Tóm tắt: Nghiên cứu sự hình thành tác nhân oxi hóa peroxymonocarbonate và ứng dụng xử lý một số hợp chất màu hữu cơ

Nghiên cứu sự hình thành tác nhân oxi hóa peroxymonocarbonate và ứng dụng xử lý một số hợp chất màu hữu cơ.Nghiên cứu sự hình thành tác nhân oxi hóa peroxymonocarbonate và ứng dụng xử lý một số hợp chất màu hữu cơ.Nghiên cứu sự hình thành tác nhân oxi hóa peroxymonocarbonate và ứng dụng xử lý một số hợp chất màu hữu cơ.Nghiên cứu sự hình thành tác nhân oxi hóa peroxymonocarbonate và ứng dụng xử lý một số hợp chất màu hữu cơ.Nghiên cứu sự hình thành tác nhân oxi hóa peroxymonocarbonate và ứng dụng xử lý một số hợp chất màu hữu cơ.Nghiên cứu sự hình thành tác nhân oxi hóa peroxymonocarbonate và ứng dụng xử lý một số hợp chất màu hữu cơ.Nghiên cứu sự hình thành tác nhân oxi hóa peroxymonocarbonate và ứng dụng xử lý một số hợp chất màu hữu cơ.Nghiên cứu sự hình thành tác nhân oxi hóa peroxymonocarbonate và ứng dụng xử lý một số hợp chất màu hữu cơ.

MINISTRY OF EDUCATION OF TRAINING HANOI NATIONAL UNIVERSITY OF EDUCATION NGUYEN THI HANH RESEARCH ON PEROXYMONOCARBONATE FORMATION AND APPLICATION IN THE TREATMENT OF SOME ORGANIC DYES Major: Analytical Chemistry Code: 9.44.01.18 PhD THESIS ABSTRACT Hanoi – 2022 Place: Hanoi National University of Education Advisors: PhD Nguyen Bich Ngan Hanoi National University of Education PhD Vu Ngoc Duy University of Science, Vietnam National University Ha Noi Reviewer 1: Assoc Prof PhD Nguyen Tuan Dung Institute of Tropical Technology Reviewer 2: Assoc Prof PhD Duong Thi Tu Anh Thai Nguyen University of Education Reviewer 3: Assoc Prof PhD Pham Thi Ngoc Mai University of Science, Vietnam National University Ha Noi The thesis is completed in Hanoi National University of Education in 2022 The thesis can be found at: - National Library of Vietnam - Library of Hanoi National University of Education LIST OF PUBLISHED PAPERS Nguyen Thi Hanh, Nguyen Thi Bich Viet, Nguyen Bich Ngan, Vu Ngoc Duy (2020), Research on the degaradation process of organic colors by advance oxidative method Journal HPU2, 69, - 11 Thi Bich Viet Nguyen, Ngan Nguyen Bich, Ngoc Duy Vu, Hien Ho Phuong and Hanh Nguyen Thi (2021), Degradation of Reactive Blue 19 (RB19) by a Green Process Based on Peroxymonocarbonate Oxidation System, Journal of Analytical Methods in Chemistry, Volume 2021, Article ID 6696600, pages (https://doi.org/10.1155/2021/6696600) Nguyen Thi Bich Viet, Nguyen Bich Ngan, Nguyen Thi Hanh, Vu Ngoc Duy (2021), Study on the formation and decomposition of peroxymonocarbonate (HCO4-) in aqueous solution, Journal of Analytical Sciences, 26 (3A), 117-120 Nguyen Thi Bich Viet, Ho Phuong Hien, Nguyen Bich Ngan, Nguyen Thuy Ha, Vu Ngoc Duy, Nguyen Thi Hanh (2021), Decolorization of Reactive blue 21 textile dye by a peroxymonocarbonate – base oxidation system, Journal of Analytical Sciences, 26 (Vol espcially),175 – 180 Nguyen Thi Hanh, Pham Thi Huyen, Nguyen Hoai Thu, Nguyen Bich Ngan, Vu Ngoc Duy, Nguyen Thi Bich Viet (2022), Study on catalytic activity of Co(II) in Rhodamine B decolorization by peroxymonocarbonate in aqueous solution, Vietnam Journal of Chemistry, 60 (special issue), 96 - 102 (DOI: 10.1002/vjch.202200089) INTRODUCTION Urgency of the thesis Environmental pollution and environmental pollution treatment are worldwide concerns, especially prioritizing effective wastewater treatment (high efficiency, short treatment time, economy) but not generating secondary waste are pollution sources Untreated wastewater discharged into natural water sources has resulted in environmental pollution by impurities, including organic dyes, growth chemicals, aromatic compounds, and agrochemicals, organic compounds containing sulfur and nitrogen Among the types of production, the textile industry generates a large amount of wastewater and causes serious pollution, especially in the country where the textile industry is considered one of the most important major export industry like Vietnam Increased concentrations of hazardous substances require efficient, cost-effective techniques for wastewater treatment Traditional treatment systems such as physicochemical methods (flocculation, adsorption, ion exchange), chemical methods (chlorination, ozonation, flocculation) are effective not yet so need enhanced treatment measures to effectively treat pollutants Some methods produce even more toxic compounds Advanced oxidation