical methods. 2. The optimal conditions were determined by the univariate method and the modeling method - experimental optimization for simultaneous determination of Cd2+ and Pb2+ on PtNFs/GC electrodes by differential pulse anodic stripping voltammetry. 3. The Cd2+ and Pb2+ analysis procedures have been developed and evaluated using the manufactured PtNFs/GC electrode with good repeatability, trueness, high accuracy, wide linear range, low detection limit. LIST OF PUBLISHED WORKS 1. Nguyễn Thị Liễu, Cao Văn Hoàng, Bùi Xuân Tỉnh, Lê Trường Giang, Nghiên cứu xác định lượng vết chì trong nước tự nhiên bằng phương pháp Von-Ampe hòa tan sử dụng điện cực màng platin/glassy cacbon, Tạp chí Hóa học, 2017, 55(3e12), 75-79. 2. Nguyễn Thị Liễu, Cao Văn Hoàng, Nguyễn Thị Thùy Linh, Bùi Văn Hào, Lê Trường Giang, Đặc tính Von-Ampe hòa tan của Pb(II) trên điện cực cacbon thủy tinh biến tính bởi platin nano dạng hạt, Tạp chí Phân tích Hóa, lý và sinh học, 2018, 23(4), 241-247. 3. Nguyễn Thị Liễu, Cao Văn Hoàng, Phạm Quốc Trung, Lê Trường Giang, Tối ưu hóa quá trình phân tích Pb(II) trên điện cực PtNFs/GC sử dụng phương pháp đáp ứng bề mặt, Tạp chí Phân tích Hóa, lý và sinh học, 2018, 23(4), 322-331. 4. Nguyen Thi Lieu, Cao Van Hoang, Pham Thi Hai Yen, Le Truong Giang, Manufacture pencil-lead electrode modified with platinum nanoparticles applicable to analyse of the trace concentration of Pb(II), Viet Nam Journal of Chemistry, 2018, 56(4e1), 124-129. 5. Thi Lieu Nguyen, Van Hoang Cao, Thi Dieu Cam Nguyen, Thi Thanh Binh Nguyen, Quoc Trung Pham, Truong Giang Le, Simultaneous effect of pH, deposition time, deposition potential, and step potential on the stripping peak current of lead, and cadmium by response surface methodology, Conference Proceedings, the 6th Analytica Vietnam Conference, 2019, 43 – 50. 6. Thi Lieu Nguyen, Van Hoang Cao, Thi Hai Yen Pham, Truong Giang Le, Fabrication of Nano Flower-shaped Platinum on Glassy Carbon Electrode as a Sensitive Sensor for Lead Electrochemical Analysis, Electroanalysis,2019, 31, 1-9, Doi: 10.1002/elan.201900021 7. Thi Lieu Nguyen, Van Hoang Cao, Thi Hai Yen Pham, Truong Giang Le, Platinum Nanoflower-Modified Electrode as a Sensitive Sensor for Simultaneous Detection of Lead and Cadmium at Trace Levels, Journal of Chemistry, Hindawi, 2019, Doi: 10.1155/2019/6235479. 8. Nguyen Thi Lieu, Cao Van Hoang, Pham Thi Tuyet Le, Le Truong Giang, Simultaneous determination of lead and cadmium in water samples using differential pulse anodic stripping voltammetry at platinum nanoflowers modified glassy electrode, Viet Nam Journal of Chemistry, 2019, 57(3), 379-383. Doi: 10.1002/vjch.201960028. 9. Lê Trường Giang, Nguyễn Thị Liễu, Đánh giá khả năng hoạt động điện hóa của các dạng tồn tại Cd, Pb trong các môi trường điện li sử dụng mô hình cânbằng hóa học, Tạp chí Hóa học, 2019, 57(6E1,2), 103-107. 10. Nguyen Thi Lieu, Pham Quoc Trung, Le Tran Thu Trang, Le Truong Giang, Simultaneous effect of pH, deposition time, deposition potential, and step potential on the stripping peak current of copper on platinum nanoflowers modified glassy carbon electrode (PtNFs/GCE) using response surface methodology, Viet Nam Journal of Chemistry, 2020, 58(3), 302-308. DOI: 10.1002/vjch.201900088. 1 INTRODUCTION 1. The urgency of the thesis Currently, in our country due to the development of industry, agriculture, daily life, transportation, etc., the environment has been seriously polluted, especially heavy metal pollution in the water environment. Heavy metals entering the human body outside the permissible level will cause serious health effects. When exposed to long-term intoxication, the metal accumulates in the body, combined with the cells, can cause cancer. Specifically, with some metals, lead is toxic to the central nervous system, peripheral nervous system, affects the enzyme system with hydrogen-containing activity groups, disturbs the hematopoietic part (bone marrow). Depending