MINISTRY OF EDUCATION AND TRAINING VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY SCIENCE AND TECHNOLOGY …… ….***………… PHAM VAN THINH SYNTHESIS OF MAGNETIC MATERIALS ON GRAPHITE VIETNAM APPLICATION IN ENVIRONMENTAL TREATMENT OF ORGANIC POLLUTION (CONGO RED) Major: Polymeric And Composite Materials Code: 9440125 SUMMARY OF POLYMERIC AND COMPOSITE MATERIALS DOCTORAL THESIS Ha Noi – 2019 The work was completed at Graduate University Science And Technology - Vietnam Academy of Science And Technology Science instructor 1: Associate Professor Ph.D Bach Long Giang Science instructor 2: Associate Professor Ph.D Le Thi Hong Nhan Reviewer 1: … Reviewer 2: … Reviewer 3: … The dissertation will be defended in front of the Ph.D Thesis, meeting at the Academy Of Science And Technology - Graduate University Science And Technology - Vietnam at… hours ’, day … month … year 201… The dissertation can be found at: - Library of Graduate University Science And Technology - Vietnam National Library PREAMBLE The urgency of the thesis The current, Environmental pollution issues such as textile color pollution, Dyeing are becoming an urgent issue in Vietnam as well as in the world It directly affects the lives, health, and activities of the people The methods of handling color pollution are very diverse However, they still exist certain limitations such as low efficiency, Complex operation, creating environmental unfriendly byproducts that limit their potential Based on the very good properties of magnetic materials, the thesis aims to use this hybrid material for the environmental treatment process of toxic organic pigments Focus on synthesizing magnetic materials (EG @ MFe2O4) of Ni, Co, and Mn metals to enhance adsorption capacity with exfoliated graphite EG @ MFe2O4 material is used to adsorb dye pollution (CR) In particular, the research results focus on evaluating and analyzing optimal adsorption parameters, kinetics, thermodynamics, adsorption isotherms, adsorption mechanism, and material recycling ability Research objectives of the thesis Researching and developing technology for producing magnetic graphite materials from Vietnamese flake graphite sources as materials to be applied in treating the organic polluted environment The main research content of the thesis - Researching and synthesizing exfoliating graphite (EG) material from graphite source in Yen Bai province, Viet Nam by the chemical method under microwave support - Research on the synthesized process of magnetic bearing EG-MFe2O4 (M = Co, Ni, Mn) from graphite materials by the sol-gel method - Analyze and identify some typical properties, structure, morphology and magnetism of EG and EG-MFe2O4 materials by modern analytical tool methods such as: X-ray diffraction spectroscopy (XRD), X-ray energy scattering spectroscopy (EDS), scanning electron microscopy (SEM), infrared spectral analysis (FTIR), vibration magnetometer (VSM) analysis, lines Adsorption / desorption curve N2 (BET, pore), XPS - Research and evaluate Congo red color adsorption capacity of EGMFe2O4 materials; kinetic studies, thermodynamics, adsorption isotherms, adsorption mechanisms and application of RSM surface response methods to optimize color adsorption conditions of materials CHAPTER OVERVIEW Graphite source material Graphite, also known as graphite, is one of the three polymorphs of carbon that exists in nature (diamonds, amorphous coal, and graphite) Graphite is a crystalline substance in the hexagonal system In the crystal lattice, a carbon atom (C) linked to C atoms is adjacent to the distance with different C atoms (about 1.42 Å), and the distance to the 4th atom is 3,35 Å Currently, the worldwide graphite ore reserves are not specifically listed, however, it is estimated at 390 thousand tons In Vietnam, according to geological exploration reports, graphite is found in Lao Cai, Yen Bai and Quang Ngai with total resources and reserves of 29,000 tons 1.2.4 Overview of material manufacturing methods