Nghiên cứu hoạt hóa persulfate bằng sắt hóa trị không và UV nhằm tạo ra hệ oxi hóa kép để phân hủy một số thuốc nhuộm họ azo trong môi trường nước tt tiếng anh

Ministry of Education and Training Ministry of National Defence Academy of Military Science and Technology Nguyen Thanh Binh STUDY ON ACTIVATED PERSULFATE BY ZERO VALENT IRON AND UV TO PRODUCE DUAL OXIDATION SYSTEM TO DEGRADE SOME AZO DYES IN WATER Major: Theoretical and Physical Chemistry Code: 44 01 19 Summary of Chemical Doctoral Thesis Hanoi - 2019 The dissertation completed at: Academy of Military Science and Technology Academic supervisors: Assoc Prof Dr Tran Van Chung Prof Dr Sc Do Ngoc Khue Reviewer 1: Prof Dr Sc Nguyen Duc Hung Reviewer 2: Assoc Prof Dr Vu Thi Thu Ha Reviewer 3: Assoc Prof Dr Nguyen Xuan Hoan The dissertation will be defended in front of Doctor Examining Committee held at Academy of Military Science and Technology on … … …, … … … …, 2019 The dissertation could be found at: - Library of Academy of Military Science and Technology - Vietnam National Library Hanoi - 2019 List of published scientific works Nguyen Thanh Binh, Do Ngoc Khue, Tran Van Chung (2017),"Persulfate activation by zero valent iron to decomposing methyl orange in water", Vietnam Journal of Catalysis and Adsorption, Vol.6, No 1, pp.73-78 Nguyen Thanh Binh, Do Ngoc Khue, Tran Van Chung, Dao Duy Hung, Vu Quang Bach (2017), "Studying degradation of methyl orange contaminated by radicals SO4 and OH", Analytica Vietnam Conference, 5th, March, Hanoi, 2017, pp 182-189 Nguyen Thanh Binh, Do Ngoc Khue, Tran Van Chung (2017), "A novel study on degradation of methyl orange by dual oxidation system", International Jounral of Development Research, Vol 07, No 05, pp 12896-12900 Nguyen Thanh Hoa, Nguyen Thanh Binh, Do Ngoc Khue, Vu Duc Loi (2018), "Application of BoX-Behnken designs in parameters optimization of AOPs combined persulfate and H2O2 activated by Fe0 under UV light for treating dye waste water”, Báo cáo Hội thảo Quốc gia Ứng dụng công nghệ cao vào thực tiễn 2018, Science Reseach and Military Technology, 8th August 2018, Hanoi Nguyen Thanh Binh, Do Ngoc Khue, Tran Van Chung, Nguyen Thanh Hoa, Doang Song Quang (2019), "Kinetic modeling of degradation for alizarin yellow R by the activated persulfate by FeO (ZVI) under UV light", Vietnam Journal of Chemistry, Vol 57, No 1, pp 46-51 Nguyen Thanh Hoa, Nguyen Thanh Binh, Do Ngoc Khue, Vu Duc Loi (2019), "Enhanced the combination of persulfate and H2O2 oxidation processes activated by FeO (ZVI) for removing methylene blue (MB)", Journal of Analytical Science, Vol 24, No 2, pp 212-219 INTRODUCTION The urgency of the thesis: In recent years, scientists have announced the application of suitable persulfate and peroxymonopersulfate oxidants to treat persistent organic polluted wastewater If these oxidants are activated these will produce free radicals with higher oxidation activity than the original oxidants Persulfate is more oxidative than hydrogen peroxide and ozone Persulfate is more stable than hydrogen peroxide and ozone in solution, solubility of persulfate is better than ozone in water In particular, it is recommended that persulfate activation process produce simultaneously free radicals SO4 (E0= 2.6V) and OH (E0= 2.8V) These radicals are high oxidation activity and decompose most organic pollutants in the water Synthetic dyes are increasingly important in life There are many different synthetic dyes, but the most important is the azo dyes The azo dyes account for over 50% of global commercial dye quantity Some azo dyes are found to cause cancer, mutagenicity and are being banned for using in the world However, they are still produced and used on a large scale in the dyeing industry so far, due to the low cost of production, easy synthesis and some color properties that meet the requirements The bonds in the azo molecule are quite stable, showing the ability to decompose and accumulate in the