Fabrication and performance on environmental applications of a novel 3d superhydrophobic material based on a loofah sponge from the natural plant

The Wenzel model supplies the following formula to decide the contact angle between the liquid and the solid: The Wenzel model considers the impact of surface roughness on the contact an

VIETNAM NATIONAL UNIVERSITY, HANOI

VIETNAM JAPAN UNIVERSITY

DO DANH QUANG

FABRICATION AND PERFORMANCE ON ENVIRONMENTAL APPLICATIONS OF A

NOVEL 3D SUPERHYDROPHOBIC

MATERIAL BASED ON A LOOFAH

SPONGE FROM THE NATURAL PLANT

MASTER’S THESIS

VIETNAM NATIONAL UNIVERSITY, HANOI

VIETNAM JAPAN UNIVERSITY

DO DANH QUANG

FABRICATION AND PERFORMANCE ON ENVIRONMENTAL APPLICATIONS OF A

NOVEL 3D SUPERHYDROPHOBIC

MATERIAL BASED ON A LOOFAH

SPONGE FROM THE NATURAL PLANT

MAJOR: ENVIRONMENTAL ENGINEERING

CODE: 8520320.01

RESEARCH SUPERVISOR:

Dr: TRAN THI VIET HA

Hanoi, 2023

COMMITMENT

I have read and understood the plagiarism violations I pledge with personal honor that

this research result 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/QD-ĐHVN dated 30/9/2021 by the

Rector of Vietnam Japan University)

Author of the thesis

Do Danh Quang

I would like to express my deepest gratitude to Dr Tran Thi Viet Ha, who enthusiastically guided, guided, and helped me so that I could complete and complete the thesis fully and in the best way

I would like to thank the teachers and assistants in the master's program in environmental engineering for enthusiastically teaching and helping me during my study at the school

The project with the code number VJU.JICA.21.03, from VNU Vietnam Japan University, fully funds the project as part of the Research Grant Program of the Japan International Cooperation Agency

Especially, I would like to thank my family’s great love, Mr Do Danh Ha, Mrs Nguyen Thi Dien, Ms Huyen Trang, and Ms Nhu Quynh, who eased and supported

me during my master's degree

Finally, I would like to thank my MEE batch 6 students and friends who have always encouraged and helped me in the past time to complete my thesis