exfoliated graphite (EG) The creation of EG materials is usually done by rapid heating of the interleaved compound, which can be carried out by various heating systems including induction plasma, laser irradiation, and flame heating In 1983, Inagaki and Muranmatsu introduced an EG-making method that does not use acids, but uses and decomposes tertiary compounds potassium-graphitetetrahydrofuran and has investigated several applications based on this new material In 1985, author S.A Alfer et al Investigated the high temperature physical and chemical properties of anodized graphite oxidation products in solid H2SO4 as a raw material to produce a new form of graphite - thermally excreted graphite (TEG) and fabricated products The word TEG has been widely used In 1991, Y Kuga and colleagues studied a method of crushing graphite compounds alternating with potassium K-GIC and exfoliating graphite KEG in a vacuum In 1991, Yoshida and colleagues also successfully researched in the production of various insertion compounds such as insertion with H2SO4, FeCl3, Na-tetrahydrofuran (THF), K-THF and CoTHF The interleaved compounds were then rapidly heated to 1000 0C to expand the graphite In summary, through the analysis of the research results of the authors who came before the thesis, we will choose the method of synthesizing EG materials by chemical methods with the insertion agent of H2SO4 and H2O2 under the support of microwaves Civil, in order to combine the good criteria such as simple method, low cost, and high adsorption efficiency At the same time under the microwave support to shorten the synthesis time as well as improve the efflux efficiency of graphite 1.3 Magnetic materials 1.3.1 Synthesis of EG@MFe2O4 materials Cobalt ferrite, nickel ferrite, and manganese ferrite are very important spinel ferrite in engineering Structurally, cobalt ferrite and nickel ferrite crystals are typical of spinel ferrite group, face centered cubic structure They are the reverse spine, Because the electron configuration of Ni2+ ions is 3d8, of Co2+ ion, is 3d7, the favorable coordination number is 6, so Ni2+ and Co2+ ions are in octahedral holes and Fe3+ ions are distributed in both octahedral and tetrahedral holes There are two approaches to synthesizing spine ferritic material: the approach from the top and the bottom The top-down approach uses physical methods, while the bottom-up approach is usually done by chemical pathways Methods of synthesis by chemical colloid can control the particle size, the collected nanoparticles have uniform size, rich shape Typical chemical methods commonly used include precipitation, reduction, explosion, thermal decomposition hot spray, micelles (reverse), sol-gel process, flocculation directly in high boiling solvents, hydro heat The division into the above methods is based on the mechanisms and conditions for conducting the particle formation reaction including germination stage and size growth Nowadays, based on chemical methods, we can create homogeneous materials with various sizes and shapes Based on the analysis, comparison of advantages and disadvantages of the above synthesis methods, the sol-gel method is an effective method to create many types of nanopowders with the desired structure and composition, Simple method, low cost and high efficiency This is also the basis for the thesis to choose the method of synthesizing magnetic materials based on EG CHAPTER EXPERIMENTAL 2.1 Materials, chemicals, laboratory and analytical equipment 2.1.1 Materials, chemicals Graphite is provided by the Institute of Materials Science, Vietnam Academy of Science And Technology, The chemicals are supplied from Chemsol, Xilong, Guangzhou brands with high quality and suitable for chemical synthesis and analysis purposes 2.1.2 Analytical equipment The structure and properties of EG and EG @ MFe2O4 are carried out on laboratory equipment as follows: Analysis of surface structure and shape of materials by scanning the Scanning Electron