environment The treatment for textile dye wastewater is always concerned by domestic and foreign scientists There are many traditional methods of treating textile dyeing wastewater In recent years, advanced oxidation methods, especially AOPs based on persulfate have been studied, applied and demonstrated the superiority in the treatment of organic decomposition in water environment That has the potential to treat dyeing textile wastewater Therefore, the thesis title name selected is "Study on activated persulfate by zero valent iron and UV to produce dual oxidation system to degrade some azo dyes in water" Objectives of the thesis: Study of dual oxidation formation in persulfate-containing solution in combination with zero valent iron powder (ZVI) and UV; Application of dual oxidation system to decompose some azo compounds: Methyl orange (MO), alizarin yellow R (AY), mordant black-T (BT) and treatment of dyeing textile village wastewater contaminated with azo dye Main contents of the thesis: - Researching on activated persulfate by ZVI combined with UV through evaluating the decomposition efficiency of MO, AY and BT - Researching reaction kinetics, calculating the thermodynamic quantities of the decomposition processes of MO, AY and BT in the activated persulfate systems by ZVI combined with UV and with out UV Studying to determine and quantify OH, SO free radicals in the activated persulfate systems - Calculating molecular structure parameters and proposing mechanism of MO, AY and BT decomposition mechanism in activated persulfate system - Study on the application of activated persulfate system by ZVI combination with UV to treat azo-contaminated wastewater in some textile dye villages: Duong noi, La phu and Van phuc Study method: Using HPLC, ICP-MS, titration, colorimetric and COD methods study the characteristics of decomposition process of azo dyes and wastewater containing azo dyes Building mathematical model approximates the concentration of SO4, OH The thesis is based on the kinetic theory of Arrhenius and Eyring equation to calculate some thermodynamic quantities Using HyperChem 8.0 software to calculate quantum parameters of methyl orange, alizarin yellow R and mordant black T The scientific and practical meaning of the thesis: Research results of the thesis contribute to clarifying and developing kinetics of AOPs processes based on activated persulfate by ZVI and UV to decompose some azo dyes in the water, at the same time creating a basis for development diversify methods of treating organic pollutants in the water in general and azo-contaminated wastewater in particular Outline of the thesis: Chapter 1: Overview; Chapter 2: Research subject and methodology; Chapter 3: Result and discussion; Conclusion CHAPTER 1: OVERVIEW 1.1 The basic concepts of oxidation systems is based on free radicals Advanced Oxidation Processes (AOPs) are a collection of oxidation processes of organic substances based on free radicals: hydroxyl OH, sulfate SO4… produced on in-situ in the process of treating contaminated water 1.2 Status of treatment technology for dying textile wastewater 1.2.1 Concept, classification of dyes 1.2.2 Azo dyes According to the dye association in the world, there are some azo dyes that cause cancer and mutate genes for humans Some typical azo dyes: Table 1.1 Molecular structure of MO, AY and BT Metyl orange (MO) C14H14N3NaO3S N N Alizarin yellow R (AY) C13H8N3NaO5 Mordant black T (BT) C20H12N3NaO7S O O S ONa N O O H3C N CH3 N H O N O H O S O Na O 1.2.3 Waste water contaminated with dye Textile dyeing wastewater is highly polluted with organic matter; especially the color of wastewater and the dyes are difficult to decompose in general, including azo dyes in particular 1.2.4 Current status of domestic and foreign research on treatment technology for textile dyeing wastewater Nowadays, there are many methods of wastewater treatment, but AOPs are suitable for treating wastewater