Considerable effort has been made to design, fabricate, and manipulate nanostructured
materials by innovative approaches. The precise control of nanoscale structures will pave the
way not only for elucidating unique size/shape dependent physicochemical properties but also
for realizing new applications in science and technology. Nanotechnology offers
unprecedented opportunities for improving our daily lives and the environment in which we
live.
This thesis mainly describes recent progress in the design, fabrication, and modification
of nanostructured semiconductor materials for environmental applications. The scope of this
thesis covers TiO2, Bi2O3 and BiOCl materials, focusing particularly on TiO2-based
nanostructures (e.g., pure, doped, coupled, mesoporous, hierarchically porous, and ordered
mesoporous TiO2).
Mesoporous titania is of particular interest since this class of materials possesses
well-defined porosity and large specific surface areas. For photocatalytic degradation of
organics, these desirable properties are anticipated to improve the efficiency. So in the first
part of work, I have synthesized the mesoporous titania by using poly ethylene glycol as a
template in dilute acetic acid aqueous solution by hydrothermal process and investigated the
effect of PEG molecular weights and thermal treatment on the resultant structure and
photocatalytic activity. When the molecular weights of PEG vary from 600 to 20,000, the
particle sizes of mesoporous-TiO2 structure decrease from 15.1 to 13.3 nm and mean pore
sizes increase from 6.9-10.6 nm. The activities of these mesoporous-TiO2 photocatalysts
prepared by using PEG are evaluated and compared with Degussa P-25 using chloro-phenol
as a testing compound. [...]
Table of Contents
CHAPTER 1
INTRODUCTION
1.1 NANOTECHNOLOGY
1.2 BACKGROUND OF TIO2
1.2.1 POLYMORPHIC FORMS OF TIO2
1.2.2 PHOTOCHEMICAL MECHANISM
1.2.3 APPLICATIONS OF TIO2
1.3 MODIFICATIONS OF TIO2 PROPERTIES
1.3.1 MODIFICATIONS OF TIO2 BY COUPLING OF SEMICONDUCTOR
1.3.2 MODIFICATIONS OF TIO2 BY DOPING
1.3.3 MODIFICATIONS OF TIO2 BY BISMUTH OXIDE
1.3.4 MODIFICATIONS OF TIO2 BY COPPER OXIDE
1.3.5 MESOPOROUS MATERIALS
1.3.6 HIERARCHICALLY POROUS NANOARCHITECTURES
1.4 PREPARATION METHODS
1.4.1 SOL-GEL PROCESS
1.4.2 HYDROTHERMAL PROCESS
1.4.3 THE EVAPORATION INDUCED SELF ASSEMBLY METHOD
1.5 BISMUTH OXYCHLORIDES
1.6 BISMUTH OXIDE
1.7 SURFACE MODIFICATIONS
1.8 SPECIFIC OBJECTIVES OF WORK
CHAPTER 2
SYNTHESIS AND CHARACTERIZATION OF MESOPOROUS TIO2 WITH ENHANCED PHOTOCATALYTIC ACTIVITY FOR THE DEGRADATION OF CHLORO-PHENOL
2. 1. INTRODUCTION
2.2.1 MATERIALS AND APPARATUS
2.2.2 CATALYST PREPARATION
2.2.3 CHARACTERIZATION
2.2.4 MEASUREMENTS OF PHOTOCATALYTIC ACTIVITIES OF CHLORO-PHENOL
2. 3 RESULTS AND DISCUSSION
2.3.1 X-RAY DIFFRACTION SPECTROSCOPY
2.3.2 N2 ADSORPTION–DESORPTION
2.3.3 SCANNING ELECTRON MICROSCOPY
2.3.4 TRANSMISSION ELECTRON MICROSCOPY
2.3.5 CHEMICAL REACTIONS MECHANISM FOR THE FORMATION OF POROUS STRUCTURE
2.3.6 PHOTOCATALYTIC DEGRADATION OF CHLORO-PHENOL
2.3.7 MECHANISM OF PHOTODEGRADATION
2.4 CONCLUSIONS
CHAPTER 3
