VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY LAI TUAN DUNG MICRO-CAPALLARIES LOTUS FABRIC- BASED AEROGEL FOR HIGH-EFFICIENCY SOLAR STEAM EVAPORATOR AND WATER PURIFICATION MASTER’S THESIS VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY LAI TUAN DUNG MICRO-CAPALLARIES LOTUS FABRIC- BASED AEROGEL FOR HIGH-EFFICIENCY SOLAR STEAM EVAPORATOR AND WATER PURIFICATION MAJOR: NANOTECHNOLOGY CODE: 8440140.11 QTD RESEARCH SUPERVISOR: Dr. PHAM TIEN THANH Prof. YOJI SHIBUTANI Hanoi. 2023 COMMITMENT I have read and understood the plagiarism violations.
I pledge with personal honor that the research is my own and does not violate the Regulation on prevention of plagiarism in academic and scientific research activities at VNU Vietnam Japan University (Issued together with Decision No 700/QĐ-ĐHVN dated 30/9/2021 by the Reactor of Vietnam Japan University). Author of the thesis Lai Tuan Dung ACKNOWLEDGEMENTS I would like to sincerely express my gratitude to my advisors, Dr. Pham Tien Thanh and Prof. Yoji Shibutani, for their invaluable guidance and support during my master's program.
Their expertise and encouragement have been instrumental in completing this research and writing this thesis. I extend my heartfelt thanks to all my labmates from both the MNT Lab and the MEE Lab for their assistance. Our time spent together and their support have greatly enriched my research projects. I am also grateful to the professors, lecturers, and staff at MNT for their assistance during my internship.
Their knowledge and guidance have been crucial in my research and studies in this field. I would like to express my appreciation to artist Phan Thi Thuan, whose help in collecting lotus fibers from lotus stems and artistic inspiration have played a significant role in my material-making and research endeavors. Lastly, I want to convey my deep appreciation to my mother, father, brother, and friends who have always been there for me, providing unwavering support and encouragement throughout my life journey. Their presence has meant everything to me.
This research has been done under the research project QG.52 “Fabrication of cellulose fibers and biomass-based photothermal materials for efficient seawater desalination” of Vietnam National University, Hanoi Lai Tuan Dung Hanoi, 2023 TABLE OF CONTENTS LIST OF TABLE. i LIST OF FIGURE. ii LIST OF ABBREVIATIONS. iv CHAPTER 1: INTRODUCTION OF SOLAR STEAM GENERATION.
The importance of creating freshwater. Desalination of seawater. Solar steam generation (SSG). Types of photothermal materials.
Inorganic semiconductor materials. Aerogel-based photothermal materials. Justify the selection of research material and method. Cellulose based aerogel fabrication procedure.
Purposes of the thesis. Fabrication of photothermal materials. Characterization of photothermal materials. Investigate the photothermal material’s performance.
Investigation of the material thermal behavior under laboratory condition. Investigation of the material’s performance under laboratory condition .18 CHAPTER 3: RESULTS AND DISCUSSIONS. Explanation on the fabrication of aerogels from Lotus fiber. Extraction of cellulose from ground sugarcane bagasse.
Preparation of white cellulose-based aerogel from extracted cellulose. Preparation of black cellulose-based aerogel from extracted cellulose. The surface morphologies of photothermal materials. SEM images of raw lotus fiber and extracted cellulose.
SEM images of the photothermal material. Brunauer-Emmett-Teller (BET) analysis results. X-ray diffraction results. Chemical composition of the photothermal material.
FT-IR spectra. Wetting behavior measurement. Mechanical properties of the photothermal materials. Evaporation performance of the aerogel.
Thermal behavior and FT-IR of the aerogel. Evaporation performance of the aerogel in the experiment condition. Evaluation the solar energy evaporation efficiency of the black aerogel in dark condition. Evaluation the structural stability of the black aerogel.