TABLE OF CONTENTS

LIST OF TABLES i

LIST OF FIGURES ii

LIST OF ABBREVIATIONS iv

CHAPTER 1: INTRODUCTION 1

1.1 Research background 1

1.2 Research significance 2

1.3 Research objectives 2

1.4 Thesis outline 3

CHAPTER 2: LITERATURE REVIEW 4

2.1 Theoretical basic 4

2.1.1 Water wettability and water contact angle 4

2.1.2 Solid surface wetting states 5

2.1.3 Model explaining the mechanism 6

2.2 Methods to fabricate the superhydrophobic surface 8

2.2.1 Dip coating 8

2.2.2 Spray coating 9

2.2.3 Polymerization techniques 10

2.2.4 In situ nanorod/particle growth 11

2.3 Oil pollution and treatment methods previous 12

CHAPTER 3: MATERIALS AND METHODOLOGIES 16

3.1 Materials 16

3.2 Methodologies 17

3.2.1 Fabrication procedure PW-PW@LS 17

3.2.2 Optimization of fabrication parameters PW-PW@LS 18

3.3 Material characterization method 18

3.3.1 Scanning electron microscopy (SEM) 18

3.3.2 Energy-dispersive X-ray (EDX) 20

3.3.3 X-ray Diffraction (XRD) 21

3.3.4 Fourier-transform infrared spectroscopy (FTIR) 22

3.3.5 Water contact angle (WCA) 23

3.4 Evaluate the application of PW-PW@LS for environmental treatment 23

3.4.1 Separation of floating oil 23

3.4.2 Oil/solvent adsorption capacity 24

3.5 Evaluate the reusability of PW-PW@LS 25

3.6 Evaluate the durability of PW-PW@LS 25

3.6.1 Mechanical durability test 25

3.6.2 Chemical durability test 25

CHAPTER 4: RESULTS AND DISCUSSION 26

4.1 Optimization of the PW-PW@LS sample fabrication parameters 26

4.1.1 Optimization of ratio ethanol: xylene in step 3: spray-coating 26

4.1.2 Optimization of wax concentration in step 3: spray-coating 27

4.2 Characterization of fabricated materials 28

4.2.1 SEM image 28

4.2.2 EDX analysis 28

4.2.3 XRD analysis 31

4.2.4 FTIR analysis 32

4.2.5 WCA measurement results 33

4.3 Evaluate the ability to remove oils and organic solvents from water 34

4.3.1 Floating oil removal experiment 34

4.3.2 Oil adsorption: Effect of contact time 35

4.3.3 Effect of temperature 37

4.3.4 Calculation of oil adsorption capacity of PW-PW@LS 39

4.3.5 Mechanism of oil-water separation 41

4.4 Reusability and durability test of PW-PW@LS 41

4.4.1 Reusability test 41

4.4.2 Mechanical durability 42

4.4.3 Chemical durability 44

CHAPTER 5: CONCLUSION AND RECOMMENDATIONS 46

5.1 Conclusion 46

5.2 Recommendations 46

REFERENCES 48

APPENDIX 54

LIST OF TABLES

Table 2.1 Advantages and disadvantages of oil pollution treatment methods 13

Table 2.2 Summary of some studies using superhydrophobic materials for oil-water separation 15

Table 3.1 The chemical formula of the material 16

Table 3.2 Conditions for optimizing the ratio of ethanol and xylene to fabricate PW-PW@LS 18

Table 3.3 Optimization of wax concentration variation for fabrication PW-PW@LS18 Table 4.1 Change the ratio of ethanol: xylene in step 3 26

Table 4.2 Change the concentration of wax in step 3 27

Table 4.3 Elemental composition of raw LS 30

Table 4.4 Elemental composition of PW-PW@LS 30

Table 4.5 R2 and constant value for different adsorption kinetic models 36

Table 4.6 Results of adsorption capacity of PW-PW@LS 40

LIST OF FIGURES

Figure 2.1 Solid surface wetting states and WCA values (Zhang & Xu, 2021) 5

Figure 2.2 Wenzel and Cassie-Baxter's analysis of the wettability of a rough surface (Teisala et al., 2014) 7

Figure 3.1 Spray gun (Wider 1, ANEST IWATA, Japan) 18

Figure 3.2 SEM TM4000Plus (Hitachi Corp., Japan) 19

Figure 3.3 EDX MisF+ instrument (Oxford Instruments plc., UK) 20

Figure 3.4 XRD MiniFlex 600 (Rigaku Corp., Japan) 21

Figure 3.5 FTIR-4600 (Jasco Corp., Japan) 22

Figure 3.6 SmartDrop WCA (Femtofab Co Ltd., Korea) 23

Figure 3.7 Experimental diagram for separating floating oil from water 23

Figure 3.8 The schematic of the abrasion test of PW-PW@LS with sandpaper 25

Figure 4.1 SEM image of LS sample a) raw, b) after pretreatment, c) PW@LS, and d) PW-PW@LS 28

Figure 4.2 EDX spectra of LS sample a) raw, b) after pretreatment, c) PW@LS, and d) PW-PW@LS 29

Figure 4.3 Element mapping on PW-PW@LS surface 30

Figure 4.4 XRD patterns of sample a) palm wax, b) raw LS, c) LS after pretreatment, d) PW@LS, and e) PW-PW@LS 31

Figure 4.5 FTIR spectra of sample a) palm wax, b) raw LS, c) LS after pretreatment, d) PW@LS, and e) PW-PW@LS 33

Figure 4.6 Digital photo of water droplets and oil (kerosene) added on the surface a) raw LS, b) PW@LS, c) PW-PW@LS Small sections stand for OCA and WCA measurements, respectively The water is stained blue 34