processes are very suitable for removing pollutants in wastewater, especially persistent organic dyes that are difficult to degrade biologically Advanced oxidation processes generate reactive oxygen species such as hydroxyl radicals •OH, oxygen singlet (1O2) and superoxide (•O2-)… which can completely remove harmful pollutants The use of ozone or oxygen as an oxidizing agent often faces the problem of low gas solubility in solution leading to high energy consumption, while treatment with H 2O2 overcomes this drawback, so it is more feasible In previous studies, Fe 2+ agent has been widely applied as a homogeneous catalyst in the decomposition of organic pollutants However, pH range for the Fenton process is quite low (pH ÷ 4) while textile dyeing wastewater is often highly alkaline (pH ÷ 12) and generates a large amount of sludge after treatment, leads to high treatment costs and secondary pollution in practical applications Therefore, it is necessary to find an advanced oxidation system that uses environmentally friendly chemicals, does not create secondary waste, has high efficiency, low cost and has potential for large-scale application to protect the environment, successfully implement the sustainable development of the economy In recent years, publications on advanced oxidation systems involving bicarbonate - activated hydrogen peroxide yield a highly active substance called peroxymonocarbonate (PMC), which is capable of degrading many stable organic dyes These studies only mention the rate constants of the forward reaction and the rate constant of the reverse reaction forming PMC Meanwhile, the kinetics of the reaction of formation and decomposition of PMC in aqueous solvent have not been studied In addition, only 13C NMR nuclear magnetic resonance method is used to analyze PMC content, so it is necessary to study more methods to analyze PMC content which are simpler and still give accurate results In addition, the works on applying PMC to process pigments focus a lot on processing efficiency, there is not enough information on the influencing factors as well as the kinetics of the decolorization process.Therefore, this thesis chooses the topic: "Research on peroxymonocarbonate formation and application in the treatment of some organic dyes" Goals of research The purpose of the thesis is to determine the optimal conditions for the formation of PMC in solution and evaluate the decolorization activity by advanced oxidation method based on H 2O2 - HCO3- system, thereby developing the technology, treatment of organic colorants in particular and nonbiodegradable organic substances in general in wastewater in Vietnam Main research objects and contents The main research objects of the thesis includes the decolorizing agent peroxymonocarbonate (PMC) and the treated objects are some organic color compounds as industrial dyes PMC is a highly active and unstable substance and should be prepared in situ from a solution of hydrogen peroxide and sodium bicarbonate Information of the formation and decomposition of PMC is essential Therefore, this thesis focuses on researching the following main contents: (1) Studying the kinetics of formation and decomposition of PMC from the reaction between hydrogen peroxide and sodium bicarbonate under different conditions: molar ratio H2O2 : HCO3-, pH, catalyst; building a kinetic model (determining reaction order, reaction rate constant) to help predict the concentration of PMC formed and decomposed over time (2) Investigation of the ability to handle the dyes: Reactive Blue 19 (RB19), Reactive Yellow 145 (RY145), Reactive Blue 21 (RB21), Rhodamine B (RhB), Methylene Blue (MB) by PMC when changing conditions such as oxidant concentration, pH, metal ion catalysts, catalyst concentration, UV radiation; building a kinetic model of the decolorization process Scientific significance, practice and new contributions of the thesis The results of the thesis contribute to adding more scientific basis to the research base on oxidizing agent PMC and the oxidizing ability of some organic dyes, in detail: - Determined the suitable temperature for the quantitative analysis of PMC in solution in the presence of H2O2 by standard iodine-thiosulfate method - Determined the optimized conditions for the fomation of PMC in solution From there, built a kinetic model of the fomation and decomposition of PMC - Determined the rule of