on the level of Pb poisoning, people can have abdominal pain, joint pain, kidney inflammation, high blood pressure, stroke, severe poisoning can cause death. Cadimi interferes with the activity of some enzymes, causes hypertension, lung cancer, perforation of the nasal septum, disturbs kidney function, destroys bone marrow and affects endocrine, blood, and heart. Therefore, to check and assess the level of lead, cadmium pollution of water sources, the analytical methods need to have high sensitivity and accuracy, capable of analyzing at trace content. Some methods of analyzing lead and cadmium include atomic absorption spectroscopy (AAS), inductively coupled plasma mass spectrometry (ICP-MS) molecular absorption spectroscopy (UV - Vis) methods. The above methods have high sensitivity and low detection limits. However, they have disadvantages such as large equipment investment, complex operating techniques; long analysis time, only perform laboratory analysis, which requires the equipment operator to be highly qualified. Meanwhile, the electrochemical analysis method, especially the stripping voltammetry of interest is a method with many advantages such as high sensitivity, short analysis time, simple operating 2 equipment, compact, capable of analyzing samples directly in the field. For the purpose of increasing the sensitivity, selectivity, lowering the detection limit ..., the electrodes used in the stripping voltammetry method tend to be denatured by nanomaterials. From the above reasons, the thesis topic “Study on fabrication nano Platinum modified glassy carbon electrode for application to analyze lead, cadmium in the water environment” was studied 2. Research objectives of the thesis - The thesis was conducted to research and develop a new type of electrode: glass charcoal electrodes modified by flower platinum nano (PtNFs/GC) and to evaluate the properties of fabricated electrodes: electrode structure, morphology, physical and chemical properties. - Studying and orienting applicability to detecting, quantifying separately and simultaneously cadmium, lead in aqueous environment by means of stripping voltammetry method with the desire that the nanostructures of the electrodes help increase the sensitivity of the analytical method. 3. The main research contents of the thesis - Study on fabrication nano Platinum modified glassy carbon electrode by chronoamperometry - Evaluate surface morphology of nano Platinum electrodes made by SEM, AFM - Evaluate physical and chemical properties of electrodes by methods: XRD, EDX, CV. - Develop the process of analyzing Cd and Pb separately and simultaneously on PtNFs /GC electrodes made by the ASV method. - Application of ASV method using PtNFs /GC electrodes to analyze Cd and Pb in some practical samples 4. The structure of the thesis 3 The thesis consists of 134 papes with 75 figures, 41 tables. The thesis includes the following sections: Introduction (3 pages); Chapter 1: Overview (26 papes); Chapter 2: Research methods and experiment (11 papes); Chapter 3: Results and discussion (75 papes); Conclusions (1 papes); Novel scientific contributions of the thesis; List of publication; References and appendices. CHAPTER 1: OVERVIEW Chapter 1 includes a general introduction of heavy metals and their harms, methods of determining trace amounts of Cd, Pb, the basis of the stripping voltammetry method, introducing some electrodes working in the method. The chapter also focuses on the presentation of Pt nanofabrication methods and the applications of Pt nanoparticles in special fields of analysis; a general overview of the research situation at home and abroad related to the topic. CHAPTER 2: RESEARCH METHOD AND EXPERIMENT 2.1. Chemistry CH3COONa, CH3COOH, H2PtCl6.6 H2O, H2SO4, K3[Fe(CN)6], NaOH, K4[Fe(CN)6], HNO3, K2HPO4, KH2PO4, H3PO4, H3BO3, KCl, HCl, CTAB, TritonX-100. Working solutions of metals: Pb2+, Cd2+, Zn2+, Cu2+, Fe3+... prepared