MISNISTRY OF EDUCATION AND TRAINING DINH THI KIM HUE PHENIKAA UNIVERSITTY MASTER THESIS IN MATERIALS SCIENCE DINH THI KIM HUE SYNTHESIS AND PHOTOCATALYTIC PROPERTIES OF BLACK TiO2 NANOMATERIALS Major: MATERIALS SCIENCE Code: 8440122 MASTER THESIS IN MATERIALS SCIENCE Hanoi – 2024 Hanoi – 2024 MISNISTRY OF EDUCATION AND TRAINING PHENIKAA UNIVERSITTY DINH THI KIM HUE SYNTHESIS AND PHOTOCATALYTIC PROPERTIES OF BLACK TiO2 NANOMATERIALS Major: MATERIALS SCIENCE Code: 8440122 MASTER THESIS IN MATERIALS SCIENCE SUPERVISORS: 1. NGUYEN VIET HUONG 2. BUI VAN HAO Hanoi – 2024 CONTENTS ACKNOWLEGEMENT .i STATEMENT OF ASSURANCE .ii LIST OF ABREVIATIONS. iii LIST OF TABLES .iv LIST OF FIGURES.
Purposes of research. Subjects and scopes of research. Methodology of research. Significance of research.
Structure of thesis. Titanium dioxide (TiO2) nanomaterials. Black TiO2 nanomaterials. N-doped TiO2 nanomaterials.
H-doped TiO2 nanomaterials. N and H co-doped TiO2 nanomaterials. Materials and equipment. Synthesis of materials.
Synthesis of TiO2 NRs. Modification of TiO2 NRs by NH3 and H2 treatments at high temperatures. Photocatalytic degradation of MB. Solar-to-steam vapor generation.
RESULTS AND DISCUSSION. Synthesis of black TiO2 NRs by NH3 treatment. Morphology of NH3-treated TiO2 NRs. Crystalline structure of NH3-treated TiO2 NRs.
Elemental compositions of NH3-treated TiO2 NRs. UV-Vis optical absorption properties of NH3-treated TiO2 NRs. Influence of NH3 treatment time. Electronic structures of N-doped TiO2.
Synthesis of black TiO2 NRs by H2 and NH3/H2 treatment. Morphology, crystalline structure and UV-Vis absorption spectra of the H2- treated TiO2 NRs. Morphology, crystalline structure and UV-Vis absorption spectra of the NH3-treated TiO2 NRs followed by H2 treatment. Photocatalytic properties of black TiO2 NRs.
Adsorption and degradation of MB by NH3-treated TiO2 NRs at various temperatures. Adsorption and degradation of MB by TiO2 NRs treated in H2 and NH3/H2 atmospheres. Photothermal conversion performance of TiN-based nanostructures achieved by NH3-treatment of TiO2 NRs at high temperatures. 75 ACKNOWLEGEMENT I would like to express my gratitude to all those who contributed to the production of this thesis.
Your support, guidance, and encouragement have been invaluable throughout this journey. First, I would like to express my most profound appreciation to my supervisors, Dr. Bui Van Hao and Dr. Nguyen Viet Huong, for their continuous support and valuable advice during my research.
It is really a great honor and privilege having the opportunity of studying and working in their group. Second, I extend my gratitude to Dr. Nguyen Ngoc Linh for conducting the DFT calculations, which played an important role in my research. In addition, I am thankful to all my professors at Phenikaa University for offering me valuable knowledge during my master's courses.
Third, I would like to thank my colleagues, friends, and anyone who helped me in my academic and personal life. Finally, I’m profoundly grateful to my family, especially my parents, for their unconditional support. Master’s student Dinh Thi Kim Hue i STATEMENT OF ASSURANCE I have completed my master’s thesis on the subject of "Synthesis and Photocatalytic Properties of Black TiO2 Nanomaterials" under the supervision of Dr. Bui Van Hao and Dr.
Nguyen Viet Huong in the ALD Research Group at Phenikaa University. I assure that the research in this thesis is original and has been conducted collaboratively by myself and other members of the ALD Research Group. The outcomes of this research are authentic and accurate, and have not been published by other authors. Throughout the research process, I have followed the standards of academic integrity by avoiding plagiarism, data fabrication, and other forms of misconduct.
