Nghiên cứu tổng hợp vật liệu từ tính trên nền graphit việt nam ứng dụng trong xử lý môi trường ô nhiễm màu hữu cơ (congo red) tt tiếng anh

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
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),
1


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 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-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
2


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
3


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 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
4


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 1 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 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
5


the 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 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

6


CHAPTER 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 V EG 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

7

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

8


Figure 3.8. SEM analysis results of (a) precursor NiFe2O4 (b), (c), (d) EG @
NiFe2O4 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).

9


Table 3.1. Compare results of BET analysis
Material SBET (m2/g) Pore radius (Å) Pore volume (cm3/g)
Graphit
6,5
12,6
0,007
EG microwave
147,5
14,0
0,153
EG furnace

100,9

12,6

0,106

3.2.2.2. Specific surface analysis BET EG@MFe2O4
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

EG@CoFe2O4
EG@NiFe2O4

SBET
(m2/g)
29,1
22,7

Pore radius
(nm)
14,3
17,3

Pore volume
(cm3/g)
0,132
0,136

EG@MnFe2O4

33,0

14,1

0,130

Material

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)
2892,7
1712,4
1639,2
1511,9
1415,4
1191,7

Link

Functional group, compound

-CH, CH2, CH3
C=O, -CHO

Ankan
Andehit và xeton
Andehite and ketones, acids, amides,
C=O, -C=O, H-O-H
water
C=C, -N-H
Aromatic group, amide
C-C
Aromatic group

OH group (of alcohol and phenol),
C-O, C-N
an aromatic amine group
10


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 3 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 / 2 to the satellite top
is 8.1 eV, which characterizes the Fe3+ cations in accordance with the

literature. As can be seen, 3 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

0

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 3 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 6 and 4 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 5 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

5

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 quả 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 at different
temperatures indicates that adsorption is a self-occurring process.
3.5.2.3. Results of isothermal adsorption
The regression coefficient (R2) obtained from the Langmuir equation is the
largest (R2> 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) at different temperatures
proves that the adsorption process is a self-occurring process.
3.5.3.3. Results of isothermal adsorption
The regression coefficient (R2) of the largest Langmuir model (R2>
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 <0).
- Isothermal adsorption of EG@MFe2O4 material according to the
Langmuir model. The adsorption process is advantageous (0Moreover, this shows that adsorption occurs mainly in monolayer
adsorption.
- Assessing the reusability of EG@MFe2O4 materials in color adsorption:
EG@MFe2O4 materials are quite stable after each test run. The material can
be reused at least 4 times.
- Regarding the CR color adsorption mechanism of EG@MFe2O4 material,
it is mainly because the functional groups on the surface of the material
interact the binding forces on the structural components of the CR molecule
leading to improved ability adsorption.
Request
In order for the results of the synthesis of magnetic materials
EG@MFe2O4 (M = Co, Mn, Ni) can be widely applied in environmental
pollution treatment, the study needs to continue studying the ability to absorb
pollution. Water contains other highly toxic pigments such as rhodamine B,
orange G, methyl red. In addition, it can be combined with businesses to build
the EG@MFe2O4 magnetic nano production model on a large scale.
NEW CONTRIBUTIONS OF THE THESIS
1.
The thesis has successfully synthesized 03 magnetic expansion
graphite materials (EG@CoFe2O4, EG@NiFe2O4, EG@MnFe2O4) by solgel method, these are materials made based on graphite source. Vietnamese

flakes form with materials contaminated in the water environment
contaminated with dyes and contaminated with oil.
2.
The dissertation has built a complete database of typical
properties of exfoliating Graphite (EG) and exfoliated magnetic graphite
(EG@CoFe2O4, EG@NiFe2O4, EG@MnFe2O4) by modern analytical tool
methods: SEM, XRD, EDS, FT-IR, XPS, VSM, BET.
23