Figure 4.7 Experimental diagram of removing floating oil from water Diesel oil is used as floating oil on seawater, and the water is dyed brilliant green for easy distinction 34

Figure 4.8 Pseudo-first-order kinetic model 35

Figure 4.9 Pseudo-second-order kinetic model 36

Figure 4.10 Effect of temperature on oil adsorption capacity 38

Figure 4.11 The density of oil and solvent at different temperatures (GmbH, 2023a, 2023b; Paleu & Nelias, 2007; Rusanov et al., 1966; ToolBox, 2018a, 2018b) 38

Figure 4.12 The adsorption capacity of PW-PW@LS for various oils and solvents 39

Figure 4.13 Effect of density on oil adsorption capacity 40

Figure 4.14 Schematic diagram of oil adsorption in PW-PW@LS a) for light oil, b) through capillary force, light oil is transported along cellulose fibers, and c) magnified photo 41

Figure 4.15 The adsorption capacity of PW-PW@LS after 10 cycles 42 Figure 4.16 Appearance shapes before and after compression of (a) raw LS, (b)

Figure 4.17 The kerosene adsorption capacity of PW-PW@LS after 20 abrasion

cycles 44

Figure 4.18 The kerosene adsorption capacity of PW-PW@LS at pH=2, pH=7, 0.5 M

NaCl 45

LIST OF ABBREVIATIONS

CVD: Chemical vapor deposition

FTIR: Fourier-transform infrared spectroscopy

KLAMG Key Laboratory of Advanced Materials for Green Growth

CHAPTER 1: INTRODUCTION

1.1 Research background

Oil spills in marine habitats and industrial wastewater discharge have increased alarmingly at a period of fast growth in the chemical sector and increasing demand for petroleum products Such events have costly consequences, with restoration operations costing billions of dollars In addition to lowering dissolved oxygen, oil spills in the ocean prevent sunlight from reaching the surface Marine animals, including seabirds covered in oil, lose their feathers, resulting in hypothermia (Mishra et al., 2022; Zhang

et al., 2019) Numerous technologies, including heating, dispersion, gravity separation, and the absorption of oily contaminants utilizing microparticles, have been developed

to address the contamination of polluted water (Gupta et al., 2017)

Scientists draw continuous inspiration from nature to innovate and enhance human life Natural phenomena serve as a driving force for the observation, study, design, and development of hydrophobic materials Among these phenomena, the remarkable concept of self-cleaning surfaces has captured the attention of scientists These surfaces show exceptional waterproof properties, with a water contact angle exceeding 150° and a sliding angle of less than 10° As a result, water droplets can effortlessly wash away from these surfaces (Kausar, 2019; Ma et al., 2006) Over time, scientists have employed various techniques, including sol-gel, anodic oxidation, chemical vapor deposition, and temperature manipulation, to modify the surface properties of materials (Zhang et al., 2008) The lotus leaf stands out among the extensively studied and renowned natural surfaces exhibiting superhydrophobic and water-repellent characteristics As water droplets roll over the surface, they effortlessly gather dirt and debris, displaying the self-cleaning ability of this hydrophobic leaf The nanostructure

of the cuticle wax on the papillae, resembling cilia, is crucial in enabling this remarkable feature (Zhang et al., 2012)

In a determined effort to create materials that own hydrophobic and superhydrophobic characteristics, researchers have conducted numerous studies These endeavors

more Recently, however, researchers have discovered the captivating potential of loofah sponges as natural sources for creating superhydrophobic surfaces These sponges (LS) contain high concentrations of lignin, hemicellulose, and cellulose within their intricate structure – specifically, an abundance of hydroxyl groups that confer innate absorptive capabilities upon them (Chen et al., 2018) The surface wettability of loofahs can be converted from hydrophilic to hydrophobic states Compared with materials such as aerogel (Yu et al., 2018), silicone (Hoshian et al., 2015), metal mesh (Wang & Xiong, 2014), or cotton (Zhou et al., 2013), the use of natural resources loofah sponge has many benefits, including three-dimensional structure, organic origin, wide availability, and reusability (Wang et al., 2019) In addition, they are biodegradable, saving on disposal costs Also, despite their usefulness in treating oil, more research must be done on using loofah sponges in treating the environment

