Tom tat tieng anh: Nghiên cứu khả năng xử lý DDT và γHCH trên một số kim loại và oxide kim loại mang trên gC3N4 bằng phương pháp phiếm hàm mật độ liên kết chặt.

MINISTRY OF EDUCATION AND TRAINING
HANOI UNIVERSITY OF EDUCATION

PHAM THI BE

STUDY ON THE ABILITY TO PROCESS DDT AND γ-HCH ON
SOME METALS AND METAL OXIDES CARRIED ON g-C3N4 BY
THE DENSITY FUNCTIONAL TIGHT BINDING METHODS

Specialization: Theoretical and Physical Chemistry
Code: 9440119

SUMMARY OF CHEMICAL PhD THESIS

HA NOI – 2022


The thesis was completed at
Department of Chemistry – Hanoi University of Education

SCIENTIFIC INSTRUCTORS:
1. Prof. Dr. Nguyen Ngoc Ha
2. Dr. Nguyen Thi Thu Ha

Review 1: Prof. Dr. Tran Thai Hoa
Review 2: Prof. Dr. Le Thanh Son
Review 3: Prof. Dr. Tran Dai Lam

The thesis will be presented before the Board of thesis review at Hanoi
University of Education on .....h..... day..... month ... year...

The thesis can be found at: National Library, Hanoi or the library of
Hanoi National University of Education


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LIST OF PUBLISHED BY AUTHOR
Phạm Thị Bé (2020), “Nghiên cứu lý thuyết khả năng hấp phụ
Dichlorodiphenyltrichloroethane trên than hoạt tính và than hoạt tính biến tính bởi
sắt bằng phương pháp phiếm hàm mật độ”, Tạp chí khoa học – Trường Đại học
Tây Nguyên, số 45, Tr. 13-19.
Nguyễn Thị Thu Hà, Phạm Thị Bé, Phùng Thị Lan, Nguyễn Thị Mơ, Lê Minh
Cầm và Nguyễn Ngọc Hà (2021), “Whether planar or corrugated graphitic carbon
nitride combined with titanium dioxide exhibits better photocatalytic
performance?”, RSC Advances, (Q1,
SCIE, IF = 3.240).

Nguyễn Thị Thu Hà, Phạm Thị Bé và Nguyễn Ngọc Hà (2021),
“Adsorption of lindane (g-hexachlorocyclohexane) on nickel modified
graphitic carbon nitride: a theoretical study”, RSC Advances,
(Q1, SCIE, IF = 4.046).
Phạm Thị Bé, Nguyễn Thị Thu Hà và Nguyễn Ngọc Hà (2021), “Nghiên
cứu lý thuyết khả năng hấp phụ Dichlorodiphenyltrichloroethane (DDT) trên
Graphitic carbon nitride (g-C3N4) và g-C3N4 biến tính bởi cluster Ni2”, Tạp
chí Xúc tác và Hấp phụ, T10(3), Tr. 106-111.
Nguyễn Thúy Hằng, Phạm Thị Bé, Nguyễn Thị Kim Giang, Nguyễn Hoàng
Hào, Nguyễn Hồng Anh và Nguyễn Thị Thu Hà (2021), “nghiên cứu lý
thuyết khả năng hấp phụ 2,4-dichlorophenoxylacetic trên carbon hoạt tính
biến tính bởi Fe và Ag”, Tạp chí Khoa học và Cơng nghệ B, T63(11DB), Tr.
02-06.
Phạm Thị Bé, Nguyễn Thị Thu Hà và Nguyễn Ngọc Hà (2021), “Nghiên cứu
lý thuyết khả năng hấp phụ Dichlorodiphenyltrichloroethane trên Graphitic
Carbon Nitride biến tính bởi sắt bằng phương pháp phiếm hàm mật độ”, Tạp
chí khoa học – Trường Đại học Tây Nguyên, số 51, Tr. 60-66.
Phạm Thị Bé, Nguyễn Hoàng Hào, Nguyễn Thị Kim Giang, Nguyễn Thị Thu
Hà và Nguyễn Ngọc Hà (2022), “Theoretical insight into the adsorption of
dichlorodiphenyltrichloroethane on titanium dioxide supported on graphitic
carbon nitride”, Russian Journal of Physical Chemistry A: Focus on Chemistry,
DOI: 10.1134/S0036024422100065 (Q4, SCIE, IF = 0.697).
Phạm Thị Bé, Bùi Cơng Trình, Nguyễn Văn Thức, Nguyễn Ngọc Hà và
Nguyễn Thị Thu Hà (2022), “Electronic and optical properties of metal
decorated graphitic carbon nitride M/g-C3N4 (M = K, Ca, Ga, Ni, Cu): a
theoretical study’, Tạp chí Hóa học (review).