Microscope (SEM) method with a magnification of 7000, using accelerating voltage source (15 kV) Analyze the structure and spatial characteristics of materials by X-ray Diffraction (XRD) with an acceleration voltage of 40 kV, current of 40 mA, Cu – Kα radiation (using Ni filter), the scan speed of 0.03o2θ / 0.2s Analysis of specific surface area (BET) and pore distribution of materials by BET adsorption method according to N2 at 77 K Analyze the composition of elements present in the material by means of EDX (Energy diffraction spectroscopy) or EDS Voltage: 15.0 kV, counting speed: 1263 cps, energy range: - 20 kEv Magnetic analysis of EG @ MFe2O4 materials through the GMW Magnet systems electromagnet vibratory sample magnetometer, by measuring the magnetization curve on the PPMS 6000 system with a very small magnetic measurement step (0.2 Oe) in the polar magnetic area This is 300 Oe Analysis of functional groups, identification of organic compounds and structural studies by FT-IR method Analysis of basic components, chemical state, the electronic status of elements on the surface of EG @ MFe2O4 materials by XPS (X-ray Photoelectron Spectroscopy) method on Kratos AXIS Supra (Kratos - Shimadzu) Model: AXIS Supra uses Mg Kα radiation 2.2 Synthesis of EG materials and EG @ MFe2O4 2.2.1 Synthetic EG materials The process of synthesizing EG materials is as follows Weigh g of graphite into a 250 ml glass beaker, suck the determined volume of H 2O2 and H2SO4 with the volume ratio of H2O2 / H2SO4 surveyed as (1,0 / 20; 1,2 / 20; 1,4 / 20; 1.6 / 20; 1.8 / 20 and 2.0 / 20), insertion time ranges from 70 to 120 minutes at room temperature After obtaining the viscous product, the mixture was washed with distilled water to the surveyed pH (from to 6), dried, dried, and dried at 80 ° C for 24 hours EG is obtained by expanding the heat in the microwave at a survey power (from 180 to 900 W) for a survey period of 10 to 60 seconds EG is then measured using a graduated volume measuring cylinder Factors affecting the expansion of graphite were investigated: Investigate the effect of the volume ratio of H2O2 / H2SO4, the effect of insertion time, the effect of pH, the effect of microwave power, the effect of heating time in the microwave 2.2.2 Synthesis of EG materials @ MFe2O4 Weigh M (NO3)2.6H2O and Fe(NO3)3.9H2O in a molar ratio of 1: (with M = Co, Ni, Mn) into Becher 250 mL containing 150 mL H2O mix well with a glass rod The mixture is stirred on the stove to a temperature of 90 ° C, then the citric acid as a complexing agent (number of moles of acid/number of moles of Fe3+/M is 3:2:1) with a rate of drop/sec Maintain the temperature at 90 ° C, stir for h Then adjust the pH with NH4OH.H2O solution so that pH8-9 After 30 minutes, adjust the pH a second time until you see a scum appear on the surface in the reaction vessel, weigh the EG mass (EG / MFe2O4 mass ratio 3: 1) slowly and gently stir until EG no longer pushes to the surface for 10 minutes The gel was finally dried at 80 ° C for 20 h to dry completely Afterward, the sample is heated in a Muffle furnace at 600 oC for hour, with a heating speed of 10 °C / minute 2.3 Evaluate the characteristic properties of EG and EG @ MFe 2O4 materials 2.3.1 Methods of measuring specific volumes of EG materials Weigh 0,2 g EG into the 50 ml measuring cylinder (diameter 20 mm) and gently shake the material evenly distributed in the cylinder, recording the volume (VEG) of the material in the cylinder Expansion coefficient (Kv), calculated by the following formula: Kv = Vt/V0 In which: Vt is the specific volume of material at the temperature of heat shock T (cm3/g); Vo is the initial specific volume of material (1.6 cm3 / g) 2.3.2 Identify the characteristic properties of EG and EG@MFe2O4 materials The structure and properties of EG and EG@MFe2O4 are performed on laboratory equipment such as SEM, XRD, BET, XPS, EDX, VSM 2.4 Evaluation of CR color adsorption capacity of EG@MFe2O4 material - The study will conduct