Evaluation of the black aerogel evaporation over time. Evaluation of the black aerogel’s self-cleaning properties .52 LIST OF TABLE Table 1. The tensile properties of cotton, viscose and lotus fiber in normal temperature state, wet state, and dry state. Composition of white and black aerogel samples.
List of equipment used for the material characterization. Young modulus of photothermal materials. Comparision of Young Modulus between lotus fiber aerogel and other natural-based aerogel. Comparison on the specifications and performance of the Cellulose based aerogel in this thesis and other type of photothermal materials.42 i LIST OF FIGURE Figure 1.
Projected water stress in 2040. Reverse osmosis is one method of desalination. The status of the renewable energy operated desalination technologies. Three components of solar steam generator.
SEM image of one spiral lotus fiber bundle with conglutination of several lotus fibers. Image of lotus fiber. Fabrication process of cellulose – based aerogel (including white and black aerogel). a) White cellulose-based aerogel, b) Black cellulose-based aerogel.
Setup of the experiment to measure thermal behavior of the aerogels. a) Solar steam generator containing water supply path, absorber and source of water b) Solar simulator. (a) Cellulose suspension, (b) PVA solution, (c) Final suspension of cellulose in PVA solution, (d) A piece of white aerogel. Crosslinking between PVA and cellulose in the white aerogel sample.
(a) Cellulose suspension in Tannic acid solution, (b) PVA + FeCl3 solution, (c) Final suspension containing cellulose PVA, Tannic acid, FeCl3, (d) A piece of black aerogel. (a) Crosslinking between PVA, tannic acid and cellulose in black aerogel. (b) Formation of complexes between tannic acid and Fe3+. SEM images of (a) raw lotus fiber (bar: 20µm), (b) extracted cellulose (bar: 20µm).
SEM images of a) white aerogel’s surface; b) cross-section and longitudinal section surface of black aerogel. BET Isotherm of the aerogels. a) XRD spectra of raw lotus fiber and extracted cellulose, .28 b) XRD spectra of white aerogel and black aerogel. FT-IR spectra of white aerogel and 3 black aerogel samples with different tannic mass in the wavenumber range of 500 – 4000 cm-1.
Photographic images of the aerogel’s contact angles and water droplet permeation processes: a) white aerogel, b) black aerogel. The process of measuring the compressive strength of photothermal materials. Compressive stress–strain curves of the aerogels with different chemical compositon. Crosslinking between tannic acid, PVA and cellulose.
Compressive loading-unloading stress-strain curves of aerogel. a) UV-VIS-IR spectra of the white and black aerogel samples and b) the maximum temperature of white and black aerogel under sun intensity 0. IR images, indicating the temperature changes before and after under sun simulator for 10 minutes: a) white sample; b) black sample. Mass change of the seawater, white aerogel, and black aerogel in the solar steam generator under light intensity 0.
Temperature variation during evaporation experiment between: a) Surface of white and black aerogel samples b) black sample surface, bulk water and black sample body. IR images, indicating the temperature change during the evaporation experiment of: a) white aerogel’s surface, b) black aerogel’s surface and c) bulk water and black aerogel’body. Evaporation rates of the seawater, white aerogel and black aerogel in dark condition. a) Black aerogel’s rate of evaporation after 20 days, b) Physical appearance of the black aerogel samples after 30 days of exposure to seawater.
a) Self-cleaning mechanism of the aerogel b) Self-cleaning performance of the black aerogel.49 iii LIST OF ABBREVIATIONS FT-IR Fourier-Transform Infrared Spectroscopy PVA Polyvinyl alcohol RO Reverse Osmosis SEM Scanning Electron Microscope SSG Solar steam generation UV-Vis-nIR Ultraviolet-Visible-Near Infrared iv CHAPTER 1: INTRODUCTION OF SOLAR STEAM GENERATION 1. The importance of creating freshwater Figure 1. Projected water stress in 2040[1]. Water stress is considered as one of the major global problems.
