PREPARATION AND CHARACTERIZATION OF NANOSTRUCTURED
BARIUM OXIDE
MASHKURAH BINTI ABD RAHIM
UNIVERSITI TEKNOLOGI MALAYSIA
PREPARATION AND CHARACTERIZATION OF NANOSTRUCTURED
BARIUM OXIDE
MASHKURAH BINTI ABD RAHIM
A dissertation submitted in partial fulfilment of the
requirements for the award of the degree of
Master of Science (Chemistry)
Faculty of Science
Universiti Teknologi Malaysia
DECEMBER 2010
iii
For my family & those that I love so much…
“There’s nothing to be ashamed of to be dependant to others.
We need others to survive. When we die, we need others.
When we were born, we need others.
The truth is, in the between, we need others the most.”
iv
ACKNOWLEDGEMENTS
In the name of Allah, the most gracious and merciful…
Praise to Allah S.W.T and salam to our prophet Muhammad S.A.W for giving me the
strength and blessing, to complete this project. During the preparation of this project
paper, I received advice and support from various individuals. All the sweat and
struggle in completing this project paper had yet to be proven worth our time. But
still I am sure of the benefits to be gained from having to finish this work.
Special thanks goes to my supervisor, Prof. Dr Abd Rahim Yacob and those
who were involved directly or indirectly in assisting my study. I appreciate for all the
kindness, concern and generosity in giving me advice, and encouragement to help me
complete this course. Also thanks to all my project team for their supports, ideas and
assistances to me in order to complete my project.
Last but not least, I would like to express my gratitude to my dearly loved
family members, my father, Mr. Abd Rahim B. Shaari, my mother, Mrs. Noraini Bt
Ahmad and all my siblings. Thanks for all the love, faith, support, motivation and
encouragement that helps me to keep on reaching for my dreams.
v
ABSTRACT
It was found that the basic catalytic property of the metal oxide was increase
with high surface area and nanosized particles. In this study, surface modified
Barium oxide (BaO) was synthesized by hydration-dehydration method. Barium
hydroxide ( Ba(OH)2) has prepared from Barium Peroxide (BaO2) which acted as
precursor. The Ba(OH)2 was calcined at a temperature of 50°C to 300°C under
vacuum atmosphere of 10-3 mbar. Prepared samples were characterized using
thermogravimetric-derivative
thermogravimetry
(TG-DTG),
fourier-transform
infrared (FTIR), X-ray powder diffraction (XRD), single point Brunauer-Emmet
Teller (BET) surface area analysis and field emission scanning electron microscope
(FESEM). The TG-DTG result shows that the major weight lost occurs at a
temperature 110°C to 150°C which was 0.7%. This indicated the decomposition of
barium hydroxide to barium oxide. The XRD diffractogram of BaO proved that
Ba(OH)2 has been transformed to BaO in tetragonal formed as the temperature
increases. The particle size for the surface modified barium oxide was calculated
using Scherer’s equation and the resulting particle size was approximately 34 nm.
Thus, the prepared surface modified BaO with nano size particles have been
produced in this study. The amount of basic sites was investigated using the most
fundamental chemical techniques of back titration and as the temperature increases
from 150°C to 300°C, the basic sites increases from 0.67 to 1.67 mmol g-1
respectively. This is most probably due to the formation of more BaO with basic sites
that occur during the activation process at temperature 300°C. The chemical
properties of the prepared surface modified BaO were measured using electron spin
resonance (ESR) method. Based on ESR study, a single peak g-value at 1.9830 was
observed throughout the 30 minutes UV radiation and shown that only one site which
active in electron trapping sites.
vi
ABSTRAK
Ia telah terbukti bahawa sifat berbes mangkin oksida alkali bumi meningkat
apabila luas permukaannya tinggi dan bersaiz nano. Dalam kajian ini, barium oksida
(BaO) disintesis melalui kaedah penghidratan-penyahhidratan. Barium hidroksida
(Ba(OH)2) telah disediakan daripada barium peroksida (BaO2) sebagai bahan
permula. Ba(OH)2 telah dipanaskan pada suhu 50°C hingga 300°C dalam keadaan
vakum atmosfera pada tekanan 10-3 mbar. Pencirian semua sampel telah dilakukan
dengan menggunakan termogravimetri-pembezaan termogravimetri analisis (TGDTG), spektroskopi inframerah (FTIR), pembelauan sinar-X (XRD), penjerapan gas
nitrogen (NA) dan mikroskop imbasan elektron (FESEM). Keputusan TG-DTG
menunjukkan purata kehilangan berat berlaku pada suhu 110°C hingga 150°C
sebanyak 0.7%. Ini menunjukkan perubahan Ba(OH)2 kepada BaO. Keputusan XRD
menunjukkan apabila suhu meningkat, Ba(OH)2 telah berubah kepada BaO dalam
bentuk tetragonal. Saiz BaO yang dihasilkan telah dikira dengan menggunakan
persamaan Scherer’s dan saiznya menghampiri 34 nm. Ini jelas membuktikan
bahawa BaO yang dihasilkan dalam penyelidikan ini adalah dalam saiz nano. Jumlah
permukaan aktif dan kekuatan alkali telah dikenalpasti dengan menggunakan teknik
asas kimia iaitu penitratan semula. Kebesan meningkat apabila suhu meningkat
daripada 150°C kepada 300°C iaitu meningkat 0.67 dan 1.67 mmol g-1. Ini
disebabkan oleh pembentukan lebih banyak permukaan aktif pada BaO pada suhu
300°C. Ciri-ciri kimia BaO yang dihasilkan diukur dengan menggunakan kaedah
resonan putaran elektron (ESR). Berdasarkan kaedah ESR, dengan radiasi UV
selama 30 minit, didapati puncak tunggal terhasil dengan nilai g adalah 1.9830 dan
jelas membuktikan bahawa hanya satu sahaja permukaan di BaO yang aktif
menangkap elektron.
vii
TABLE OF CONTENTS
CHAPTER
1
TITLE
PAGE
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENTS
iv
ABSTRACT
v
ABSTRAK
vi
TABLE OF CONTENTS
vii
LIST OF TABLES
x
LIST OF FIGURES
xi
LIST OF SCHEME
xiii
LIST OF SYMBOLS
xiv
LIST OF APPENDIX
xv
INTRODUCTION
1.1
Background of Research
1
1.2
Problem Statement
2
1.3
Significance of Research
2
1.4
Objectives of Research
3
1.5
Scope of Research
4
viii
2
LITERATURE REVIEW
2.1
Catalyst
5
2.2
Alkaline Earth Metal Oxide
6
2.3
Barium Oxide
7
2.4
Characterization Technique
10
2.4.1
11
Thermogravimetry-Derivative
Thermogravimetry (TG-DTG)
2.4.2
Fourier Transform Infrared (FTIR)
11
2.4.3
X-ray Powder Diffraction (XRD)
12
2.4.4
Nitrogen Adsorption (NA)
2.4.4.1
Single Point Brunauer-Emmet
15
Teller (BET)
2.4.5
Field Emission Scanning Electron Microscope
15
(FESEM)
2.4.6
3
Electron Spin Resonance (ESR)
16
EXPERIMENTAL
3.1
Instrumentation
21
3.2
Chemical Reagent
23
3.3
Catalyst Preparation
23
3.3.1
23
Preparation of Barium Hydroxide via
Hydration method
3.3.2
Activation BaO using High Vacuum Pump
24
System
4
3.4
Sample Characterization
25
3.5
Basicity Analysis
26
RESULTS AND DISCUSSION
4.0
Introduction
27
ix
4.1
Preparation of Nano Barium Oxide
27
4.2
Characterization Techniques
28
4.2.1
Thermogravimetry Derivative
28
Thermogravimetry(TG-DTG)
4.2.2
Fourier Transform Infrared (FTIR)
30
4.2.3
X-ray Powder Diffraction (XRD)
34
4.2.4
Nitrogen Adsorption (NA)
4.2.4.1
4.2.5
Single Point BET Surface Area
Field Emission Scanning Electron
38
38
Microscope (FESEM)
5
4.2.6
Basicity analysis for prepared BaO
40
4.2.7
Electron Spin Resonance (ESR)
42
CONCLUSION
45
REFERENCES
46
Appendix 1
49
x
LIST OF TABLES
TABLE NO.
2.1
TITLES
Advantages and disadvantages of homogeneous and
PAGE
6
heterogeneous catalyst
2.2
Physical properties of BaO
9
3.1
Annealing temperature in surface modified BaO
24
4.1
Peaks assignment for commercial BaO2
31
4.2
Peaks assignment for prepared Ba(OH)2
32
4.3
XRD peaks assignment for commercial BaO2
35
4.4
List of peaks assignment for Ba(OH)2 and the
37
prepared nano BaO
4.5
SBET for prepared BaO
38
xi
LIST OF FIGURES
FIGURE NO.
