THE IMPACT OF HYDROTHERMAL FACTORS ON QUASI-ONE-DIMENSION TIO2 NANOSTRUCTURE, CRYSTAL SIZE AND BANDGAP

Get Complete Project Material File(s) Now! »

Chemical/physical vapor deposition

Vapor deposition involves producing a vapor which is condensed onto a heated solid. The process is usually executed in a vacuum chamber. The method is designated as a physical vapor deposition (PVD) if the final product does not involve a chemical reaction, otherwise the process is designated as a chemical vapor deposition (CVD).
Producing TiO2 nanowires using a simple PVD method is illustrated in the SEM image shown in Figure 1.14 [39]. In a typical synthesis process, 1.5 g of source material (pure Ti metal powder) and a Si (100) substrate are separately placed on 2 graphite boats in a horizontal tube furnace. In this system, the source Ti powder is in the high-temperature zone and the Si (100) substrate is in the low-temperature zone. The furnace is set at 1050oC in the high-temperature zone and 850oC in the low-temperature zone. The PVD process is initiated when an Ar/O2 mixture gas flowing at a pressure of 40,000 Pa (300 Torr) is used to convert Ti into a layer of TiO2 nanowires [39].

Electrochemical methods

The electrochemical methods include electrodeposition and electrochemical etching/anodization. Electrodeposition is commonly used to produce a TiO2 nanocoating on a substrate by the action of reducing titanium ions in an electrolyte at the cathode surface. TiO2 nanowires coating can be synthesized using a template such as an alumina membrane on Al substrate. Typically, titanium deposits into the pores of the template utilizing 0.2 M TiCl3 solution as the electrolyte [41]. Anatase TiO2 nanowires are produced after heating the Ti infused alumina membrane coating at 500oC for 4 h in the open furnace (Figure 1.16). Next, the alumina membranes are partly removed by a chemical etching process in a 3 M NaOH for 5 min.
Besides the electrodeposition method, electrochemical etching/anodization method is a versatile process which allows the production of a dense and well defined TiO2 nanomaterial onto titanium surface [1, 30, 42, 43]. When titanium metal is exposed to a sufficiently high anodic voltage in a cell, electrochemical oxidation produces Ti4+ (Ti →Ti4+ + 4e-). Next, the Ti4+ ions react with O2- in the electrolyte (Eq. 1.2) to form a compact TiO2 layer [27, 43, 44].

Growth of quasi-one-dimension TiO2 nanostructure

Rapid growth in one direction is crucial in obtaining Q1D TiO2 nanostructures during the evolution of nanocrystal [29]. Synthesis of Q1D TiO2 nanostructures have been achieved by various approaches including sol–gel methods, template-assisted methods, hydro/solvothermal approaches, and electrochemical means [29, 43]. In the previous section for synthesis of TiO2 nanomaterials, many examples were discussed for producing TiO2 Q1D nanomaterials. Hydrothermal method is a simple approach for scale-up without the use of any templates and surfactants [43]. The hydrothermal process is a soft-chemical technique as the reactions occur at relatively low temperatures. The morphology and crystal structure are controllable by manipulating the synthesis parameters such as reaction temperature and alkaline concentration [37, 43]. This protocol has been employed in this study and is discussed in detail below.

Alkaline hydrothermal method and its parameters

The hydrothermal synthesis protocol involves the treatment of a TiO2 precursor with concentrated alkaline solutions sealed in a Teflon-lined stainless steel autoclave at elevated temperatures (110-200oC) for 24-120 h [44]. Subsequently, the powders were washed with 0.1 M HCl, then distilled water for at least 5 times until pH was close to 7 and calcinated from 300-500oC to increase the crystallinity of the product.
The TiO2 precursor can be hydrothermal treated with various hydrothermal solutions such as NaOH, KOH and Na2S. However, the precursor incompletely reacts with either KOH or Na2S even after mixing for 2 weeks. Therefore, the NaOH solution is preferred as a hydrothermal solution. Hydrothermal treatment times varies from 24 h to 120 h [37]. For potential application and scale-up in industry, short time synthesis is usually preferred. In this project, we only consider 24 or 48 h as the reaction time.

Preparation of the quasi-one-dimension TiO2 photocatalyst

Q1D TiO2 photocatalyst was prepared using the process described in Chapter 2 (Section 2.4.2). Briefly, homogeneously mix a specified quantity of TiO2 NPs (Aeroxide TiO2 P25, Evonik Industries, Germany) with 70 mL of a NaOH solution. The resulting suspension was transferred into a 100-mL Teflon lined stainless-steel autoclave. The autoclave was maintained at a desired temperature (Table 3.1) for 48 h and subsequently, cooled to room temperature. Next, the suspension was centrifuged to obtain a white precipitate. The precipitate was washed with 1 L of 0.1 M HCl for 24 h at room temperature. The white precipitate was repeatedly washed (5 times) with deionized water. The washed mixture was centrifuged after each wash. Finally, the collected white precipitate was calcined at 400oC for 2 h to produce Q1D TiO2 [16]. The selected experimental levels were based on previous studies (Table 3.1) [8].