1

INTRODUCTION
1. The reason for choosing topic
Environmental pollution caused by chemical agents is always a news
issue, urgent and receives the attention of the whole society. Vietnam is an
agricultural country with a very large area of rice and cash crops, which
means regular use of pesticides and growth stimulants. In addition, in many
provinces and cities in our country, there are many storages of pesticides
that have been seriously degraded. The drainage system at the warehouses
is almost nonexistent, so when heavy rains form a surface stream that
washes away residual pesticides, polluting groundwater, surface water and
soil pollution on a large scale.
Among

the

pesticides

belonging

to

the

POPs

group,

dichlorodiphenyltrichloroethane (DDT) and hexachlorocyclohexane (HCH)
have been widely used in agricultural production in our country as well as in
many other countries around the world. Residues of the these substances in

soil and water are still very high and therefore need to be treated.
Among the methods used to treat POPs, advanced oxidation process
using photocatalyst systems is receiving the attention of scientists.
For the reasons mentioned above, we select the research problem:
Study on the ability to process DDT and γ-HCH on some metals and
metal oxides carried on g-C3N4 by the density functional tight binding
methods.
2. Research objective and tasks
a. Research objective
The objective of this study is use computational chemistry methodsto
study the structute, electronic properties and optical properties of g-C3N4
based photocatalysts; g-C3N4 modified by metals: Me/g-C3N4 (Me = K, Ca,
Ga, Fe, Ni và Cu); g-C3N4 modified by metal oxide MexOy/g-C3N4 (MexOy


2

= ZnO và TiO2); study the ability of adsorption, decomposition and
metabolism of some pesticides belonging to the POPs group (DDT and
HCH) on these material systems; clarify the nature of the interaction
between POPs with metal centers, catalytic metal oxides; predict reaction
directions, preferred reaction products. Thereby contributing to the direction
of the experiment to synthesize highly effective materials in POPs treatment.
b. Research tasks
- Researching domestic and foreign documents, analyzing and
reviewing published research works closely related to the thesis topic,
presenting outstanding issues, thereby pointing out the issues that the thesis
should focus on solving research;
- Studying the theorytical basis of computational chemical methods in
thesis (density functional method GFN2-xTB, CREST method, RP transition

state determination method, dynamic method MD).
- Studying the geometric structure, electronic properties and optical
properties of g-C3N4; g-C3N4 modified by metals: Me/g-C3N4 (Me = K, Ca,
Ga, Fe, Ni và Cu); g-C3N4 modified by metal oxide MexOy/g-C3N4 (MexOy
= ZnO và TiO2);
- Study the adsorption capacity of DDT and HCH on g-C3N4, Me/gC3N4 (Me = Fe, Ni) and TiO2/g-C3N4.
- Study on the degradability of DDT and HCH decomposition under
photocatalytic effect.
3. Scope and object of the study
a. Research object
Research focuses on materials systems based on g-C3N4: g-C3N4
modified by some metals and: g-C3N4 modified by some metals oxides; and
POPs pesticides include: DDT and HCH.
b. Research Scope


3

Study to clarify the molecular nature of interactions between metal
atoms, semiconductor oxide cluster with g-C3N4, to clarify the influence of
g-C3N4 modification on electronic and optical properties. And the
adsorption and degradability of this photocatalyst for pesticides belonging
to the POPs group (DDT, HCH).
4. Scientific and practical significance of the thesis
a. Scientific significance of the thesis
Theoretical calculations used in the thesis will provide necessary
information at the molecular level on the nature of interactions between
metals, semiconductor oxides and g-C3N4, electron structure of material
systems. On the basic of g-C3N4, predicting optical properties such as band
gap value, UV-Vis spectra, ... of Me, MexOy systems carried on g-C3N4.