TITLES
PAGE
1.1
Layout of research scope
4
2.1
Ions in low coordination on the surface of MgO
10
2.2
Simplified X-ray diffractometer diagram
13
2.3
Pictorial view of Bragg’s Law
14
2.4
The diagram of ESR spectrometer
17
2.5
Zeeman energy levels of an electron in an applied magnetic field
18
2.6
ESR sample cell
19
3.1
Diagram of vacuum system
24
3.2
Flow Chart of how prepared BaO was prepared
25
4.1
TGA-DTA decomposition of Ba(OH)2
28
4.2
Percentage of weight lost at different temperature regions
29
from TGA
4.3
Illustration for (a) unassociated hydroxyl bond and
30
(b) stretching vibration of adsorbed water molecule
4.4
FTIR spectrum for commercial BaO2
31
4.5
FTIR spectrum for prepared Ba(OH)2
32
4.6
FT-IR spectrum for (a) Ba(OH)2, (b)BaO-50, (c)BaO-100,
33
(d)BaO-150, (e) BaO-200 (f)BaO-250 (g)BaO-300
4.7
XRD diffractograms for commercial BaO2
34
4.8
XRD diffractograms for (a)Ba(OH)2 (b)BaO-100
36
(c) BaO-200 (d) BaO-300
4.9
(a) FESEM micrograph for Ba(OH)2 with magnification
25,000X
39
xii
(b) FESEM micrograph for BaO with magnification
39
25,000X
4.10
Amount basic sites of the prepared nano BaO
40
4.11
(a) No peak recorded using ESR for the sample after
42
2 minute UV
(b) Peak recorded using ESR for the sample after 30 minute UV
irradiated
43
xiii
LIST OF SCHEME
SCHEME NO.
4.1
TITLE
Schematic diagram in the determination of amount basic site
for prepared nano BaO
PAGE
40
xiv
LIST OF SYMBOLS
ºC
- degree Celcius
cm-1
- Wave number
g
- Gram
MHz
- Mega hertz
mmol
- Milimole
m
- Micrometer
g
- Gram
cm
- Centimeter
K
- Kelvin
Eq
- Equation
kV
- Kilo volt
mA
- Mili ampere
mL
- Mililiter
nm
- Nanometer
ID
- Internal diameter
θ
- Half angle of diffraction beam
λ
- Wavelength
xv
LIST OF APPENDIX
APPENDIX
1
TITLES
Sample calculation for particle size, D using
Schererr’ Equation (Eq. 3.1)
PAGE
49
CHAPTER 1
INTRODUCTION
1.1
Background of Research
Chemical reactions which are promoted by catalyst have two types of
reactions which are either acid-catalyzed or base-catalyzed reactions. In acidcatalyzed reactions, reactants act as base toward the acid catalysts, while in basecatalyzed reactions, reactants act as acids toward the base catalysts. In contrast to
extensive studies of solid acid catalysts, fewer efforts have been given to the study of
solid base catalysts. Certain metal oxides with a single component were found to act
as solid base catalysts in the absence of such alkali metals as Na and K. In recent
years, non oxide type catalysts have been recognized as solid base catalysts or
heterogeneous basic catalysts (Hattori, 2001).
Alkaline earth metal oxides were used for the catalysts and starting materials
for basic heterogeneous reaction. Barium oxide (BaO) is one of the compounds in
alkaline earth metal oxide series. The chemical characteristic of BaO is the same as
MgO and CaO since they were in the same group in the periodic table. Physicochemical properties of BaO such as surface area, particle size and basicity on the
other hand lies on their method of preparation, since different method of preparation
would yield different product with different characteristics and properties. Alkaline
earth metal oxide can be prepared by various preparation methods. This project was
focused on the preparation of BaO from hydration-dehydration process at various
temperatures.
2
1.2
Problem Statement
The knowledge about the actual catalytic sites or surface defect responsible
for the reactivity remains unanswered. For most of the materials called solid base, the
catalytic activities are on the removal of water and carbon dioxide from the surfaces.
The nature of the surface basic sites varies with the severity of the pre-treatment
conditions. Besides removing of water and carbon dioxide, rearrangement of surface
and bulk atoms occurs during pre-treatment, which changes the number and nature of
the basic sites with increasing pre-treatment temperature. Therefore, the optimum
pre-treatment temperature varies with the type of reaction (Yacob et al., 2009).
In local
industry, conventional biodiesel
was manufactured using
homogeneous base catalyst such as potassium hydroxide and sodium hydroxide via a
process called transesterification. The homogeneous base catalyst has the advantage
of a fast reaction rate under mild condition, but requires a large amount of water to
wash the catalyst off the product. Furthermore, the washing operation produces
saponification and stable emulsion. This will lower the yields and is environmentally
harmful.
In the other hand, although sulfuric acid can catalyze the transesterification,
the acid catalyzed give slower reaction. Many researchers have studied to develop
other methods that can solve these problems. They found that heterogenous base
catalyst will make more economic advantage, easy separation from the reaction
mixture and reduce environmental pollution (Hattori et al., 1998).
1.3
Significance of Research
Solid-base catalysts have many advantages over liquid
bases or
organometallics. They present fewer disposal problems, while allowing easier
separation and recovery of the products, catalysts, and solvent. They are
noncorrosive. Thus, solid-base catalysts offer environmentally benign and more
3
economical pathways for the synthesis of fine chemicals. Because of these
advantages, study on the synthesis of fine chemicals using solid bases as catalyst has
increased over the past decade.
Barium oxide was prepared under vacuum atmosphere at various
temperatures. Generation of basic sites at surface was dependence to the pretreatment at high temperature. Basically, surface of these materials were covered
with adsorbent molecule such as carbon dioxide, water and in some cases, oxygen as
they handed in air.
The way to remove molecule covering the surfaces depends on the severity of
pre-treatment. As the temperature increase, the molecule covering the surface was
successively desorbed according to the strength of the interaction with the surface
sites. The sites that appear on the surfaces by pre-treatment at low temperature were
suggested to be different from those appearing at high temperatures. If simple
desorption of molecules occurs during pre-treatment, the basic sites that appear at
high temperatures should be strong (Hyun et al., 2001).
1.4
Objectives of Research
This study has the following objectives:
1. To prepare BaO via hydration-dehydration method from 50°C to
300°C respectively under vacuum atmosphere.
2. To identify and characterize the prepared BaO by various methods
such as TG-DTG, FT-IR, XRD, BET and FESEM that explains the
surface of BaO.
3. Back titration to determine the basicity of the prepared BaO effect
by temperature of hydration-dehydration.
4. To investigate the ability of the surface defect to trap electron using
Electron Spin Resonance (ESR) spectroscopy and determine the
amount of basic sites.
4
1.5
Scope of Research
This study focus on the preparation of surface modified BaO using hydrationdehydration method. Figure 1.1 shows overview the schematic layout of research
scope where barium peroxide was used as the starting material. The prepared
Ba(OH)2 was calcined at various temperatures: 50°C, 100°C, 150°C, 200°C, 250°C
and 300°C for two hours respectively. The sample was characterized using
thermogravimetric-derivative
thermogravimetry
(TG-DTG),
fourier-transform
infrared (FTIR), X-ray powder diffraction (XRD), nitrogen adsorption (single point
BET analysis) and field emission scanning electron microscope (FESEM).
Prepare Ba(OH)2 from
barium peroxide
Synthesis of BaO from Ba(OH)2
Hydration-dehydration method at
various temperatures (50°C-300°C)
about two hours
Characterization
techniques
TG-DTG
FTIR
XRD
BET
FESEM
ESR study
Back titration
Figure 1.1
Layout of research scope
CHAPTER 2
LITERATURE REVIEW
2.1
Catalyst
According to the basic concept, catalyst can be defined as a substance that
increases the rate of reaction without being consumed nor produced in the process. A
catalyst provides an alternative route of reaction where the activation energy is lower
than the original reaction. Typically, catalyst added to a reaction system to increase
the speed of a chemical reaction approaching a chemical equilibrium.
At the same time, catalysis is important in chemistry phenomena reactivity
either as homogeneous or heterogeneous catalyst. In homogeneous catalysis, a
catalyst is in the same phase (usually liquid or gas reaction mixture) as the reactants
and products. A catalyst that is in a different phase (usually solid in liquid reaction
mixture) from the reactants is called heterogeneous catalyst (Sheldon et al., 2001).
Heterogeneous catalysis is an economically and ecologically important field
in catalysis research because heterogeneous catalysts have many advantages such as
non-corrosive and environmentally friendly. They are present fewer disposal
problems than do homogeneous catalysts and also much easier to separate from
liquid. Many types of heterogeneous solid base catalysts, such as alkaline earth metal
oxides and hydroxides, have been studied for the transesterification of vegetable oils
using various metal oxides compounds supported on alumina zeolite. The order of
activity among alkaline metal oxide catalysts are BaO > SrO > CaO > MgO. The
6
active ingredients in most supported metal oxide catalysts are easily corroded by
methanol and have short catalyst lifetimes (Yoosuk et al., 2010).
Table 2.1: Advantages and disadvantages of homogeneous and heterogeneous
catalyst
Types of catalyst
Homogeneous catalyst
Advantages
Disadvantages
High selectivity
Scale-up can be
Ease of heat
costly, difficult,
dissipation from
and dangerous
exothermic
Difficulties in
reactions
handling
High activity
Difficulties in
towards reaction
separation
due to kinetic factor
Easy to use and
separate
Catalysts are robust
Heterogeneous catalyst
at high temperature
Difficult to accept
and pressure
high active
High activity
component
towards reaction
loading to further
due to high surface
improve strength
area
and impact
Convenient to
Difficult to modify
handle
No solvents are
required
2.2
Alkaline Earth Metal Oxide
The study of alkaline earth metal oxides is great interest for many reasons.