1.2 Research significance

The problem of oil pollution is hot in the world Using natural materials that are environmentally friendly, cheap, and easy to manufacture is necessary and proper to deal with such a problem

Accordingly, this study will focus on creating and testing anti-wetting surfaces made

of LS that can be used to address environmental issues and pave the way for further research in this area

1.3 Research objectives

The objectives of this research are as follows:

1 Fabrication of superhydrophobic surface on the LS base

2 Optimization of superhydrophobic surface fabrication parameters on LS base

3 Characterization of fabricated LS surface using SEM, EDX, FTIR, XRD, and WCA techniques

4 Evaluation of applicability of fabricated LS in environmental treatment (e.g., oil water separator)

5 Evaluation of reusability and durability of fabricated LS (e.g., pH, abrasion, compression)

1.4 Thesis outline

This thesis is divided into five chapters The primary contents of the chapters are as follows:

Chapter 1 outlines the study’s objectives and supplies a brief overview of the context

and significance of the study

Chapter 2 offers superhydrophobic surface fundamental concepts, production

techniques, and applications Processes to remove oil from water are given special attention

Chapter 3 explains the tools and techniques used in this investigation The details of

the experiments, such as chemical setup, experimental design, analytical procedures, and experimental tools, are included

Chapter 4 gives the test and characterization analysis findings and discusses them Chapter 5 presents the most critical research findings and suggests areas that need

more investigation

CHAPTER 2: LITERATURE REVIEW

2.1 Theoretical basic

2.1.1 Water wettability and water contact angle

Wettability measures a liquid's ability to spread across and be absorbed by a surface (Law & Zhao, 2016)

The wettability of a surface and liquid can be affected by its chemical and physical properties In other words, these properties affect the capacity of a surface to be wetted

by a liquid (Wang et al., 2007) Highly wettable surfaces will allow liquids to spread out quickly and form a thin film, while surfaces that are not wettable will cause liquids

to bead up and not spread out quickly Effective performance in applications like water filtration, repellency, or attachment requires careful consideration of these traits

The wettability is assessed using the contact angle It is based on the intermolecular interactions when a little drop of water strikes the surface The lower contact angle shows the greater wetting capacity for material, while higher angles imply less wetness potential If a surface is hydrophilic or hydrophobic, it can be determined qualitatively using the contact angle (Sarkar et al., 2022) In addition, Thomas Young supplied the earliest explanation of the water contact angle in 1805:

S V S L Y

In summary, wettability is a crucial property of surfaces that decides how easily a liquid can wet them Understanding a surface's wettability is essential for various

applications and can be influenced by various factors, including surface chemistry, roughness, and temperature

2.1.2 Solid surface wetting states

There are three wetting states for solid surfaces: thoroughly wet, somewhat wet, and not wet (Moon et al., 2016) The water contact angle measures surface wettability and can calculate surface hydrophobicity

The liquid spreads over the solid surface and forms a thin film upon complete wetting The solid and liquid have a 0° contact angle, which means they are strongly drawn to one another and thoroughly wet to one another (Kumar et al., 2007)

In partial wetting, the liquid spreads to some amount over the solid surface but does not create a thin film The contact angle between the liquid and solid is more than 0° but less than 90° The liquid is only partially drawn to the solid (Stocco et al., 2017)

Figure 2.1 Solid surface wetting states and WCA values (Zhang & Xu, 2021)