containing persistent organic matter including azo dyes CHAPTER 2: RESEARCH SUBJECT AND METHODOLOGY 2.1 Research subject Studying of activated persulfate by zero valent iron (ZVI) combined with UV to produce a dual oxidation system consisting of free radicals SO4, OH These radicals are high oxidizing activity to decompose some dyes azo (MO, AY and BT) in water environment 2.2 Instruments and chemicals 2.2.1 Instruments - High performance liquid chromatography machine (HPLC), plasma induction mass spectrometer (ICP-MS), CHYO analytical balance, pH meter - The system of self-made device of UV activated persulfate for oxidizing the azo: MO, AY, BT and wastewater of textile dyeing villages 2.2.2 Chemicals - Methyl orange (MO), alizarine yellow R (AY), mordant black - T (BT), methanol (ETA), buthanol (TBA), zero valent iron powder (ZVI), sodium persulfate Na2S2O8 (PS)…are high analytical cleanliness - Solvents: acetonitrile, ethanol, methanol with cleanliness for HPLC analysis 2.3 Methods of analysis 2.3.1 High performance liquid chromatography method The concentration of MO, AY and BT in solution is determined by HPLC 2.3.2 Inductively coupled plasma - mass spectrometry method The ICP-MS method was used to determine the total concentration of iron ions (Fe2+ and Fe3+) in solution 2.3.3 Titration method Titration method for determination of S2O82 concentration in solution at the reaction time 2.3.4 Method of determining COD According to TCVN 2.4 Experimental methods 2.4.1 Survey, evaluating the decomposition efficiency of AZOs in systems: ZVI/AZOs, PS/AZOs, ZVI/PS/AZOs and ZVI/AZOs/UV, PS/AZOs/UV, ZVI/PS/AZOs/UV The decline of AZOs dye concentration over time is determined by HPLC method The decomposition efficiency of AZOs is calculated according to the formula: C -C (2.9) H(%) = t x100 C0 H (%): degradation performance of AZOs (%); C0, Ct: concentrations at t= and t minute 2.4.2 Survey of affecting factors on the degradation efficiency of AZOs in systems: ZVI/PS/AZOs and ZVI/PS/AZOs/UV - Effect of persulfate concentration: 0.1 mM; 0.5 mM; 1.0 mM; 2.0 mM; 3.0 mM - Effect of ZVI content: 0.056 g/L; 0.5 g/L; 1.0 g/L; 2.0 g/L - Effect of AZOs concentration: 0.05 mM; 0.1 mM; 0.2 mM; 0.25 mM - Effect of pH at: 2.5; 4.5; 7.0; 10.0 - Effect of temperature at: 25 C; 35 C; 45 C; 55 C 2.4.3 Qualitative survey of free radicals OH and SO4 in ZVI/PS/AZOs and ZVI/PS/AZOs/UV systems The basis of this method is based on the large variation of the reaction rate constants between the OH and SO4 with ethanol (ETA) and tert butyl alcohol (TBA) Investigation of decomposition of AZOs with the presence of large quantities of ETA and TBA (molar ratio nETA: nAZOs = 1000: and nTBA: nAZOs = 1000: 1) 2.4.4 Quantitative survey of free radicals OH and SO4 in ZVI/PS/AZOs and ZVI/PS/AZOs/UV systems Building mathematical model to determine the approximate concentration of free radicals OH, SO4 in ZVI/PS/AZOs and ZVI/PS/AZOs/UV systems at a specified time It is necessary to determine the concentration of S2O82 and the total amount of iron ions(Fe2+, Fe3+) at the time of reaction It is based on the reaction rate constants of the component reaction stages On the basis of the law of mass effect and stable concentration state principle to build the equation to calculate the concentration of free radicals OH, SO4 2.4.5 The theoretical equations applied in reaction kinetic research - Arrhenius equation (1889) - Eyring equation (1935) 2.4.6 The basis of quantum computing methods 2.4.7 Treating textile dye wastewater of La Phu, Duong Noi and Van Phuc villages Based on comparing the effectiveness of AZOs degradation of different activated persulfate systems, to select the most effective system This system will apply to the actual wastewater treatment CHAPTER 3: RESULTS AND DISCUSSION 3.1 Survey, evaluating the efficiency of the PS activation methods in different conditions 3.1.1 The PS activation under without UV 8.0 H (%) ZVI/MO ZVI/AY