HUE UNIVERSITY

HUE UNIVERSITY OF SCIENCES

MAI THI THANH

STUDY ON MODIFICATION OF ZIF-8 MATERIAL

AND ITS APPLICATIONS

Major: Theoretical Chemistry and Physical Chemistry

Code: 62.44.01.19

PhD DISSERTATION ABSTRACT

Hue, 2017

1

The thesis has been completed at Department of Chemistry, Hue University of Sciences, Hue

University.

Instructor: 1. Prof. Dr. Đinh Quang Khieu

2. Prof. Dr. Nguyen Phi Hung

Examiner 1 : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . .

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Examiner 2 : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . .

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Examiner 3 : : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . .

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The dissertation will be defended at .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..

Time: . . . date . . . month . . . year 2017

The dissertation could be found at: .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1

INTRODUCTION

1. Research motivation

In the recent years, Metal-organic materials (MOFs) has played an important role for

organophosphates. In the past decade, MOFs are researched on theoretical as well as practical basis. MOFs

attract attention as materials for gas storage, gas adsorption, gas separation and catalysts because of their

high specific surface areas. MOFs are formed by self-sorting and links of linkers and metal ions or metal

clusters. In the MOFs, metal cluster (Cu, Zn, Al, Ti, Cr, V, Fe, ...) and organic bridges (ligands) create a

three-dimensional space with a very large volume of capillary approximate 4.3 cm3.g

-1, a large surface area

and no specific surface limit.

The properties of the metal clusters, ligands, and synthesis conditions can form variety in the types

of MOFs. Di-, tri- and tetra- benzenecarboxylic acids, they are combined with metals such as Zn, Ni, Fe,

Cr,... in order to form various types of MOFs, such as MOF-5, MOF-2, MOF-0, MOF-177, MIL-101,

MOF-199,... For using the imidazolate ligands, Zeolitic imidazolate frameworks (ZIFs) are composed. The

variety of center metal ions and hydrocarbon in imidazoles can form variety in the types of ZIFs, such as

ZIF-8, ZIF-78, ZIF-68, ZIF-69, ZIF-79, ZIF-100,...

In the great MOFs family, ZIFs are topologically isomorphic with zeolites, which has attracted the

attention of many scientists due to the variety of frames, flexibility of denaturation, resistance to thermal

changes, porous, high surface area and chemical stability. ZIFs are being investigated for wide

applications such as catalysts, gas sensors, adsorption, composites, gas separations. In the ZIFs, ZIF-8 are

the most studied materials. Because of the pore size ranges from 3.4 -11.4 Å and hydrophobic properties

of the pore surface, ZIF-8 have the potential to separate linear alkanes from a mixture of branched alkanes,

catalysis for the Knoevenagel reaction. ZIF-8 was known as the adsorbent, gas storage and gas

separation,... In Vietnam, ZIF-8 were also investigated to catalysis for the alkylation reaction as Friedel-

Crafts reaction between anisole with benzyl bromide. Although ZIF-8 has a high chemical stability, the

dye adsorption capacity and optical catalytic activity of this material are very low. Furthermore, other

potantial application of ZIF-8 such as electrode denaturation, metal nano-metal oxide synthesis, p-n

nanofibre nanofibers haven't much been reseached. Therefore, the study of surface improvement and

extending the application of ZIF-8 in dye adsorption as well as optical catalysis are great significance for

science, practice and curent affairs.

Based on above reasons and the condition research in Viet Nam, we choose the subject: "Study on

modification of ZIF-8 material and its applications".

2. New contribution of the thesis

This is the first report about using modified electrode based ZIF-8 (BiF/NaF/ZIF-8/GCE) for

determination of Pb(II) in aqueous solution by DP-ASV methods.

2

This is the first time, Fe(II) and Ni(II) are directly introduced into ZIF-8 to form Fe-ZIF-8 and Ni-

ZIF-8.

Natarajan - Khalaf equation and recovery method were combined to reseach reversible adsorption

kinetics onto the ZIF-8 and Fe-ZIF-8 materials. The RDB adsorption onto ZIF-8 and Fe-ZIF-8 involve a

phylsical - chemical mechanism. The introduction of iron into ZIF-8 provided a much lager adsorption

catacity of RDB than ZIF-8 without iron.

The first time, p-NiO/n-ZnO nanoparticles that had good photocatalytic activity, were prepared by

the thermal treatment of Ni-ZIF-8.

The contents of the dissertation consist of 128 pages, 22 tables, 47 figures, 222 references. The

layout of the thesis is as follows:

Introduction: 2 pages

Chapter 1. Literature review: 37 pages

Chapter 2. Objectives, content, research methods and experimental methods: 19 pages

Chapter 3. Results and Discussion: 67 pages

Chapter 4. Conclusions: 2 pages

Chapter 1. LITERATURE REVIEW

1.1. Metal organic frameworks (MOFs)

1.2. Zeolite imidazole framework -8 (ZIF-8)

1.3. Synthesis ZIF-8

1.4. Modification of ZIF-8

1.5. Application of ZIF-8 as modified electrode

1.6. Application of ZIF-8 as gas adsorption

1.7. Solution absorbent onto ZIF-8 and some issues of adsorption study

1.8. Photocatalysis reaction

Chapter 2. AIMS, CONTENTS AND EXPERIMENTAL METHODS

2.1. Aims

Synthesis and iron, nickel doped zeolite imidazolate framework-8 (Fe-ZIF-8, Ni-ZIF-8). This

materials have hight photocatalytic and adsorption activation. Using ZIF-8 in modified electrode and Ni-

ZIF-8 in synthesis of NiO-ZnO semiconductor nanoparticles.

2.2. Contents

2.2.1. Synthesis of ZIF-8

2.2.2. Voltammetric determination of lead ions using modified electrode based on ZIF-8.

2.2.3. Synthesis of Fe-ZIF-8 and its application for CO2, CH4 adsorption; RDB adsorption and visible -

light-driven photocatalytic degradation of RDB dye.

3

2.2.4. Ni-ZIF-8 that is used to synthesis of p-NiO/n-ZnO with hight photocatalytic activation, is formed

from (Ni(II), Zn(II)) mixed.

2.3. Research methods

X-ray diffraction method (XRD), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron

Microscopy (SEM), Transmission electron microscopy (TEM), Nitrogen adsorption/desorption isotherms,

Diffuse reflectance ultraviolet visible Spectroscopy (UV - Vis), Atomic Absorption

Spectrophotometric(AAS), Dynamic light scattering(DLS), Methods of statistical analysis.

Chapter 3. RESULTS AND DISCUSSION

3.1. Synthesis ZIF-8 and electrochemistry determination of Pb(II) by DP-ASV using ZIF-8 based

modified electrode

3.1.1. Physical chemistry characterization of ZIF-8

10 20 30 40 50 60

(334)

(13

4)(0

13)

(022)

(112)

(002)

(011)

(233)

(222)

(114)

ZIF-8

50

0 C

ps

Inte

nsi

ty (

abr)

2theta (degree)

Figure 3.1. XRD pattern of ZIF-8

XRD pattern of ZIF-8 is shown in Figure 3.1. The XRD pattern of ZIF-8 was agreed well with

patterns from references and no obvious peaks of impurities can be detected in the XRD patterns. There

are well defined diffractions (011), (022), (112), (022), (013), (224), (114), (233), (134) and (334) at two

theta of 7.2; 10.1; 12.7; 14.9; 16.1; 22.1; 24.9; 25.5 and 26.5 degree, respectively in the XRD pattern of

ZIF-8 indicating that the crystallinity of ZIF-8 in this work was relatively high.