effect of molar ratio H2O2: NaHCO3, metal ion catalysts, pH, UVC light to the ability to decolorize and mineralize organic dyes - PMC when combined with UVC light has the effect of decolorization, mineralization organic dyes, reducing COD and TOC values These results are the basis for the application of oxidizing agent PMC to degrade organic dyes in the treatment environment Structure of thesis The thesis consists of 115 pages, introduction pages, overview 35 pages, experimental and research methods 18 pages, results and discussion 57 pages, conclusion pages The thesis consists of 49 figures and 25 tables 15 pages of references with 138 documents There is also an appendix with a length of 17 pages CHAPTER OVERVIEW Chapter introduces information about the issues under the research scope of the thesis, including: 1.1 Textile dyeing wastewater pollution in Vietnam: an introduction to the status of water pollution and textile dyeing wastewater in Vietnam; toxicity of textile dyeing wastewater directly and indirectly to humans, aquatic species and the environment 1.2 Organic color compounds - Dyes : how to classify dyes, the level of loss to the environment of reactive dyes is the most On that basis, focus on introducing research subjects which are Reactive Blue 19, Reactive Blue 21, Reactive Yellow 145, Rhodamine B, Methylene Blue: structure, properties and toxicity 1.3 Textile dyeing wastewater treatment methods: introduction of traditional treatment methods and advanced oxidation methods On that basis, the research situation on the treatment method of selected colorants is introduced 1.4 Peroxymonocarbonate oxidizing agent made from hydrogen peroxide bicarbonate system: introduction to the properties of hydrogen peroxide bicarbonate system and peroxymonocarbonate is an oxidizing agent From there, the analytical methods to determine PMC and peracids are presented as well as the application of PMC in the treatment of organic pollutants, especially organic dyes CHAPTER EXPERIMENTAL AND RESEARCH METHODS 2.1 Chemicals, tools and equipment 2.2 Experimental process 2.2.1 Develop a procedure to determine concentration of peroxymonocarbonate in solution a Synthesis PMC and titration to determine PMC concentration in solution The process of synthesizing and determining PMC concentration by low temperature iodine - thiosulfate titration method is diagrammed in Figure 2.1, consisting of main steps: Step 1: Synthesize PMC Mix 50 mL of M HCO3- solution and 10.2 mL of 30% H 2O2 solution at room temperature, make up to 100 mL with double distilled water (the initial concentration of the substances in the solution HCO3- 0.5 M, H2O2 M) Step 2: Titrate to determine the concentration of PMC by iodine thiosulfate method at low temperature *Cooling PMC solution: - Prepare the mixture of ice - salt: mix kg of crushed ice with kg of salt (2:1 ratio in mass), the lowest temperature measured of the mixture is -20oC - Take exactly mL of PMC solution into a conical flask, add mL of ethanediol to prevent the solution from solidifying at low temperatures below 0°C Immerse the flask in the ice - salt mixture to reach the test temperature The initial temperature is maintained and monitored throughout the titration using the MULTI - THERMOMETER electronic thermometer *Titration to determine PMC concentration by iodine - thiosulfate method: Adjust the pH of the test solution to pH = with HCl solution, add the exact amount of 1.2450 grams of KI (which is the maximum amount of KI that reacts completely) with mL of PMC if the PMC synthesis efficiency is considered to be 100% based on 0.5 M NaHCO3) Close the mouth of the conical flask and leave in the dark for minutes Titrate with 0.5 M Na2S2O3 solution until a light yellow color appears, add 2-3 drops of starch indicator and then titrate until the blue color disappears The experiments were repeated times and the average results were taken HCO3- M H2O2 30% Solution HCO4+ C2H4(OH)2 Place in ice - salt + HCl (pH = 5) + KI, wait minutes + Na2S2O3 0,5 M Soution after titration Figure 2.1 Procedure for synthesis and determination of PMC concentration by low temperature iodine - thiosulfate titration method b Investigate the effect of temperature Preliminary investigation of the influence of temperatures below oC (from -18oC to 4oC) shows that at some temperatures, volumes of Na 2S2O3 are similar, which can be considered in terms