experiments: Surveying the effect of time and concentration, examining the effect of solution pH - Optimize congo red color adsorption capacity of EG and EG@MFe2O4 materials by surface response method - Investigation of kinetics, thermodynamics, adsorption isotherms, reusability of materials, the Proposed adsorption mechanism CHAPTER RESULTS AND DISCUSSION 3.1 The result of EG material synthesis with the help of microwaves  Research results of the effect of H2O2 / H2SO4 volume insertion ratio on the expansion of EG material: The maximum insertion volume observed when H2O2 / H2SO4 volume ratio is 1,4 / 20; The expansion volume corresponds to 131,7 mL / g corresponding to the expansion coefficient Kv = 82,3  Research results of the effect of the insertion time to the expansion of EG material: The expansion ability of the graphite material The insertion time of H2O2 / H2SO4 is 100 minutes, the expansion volume of graphite is the largest, medium average after experiments Kv = 105.2 and decrease with increasing time of insertion to 110, 120 minutes  Research results of the effect of pH on the expansion of EG material: Graphite samples at pH3, the expansion is highest with the VEG volume of 191.7 mL/g and coefficient Kv = 119.8 When washing the material mixture to a pH value > 3, the resulting EG volume tends to decrease on average VEG = 151.7 mL / g, with a coefficient Kv = 94.8 (at pH6)  Research results of the influence of microwave power on the expansion of EG material: The coefficient of volumetric expansion increases steadily and reaches a maximum at 720 W With V EG of 196.7 correspondings to Kv reaches 122, When the furnace capacity was increased to 900 W, the coefficient of volume expansion was reduced, Kv = 103.1 Research results of the effect of microwave time on the expansion of EG material: With the microwave time of 30 seconds, the volumetric expansion of graphite is the largest Average after experiments Kv = 102.1 and decrease with increasing microwave time to 50, 60 seconds, corresponding to the expansion coefficient of materials Kv = 67.7 and 60.4 3.2 Result of analyzing properties of EG material and EG @ MFe2O4 material (M = Co, Mn, Ni) 3.2.1 SEM analysis results 3.2.1.1 SEM analysis results of EG material The results of SEM analysis show that the expanded graphite has many large pores inside, has a deep shape with many folds, sharp twists and the expansion volume increases significantly, with many wrinkles (Figure 3.6) Figure 3.6 SEM analysis results of EG material 3.2.1 Analysis of SEM surface structure of EG @ MFe2O4 material 1064,5 524,5 C-N Fe-O The aliphatic amine group MFe2O4 3.2.3.2 FT-IR analysis of EG material @ MFe2O4 Figure 3.12 FT-IR analysis diagram of EG and EG @ MFe2O4 materials Through FT-IR analysis results in Figure 3.12, EG@MFe2O4 materials still have the same functional groups as on EG materials, proving that the process of inserting precursor materials MFe2O4 did not affect much to bonding, functional groups on EG materials Specific results are shown in Table 3.3 and figure 3.12 3.2.4 Phân tích XRD 3.2.4.1 XRD analysis of EG material The X-ray diffraction diagram of EG expands the phase structure to a peak d002 at 2Ө = 26.89 degrees with an intensity much lower than that of the original graphite This is explained by the process of removing layers of graphite along the C-axis in EG manufacturing, significantly reducing the crystal structure in graphite As a result, the peak d 002 of EG is lower than the peak d002 of the original graphite (Figure 3.13) 11 Figure 3.13 XRD diagram of (a) Graphite, (b) EG 3.2.4.2 XRD analysis of EG@MFe2O4 material In general, XRD schemes for EG @ MFe2O4 materials (M = Co, Ni, and Mn) corresponding to Figures 3.14 (a, b and c) all show the characteristic vertices of the group of above materials However, when looking at the EG @ MFe2O4 diagram, we found that the intensity of these peaks is much lower than the precursor diagram of MFe2O4, proving that the precursor