TEM observation of ZIF-8 is presented in Figure 3.2a. The morphology of ZIF-8 consisted of nano

spherical particles around 33-45 nm in diameters. The mean size (M) of ZIF-8 is M = 30.9 nm with

standard deviation (SD) = 4.9. The crystallite size was evaluated by Sherrer’s equation from peak (011),

this result was listed in Table 3.1. The particle size was also analyzed by DSL as shown in Figure 3.2b.

The distribution curve exhibited the symmetric bell-shape indicating the particle size had normal

distributions. The agglomerate mean size of ZIF-8 estimated by DLS was 70.7 nm. The crystallite size

was calculated by XRD. The fact the mean size calculated by XRD was similar to that calculated TEM

(dXRD/ dTEM = 1,6) indicating that the single phase of ZIF-8 with high crystalinity was obtained. Since the

4

agglomerate sizes were only approximate 2.3 times the size of particle or crystallite size the agglomerates

observed by TEM were loosen and highly dispersible. The comparíon result is listed in Table 3.1.

Figure 3.2. TEM observation (a) and size distribution curve (b) of ZIF-8

Table 3.1. The size of ZIF-8 was also analyzed by different method

Notation dTEM (nm) dXRD (nm) dDLS (nm) dDLS/ dTEM dXRD/dTEM

ZIF-8 30,9 ± 0,098 49,5 70,7 2,3 1,6

This ZIF-8 was found to be thermal stability up to 400 oC; stable in ambient, in water at room

temperature, in diferrent solvent at boiling temperature and was stable in the pH range 2.7 to 12.0.

3.1.2. Electrochemistry determination of Pb(II) by DP-ASV using ZIF-8 based modified electrode

3.1.2.1. Surveying voltammetric characteristics of Pb(II) on different electrode

-0.8 -0.7 -0.6 -0.5 -0.4

1.0

1.5

2.0

2.5

3.0

3.5

4.0

A

I (

A)

E (V)

(a) BiF/NafZIF-8/GCE

(b) BiF/Naf/GCE

(c) Naf/GCE

(d) NafZIF-8/GCE

(e) GCE

(f) BiF/GCE

-1.2 -0.8 -0.4 0 0.4

-30

-20

-10

0

10

20

30

(B)

I(

A)

E (V)

pH = 2.7

pH = 3.2

pH = 3.6

pH = 4.1

pH = 4.6

pH = 4.9

pH = 5.6

Figure 3.3. A) DP-ASVs of Pb(II) on different electrode and B) Anodic stripping current of Pb(II)

at different pH

In order to verify the electrochemical activity of ZIF-8 in the modified GCE for detection of

Pb(II), the electrochemical experiments in GCE modified with and without ZIF-8 were performed by DP-

ASVs. As can be seen in Figure 3.3A, the stripping voltammetry peak varied from -0.624 to -0.586 V.

The intensity of Ip at BiF/Naf/ZIF-8/GCE was 1.82 fold in compared with that at BiF/GCE as well as

Naf/ZIF-8/GCE. This BiF/Naf/ZIF-8/GCE was significantly improved the sensitivity of Pb(II)

determination.

5

The effect of pH on the response of Pb(II) been shown in Figure 3.3B. The best signal intensity was

reached at pH = 3.3. The linear relationship between pH and anodic peak potential, Epa can be expressed

as follows:

Epa (mV) = (-0.031 0.010) pH – (-0.428 0.041 (R = -0.9651, p ≤ 0.001) (1)

The slope of regression is close to theoretical value of

0 (25

oC) indicating the participation of

the one proton and two electrons in the electrochemical process.

3.1.2.2. Effects of scan rate ()

The effect of scan rate on Epa and Ipa was investigated by CV as shown in Figure 3.4A. Peak current

increased with an increase in the scan rate from 20 – 500 mV.s-1

indicated that the electron transfer

reaction involved with a surface-confined process. The peak potential shifted to higher potential as scan

rate increased, then it is concluded that electron transfer in Pb(II) electrooxidation was irreversible. The

linear relationship between lnIp and lnv was obtained as shown in Figure 3.4b with its slope of 0.883.

Then it was concluded that the oxidation of Pb(II) on the modified electrode was an adsorption- diffusion

controlled process.

The imime groups of imidazole in ZIF-8 bind Pb(II) to surface complexes because of its high

affinity to Pb(II) ions. The Pb(II) were accumulated in electrode due to the reduction reaction, and then

dissolved in solution through oxidation reaction. The electrochemical reactions could occur as follows

illustration in Figure 3.5.

-1.2 -0.8 -0.4 0 0.4

0

50

100

150(a)

I (

A)

E (V)

= 20 mV/s

= 40 mV/s

= 50 mV/s

= 75 mV/s

= 100 mV/s

= 200 mV/s

= 300 mV/s

= 400 mV/s

= 500 mV/s

3 4 5 6

2

3

4

5

(b)

lnIp,Pb = 0,8834.ln-0,577 R2

= 0,9849

lnI p

,Pb

ln

Figure 3.4. a) CVs of BiF/Naf/ZiF-8/GCE with increasing of scan rate to inner to outer: 20-500 mV.s-1

; b)

Linear regression of lnIp vs. lnv.

Figure 3.5. Mechanisms for Pb(II) determination on BiF/Naf/ZIF-8/GCE electrode by DP-AVS.

6

3.1.2.3. The reliability of Voltammetric method using BiF/Naf/ZIF-8/GCE electrode for

Pb(II) determnation

The response current peak (Ip) was linear in the concentration range 12 ppb to 100 ppb as shown in

Figure 3.6a. Linear regression equation of the calibration curves was shown in Figure 3.6b.

-0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2

0

10

20

30

40

(a)

I(

A)

E (V)

12 ppb

100 ppb

Figure 3.6. a) The DP-ASV curves of Pb(II) with increasing Pb(II) from 12-100 ppb; b) The linear

regression of Ip vs. CPb(II).

Sensitivity obtained the slope of the calibration curve was 0.290 μA/ppb. The limit of detection

(LOD) calculated based on the concentration from 12 ppb to 100 ppb. The LOD was found to be 4.16 ppb.

The limit of quantitation (LOQ) calculated from 10Sy/b was 13.9 ppb.

3.2. Synthesis of iron doped ZIF-8 and its applied adsorption, photocatalysis

3.2.1. Synthesis of iron doped ZIF-8

Figure 3.7 shows XRD patterns of ZIF-8 and Fe- ZIF-8 with different ratio Fe/(Zn+Fe). The XRD

patterns of ZIF-8 in this work were agreed well with these before reports references. The intensity of

these diffractions decreased with an increase in the amount of iron incorporated and were not observed as

the molar ratio of iron reached at 40%. Thus, conditions of this study, the limit for iron doped to ZIF-8

from the mixture of Zn(II) and Fe(II) with a molar ratio of Fe(II) / (Fe(II) + Zn(II)) in the initial mixture

was 30%.