of temperature range Therefore, investigating the effect of low temperature below oC on titration of solutions of H2O2 and PMC was conducted in temperature ranges: -18 oC ÷ -10oC; - oC ÷ -5 oC; -5 oC ÷ oC - Take mL of solution H2O2 M into a conical flask (control, with the same concentration as in PMC solution, pH = 5), add mL of ethanediol, cool down to different temperature ranges Add KI and titrate with Na2S2O3 0.5 M Particularly with the temperature of -18 oC ÷ -10 oC, preliminary survey shows 10 that the volume of Na2S2O3 0.5 M is very small, so Na 2S2O3 0.1 M solution is used instead H2O2 reacts with I- according to the reaction: H2O2 + 3I- + 2H+ → I3- + 2H2O (2.1) Titrate the amount of I3 produced with solution Na2S2O3 according to the reaction: I3- + S2O32- → S4O62- + 3I(2.2) Therefore, the concentration of H2O2 in the solution is calculated by the formula: - Take mL of PMC solution, add mL of ethanediol, cool down to different temperature ranges, add 14 mL of HCl M to adjust to pH = 5, add KI and titrate with solution Na2S2O3 0.5 M Immediately after adding KI to the flask, the solution appears yellowbrown due to the reaction between PMC and I - to produce I2 according to the reaction: HCO4- + 3I- + 2H+ → HCO3- + I3- + H2O (2.3) Titrate the amount of I3 produced with Na2S2O3 according to the reaction 2.2 Therefore, PMC concentration is calculated by the formula: 2.2.2 Investigate factors affecting peroxymonocarbonate formation and decomposition 2.2.2.1 Effect of molar ratio H2O2 : HCO3- Mix 50 mL of solution HCO3- M with volumes of H2O2 30% solution (9.8 M) to obtain the molar ratios of the two substances, add volumes of HCl M, make up to 100 mL with double distilled water to adjust to pH = The specific conditions are presented in Table 2.1 In which, the concentration of HCO 3- 0.5 M is fixed, the concentration of H 2O2 is in turn 1; 2; 2.5; 3; and 4.5 times the concentration of HCO3- The reaction mixtures were conditioned for 40 to reach equilibrium at room temperature of 25 ± 1°C Take exactly mL of sample solution, add KI, and determine the concentration of PMC according to the iodine-thiosulfate titration method Table 2.1 Synthesis of PMC at different molar ratios of H2O2 : NaHCO3 Molar ratio H2O2 : HCO31 : : 2.5 : : : 4.5 : Volume HCO3 M (mL) 50 50 50 50 50 50 Volume H2O2 30% (mL) 5.10 10.2 12.75 15.3 20.4 22.95 0 pH H2O2 : HCO3 initial 8.62 8.55 8.37 8.27 8.11 8.08 Volume HCl 3M (mL) 0.4 0.25 0.2 0.15 0.1 0.05 Distilled water (mL) Define level 100 mL 14 2.2.3.3 Evaluation of the H2O2 decolorization ability To be able to confirm that the main color processing ability is due to PMC, the experiments to evaluate the decolorization ability of H2O2 were conducted independently at room temperature, pH = 8, H2O2 concentration 20 mM, RB19 100 mg/ L without and with catalyst Co2+ 0.1 mg/L in 120 minutes 2.2.3.4 Evaluation of the effect of PMC concentration To investigate the effect of PMC concentration (through the effect of NaHCO3 concentration), the experiment was conducted with the general procedure for decolorization experiments with RB19 In which, NaHCO concentration changed from 10, 20, 30, 50, 70, 100 mM, keeping the molar ratio H2O2 : NaHCO3 = : 1, pH = 8, room temperature 25 ± oC, Co2+ 0.1 mg/L within 200 minutes 2.2.3.5 Evaluation of the catalytic effect of metal ions on the decolorization process Testing the experimental activity of metal ions was performed with Ni 2+, Mn2+, Zn2+, Co2+ all having a concentration of 0.1 mg/L at pH = 8, NaHCO 10 mM, H2O2 20 mM, RB19 100 mg/L, temperature 25 ± oC To known role of Co2+ in to the RB19 process by H2O2 + HCO3-, variation of RB19 is researched through independent experiments, including: RB19 + H2O2 2+ RB19 + H2O2 + Co RB19 + H2O2 + HCO3 2+ RB19 + H2O2 + HCO3 + Co Conditions are the same in all experiments: NaHCO3 10 mM, H2O2 20 mM, RB19 100 mg/L, Co2+ 0,1 mg/L, pH = 2.2.3.6 Evaluation of the effect of catalyst concentration The experiment was conducted with the general procedure for decolorization experiments with Co2+, RB19 100 mg/L, NaHCO3 20 mM, H2O2 40 mM, pH = In which, the concentration of Co2+ changed from 0.01; 0.02; 0.04; 0.06; 0.1 mg/L 2.2.3.7 Evaluation of the effect of pH To study the influence of pH on the color processing, RB19 was investigated at different values In fact, textile dyeing wastewater has an alkaline environment, so the selected pH values for