Scalable and flexible photothermal material based on bacterial cellulose for solar steam generation

VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY NGUYEN THI KIEU TRANG SCALABLE AND FLEXIBLE PHOTOTHERMAL MATERIAL BASED ON BACTERIAL CELLULOSE FOR SOLAR STEAM GENERATION MASTER'S THESIS VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY NGUYEN THI KIEU TRANG SCALABLE AND FLEXIBLE PHOTOTHERMAL MATERIAL BASED ON BACTERIAL CELLULOSE FOR SOLAR STEAM GENERATION MAJOR: NANOTECHNOLOGY CODE: 8440140.11QTD RESEARCH SUPERVISOR: Dr PHAM TIEN THANH Hanoi, 2021 ACKNOWLEDGEMENT Firstly, I'd want to express my gratitude to Dr Pham Tien Thanh, one of my supervisors at Vietnam Japan University, for his excitement, support, and patient guidance throughout the preparation of my master thesis I'd want to take this opportunity to thank Dr Nguyen Hoang Duong and Dr Nguyen Duc Cuong for their assistance Their suggestions have been quite useful in my research I also thank all member of MNT Lab and MEE Lab for helping and supporting me in my lab works I really enjoy and appreciate not only researching but also around time here Last but not least, I really want to thank to MNT’s lectures for their support me during the internship period Without them, I could not have enough knowledge and experience to research and study in here I want to express my gratitude to my mother, father, brother, and friends, who have always been there for me and have always supported and encouraged me throughout my life This work is fully supported by the project with the code number of VJU.JICA.21.03, from Vietnam Japan University, under Research Grant Program of Japan International Cooperation Agency Nguyen Thi Kieu Trang Hanoi, 2021 TABLE OF CONTENTS LIST OF TABLES i LIST OF FIGURES ii LIST OF ABBREVIATIONS iv CHAPTER 1: INTRODUCTION 1.1 Clean water issue .1 1.2 Solar steam generation .2 1.2.1 Design of solar steam generation (SSG) .3 1.2.2 Photothermal materials 1.3 Purpose of thesis CHAPTER 2: EXPERIMENTAL METHOD 2.1 Fabrication of photothermal material .8 2.1.1 Fabrication of bacterial cellulose (BC) .8 2.1.2 Fabrication of photothermal material 2.2 Characterization of photothermal materials .9 2.3 Solar steam generation systems .10 2.3.1 Construction SSG system 10 2.3.2 Evaluate the water evaporation ability of SSG system .11 CHAPTER 3: RESULTS AND DISCUSSION .14 3.1 The surface morphologies of BTF materials 14 3.2 The surface structure of BTF materials 17 3.2.1 FTIR 17 3.2.2 XRD and EDS 18 3.2.3 Iron-tannic acid complexes .20 3.3 The photothermal materials: BTF 21 3.3.1 Absorption 21 3.3.2 Thermal conductivity 22 3.3.3 Contact angle .23 3.3.4 Evaluation of light to heat conversion 23 3.4 Performance of SSG system 25 3.4.1 SSG system under solar simulator 25 3.4.2 SSG system under natural sun condition 29 3.4.3 Stability of photothermal material BTF 30 3.4.4 Self-cleaning property .31 3.4.5 Quality of freshwater collected from SSG 32 CONCLUSION .36 REFERENCES 37 LIST OF TABLES Table 3.1 Composition of BC, BC-TA and BTF 19 i LIST OF FIGURES Figure 1.1 (a) Distribution of water on the Earth [6], (b) saline intrusion warning in the Mekong Delta [30] Figure 1.2 Metal nanoparticle [31] Figure 1.3 CuFeSe2 NPs - decorated wood membrane for solar steam generation [19] .5 Figure 2.1 Bacterial cellulose fabrication process .8 Figure 2.2 Preparation of photothermal material Figure 2.3 Some instruments in this study (a) JSM-IT100 InTouchScopeTM Scanning Electron Microscope (b) Oriel® Sol1ATM Solar Simulators (c) FLIR C2 Camera (d) X-ray Diffraction (XRD Mini Flex 600) (e) UV-VIS Lambda 950 10 Figure 2.4 The structure of steam generation part of SSG system 11 Figure 2.5 Evaluating the steam evaporation index of SSG in the laboratory condition 12 Figure 2.6 The experiment of collecting purified from seawater of SSG system 12 Figure 3.1 Images of BC growth in days 14 Figure 3.2 The change of materials during the fabrication of photothermal materials 15 Figure 3.3 SEM images of BC and BTF materials 16 Figure 3.4 BET of BC 17 Figure 3.5 FT-IR spectra of BC and BTF materials show difference of peak 18 Figure 3.6 XRD spectra of BC and BTF materials show slightly changes in the diffraction peaks .19 Figure 3.7 Schematic representation of cellulose with hydrogen bonded tannic acid 20 Figure 3.8 The possible complexation mechanism of TA with Fe3+ .20 Figure 3.9 Absorption spectra of the BC and BTF in dry/wet condition 22 Figure 3.10 Thermal conductivity of BTF 22 Figure 3.11 Contact angle of BTF 23 Figure 3.12 The maximum temperatures of BC and BTF materials 24 Figure 3.14 The mass