from standard solution for AAS with a concentration of 1000 ppm. 2.2. Fabrication electrodes Glassy carbon (GC) was chosen as the ground electrode for platinum nano. First, the GC electrode (d = 3.0 mm) is treated by polishing the surface with ultrafine sandpaper, rinsing with distilled water in an ultrasonic bath. The electrodes are then electrically cleaned by applying a voltage of E = -1.0 V (with Ag / AgCl) in a 0.5 M H2SO4 acid solution for 200 s. Platinum nanoparticles were precipitated on the GC surface from the H2PtCl6 solution with a concentration of 1mM in the phase of 0.1 M H2SO4 by chronoamperometry method, using 3 electrodes 4 RE, CE, WE: GC, the fixed voltage is applied to the system for a certain period. Figure 2.2. Simulation of electrode fabrication process PtNFs/GC - Deposition potential (EPt) investigated: -0.5 V; -0.3 V; -0.2 V; 0.0 V; 0.2 V with tPt = 150 s with stirring of solution. - Deposition time (tPt) investigated 50 s; 100; 150 s; 200 s; 300 s with EPt = -0.2 V with stirring of solution. - The stirring and not stirring the solution: EPt = -0.2 V; tPt = 150 s 2.3. Characterizations Characterizations techniques: XRD, EDX, SEM, AFM 2.4. Application of Cd and Pb analysis on PtNFs/GC electrodes - The enrichment process by electrodeposition then dissolving sweep is carried out right in the solution containing Cd, Pb (different pulse anodic stripping voltammetry method - DPASV) - Optimize the analysis conditions including electrolytic solution, pH, preconcentration potential, accumulation time, pulse amplitude, step potential, electrode cleaning mode, interfering substances. 2.5. Experimental modeling studies the simultaneous effect of pH, tdep, Edep and Ustep on the stripping peak current (Ip) of Cd, Pb 2.6. Evaluate the reliability of the method and process empirical data 2.7. How to prepare the actual sample for the analysis process of Cd, Pb 5 CHAPTER 3: RESULTS AND DISCUSSION 3.1. Fabrication electrodes 3.1.1. Survey manufacturing conditions Figure 3.1. The cyclic voltammograms of a glassy carbon electrode in 0.1 M H2SO4 solution and in 0.1 M H2SO4 solution containing 10.0 mM H2PtCl6 solution (a); a glassy carbon electrode and Pt/GCE in 0.1 M H2SO4 solution (b), scanning rate of 0.1 V/s Figure 3.1a is the CV curve of the GC electrode in a 10 mM H 2PtCl6 solution + 0.1 M H2SO4 with three potential regions: the hydrogen region (from -0.2 to + 0.15 V) characterized by the presence of adsorbed hydrogen on the electrode surface that shows peaks corresponding to the adsorption/desorption of hydrogen with different energies, a broad oxidation peak for the Pt – oxide formation (commences at ca. 0.8 V and extends up to 1.2 V), and a single reduction peak at 0.5 V corresponding to the reduction of Pt(IV) to Pt(0) on the electrode surface. Our results were in agreement with other observational studies. From the results in Figure 3.1a shows that to create platinum particles on the GC by the static potential method, the applied voltage has a negative value more than 0.3 V. The effect of deposition potential (EPt) and time (tPt) to composition, properties of Pt layer will be shown in the following studies. 6 From figure 3.1b shows that when the granular layer of platinum is precipitated onto the GC to form a Pt/GC electrode, the obtained circular potential sweep has a characteristic line shape of the platinum material with the reduction puck at about 0.5 V. (compared to Ag/AgCl), this is entirely consistent with previous similar claims. This result proves that platinum has been put above GC. 3.1.2. Formation of PtNFs/GCE 3.1.2.1. Images of electrode surfaces and SEM images of Pt / GC; GC Images of the electrode surface before (GC) and after making platinum nanolayer (Pt/GC) are shown in Figure 3.2. Figure 3.2. GC electrode before (a) and after platinum nanoparticle creation (b) Figure 3.3. SEM image of GC electrode before (a) and after platinum nanoparticle creation (b)