investigation are pH = 7, 8, and 10, other experimental conditions are kept constant: RB19 100 mg/L, NaHCO3 10 mM, H2O2 20 mM, Co2+ 0.1 mg/L, room temperature 25 ± 1oC 2.2.3.8 Kinetic model of decolorization by concentration of HCO3- and metal ions To study the kinetics of the reaction and determine the partial reaction order of HCO3-, make surveys with concentrations of HCO 3- 5, 10, 15, 25, 30 mM, H2O2 40 mM, Co2+ 0.1 mg/L, pH = at room temperature 25 ± 1oC 15 To study the kinetics of the reaction and determine the partial reaction order of Co2+, make survey with concentrations of Co2+ 0.01; 0.02; 0.04; 0.06; mg/L, HCO3- 20 mM, H2O2 40 mM, pH = at room temperature 25 ± 1oC 2.2.3.9 Evaluation of the effects of UVC radiation Studying 10 independent experiments (without UVC and UVC irradiation for reaction systems respectively), kept fixed RB19 100mg/L; pH = 8, temperature 25 ± 1oC RB19 RB19 – H2O2 20 mM 2+ RB19 – H2O2 20 mM – Co 0,1 mg/L RB19 – H2O2 20 mM – HCO3 10 mM 2+ RB19 – H2O2 20 mM – HCO3 10 mM – Co 0.1 mg/L Decolourization experiments without UVC irradiation for comparison were performed as described in Figure 2.2 Decolourization experiments with UVC irradiation were performed as described in Figure 2.3 Figure 2.3 The continuous UV- irradiated system for the decolorization 2.2.4 Evaluation ability of decoloration other color compounds by peroxymonocarbonate Experiments to evaluate PMC's ability to process RY145, RB21, RhB and MB dyes were conducted similarly to those of RB19 in order to compare and then make general rules In addition, a number of surveys on UVA rays and ultrasonic vibration are presented to obtain more information when applying PMC to degrade various dyes in practice 2.2.4.1 Construction standard curve of dyes 2.2.4.2 Evaluation of PMC to treat dyes according to the concentration of oxidants 2.2.4.3 Evaluation of PMC to treat dyes with metal ion catalysis 2.2.4.4 Evaluation of PMC to treat dyes by pH 2.2.4.5 Evaluation of PMC to handle dyes when combining PMC and UV 2.2.5 Comparison of the degradability of dyes 2.3 Research Methods 2.3.1 Nuclear magnetic resonance spectroscopy 13C NMR 2.3.2 Iodine - thiosulfate titration methods 2.3.3 Molecular absorption spectroscopy UV-Vis 16 2.3.4 High performance liquid chromatography HPLC 2.3.5 Method analysis COD index 2.3.6 Method analysis TOC index 17 CHAPTER RESULTS AND DISCUSSION 3.1 Formation and decomposition of peroxymonocarbonate in solution 3.1.1 Formation of peroxymonocarbonate in the reaction system The presence of ion HCO4- in the solution is proved by 13C NMR of HCO3+ H2O2 solution with D2O solvent The results are presented in figure 3.1 Figure 3.1 Nuclear magnetic resonance spectroscopy 13C of HCO4- and HCO33.1.2 Analytical procedure for the determination of peroxymonocarbonate At temperatures below -10°C, the iodine-thiosulfate titration almost exactly reacts to the amount of HCO4- present in the solution Therefore, in the process of synthesizing and determining PMC concentration by low temperature iodine thiosulfate titration method (Figure 2.1), the temperature of the analytical solution is always maintained below -10oC The reaction should be titrated at a moderate rate so that the temperature does not change suddenly 3.1.3 Factors affecting the formation and decomposition of peroxymonocarbonate 3.1.3.1 Effect of molar ratio H2O2 : HCO3Figure 3.2 Effect of molar ratio H2O2 : NaHCO3 on the amount of HCO4- To clarify the variation of PMC concentration over time at the molar ratio H2O2 : NaHCO3 = : and 2.5 : 1; pH = 8, PMC concentration was determined over a period of 240 from the start of mixing (Figure 3.3) Figure 3.3 The concentration of PMC obtained from the system H 2O2 : NaHCO3 = : and 2.5 : 18 Molar ratio of H2O2 : NaHCO3 = : just created HCO4- is high, it is not necessary to use excess H2O2 so it should be used in further studies 3.1.3.2 Effect of pH Variation of HCO4- concentration over time at mole ratio H 2O2 : NaHCO3 = : and different pH values are presented in Figure 3.4 Figure 3.4 Variation of HCO4- concentration over time at different pH Therefore, the optimal pH for PMC formation is pH = ÷ 10 3.1.3.3 Effect of metal ions on the stability of PMC Figure 3.5 Variation of total concentration of HCO4– and H2O2 19 A first-order kinetic model has been built to model the reaction rate of the H2O2 - HCO3– - Co2+ system, the results are shown in Figure 3.6 