ZVI/BT 6.0 4.0 2.0 t (minute) 0.0 10 15 20 25 30 35 Figure 3.1 The decomposition efficiency of MO, AY and BT in systems: ZVI/MO; ZVI/AY ZVI/BT (conditions: CZVI= 0.5 g/L; CAZOs= 0.1 mM; pH= 4.5; t= 25 C) 30.0 25.0 20.0 15.0 10.0 5.0 0.0 H (%) PS/MO PS/AY PS/BT t (minute) 10 15 20 25 30 35 Figure 3.2 The decomposition efficiency of MO, AY and BT in systems: 1.PS/MO; PS/AY PS/BT (conditions: CPS= 1.0 mM; CAZOs= 0.1 mM; pH=4.5; t= 25 C) 100.0 H (%) ZVI/PS/MO 80.0 ZVI/PS/AY 60.0 40.0 20.0 t (minute) 0.0 10 15 20 25 30 35 Figure 3.3 The decomposition efficiency of MO, AY and BT in systems: ZVI/PS/MO; ZVI/PS/AY ZVI/PS/BT (conditions: CZVI= 0.5 g/L, CPS=1.0 mM; CAZOs= 0.1 mM; pH= 4.5; t= 25 C) 3.1.2 PS activation under UV conditions 20.0 H% ZVI/MO/UV 15.0 ZVI/AY/UV 10.0 5.0 t (minute) 0.0 10 15 20 25 30 35 Figure 3.4 The decomposition efficiency of MO, AY and BT in systems: ZVI/MO/UV; ZVI/AY/UV ZVI/BT/UV (conditions: CZVI= 0.5 g/L; CAZOs= 0.1 mM; pH= 4.5; t= 25 C, I= 785 Lux, = 254 nm) 100.0 H% PS/MO/UV PS/AY/UV PS/BT/UV 80.0 60.0 40.0 20.0 t (minute) 0.0 10 15 20 25 30 35 Figure 3.5 The decomposition efficiency of MO, AY and BT in systems: PS/MO/UV; PS/AY/UV PS/BT/UV (conditions: CPS= 1.0 mM; CAZOs= 0.1 mM; pH= 4.5; t= 25 C, I= 785 Lux, = 254 nm) 100.0 H% 80.0 60.0 ZVI/PS/MO/UV ZVI/PS/AY/UV ZVI/PS/BT/UV t (minute) 40.0 20.0 0.0 10 15 20 25 30 35 Figure 3.6 The decomposition efficiency of MO, AY and BT in systems: 1.ZVI/PS/MO/UV; ZVI/PS/AY/UV ZVI/PS/BT/UV (conditions: CZVI = 0.5 g/L; CPS= 1.0 mM; CAZOs= 0.1 mM; pH= 4.5; t= 25 C, I= 785 Lux, = 254 nm) 10 100 H(%) 80 60 40 H% (ZVI/PS/BT) H% (ZVI/PS/BT/UV) 20 0 0.5 1.5 2.5 [PS] (mM) 3.5 Figure 3.15 Effect of [PS] on the BT decomposition efficiency in systems: ZVI/PS/BT; ZVI/PS/BT/UV for 30 minutes 3.1.3.3 Effect of AZOs concentration Surveying the effect of the AZOs concentration (0.05mM; 0.1mM; 0.15mM; 0.2mM; 0.25mM) affected the AZOs degradation efficiency in systems: ZVI/PS/AZOs (conditions: CZVI= 0.5 g/L; CPS= 1.0 mM; pH= 4.5; t= 25 C) and ZVI/PS/AZOs/UV (conditions: CZVI= 0.5 g/L; CPS= 1.0 mM; pH = 4.5; t= 25 C; I= 785 Lux; = 254 nm) The results shown in Figure 3.16, Figure 3.17 and Figure 3.18 100 H(%) 80 60 40 H % (ZVI/PS/MO) H % (ZVI/PS/MO/UV) 20 0 0.05 0.1 0.15 0.2 [MO] (mM) 0.25 0.3 Figure 3.16 Effect of [MO] on the MO decomposition efficiency in systems: ZVI/PS/MO; ZVI/PS/MO/UV for 30 minutes 100 80 60 40 20 H(%) H % (ZVI/PS/AY) H % (ZVI/PS/AY/UV) 0.05 0.1 0.15 [AY] (mM) 0.2 0.25 0.3 Figure 3.17 Effect of [AY] on the AY decomposition efficiency in systems: ZVI/PS/AY; ZVI/PS/AY/UV for 30 minutes 11 100 H(%) 80 60 40 H % (ZVI/PS/BT) H % (ZVI/PS/BT/UV) 20 0 0.05 0.1 0.15 [BT] (mM) 0.2 0.25 0.3 Figure 3.18 Effect of [BT] on the BT decomposition efficiency in systems: ZVI/PS/BT; ZVI/PS/BT/UV for 30 minutes 3.1.3.4 Effect of pH The efficiency of the AZOs decomposition in systems: ZVI/PS/AZOs (conditions: CZVI = 0.5 g/L; CPS= 1.0 mM; CAZOs= 0.1 mM; t = 25 C) and ZVI/PS/AZOs/UV (conditions: CZVI= 0.5 g/L; CPS= 1.0 mM; CAZOs= 0.1 mM; t = 25 C; I = 785 Lux;  = 254 nm) will be studied at pH = 2.5; 4.5; 7.0; 10.0 H(%) 100 80 60 40 H% (ZVI/PS/MO) H% (ZVI/PS/MO/UV) 20 pH 0 2.5 7.5 10 Figure 3.19 Effect of pH on the MO decomposition performance in systems: ZVI/PS/MO; ZVI/PS/MO/UV for 30 minutes 100 H(%) 80 60 40 H% (ZVI/PS/AY) H% (ZVI/PS/AY/UV) 20 pH 0 2.5 7.5 10 Figure 3.20 Effect of pH on the AY decomposition performance in systems: ZVI/PS/AY; ZVI/PS/AY/UV for 30 minutes 12 100 80 60 40 20 H(%) H% (ZVI/PS/BT) H% (ZVI/PS/BT/UV) 2.5 pH 7.5 10 Figure 3.21 Effect of pH on the BT decomposition performance in systems: ZVI/PS/BT; ZVI/PS/BT/UV for 30 minutes 3.1.3.5 Effect of temperature The effect of temperature changes (25 C; 35 C; 45 C; 55 C) on the AZOs degradation efficiency in systems: ZVI/PS/AZOs (conditions: CZVI= 0.5 g/L; CPS= 1.0 mM; CAZOs= 0.1 mM; pH= 4.5) and ZVI/PS/AZOs/UV (conditions: CZVI= 0.5 g/L; CPS= 1.0 mM; CAZOs= 0.1 mM; pH = 4.5; I = 785 