From there, predict and explain the adsorption and hotocatalytic degradation
of DDT and HCH of these material systems. The obtained results can be
useful references for scientist, graduate student in the field of adsorptioncatalysis, computational chemistry.
b. Practical significance of the thesis
Due to the toxic nature, persistent in the environment, difficult to
biodegrade and chemically and especially dangerous to human health of
DDT and HCH, the study of material systems to decompose these
substances is very important. This has important practical significance.
Besides, with Vietnam participation in the Stockholm Convention and in the
context of widespread use of pesticides in our country, the problem of
handling POPs pesticides should be studied. The obtained results can
provide useful information in the development of adsorption-photocatalytic
technology to treat organic pesticides in the form of POPs.
5. New points of the thesis


4

- The geometrical structures, electronic and optical properties of graphitic
carbon nitride (g-C3N4) in corrugated (cGN) and planar forms (pGN); gC3N4 doped with metals (K, Ca, Ga, Fe, Ni, Cu), and g-C3N4 combined with
semiconductor oxides (ZnO)3, (TiO2)7 were studied;
- The interaction energy, and electronic properties (ionization energy – IP,
electron affinity – EA, global electrophilic index – GEI, fractional occupied
density – FOD, … ) of the studied systems were calculated for clarifying the
influence of the inclusion of metal atoms and metal oxides on the structure
and properties of g-C3N4;
- It has been predicted that Fe/g-C3N4, Ni/g-C3N4, and TiO2/g-C3N4 have the
potential to be used as photocatalysts for the decomposition of DDT and
HCH;
- The adsorption of DDT and HCH on Fe/g-C3N4, Ni/g-C3N4, and TiO2/gC3N4 was studied in detail. The preferred adsorption sites, the structural

parameters of the adsorption configurations, the adsorption energy, as well
as population analysis were determined to figure out the nature of the
adsorption process. It has been shown that the adsorption of DDT and HCH
on modified g-C3N4 material systems is chemical in nature, while the
adsorption process on primitive g-C3N4 is physisorption. The influence of
different solvents (water solvent, ethanol, acetonitrile, and benzene) on the
adsorption process has also been studied;
- The thermal stability of the DDT, HCH adsorption configurations was
evaluated utilizing molecular dynamics method;
- A new mechanism for DDT and HCH decomposition has been proposed.
This mechanism proposes receiving electrons directly from photocatalyst
causes decomposition of DDT, HCH through cleavage of C - Cl bonds.
6. The layout of the thesis
Introducing the reasons for choosing the topic, the purpose, and scope


5

of the research, the new points of the thesis, the scientific and practical
significance of the thesis.
Chapter 1: Introduce the theoretical basis including the problems of
quantum chemical theory.
Chapter 2: Overview of the research system and method of calculation.
Chapter 3: Research results and discussion.
Conclusion: Briefly summarize the results of the thesis.