Figure 3.6 Kinetic model of the decomposition process of H2O2 - HCO3– - Co2+ 3.1.3.4 Kinetic model of peroxymonocarbonate formation and decomposition The optimal results of the PMC formation rate (k) and PMC decomposition rate (k') values at each pH value are presented in table 3.4 Table 3.4 Rate constant for formation and decomposition of HCO40.0235 0.0105 0.0082 0.0076 0.0054 0.0050 The results show a trend that with increasing pH, the k:k' ratio increases, that is, the formation of HCO4- dominates (this advantage also increases with the increase of pH) than its decomposition * Discuss the mechanism of formation of peroxymonocarbonate in solution In a neutral and weakly alkaline environment, HCO3- ions occupy the majority of the mole fraction compared to H2CO3 and CO32- forms, HCO3- mole fraction dependence on pH, so pH has effect on HCO4- formation The correlation between the rate constant of the formation reaction k (min-1) and the mole fraction of HCO3- according to pH is presented in Figure 3.8 20 Figure 3.8 Correlation between the dependence of the molar fraction of bicarbonate on pH and the reaction rate constant for the formation of PMC k (min-1) Thus, there is a good agreement between the change in mole fraction of HCO3 and the change in the constant k As the pH increases, the molar fraction of HCO3- and the value of the rate constant for the formation of PMC(k) also increase accordingly and peak at about pH = 3.2 Evaluation of peroxymonocarbonate to treat RB19 3.2.1 Evaluation of the RB19 calibration curve 3.2.1.1 Optimized wavelength: 592 nm 3.2.1.2 Calibration curve and statistical processing RB19 Abs = (8,4 ± 0,02).10-3.CRB19 (mg/L); R2 = 0,9999, LOD = 0,7 mg/L; LOQ = 2,3 mg/L 3.2.2 Ability decolorization RB19 of H2O2 Under research conditions, H2O2 hardly treats the RB19 Therefore, the influence of H2O2 can be ignored when evaluating the decolorization activity of PMC solution in later experiments 3.2.3 Effect of peroxymonocarbonate oxidant concentration Figure 3.12 Processing performance RB19 color with different concentrations HCO3- Condition H2O2 : HCO3- = : 1, pH = NaHCO3 concentrations are 50 and 70mM, both gave the best RB19 decolorization efficiency and were quite similar (reached nearly 20% after 200 minutes) 3.2.4 The effect of metal ion catalysis Figure 3.13 Effect of metal ions to decolorization efficiency of RB19 100 mg/L Condition: [HCO3-] = 10 mM, [H2O2] = 20 mM, pH = 8, [M2+] 0,1 mg/L 21 Among the investigated metal ions (Ni2+, Mn2+, Zn2+, Co2+), only Co2+ catalyst showed the strongest RB19 decomposition efficiency 3.2.5 Effect of catalytic ion concentration Co2+ With a concentration of 0.1 mg/L Co2+, the decolorization reaction efficiency after 45 minutes reached the highest at 86% However, cobalt is a heavy metal, the allowable cobalt concentration in water is 0.1 mg/L, so the Co 2+ catalyst concentration is chosen to be mg/L for further studies 3.2.6 Effect of pH Figure 3.16 Effect of pH to decolorization efficiency of RB19 Condition:[HCO3-] = 10 mM, [H2O2] = 20 mM, [Co2+] = 0,1 mg/L Although at pH = 9, 10, the decomposition of RB19 is better, but from an economic point of view, raising the pH to high for treatment, then adding acid to neutralize it before being discharged into the environment It also means consuming chemicals, increasing the cost of color treatment Furthermore, the HCO3- - H2O2 system itself is a buffer system with pH = - depending on the molar ratio of the two substances Therefore, pH = is chosen to continue investigating other conditions for RB19 degradation with the aim of finding the most optimal degradation conditions for RB19 pigment both in terms of treatment efficiency as well as economic efficiency and environmental friendliness 3.2.7 Kinetics of the reaction according to the concentration of HCO3- and concentration of Co2+ 3.2.7.1 Experimental reaction order for HCO3- : Order 1.7 3.2.7.2 Experimental reaction order for Co2+ : Order 1.2 22 3.2.8 Evaluation of color processing ability when combining PMC and UV Table 3.9 Decolorization efficiency of RB19 in the absence of UV and with UV of some reaction systems, [RB19] = 100 mg/L; pH = Decolorization efficiency (%) Oxidation system Non UV UV RB19 0,0 3.7 ± 0.3 0,0 83.6 ± 3.6 RB19 – H2O2 20 mM 2+ 1.8 ± 0.2 91.1 ± 2.9 RB19 – H2O2 20 mM – Co 0,1 mg/L 4.7 ± 2.7 96.7 ± 2.3 RB19 – H2O2 20 mM – HCO3- 10 mM RB19 – H2O2 20 mM – HCO3- 