0 10 20 30 40 50 60 70

ZIF-8

Fe-ZIF-8(20%)Fe-ZIF-8(30%)

Fe-ZIF-8(10%)

Fe-ZIF-8(40%)

10

00

cp

sIn

te

nsit

yä (

ab

r)

2 theta (degree) Figure 3.7. XRD pattern of ZIF-8 and Fe-ZIF-8

The composition of oxidation states, content of zinc and iron are analyzed by XPS and AAS. The

results are presented in Table 3.2. The main iron in Fe-ZIF(10%) was Fe(II) but Fe(II) and Fe(III)

20 40 60 80 1000

10

20

30Ip,Pb = (-2,601 ± 0,697) + (0,290 ± 0,012).CPb

r = 0,999

I p,P

b (

A)

CPb

(ppb)

7

coexisted in Fe-ZIF-8(20%) and Fe-ZIF-8(30%).

Table 3.2. Chemical composition of ZIF-8 and Fe-ZIF-8 analyzed by AAS and XPS

Notation

AAS XPS

Zn

(mol.g-1

)

Fe

(mol.g-1

)

Molar ratio

Fe/(Zn+Fe)

Initial molar

ratio

Fe/(Zn+Fe)

Fe(II)

(%)

Fe(III)

(%)

ZIF-8 0,043 - 0 - - -

Fe-ZIF-8(10%) 0,038 0,005 0,116 0,100 100 0,000

Fe-ZIF-8(20%) 0,033 0,012 0,267 0,200 17,940 82,060

Fe-ZIF-8(30%) 0,027 0,022 0,449 0,300 43,670 56,330

Figure 3.8 shows the nitrogen adsorption/desorption isotherms of ZIF-8 and Fe-ZIF-8. All samples

exhibited a type IV according to IUPAC. The introduction of iron into ZIF-8 lowers the specific surface

area, The specific surface areas were 1484, 1469, 1104, and 735 m2.g

-1 for ZIF-8, Fe-ZIF-8 (10%), Fe-

ZIF-8(20%) and Fe-ZIF-(30%), respectively.

0.0 0.2 0.4 0.6 0.8 1.0 1.2

150

200

250

300

350

400

450

500

550

600

650

700

750

800

ZIF-8

Fe-ZIF-8(30%)

Fe-ZIF-8(20%)

Fe-ZIF-8(10%)

Ad

so

rb

ed

ï(cm

3.g

-1 S

TP

)

Relative pressure (P/Po)

Figure 3.8. Nitrogen adsorption/desorption isotherms of ZIF-8 and Fe-ZIF-8

Figure 3.9 present DR-UV-Vis spectra and Tauc’s plots of ZIF-8 and Fe-ZIF-8. The energy band

gap of samples was determined on Tauc's aquation and the results are shown in Table 3.3. ZIF-8 had the

highest absorption peak around 230 nm. Remarkable, the Fe doped ZIF-8 showed a remarkable

absorption band shift toward the longer wavelength region.

200 300 400 500 600 700 800

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Ab

so

rb

ï (%

)

wavelength (nm)

ZIF-8

Fe-ZIF-8(10%)

Fe-ZIF-8(20%)

Fe-ZIF-8(30%)

ZnO

Figure 3.9. DR-UV-Vis spectra (left) and Tauc’s plots (right) of ZnO, ZIF-8 and Fe-ZIF-8.

8

Table 3.3. The energy band gap (Eg) of ZIF-8 and Fe-ZIF-8

Notation Eg1(eV) Eg2(eV) Eg3(eV) Eg4(eV)

ZIF-8 5.2 3.5 2.1 1.8

Fe-ZIF-8(10%) 4.7 / 2.2 /

Fe-ZIF-8(20%) / / 2.2 /

Fe-ZIF-8(30%) / / 2.1 /

3.2.2. The CO2 and CH4 adsorption onto ZIF-8 and Fe-ZIF-8

The CO2 and CH4 adsorption capacities are shown in Figure 3.10 and Table 3.4. The results show that

the CO2 adsorption capacity onto materials is much higher than that of CH4. It is remarkable, the CO2 and

CH4 adsorption capacity onto ZIF-8 was significantly higher than that on Fe-ZIF-8 and decreased with an

increase in the amount of iron incorporated.

0 5 10 15 20 25 30 35

0

2

4

6

8

10

12

14

ZIF-8

Fe-ZIF-8(10%)

Fe-ZIF-8(20%)

Fe-ZIF-8(30%)

Ad

so

rp

tio

n c

ap

acit

y (

mm

ol.g

-1

)

Pressure (bar)

(a)-CO2

5 10 15 20 25 30 35

1

2

3

4

ZIF-8

Fe-ZIF-8(10%)Fe-ZIF-8(20%)

Fe-ZIF-8(30%)

Ad

sorp

tion

ca

tacip

y(m

mo

l.g

-1)

Pressure (bar)

(b)- CH4

Figure 3.10. CO2 (a) and CH4(b) adsorption/desorption isotherms of ZIF-8 and Fe-ZIF-8

Table 3.4. The CO2 and CH4 adsorption capacities on ZIF-8 and Fe- ZIF-8 at 30 bar, 298 K

Notation SBET

(m2.g

-1)

Vpore

(cm3.g

-1)

CO2

(mmol.g-1

)

CH4

(mmol.g-1

)

ZIF-8 1484 1,16 11,176 3,539

Fe-ZIF-8(10%) 1469 0,64 5,986 2,556

Fe-ZIF-8(20%) 1104 0,5 5,032 2,438

Fe-ZIF-8(30%) 735 0,38 2,649 1,120

The Henry constant values obtained from the CO2 and CH4 adsorption onto ZIF-8 and Fe-ZIF-8

samples are presented in Table 3.5. The Henry constant values of CO2 adsorption were much higher than

that of CH4 adsorption. The Henry constant of gas adsorption onto ZIF-8 was much greater than onto Fe-

ZIF-8 and decreased with an increase in the amount of iron incorporated. The experimental data of CO2 and

CH4 adsorption onto ZIF-8 and Fe-ZIF-8 were fitter to Langmuir model than to Freundlich model.

9

Table 3.5. The Henry constant of CO2 and CH4 adsorption onto the ZIF-8 and Fe-ZIF-8

3.2.3. RDB adsorption

3.2.3.1. Effect of Initial RDB Concentration

Effect of contact time on the adsorption onto ZIF-8 and Fe-ZIF-8 at various Initial RDB

Concentration (30-50 mg.L-1

) are shown in Figure 3.11. The adsorption capacity of adsorbent increases

with an increased the initial concentrations from 30 to 50 mg.g-1

. The RDB adsorption of Fe-ZIF-8 was

higher than that of ZIF-8 in the same initial concentration. Figure 3.11 indicates that the adsorption of

RDB was fast in the earlier stage (0-50 minutes) and gradually reached the equilibrium at around150

minutes.

0 50 100 150 200 250

0

5

10

15

20

25

30

35

40

45

ZIF-8

qe

(mg

.g-1

)

Time(minute)

30 mg.L-1

40 mg.L-1

50 mg.L-1

0 50 100 150 200 250

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

Fe-ZIF-8(10%)

qe

(mg

.g-1

)

Time(minute)

30 mg.L-1

40 mg.L-1

50 mg.L-1

0 50 100 150 200 250

0

10

20

30

40

50

60

70

80

90

100

Fe-ZIF-8(20%)

qe

(mg

.g-1

)

Time (minute)

30 mg.L-1

40 mg.L-1

50 mg.L-1

0 50 100 150 200 250

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

Fe- ZIF-8(30%)

qe

(mg

.g-1

)

Time (minute)

30 mg.L-1

40 mg.L-1

50 mg.L-1

Figure 3.11. Effect of contact time on the adsorption of RDB by ZIF-8 and Fe-ZIF-8

Piecewise linear regression are applied to analyze data experimental by Webber’s plot. Figure

3.12 illustrates experimental data and piecewise linear regression lines with initial concentration 50 mg L-

1. The experimental points seem to be close to regression lines for two or three linear segment lines. We

could not estimate visually which one is more likely correct. The well-known statistical method for model

comparison is Akaike’s Information Criterion (AIC). The values of AICc for one segment, two segments

and three segments models for varial concentrations were presented in Table 3.6. The experimental data

Notation

CO2 CH4

Henry constant

(mmol.(g.bar)-1

)

R2 Henry constant

(mmol.(g.bar)-1

)

R2

ZIF-8 1,55 0,959 0,38 0,998

Fe-ZIF-8(10%) 1,02 0,913 0,30 0,946

Fe-ZIF-8(20%) 1,02 0,912 0,19 0,987

Fe-ZIF-8(30%) 0,80 0,944 0,18 0,948

10

fited to two linear segments model because of the lowest value of AICc in this model.