Non-wetting occurs when the liquid does not wet the solid surface and instead produces droplets on the surface The liquid-solid contact angle is close to 90°, indicating that the liquid is not attracted to the solid and does not wet it (Neitzel & DellAversana, 2002) Superhydrophobic surfaces have been measured to have contact angles greater than 150° Furthermore, it is acknowledged that a surface must have low

contact angle hysteresis and a low sliding angle to qualify as a superhydrophobic surface (Webb et al., 2014) Numerous factors can affect the efficacy of wetting on a solid surface These may include attributes of both the liquid and solid components, and environmental conditions such as temperature and pressure (Ismail et al., 2020) Surface energy within solids, surface tension in liquids, and any roughness on a given solid's exterior are all relevant considerations that can affect wetting performance

2.1.3 Model explaining the mechanism

Wenzel and Cassie-Baxter's ideas about how often to water plants have the most support in the scientific literature (Mądry & Nowicki, 2021)

The Wenzel model is a model that describes the wetting behavior of a solid surface by

a liquid The Wenzel model was introduced in 1936 by R Wenzel It is considered that the liquid conforms to the solid surface's roughness, which puts the liquid in direct touch with any little lumps or imperfections on the surface (Robert & Chemistry, 1936)

The Wenzel model supplies the following formula to decide the contact angle between the liquid and the solid:

The Wenzel model considers the impact of surface roughness on the contact angle to predict the wetting behavior of rough surfaces However, it cannot accurately predict how smooth surfaces will get wet because it does not consider the effect of the solid’s and liquid's chemical and physical properties (Teisala et al., 2014; Webb et al., 2014) The Cassie-Baxter model is a theory that explains how a liquid will adhere to a solid surface The Cassie-Baxter model was proposed in 1944 by A B D Cassie and S

Baxter It is assumed that the liquid sits on a layer of air trapped between the rough parts of the solid surface (Cassie & Baxter, 1944)

The Cassie-Baxter model supplies the following formula to decide the contact angle between the liquid and the solid:

C B f Y

Where rf is the actual wetted area divided by the predicted wetted area of the surface, f

is the percentage of the predicted wetted surface area caused by the liquid, and θCB is the Cassie-Baxter CA on the rough surface

The Cassie-Baxter model helps predict the wetting behavior of smooth and rough surfaces, as it considers both the surface roughness and the chemical and physical properties of the solid and liquid It is often used with the Wenzel model to predict how complex surfaces will behave when wet (Teisala et al., 2014; Webb et al., 2014) Overall, the Cassie-Baxter model is more exact and complete than the Wenzel model because it considers a greater variety of elements that might affect a surface's wetting behavior However, the Wenzel model remains popular because it is simple to grasp and can predict how rough surfaces behave when wet

Figure 2.2 Wenzel and Cassie-Baxter's analysis of the wettability of a rough surface

(Teisala et al., 2014)

2.2 Methods to fabricate the superhydrophobic surface

2.2.1 Dip coating

Dip-coating is a simple and cost-effective method for fabricating superhydrophobic

surfaces (Himma et al., 2017) In this method, a substrate is immersed in a solution holding the desired coating material and then withdrawn at a controlled speed One can control the resulting film thickness by adjusting the coating solution's withdrawal speed and concentration (Grosso, 2011)

According to the survey, there have been many studies using dip coating as a method

to fabricate superhydrophobic surfaces One such study, published in 2016 by Abeywardena et al., used superhydrophobic precipitated calcium carbonate to coat the surface of the polyester fabric by a dipping coating method Superhydrophobic calcium carbonate is prepared from dolomite and stearic acid The resulting polyester fabric surface has a WCA of 161.9° (±0.1°) (Abeywardena et al., 2021)

Furthermore, in 2019, Lee et al used dipping silica nanoparticles on the surface of the polylactic acid filament The resulting superhydrophobic surface has a WCA higher than 150° and SA smaller than 10° (Lee et al., 2019)

In a 2021 publication by Chen et al., superhydrophobic surfaces were constructed on polyurethane sponges using dip coating The coating in this study was composed of polydopamine and graphene oxide Finally, obtained sponge surface with outstanding anti-droplet adhesion performance with WCA over 160° (Chen et al., 2021)

These studies have found that dip coating can be an effective method for creating superhydrophobic surfaces, as it allows for reasonable control over the thickness and uniformity of the coating (Daoud, 2013) It is also a scalable, quickly adapted method for large-scale production (Cui et al., 2009)