Impacts of factor variables on the bandgap

The bandgap for all the Q1D TiO2 samples are shown in Table 3.2 and the main effect of 3 hydrothermal synthesis factors on the bandgap is shown in Figure 3.3. Decreasing temperature (120oC) and NaOH concentration (5M) were linked to the lowest bandgap. A mid-level temperature set at 150oC as well as the mid-level NaOH concentration of 10 M were closely linked to increasing the bandgap. Either increasing or decreasing temperatures (NaOH concentrations) resulted in decreasing the bandgap. Interaction plots at all level factor categories (Figure 3.3b) indicate a similar pattern as that shown in the main effect plot.

Table of contents :

DECLARATION OF CO-AUTHORSHIP / PREVIOUS PUBLICATION
ABSTRACT
DEDICATION
ACKNOWLEDGEMENTS
LIST OF ABBREVIATIONS/SYMBOLS
GENERAL INTRODUCTION
1. STATE OF THE ART: FABRICATION AND PHOTOCATALYTIC PROPERTIES OF TIO2 NANOMATERIALS
1.1. Introduction
1.2. Principles of photocatalysis
1.3. TiO2 nanomaterials morphologies and crystallographic structures
1.4. TiO2 nanomaterials synthesis
1.4.1. Sol-gel method
1.4.2. Sol method
1.4.3. Hydrothermal method
1.4.4. Solvothermal method
1.4.5. Chemical/physical vapor deposition
1.4.6. Electrochemical methods
1.4.7. Direct oxidation method
1.4.8. Surfactant-controlled method
1.4.9. Other methods
1.5. Preparation of quasi-one-dimension TiO2 nanostructure
1.5.1. Why quasi-one-dimension TiO2 nanostructure?
1.5.2. Growth of quasi-one-dimension TiO2 nanostructure
1.5.3. Alkaline hydrothermal method and its parameters
1.5.4. Quasi-one-dimension TiO2 nanostructure formation mechanisms for alkaline hydrothermal method
1.6. Plasma thin film and its applications
1.6.1. Advantages of TiO2 thin film or coating
1.6.2. Plasma enhanced chemical vapor deposition (PECVD)
1.6.3. Magnetron sputter deposition
1.7. Modifications of TiO2 nanomaterials
1.7.1. Modifying TiO2 crystal structure and morphology
1.7.2. Metal and nonmetal doping
1.7.3. Depositing noble metals
1.7.4. Semiconductor coupling
1.7.5. Enhancing TiO2 with carbon materials
1.8. Summary of the research objectives
1.9. References
2. MATERIALS AND EXPERIMENTAL METHODS
2.1. Introduction
2.2. Chemicals
2.3. Characterization instruments and processes
2.3.1. Electron microscopy
2.3.2. Raman spectra
2.3.3. X-ray diffraction (XRD) analysis
2.3.4. Diffuse reflectance UV-visible spectroscopy (DRS) and dye concentration
2.3.5. X-ray photoelectron spectroscopy (XPS)
2.3.6. Brunauer–Emmett–Teller (BET) and specific surface area (SSA)
2.3.7. High performance liquid chromatograph (HPLC)
2.3.8. Gas chromatograph (GC)
2.3.9. Photoelectrochemical measurements
2.3.10. Photocatalytic reactor
2.3.11. Optical emission spectroscopy of plasma
2.3.12. Thin film photocatalytic activity test
2.4. Graphene oxide (GO) and quasi-one-dimension (Q1D) TiO2 synthesis
2.4.1. Synthesis of graphene oxide (GO)
2.4.2. Hydrothermal synthesis
2.4.3. Plasma process used for deposition
2.5. References
3. THE IMPACT OF HYDROTHERMAL FACTORS ON QUASI-ONE-DIMENSION TIO2 NANOSTRUCTURE, CRYSTAL SIZE AND BANDGAP
3.1. Introduction
3.2. Experimental
3.2.1. Preparation of the quasi-one-dimension TiO2 photocatalyst
3.2.2. Characterization studies
3.2.3. Experimental design, optimization study and statistical analysis
3.3. Results and discussion
3.3.1. Morphology
3.3.2. Bandgap (eV)
3.3.3. Analysis of the experimental design
3.3.3.1. Impacts of factor variables on the bandgap
3.3.3.2. Model fitting using analysis of variance (ANOVA)
3.3.3.3. Factor interaction plots
3.3.4. Response model verification, optimization and validation
3.3.5. Phase structure analysis
3.3.6. Crystal size and specific surface area (SSA)
3.3.7. Effects of crystal size/specific surface area on Q1D TiO2 bandgap
3.4. Conclusions
3.5. References
4. OPTIMIZING QUASI-ONE-DIMENSION TIO2 PHOTOCATALYST: PHOTODEGRADING AQUEOUS ORGANIC POLLUTANTS AND PHOTOCATALYTIC HYDROGEN PRODUCTION
4.1. Introduction