MESOPOROUS TITANIA WITH HIGH CRYSTALLINITY DURING SYNTHESIS BY DUAL TEMPLATE SYSTEM AS AN EFFICIENT PHOTOCATALYST
3.1 INTRODUCTION
3.2 EXPERIMENTAL SECTION
3.2.1 MATERIALS AND APPARATUS
3.2.2 SYNTHESIS OF MESOPOROUS TIO2
3.2.3 CHARACTERIZATION
3.2.4 PHOTOCATALYTIC ACTIVITY OF PHENOL
3.3 RESULTS AND DISCUSSION
3.3.1 THERMOGRAVIMETRIC ANALYSIS
3.3.2 X-RAY DIFFRACTION
3.3.3 THERMAL STABILITY
3.3.4 N2 SORPTION DATA
3.3.5 TRANSMISSION ELECTRON MICROSCOPE
3.3.6 PHOTOCATALYTIC ACTIVITIES
3.3.7 MECHANISM FOR PHENOL DEGRADATION
3.4 CONCLUSIONS
CHAPTER 4
STUDY ON HIGHLY VISIBLE LIGHT ACTIVE BI2O3 LOADED ORDERED MESOPOROUS TITANIA
4.1 INTRODUCTION
4.2. EXPERIMENTAL SECTION
4.2.1 MATERIALS AND APPARATUS
4.2.2 SYNTHESIS OF MESOPOROUS TIO2 WITH BISMUTH OXIDE IMPREGNATION
4.2.3 CHARACTERIZATION
4.2.4 MEASUREMENTS OF PHOTOCATALYTIC ACTIVITIES
4. 3 RESULTS AND DISCUSSION
4.3.1 THERMOGRAVIMETRIC ANALYSIS
4.3.2 X-RAY DIFFRACTION
4.3.3 RAMAN SPECTRA
4.3.4 TRANSMISSION ELECTRON MICROSCOPY
4.3.5 UV–VIS ABSORPTION SPECTRA
4.3.6 PHOTOLUMINESCENCE SPECTRA
4.3.7 FOURIER TRANSFORM INFRARED SPECTRA
4.3.8 N2 ADSORPTION-DESORPTION
4.3.9 X-RAY PHOTOELECTRON SPECTROSCOPY
4.3.10 MECHANISM OF THE FORMATION OF MESOPOROUS TIO2 WITH WELL-ORDERED PORE MORPHOLOGY AND BI2O3 ASSISTED PHOTOCATALYTIC PROCESS
4.3.11 PHOTOCATALYTIC ACTIVITY
4.3.12 KINETICS OF REACTION
4.4 CONCLUSIONS
CHAPTER 5
BISMUTH-DOPED ORDERED MESOPOROUS TIO2: VISIBLE-LIGHT CATALYST FOR SIMULTANEOUS DEGRADATION OF PHENOL AND CHROMIUM
5.1 INTRODUCTION
5.2 EXPERIMENTAL SECTION
5.2.1 MATERIALS AND APPARATUS
5.2.2 CATALYST PREPARATION
5.2.3 CHARACTERIZATION
5.2.4 PHOTOCATALYTIC ACTIVITY
5.3 RESULTS AND DISCUSSION
5.3.1 X-RAY DIFFRACTION
5.3.2 UV–VIS ABSORPTION SPECTRA
5.3.3 RAMAN SPECTRA
5.3.4 PHOTOLUMINESCENCE SPECTRA
5.3.5 TRANSMISSION ELECTRON MICROSCOPY
5.3.6 N2 ADSORPTION-DESORPTION
5.3.7 X-RAY PHOTOELECTRON SPECTROSCOPY
5.3.8 PHOTOCATALYTIC ACTIVITY
5.3.9 MECHANISM OF PHOTODEGRADATION
5.4 CONCLUSION
CHAPTER 6
IONIC LIQUID ASSISTED MESOPOROUS TITANIA DOPED WITH COPPER AS A VISIBLE LIGHT PHOTOCATALYST
6.1 INTRODUCTION
6.2 EXPERIMENTAL SECTION
6.2.1 MATERIALS AND APPARATUS
6.2.2 CATALYST PREPARATION
6.2.3 CHARACTERIZATION
6.3 RESULTS AND DISCUSSION
6.3.1 X-RAY DIFFRACTION SPECTROSCOPY
6.3.2 UV-VISIBLE DIFFUSE REFLECTANCE SPECTRA
6.3.3 RAMAN SPECTRA
6.3.4 TRANSMISSION ELECTRON MICROSCOPY
6.3.5 FOURIER TRANSFORM INFRA-RED
6.3.6 NITROGEN SORPTION DATA
6.3.7 ENERGY DISPERSIVE X-RAY SPECTROSCOPY
6.3.8 X-RAY PHOTOELECTRON SPECTROSCOPY
6.3.9 EPR SPECTROSCOPY
6.3.10 MEASUREMENT OF PHOTOCATALYTIC ACTIVITY
6.3.11 MECHANISM OF PHOTODEGRADATION
6.4 CONCLUSIONS
CHAPTER 7
WO3/BIOCL A NOVEL HETEROJUNCTION AS VISIBLE LIGHT PHOTOCATALYST
7.1 INTRODUCTION
7.2 EXPERIMENTAL
7.2.1 MATERIALS AND APPARATUS
7.2.2 CATALYST PREPARATION
7.2.3 CATALYST CHARACTERIZATION
7.2.4 PHOTOCATALYTIC ACTIVITY
7.3 RESULTS AND DISCUSSION
7.3.1 X-RAY DIFFRACTION SPECTROSCOPY
7.3.2 UV-VISIBLE DIFFUSE REFLECTANCE SPECTRA
8.3.3 RAMAN SPECTRA
7.3.4 SCANNING ELECTRON MICROSCOPY
7.3.5 TRANSMISSION ELECTRON MICROSCOPY
7.3.6 ENERGY DISPERSIVE X-RAY SPECTROSCOPY