10 mM – Co2+ 79.9 ± 3.5 97.6 ± 3.1 0.1 mg/L Thus, it is proved that the system H2O2 − HCO3- − Co2+ effectively treats RB19 color even without UV rays 3.2.9 Products after RB19 treatment with peroxymonocarbonate 3.2.9.1 HPLC results Figure 3.22: The chromatograms of the RB19 after degradation 10, 30, 60 Most of the intermediate products at 10 were not observed after the 30 reaction time, and the chromatogram obtained with the solution at 60 showed no signal showed the efficiency of complete mineralization of RB19 by the H2O2 - HCO3- - Co2+ system 3.2.9.2 Results COD and TOC The COD values of the initial and final reaction solutions were determined to be 315 and 12.5 mg O 2/L, respectively, of which 100 mg/L RB19 was degraded by the PMC system ([H 2O2] = 20 mM, [HCO3-] = 10 mM, [Co2+] = 0.1 mg/L, pH = 8, UVC irradiation 60 min) Total organic carbon value TOC = TC – TIC, measured for the final solution, resulted in 15.2 mg/L in agreement with the COD value Thus, the H2O2 - HCO3- - Co2+ system has a good mineralization ability of RB19 with a COD reduction efficiency of 96% 3.3 Evaluation of peroxymonocarbonate to treat other dyes 3.3.1 The ability of peroxymonocarbonate to treat dyes according to the concentration of oxidizing agent Figure 3.24 Effect of HCO3- concentration on RY145 decolorization efficiency Condition: molar ratio H2O2 : HCO3- = 2: 1, pH = Figure 3.25 Effect of HCO3- concentration on RB21 decolorization efficiency Condition: molar ratio H2O2 : HCO3- = 2: 1, pH = 23 Summary: The dependence of decolorization efficiency on PMC concentration (or HCO3- concentration) follows a general rule The optimal concentration of HCO3- is 50 ÷ 70 mM, when the concentration of HCO3- is too small or too large, it is not favorable for the decolorization process 3.3.2 The ability of peroxymonocarbonate to treat dyes with metal ion catalysis Figure 3.26 Effect of ion metal catalyst on RY145 decolorization efficiency Condition: RY145 50 mg/L, HCO3– 10 mM, H2O2 20 mM, pH = Figure 3.27 Effect of ion metal catalyst on RB21 decolorization efficiency Condition: RB21 50 mg/L, HCO3– 50 mM, H2O2 100 mM, pH = Summary: The activity of metal ion catalysis for decolorization reactions by PMC system follows the general rule: among the studied transition metal ions, Co2+ 0.1 mg/L gives the catalytic efficiency outstanding To see more clearly the combined effect of HCO4- and Co2+, the rate of RhB decolorization reaction was considered in systems with simultaneous changes in HCO3- and Co2+ concentrations The speed constant values (k, min-1) are presented in Figure 3.28 Figure 3.28 First-order rate constant of RhB mg/L decolorization reaction Condition: HCO3– 0, 10, 15, 20 mM; H2O2 40 mM; Co2+ 0; 0,1; 0,2 mg/L; pH Thus in the absence of Co2+, a higher concentration of HCO3– would increase the rate of the reaction (k increases from 0.00095 to 0.00187 min-1 when [HCO3–] from to 20 mM) This enhancement is due to the formation of PMC which is more reactive than H2O2 When 0.1 and 0.2 mg/L Co 2+ were present, the reaction rate increased nearly 10 times and 17 times, respectively However, in the absence of HCO3– (no HCO4–), in the presence of 0.2 mg/L Co2+, the reaction rate only doubled It is clear that the combination of HCO4– with Co2+ increases the reaction 24 rate far superior to that of HCO4– or Co2+ alone In other words, there is a synergistic effect when HCO4– and Co2+ are both present in the PMC-based oxidation system 3.3.3 The ability of peroxymonocarbonate to treat dyes according to pH Figure 3.29 Effect of ion pH on RY145 decolorization efficiency Condition: HCO3– 50 mM, H2O2 100 mM, Co2+ 0,1 mg/L Figure 3.30 Effect of ion pH on RB21 decolorization efficiency Condition: HCO3– 50 mM, H2O2 100 mM, Co2+ 0,1 mg/L Summary: The pH affects the decolorization reaction by PMC according to the general rule: the pH of the weak alkaline region (pH = ÷ 10) is favorable for the dyes treatment reaction, when the pH is too low (pH < 7) or too high (pH > 11), the PMC system gives low decolorization efficiency 3.3.4 Color processing ability when combining peroxymonocarbonate and UV Without and with UVC irradiation, the decolorization efficiency of the systems decreases in the order: H2O2 - HCO3– - Co2+ > H2O2 - HCO3- > H2O2 Co2+ > H2O2 In addition, the effects of some other energy sources on the decolorization of MB (UVA rays) and RhB (ultrasonic vibrations) were also studied