Several factors can affect the quality of a coating, including the substrate’s surface roughness, the coating solution's thickness, and the drying conditions For example, these factors may affect the coating's properties In addition, dip-coating may not be suitable for coating complex or irregularly shaped surfaces

2.2.2 Spray coating

Spray-coating is a popular approach for creating superhydrophobic surfaces This

approach spreads ultrafine particles across the material’s surface using a spray cannon

or similar equipment Compared to alternative processes such as dip coating or spinning coating, this approach is frequently favored because of its simplicity, ease of operation, and quick production time (Teisala et al., 2014) These surfaces may be created using other coating processes, such as electrostatic spray coating and airless spray coating

However, there are significant limits when using spray coating to create superhydrophobic surfaces For example, this technique may not achieve a high degree

of surface roughness, and the coatings fabricated may be less durable than those prepared by other methods Furthermore, spray coatings can be disturbed and excess coating produced, which can be challenging to regulate and result in waste and environmental problems (Manoharan & Bhattacharya, 2019)

Although spray coating has limitations, it remains a powerful and frequently applied method for producing superhydrophobic surfaces used in various inquiries and practical uses Several research studies have used spray coating for creating superhydrophobic surfaces, such as:

A study published by Wang et al in Applied Thermal Engineering in 2023 used film spray coating to create a superhydrophobic film heater The researchers used SiO2powder to enhance the superhydrophobic strength of the material Research shows the superhydrophobic membrane is stable with WCA = 140° after 150 peeling cycles (Wang et al., 2023)

wet-In another study published in 2023, Cao et al developed a superhydrophobic material using the electrostatic spraying method In this study, polyvinylidene fluoride (PVDF) and SiO2 nanoparticles were sprayed onto the surface of iron sheets The character and durability of superhydrophobic surfaces have been investigated Notably, after 600 abrasion cycles, the WCA superhydrophobic coating increases from 155° to 161.7°, which is rare in previous studies (Cao et al., 2023)

Another publication by Li et al., in 2023, developed a process in which a superhydrophobic surface is produced by spraying SiO2 nanoparticles onto a steel/glass sheet The WCA measurement of the surface is as high as 153.7°, and the

SA angle is less than 4° (Li et al., 2023)

2.2.3 Polymerization techniques

Polymerization techniques are methods used to synthesize polymers, which are large molecules of repeating units called monomers These techniques can create various polymers with different properties and applications, including superhydrophobic materials (Liu et al., 2020)

Several polymerization techniques can be used to manufacture superhydrophobic surfaces, including (Teisala et al., 2014; Wei et al., 2020):

Addition polymerization: This involves the addition of unsaturated monomers to form a polymer chain Heat, light, or chemical initiators can start further polymerization

Condensation polymerization occurs when two or more monomers combine to form

a polymer chain, releasing a small molecule like water or methanol as a byproduct

Radical polymerization: Heat, light, or chemical initiators can generate a radical species that can start a polymer chain radical polymerization Radical polymerization can be either anionic or cationic

Copolymerization combines two or more different monomers to create a copolymer with intermediate properties between the individual monomers

Servals research has used the polymerization process to create superhydrophobic surfaces, including:

In 2023, a publication by Yu et al reported on the successful fabrication of superhydrophobic coating films on glass plates Coatings were made using polymeric fluorinated silica nanoparticles through step transfer-addition and radical-termination (START) polymerization The large-scale fabricated coating yields a

superhydrophobic surface state with a WCA of 172.6° and a SA close to 0° (Yu et al., 2023)

Another study was published in 2023 by Huang et al., Through one-pot emulsion polymerization of polydimethylsiloxane (PDMS), this research has created superhydrophobic melamine foam The superhydrophobic melamine surface has a water contact angle and rolling angle of 156.8° and 3°, respectively (Huang et al., 2023)