7.3.7 NITROGEN SORPTION DATA
7.3.8 THERMOGRAVIMETRIC ANALYSIS
7.3.9 MEASUREMENT OF PHOTOCATALYTIC ACTIVITY
7.3.10 MECHANISM FOR THE DEGRADATION
7.4 CONCLUSIONS
CHAPTER 8
SUMMARY AND CONCLUSIONS
Research Objectives and Focus
The research primarily aims to advance the design, fabrication, and modification of nanostructured semiconductor materials for environmental applications, specifically focusing on overcoming the limitations of titanium dioxide (TiO2) photocatalysts. The work investigates various doping and composite strategies to enhance photocatalytic efficiency under visible light, targeting the degradation of organic pollutants such as phenol, chloro-phenol, and dyes.
- Synthesis of mesoporous TiO2 using template-assisted methods (e.g., PEG, Pluronic P123, and ionic liquids) to improve crystallinity and thermal stability.
- Development of heterojunction-based photocatalysts (e.g., Bi2O3/TiO2, WO3/BiOCl) to extend light absorption into the visible region.
- Evaluation of photocatalytic mechanisms, charge separation efficiency, and the role of surface defects in enhancing degradation rates.
- Systematic characterization of material structure using XRD, TEM, XPS, and BET to establish structure-performance relationships.
- Application of these catalysts in the simultaneous degradation of organic pollutants and reduction of toxic heavy metal ions like Cr(VI).
Excerpt from the Book
1.1 Nanotechnology
In the last decades, a little word attracted enormous attention, interest and investigation from all over the world: “nano”. What it presents in terms of science and technology, which are also called nanoscience and nanotechnology, is much, much more than just a word describing a specific length scale. It has dramatically changed every aspect of the way that we think in science and technology and will definitely bring more and more surprises into our daily life as well as into the world in the future [1].
What is actually so exciting about “nano”? “Nano” means one billionth (10-9), so 1 nanometer refers to 10-9 meter and is expressed as 1 nm. 1 nm is so small that things smaller than it can only be molecules, clusters of atoms or particles in the quantum world. Nanometer is a special point in the overall length scale because nanometer scale is the junction where the smallest manufacturable objects “meet” the largest molecules in nature. The structures, devices and systems having at least one dimension in nanometer scale are not only smaller than anything that we’ve ever made before, but also possibly the smallest solid materials that we are able to produce. Besides, in nanometer scale, the properties of materials that we are familiar with in our daily life, such as color, melting point, electronic, catalytic or magnetic properties [2], will change dramatically or be replaced by completely novel properties due to what is usually called size effect [3]. “At this size scale, everything, regardless of what it is, has new properties. And that is, where a lot of the scientific interest is. All these make “nano” so fascinating.