changes in seawater evaporation under dark condition 26 Figure 3.15 The maximum temperatures of BC and BFT materials based SSG surface .27 Figure 3.16 Infrared photos of the BTF based SSG surface during evaporation process 27 Figure 3.17 The evaporation rate of BTF with different thickness under sun .28 Figure 3.18 Mass change of functionalized material under natural sun 29 Figure 3.20 Cycling stability of the SSG system under sun illumination with 60minutes irradiation for each cycle 31 ii Figure 3.21 Self-cleaning process of BTF material with the salt mas of g 31 Figure 3.22 Mechanism of self-cleaning process of BTF .32 Figure 3.23 The steam condensed on the glass and flowed down to the water tank 33 Figure 3.24 The volume of purified water from SSG system 34 Figure 3.25 The electrical resistances of seawater, desalinated water and domestic water 35 iii LIST OF ABBREVIATIONS AuNPs Gold nanoparticles BC Bacterial cellulose BTF BC-TA-Fe3+ BET Brunauer–Emmett–Teller EDS Energy Disperse X-Ray Spectroscopy FTIR Fourier-Transform Infrared Spectroscopy LSPR Localized surface plasmon resonance NPs Nanoparticles SEM Scanning Electron Microscope SSG Solar steam generation XRD X-ray powder diffraction iv CHAPTER 1: INTRODUCTION 1.1 Clean water issue Water comprises 70% of our planet, and it's safe to assume that water will continue to be plentiful On the other hand, soft drinks, which we consume on a daily basis, are quite rare Fresh water accounts for only 2.5% of the total water available on earth, which will not be enough to meet the needs of the world's growing population By 2050, water demand is expected to rising by 400% and 130% from industrial and residential consumption, with more than 40% of the world's population facing extremely water shortages [5] About 1.1 billion people not have access to clean water, out of a total of 2.7 billion people experience water scarcity for at least one month of the year Rivers, wetlands, and aquifers are drying up or becoming unusable due to pollution About half of the world's wetlands have been lost Agriculture uses the most water of any source and loses a significant amount of water due to inefficiency Climate change is altering weather and water patterns all over the world, resulting in water shortages and droughts in some places and flooding in others [17] In terms of the atmosphere, water scarcity on Earth is manifested by negative environmental phenomena such as rising salinity and shrinking fresh water supplies on the land surface, such as lakes, rivers, and ponds [16] Vietnam is the world's 13th most populated nation, with nearly two-thirds of the population living along the country's three major river basins: Thai Binh, Mekong Delta, and Dong Nai In the Mekong Delta, the extent of saline intrusion in these rivers has been deeper than the same period in 2016 by about to 11 km The phenomenon of saline intrusion in the Mekong Delta affects not only agricultural production but also water supply and living conditions for millions of coastal people [29] Protecting the climate, biodiversity, and communities on Earth requires developing strategies to reduce the rise in water scarcity To alleviate water shortage, various solutions have been suggested, such as improving water filtration systems, encouraging water conservation Among these options, the use of freshwater processing technology from seawater has gotten a lot of attention in recent decades An applied technology's main value is improving seawater metabolic efficiency while lowering energy consumption Figure 3.14 The mass changes in seawater evaporation under dark condition and sun illumination for 60 minutes The changes in surface temperature of the SSG systems during evaporating seawater under sun condition was shown in figure 3.15 Infrared photos of the BTF based SSG surface during evaporation process were also shown in figure 3.16 The initial temperature of the SSG surface before illumination was 23 °C After light illumination, the surface temperature of the SSG rapidly grew in 400s and became stable at approximately 41 °C for the BTF material, 32 °C for the BC material The surface temperature of the BTF could not increase higher because the transfer water to the top surface of BFT was always kept stable through the 3D network structure in the BTF This feature reduced heat loss due to heat radiation to the surrounding environment, leading to the increase in the water evaporation efficiency 26 Figure 3.15 The maximum temperatures of BC and BFT materials based SSG surface during seawater evaporation process Figure 3.16 Infrared photos of the BTF