6

Chapter 1. THEORY BASIS

1.1. Density functional theory
DFT theory calculates electron correlations over electron density
functions. The DFT functions divide the electronenergy into parts that can
each be calculated separately such as: kinetic energy, electron-nuclear
interaction, Coulomb repulsion and some exchange correlations
calculated for the corresponding part. Remaining electron- electron
interaction (which itself is divided into two separate parts, the exchange
energy and the correlation energy).
1.2. GFN-xTB method
GFN-xTB is a semi-empirical tight binding (TB) method for the
calculation of structure, vibrational frequencies and noncovalent
interactions of large molecular systems with 1000 or more atoms. GFN
indicates the design of the approach to yield reasonable geometries,
vibrational Frequencies, and Noncovalent interactions, and “x” stands for
extensions in the AO basic set and the form of the Hamiltonian. In general,
GFN-xTB provides for molecules from the whole periodic table higher
accuracy for the target properties than existing ‘general-purpose’ semiempirical approaches. It is applicable to a wider range of systems and is
computationally and numerically more robust than other schemes with
comparable accuracy.
1.3. Moleculer Dynamic method (MD)
Moleculer Dynamic method are used in chemistry, for example, for
studies of the effect of tamperature on reactions, product stability with
respect to temperature, time, … which cannot be calculated. Directly from
the results of solving the Schrödinger equation. The MD method generally
revolves around the use of Newton’s second law F = ma.


7

1.4. Reaction path Estimates

By default three runs with increasing push/pulling strengths
 -k 2 =  2 - 4  × k1 

at typical values of α = 0.5-1 are conducted. Very tight

optimization thresholds are applied in order to avoid trapping in spurious
geometries. The subsequent incomplete optimizations without the biasing
potential at every point of the path (tylically 30 -200) are limited to 2-4
geometry optimizations steps such as a fall-back to the reactant/product is
prevented. It is recommended that the use checks the resulting path for
chemical reliability.


8

Chương 2. LITERATURE REVIEW
2.1. Dichlorodiphenyltrichloroethane (DDT)
DDT - Dichlorodiphenyltrichloroethane is a very stable and toxic
substance that takes a long time to decompose in the natural environment.
DDT has been used as a miracle drug to kill pests, asimple and cheap
solution to very effectively kill crop pets, contributing to improving
productivity and killing many harmful insects, human diseases such as lice,
mosquitoes, …
2.2. Hexachlorocyclohexane (HCH)
HCH - Hexachlorocyclohexane is toxic to humans and animals and is
also a slow decomposer. HCH is used to kill pests. Weeds, fast effects and
simple reuse.
2.3. Graphitic carbon nitride (g-C3N4)
g-C3N4 has become a hot spot in materials science thanks to its
distinctive electronstructure. With medium band gap energy as well as

thermal stability, and many valuable properties such as: low density,
noncorrosion, impremeability. g-C3N4 has become one of them.
Photocatalyst materials are the most promising and have been studied for
applications in many reactions such as water spitting, pollutant degradation
and CO2 reduction. However, in the pure from g-C3N4 has the disadvantage
of easy recombination of photogenerated electrons and holes, small specific
surface area, and poor photocatalytic ability. Therefore, there have been
many studies on modifying g-C3N4 surface by metal or metal oxide to
overcome this shortcoming.
2.4. Research in the country and in the world
Researches on the application of g-C3N4 in POPs treatment, including


9

DDT and HCH treatment, are still limited, and if any, are maiinly
experimental studies, theoretical studies. Guide for experimental research is
quite limited.
2.5. Method of calculation
All optimization and energy calculations were performed using the semiempirical tight binding based quantum chemistry method (GFN2-xTB). The
preferred site was determinef by classical force firld combined molecular
method – the reaction Path method. Besides, a number of other mrthods are
used in combination to study the thermal stability of the adsorption systems
(molecular dynamics simulation-MD). These methods are all proven methods
suitable for research systems. The results obtained are reliable.


10

Chapter 3. RESULTS AND DISCUSSION

3.1. GEOLOGICAL STRUCTURE, ELECTRON PROPERTIES AND
OPTICAL PROPERTIES OF g-C3N4
3.1.1. Geological structure of g-C3N4

Figure 3.1. Optimized structure of cGN

Figure 3.2. Optimized structure of pGN


11

Table 3.1. The structural parameters of cGN và pGN
Calculated using the GFN2-xTB method
Parameter

cGN

pGN pGN [116]*

d(C-N2), Å 1,323 1,323

1,330

d(C-N1), Å 1,397 1,408

1,460

The structural parameters obtained by the GFN2-xTB method are very close
to the results calculated according to the density functional theory for the
studied system.

