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
Trang 1GRADUATE 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
Trang 2Science instructor 1: Associate Professor Ph.D Bach Long Giang
Science instructor 2: Associate Professor Ph.D Le Thi Hong Nhan
The dissertation can be found at:
- Library of Graduate University Science And Technology
- Vietnam National Library
The work was completed at Graduate University Science And
Technology - Vietnam Academy of Science And Technology
Trang 3PREAMBLE
1 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
2 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
3 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),
Trang 4infrared spectral analysis (FTIR), vibration magnetometer (VSM) analysis, lines Adsorption / desorption curve N2 (BET, pore), XPS
- Research and evaluate Congo red color adsorption capacity of MFe2O4 materials; kinetic studies, thermodynamics, adsorption isotherms, adsorption mechanisms and application of RSM surface response methods
EG-to optimize color adsorption conditions of materials
CHAPTER 1 OVERVIEW
1 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 4 C atoms is adjacent to the distance with
3 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-graphite-tetrahydrofuran 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
Trang 5In 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@MFe 2 O 4 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
Trang 6division 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 2 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: 0 - 20 kEv Magnetic analysis of EG @ MFe2O4 materials through
Trang 7the 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 @ MFe 2 O 4
2.2.1 Synthetic EG materials
The process of synthesizing EG materials is as follows Weigh 1 g of graphite into a 250 ml glass beaker, suck the determined volume of H2O2 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 1 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: 2 (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 1 drop/sec Maintain
Trang 8the temperature at 90 ° C, stir for 1 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 1 hour, with a heating speed of 10 °C / minute
2.3 Evaluate the characteristic properties of EG and EG @ MFe 2 O 4 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@MFe 2 O 4
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
Trang 9CHAPTER 3 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 3 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 VEG of 196.7 correspondings to Kv reaches 122, 9 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 3 experiments Kv = 102.1 and
Trang 10decrease 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 @ MFe 2 O 4 material
Trang 11Figure 3.8 SEM analysis results of (a) precursor NiFe2O4 (b), (c), (d) EG @
NiFe 2 O 4 material EG@MFe2O4 (magnetic graphite) material analyzed on surface morphology through SEM image shows that SEM image of EG@MFe2O4, porous structure and has a lot of depth in and between EG@MFe2O4 Therefore, there is no significant difference between EG and EG@ MFe2O4 showing that ferrite cobalt, manganese, and nickel are evenly distributed on the surface of EG@MFe2O4 (Figure 3.8)
3.2.2 BET specific surface area analysis
3.2.2.1 BET specific surface area analysis of EG material
BET analysis results (Table 3.1) show that after peeling with a microwave, the specific surface area and the pore volume of EG materials increased The surface area of graphite after peeling increased about 23 times that of the original flake graphite (from 6.5 m2/g to 147.5 m2/g) and the pore volume of the material also increased significantly increased (from 0.007 cm3/g to 0.153 cm3/g)
Trang 12Table 3.1 Compare results of BET analysis
Material SBET (m2/g) Pore radius (Å) Pore volume (cm3/g)
EG microwave 147,5 14,0 0,153
3.2.2.2 Specific surface analysis BET EG@MFe 2 O 4
Results of surface area analysis according to BET results and porosity volume of EG @ MFe2O4 are shown in Table 3.2
Bảng 3.2 Diện tích bề mặt riêng theo BET của các vật liệu
Material SBET
(m2/g)
Pore radius (nm)
Pore volume (cm3/g)
3.2.3 FT-IR analysis
3.2.3.1 FT-IR analysis of EG material
Specific results are shown in Table 3.3 So with the above analysis results show that the surface of EG material contains many functional groups as well as many types of chemical bonds convenient for adsorption
Table 3.3 FTIR results of EG and EG@MFe2O4 materials
Frequency
(cm-1) Link Functional group, compound
2892,7 -CH, CH 2 , CH 3 Ankan
1712,4 C=O, -CHO Andehit và xeton
1639,2 C=O, -C=O, H-O-H Andehite and ketones, acids, amides,
water 1511,9 C=C, -N-H Aromatic group, amide
1415,4 C-C Aromatic group
1191,7 C-O, C-N OH group (of alcohol and phenol),
an aromatic amine group
Trang 131064,5 C-N The aliphatic amine group
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 d002 of EG is lower than the peak d002 of the original graphite (Figure 3.13)