material MFe2O4 is not only distributed on the surface of EG material, but it is also distributed in the pore structure and folds of EG Figure 3.14 XRD diagram of a) EG @ CoFe2O4, b) EG @ NiFe2O4 c) EG@MnFe2O4 12 3.2.5 Results of X-ray energy dispersion analysis (EDX) Table 3.5 EDX analysis results of magnetic graphite samples Sample %C %O %Fe %Co %Mn %Ni %Al %Si %S Sum EG@CoFe2O4 89.31 9.47 0.71 0.36 - - 0.07 0.08 - 100 EG@NiFe2O4 89.46 8.37 1.28 - - 0.66 0.11 0.09 0.03 100 EG@MnFe2O4 91.85 5.93 0.76 - 0.65 - 0.54 0.09 0.18 100 3.2.5 Results of energy scattering analysis (XPS) XPS analysis results are shown in Figure 3.15-3.17 In general, among the surveyed factors, peak C1 is measured with high intensity Analysis of XPS C 1s spectrum shows that the peaks corresponding to the energy level of 287.48 eV are of C = O or O-C = O links, the three peaks at the energy level of 288.21; 288.05 and 289.5 eV are linked OC = O, peak at energy level 288.29 eV is C = O link or OC = O, peak at energy level 291.28 eV marks the presence of group CO3, the two peaks at the energy levels of 287.7 and 287.9 eV are of C = O bonds Meanwhile, the typical XPS signals of O 1s are shown in, with peaks corresponding to the associated energy 535,3; 534.28; 533.1; 532.8; 530.0 eV, corresponding to the covalent O, C-O-C, CO / C = O, and O-C bonds In addition, Fe's XPS spectrum is divided into two regions: Fe 2p3/2 and Fe 2p1/2 It is clear that a split energy orbital is found to be 13.5 eV, while the distance from Fe 2p1 / to the satellite top is 8.1 eV, which characterizes the Fe3+ cations in accordance with the literature As can be seen, samples of EG@MFe2O4 materials all have the XPS similarity of the elements C, O, Fe This is entirely consistent and the difference here observed is the intensity and peak signal of the metals Mn, Ni, and Co The 2p Mn spectrum shows two extra levels of spin-orbit separating between 2p 3/2 and 2p 1/2 with their binding energy distances of about 11.8 eV This distance is close to the energy separating the rotational trajectory (~ 11.62 eV) of manganese oxide (II) In particular, a satellite peak appeared at 647 eV, nearly 6.8 eV from the 2p½ state, suggesting the existence of Mn2+ in the structure of EG@MnFe2O4 The detailed chemical 13 binding states of Co are shown Specifically, the two peaks at 781.1 eV and 786.9 eV are assigned to Co 2p3/2, while the two peaks at 797.1 eV and 803.6 eV represent the characteristic signal of Co 2p1/2 Co 2p spectra show that Co exists in 2+ oxidation state because Co3+ cations with low spin can give rise to much weaker satellite features than Co2+ cations with high spins with orbital electrons unmatched treatment Furthermore, the majority of Co2+ cations occupy octahedral sites in the CoFe2O4 lattice The XPS spectrum of Ni 2p3/2 can be divided into two regions with two peaks, respectively, about 855.3 and 862.4 eV, while Ni 2p1/2 appears at two peaks at the signal of 872.9 eV and 880.4 eV 3.2.7 Analysis results of Vibrating Specimen Magne- tometer - VSM The saturation magnetic field (Ms) obtained by EG@CoFe2O4 at room temperature was 32 emu/g, two materials EG@NiFe2O4 and EG@MnFe2O4 with magnetization respectively 14,2 emu/g and 1,5 emu/g 3.2.8 Titration results by Boehm method The results are presented in Table 3.6 Table 3.6 The results determine the functional groups acid, base on the material Sample Amount of functional group (mmol/g) Carboxyl Phenol Lacton Total acids Total base MFe2O4 0 0 EG@CoFe2O4 0,028 0,051 0,039 0,108 0,198 EG@NiFe2O4 0,022 0,052 0,037 0,098 0,196 EG@MFe2O4 0,020 0,044 0,032 0,096 0,156 3.3 Results of the survey on factors affecting the CR color adsorption capacity of EG@MFe2O4 3.3.1 Effect of time and concentration 14 The general trend of the EG@MFe2O4 material group is that the discoloration occurs quickly in the first 30 minutes, then increases slowly and reaches equilibrium The prolongation of adsorption time at subsequent times increases the ability of adsorption