3.1.2. Electron properties and optical properties of g-C3N4
Table 3.2. Parameters IP, EA and GEI of cGN và pGN
IP, eV

EA, eV

GEI, eV

cGN

7,0856

2,2618

2,2641

pGN

6,6276

2,1531

2,1539

The IP and EA values of pGN are both lower thn that of cGN. The
GEI values of cGN and pGN are relatively high, and both indicate high
electron acceptability of pGN as well as cGN.

Figure 3.3. HOMO và LUMO of cGN depicted at an isovalue 0,03 e Å-3

12

Figure 3.4. HOMO và LUMO of pGN depicted at an isovalue 0,03 e Å-3
Observing HOMO and LUMO images can lead to the conclusion that
N2 atoms will be chemically more reactive than N1 atoms.
An effective photocatalyst is a material that satisfies the following two
requirements: (1) the recombination rate of h+ and e* is low, (2) h+ and e*
can be generated under visible light irradiation.
Starting from the first requirement, we propose three hypotheses for
the explanation of an effective separation of h+ and e*:
(1-a) The reduction and oxidation sites are located separately to
facilitate photocatalytic reaction;
(1-b) The greater the distance between h+ and e* is, the more efficient
the separation is;
(1-c) The electron density of HOMO (where h+ is formed) as well as
LUMO (where e* is generated) in narrow space results in high densities of
h+ and e*, which would be more effective for the electron transfer process.
Observing the HOMO and LUMO images of cGN and pGN in figure 3.3
and figure 3.4, the HOMO and LUMO of cGN and pGN are distributed in
different spatial rigions and spread over many atoms, resulting in density
photogenerated electrons and holes are quite small. Hower, the
photogenerated electron and hole are far apart resulting in efficient
separation and slow recombination. The same is true for pGN. These


13

structural features, combined with moderate band gap energies, explain the
photocatalytic activity of g-C3N4.

Table 3.3. The parameters of the first excitation of g-C3N4
Excitation
energy (eV)

Oscillator
strength

The amplitude of MO transition

f x 104

cGN

4,235

9,93

pGN

3,841

7,07

0,07 (H-4

0,06 (H-4

0,06 (H-1

 L)

 L+3)

 L+1)

0,11 (H-1

0,08 (H

0,06 (H

L+12)

L+22)

L+15)

Figure 3.5. Molecular orbitals involved in the first excitation of cGN
depicted at an isovalue 0,03 e Å-3

The MOs involved in the first excited states of cGN are distributed in
a narrower space than that of pGN. Athough the excitation energy in the first
excited staten of cGN is large than that of pGN (4.235 eV and 3.841 eV).
But, according to hypothesis (1-c) proposed above: The elecron density of
H as well as L concentrated in the narrow region would be better, so cGN is
predicted to have higher photocatalytic activity than pGN. This result is
completely consistent with previously published studies on the catalytic
activities of cGN and pGN.

14

Figure 3.6. Molecular orbitals involved in the first excitation of pGN
depicted at an isovalue 0,03 e Å-3

cGN

pGN

Hình 3.7. FOD plots of cGN and pGN depicted at an isovalue 0,03 e Å-3
Observing the FOD images of cGN and pGN can once again confirm
that the N2 atoms are more chemically active than the N1 aroms.
3.2. MODIFIED g-C3N4 BY METALS (Me) AND CLUSTER OXIDE
METALS (MexOy)
3.2.1. Modified g-C3N4 by metals Me (K, Ca, Ga, Fe, Ni and Cu)

K/cGN (a) và K/pGN (b)

Ca/cGN (a) và Ca/pGN (b)

Figure 3.8. Optimized structure


15

Ga/cGN (a) và Ga/pGN (b)

Fe/cGN (a) và Fe/pGN (b)

Figure 3.9. Optimized structure

Ni/cGN (a) và Ni/pGN (b)