According to the United Nations, a region is considered "water-stressed" when it withdraws 25 percent or more of its renewable freshwater resources[2].4% of the world's total renewable freshwater resources were extracted. However, there are already regions experiencing serious problems. Northern Africa has critical levels of water stress, whereas Central and Southern Asia have high water stress. On the opposite end of the 1 spectrum, 31% of the global population remained in the "no stress" category.
According to the World Resources Institute's projections for 2040, the problem will only become more widespread. According to a report by the Economist Intelligence Unit, urbanization, population growth, climate change, and economic growth are exerting pressure on water systems[3]. According to the projections, 44 nations will experience "extremely high" or "high" water stress by 2040. According to a report by The Economist, a growing number of regions, particularly in East and South-East Asia, are at an increased risk of flooding, which can overwhelm sanitation systems and contaminate potable water sources[3].
In order to safeguard the well-being of communities in affected areas, achieve the UN Sustainable Development Goal 6 on clean water and sanitation, and protect the environment and biodiversity, it is crucial to address water scarcity. While human activities have contributed to the water crisis, humans have also developed technologies to improve freshwater acquisition and conservation. Various remedies for water scarcity have been developed, including the construction of dams and reservoirs, the practice of rainwater harvesting, the establishment of aqueducts, the implementation of desalination processes, water reuse systems, and water conservation measures. Over the years, numerous scientists and organizations have dedicated their efforts to advancing seawater desalination technology with the aim of enhancing efficiency and reducing energy consumption.
By continually improving desalination techniques, it becomes possible to alleviate water scarcity, enhance access to clean water, and mitigate the impact of the water crisis on both humans and the environment. These efforts align with the objectives of sustainable development and contribute to a more sustainable future for all. Desalination of seawater 2 Figure 1. Reverse osmosis is one method of desalination[4].
Desalination is a method which involves removing dissolved salt and minerals from seawater or saline groundwater. This method has the benefit of a practically unlimited supply of saltwater. There are numerous methods for desalinating seawater, such as boiling, filtration, electrodialysis (using an electric current to remove the ions that make up salts), and reverse osmosis (Figure 1. All of these processes are moderately to extremely expensive and require substantial energy input, making the produced water significantly more expensive than that from conventional sources.
Additionally, the process generates highly saline wastewater that must be disposed of and has a significant impact on the environment. Therefore, affordable desalination technologies that utilize renewable energy sources must be developed to address the water shortage and ensure a sustainable future for future generations. Research and development of desalination technologies based on renewable energy sources, such as solar, wave, wind, and geothermal energy, are depicted in Figure 1. The status of the renewable energy operated desalination technologies[5].
Solar Still, PV RO, Solar thermal MED, and Wind RO have reached the application stage among the technologies based on renewable energy. Solar evaporation: Solar Still and Solar thermal MED transform solar energy into heat in order to evaporate water. Per cubic meter of desalinated water, their operating costs range between 1. Consequently, these technologies have the potential to be used as inexpensive desalination technologies in countries with a high number of sunlight hours, such as Vietnam, Bangladesh, etc.
The performance of solar steam generator technologies is primarily determined by their solar energy conversion efficiency. By creating a new photothermal material with increased solar energy conversion efficiency, the efficiency of solar evaporation could be improved. Consequently, the objective of my thesis is to produce a new photothermal material with a high solar energy conversion efficiency so as to fully realize the potential of a solar steam generator for desalination. In the following section, the working principle of a solar steam generator will be discussed.
Solar steam generation (SSG) Solar irradiation is a promising renewable energy source because the hourly solar flux incident on the earth's surface exceeds the annual global energy demand[6]. The earth receives 1361 W/m2 of solar radiation annually, of which 70% is absorbed and the remainder is either reflected or scattered[7]. As a tropical nation, Vietnam has a large number of sunshine hours (2000 – 6000 hours/year, or 6 – 7 hours/day) and an average annual solar irradiance of 5 kW/h/m2, creating favorable conditions for the implementation of solar energy-related technologies.