0 2 4 6 8 10 12 14 16

ZIF-8one segment

two segments

three segments

10

qe(m

g.g

-1)

time1/2(minute1/2)

0 2 4 6 8 10 12 14 16

Fe-ZIF-8(10%)one segment

two segments

three segments

10

qe(m

g.g

-1)

time1/2(minute1/2)

2 4 6 8 10 12 14 16

one segment

two segments

three segments

Fe-ZIF-8(20%)10

qe

(mg

.g-1

)

time1/2(minute

1/2

) 0 2 4 6 8 10 12 14 16

one segment

two segments

three segments

Fe-ZIF-8(30%)

10

qe

(mg

.g-1

)

time1/2

(minute1/2

)

Figure 3.12. Plot of piecewise linear regression for one, two and three segments based Webber’s model.

Table 3.6. Comparison of piecewise linear regression for one, two and three linear segments by

AIC

Adsorbent CRDB

mg.L-1

One linear segment

regression

Two linear segments

regression

Three linear segment

regression

SSE R2 AIC SSE R

2 AIC SSE R

2 AIC

ZIF-8 30 247,1 0,905 62,7 82,9 0,968 39,3 82,9 0,968 45,3

40 736,8 0,858 91,1 189,4 0,964 60,8 189,4 0,964 66,8

50 619,3 0,884 89,5 33,9 0,994 16,1 33,9 0,995 22,5

Fe-ZIF-8

(10%)

30 835,1 0,650 94,4 54,1 0,977 28,5 54,1 0,977 34,2

40 2070,8 0,973 118,0 317,8 0,967 72,8 317,8 0,967 80,2

50 984,3 0,846 98,7 23,7 0,996 6,8 21,3 0,997 10,0

Fe-ZIF-8

(20%)

30 2487,1 0,028 119,2 114,8 0,955 47,3 114,8 0,955 53,8

40 911,0 0,286 96,6 31,1 0,999 13,8 29,2 0,977 18,2

50 782,1 0,823 92,7 39,4 0,991 20,0 60,6 0,999 37,2

Fe-ZIF-8

(30%)

30 990,1 0,130 96,2 90,5 0,921 41,4 211,4 0,812 69,7

40 957,3 0,501 97,9 62,9 0,981 33,6 54,0 0,987 34,2

50 304,5 0,600 66,7 186,2 0,496 59,4 187,9 0,499 66,6

Results of piecewise two linear segments regression for different initial concentrations are shown

in Table 3.7. This value of the intercept was significantly different from zero. It means the line did not

pass through the origin. Then, adsorption of RDB dye onto ZIF-8 or Fe-ZIF-8 were controlled by film

diffusion.

11

Table 3.7. Results of piecewise regression for the two linear segments for ZIF-8 and Fe-ZIF-8

(The values in parentheses are at a 95% confidence level )

Adsorbent

ZIF-8

Concentration

(mg.L-1

)

The first linear segment The second linear segment

Intercept 1 Slope 1 Intercept 2 Slope 2

30 -2,83

(-5,11: -0,55)

4,68 19,16

(17,58: 20,74)

0,75

40 -10,29

(-17,10: -3,47)

4,83 27,06

(25,29: 28,83)

0,67

50 -10,19

(-12,28: -8,10)

5,58 34,85

(32,21: 37,49)

0,52

Fe-ZIF-8

(10%)

30 22,58

(20,16: 24,99)

3,85 78,07

(74,99: 81,15)

-1,97

40 8,13

(2,64: 13,63)

6,82

98,79

(93,99: 103,59)

-2,26

50 25,38

(23,59: 27,16)

6,01 80,15

(78,58: 81,72)

-0,15

Fe-ZIF-8

(20%)

30 37,16

(33,88: 40,43)

9,43 103,84

(98,23: 109,45)

-2,63

40 39,35

(34,52: 44,18)

6,64 78,37

(77,28: 79,46)

-0,69

50 53,03

(49,70: 56,36)

4,75 94,25

(93,08: 95,42)

0,09

Fe-ZIF-8

(30%)

30 31,84

(27,24: 36,43)

5,46 73,11

(69,12: 77,10)

-2,39

40 21,54

(17,89: 25,19)

5,34 64,56

(59,92: 69,21)

-0,89

50 63,28

(57,47: 69,09)

2,68 82,809

(81,11: 84,51)

-0,57

In the present study, the pseudo first order kinetics model of Natarajan-Khalaf was used to analyse

the experimental data. The results are listed in Table 3.8. The high coefficient of determination, R2 (0.973-

0.998) imply that this model was compatible with the experimental data. The adsorption kinetics can be

significantly improved by the introduction of iron into the ZIF-8. As shown in Table 3.8 the rate constants

for adsorption could be increased approximately 5 times by Fe-ZIF-8 and the kinetics with Fe ZIF-8 were

faster than that with ZIF-8.

12

Table 3.8. Rate constants for the adsorption and the rate constants for the forward and reverse

process and equilibrium constants at different concentrations for ZIF-8 and Fe-ZIF-8

Adsorbent CRDB

(mg.L-1

)

kads

(minute-1

)

ka

(minute-1

)

kb

(minute-1

)

K0 R2

ZIF-8 30 0,0023 0,0009 0,0014 0.6751 0,995

40 0,0025 0,0009 0,0016 0.5631 0,998

50 0,0046 0,0015 0,0031 0.5043 0,990

Fe-ZIF-8

(10%)

30 0,0115 0,0077 0,0038 1.9858 0,991

40 0,0122 0,0081 0,0041 1.9787 0,991

50 0,0184 0,0113 0,0071 1.5927 0,980

Fe-ZIF-8

(20%)

30 0,0253 0,0151 0,0102 1.4803 0,993

40 0,0276 0,0179 0,0097 1.8396 0,988

50 0,0322 0,0225 0,0097 1.8424 0,994

Fe-ZIF-8

(30%)

30 0,0299 0,0164 0,0135 1.2105 0,910

40 0,0322 0,0168 0,0155 1.0822 0,989

50 0,0345 0,0199 0,0146 1.3596 0,994

3.2.3.2. Effect of temperature

0 50 100 150 200 2500

5

10

15

20

25

30

35

40

45

50

55

60

298 K

308 K

318 K

ZIF-8qe

(mg

.g-1

)

time (minute) 0 50 100 150 200 250

0

10

20

30

40

50

60

70

80

90

100

110

318 K308 K

298 K

Fe-ZIF-8(10%)

qe

(mg

.g-1

)

time (minute)

0 50 100 150 200 2500

10

20

30

40

50

60

70

80

90

100

110

298 K

308 K

Fe-ZIF-8(20%)

318 K

qe

(mg

.g-1

)

time (minute) 0 50 100 150 200 250

0

10

20

30

40

50

60

70

80

90

100

110

298 K

308 K

318 K

Fe-ZIF-8(30%)

qe

(mg

.g-1

)

time (minute)

Figure 3.13. Effect of temperature on adsorption of RDB dye onto ZIF-8 (a) and Fe-ZIF-8 (b)

Adsorption thermodynamics was conducted by varying the temperature from 298 K to 318 K as

shown in Figure 3.13. The results showed that equilibrium adsorption capacity, qeq of both adsorbents

increased with an increase in temperature which indicated that the process was endothermic. The

equilibrium adsorption capacity of Fe-ZIF-8 is higher than that of ZIF-8 for each corresponding

temperature.