Cu/cGN (a) và Cu/pGN (b)

Figure 3.10. Optimized structure
Table 3.4. The calculated formation parameters of Me (K, Ca, Ga, Fe,
Ni và Cu) trên g-C3N4
Eint,
Configuration

(kJ

dmin, Å

mol-1)

Total

BO with N

q(Me),

BO

atoms

e

Me/cGN

K/cGN

-209,4

2,588

0,330

0,101

+ 0,627

Ca/cGN

-366,3

2,703

1,594

0,752

+ 0,480


16

Ga/cGN

-460,9

2,188

1,338

1,078

+0,271

Fe/cGN

-1178,3

1,873

2,620

1,414

+0,023

Ni/cGN

-443,8

1,957

2,611

2,184

+0,444

Cu/cGN

-383,3

1,904

1,506

1,251

+0,262

Me/pGN
K/pGN

-164,9

2,706

0,095

<0,05

+ 0,549

Ca/pGN

-293,3

2,459

1,165

0,497

+ 0,431

Ga/pGN

-414,5

2,212

1,345

1,076

+0,257

Fe/pGN

-408,9

2,463

1,618

0,800

+0,375

Ni/pGN

-312,9

2,019

1,841

1,140

+0,457

Cu/pGN

-307,0

2,038

1,167

0,954

+0,383

Figure 3.11 and figure 3.12 prediced Fractional Occupation DensityFOD of Me/cGN và Me/pGN.

Figure 3.11. FOD plots of Me/cGN(pGN) (Me = K, Ca, Ga, Cu)
depicted at an isovalue 0,03 e Å-3


17

Fe/cGN and Ni/cGN

Fe/pGN and Ni/pGN

Figure 3.12. FOD plots of Me/cGN depicted at an isovalue 0,03 e Å-3
3.2.2. Modified g-C3N4 by oxide metals MexOy (ZnO, TiO2)

ZnO/cGN

ZnO/pGN
Figure 3.10. Optimized structure

Table 3.5. The calculated formation parameters of ZnO on cGN and pGN
Configuration Eint, (kJ mol-1)
ZnO/cGN

ZnO/pGN

-356,6

-252,6

dmin (Å)

BO

d(Zn1-N) =

BO(Zn1-N) =

1,849

0,869

d(Zn2-N) =

BO(Zn2-N) =

2,071

1,054

d(Zn3-N) =

BO(Zn3-N) =

1,962

0,808

d(Zn1-N) =

BO(Zn1-N) =

2,245

0,149

d(Zn2-N) =

BO(Zn2-N) =


18

2,299

0,146

d(Zn3-N) =

BO(Zn3-N) =

2,281

0,158

TiO2/cGN

TiO2/pGN
Figure 3.113. Optimized structure

Table 3.6. The calculated formation parameters of TiO2 on cGN and pGN
Configuration Eint, (kJ mol-1)

TiO2/cGN

-376,3

dmin (Å)

BO

d(Ti1-N) = 2,116

BO(Ti1-N) =

d(Ti2-N) = 2,006

0,346

d(Ti3-N) = 2,439

BO(Ti2-N) =
0,540
BO(Ti3-N) =
0,256

TiO2/pGN

-268,3

d(Ti1-N) = 2,718

BO(Ti1-N) =

d(Ti2-N) = 2,749

0,272
BO(Ti2-N = 0,127

3.3. ELECTRON PROPERTIES AND OPTICAL PROPERTIES OF
Me (Me = Ni, Fe)/g-C3N4, TiO2/g-C3N4
Table 3.7. The calculated IP, EA and GEI of g-C3N4, Me/g-C3N4 (Me =
(Fe, Ni), TiO2/g-C3N4