Summary of Chapters
CHAPTER 1: This chapter introduces nanotechnology and the fundamental background of TiO2, detailing its polymorphic forms, photochemical mechanisms, and existing modification strategies for environmental applications.
CHAPTER 2: Focuses on the synthesis and characterization of mesoporous TiO2 using PEG as a template to improve its photocatalytic activity for the degradation of chloro-phenol.
CHAPTER 3: Describes a dual-template system (P123 and PEG) to synthesize mesoporous TiO2 with higher crystallinity and thermal stability for enhanced phenol degradation.
CHAPTER 4: Investigates ordered mesoporous TiO2 loaded with Bi2O3 to create visible light active photocatalysts, examining their efficiency in degrading organic dyes.
CHAPTER 5: Explores the synthesis of Bi-doped ordered mesoporous TiO2 for the simultaneous photocatalytic degradation of phenol and reduction of chromium.
CHAPTER 6: Details the use of room-temperature ionic liquids as a template for synthesizing mesoporous TiO2, followed by copper doping to improve visible light photocatalytic performance.
CHAPTER 7: Presents the development of a novel WO3/BiOCl heterojunction as a visible light photocatalyst, demonstrating its efficiency in the decomposition of rhodamine B.
CHAPTER 8: Provides a comprehensive summary and the main conclusions drawn from the entire study regarding the development of high-performance nanostructured photocatalysts.
Keywords
mesoporous TiO2, bismuth doping, copper doping, BiOCl, hierarchical macro/mesoporous structure, photocatalysis, nanotechnology, semiconductor materials, visible light activity, environmental remediation, photocatalytic degradation, heterojunctions, sol-gel method, hydrothermal synthesis, specific surface area
Frequently Asked Questions
What is the core focus of this research?
This research focuses on the design, synthesis, and characterization of advanced nanostructured materials, particularly based on titanium dioxide (TiO2) and bismuth-based compounds, to function as efficient photocatalysts for environmental purification.
What are the primary themes of the work?
The core themes include tailoring the pore structure and crystalline nature of semiconductors, doping with metal ions (such as Bi and Cu), and creating heterojunctions to achieve visible light responsiveness.
What is the main objective of the thesis?
The primary objective is to develop new synthesis routes that result in highly crystalline, thermally stable, and visible-light-active photocatalysts that outperform standard materials like Degussa P25.
Which scientific methods are primarily utilized?
The study utilizes sol-gel, hydrothermal, and evaporation-induced self-assembly (EISA) methods, along with various characterization techniques like XRD, TEM, XPS, FTIR, and BET surface analysis.
What does the main body of the work cover?
The main body systematically explores different template systems (P123, PEG, ionic liquids) and chemical modifications to optimize TiO2 and BiOCl architectures for the effective degradation of organic pollutants and heavy metals.
How would you describe the key characteristics of the photocatalysts developed?
The materials are characterized by well-defined mesoporous channels, high specific surface areas, nanocrystalline anatase structures, and enhanced visible light absorption due to effective doping and heterojunction formation.
How is the stability of mesoporous TiO2 maintained at high temperatures?
The research demonstrates that using dual-template systems and specific hydrolytic retardants like acetic acid helps maintain the mesoporous architecture, effectively delaying phase transformation and pore collapse up to 700-800°C.
What unique benefits does the WO3/BiOCl heterojunction provide?
The WO3/BiOCl heterojunction facilitates effective charge separation by utilizing the staggered band alignments of the two semiconductors, which prevents electron-hole recombination and enhances the efficiency of rhodamine B degradation under visible light.
How does the Bi-doped TiO2 behave during simultaneous contaminant degradation?
The Bi-doped TiO2 successfully degrades phenol while simultaneously reducing chromium (VI) to chromium (III), showing that the presence of one pollutant can mutually enhance the degradation pathway of the other through efficient charge transfer management.
- Quote paper
- Shamaila Sajjad (Author), 2011, Synthesis, characterization and applications of nanomaterials in the field of photocatalysis, Munich, GRIN Verlag, https://www.hausarbeiten.de/document/175947