The thermodynamic parameters including activation energy, Kd, ka and kb are presented in Table

3.9. The results showed that the increasing adsorption constant with an increase in temperature. It is worth

noting that the Kd in the case of Fe-ZIF-8 is higher and increases much faster than that in the case of ZIF-

13

8. The activation energy values of ZIF-8 is much higher than that of Fe-ZIF-8. The adsorption mechanism

of RDB dye onto ZIF-8 and Fe-ZIF-8 involved a physical-chemical mechanism and not purely physical or

chemical.

Table 3.9. Activation energy, equilibrium and rate constants for RDB dye adsorption, and rate constants

for forward and reverse process of RDB adsorption onto ZIF-8 and Fe-ZIF-8

Adsorbent Temperature

(K)

Kd qeq

(mg.g-1

)

ka

(x103)

(min-1

)

kb

(x103)

(min-1

)

kads

(x103)

(min-1

)

R2 Ea

(kJ.mol-1

)

R2

ZIF-8 298 1,27 28,89 0,89 1,80 2,70 0,990 48,27 0,991

308 1,57 43,949 1,91 2,69 4,61 0,988

318 1,84 53,029 3,91 5,30 9,21 0,973

Fe-ZIF-8

(10%)

298 3,40 62,92 11,36 7,06 18,42 0,988 12,51 0,972

308 4,08 77,50 12,85 7,88 20,73 0,994

318 5,86 87,64 17,76 7,57 25,33 0,991

Fe-ZIF-8

(20%)

298 2,32 60,28 8,88 9,54 18,42 0,991 19,11 0,995

308 4,18 78,33 14,43 8,60 23,03 0,993

318 7,24 94,58 22,65 7,29 29,94 0,942

Fe-ZIF-8

(30%)

298 1,48 46,39 5,98 10,14 16,12 0,986 14,11 0,955

308 3,47 72,64 12,05 8,68 20,73 0,996

318 5,90 87,78 17,042 5,988 23,03 0,981

Table 3.10. Thermodynamic parameters for the adsorption of RDB dye onto ZIF-8 and Fe-ZIF-8

Adsorbent ΔG

0(kJ)

ΔH0(kJ) ΔS

0(J) R

2

298 K 308 K 318 K

ZIF-8 -0,6 -1,4 -1,6 16,0 55,8 0,983

Fe-ZIF-8(10%) -1,1 -3,6 -4,7 51,6 170,0 0,980

Fe-ZIF-8(20%) -2,1 -3,7 -5,2 44.9 157,6 1

Fe-ZIF-8(30%) -1,0 -3,2 -4,7 54,7 187,2 0,986

The Kd constant is used to determine thermodynamic parameters. The results are presented in Table

3.10. The adsorption process using ZIF-8 and Fe-ZIF-8 was endothermic as indicated by the positive sign

of the ΔH0, ΔG

o value increases with a temperature increase. As the Gibbs free energy change is negative

and accompanied by the positive standard entropy change, the adsorption reaction is spontaneous with

high affinity. The possible mechanisms of RDB adsorption onto ZIF-8 or Fe-ZIF-8 are illustrated in

Figure 3.14.

14

Figure 3.14. The proposed mechanism of RDB adsorption onto ZIF-8 or Fe-ZIF-8 at pH < pHZPC

3.2.3.3. Isotherm adsorption

Table 3.11. The parameters of Langmuir and Freundlich model

Adsorbent Langmuir model Freundlich model

KL

(L.mg-1

)

qm

(mg.g-1

)

R2 n KF

(mg.g-1

.mg.L-1

)n

qm

(mg.g-1

)

R2

ZIF-8 0,59 133,8 0,974 7,80 82,34 127,35 0,878

Fe-ZIF-8(10%) 0,57 193,6 0,958 4,43 92,02 222,33 0,961

Fe-ZIF-8(20%) 0,25 197,9 0,97 4,35 70,41 213,83 0,975

Fe-ZIF-8(30%) 0,58 173,9 0,969 5,12 91,35 196,04 0,964

The experimental data are analyzed according to the non-linear form of Langmuir and Freudlich

model. The parameters of models are listed in Table 3.11. The high value of R2 suggest that the isothermal

data of ZIF-8 could be well represented by the Langmuir model. For Fe-ZIF-8 both models exhibited

similar values of R2 and χ

2. Moreover, favourable characteristic parameters of RL for Langmuir isotherm

and n for Freundlich isotherm were 0 < RL = 0.034 < 1 and 2 < n = 4.43 < 10, which indicated that both

*Electrostatic interaction

*The hydrophobic and

π−π interaction between

the aromatic rings the

aromatic imidazole rings

*coordination of the

nitrogen atoms or oxygen

in RDB molecules to the

Fe2+

ions in the ZIF-8

framework

15

isotherms were favourable. In the Fe-ZIF-8, adsorption capacity for Fe-ZIF-8(20%) is much higher than

that for Fe-ZIF-8(10%) and Fe-ZIF-8(30%).

3.2.4. Photocatalytic degration of RDB dye in ZIF-8 and Fe-ZIF-8 by sunlight

Figure 3.15 shows kinetics of degradation reaction of RDB with different codition. The result

indicate that the decolorization of RDB without catalyst was also not observed during sun light

illumination indicating RDB was stable for sun light in studied condition. Leaching experiment was

also conducted in which Fe-ZIF-8 catalyst was filtered after 60 reaction minutes; the decolorization of dye

was stopped despite of still remaining sunlight illumination indicating Fe-ZIF-8 is a heterogeneous

catalyst.

0 50 100 150 200 250 300

0.0

0.2

0.4

0.6

0.8

1.0

60

Fe-ZIF-8(10%)

Ct

/C0

time ( minute)

sunlight illumination

catalysts + sunlight illumination

removing catalysts after 60 minutes

0 50 100 150 200 250 300

0.0

0.2

0.4

0.6

0.8

1.0

Fe-ZIF-8(20%)

Ct

/C0

time ( minute)

sunlight illumination

catalysts + sunlight illumination

removing catalysts after 60 minutes

0 50 100 150 200 250 300

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

60

IF

Fe-ZIF-8(30%)

Ct

/ C

0

time (minute)

sunlight illumination

catalysts + sunlight illumination

removing catalysts after 60 minutes

Figure 3.15. Degradation of RDB with different codition

The influence of the initial concentration on the photocatalytic degradation rate of RDB over

various catalysts was shown in Figure 3.16. Therefore, the catalytic activity decreased in the order of

Fe-ZIF-8(10%) > Fe-ZIF-8(20%) > Fe-ZIF-8(30%).