19

IP, eV

EA, eV

IP-EA, eV

GEI, eV

cGN and cGN modified
cGN

7,0856

2,2618

4,8238

2,2641

Fe/cGN

5,9824

2,8724

3,1100

3,1514

Ni/cGN

6,0526

2,2535

3,7991

2,2700

TiO2/cGN

7,3451

3,2069

4,1382

3,3633

pGN and pGN modified
pGN

6,6276

2,1531

4,4745

2,1539

Fe/pGN

5,8952

2,5282

3,3670

2,6342

Ni/pGN

5,6250

2,1298

3,4952

2,1506

TiO2/pGN

6,9409

3,1891

3,7518

3,4190

Table 3.8. Band gap energy (Eg), values EVB và ECB of g-C3N4, Me/gC3N4 (Me = Ni, Fe), TiO2/g-C3N4
χ , eV

Eg, eV

EVB, eV

ECB, eV

cGN

4,6737

3,274

1,8107

-1,4633

Fe/cGN

4,4274

3,224

1,5394

-1,6846

Ni/cGN

4,1531

3,287

1,2966

-1,9904

TiO2/cGN

5,2760

3,160

2,3560

-0,804

pGN

4,3904

3,192

1,4864

-1,7056

Fe/pGN

4,2117

3,665

1,5442

-2,1208

Ni/pGN

3,8774

3,317

1,0359

-2,2811

TiO2/pGN

5,0650

3,246

2,1880

-1,058


20

Systems cGN, Fe/cGN, Ni/cGN

Systems pGN, Fe/pGN, Ni/pGN

and TiO2/cGN

and TiO2/pGN

Figure 3.14. Graph of CB and VB energy


21

3.4. THE ABSORPTION OF DDT AND HCH ON g-C3N4, Me/g-C3N4

(Me = Fe, Ni) AND TiO2/g-C3N4
The adsorption capacity of DDT and HCH was studied on g-C3N4,
Me/g-C3N4 (Me = Fe, Ni) and TiO2/g-C3N4 in the absence of solvents and
in 4 different solvents: Water, ethanol, acetonitrile and benzene. The
adsorption parameters are considered as adsorption energy (Eads), minimum
distance from adsorbent (dmin), BO bond order according to Wiberg scale
and charge on atoms according to Hirshfeld. The results obtained were that
DDT and HCH were physically adsorbed on the original g-C3N4 material
systems adsorb DDT and HCH better than the outstanding primitive g-C3N4.
The nature of this adsorption force is chemisorption. In the presence of
solvent, the adsorption process still occurs and there is no significant
change.
The thesis also studied the kinetics of DDT and HCH adsorption on
Me/g-C3N4 (Me = Fe, Ni) and TiO2/g-C3N4 was favorable or not by conducting
a sugar study. DDT and HCH adsorption reactions on this system are
molecular superdynamics-Reaction Path (RP) method. The results showed that
the adsorption of DDT and HCH on the systems Me/g-C3N4 (Me = Fe, Ni) and
TiO2/g-C3N4 had Ea = 0, indicating that the (chemical) adsorption stage was
does not go through the transition state. Thus, the adsorption process of DDT
and HCH on thse systems is very favorable.
The thesis conducts thermal stability analysis of the adsorption
congigurations at 298K, 323K, and also investigates at some higher
temperatures (373K, 473K, 573K, 673K) using the analysis dynamics
simulation method MD. The simulation time is 50 ps with a time step of 4
fs. The obtained results show that these adsorption configurations are stable
at the considered temperatures.


22

3.5. PROPOSED NEW MECHANISM OF DDT AND HCH
DECLARATION UNDER THE PHOTOCATALY
In this study, the thesis proposes a photocatalyst mechanism to directly
decompose difficult to decompose organic pollutants, without requiring the
presence of dissolved oxygen. In this mechnism, electrons in the first excited
state in the photocatalyst (adsorbent) are transferred to the sorbent
(POPs).When adsorbents (POPs) gain this electron, they easily decompose
into less toxic, more environmentally friendly compounds.

a. DDT initial

b. DDT after receiving 1 electron

Figure 3.125. Comparison of C-Cl bond lengths in DDT molecular

a. HCH initial

b. HCH after receiving 1 electron

Hình 3.136. Comparison of C-Cl bond lengths in HCH molecular