Earlier works has proved that nanocrystalline in group IIA exhibit remarkable
7
capacities and rates for sulfur dioxide, hydrogen halides, nitrogen oxides,
chlorocarbons and other polar organic compounds.
Oxide materials are also used in large quantity as catalyst in industrial for
performing total or partial oxidation, and the reduction and oxidation of the surface
play a key role in these processes (Singh et al., 2007).
These oxides have long been considered a typical case for understanding
bonding in ionic oxides and are also one of the most fundamental materials for
industrial science. These oxides are a major constituent of the earth’s lower mantle
(between 600 and 2900 km in depth). The electronic structure, structural phase
transitions, elasticity, thermal properties, stability and the equation of state of these
oxides have been extensively studied theoretically and experimentally (Kouzu et al.,
2008).
In the periodic table, alkaline earth metal oxide is an element in Group IIA.
The elements of alkaline earth metal are beryllium, magnesium, calcium, strontium,
barium, and radium (Singh, 1976). The metal oxides have long been known as basic
solid catalytic materials. It has been revealed that not only single component metal
oxides but also alkaline earth modified oxides and alkaline earth ion exchanged
zeolite exhibit basic properties on the surface. Since acidic carbon dioxide desorbs at
a higher temperature from stronger basic sites, the base strength is in the order:
BaO/Al2O3 > SrO/Al2O3 > CaO/Al2O3 > MgO/Al2O3.The calcinations temperature
influence the basic properties of metal oxide but the strength of basic sites is not
influence. However, increase temperature, will influence the amount of basic sites
(Chen et al., 1998).
2.3
Barium Oxide
The metal oxide has high lattice enthalpies. Atomic and ionic radii increase
smoothly down the Group. High surface area mesoporous and shaped form of metal
8
oxide is desirable for these applications. The unique in its basicity and forms a class
apart from other supports such as alumina, zeolite, activated carbon, silica which are
acidic, neutral or amphoteric (Tang et al., 2008). Oxide surfaces are of particular
interest due to their importance in environmental processes. Since many mineral oxides
are primary constituents of the earth’s crust. Oxide surfaces provide stable supports both
thermally and mechanically (Suchan, 2001).
Previous study has shown that metal oxide is expected to be a good catalyst
supports because it have huge surface areas, enhanced surface reactivity which due to
their unusual crystal shapes with a high ratio of coordinative unsaturated edge and
corner surface sites as well as defect sites that are inherently more reactive toward
incoming adsorbates (Khaleel et al., 1999). The properties of metal oxide are also
similar to barium oxide (BaO) because it is one of element in the alkaline earth metal
oxides group.
Several barium compounds are interesting as a starting material for
processing refractory and engineering ceramic, for example barium oxide (BaO),
barium monoaluminate (BaO.Al2O3) and barium hexaaluminate (BaO.6Al2O3) are
refactory materials having boiling temperature of about 1890°C, 1800°C and 1900°C
respectively.
Base catalyst exhibit high catalytic activities and a number of basic
heterogeneous catalysts have been developed, such as metal oxide, zeolites, hydrotalcites, and anion exchange resins. BaO is a heterogeneous catalyst known as base
catalyst. It has many advantages, such as higher activity, mild reaction conditions,
long catalyst lifetimes, low catalyst cost and so on (Kawashima et al., 2008). Table
2.2 shows briefly physical physical properties of BaO used in a reaction mixture.
Barium oxide can be utilized in a variety of applications because of its physical and
chemical qualities.
9
Table 2.2: Physical properties of BaO
No
Properties
Description
1
Density
3.51 g/cm3 at room temperature
2
Melting point
727°C at Standard Atmospheric Pressure
3
Boiling point
1897°C at Standard Atmospheric Pressure
4
Color
Silvery white
5
Molecular weight
169.34 g mol-3
6
Enthalpy of formation
502.9 kJ/mol at 298.15 K
One of factor that gives big impact in determines the chemical reactivity of
BaO is surface defect itself. The surfaces of the basic catalysts were covered with
carbon dioxide, water, and in some cases, with oxygen. Pre-treatment at high
temperatures is required to have basic sites exposed on the surfaces. Taking
magnesium oxide as an example, while evacuating magnesium hydroxide of a
catalyst precursor, water, and carbon dioxide begin to evolve at about 700 K. At this
temperature, the catalytic activities for different types of reactions appear and
increased with increasing the pre-treatment temperature to give maximum activities
at certain temperatures. Then, the activities decreased with further increased in the
evacuation temperature.
The situation was similar to the metal oxides, for example BaO. They exhibit
basic sites if the oxide surfaces appear on pre-treatment at high temperatures. The
nature of the basic sites generated by removing the molecules covering the surfaces
depends on the severity of the pre-treatment. The changes in the nature of basic sites
are reflected in the variations of the catalytic activities as a function of pre-treatment
temperatures. As the pre-treatment temperature increases, the molecules covering the
surfaces are successively desorbed according to the strength of the interaction with
the surface sites.
10
Figure 2.1
Ions in low coordination on the surface of MgO
From Figure 2.1 shows that there are several Mg–O ion pairs of different
coordination numbers on the surface of MgO. Ion pairs of low coordination numbers
exist at corners, edges, and high Miller index surfaces. Among the ion pairs of
different coordination numbers, the ion pair of three-fold Mg2+ three-fold O2− is most
reactive and adsorbs carbon dioxide most strongly. At the same time, the ion pair is
most unstable and tends to rearrange easily at high temperature.
The appearance of such highly unsaturated sites by the removal of carbon
dioxide and the elimination by the surface rearrangement compete, which results in
the activity maxima with change in the pre-treatment temperature. It is essential to
remove the adsorbed carbon dioxide, water, and, in some cases, oxygen from the
surfaces to generate basic sites, though variety of pre-treatment temperatures.
2.4
Characterization Technique
Characterization of the catalyst was conducted by several instruments:
i.
Thermogravimetry derivative thermogravimetry (TG-DTG)
ii.
Fourier transform infrared (FTIR)
iii.
X-ray powder diffraction (XRD)
11
iv.
Nitrogen adsorption (NA) {Single point Brunauer-Emmet Teller
(BET)}
2.4.1
v.
Field emission scanning electron microscope (FESEM)
vi.
Electron spin resonance (ESR)
Thermogravimetry-Derivative Thermogravimetry (TG-DTG)
The term thermal analysis (TA) used to describe analytical experimental
techniques which investigate the behavior of a sample as a function of temperature.
The ability of these techniques to characterize quantitatively and qualitatively a huge
variety of materials over considerable temperature range has been pivotal in their
acceptance as analytical technique. In TG-DTG, the sample was done in air and
nitrogen gas. The sample of Ba(OH)2 was analyzed using Metler-Toledo Q100.
The instrument of TG-DTG at heating rate of 10°C/min to determine thermal
decomposition and weight loss of sample. The result of detection is presented
graphically as a plot of weight persentage versus time or temperature. Such plot is
known as thermogram. From the thermogram, can determine the step of sample
decomposition, the thermal stability and the temperature at which certain reaction
takes place. In this paper, TGA are important in determining the optimum
temperature for the production of BaO via decomposition of their hydroxide, and
also to ensure the conversion of Ba(OH)2 to BaO has completed.
2.4.2
Fourier Transform Infrared (FTIR)
Infrared (IR) spectroscopy is a powerful tool for identifying types of chemical
bonds in a molecule by producing an infrared absorption spectrum. By interpreting
the infrared absorption spectrum, the chemical bonds in a molecule can be
determined. The absorption measurement is on different IR frequencies by a sample
positioned in the path of an IR beam. Functional groups absorb difference
12
characteristic frequencies of IR radiation. Molecular bonds vibrate at various
frequencies depending on the elements and the type of bonds. For any given bond,
there are several specific frequencies at which it can vibrate.
The IR portion of the electromagnetic spectrum is divided into three region;
the near-, mid- and far- IR, named for their relation to the visible spectrum. The farIR, (400-10 cm-1) has low energy and may be used for rotational spectroscopy. The
mid-IR (4000-400 cm-1) may be used to study the fundamental vibrations and
associated rotational vibration structure, whilst the higher energy near-IR (140004000 cm-1) can excite overtone or harmonic vibrations.
Chemical bonds have specific frequencies which vibrates corresponding to
their energy levels. The resonance frequencies or vibration frequencies are
determined by the shape of the molecular potential energy surfaces, the masses of the
atoms and eventually by the associated vibrancies coupling. In order for a vibration
mode in a molecule to be IR active, it must be associated with changes in the
permanent dipole (Ratna, 2007).
2.4.3
X-ray Powder Diffraction (XRD)
XRD is an instrumental technique that used to identified minerals as well as
other crystalline materials. It is an electromagnetic radiation with wavelengths of the
order of 10-10 m and typically generated by bombarding a metal with high energy
electrons and the phenomenon of diffraction of the interference caused by an object
in the path of waves (Atkins, 2002). It occurs when the dimensions of the diffracting
objects are comparable to the wavelength of the radiation. The pattern of varying
intensity that results from the phenomenon is called the diffraction pattern.