Lux;  = 254 nm) are shown in Figure 3.22, Figure 3.23 and Figure 3.24 100.00 80.00 60.00 40.00 20.00 0.00 H(%) H% (ZVI/PS/MO) H% (ZVI/PS/MO/UV) 20 30 40 50 t (C) 60 70 Figure 3.22 Effect of the temperature on the MO decomposition performance in systems: ZVI/PS/MO; ZVI/PS/MO/UV for 20 minutes 100.00 80.00 60.00 40.00 20.00 0.00 H(%) H% (ZVI/PS/AY) H% (ZVI/PS/AY/UV) 20 30 40 50 t (C) 60 70 Figure 3.23 Effect of the temperature on the AY decomposition performance in systems: ZVI/PS/AY; ZVI/PS/AY/UV for 20 minutes 13 100.00 H(%) 80.00 60.00 40.00 H% (ZVI/PS/BT) H% (ZVI/PS/BT/UV) 20.00 0.00 20 30 40 50 t (C) 60 70 Figure 3.24 Effect of the temperature on the BT decomposition performance in systems: ZVI/PS/BT; ZVI/PS/BT/UV for 20 minutes 3.2 Investigation of the kinetic characteristics of the AZOs decomposition process in the activated persulfate system 3.2.1 The kinetic characteristics of AZOs decomposition under without UV condition 3.2.2 The kinetic characteristics of AZOs decomposition under with UV Table 3.6 The temperature effect on the AZOs reaction kinetics in the ZVI/PS/AZOs system and the ZVI/PS/AZOs/UV systems (Conditions: CZVI= 0.5 g/L; CPS= 1.0 mM; CAZOs= 0.1 mM; pH= 4.5; I= 785 Lux; λ = 254 nm) The systems ZVI/PS/MO ZVI/PS/MO/UV ZVI/PS/AY ZVI/PS/AY/UV T (K) Kinetics equations ln(C/C0)=-kbk.t kbk (min-1) R2 298 308 318 328 298 308 318 328 298 308 318 328 298 308 y=-0.0454x y=-0.0782x y=-0.1292x y=-0.1775x y=-0.1122x y=-0.1379x y=-0.1774x y=-0.2181x y=-0.0419x y=-0.0660x y=-0.0973x y=-0.1368x y=-0.0828x y=-0.1065x 0.0454 0.0782 0.1292 0.1775 0.1122 0.1379 0.1774 0.2181 0.0419 0.0660 0.0973 0.1368 0.0828 0.1065 0.9878 0.9896 0.9982 0.9951 0.9925 0.9917 0.9991 0.9965 0.0419 0.9804 0.9713 0.9875 0.9906 0.9886 14 The systems T (K) Kinetics equations ln(C/C0)=-kbk.t kbk (min-1) R2 318 y=-0.1292x 0.1292 09883 328 y=-0.1788x 0.1788 0.9946 298 y=-0.0306x 0.0306 0.9977 308 y=-0.0510x 0.0510 0.9795 ZVI/PS/BT 318 y=-0.0682x 0.0682 0.9750 328 y=-0.0875x 0.0875 0.9779 298 y=-0.0558x 0.0558 0.9934 308 y=-0.0776x 0.0776 0.9880 ZVI/PS/BT/UV 318 y=-0.0993x 0.0993 0.9959 328 y=-0.1308x 0.1308 0.9969 The AZOs decomposition reaction of in systems ZVI/PS/AZOs and ZVI/PS/AZOs/UV follows pseudo first order kinetic model, with the quite high correlation (R2) Thus, the pseudo first order kinetic model for the AZOs decomposition in activated persulfate systems under without and with UV is appropriate in the 30-minute survey period 3.2.3 Results of calculating kinetic and thermodynamic parameters according to Arrhenius and Eyring equation for systems: ZVI/PS/AZOs and ZVI/PS/AZOs/UV Table 3.7 Activation energy Ea and pre-exponential constant A according to Arrhenius equation for systems: ZVI/PS/AZOs and ZVI/PS/AZOs/UV (Conditions: CZVI= 0.5 g/L; CPS= 1.0 mM; CAZOs= 0.1 mM; pH= 4.5; I = 785 Lux; λ = 254 nm) Systems T(K) lnkbk=f(1/T) R2 Ea(kJ/mol) A 298 308 y=ZVI/PS/MO 0.9925 37.4 e7.9 318 47500.1x+7.9 328 298 308 y=ZVI/PS/MO/UV 0.9975 18.2 e1.1 2193.8x+1.1 318 328 298 308 y=ZVI/PS/AY 0.9987 32.0 e5.7 3853.8x+5.7 318 328 ZVI/PS/AY/UV 298 y=0.9856 20.2 e1.6 15 T(K) lnkbk=f(1/T) R2 Ea(kJ/mol) A 308 2440.3x+1.6 318 328 298 308 y=ZVI/PS/BT 0.9781 28.0 e3.8 3379.3x+3.8 318 328 298 308 y=ZVI/PS/BT/UV 0.9982 22.7 e2.2 2740.8x+2.2 318 328 Table 3.8 Results of calculating H#, S# and G# according to Eyring equation in the systems: ZVI/PS/AZOs and ZVI/PS/AZOs/UV (conditions: CZVI= 0.5 g/L; CPS= 1.0 mM; CAZOs= 0.1 mM; pH= 4.5; I= 785 Lux; λ= 254 nm) Systems Systems ZVI/PS/MO ZVI/PS/MO/UV ZVI/PS/AY ZVI/PS/AY/UV ZVI/PS/BT T(K) 298 308 318 328 298 308 318 328 298 308 318 328 298 308 318 328 298 308 318 328 H (kJ/mol) S (J/mol.K) G# (kJ/mol) 34.816 -187.55 90.705 15.641 -244.74 88.574 29.442 -206.39 90.946 17.691 -240.42 89.337 25.497 -221.86 91.613 16 Systems T(K) H (kJ/mol) S (J/mol.K) G# (kJ/mol) 298 308 ZVI/PS/BT/UV 20.189 -235.11 90.251 318 328 3.3 Research to determine free radicals OH and SO4 in the activated persulfate systems