MB is completely decolorized by the H2O2 - HCO3– - Co2+ system in just 10 minutes, when using UVC light, the decolorization occurs almost immediately The results of MB decolorization with different systems show that UVA rays also increase the efficiency of PMC colorants (completely decolorize MB in minutes) When PMC and ultrasonic vibration or UVC are combined to treat RhB, it has been shown that both UVC radiation and ultrasonic vibration can increase the reaction rate The 100 W ultrasonic source treated 78% of the RhB, compared with a decolorization efficiency of 65% in the absence of ultrasound Under UVC irradiation, the decolorization efficiency is much greater, almost 100% of RhB is decolorized in 20 Summary: The combined treatment of dyes with PMC and UVC light shows outstanding treatment efficiency Therefore, the H2O2 - HCO3– - Co2+ UVC system shows potential for practical applications 3.4 Comparison of the degradability of dyes The ability to degrade dyes by PMC depends on the molecular structure The durability, difficulty of degradiation of the dyes decreases in the order: RY145 > RB21 > RB19 > RhB > MB The process of breaking the chromophore is easier than the breaking of the aromatic rings Thanks to the presence of UVC rays and PMC, the 25 decomposition of dyes occurs faster, more completely and more thoroughly This can be explained by the role of UVC rays in breaking the weak O-O bonds in HCO4- and H2O2, thereby generating more free radicals PMC is capable of both destroying chromogenic groups and aromatic rings into simpler, less toxic open-chain organic compounds, and finally, almost complete mineralization of dyes can occur into CO2 and H2O 26 CONCLUSION The thesis has studied the process of formation and decomposition of peroxy monocarbonate (PMC) in the aqueous environment and evaluated the ability of this agent to treat some organic dyes The obtained results show: The analytical procedure has been developed to determine the content of PMC in the solution in the presence of H 2O2 by titration method of iodine thiosulfate at a low temperature of -10oC Determined the optimal conditions for the formation of PMC in solution have been determined: the maximum PMC formation efficiency is 70% in NaHCO 0.5 M solution (molar ratio H2O2 : HCO3- = : and 2.5: 1), pH = ÷ 10 in the period from 40 to 100 minutes after mixing two solutions of NaHCO3 and H2O2 Built a kinetic model of the formation and decomposition of PMC: - The PMC formation rate at pH = ÷ 10 is about 11 times higher than the decomposition rate - Built a kinetic model of the formation and decomposition of PMC and determined the reaction order with HCO3- and Co2+ catalysts are first order and have been verified - In the presence of Co2+, PMC decomposes in two stages: before 100 minutes (calculated from the time of mixing two solutions of NaHCO3 and H2O2) occurs slowly, after 100 minutes, the decomposition rate is twice as fast as the previous stage The law of influence of the molar ratio of H2O2 : NaHCO3, catalytic metal ions, pH, UVC light has been determined on the ability to decolorize and mineralize dyes Optimum conditions of PMC system for decolorization: molar ratio H2O2 : NaHCO3 = : 1; HCO3- = 50 mM ÷ 70 mM; Co2+ catalyst 0.1 mg/L; pH = ÷ 9; combined with UVC irradiation at a wavelength of 254 nm A kinetic model of the decolorization reaction has been built: the order of dyes, HCO3- , Co2+ is order 1; 1.7 and 1.2, respectively PMC, when combined with catalyst and UVC irradation, has the effect of decolorizing, reducing aromatic rings and mineralizing organic dyes, reducing COD and TOC values After 30 minutes of UVC irradiation, the system of HCO3- 50 mM, H2O2 100 mM, Co2+ 0,1 mg/L, pH = decolorized 85% - 100% of all dyes COD and TOC treatment efficiency is from 60% to 96% ... of some organic dyes, in detail: - Determined the suitable temperature for the quantitative analysis of PMC in solution in the presence of H2O2 by standard iodine-thiosulfate method - Determined... experimental conditions are presented in Table 2.3 Table 2.3 Experimental conditions to study the stability of PMC Sampl [H2O2] M [HCO3-] M Co2+ mg/L e 0.4 0.4 0.1 0.4 0.2 0.4 0.2 0.1 Take mL... optimization method with experimental data, using the Solver function in MS Excel to find a suitable value for the model The computational model best describes the experimental curve Optimization steps