Figure 2.2 shows simplified X-Ray diffractometer that consists of X-ray
source (X-ray tube), X-ray detector and the sample during X-ray scan. Both X-ray
13
tube and the detector move through the angle (θ) and the sample remain stationary
(Flohr 1997).
Figure 2.2
Simplified X-ray diffractometer diagram
XRD instrument provides the researcher with a fast and reliable tool for
routine mineral identification. Other information obtained can include the degree of
crystallinity, the structural state, possible deviations of the minerals from their ideal
compositions and degree of hydration for minerals that contain water in their
structure (Hanis, 2006). There are many different sets of planes in crystal. Each set of
planes has a specific interplanar distance that will give rise to a characteristic angle
of diffracted X-rays. The relationship between wavelength (λ), atomic spacing (d)
and angle (θ) was solved as the Bragg’s Law in Equation 2.1 and Figure 2.3 shows
the pictorial representative of the Equation.
n λ = 2 d sin θ
Where;
n = the order of the diffracted beam
λ = wavelength of the incident X-ray beam
d = the distance between adjacent planes of atoms (d-spacing)
θ = the angle of the incident X-ray beam
(Eq. 2.1)
14
Figure 2.3
Pictorial view of Bragg’s Law
Since λ is known and θ can be measured, then the d-spacing can be
calculated. The characteristic set of d-spacing generated in a typical X-ray scan
provides a unique fingerprint of the material. Proper interpretation by comparing it
with the standard reference patterns and measurements, this fingerprint will provide
the identification of the material. A diffraction pattern contains a lot of structural
information; the angular position of the reflections is related to the size and shape of
the unit cell while the intensities reflect the lattice symmetry and the electron density
within the unit cell. X-ray diffraction used to obtain information about the structure
and composition of the crystalline material.
The powder XRD pattern of a particular barium oxide was characteristic of
its framework structure and can be considered as its fingerprint. Through this XRD
technique the phase presents in the sample and signify whether the solid sample is
crystalline or amorphous phase was identified. Crystallinity of prepared barium oxide
was monitored by X-ray Powder Diffraction Bruker Advance D8 using Siemens
5000 diffractometer with Cu-Kα radiation (λ=1.5406 Ǻ, 40 kV, 40 mA). Scan
performed in step mode of 0.05 seconds/step and the range of the 2θ will be from 10°
to 90° (Atkins, 2002).
15
2.4.4
Nitrogen Adsorption (NA)
2.4.4.1 Single Point Brunauer-Emmet Teller (BET)
Adsorption was a process that occurs when a gas or liquid solute accumulates
on the surface of a solid or, more rarely, a liquid (adsorbent), forming a molecular or
atomic film (the adsorbate). Adsorption was usually described through isotherms that
was, functions which connect the amount of adsorbate on the adsorbent, with its
pressure (for gas) or concentration (for liquid). The most widely used isotherm
dealing with multilayer adsorption was the BET model and a well-known rule for the
physical adsorption of gas molecules on a solid surface. In 1938, Stephen Brunauer,
Paul Hugh Emmett, and Edward Teller published an article about the BET theory in
a journal for the first time; “BET” consists of the first initials of their family names
(Ratna, 2007).
It is important to obtain detail information about surface area, the porosity of
materials and the surface morphology of a solid. In this research, the surface area of
samples was determined by single point BET at 77 K. Samples were degassed at
150°C for an hour to eliminate impurities as well as dehydration purpose. The
adsorption and desorption process was carried out until constant values obtained in
order to get the specific surface area of the samples accurately.
2.4.5
Field Emission Scanning Electron Microscope (FESEM)
Field emission scanning electron microscope (FESEM) is a type of scanning
electron microscope (SEM) creates various images by focusing a high energy beam
of electron onto the surface of a sample and detecting signals from the interaction of
the incident electrons with the surface of the sample. The samples was sputtered on
aluminum stub that cover with carbon cement tape then place in to vacuum chamber
of FESEM to study the size and shape of the samples or its surface morphology. The
morphology scanning was done in different magnification to obtain clear images.
16
When the electrons are liberated from a field emission source and accelerated
in high electrical field gradient. Within the high vacuum column these so-called
primary electrons are focused and deflected by electronic lenses to produce a narrow
scan beam that bombard the object. As a result secondary electrons are emitted from
each spot on the object. The angle and velocity of these secondary electrons relates to
the surface of the object. A detector catches the secondary electrons and produces an
electronic signal. This signal was amplified and transformed to a video scan-image
that can be seen on a monitor image that can be saved and processed further.
2.4.6
Electron Spin Resonance (ESR)
Electron spin resonance (ESR) or electron paramagnetic resonance (EPR)
spectroscopy is a physical method of observing resonance absorption of microwave
power by unpaired electron spins in magnetic field. This technique has developed
into a most direct, sensitive and powerful non-destructive method for the
characterization of species with unpaired electron (Wertz et al., 1973). ESR is a
technique for system with net electron spin angular momentum. This system
includes: (i) free radicals formed during chemical reactions or by radiation in the
solid, liquid or gaseous state, (ii) some point defects (localized crystal imperfections)
in solids, (iii) biradicals, (iv) system in triplet states, (v) systems with three or more
electrons, (vi) most transition metal ions.
To obtain an absorption by a paramagnetic species by ESR, it is either by
fixing the magnetic field and varies the frequency or fixes the frequency and varies
the magnetic field. However, the later is more favorable with the frequency being in
the microwave region (λ = 3 cm and ν ≈ 9 GHz) and the magnetic field being
centered around 3000 Gauss (Atkins, 2002).
17
Figure 2.4
The diagram of ESR spectrometer
Figure 2.4 shows the diagram of the ESR spectrometer consists of a
microwave source (a klystron), a cavity in which the sample is inserted, a microwave
detector and an electromagnet. The ESR spectrum is obtained by monitoring the
microwave absorption as the field is changed (Ratna, 2007). In the presence of
magnetic field, an interaction between the magnetic moment of an unpaired electron
and the applied field will occur and these energy which yields different spin stakes
known as “Zeeman Energy”. The Zeeman energy is given by;
Ez = g β Ms H
(Eq. 2.2)
Where
Ez is the Zeeman energy
Ms represent the magnetic quantum number
β is the electronic Bohr magnet on with a value of 9.22733 x 10-28 J/ Gauss
g is the spectroscopic splitting factor which has a value of 2.0023 for a free electron
18
The possible values of Ms are + ½ and - ½ for an electron. Hence, the two
possible values of the Zeeman energy are + ½ g β H (α state) and - ½ g β H (β state)
which is represented in Figure 2.5.
Zeeman energy levels of an electron in an applied magnetic field.
Figure 2.5
The direction of the spin is changed by the absorption of microwaves when
energy different (Δ E = g β H) is equal to the quantum energy of an electromagnetic
wave, hν, where h is the Planck’s constant and ν is the frequency of an
electromagnetic radiation. This absorption of the electromagnetic wave (microwave)
by the unpaired electron is called “electron spin resonance”. The resonance condition
is represented by
Δ E = g β Hr = hν
(Eq. 2.3)
Hr is the resonance magnetic field. ESR spectrum would consist of one line if
interaction of an unpaired electron was observed in an external field. However, in
ESR spectroscopy; the important aspect describes the magnetic coupling that can
occur between the spin of the unpaired electron and those of the nearby magnetic
19
nuclei in the molecule. Thus, the local field experienced by the electron will be
influenced by the applied magnetic field H, and the field due to the magnetic nuclei
which results in multiple transitions known as “hyperfine structure” (Yacob, 1996).
According to Atkins et al., (2002), hyperfine structure means the structure of the
spectrum that can be traced to interactions of the electrons with other nuclei as a
result of the latter’s point electric charge. The “hyperfine coupling” is the term used
to describe the magnetic coupling that occur between the spin of unpaired electron
and those of the nearest magnetic nuclei in the molecule (Symons, 1978).
Figure 2.6
ESR sample cell
Figure 2.6 shows example of ESR sample tube .The ESR instrument was
used to investigate the surface defect in metal oxide samples that have been prepared.
The sample cell was designed to fit the vacuum and specially used to study surface
defect and trapped electron centers in samples. A quartz tube sample holder was
attached with ESR tube. In this study, ESR was used to investigate the surface defect in
MgO samples that have been prepared. It was recorded using JEOL JES-FA 100
spectrometer, operating at X-band frequencies and 100 kHz, interfaced to a computer
with JEOL system software.
In other hand, measurement of the aqueous-soluble basicity for the prepared
samples also done and conducted by back titration where mixing 100 mg of sample
in 10 mL of distilled water and leave for 24 h. The slurry obtained then will be
20
separated using a centrifuge and the resulting solution will be neutralized with 10 mL
of 0.05 M HCl. The subsequently remaining acid will be titrated with 0.02 M NaOH
and phenolphtalien will be use as an indicator.