significantly The adsorption capacity between magnetically attached peeling graphite materials is based on their adsorption capacity when reaching their equilibrium: EG@CoFe2O4>EG@NiFe2O4>EG@MnFe2O4 (corresponding to 98.60 mg/g, 92, 97 mg/g, 56.72 mg/g) 3.3.2 Effect of solution pH The best pH for CR adsorption is and for EG@MFe2O4 and MFe2O4, respectively 3.3.3 Effect of material mass When increasing the absorbing mass, from 0.3 g/L to 0.5 g/L the increased adsorption capacity proves that the adsorption capacity of EG@ MFe2O4 increases, at dosages greater than 0.6 and 0.7 g/L, the value capacity tends to decrease 3.3.4 FT-IR analysis results of EG@MFe2O4 material after CR adsorption Before the adsorption of congo red color on the surface of the material, there are typical peaks; however, after color adsorption, the two peaks are 1511.9 (of C = C bond in the aromatic ring and 1191.8 cm-1 (of the CO bond in the OH group of alcohols and phenols) has disappeared This may be because, during the color adsorption process, this group of bonding groups has joined with the functional groups in the molecule In addition, after adsorption on EG@CoFe2O4, there is a peak of 1639.2 cm-1 (the characteristic peak of HOH deformation variation of physical adsorption water and C = O in the aldehydes and ketones functional groups), acid Explain the adsorption mechanism 15 Based on FT-IR analysis results, Boehm titration shows that CR color adsorption of EG@MFe2O4 and MFe2O4 materials can be explained by the following adsorption mechanisms EG@MFe2O4 and MFe2O4 materials have more CR adsorption capacity with MFe2O4 This result can be explained by the role of the chemical functional groups on the surface of EG@MFe2O4 As mentioned from the characterization section, EG@MFe2O4 has been shown to contain many functional groups including (carboxylic acid, lactone, phenol, and basic groups), while they cannot be found in MFe2O4 (table 3.6) During adsorption, the presence of functional groups can contribute to the interaction with CR molecules (Figure 3.27) Therefore, CR molecules were captured on the surface of EG@MFe2O4 better than on the surface of MFe2O4 Section 3.3.2 shows that the CR dye adsorption capacity of materials changes when solution pH is changed, which shows that there was strong electrostatic interaction and ion exchange occurred between objects EG@ MFe2O4 material and CR dye molecule At the same time as we know, CR molecules are made up of aromatic, amine (-NH2) and imin (-N = N-) rings while the four functional groups mentioned containing hydrogen-yielding groups (-OH groups, -NH2, -C6H4OH) and hydrogen receiving groups (CHO, N = N, -COO-) Therefore, the type of hydrogen bonding can be formed between CR molecules and functional groups, enhancing adsorption efficiency The interactions n-π (or interactive for-receive electronics n-π) interaction, the carbonyl functional groups on the EG@MFe2O4 surface act 16 as electron donors, and the dye aromatic rings act as an electronic receiver FTIR spectrum of EG@MFe2O4 shows that the C-O peak position changes after adsorption (peak at 1383 cm-1 figure 3.25) The change of C-O peak position after adsorption proves that n-π interactions In addition, EG@MFe2O4 is covered with an outer layer of EG EG is a source of carbonates containing many aromatic rings in the structure As a result, π-π interactions can be formed between aromatic rings of CR molecules and EG layers of EG@MFe2O4 materials, resulting in improved adsorption capacity Figure 3.27 CR adsorption mechanism of EG@MFe2O4 (M = Co, Ni, and Mn) The adsorption of CR compared to MFe2O4 still occurs probably due to the existence of weak forces including metal oxygen-oxygen bridges and van der Waals This research has shown that electron-rich atoms like oxygen can interact with the metal/oxide position to form an intermediate bridge called oxygen-metal oxygen Because these forces are weak, the adsorption of CR of MFe2O4 is negligible 17 3.4 Results of optimizing