based SSG surface during evaporation process In the dark conditions, the evaporation rate of the blank seawater and the BTF based SSG were 0.06, 0.11 kg m-2 h-1, respectively, this result was used to calculate the 27 evaporation efficiency of SSG system The evaporation efficiency was calculated by the following formula 1: ƞ𝑒𝑞 = 𝛥𝑚ℎ𝐿𝑉 𝐼 where Δm is the water evaporating amount under illumination (evaporation rate under illumination - evaporation rate under dark condition); hLV denotes the enthalpy of water vaporization (2260 J g-1); and I is the received power density of solar illumination The water evaporation efficiency of the SSG system based on the BC and BTF materials are 33.9% and 91%, respectively, which is comparable to that of the previous reported SSG systems This high efficiency was achieved due to the remarkable properties of the BTF material including (1) the super hydrophilic surface, (2) the 3D network structure (layers) of nanocellulose fibers for rapid water transportation, (3) high light absorption, (4) reduction of heat loss by heat radiation to the ambient (low surface temperature) and conduction heat loss due to the low thermal conductivity of the BC material (0.4–0.8 W m-1 K-1 as previous reports regarding the BC material) Figure 3.17 The evaporation rate of BTF with different thickness under sun 28 To evaluate the effect of thickness of BTF material on evaporation performance, water evaporation experiment was performed with BTF material with thickness of 3,5,7 mm, respectively, and water evaporation results as shown in figure 3.17 The results show that the water evaporation efficiency of the SSG system of the mm thick sample is 1.56, while the 3,7 mm thickness is 1.54 and 1.56 kg m-2 h-1, respectively It can be seen that the thickness of the BC layer does not affect the water evaporation efficiency of the system much, this efficiency is about 1.56 kg m-2 h-1 Therefore, BC with a thickness of 3-5 mm is a suitable thickness to fabricate BTF samples 3.4.2 SSG system under natural sun condition Figure 3.18 Mass change of functionalized material under natural sun In fact, the intensity of sunlight is not fixed due to the influence of a number of factors such as clouds, wind, temperature, and humidity Therefore, the steam generation capacity is measured under the natural sunlight of a day with different power of sunlight as shown in Figure 3.18 29 Within 60 minutes, with a power of 0.9 - 1.2 kW.m-2, figure 3.18 shows that the amount of water evaporated was found to be about 2.0 kg.m-2 The intensity of sunlight directly affects the vaporization of photothermal materials in natural sunlight The decreasing light intensity leads to a decrease in the photon energy This leads to a drop in the temperature of the feedstock and inefficient steam generation In summary, the water evaporation of the SSG system is based on the intensity of sunlight 3.4.3 Stability of photothermal material BTF Figure 3.19 Stability of BTF material under various conditions: a) acid, b) alkaline, c) ultrasonic vibration The structural stability of BTF material was evaluated by cycling test under sun condition and seawater with 30minutes irradiation for each cycle The SSG system based on BTF material exhibited a good stable mass change and the evaporation rate was 1.56 kg m-2 h-1 during 12 cycles testing shown in figure, which was slightly changed In addition, the structural stability of BTF material was also evaluated under various 30 conditions such as acid (pH = 4), alkaline solution (pH = 10) for 24 hours and ultrasonic vibration for 60 minutes Figure 3.19 (a-c) exhibited the surface of the BTF samples after the being treated It could be seen that no changes were observed in the BTF surfaces and remained blackness This result proved that the BTF material has great durability under many different conditions and were able to maintain evaporation performance for long time Figure 3.20 Cycling stability of the SSG system under sun illumination with 60minutes irradiation for each cycle 3.4.4 Self-cleaning property Figure 3.21 Self-cleaning process of BTF material with the salt mas of g 31 Figure 3.22 Mechanism of self-cleaning process of BTF The self-cleaning property of BTF material was also verified by placing g of salt crystals on the surface of the BTF material, the BTF material was placed on top of a beaker filled with seawater as shown in Figure We can see that the amount of salt crystals decreases over time, after 180 minutes almost no salt crystals can be observed at the BTF surface This self-cleaning phenomenon is due to the fact that water