CHAPTER 3
EXPERIMENTAL
3.1
Instrumentation
The physical characterization of the prepared barium oxide was done using
TG-DTG, FTIR, XRD, BET surface area and FESEM. Besides that, ESR has also
used in this study to investigate the ability of the surface defect BaO to trap proton.
For thermogravimetry analysis, the thermogram was obtained using MettlerToledo TG 50 analyzer. The sample was placed in a ceramic crucible in the TG
analyzer. The sample was then heated from 40°C to 900°C with the rate of 10°C per
minutes with nitrogen gas flow to ensure inert atmosphere.
Fourier transform infrared (FTIR) was used to measure the vibration
frequencies for all the molecules thus identifying and determining specific functional
group in this study. FTIR analysis was carried out using Perkin Elmer Spectrum
FTIR spectrometer and the spectrum recorded in a spectral range of 4000 to 400
cm-1.
A ground solid prepared of BaO (1 mg) was milled with potassium bromide
(KBr) with molar ratio 1:100 to form a mixture solid. In this technique, KBr was
used as a binder to form transparent and very thin pallet. This mixture has then
compressed into a thin pellet with a pressure of 10 ton for 5 minutes. Then, the KBr
disc has analyzing FTIR analyzer.
22
Bruker X-ray powder diffractometer was used to observe the characterization
of the Ba(OH)2 and prepared BaO. Through this XRD technique the phase presents
in the sample has identified whether the solid sample is crystalline or amorphous
phase. The X-ray diffractograms were recorded with CuKα as the radiation source
with λ = 1.548 Å at 40 kV and 30 mA. The 2θ range was from 10° to 90° at a step
width of 0.05 and step time of 1 sec. The identification of peaks is based on database
(PDF 2 files) incorporated in the software. The particle size prepared of BaO has also
been determined from the XRD diffractogram by Scherrer’s Equation (Equation 3.1).
(Eq. 3.1)
Where k is a shape factor (0.94), λ represent the wavelength of CuKα
(0.15418 nm), β corresponded to the full width at half height of the reflection and θ is
the Bragg diffraction angle in radian. In practice the value of θ is in degrees,
therefore equation 3.1 becomes equation 3.2 where
(Eq. 3.2)
Single point BET surface area was measured at a temperature of 77 K using
the Micromeritics Pulse Chemisorb 2705 while N2 adsorption was carried out using
Micromeritics ASAP 2000. Sample was first degassed at 200°C. Then, the specific
surface area of sample was calculated and determined.
The field emission scanning electron microscopy (FESEM) using a FESEM
6701 F microscope was used to study the surface morphology. The ground prepared
sample was sputtered on aluminium stub that has covered with carbon cement tape
and coated with platinum. The stub was placed into the vacuum chamber of FESEM
instrument. The prepared sample morphology scanning was obtained under different
magnification to obtain clear images (Asyraf, 2010).
23
ESR spectra in this work were recorded with a JEOL JES-FA 100
spectrometer, operating at X-band frequencies and 100 KHz, interfaced to a
computer with JEOL system software incorporated within the computer. The ESR
sample tube was made of quartz with 2 mm in diameter. The peak intensity and the g
value were calculated automatically by the JOEL data analysis software.
3.2
Chemical Reagent
Chemical reagent used in this study is barium peroxide powder (85-90%)
with molecular weight of 169.34 g mol
-1
purchased from Fison laboratory reagent
laboratory FSA supplies.
3.3
Catalyst Preparation
Surface modified prepared BaO was prepared via hydration dehydration
method. This method required barium peroxide as a starting material and
modification from oxide compound to hydroxide compound was done using distilled
water. BaO was prepared by thermal decomposition of barium hydroxide at various
temperatures under vacuum atmosphere.
3.3.1
Preparation of Barium Hydroxide via Hydration method
The distilled water (250 ml) was used to disperse the barium peroxide powder
(20 g) and it was reflux at 100°C for 24 hours. This reflux was carried out to obtain
Ba(OH)2. Then, Ba(OH)2 powder was filtered, washed, and dried. The Ba(OH)2 was
dried in oven for overnight at 120°C. This process removed water from Ba(OH)2 and
become dehydrated. Dried Ba(OH)2 was ground using mortar and paste to form a fine
powder of Ba(OH)2 and characterized using FTIR, BET and TG-DTG.
24
3.3.2
Activation BaO Using High Vacuum Pump System
Ba(OH)2 was added to a high vacuum pump system and calcined at various
temperatures. The Ba(OH)2 was heated according to the calcinations temperature and
time of heating as depicted in Table 3.1.
Table 3.1: Annealing temperature in surface modified BaO
Samples
BaO-50
BaO-100
BaO-150
BaO-200
BaO-250
BaO-300
Annealing Temperature (°C)
50
100
150
200
250
300
Time (hours)
2
2
2
2
2
2
This activation step has conducted to produce a surface area and nanosized
barium oxide. A high pump system was required, in order to run the activation
process. A vacuum system of less the 10-5 mBar was used to produce nano sized
prepared BaO. Diagram of vacuum system has shown in Figure 3.1.
Figure 3.1
Diagram of vacuum system
25
The pumping system consists of double stage rotary pump, vacuum line and it
was connected to mercury nanometer. A small quantity of Ba(OH)2 sample prepared
at range 0.80 g to 1.00 g has transferred to a quartz tube. The sample was heated
using a micro burner heater at different temperature (50°C to 300°C). This activation
of the sample was carried out for 2 hours. Figure 3.2 shows a flow chart of how
prepared BaO was synthesized.
BaO2 (s)
H2O, boiling chip, 100°C at 24 hours
Ba(OH)2 (l)
Dried at 120°C and overnight
Ba(OH)2 (crystals)
Calcination at 50-300°C
Prepared BaO
Figure 3.2
3.4
Flow chart of how prepared BaO was prepared.
Sample Characterization
The prepared BaO was characterized using fourier transform infra-red
(FTIR), X-ray diffraction (XRD), single point Brunauer - Emmet Teller (BET), field
emission scanning electron microscopy (FESEM) and electron spin resonance (ESR)
26
excluded thermogravimetry - derivative thermogravimetry (TG-DTG) which applied
for prepared the Ba(OH)2 only. The amount basic sites of prepared BaO determined
using back titration method.
3.5
Basicity Analysis
Measurement of the aqueous soluble basicity was conducted by mixing 100
mg of sample with 10 ml of distilled water shakes and leaved for 24 hours. The
slurry obtained was separated by a centrifuge and the resulting solution was
neutralized with 10 ml of 0.05 M HCl. Subsequently, remain acid was titrated with
0.01 M NaOH and phenolphthalein was employed as an indicator.
CHAPTER 4
RESULTS AND DISCUSSION
4.0
Introduction
The barium oxide characterizations were conducted using fourier transform
infra-red (FTIR), X-ray diffraction (XRD), single point Brunauer - Emmet Teller
(BET), field emission scanning electron microscopy (FESEM) and electron spin
resonance (ESR), excluding thermogravimetry-derivative thermogravimetry (TGDTG) which was applied for Ba(OH)2 only.
4.1
Preparation of Nano Barium Oxide
Firstly, powder barium peroxide (BaO2) was dispersed in distilled water and
refluxed for 24 hours at water boiling temperature. This process is called hydration
and precipitate Ba(OH)2 was collected by filtration and further dried in oven at
105°C. The prepared sample Ba(OH)2 was calcined at different temperatures under
vaccum atmosphere (10-3 mbar) to yield nano BaO. A study by Murphy et al.,(1999)
on the preparation of metal oxide, found that heat and vacuum can extract water
molecules which is the by product in this reaction leaving cavities and pore created at
surface of metal oxide.
28
4.2
Characterization Techniques
4.2.1
Thermogravimetry-Derivative Thermogravimetry (TG-DTG)
Figure 4.1 shows the TG-DTG decomposition of Ba(OH)2. In this study, TGDTG was important in determining the optimum temperature for the production of
prepared BaO via decomposition of their hydroxide, and also to ensure that the
conversion of Ba(OH)2 to BaO is completed.
Figure 4.1
TGA-DTA decomposition of Ba(OH)2
29
Figure 4.2
Percentage of weight lost at different temperature regions from TGA
Based on Figure 4.2, the first region of weight lost occurred at 30°C to 50°C
of about 0.1%. This is related to the removal of adsorbed water molecule at the
surface of barium hydroxide. The major weight lost occurred at 110°C to 150°C
which is 0.7% and indicates the decomposition of barium hydroxide to barium oxide.
This condition can be referred to the beginning of the formation of BaO from their
respective hydroxide and released water as the by product. The decomposition
profile assists to facilitate the optimum temperature for the formation of BaO from
dehydration of Ba(OH)2. Chemical equation of the decomposition can be described
as below:
Ba(OH)2
BaO
H2O
(Eq. 4.1)
Weight loss for the temperature region 330°C to 400°C and 600°C to 660°C
were quite similar. This can be associated to the complete decomposition of Ba(OH)2
and the formation of surface modified BaO. The decomposition of barium hydroxide to
barium oxide occurred earlier at the temperature 110°C due to the dehydration of water
bonded molecule on the surface of smaller Ba(OH)2 particles.