by ZVI without UV and with UV 3.3.1 Qualitative study of free radicals OH and SO4 in the ZVI/PS/AZOs system In experiments with molar proportions of organic substances in the systems following: [AZOs]: [ETA] = 1: 1000; [AZOs]: [TBA] = 1: 1000 The amount of ETA, TBA is very large compared to AZOs to ensure that free radicals will interact immediately with these substances In these systems, monitoring the decline in concentration [AZOs] over time to assess the presence of free radicals OH and SO4 The AZOs concentration reduction in reaction systems in the following order: 1.ZVI/PS/AZOs > 2.ZVI/PS/AZOs + BTA > 3.ZVI/PS/AZOs + ETA > AZOs According to these results, they can confirm that the activated persulfate system by ZVI has produced in-situ free radicals OH and SO4 to decompose organic substances in the system These results are also consistent with the research of Buxton and his colleagues using nitrobenzene, hexacloethane to distinguish the presence of OH and SO4 3.3.2 Studying on quantification of free radicals OH, SO4 in the activated persulfate systems by ZVI without and with UV 3.3.3.1 Building mathematical model to quantify free radicals OH and SO4 in the activated persulfate systems by ZVI without and with UV 3.3.2.2 The approximate quantification results of free radicals OH, SO4 in the activated persulfate systems by ZVI without and with UV 17 Table 3.10 The calculation results of [SO4], [OH] in reaction systems: ZVI/PS/AZOs and ZVI/PS/AZOs/UV (conditions: CZVI= 0.5 g/L; CPS= 1.0 mM; CAZOs= 0.1 mM; pH= 4.5; I= 785 Lux; λ= 254 nm) Systems t(min) [SO4] mM [OH] mM ZVI/PS/MO ZVI/PS/MO/UV ZVI/PS/AY ZVI/PS/AY/UV ZVI/PS/BT ZVI/PS/BT/UV 10 1.01.10-3 2.28.10-7 20 9.11.10-4 4.67.10-7 30 8.91.10-4 5.38.10-7 10 9.58.10-4 3.11.10-6 20 8.45.10-4 4.97.10-6 30 8.05.10-4 6.55.10-6 10 1.02.10-3 2.11.10-7 20 9.59.10-4 3.58.10-7 30 9.41.10-4 4.12.10-7 10 9.64.10-4 3.58.10-7 20 8.93.10-4 6.47.10-7 30 8.58.10-4 8.10.10-7 20 1.02.10-3 5.21.10-6 30 8.91.10-4 5.61.10-7 20 9.01.10-4 6.32.10-7 30 8.52.10-4 8.57.10-7 The pseudo first-order kinetic model is suitable for decomposition of AZOs in activated persulfate systems by ZVI under condition without and with UV The mathematical model has allowed determining the concentration of free radicals OH, SO4 and rate constant k17, k18 between free radicals OH, SO4 and AZOs These values reflect the correctness of the experimental results Thus, this mathematical model is also suitable for these studies 3.4 Calculating some quantum structural parameters and proposing MO, AY and BT decomposition mechanism in the activated persulfate system 3.4.1 Some structural parameters and ability of decomposing AZOs 18 Using Hyperchem 8.0 software to optimize molecular structure and calculating some quantum parameters: Charge density on atoms of the MO, AY and BT molecules and energy values of these molecules 3.4.2 The estimated mechanism of the AZOs decomposing in activated persulfate systems Based on the calculation results of quantum parameters of MO, AY, BT molecules and characteristics of free radicals OH, SO4 proposed the AZOs (MO, AY and BT) decomposition mechanism following stages: (I) Free radicals OH, SO4 attack on locations with high electronic density on the surface of AZOs molecules forming complexes: OH attacks on carbon position in the benzene ring with the high electronic density and separates H atoms in the CH bond to form COH on the benzene ring; the bond of azo functional groups with benzene rings is broken by radicals OH, SO4; (II) Intermediate complexes are decomposed into simple molecules that are stable in the form of benzene derivatives; (III) Free radicals bond with the intermediate derivatives of benzene to form the unstable complexes; (IV) The unstable complexes are oxidized into carboxylic acids, derivatives of carboxylic acids; (V) Carboxylic acids and their derivatives are oxidized by radicals  OH, SO4 into inorganic substances 19 + The expected MO