4.2. Photocatalytic experiments
4.2.1. Preparation of the Q1D nanometric TiO2 photocatalyst
4.2.2. Photocatalysis of selected organic pollutants
4.2.3. Photocatalytic hydrogen production
4.3. The impact of hydrothermal factors on the photodegradation of aqueous organic pollutants
4.3.1. Selecting model chemicals to assess implementing photodegradation as a technology for treating wastewater effluents and drinking water supplies
4.3.2. Experimental design and statistical analysis
4.3.3. Rhodamine b photocatalysis
4.3.4. Impact of hydrothermal conditions on the apparent rhodamine b degradation constant k
4.3.5. Modeling and optimization of hydrothermal synthesis
4.3.6. Response surface model development
4.3.7. Response surface model verification
4.3.8. Photocatalysis of other pollutants using the optimized Q1D TiO2
4.3.9. Photodegradation conclusions
4.4. The impact of hydrothermal synthesis factors on photocatalytic hydrogen production from water-ethanol mixture
4.4.1. Introduction: Photocatalytic hydrogen production
4.4.2. Experimental design and statistical analysis
4.4.3. Photocatalytic hydrogen production
4.4.4. Impact of hydrothermal conditions on hydrogen production rate
4.4.5. Modeling and effects of factors on response variable hydrogen production rate
4.4.6. Response surface model development
4.4.7. Response surface model verification
4.4.8. Phase structure, crystal size and bandgap
4.4.9. Conclusions: Photocatalytic hydrogen production
4.5. Conclusions
4.6. References
5. ENHANCED TIO2 NANORODS PHOTOCATALYSTS WITH PARTIALLY REDUCED GRAPHENE OXIDE AND AG NANOPARTICLES FOR DEGRADING AQUEOUS HAZARDOUS POLLUTANTS
5.1. Introduction
5.2. Experimental
5.2.1. Synthesis of reduced graphene oxide-TiO2 nanorods (designated as GT) photocatalyst with varied RGO atomic oxygen-to-carbon (O/C) ratio
5.2.2. Ag-RGO-TiO2 nanorods (designated as Ag-GT) synthesis and Ag-GT film preparation
5.2.3. Characterization studies
5.2.4. Photoelelctrochemical measurements
5.2.5. Photocatalytic activity under ultraviolet (UV) light
5.2.6. Ag-GT film photocatalytic activity under visible irradiation
5.3. Graphene based TiO2 nanorods (GT) photocatalyst with optimum RGO atomic oxygen-to carbon (O/C) ratio
5.3.1. The graphene based TiO2 nanorods (GT) morphology and phase structure 166
5.3.2. Removing oxygen-containing groups and adjusting the the atomic oxygen-to-carbon (O/C) ratio of reduced graphene oxide (RGO)
5.3.3. Interaction between reduced graphene oxide (RGO) and TiO2 nanorods (TNRs)
5.3.4. Optical response and bandgap
5.3.5. Charge transportation and separation
5.3.6. Photocatalytic activity
5.3.7. The mechanism of reduced graphene oxide (RGO) atomic oxygen-to-carbon (O/C) ratio
5.4. Ag-reduced graphene oxide-TiO2 nanorods (Ag-GT) photocatalyst with optimum Ag loading
5.4.1. Morphology analysis
5.4.2. Structure analysis
5.4.3. Diffuse reflectance UV-visible spectroscopy (DRS) and bandgap
5.4.4. Photoelectrochemical studies
5.4.5. Photocatalytic activity
5.4.6. Reaction mechanism
5.5. Conclusions
5.6. References
6. ONE-STEP DEPOSITION OF NANO-AG-TIO2 COATINGS BY ATMOSPHERIC PRESSURE PLASMA JET FOR DEGRADING TRACE PHARMACEUTICAL USING SOLAR ENERGY
6.1. Introduction
6.2. Experimental Methods
6.2.1. Optical emission spectroscopy of atmospheric pressure plasma jet (APPJ) plasma
6.2.2. Thin film characterization
6.3. Results and discussion
6.3.1. Plasma jet characterization
6.3.2. Morphology and Ag diffusion in composite Ag-TiO2 thin films
6.3.3. Effect of Ag incorporating on the crystal structure
6.3.4. Photocatalytic activity
6.3.5. Mechanism of photocatalytic oxidation by Ag-TiO2
6.4. Conclusions
6.5. References
7. GENERAL CONCLUSIONS AND RECOMMENDATIONS
RESUME DE LA THESE
8. ENGINEERING SIGNIFICANCE
APPENDICES
Chapter 3: copyright
Chapter 5: copyright
LIST OF PUBLICATIONS AND CONFERENCES
VITA AUCTORIS

READ  Experimental investigation of TSP clogging phenomenon

GET THE COMPLETE PROJECT

Related Posts