30
4.2.2
Fourier Transform Infrared (FTIR)
The chemical bonds in a molecule can be determined by the data from an
infrared absorption spectrum. In the previous study conducted by Taya,. (2003), peak
around 3486-3441 cm-1 was assigned to the presence of hydroxyl groups and
adsorbed moisture.
According to Knozinger et al., (1993), there are two types of OH bonding
observed on the IR spectrum for BaO. First, is the OH stretching and bending mildly
bonded with Ba cation and secondly, OH stretching and bending weakly attached at
the surface of the samples bonded to the anion. Figure 4.3 shows the illustrations for
(a) unassociated hydroxyl bond and (b) stretching vibration of the adsorbed water
molecule. These two types of bonding were observed in the surface of BaO.
H
O
H
H
O
O
Ba
O
Ba
a) Type
(a) A
Figure 4.3
O
Ba
O
Ba
b) Type
(b) B
Illustrations for (a) unassociated hydroxyl bond and (b) stretching
vibration of adsorbed water molecule
31
Transmittance
1637.47
%T
3446.75
3381.85
1447.88
4000.0
3600
3200
2800
2400
2000
1800
1600
1400
1200
1000
800
600
400.0
c m-1
Wavenumber
Figure 4.4
FTIR spectrum for commercial BaO2
For comparison, commercial BaO2 and the prepared Ba(OH)2 were separately
characterized using FTIR. Based on Figure 4.4 for commercial BaO2, there are four
major peaks present. The peak at 3446.75 cm-1 and 1637.47 cm-1 are assigned to OH
stretching and bending, bonded with Ba. On the other hand, peaks at 3381.85 cm-1
and 1447.88 cm-1 represent the OH stretching and bending, attached at the surface of
the sample. Table 4.1 shows peaks assignment for commercial BaO2.
Table 4.1: Peaks assignment for commercial BaO2
Wavelength number (cm-1)
Peaks Assignment
3446.75
OH bonds stretching vibration, bonded with Ba
3381.85
1637.47
1447.88
OH bonds stretching vibration, attached at
surface of the sample
OH bonds bending vibration, bonded with Ba
OH bonds bending vibration, attached at surface
of the sample
32
Transmittance
%T
1638.13
3484.01
3366.99
1440.06
4000.0
3600
3200
2800
2400
2000
1800
1600
1400
1200
1000
800
600
400.0
c m-1
Wavenumber
Figure 4.5
FTIR spectrum for prepared Ba(OH)2
Figure 4.5 for prepared Ba(OH)2 also shows four main peaks. The peaks at
present at 3484.01 cm-1 and 1638.13 cm-1 has assigned to OH stretching and bending,
bonded with Ba respectively whereas 3366.99 cm-1 and 1440.06 cm-1 represent to OH
stretching and bending, attached at surface of sample. The intensity of OH stretching
bonded with Ba in the commercial BaO2 indicates that Ba(OH)2 was mixed with
commercial BaO2 sample. Table 4.2 shows peaks assignment for prepared Ba(OH)2.
Table 4.2: Peaks assignment for prepared Ba(OH)2
Wavelength number (cm-1)
Peaks Assignment
3484.01
OH bonds stretching vibration, bonded with Ba
3366.99
1638.13
1440.06
OH bonds stretching vibration, attached at surface
of the sample
OH bonds bending vibration, bonded with Ba
OH bonds bending vibration, attached at surface
of the sample
33
Transmittance
(g)
(f)
(e)
(d)
%T
(c)
(b)
(a)
4000.0
3600
3200
2800
2400
2000
1800
1600
1400
1200
1000
800
600
400.0
cm-1
Wavenumber
Figure 4.6
FTIR spectrum for (a) Ba(OH)2, (b) BaO-50, (c) BaO-100, (d) BaO-
150, (e)BaO-200 (f) BaO-250 (g) BaO-300
Figure 4.6 shows FTIR spectra for all the prepared BaO. There are two types
of OH bonding exist in these spectra. First, is the OH stretching and bending bonded
with Ba (red region) and secondly, OH stretching and bending attached at the surface
of the sample (blue region). The spectrum of unassociated hydroxyl (OH) stretching
appeared at 3483.47 cm-1 and bending bond at 1637.24 cm-1. On the other hand peak
at 3376.73 cm-1 and 1455.99 cm-1 represent to OH stretching and bending, attached at
surface of sample respectively. As the temperature was raised, the peak intensity of
OH bending bonded with Ba still appears. This may be caused by the hygroscopic
characteristic of the sample itself that easily absorb water molecule during the
preparation of sample when the characterization process is done.
It can be concluded that when activation was conducted using the vacuum
system, the water molecule from Ba(OH)2 had been eliminated. But, the OH bending
bonded with Ba cannot be broken easily. This is because the temperature is not high
34
enough to separate the bond. The much higher temperature is needed to break this
bond. Ba(OH)2 was heating using vacuum pump system to dehydrate the water
molecule from the surface of BaO. When these occur, there are empty pores on the
surface that had been change. The empty pores increased the surface area of BaO.
4.2.3
X-ray Powder Diffraction (XRD)
X-Ray Powder Diffraction (XRD) gives information on the crystallinity of
the sample. Powder XRD patterns were collected in order to investigate
diversification of the transformation before and after the heating process of the
sample. The diffractogram were useful to determine the type of crystallite as well as
the purity of the sample. The XRD diffractogram for commercial BaO2 is shown in
Figure 4.7.
Intensity (Cps)
2θ(°)
Body centered tetragonal BaO2 ( BCT )
Figure 4.7
XRD diffractogram for commercial BaO2
In Figure 4.7, commercial BaO2 show six characteristic peaks at 26.04°,
26.80°, 33.26°, 42.73°, 46.43°, 47.8° respectively, which has assigned to body
35
centered tetragonal BaO2. From this diffractogram it can be summarized that
commercial BaO2 which is the starting material for this study is in the form of body
centered tetragonal shape. The sharp peak present on this diffractogram indicates that
commercial BaO2 was highly crystalline. Table 4.3 summarizes the peaks from the
diffractogram obtained that have been identifying by referring to ICSD (Inorganic
Crystal Structure Database) 1997 for BaO2.
Table 4.3: XRD peaks assignment for commercial BaO2
Sample
BaO2
d(Ǻ)
Peak
2θ (º)
d(Ǻ)
26.04
3.42
3.41
002
BCT BaO2
26.80
3.32
3.32
101
BCT BaO2
33.26
2.69
2.69
110
BCT BaO2
42.73
2.11
2.11
112
BCT BaO2
46.43
1.95
1.95
103
BCT BaO2
47.80
1.90
1.90
200
BCT BaO2
reference
Miller indices ( hkl )
assignment
BCT= body centered tetragonal phase
The hydration process of commercial BaO2 was yield Ba(OH)2. The XRD
diffractogram for Ba(OH)2 and the prepared BaO at temperature 100°C, 200°C and
300°C have illustrated in Figure 4.8 (a)-(d) respectively. Based on Figure 4.8 (a)
there are five typical diffraction peaks at 24.03°, 26.47°, 27.03°, 31.07° and 34.27°
which may assigned to the characteristic peak of orthorhombic Ba(OH)2 crystals.
This finding indicates that the commercial BaO2 was well dispersed in water and
surface hydroxylation has transformed BaO2 to Ba(OH)2. As had been seen on the
diffractogram of Ba(OH)2, the peaks become broader compared to the original
diffractogram of BaO2.
36
Intensity (Cps)
(d)
(c)
(b)
(a)
10
20
30
40
50
60
2θ(º)
Tetragonal BaO
Orthorhombic Ba(OH)2
Figure 4.8
XRD diffractogram of (a) Ba(OH)2 (b) BaO-100 (c) BaO-200
(d) BaO-300
As the temperature increased (b)-(d), decomposition begins, tetragonal BaO
crystal started to appear. As example, From Figure 4.8 for BaO 100°C (b), it
indicates that some of free Ba(OH)2 has been transformed into BaO in tetragonal
formed but the transformation was not completely done because some OH groups are
still not completely removed. These happen most possibly due to the fact that
increasing the temperature will change the sample characteristic and the hydroxides
has probably eliminated from the sample or completely change to BaO. These results
again support the result from TGA and FTIR discussed earlier.
37
Table 4.4: List of peaks assignment for Ba(OH)2 and the prepared BaO
Samples
Ba(OH)2
BaO-100
BaO-200
BaO-300
d( Ǻ )
Miller indices
Reference
(hkl)
3.70
3.69
002
Orthorhombic Ba(OH)2
26.47
3.36
3.39
102
Orthorhombic Ba(OH)2
27.03
3.20
3.25
301
Orthorhombic Ba(OH)2
31.07
2.88
2.88
132
Orthorhombic Ba(OH)2
34.27
2.61
2.62
142
Orthorhombic Ba(OH)2
19.11
4.64
4.66
-111
Orthorhombic Ba(OH)2
24.21
3.67
3.69
002
Orthorhombic Ba(OH)2
30.15
2.96
3.10
110
Tetragonal BaO
34.24
2.62
2.58
101
Tetragonal BaO
34.97
2.26
2.22
111
Tetragonal BaO
24.02
3.70
3.69
002
Orthorhombic Ba(OH)2
24.34
3.67
3.69
002
Orthorhombic Ba(OH)2
27.93
3.18
3.19
001
Tetragonal BaO
28.19
3.16
3.19
201
Tetragonal BaO
34.84
2.57
2.58
101
Tetragonal BaO
23.94
3.71
3.69
002
Orthorhombic Ba(OH)2
26.97
3.30
3.32
101
Tetragonal BaO
30.13
2.96
3.10
110
Tetragonal BaO
34.64
2.58
2.58
101
Tetragonal BaO
2θ (º)
d( Ǻ )
24.03
Peaks assignment
Table 4.4 shows the list of peaks assignment for Ba(OH)2 and the prepared
BaO. The particle size for the prepared nano BaO was calculated using Sherrer’s
equation and the resulting particle size were of approximately 34 nm. Thus, the size
of the prepared BaO was actually larger rather than 10 nm for MgO (Asyraf, 2010)
from previous study. The calculation for particle size using Sherrer equation is
shown in the Appendix 1.