The linear regression of the lnro against lnCo gives a straight line with slope equals n and the

intercept on the ordinate provides lnki (inset of Figure 3.16). The values of n and k calculated were

listed in Table 3.12. Linear regression provide a good compatibility with very high coefficient of

determination (R2 =0.99). In the this study, the value of n varying from 0.412-0.456 could be due to

contribution of both adsorption and photocatalytic reaction.

16

0 50 100 150 200 250 3000

5

10

15

20

25

30

35

40

45

Fe-ZIF-8(10%)

Ct

(mg

.L-1

)time (minute)

10 mg.L-1

20 mg.L-1

30 mg .L-1

40 mg.L-1

2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8-1.0

-0.9

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3 Fe-ZIF-8 (10%)

y = 0.412x -1.882 R2 = 0.991

lnr0

lnC0

0 50 100 150 200 250 3000

5

10

15

20

25

30

35

40Fe-ZIF-8(20%)

Ct (

mg.

L-1

)

time (minute)

10 mg.L-1

20 mg.L-1

30 mg.L-1

40 mg.L-1

2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8

-1.0

-0.9

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3Fe-ZIF-8(20%)

y = 0.456x-1.989 R2 = 0.996

lnr0

lnC0

0 50 100 150 200 250 3000

5

10

15

20

25

30

35

40Fe-ZIF-8(30%)

C t

(mg

.L-1

)

time (minute)

10 mg.L-1

20 mg.L-1

30 mg.L-1

40 mg.L-1

2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8-1.2

-1.1

-1.0

-0.9

-0.8

-0.7

-0.6

-0.5 Fe-ZIF-8(30%)

y = 0.446x -2.171 R2 = 0.994

lnr0

lnC0

Figure 3.16. Photocatalytic degradation reaction of RDB with different initial concentrations

Table 3.12. The reaction order and rate constant

Notation Reaction order (n) ki((mg.L-1

)1-n

.minute-1

) R2

Fe-ZIF-8(10%) 0,412 0,152 0,991

Fe-ZIF-8(20%) 0,456 0,139 0,996

Fe-ZIF-8(30%) 0,446 0,114 0,994

In Fe-ZIF-8, the LUMO is mainly contributed by empty Zn or Fe orbitals. The valance orbitals of

Fe in Fe-ZIF-8 provide the higher HOMO (highest occupied molecular orbital) level that brings absorption

to the visible region. This reason explained why Fe-ZIF-8 could catalyze in visible region. This

argument is illustrated in Figure 3.17.

17

Figure 3.17. Photocatalytic reaction mechanism of RDB on Fe-ZIF-8 catalyst under sun light

illumination

3.3. Synthesis Ni-ZIF-8 and its application synthesis p-ZnO / n-NiO nano

3.3.1. Synthesis Ni-ZIF-8

5 10 15 20 25 30

334

134

23

3

1142

22

013

022

112

00

2

01

1

Ni-ZIF-8(90%)

Ni-ZIF-8(80%)

Ni-ZIF-8(60%)

Ni-ZIF-8(50%)

Ni-ZIF-8(40%)

Ni-ZIF-8(30%)

Ni-ZIF-8(20%)

Ni-ZIF-8(10%)

ZIF-8

500 c

ps

Inte

nsi

ty(a

br)

2 theta (degree)

Figure 3.18. XRD patterns of Ni-ZIF-8 with different molar rate of Ni(II) / (Zn(II)+Ni(II))

Figure 3.18 presents XRD patterns of Ni-ZIF-8 with different molar rate of Ni(II) /

(Zn(II)+Ni(II)). The result indicate that peaks of Ni-ZIF-8(10%), Ni-ZIF-8(20%), Ni-ZIF-8(30%), Ni-ZIF-

8(40%), Ni-ZIF-8(50%), Ni-ZIF-8(60%) and Ni-ZIF-8(80%) were agreed well with that of ZIF-8. The

XRD pattern also indicated, Ni-ZIF-8(90%) was not observed characteristic peaks of ZIF-8, thus ZIF-8

did not exist at this rate. In this study, the max initial molar ratio of Ni(II)/ (Ni(II )+ Zn(II)) for synthesis

of Ni-ZIF-8 is 80%.

18

3.3.2. Synthesis of p-NiO / n-ZnO nanoparticles

5 10 15 20 25 30 35

Ni-ZIF-8(10%)

p-NiO/n-ZnO(10%)

Ni-ZIF-8(10%)

Inte

nsit

y(a

br)

50

0 C

ps

2 theta (degree) 5 10 15 20 25 30 35

Ni-ZIF-8 (50%)

p-NiO/n-ZnO(50%)

Ni-ZIF-8(50%)

50

0 C

ps

Inte

nsit

y (

ab

r)

2 theta (degree)

5 10 15 20 25 30 35

50

0 C

ps

p-NiO/n-ZnO(80%)

Ni-ZIF-8(80%)

Ni-ZIF-8 (80%)

Inte

nsit

y (

ab

r)

2 theta (degree)

Figure 3.19. XRD patterns of Ni-ZIF-8 and p-NiO/n-ZnO nanoparticles

The XRD patterns of Ni-ZIF-8 and p-NiO/ n-ZnO were showned in Figure 3.19. The results

suggested that the material was heated at 500 0C, the peaks of Ni-ZIF-8 disappeared and no characteristic

peaks appeared, almost amorphous material.

Figure 3.20 presents TEM images of Ni-ZIF-8(80%) and p-NiO/ n-ZnO(80%) nanoparticles. Ni-

ZIF-8 particles involve spherical particles with size around 40-50 nm. After heating, the p-NiO/ n-ZnO

particles exist in two sizes mixed of 10-15 nm and 40-50 nm. This result again confirms that these oxides

are mixed at nm level and form to much inter-heterogeneous regions.

Figure 3.20. TEM observation of Ni-ZIF-8(80%) and p-NiO/n-ZnO(80%)

Table 3.13 presents chemical composition of materials by elemental analysis and AAS method. The

nikel composition of Ni-ZIF-8 increased with an increased in nikel amount incorporated and nikel amount

of p-NiO/n-ZnO nanoparticles increased with an increased in nikel amount in precursor. The C, H, N

19

elements exist in small amounts in the p-NiO/ n-ZnO(80%) but are almost absent in the p-NiO/ n-

ZnO(10%), p -NiO/ n-ZnO(50%).

Table 3.13. Chemical composition of materials Ni-ZIF-8 và p-NiO/n-ZnO analyzed

by elemental analysis and AAS method

Notation C

(%)

H

(%)

N

(%)

Zn

(g.kg-1

)

Ni

(g.kg-1

)

Initial molar ratio

Ni(II)/ (Zn(II)+ Ni(II))

Ni-ZIF-8(10%) 40,81 4,12 24,18 233,80 1,26 0,1

Ni-ZIF-8(50%) 40,22 3,57 23,99 229,30 7,93 0,5

Ni-ZIF-8(80%) 42,69 4,56 25,41 225,00 32,00 0,8

p-NiO/n-ZnO(10%) 0,00 0,00 0,00 744,00 3,80 0,1

p-NiO/n-ZnO(50%) 0,00 0,00 0,00 724,00 26,56 0,5

p-NiO/n-ZnO(80%) 0,10 0,17 0,06 718,00 82,70 0,8

The DR-UV-Vis spectra of Ni-ZIF-8 and p-NiO/n- ZnO are presented in Figure 3.21. The

adsorption peak in the spectra of Ni-ZIF-8 are similar but much higher than that of ZIF-8. The DR-UV-

Vis spectra of p-NiO/n-ZnO nanoparcles was agreed with that of ZnO. But, the intensity of adsorption

peak of p-NiO/n-ZnO were much highter than that of ZnO. The energy band gap of samples is determined

base on Tauc aquation. The results are showned in Table 3.14.