decomposition mechanism: O S N H3C O N N HO* ; SO4 * CH3 SO4 * HO* O S O O N H3C O (I) N HO * N SO4 * CH3 O O S HO O N H SO3 O + H3C N + + N O OH + SO4 * + HO* S HO H N O O N HO* SO3 O H3C CH3 HO* O OH SO4 * O S HO N (II) SO4 * HO* HO* SO4 * O O3S CH3 SO4 * HO* S HO O (III) O3S SO4 * HOOC-(CH2)4-(NH)2-COOH + HO*, SO4 * HOOC-(CH2)4-COOH + H2N-COOH (IV) + HO*, SO4 * CO2 + H2 O + NO3 + SO24 (V) Figure 3.41 Diagram of the expected MO decomposition mechanism 20 + The expected AY decomposition mechanism: OH N COO N O2N + HO*; SO4 * SO4 * OH HO* N (I) COO N HO* O2N SO4 * OH N (II) NH + O2N SO3 HO* OH O2N N COO + HO COO + HO*; SO4 * + HO*; SO4 * + HO ; SO4 * HO* OH OH HO* OH OH (III) NH SO3 SO4 * HOOC-(CH2)4-(NH)2-COOH + HO* SO4 * HO COO SO4 * HOOC-(CH2)4-COOH COO SO4 * (IV) + HO*; SO4 * CO2 + H2 O + NO3 + SO24 Figure 3.42 Diagram of the expected AY decomposition mechanism (V) 21 + The expected BT decomposition mechanism: NO2 N OH N SO3 HO + HO*; SO4 * HO * NO2 HO* SO4 * N OH (I) N SO4 * SO3 HO OH HO + HO N HO NO2 HO SO3 + NH HO SO3 HO NO2 (II) SO3 OH + HO *;SO4 * + HO*; SO4 * + HO*; SO4 * OH HO* HO N NO2 HO SO4 * HO HO* SO3 HO* HO SO4 * NH SO3 HO HO NO2 (III) SO4 SO3 OH HOOC-CH2-CH2-(NH)2-COOH + COOH + HOOC-CH2-CH2-CH2-COOH HOOC-CH2-CH2-CH-COOH (IV) OH + HO*; SO4 * CO2 + H2 O + NO3 + SO4 Figure 3.43 Diagram of the expected BT decomposition mechanism (V) 22 3.5 Application of the activated persulfate system with UV to treat azo-contaminated wastewater from some textile dye villages Table 3.14 Results of pre- and post-treatment analysis of the textile dye village’s wastewater: Duong Noi, La Phu and Van Phuc Wastewater Characte ristics unit QCVN40:2011/ BTNMT Pretreat Posttreat A B Color Pt/Co 50 150 1860 75 Duong Noi, COD mg/l 75 150 1020 130 after 2h pH 6-9 5.5-9 7.9 5,5 treatment TDS mg/L 551 28 Color Pt/Co 50 150 395 22 La Phu, COD mg/l 75 150 440 110 after 1h pH 6-9 5.5-9 7.6 5.0 treatment TDS mg/L 462 24.7 Color Pt/Co 50 150 5662 55 Van Phuc, COD mg/l 75 150 2900 140 after 3h pH 6-9 5.5-9 6.2 4.8 treatment TDS mg/L 1317 39.5 The application of ZVI/PS/wastewater/UV system for the textile dyeing wastewater treatment in this study compares with some other results of wastewater treatment of the textile dyeing villages as Fenton - electrochemical, Fenton, Catalyst-oxidation in other documents, this ZVI/PS/wastewater/UV system gives the best results in COD reduction Following these results, the ZVI/PS/wastewater/UV system has great potential in the application of organic pollution treatment in water environment CONCLUSION * The thesis has solved the following issues: Studying on activated persulfate by chemical method was carried out based on the results of comparing the AZOs decomposition efficiency of systems without UV (ZVI/AZOs, PS/AZOs, ZVI/PS/AZOs) and with UV (ZVI/AZOs/UV, PS/AZOs/UV, ZVI/PS/AZOs/UV) Research results have indicated that for activated persulfate systems by ZVI, UV produced a dual oxidation system of free radicals (OH, SO4) These free radicals decompose strongly AZOs in the water samples Systems of ZVI/PS/AZOs and ZVI/PS/AZOs/UV have the best AZOs decomposition performance: 23 + The ZVI/PS/AZOs system: after reaction time of 30 minutes HMO= 73.65 %; HAY= 71.42 %; HBT= 58.94 % + The ZVI/PS/AZOs/UV system: after reaction time of 30 minutes HMO,UV= 95.89 %; HAY,UV= 90.99 %; HBT,UV= 79.85 % Studying the effect factors (ZVI, PS, AZOs, pH and temperature) on the activated persulfate systems by ZVI without UV and with UV (ZVI/PS/AZOs and ZVI/PS/AZOs/UV) was performed in detail Research results of effect factors have shown optimal conditions to decompose AZOs best in the ZVI/PS/AZOs and ZVI/PS/AZOs/UV systems are: [ZVI]= 0.5 g/L; [PS]= 3.0 mM; [AZOs] = 0.05 mM; pH = 2.54.5; t = 55 C Studying the AZOs decomposition kinetics in the activated persulfate systems by ZVI without and with UV was carried out Research results have indicated that the AZOs decomposition in the ZVI/PS/AZOs and