38
4.2.4
Nitrogen Adsorption (NA)
4.2.4.1 Single Point BET Surface Area
Table 4.5 showed the surface area for prepared BaO sample using single
point surface area. The BET surface area for BaO 50°C, BaO 100°C, BaO 150°C,
BaO 200°C, BaO 250°C, BaO 300°C were 6.13 m2 g-1, 7.43 m2 g-1,5.80 m2 g-1,6.01
m2 g-1, 4.11 m2 g-1 and 4.23 m2 g-1 respectively.
Table 4.5: SBET for prepared BaO
Samples
Annealing temperature ( °C )
SBET ( m2 g-1 )
BaO 50°C
50
6.13
BaO 100°C
100
7.43
BaO 150°C
150
5.80
BaO 200°C
200
6.01
BaO 250°C
250
4.11
BaO 300°C
300
4.23
The absorption of water which formed micropore influence the amount of
surface area produced in the sample. As mention early, OH ions are present near
vacant Ba sites in the lattice. The small surface area of BaO is due to the loss of
small amount of OH ions from the lattice and also caused by rupture surface. From
Table 4.5, it can be seen that when temperature increase, the surface area decreased.
It is because, the temperature increased, the micropore ruptured due to very high
temperature exerted to the surface of BaO.
4.2.5
Field Emission Scanning Electron Microscopy (FESEM)
Field emission electron microscope (FESEM) analysis was employed to study
the surface morphology of Ba(OH)2 and prepared BaO. The structural changes in
39
Ba(OH)2 during modification process can be thoroughly studied using the FESEM
micrographs. The morphologies of Ba(OH)2 and prepared BaO illustrated in Figure
4.9.
Figure 4.9 (a) FESEM micrograph for Ba(OH)2 with magnification 25,000X
From Figure 4.9 (a), it shown that each orthorhombic of Ba(OH)2 consist of
bulky particles and its agglomerates. The properties of the prepared BaO was
strongly affected by the temperature and time taken for decomposing the Ba(OH)2.
On the other hand, Figure 4.9 (b) shown clearly that the prepared BaO was tetragonal
and was proven by XRD result as discussed in the Table 4.4.
Figure 4.9 (b) FESEM micrograph for BaO with magnification 25,000X
40
4.2.6
Basicity Analysis for Prepared BaO
The amount of basic sites present after heating under vacuum for the prepared
nano BaO was determined by back titration. Basically, higher amount of basic site
where basicity of BaO was capable to abstract more proton, thus the back titration of
any standard base (NaOH) was recorded a lower volume. The advantage of this
analysis, when basicity of the prepared BaO was already known, transesterification
catalyst performance able to predict.
Scheme 4.10 was the proposed mechanism in the experiment to determine the
amount of the basic site present after heating under vacuum for modification. In this
reaction, the prepared nano BaO was leave for 24 hours in distilled water to let the
nano prepared BaO submerge into distilled water. H+ ion was provided by distilled
water and this H+ ion will abstract by the lone pair of oxygen from prepared nano
BaO as much as it capable and leave the -OH ion. The back titration technique was
then applied to estimate how much H+ ion had been abstracted by the prepared of
BaO.
Ba-O + H+…………-OH
Ba-O………….. H+ + -OH
(1)
Neutralization using exact amount of HCl
-
OH + HCl
H2O + Cl-
(2)
NaCl + H2O
(3)
Back titration
HCl + NaOH
Scheme 4.1: Schematic diagram in the determination of amount basic site for nano
BaO
The mechanism in the determination of amount basic site for nano BaO
started with the abstraction of proton by nano BaO which is provided by distilled
41
water. At this step, the capability of proton abstraction at nano BaO lies on their
basicity. The basicity will be increased if more of the basic sites is created and
exposed. Filtering of the substrate is required before go through to second step. This
is because if the abstracted proton or nano BaO still in the reaction vessel, it will
caused a doubling effect of error in neutralization process (step 2), thus will effect to
our final reading.
Second step is known as neutralization steps. Here, a standard and
concentration of hydrochloric acid was used to neutralize the left behind hydroxide
ion which supply chloride ion. Finally, chloride ions that produced were reacted with
known concentration of Sodium Hydroxide solution. This step is required to
calculate the amount of proton from hydrochloric acid reacted with hydroxide ion
from (step 1), furthermore the amount of abstracted proton can be determined.
Amount of basic sites (mmol/g)
Amount basic sites of the prepared BaO
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
1.67
1.37
0.86
0.65
0.6
BaO-50˚C
BaO-100˚C
0.67
BaO-150˚C
BaO-200˚C
BaO-250˚C
BaO-300˚C
Samples
Figure 4.10
Amount basic sites of the prepared nano BaO
The graph at Figure 4.10 shows the amount of basic sites recorded in
millimole per gram for the prepared nano BaO calcined at 50°C, 100°C, 150°C,
200°C, 250°C and 300°C respectively. The lower result for prepared BaO at 50°C
and BaO at 100°C due to incomplete formation of BaO from Ba(OH)2 . As the
42
temperature increases from 150°C to 300°C, the basic sites increases. This is most
probably due to the formation of more BaO with basic sites that occur during the
activation process. The basic sites have formed in the surface of BaO, when
specimens calcined at high temperature. This again represented the finding from
Hattori et al., (2001) which basicity of O 2- is higher than OH by ESR result.
4.2.7
Electron Spin Resonance (ESR)
ESR analysis was carried out using a special designed sample cell (Figure 2.6),
to further study the surface of the samples. ESR method is a technique for studying the
chemical species that have one or more unpaired electrons. The samples that have been
chosen were Ba-200°C due to high surface area analyzed using nitrogen gas adsorption.
Figure 4.11 (a): No peak recorded using ESR for the sample after 2 minute UV
The sample was first degassed under vacuum (10-3 mbar) and then introduced to
hydrogen gas (H2). Later in the ESR instrument, the sample was irradiated with ultra
violet (UV) light through the instrument cavity. Figure 4.11 (a) shows that after 2
minutes, the sample was irradiated with ultra violet (UV) light; there was clear spectrum
with no peak observed. This showed that there were no free electrons trapped or
localizes in the surface of the samples.
43
The H2 gas trapped in the sample was homolytically cleaved after irradiated by
the UV light. The direct introduction of UV then produced free hydrogen radicals (H·),
being very unstable on the surface of the samples. They are easily ionized to produce
protons (H+) and an electron. The H+ then attached to the side of the sample pores.
Consequently, the electron will be trapped inside the pores. This process is given in
equations below:
H2
hν
2H
hν
2H
2H
(Eq. 4.2)
2e
(Eq. 4.3)
Mn2+
1.9830
Figure 4.11 (b): Peak recorded using ESR for the sample after 30 minute UV irradiated
Figure 4.11 (b) showed the recorded spectrum for the sample after 30 minutes
simultaneously irradiated with UV light. There was only a single peak observed with the
g-value of 1.9830. Variation from g =2.0023, the g-value for free electron, indicates the
probability interaction of the free electron with the p orbital of the Ba atoms.
44
From result obtained, BaO shows a positive result on trapped electron. There are
no changes in g value recorded after the 30 minutes of UV irradiation indicates that there
is only one site which is active in electron trapping sites occur a g-value (1.9830). The
two peaks on the left and right of Figure 4.11 (b) refers to the internal Mn2+ standard of
the ESR spectrometer.
According to Murphy et al. (1999), the ionic oxide surface will adsorb H2
molecule and heterolytically cleavage to form H + and H-. The UV irradiation cause the
hydrogen, H2 to form H·. Where H- was released an electron and proton, H+ being
stabilized by nearest O2- and form hydroxyl group (OH). The proton at this hydroxyl
group has magnetically attracted with trapped unpaired electron in the vacancy. Hence, a
single and intense peak would be observed in ESR spectrum at the UV irradiation
occurring.
Paramagnetic probes may localize in pores by different environmental mobility
and polarity of the surface of the samples. With ESR technique, the precise structural
and dynamical information about the probe and their environment can be studied by
means of an accurate analysis of the spectral line shape (Kasai et al., 1976). Under
conditions where the exchange rate among different pores is low, the ESR signals at each
site will contribute to superimposed adsorptions of overall spectra (Ottaviani et al.,
1993).
