mai thi thanh study on modification of zif8 material and its applications

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 Electr[r]

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

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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 :

Examiner 2 :

Examiner 3 : :

The dissertation will be defended at

Time: date month year 2017 The dissertation could be found at:

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

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

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

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

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

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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 resultis 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

(e) GCE (f) BiF/GCE

-30 -20 -10 0 10 20

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

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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, E pa 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 (25o

C) 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

2 3 4

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(b) lnIp,Pb = 0,8834.ln-0,577 R 2 = 0,9849

I 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 lnI p vs lnv

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

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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

The limit of quantitation (LOQ) calculated from 10S y /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%

ZIF-8

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

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)

0 10 20

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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

Zn (mol.g -1 )

Fe (mol.g -1 )

Molar ratio Fe/(Zn+Fe)

Initial molar ratio Fe/(Zn+Fe)

Fe(II) (%)

Fe(III) (%)

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%)

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

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

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

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

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ZIF-8

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

Figure 3.10 CO 2 (a) and CH 4 (b) adsorption/desorption isotherms of ZIF-8 and Fe-ZIF-8

Table 3.4 The CO 2 and CH 4 adsorption capacities on ZIF-8 and Fe- ZIF-8 at 30 bar, 298 K

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

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Table 3.5 The Henry constant of CO 2 and CH 4 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

10 20 30 40 50 60 70 80

10 20 30 40 50 60 70 80 90 100

10 20 30 40 50 60 70 80

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-

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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

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

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

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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

5 10 15 20 25 30 35 40 45 50 55 60

10 20 30 40 50 60 70 80 90 100 110

10 20 30 40 50 60 70 80 90 100 110

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-

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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

kb

(x10 3 ) (min -1 )

kads

(x10 3 ) (min -1 )