transported from bulk seawater to the surface dissolves salt crystals into ions, which diffuse back down to bulk seawater according to BC's 3D network This property can reduce the amount of salt crystals that form during water purification, when water evaporation is not taking place (such as at night) This property makes the material can be used for a long time in real conditions 3.4.5 Quality of freshwater collected from SSG 32 Figure 3.23 The steam condensed on the glass and flowed down to the water tank 33 Figure 3.24 The volume of purified water from SSG system To investigate the SSG systems in real conditions, a simple and low-cost solar desalination device was prepared as show in figure 3.24 The sizes of the device are, 250 mm high, 200 mm long and 120 mm wide by using a glass BTF material used in the experiment were synthesized from April 2021 By the time of starting the experiment in May, the materials had been stored for 30 days The area of BTF material was 100 cm2 The seawater was evaporated and condensed on the top glass surface under sunlight conditions from 9:00 AM to 5:00 PM in Hanoi, Vietnam for up to 10 days (May and June) Figure 3.25 exhibits the desalinated water from seawater per day under above conditions Studies was found that the produced pure water per day was 5.0-5.6 kg m-2 on the sunny days and 3.0-3.9 kg m-2 on cloudy days Because the outdoor conditions are unstable (e.g solar flux, humidity and temperature), and the sunlight intensity propagating to the BTL surface deceased due to the top glass of device The freshwater could be up to 6–12 liter/m2/day if our SSG system is tuned This covers a portion of a person's daily water usage On the 10th day of outdoor evaporation, BTF was stored for quite a long time about 60 days The amount of fresh water collected in the 10th day is 34 still up to kg/m2 This result shows that BTF has excellent stability and potential for long-term solar steam generation Moreover, the photothermal material based on BC can be expanded to any desired area Because, the area of BC depends on the contact surface area of the solution and the air If the contact surface area is 200 cm2, the area BC formed is also 200 cm2 Seawater Purified water Domestic water Figure 3.25 The electrical resistances of seawater, desalinated water and Domestic water domestic Seawater Purified waterwater To assess the purity of water, a multimeter with constant electrode spacing is used The Domestic waterreflect the water ohmic value obtained from a resistance test can be used to directly Seawater Purified water quality Sea water has a high concentration of salt ions, so it has a high conductivity and low ohmic value Desalinated water has awater lower ion concentration than seawater, so the Domestic water Seawater Purified conductivity of the water decreases and the Ohm value increases Real seawater, filtered water, and domestic water all had resistance values of 0.019, 0.24, water and 0.34 M, showing Domestic Seawater Purified water that natural saltwater had been effectively purified The resulting of resistances indicated that the concentrations of ions including in the desalinated water was Domestic water Seawater Purified cations water and anions significantly reduced, the quality of the water was similar with domestic water and can be used as freshwater The performances of the SSG based on the water BTF materials under Domestic Seawater Purified water outdoor conditions shows great potential for the practical application of seawater desalination However, specific results of salt ion concentration analysis after seawater Domestic water Seawater Purified water desalination and performance of SSG system under practical conditions will be reported in the future 35 CONCLUSION In conclusion, this research proposed the photothermal material based on the BC material for SSG system by functionalizing BC in TA and Fe3+ solutions The SSG system utilizing BTF material achieved the water evaporation rate of 1.56 kg m-2 h-1, and energy conversion efficiency of 91% under sun illumination The high efficiency of BTF material was achieved due to the outstanding characteristics of BTF materials 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potential for long-term solar steam generation Moreover, the photothermal material based on BC can be expanded to any desired area Because, the area of BC depends on the contact surface... practical conditions will be reported in the future 35 CONCLUSION In conclusion, this research proposed the photothermal material based on the BC material for SSG system by functionalizing BC in TA and