2.2.4 In situ nanorod/particle growth

In situ, nanorod/particle growth is a cycle that involves making nanorods or

nanoparticles immediately on a substrate surface rather than making them freely and a while later saving them (He et al., 2019) This technique is habitually used to develop superhydrophobic surfaces because the later nanostructures may offer the high surface harshness and low surface energy expected to accomplish a superhydrophobic impact There are a few ways to achieve in situ growth of nanorods or nanoparticles, including chemical vapor deposition (CVD), electrodeposition, and solution-based methods such

as sol-gel synthesis and electroless plating (Teisala et al., 2014; Wei et al., 2020) Every strategy has benefits and drawbacks, and the decision might rely upon the application's prerequisites For instance, CVD is a high-temperature process that can orchestrate many materials yet may not be reasonable for explicit substrates

Chemical vapor deposition (CVD) and plasma processing can fabricate superhydrophobic surfaces

CVD involves introducing a gas mixture into a reaction chamber, where it reacts to create a solid material on a substrate This process can deposit a thin film of materials, including superhydrophobic coatings CVD has been used to deposit various superhydrophobic materials, including silicon dioxide and fluorinated polymers (Alf et al., 2010)

Plasma processing involves creating plasma, a high-energy state of matter with charged particles Plasma can change the surface properties of materials, including

creating superhydrophobic surfaces Plasma processing has created superhydrophobic coatings on various materials, including metals and polymers (Jafari et al., 2013) Several studies are using CVD and plasma processing to create superhydrophobic surfaces, such as:

The study by Huang et al., 2019 published on developing Al-based superhydrophobic coatings with micro-nano hierarchical surface structure prepared by plasma spray method (Huang et al., 2019)

Furthermore, in 2022, Fu et al successfully fabricated a ceramic-based superhydrophobic surface on aluminum through plasma electrolytic oxidation and CVD methods The superhydrophobic coating is created from silica nanoparticles WCA of aluminum surface as high as 160.5  ±  3.2° and SA of 3  ±  0.5° (Fu et al., 2022)

2.3 Oil pollution and treatment methods previous

In recent years, oil pollution has become a major environmental issue of global concern This problem’s harmful effects include affecting the surrounding ecosystem, human, and animal health Therefore, measures to treat oil pollution are being considered by many researchers Table 2.1 summarizes the advantages and disadvantages of some measures to treat contaminated oil

Table 2.1 Advantages and disadvantages of oil pollution treatment methods

Physical separation (Dave &

Ghaly, 2011; Hoang et al., 2018) can remove large amounts of oil

unsuitable for tiny oil droplets or dissolved oil; labor-intensive; may not be suitable for use in specific environments Bioremediation (Dave & Ghaly,

2011; Wang et al., 2017)

can remove small and large oil droplets; less toxic than chemical methods in general

may need to be faster to work; may not

be effective in specific environments

Chemical dispersion (Hoang et

al., 2018; Wang et al., 2017)

can break down large amounts of oil

negatively affects the environment due to the toxicity of chemicals

Mechanical recovery (Dave &

Ghaly, 2011; Hoang et al., 2018)

can remove large amounts of oil; suitable for use in a wide range of environments

labor-intensive; may not be suitable for use in specific environments

Burning (Al-Majed et al., 2012) can quickly remove large amounts of oil be used in remote

locations

produce air pollution; may not be suitable for use in specific environments; can be labor-intensive; may not be effective at removing tiny oil droplets

Superhydrophobic materials

(Kukkar et al., 2020; Mishra et

al., 2022; Zamparas et al., 2020)

 Effectively repel oil: Superhydrophobic materials

have a highly water-repellent surface that can also effectively repel oil Superhydrophobic surfaces can stop oil from spreading and even stop spills before they do much damage

materials can be applied to various surfaces, including uneven or rough ones, making them suitable for use in various environments

It may be used in hazardous environments: hydrophobic materials are ideal for hazardous environments where human presence is not applicable since they work independently without any intervention from humans