200 300 400 500 600 700 800 900-0.2-0.10.00.10.20.30.40.50.60.70.80.91.01.11.21.31.41.51.6

(a)Ni-ZIF-8(80%)

Ni-ZIF-8(10%)

Ni-ZIF-8(50%)

ZIF-8

ï A

bso

rb (

%)

wavelength (nm)

1 2 3 4 5 6 7-20

0

20

40

60

80

100

120

140

160

180

200 (b)

Ni-ZIF-8(80%)

Ni-ZIF-8(50%)Ni-ZIF-8(10%)

(a

lp

ha

*E

)2

Eg(eV)

200 300 400 500 600 700 800 900 10000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6(c)

Ni-ZIF-8(80%)

p-NiO/n-ZnO(80%)

p-NiO/n-ZnO(50%)

p-NiO/n-ZnO(10%)

ZnO

Ab

so

rb

(%

)

wavelength (nm)

0 1 2 3 4 5 6 7 80

20

40

60

80

100

120

140

160

180

p-NiO/n-ZnO(10%)

(d)

p-NiO/n-ZnO(50%)

p-NiO/n-ZnO(80%)

(a

lp

ha

*E

)2

Eg(eV)

Figure 3.21. DR-UV-Vis spectra (a, c) and Tauc's plot of Ni-ZIF-8 and p-NiO/n- ZnO

20

Table 3.14. Energy band gap of Ni-ZIF-8 and p-NiO/n-ZnO

Notation Eg1 (eV) Eg2 (eV) Eg3 (eV) Eg4 (eV)

Ni-ZIF-8(10%) 1,84 3,02 4,43 5,02

Ni-ZIF-8(50%) 1,79 3,10 4,36 4,84

Ni-ZIF-8(80%) 1,68 2,98 3,92 4,04

p-NiO/n-ZnO(10%) 1,6 3,08 / /

p-NiO/n-ZnO(50%) 1,6 3,13 / /

p-NiO/n-ZnO(80%) 0,9 3,12 / /

Figure 3.22. XPS spectra of Ni-ZIF-8(80%) and p-NiO/n-ZnO (80%)

Figure 3.22. presents XPS spectra of Ni-ZIF-8(80%) and p-NiO/n-ZnO (80%). The results show

that, there are a shift in the binding energies of peaks to the states of Ni(II) in the p-NiO/ n-ZnO(80%) and

higher than that of Ni-ZIF-8(80%) around 0.32 - 1.03 eV. Especially, for Zn(II) from two Zn2p3/2

(1020.59 eV) and Zn2p1/2 (1043.65 eV) states with two binding energies in Ni-ZIF-8(80%) changed to 5

binding energy levels of two oxidation states Zn2p1/2 (at 1039.4 eV, 1043.35 eV and 1046.16 eV) and

Zn2p1/2 (at 1023.13 eV and 1020 eV) in p-NiO/n-ZnO(80%). Thus, There are binding energy transfed of

Ni(II) and Zn(II) in p-NiO/ n-ZnO(80%). This result shows that electrons could move from Ni(II) to

Zn(II) and exist Ni-O-Zn bonds on p-NiO/ n-ZnO heterojunction.

21

3.3.3. Adsorption and photocatalytic activity of Ni-ZIF-8, p-NiO/n-ZnO, ZnO and NiO

Figure 3.23 presents degradation RDB, base fuchsin, MB in dark and photocatalytic reaction by sun

light. For p-NiO/n-ZnO, (Ct/Co) ratio of RDB, base fuchsin and MB hadn't change in dark, But under sun

light, Ct/Co of RDB, base fuchsin and MB decreased 98 %, 90% and 40%, respectively. The results

indicated that photocatalytic activity of p-NiO/n-ZnO was improved much highter than that of NiO and

ZnO.

0.0

0.2

0.4

0.6

0.8

1.0

(A1

) - RDB

ZIF-8

ZnO

NiO

Ni- ZIF-8

p-NiO/n-ZnO

1201008060400 20

sunlight illuminationin the dark

Ct/C

o

time (minute)

300 400 500 600 700 800

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75 (A2

)- RDB/ p-NiO/n-ZnO

Ab

so

rb

ï (A

bs)

wavelenght (nm)

Intial

after 60 minutes

after 120 minutes

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

(B1

) - Fuchsin base p-NiO/n-ZnO

Ni-ZIF-8

ZIF-8

ZnO

NiO

sunlight illuminationIn the dark

1201008060400 20

Ct/C

o

time (minute)

350 400 450 500 550 600 650 700

0.0

0.5

1.0

1.5

2.0

2.5(b

1) -Fuchsin base/ p-NiO/n-ZnO

Ab

so

rb

ï (A

bs)

wavelength (nm)

Inatial

after 60 minutes

after 120 minutes

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

(c1

) - MB

Ni-ZIF-8

ZnO

NiO

ZIF-8

p-NiO/n-ZnO

sunlight illuminationIn the dark

1201008060400 20

Ct/

Co

time (minute) 400 450 500 550 600 650 700 750

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

(C2

)- MB/ p-NiO/n-ZnO

Ab

so

rb ï(

Ab

s)

wavelength(nm)

initial

after 60 minutes

after 120 minutes

Figure 3.23. photocatalytic activity of ZIF-8(80%), Ni-ZIF-8(80%), ZnO, NiO và p-NiO/n-ZnO and

absorbed spectra of before ; after photocatalytic reaction solutions

Under sun light (UV and visible region), electron - hole pairs of p-NiO/n-ZnO can be combined

with these different mechanisms:

(i) Visible light could be photogenerated stimulation, the mechanism was illustrated in Figure 3.24:

22

Figure 3.24. Photocatalytic reaction mechanism on p-NiO/n-ZnO catalyst under sun light (visible region)

(ii) In the sun light, there are amount of UV light. The NiO-ZnO heterojunction was excited by UV

light, the mechanism was illustrated in Figure 3.25a and Figure 3.25b:

Figure 3.25. Photocatalytic reaction mechanism on p-NiO/n-ZnO catalyst under sun light (UV region)

Interestingly, p-NiO/ n-ZnO could be separate and recover from the aqueous solution after

the reaction base on their magnetic.

23

CONCLUSION

3.1. Synthesis ZIF-8 from Zn(II) and 2-methyl imidazole in methanol solvent at room temperature.

The properties of ZIF-8 was hight surface area of 1484 m2/g, stable in ambient condition for a year, in

water at least for 14 days, in water and organic solvents for 8 hours at boiling conditions and in the pH

range 2,7 to 12,0.

3.2. The ZIF-8 was used as an modyfied electrode (BiF/Naf/ZIF-8/GCE ) for the determination of

Pb(II) by ASV. The characteristic of electrochemical process on electrode surface, such as: participation

of the one proton and two electrons, the electrons transfer coefficient α = 0.458 and the electron transfer

rate constant Ks = 248.3 s-1

. The lead oxidation process was irreversible. Under the optimal conditions,

the peak current of Pb(II) was linearly proportional to its concentration over the range 12 to 100 ppb. The

limit of detection and the limit of quantitation were 4.16 ppb and 12.5 ppb, respectively. The ensitivity

was 0.290 μA/ppb. For our knowledge, this is the first time, ZIF-8 has been known as a potential

electrode modifier for lead determination in aqueous solution by DP-ASV.