Supervisor 1 Supervisor 2 Master’s student Nguyen Viet Huong Bui Van Hao Dinh Thi Kim Hue ii LIST OF ABREVIATIONS Abbreviation Name CBM Conduction Band Minimum CVD Chemical Vapor Deposition DFT Density-Functional Theory DOS Density Of States DP Dibutyl Phthalate EDX Energy-Dispersive X-Ray Analysis FE-SEM Field-Emission Scanning Electron Microscopy GGA Generalised Gradient Approximation IPAN Isopropylamine MB Methylene Blue NRs Nanorods PBE Perdew-Burke-Ernzerhof PDOS Projected Density of States PS Polystyrene PVD Physical Vapor Deposition PVP Polyvinylpyrrolidone TBAOH Tetrabutylammonium Hydroxide UV Ultraviolet UV-Vis Ultraviolet-Visible VBM Valence band maximum XPS X-ray photoelectron spectroscopy XRD X-Ray diffraction iii LIST OF TABLES Table 1. Nitrogen sources for N-doped TiO2.1: Bandgap of the as-synthesized TiO2 NRs and the N-doped TiO2 NRs.2: Formation energy, in eV, of the four N-doping defects in the TiO2 anatase and rutile phases. Bandgap of the N-doped TiO2 NRs before and after the H2 treatment. Solar water evaporation performance of various photothermal materials reported in the literature.
56 iv LIST OF FIGURES Figure 1. Three main polymorphs of TiO2: a) Anatase, b) Rutile, and c) Brookite. Ti and O atoms are denoted as the cyan and red balls, respectively [21]. Synthesis of black TiO2 by H2 treatment at different temperatures [34].1: Process flow of the synthesis of TiO2 NRs by hydrothermal method.2: Process flow of the synthesis of black TiO2 NRs by NH3 and H2 treatments at high temperatures.3: Standard curve for MB concentration.
a) Photograph of solar-to-team generation system at Phenikaa University, b) the filtration sheet containing 20 mg of material, (c) the Petri dish containing water covered with a styrofoam, (d) a part of filtration sheet containing material after covered by another styrofoam. SEM images of (a) the as-synthesized TiO2 NRs and the NRs after treated in NH3 for 2h at different temperatures: (b) 400 °C, (c) 500 °C, (d) 600 °C, (e) 700 °C, (f) 800 °C, (g) 900 °C, (h) 1000 °C, and (i) 1100 °C. The pictures on the right side of the SEM images show the color of the powders. XRD patterns of the as-prepared TiO2 NRs and the NRs after the treatment in NH3 at different temperatures in the range of 400 – 1100 °C.
a) UV-Vis absorption spectra of the TiO2 NRs before and after the NH3 treatment for 2 h from 400 to 1100 °C (N400 – N1100) and b) bandgap energy determination of as-synthesized TiO2 and N400, N500, N550 samples. SEM images of the TiO2 NRs treated in NH3 at different temperatures and treatment times: (a) 700 °C for 2 h, (b) 700 °C for 5 h, (c) 800 °C for 2 h, (d) 800 °C for 5 h, (e) 900 °C for 2 h, and (f) 900 °C for 5 h. Electronic structures of the four N-related defective TiO2 considered in this work, which are formed within (a) anatase (A) and (b) rutile (R) TiO2. The deep defect states are denoted with the filled blue or empty white arrows, corresponding to occupied or unoccupied states, respectively.
The up (down) arrows correspond to the spin channel up (down) of the Kohn-Sham states. The TiO2 crystal is visualized with the ball-and-stick model, where the large blue, small red, and gray balls are denoted for the Ti, O, and N atoms, respectively. The two different colors of the density isosurfaces refer to the sign of the wave function. SEM images of TiO2 NRs treated in (a) N2 and (b) diluted H2 at 700 C for 2 h.
(c) XRD patterns and (b) UV-Vis absorption spectra of the N2- and H2-treated TiO2 NRs. The plots on the right side of (d) is a zoom-in of the spectral region marked as the dotted rectangle. For comparison, in (c) and (d) the XRD patterns and UV-Vis absorption spectra of the as-synthesized and the NH3-treated TiO2 are added. SEM images of TiO2 NRs after the treatment in NH3 at different temperatures for 2 h: (a) 400 °C, (b) 500 °C, (c) 550 °C, and (d) 600 °C, followed by the H2 treatment at 500 °C for 2 h.