ZVI/PS/AZOs/UV systems follows the rules of the pseudo first order reaction kinetics These are based on the graph ln(C/C0)= f(t) to calculate the pseudo first order rate constants: The ZVI/PS/AZOs system (kMO= 0.0454 minutes-1; kAY= 0.0419 minutes-1; kBT=0.0306 minutes-1) and ZVI/PS/AZOs/UV system (kMO,UV= 0.1122 minutes-1; kAY,UV= 0.0828 minutes-1; kBT,UV= 0.0558 minutes-1) Calculating thermodynamic parameters for the AZOs decomposition reaction in systems includes ZVI/PS/AZOs and ZVI/PS/AZOs/UV according to Arrhenius equation as Ea,MO= 37.413 kJ/mole; Ea,AY= 32.040 kJ/mole; Ea,BT= 28.095 kJ/mole; Ea,MO,UV= 18.239 kJ/mole; Ea,AY,UV= 20.288 kJ/mole; Ea,AY,UV= 22.787 kJ/mol According to Eyring equation, free activation energy as G#MO = 90.705 kJ/mole; G#AY= 90.946 kJ/mole; G#BT= 91.613 kJ/mole; G#MO,UV = 88.574 kJ/mole; G#AY,UV= 89.377 kJ/mole; G#BT,UV= 90.251 kJ/mol Calculation results and analysis of thermodynamic parameters show that the Eyring model is more suitable than Arrhenius in this study Studying the qualitative determination of free radicals SO4,  OH was based on the difference of the reaction between free radicals SO4, OH with ETA and BTA The results indicate that there are two free radicals SO4, OH in the ZVI/PS/AZOs system The mathematical model has been established to determine the concentration of free radicals SO4, OH and the reaction rate constants of reaction between free radicals OH, SO4 and AZOs (k17(HO,AZOs), k18(SO4,AZOs)) in systems: ZVI/PS/AZOs and 24 ZVI/PS/AZOs/UV Calculation results are quite consistent with the experimental decomposition efficiency of AZOs and the kinetics model of the pseudo first order reaction Calculating quantum parameters, molecular structure of MO, AY and BT by HyperChem software It is based on the characteristics of AZOs molecular structure and free radicals SO4, OH, that has proposed the mechanism of the AZOs mineralization decomposition of MO, AY and BT according to the five stages in systems: ZVI/PS/AZOs and ZVI/PS/AZOs/UV Application of the activated persulfate system by ZVI with UV (ZVI/PS/wastewater/UV) to treat textile dyeing wastewater of La Phu, Duong Noi and Van Phuc villages through COD and color reduction was carried out The COD results are quite good compared to previous studies * New contributions of the thesis: The thesis has built method of activating persulfate by ZVI combined with UV to decompose some azo dyes MO, AY and BT in water The thesis has provided a pseudo first order reaction kinetic model and calculated some thermodynamic parameters of the AZOs decomposition in the ZVI/PS/AZOs and ZVI/PS/AZOs/UV systems * Further research directions: Study and experiment with other methods to determine free radicals OH, SO4 to compare with the quantitative mathematical models as presented in this thesis Study to clarify intermediate products during the AZOs mineralization process of AZOs reacting with free radicals OH, SO4 From those results to build a suitable decomposing mechanism of reaction AZOs with OH, SO4 is more explicit Study to compare the AZOs decomposition efficiency by AOPs based persulfate with other AOPs such as: Fenton, Fenton/UV, O3/UV From those researches to evaluate the economic efficiency and to apply for the actual treatment of organic waste water in general and the pollution of azo dyes in particular ... evaluating the decomposition efficiency of AZOs in systems: ZVI/AZOs, PS/AZOs, ZVI/PS/AZOs and ZVI/AZOs /UV, PS/AZOs /UV, ZVI/PS/AZOs /UV The decline of AZOs dye concentration over time is determined by... (ZVI/AZOs /UV, PS/AZOs /UV, ZVI/PS/AZOs /UV) Research results have indicated that for activated persulfate systems by ZVI, UV produced a dual oxidation system of free radicals (OH, SO4) These free radicals... (ZVI/PS/AZOs and ZVI/PS/AZOs /UV) for AZOs decomposition results outperformed the other systems This is confirmed in these systems (ZVI/PS/AZOs; ZVI/PS/AZOs /UV) with the existence of strong oxidizing