the adsorption capacity of congo red dyes of EG and EG@MFe2O4 materials by surface response method 3.4.1 The result optimizes congo red color adsorption capacity of EG material The results fit well with the predicted values, showing the reliability of the proposed model (Table 3.11) Table 3.11 Table of CR adsorption results using the optimal conditions on DX11 pH Concentration Time Material (mg/L) (-) (minute) Ability adsorption (mg/g) Expected Guess Reality Error EG 45 190 67,18 66,62 0,56 1,00 3.4.2 The result optimizes the Congo red color adsorption capacity of EG @ MFe2O4 material 3.4.2.1 Results of material optimization EG@CoFe2O4 The results fit well with the predicted values, showing the reliability of the proposed model (Table 3.15) Table 3.15 Table of CR adsorption results using the optimal conditions on DX11 Ability pH Concentration Time adsorption (mg/g) Expected material (-) (mg/L) (minute) Guess Reality Error EG@CoFe2O4 6,05 58,20 189 88,60 87,46 1,14 1,00 CoFe2O4 4,1 60,58 186 41,89 42,95 1,06 1,00 3.4.2.2 Material survey results EG@NiFe2O4 The results fit well with the predicted values, showing the reliability of the proposed model (Table 3.19) 18 Table 3.19 Table of CR adsorption results using the optimal conditions on DX11 Ability pH concentration Time adsorption (mg/g) Expected Material (-) (mg/L) (minute) Guess Reality Error EG@NiFe2O4 6,2 48,25 179 87,85 86,90 0,95 1,00 NiFe2O4 4,0 52,7 188 38,16 37,01 1,15 1,00 3.4.2.3 Surveying materials EG@MnFe2O4 The results fit well with the predicted values, showing the reliability of the proposed model (Table 3.23) Table 3.23 Table of CR adsorption results using the optimal conditions on DX11 Ability pH concentration Time adsorption (mg/g) Expected Material (-) (mg/L) (minute) Guess Reality Error EG@MnFe2O4 5,7 57,7 181 60,6 62,0 1,4 1,00 MnFe2O4 6,0 62,0 182 10,4 11,1 0,7 1,00 3.5 Kinetic results, thermodynamics, isotherms adsorbed 3.5.1 Material survey results EG@CoFe2O4 3.5.1.1 Adsorption kinetic results A quadratic kinematic model can be used to predict the adsorption kinetics because it gives R2 (0.99) better than the first-order kinetics model (0.83) and Q2 of EG@CoFe2O4 materials with a price The value (38.18 - 99.01 mg/L) is greater than the Q2 value of CoFe2O4 material (30.08 - 48.22 mg/L), which demonstrates the ability to adsorb congo red color of EG@ CoFe2O4 material is better than CoFe2O4 material 3.5.1.2 Thermodynamic adsorption results From the Van't Hoff equation with R2 = 0.84, enthalpy, entropy, and Gibbs free energy are determined, positive values of H indicate that the adsorption process is the endothermic process and positive values of S 19 show the good affinity between CR substrate and EG@CoFe2O4 adsorbent Meanwhile, the negative value of G at different temperatures indicates that the adsorption process is a self-occurring process 3.5.1.3 Results of isothermal adsorption The regression coefficient (R2) of the Langmuir model achieved the largest (R2 = 0.99), showing that the model is highly compatible with experimental results In particular, the description for adsorption processes by adsorption models is arranged in the following order: Langmuir> Freundlich> Temkin> R-D The characteristic Langmuir coefficient RL less than 1.0 indicates that the adsorption process is favorable Moreover, this suggests that the adsorption occurs mainly as monolayer adsorption 3.5.2 Material survey results EG@NiFe2O4 3.5.2.1 Kết động học hấp phụ A secondary kinematic model can be used to predict the Q2 adsorption kinetics of EG@NiFe2O4 (37.85 - 93.11) higher than Q2 of NiFe2O4 materials (28.48 - 44.36 ) it shows that the ability to adsorb congo red color of EG@NiFe2O4 material is higher than that of NiFe2O4 material 3.5.2.2 Thermodynamic adsorption results From Vant Hoff's equation with R2>0.9, enthalpy, entropy, and Gibbs free energy are determined, positive values of H (H>0) show that the effect of temperature is very important and adsorption process is the