3.3. The ZIF-8 material was directly modified by iron (Fe(II)) with The modification direct of ZIF-

8 by Fe with the intial molar ratios Fe(II)/(Fe(II)+Zn(II)) limit reached 30%. Then the low molar rate of

Fe(II), a part of Zn(II) of crystals are isomorphous replaced by Fe(II) and Fe-ZIF-8 was hight surface

area. However, at the hight molar rate, Fe(II) and Fe(III) were either isomorphous replace or distribute in

porous of the material. The ZIF-8 and Fe-ZIF-8 have hight CO2 and CH4 adsoption activation. Adsoption

capacity of CO2 onto are higher than that of CH4. The adsoption capacity of gas onto ZIF-8 is much higher

than that onto Fe-ZIF-8. The adsoption capacity of gas decreased with an increase in iron amount

incorporated.

3.4. The ZIF-8 and Fe-ZIF-8 were used for the removal of Remadazol deep black RGB (RDB)

from aqueous solutions. Natarajan - Khalaf equation and recovery method were combined to reseach

reversible adsorption kinetics onto the ZIF-8 and Fe-ZIF-8 materials. The RDB adsorption onto ZIF-8 and

Fe-ZIF-8 involved a phylsical - chemcal mechanism. The diffusion of RDB into these materials was

essentially film-diffusion and best fit with two segments linear regression of Weber's model. The

introduction of iron into ZIF-8 provided a much lager adsorption catacity and faster adsorption kinetic of

RDB than ZIF-8. The adsorption activity due to the electrostatic interaction and the hydrophobic and π−π

interaction between the aromatic rings of the RDB dye and the aromatic imidazole rings of the adsorbent

for ZIF-8, the coordination of the nitrogen atoms and oxygen in carboxyl group in RDB molecules to the

Fe(II) in Fe-ZIF-8 framework. The ZIF-8 and Fe-ZIF-8 were reusability by NaOH 0.001M. The

adsorption capacity was seem unchangeable and structure were not broken after three cycles.

3.5. The study on photocatalytic activity of ZIF-8 and Fe-ZIF-8 in degradation RDB dye under

sunlight. The iron doped ZIF-8 brought a red shift and drove the band gap in visible light. The Fe-ZIF-8

can act as a sun-light-driven photocatalyst for highly efficient degradation of RDB dye. Fe-ZIF-8 material

24

was stable in photocatalyst condition. The photocatalytic activity and structure of Fe-ZIF-8 were not

broken after three cycles.

3.6. The p-NiO/n-ZnO nanocparticles with 10-15 nm level were synthesised from Ni-ZIF-8 and

were hight photocatalytic activity under sunlight. The p-NiO/n-ZnO material had paramagnetism and

hight photocatalytic degradation of RDB dye, Fuchsin basic and methylene blue under sunlight. For our

knowledge, this is the first report about p-NiO/n-ZnO nanocparticles were prepared by the thermal

treatment of Ni-ZIF-8.

List of articles related to dissertation

I. National articles

1. Mai Thi Thanh, Nguyen Thi Cam Vy, Tran Thanh Minh, Nguyen Phi Hung, Đinh Quang Khieu

(2014), Using Rietveld refinement method for studying XRD pattern of zeolite imidazole

framework ZIF-8, Viet Nam Journal of Catalysis and Adsorption, vol 3(N03), pp. 134-149.

2. Mai Thi Thanh, Nguyen Phi Hung, Hoang Van Đuc, Đinh Quang Khieu(2015), A study on

synthesis of ZIF-8 by hydrothermal process, Viet Nam Journal of Science and Technology, 53(1B),

pp. 333-340.

3. Mai Thi Thanh, Nguyen Phi Hung, Đinh Quang Khieu, Ho Tan Hau, Pham Thi Thanh Ha (2017),

Synthesis NiO-ZnO nanoparticles from Ni-ZIF-8 precursors and photocatalytic activity under

sunlight , Viet Nam Journal of Catalysis and Adsorption, T6(N02), pp. 107-114.

4. Mai Thi Thanh, Vo Trieu Khai, Mai Van Bay, Nguyen Phi Hung, Đinh Quang Khieu (2015), A

comparative study on structures of ZIF-8 and ZnO, Journal of Catalysis and Adsorption, T4.

(No.4B), pp.136-140.

5. Nguyen Hai Phong, Mai Thi Thanh, Duong Cat Tien, Mai Xuan Tinh, Nguyen Phi Hung, Dinh

Quang Khieu (2017), Zeolite Imidazole Framework-ZIF-8: Synthesis and Voltammetric

Determination of Lead Ions Using Modified Electrode Based on ZIF-8, VNU Journal of Science:

Natural Sciences and Technology, Vol. 32, No. 1S , pp. 198-206.

6. Mai Thi Thanh, Bui Thi Minh Chau, Ho Van Thanh, Đinh Quang Khieu (2017), facile synthesis of

NiO-ZnO nanoparticles by pyrolysis of Ni-ZIF-8 and photocatalytic activity under sunlight, Hue

University Journal of Science, vol 3, pp.117-124, T126. (No.1A), pp.51-58.

7. Mai Thi Thanh, Đinh Quang Khieu, Pham Thi Anh Thu, Ho Van Thanh (2017), Synthesis of iron

modified zeolitic imidazolate framework-8(Fe-ZIF-8) and photocatalytic activity by sunlight,

Journal of Science and Technology, Hue University - College of Sciences, T7.(No.1). pp.53-66.

8. Mai Thi Thanh, Le Thi Nhat Tram (2016), Synthesis of zeolitic imidazolate framework-8 (ZIF-8)

by the solvent thermal method, Quang Nam university Journal of Science, No. 9. Tr. 120-124.

II. Proceedings of International conference

9. Mai Thi Thanh, Nguyen Hai Phong, Tran Thanh Minh, Phan The Binh, Nguyen Phi Hung,

Nguyen Thi Vuong Hoan, Dinh Quang Khieu (2017), Voltametric determination of lead ions using

modified electrode based on zeolite imidazole framework-8, Conference proceeding, Analytical

Vietnam conference 2017, Hanoi, March 29-30, 2017, pp.84 -95.

III. International articles (ISI)

10. Mai Thi Thanh, Tran Vinh Thien, Vo Thi Thanh Chau, PhamDinh Du, Nguyen Phi Hung, and

Dinh Quang Khieu, Synthesis of Iron Doped Zeolite Imidazolate Framework-8 and Its Remazol

Deep Black RGB Dye Adsorption Ability, Journal of Chemistry, Volume 2017, Article ID

5045973, 18 pages. IF = 1.3

11. Mai Thi Thanh, Tran Vinh Thien, Pham Dinh Du,

Nguyen Phi Hung, Dinh Quang Khieu, iron

doped zeolitic imidazolate framework (Fe-ZIF-8): synthesis and photocatalytic degradation of RDB

dye in Fe-ZIF-8, Journal of Porous Mater, Volume 2017, DOI 10.1007/s10934-017-0498-7, 13

pages, IF = 1.65.

12. Dinh Quang Khieu, Mai Thi Thanh, Tran Vinh Thien, Nguyen Hai Phong, Hoang Van Duc, Pham

Dinh Du, Nguyen Phi Hung, Zeolite imidazole Framework-8 (ZIF-8): Synthesis and

Electrochemistry Determination of Pb(II) Using ZIF-8 Based Modified Electrode. (Đã nộp đến

Journal of Scanning).