This technique further supports the finding from the FESEM and BET showing
the presence of pores and cavity. The pores and cavity easily trapped electron from H 2
with the presence of UV light. Blue coloration of trapped electron has not detected most
probably due to the surface area not high enough and the diminishing of pairing out of
the electron.
CHAPTER 5
CONCLUSION
This study had successfully prepared nano BaO via hydration-dehydration
method and the entire stated objectives have been accomplished. The formation of
BaO from dehydration of Ba(OH)2 started at temperature above than 100ºC was
supported by Thermogravimetry analysis (TGA) of Ba(OH)2. As the temperature
increase, the crystallinity of BaO also increases with surface modification. This
statement is supported by data obtained from FTIR which indicates unassociated OH
peak did not appear at BaO spectra when the temperature of dehydration above
200°C and XRD analysis depicts decreases of characteristic peak of Ba(OH)2 and
distinguishing peak of BaO.
From FESEM images, it proved that Ba(OH)2 consist of bulky particles and
its agglomerates each other and the shape of BaO was tetragonal shape . The data
from basicity study shows that when temperature increases from 150°C to 300°C, the
basic sites increase. This is most probably due to the formation of more BaO with
basic sites that occur during the activation process. The ESR study of paramagnetic
probe (H radical) in Ba 200ºC showed that after 2 minute irradiated with UV, sample
of Ba 200ºC give clear spectrum with no peak observed. From ESR result shows that
there were no free electrons trapped or localizes in the surface of the prepared BaO after
2 minutes irradiated with UV. After 30 minutes the sample irradiated with UV light,
there was only a single peak observed with the g value of 1.9830, which is active in
electron trapping sites.
REFERENCES
Amat Mustajab, M.K.A. (2010). Nano Structured Metal Oxide In Base Catalytic
Transesterification of Palm Oil to Biodiesel. Master. Thesis. Universiti
Teknologi Malaysia, Skudai.
Atkins and Paula J. R. (2002). Atkins Physical Chemistry. (7th ed.). Great Calrendon
Street, N.Y.: Oxford University Press Daniela.
Boonyawan. Y., Pawnprapa. K., Puttasawata. B. and Parncheewa. U. (2010).
Magnesia modified with strontium as a solid base catalyst for
transesterification of palm olein. Chem. Eng. J. 162, 58–66.
Flohr, J. K. (1997). X-ray Powder Diffraction. Francis. A.F. Science for A Changing
World. (pp. 53-59). U.S: Department of the Interior.
Hairoldin, A.T. (2003). Kajian Spektroskopi Barium Oksida (BaO) Berluas
Permukaan Tinggi. Bachelor. Thesis. Universiti Teknologi Malaysia, Skudai.
Hajime, K. and Hattori, H. (1998). Cyanoethylation of Alcohols over Solid Base
Catalysts. J. Catal. Today. 44, 277-283.
Hanis Mohd Yusoff (2006). Stability Of Cypermethrin Against A Prepared High
Surface Area Magnesium Oxide. Master. Thesis. Universiti Teknologi
Malaysia, Skudai.
Hattori, H. (2001). Solid Base Catalysts: Generation of Basic Sites and Application
to Organic Synthesis. J. Appl. Catal. 222, 247-259.
Hyun, S. J., Jung, K. L., Jin, Y. K. and Kug, S. H. (2001). Crystallization Behaviors
47
of Nanosized MgO Particles from Magnesium Alkoxides. J. Colloid Interface
Sci. 259, 127–132.
Itatani, K., Nomura, M., Kishioka, A. and Kinoshita, M. (1986). Sinterability of
Various High Purity Magnesium Oxide Powders. J. Mater. Sci. 21, 14291435.
Kasai, P. and Bishop, R.J. (1976). Zeolite Chemistry and Catalysis. Rabo, J. A. (Ed.)
ACS Monograph (pp. 451-457). Washington: American Chemical Society.
Kawashima, A., Matsubara, K. and Honda, K. (2008). Development of
Heterogeneous Base Catalyst for Biodesel Production. J. Bioresour. Technol.
99, 3439-3443.
Khaleel, A., Pramesh, N., Kapoor, L. and Kenneth J. K. (1999). Nanocrystalline
Metal Oxides As New Adsorbents For Air. J. Nanopart. Res. 11, 459–468.
Kouzu, M., Kasuno, T., Tajika, M., Yamanaka, S. and Hidak, J. (2008). Active Phase
of Calcium Oxide used as Solid Base Catalyst for Transesterification of
Soybean Oil with Refluxing Methanol. J. Appl. Catal. 334, 357-365.
Murphy, D.M., Robert, D.F., Ian, J.P., Christopher C.R. and Yacob, A.R. (1999).
Surface Defect Sites Formed on Partially and Fully Dehydrated MgO: An
EPR/ENDO Study. J. Phys. Chem. B. 103, 1944-1953.
Nur Syazeila Binti Samadi (2008). Transesterification of Palm Oil to Biodiesel using
A Prepared High Surface Area of Magnesium Oxide as a Solid Base Catalyst.
Master. Thesis. Universiti Teknologi Malaysia, Skudai.
Ottaviani, M.F., Garibay, M.G. and Turro, N.J. (1993). Tempo Radicals as EPR
Probes to Monitor the Adsorption of Different Species into X Zeolite.
Colloids Surf., A. 72, 321-332.
Ratna Sari Dewi Binti Dasril (2007). Preparation and Characterization of Tungsten
Carbide from Carbon of Palm Kernel Shells. Master. Thesis. Universiti
Teknologi Malaysia, Skudai.
48
Sheldon, R. A. and Bekkum, H. V. (2001). Fine Chemicals Through Heterogenous
Catalysis. J. Appl. Catal., A. 454, 233-242.
Singh, S.P., Seema, G. and Goyal, S.C. (2007). Elastic properties of Alkaline Earth
Oxides under High Pressure. J. Phys. Chem. B. 391, 307–311.
Singh, J., Chen, Y.W., Chen, H.Y. and Lin, W.F. (1998). Basicities of AluminaSupported Alkaline Earth Metal Oxides. React. Kinet. Catal. 65, 83-86.
Suchan M. Marie (2001). Molecule Surface Interactions in HCl/MgO and
Water/MgO Systems. Ph.D. Thesis. University of Southern California.
Tang, Z. W., Claveau, D., Corcuff, R., Belkacemi, K. and Arul, J. (2008).
Preparation of Nano CaO using Thermal Decomposition Method. Mater. Lett.
62, 2096-2098.
Wertz, J. E. and Bolton, J. R. (1973). Electron Spin Resonance: Elementary Theory
and Practical Applications. (2th ed.) United State of America: McGraw Hill.
Yacob, A. R., Amat Mustajab, M. K. A. and Samadi, N. S. (2009). Cacination
Temperature of nano MgO Effect on Base Transesterification of Palm Oil.
International Conference of Energy and Enviroment. 21-24 November.
Singapore, 408-412.
Yacob, A.R., (1996). Matrix Isolation Study of Group One Alkali Metals. Ph.D.
Thesis. University of Wales, Cardiff. M. Phill.
49
APPENDIX
Appendix 1: Sample calculation for particle size, D using Schererr’ equation
(Eq. 3.1)
Samples
BaO2
Ba(OH)2
Ba-50
Ba-100
2θ
θ
β
D
26.80
13.40
0.135
63.24
26.04
13.02
0.129
66.07
33.26
16.63
0.156
55.56
42.73
21.37
0.150
59.45
46.43
23.22
0.256
35.30
47.80
23.90
0.181
50.18
24.03
12.02
0.275
30.87
26.47
13.24
0.157
54.34
27.03
13.52
0.212
40.29
31.07
15.54
0.203
42.46
34.27
17.14
0.146
59.52
34.37
17.19
0.132
65.85
27.93
13.97
0.154
55.57
42.37
21.19
0.305
29.20
45.06
22.53
0.450
19.98
47.19
23.60
0.368
24.63
24.21
12.11
0.260
32.67
19.11
9.56
0.306
27.52
25.82
12.91
0.227
37.53
34.97
17.49
0.337
25.84
34.24
17.12
0.118
73.64
30.15
15.08
0.445
19.33
47.16
23.58
0.166
54.58
50
Ba-150
Ba-200
Ba-250
Ba-300
42.31
21.16
0.234
38.05
24.10
12.05
0.277
30.66
34.82
17.41
0.208
41.84
47.13
23.56
0.330
27.45
42.28
21.14
0.243
36.64
27.95
13.98
0.152
56.30
39.74
19.87
0.149
59.26
24.02
12.01
0.156
54.42
24.34
12.17
0.184
46.17
42.20
21.10
0.187
47.60
34.84
17.42
0.259
33.60
47.05
23.53
0.380
23.84
28.19
14.09
0.280
30.58
24.15
12.08
0.281
30.22
34.81
17.41
0.316
27.54
30.13
15.07
0.253
33.99
47.18
23.59
0.321
28.23
45.14
22.57
0.344
26.14
42.37
21.19
0.321
27.75
23.94
11.97
0.170
49.94
24.45
12.23
0.338
25.14
46.94
23.47
0.216
41.91
34.64
17.32
0.248
35.08
26.97
13.49
0.171
49.94