endothermic process, positive value of S (S>0) shows good affinity between CR substrate and EG@NiFe2O4 adsorbent Meanwhile, G 0.96), showing that the model is highly compatible with the experimental results In particular, the description for adsorption processes by adsorption models is arranged in the following order: Langmuir > Freundlich > Temkin > R-D The characteristic Langmuir coefficient RL 20 less than 1.0 indicates that the adsorption process is favorable Moreover, this suggests that the adsorption occurs mainly as monolayer adsorption 3.5.3 Material survey results EG@MnFe2O4 3.5.3.1 Adsorption kinetic results A quadratic kinematic model can be used to predict adsorption kinetics because the value (R2 = 0.99) is better than the first and second kinetic models of EG@MnFe2O4 (29,61 - 57,54) is also higher than the Q2 of MnFe2O4 material (6.34 -18.19) which shows that the capacity of adsorption on congo red color of EG@NiFe2O4 material is higher than that of NiFe2O4 material 3.5.3.2 Thermodynamic adsorption results From Vant Hoff's equation with R2> 0.9, enthalpy, entropy, and Gibbs free energy constants were determined The results shown in Table 3.36 show that the value (ΔH>0) shows that the adsorption process is the endothermic process and (ΔS>0) shows a good affinity between CR substrate and adsorbent EG@MnFe2O4 Meanwhile, (ΔG 0.95) shows that the model is highly compatible with experimental results In particular, the description for adsorption processes by adsorption models is arranged in the following order: Langmuir>Freundlich>Temkin>R-D Where a Langmuir model can be used to describe the CR adsorption by EG@MnFe2O4 and MnFe2O4 on the other hand, the characteristic Langmuir coefficient RL less than 1.0 indicates that the adsorption process is favorable At the same time, this shows that adsorption occurs mainly in monolayer adsorption 3.6 Reusability In the first cycle, the CR decomposition rate of the EG@MFe2O4 sample was 100%, then decreased rapidly and only obtained 8.38%, 13.29%, and 9.46%, respectively, corresponding to EG@CoFe2O4, 21 EG@NiFe2O4, and EG@MnFe2O4 in the 5th experiment Through the analysis above, the material is capable of being reused at least four times CONCLUSIONS AND RECOMMENDATIONS Conclude The study has done the following - Successfully prepared EG material with the support of microwaves with the following conditions: the volume insertion ratio of H2O2/H2SO4 is 1.4/20, the insertion time of 100 minutes, the value pH3, power and microwave time are 720 W and 30 seconds respectively - Research successfully prepared 03 types of materials EG@ CoFe2O4, EG@NiFe2O4, EG@MnFe2O4 by sol-gel method; in which EG@MnFe2O4 material has relatively large pore size (33 m2/g) and has a high magnetization (EG @ CoFe2O4 = 32 emu/g), so the material is convenient for adsorption process and the ability to recover materials after adsorption as well as reuse - Optimize CR color adsorption conditions of EG@MFe2O4 materials (M = Co, Ni, Mn) by surface response method (RSM), in which the conditions are optimal with EG@CoFe2O4 materials : pH6.05, concentration of 58.2 (mg/L), time of 189 minutes and CR adsorption capacity of the material is 87.46 mg/g; EG@NiFe2O4 material: pH6,2, concentration of 48,25 (mg/L), duration of 179 minutes and CR adsorption capacity of the material is 86,90 mg/g; EG@MnFe2O4 material: pH5,7, concentration 57,7 (mg/L), time 181 minutes and CR adsorption capacity of the material is 62 mg/g - Surveying the kinetic process: the adsorption kinetics of EG@ MFe2O4 materials follow the second kinematic model, the adsorption speed can be controlled by chemical adsorption through ion exchange mechanism between adsorbent and adsorbent by chemical sorbent bonds 22 - Thermal process survey: the color adsorption process of EG@MFe2O4 material is the endothermic process (∆H>0), which has a good affinity between CR substrate and EG @ MFe2O4 adsorbent (∆S> 0) ), and the adsorption process is a self-occurring process (∆G