The color of the powders before and after the H2 treatment is shown by the photographs on the right side of the SEM images. (a) XRD patterns and (b) UV-Vis absorption spectra of the TiO2 NRs treated in NH3 followed by the H2 treatment. In (a), the XRD pattern of the as- vi synthesized TiO2 is added as the reference; in (b), the absorption spectra of the as- synthesized TiO2 and the TiO2 treated in NH3 without the H2 treatment step are also added for comparison. The arrows in (b) show the change in the absorption behavior after the H2 treatment.
Adsorption and photodegradation of MB under visible-light irradiation by TiO2 NRs before and after the NH3 treatment at different temperatures. Adsorption and photodegradation of MB under visible-light irradiation by TiO2 NRs treated in a) N2 and diluted H2 at 700 °C for 2 h, b) NH3 in the temperature range of 400 – 600 °C for 2 h, followed by the H2 treatment at 500 °C for 2 h. In a), the adsorption and photodegradation of MB by the as-synthesized TiO2 is added as the reference. In b), the adsorption and photodegradation of MB by the TiO2 treated in NH3 without the H2 treatment step are also added for comparison.
The dotted arrows in (b) show the change in MB adsorption and photodegradation efficiency of the materials after the H2 treatment. The surface temperature distribution measured for the as-synthesized TiO2 NRs, N1000, and N1100 before (a, c, and e, respectively) and after (b, d, and f, respectively) the irradiation by the simulated solar light of 0.6 sun for 20 min. Evaporation rate of as-synthesized TiO2 NRs and NH3-treated TiO2 NRs at high temperatures. ---------------------------------------------------------------------------- 56 vii INTRODUCTION Nowadays, a large amount of untreated wastewater is released into the environment, which contains various types of pollutants such as heavy metals, inorganic and organic compounds.
These pollutants cause a lot of negative effects on human health and the environment. Hence, it is important to develop effective materials and technologies for degrading the pollutants and producing freshwater from wastewater. As an excellent photocatalyst for environmental remediation applications, titanium oxide (TiO2) has attracted enormous attention in the last decades thanks to its high chemical and physical stabilities, non-toxicity, and excellent photocatalytic activity. However, due to its large bandgap (i.2 eV) [1], TiO2 only absorbs light in the UV region and therefore it is only photocatalytically active under the irradiation of UV light sources.
This hinders the practical application of TiO2 when using sunlight as the natural light source for photocatalysis because only approximately 5% of the entire solar energy is in the UV region [1]. Therefore, it is important to extend the light absorption of TiO2 to the visible range, which accounts for 42 – 45% of solar energy, so that it can harvest sunlight more efficiently for photocatalysis applications. Among various strategies that have been developed for enabling visible-light absorption of TiO2, doping is one of the most common approaches. By introducing other elements, either metals (e., Pt, Ag, Au, Co, Ni, Cr, Cu, Fe, Mn, V, W) [2–4] or non- metals (e., N, S, C, B, P, F) [5], the bandgap of TiO2 can be significantly reduced.
This is because the presence of the dopant atoms can induce the formation of new energy levels in the bandgap of TiO2, which consequently enables the electronic transitions under the excitation of photons with energies lower than the bandgap energy. By doing so, the light absorption of TiO2 can be extended deeply into the visible region. This research focuses on the fabrication of black TiO2 nanomaterials, which are TiO2- based materials that commonly absorb visible light efficiently and exhibit excellent 1 visible-light photocatalytic performance. Starting with a hydrothermal method for the fabrication of TiO2 nanorods (NRs), high temperature treatments of the materials were applied in various atmospheres, i.
This treatment aims to either dope the TiO2 with N (i., N-doped TiO2) as it has been reported by other studies [6–8], or generate defects in the TiO2 lattice, both of which result in the formation of black TiO2. As the high temperature treatment can cause many effects on the morphology, structure, composition, and properties of the materials, it is important to investigate how they evolve during the treatment, and how those parameters influence the performance of the materials.