Super- Low toxicity: Since superhydrophobic materials do

not need chemicals, they may be less toxic than other ways

to clean up oil pollution

 Long-lasting: Some superhydrophobic materials can

be very durable and last long, so they may not need to be used as often as other ways to treat oil pollution

With such advantages, superhydrophobic materials are opening new research avenues for treating contaminated oil Moreover, it is attractive to many researchers The following table summarizes some recent studies:

Table 2.2 Summary of some studies using superhydrophobic materials for oil-water separation

Water contact angle

Type of oil Separation

efficiency Reference

―Superhydrophobic meshes that can repel

hot water and strong corrosive liquids used

for efficient gravity-driven oil/water

separation.‖

Stainless steel mesh

2016)

―Robust superhydrophobic/ super oleophilic

sponge for effective continuous absorption

and expulsion of oil pollutants from water.‖

Polyurethane (PU) sponge

al., 2013)

―Superhydrophobic coating on fiberglass

cloth for selective removal of oil from

water.‖

al., 2015)

―Preparation of superhydrophobic magnetic

sawdust for effective oil/ water separation.‖

2020)

In summary, previous superhydrophobic surface fabrication used artificial cellulose fibers such as melamine and polyurethane sponges These substrates are not biodegradable Therefore, using LS as a base material to create superhydrophobic materials can solve the problem

of biodegradation

CHAPTER 3: MATERIALS AND METHODOLOGIES

Table 3.1 The chemical formula of the material

Loofah sponge

Wax

1H,1H,2H,2H-Perfluorodecyltrichlorosilane

3.2 Methodologies

3.2.1 Fabrication procedure PW-PW@LS

Step 1: Pretreatment of loofah sponge (LS)

Firstly, the raw LS measuring 5x5 cm2, with an average weight of 2.2 grams, was washed three times with deionized water to remove all dirt, soil, and sand Then, 100

mL of 0.5M NaOH was used to alkalize to remove fatty and sticky components, hemicellulose, and lignin, to increase surface roughness and improve the response to denaturants Finally, the LS was washed three times with industrial alcohol (use volume is 50 mL) and dried at 40°C using an oven (Thermo Scientific, USA) for 5 h

Step 2: Fabrication of PW@LS coating

Subsequently, 4g of the wax was dissolved in 100mL of xylene at 60°C for 15 min by magnetic stirrer with a hot plate (Lanphan 85-2, China) Add 0.1mL FTDS (96%) to the above solution, ultrasonic vibration (40kHz), for 15 minutes to obtain a homogeneous solution mixture Then, the LS was immersed in the prepared xylene solution for 12 h After drying at 40°C for 4 h, the sponge samples coated with palm wax were named PW@LS

Step 3: Fabrication of PW-PW@LS coating

In this step, absolute ethanol is used to increase the surface roughness Ethanol is added to a solution of wax-xylene with ethanol: xylene by volume ratio The concentration of wax in the mixture of ethanol: and xylene wax was kept at 0.01 g/mL The resulting emulsion was poured into a container, using a spray gun (Wider 1, ANEST IWATA, Japan) to spray the emulsion at a pressure of 0.2-0.5 MPa onto the PW@LS sample from 10-15 cm with the spray angle perpendicular to the loofah surface After drying under room conditions, the final sample was named PW-PW@LS

Figure 3.1 Spray gun (Wider 1, ANEST IWATA, Japan)

3.2.2 Optimization of fabrication parameters PW-PW@LS

(i) Ratio ethanol and xylene

In step 3, the ratio of ethanol and xylene was considered by volume in the table below

Table 3.2 Conditions for optimizing the ratio of ethanol and xylene to fabricate

PW-PW@LS

(ii) The concentration of palm wax

In step 3, with the most optimal ethanol: xylene ratio, the concentration values of palm wax were changed to produce different sponges

Table 3.3 Optimization of wax concentration variation for fabrication PW-PW@LS

3.3 Material characterization method

3.3.1 Scanning electron microscopy (SEM)

Scanning electron microscopy is one of the most popular analytical methods to decide material properties, microcrystalline structure, and size distribution The resolution of this method reaches several nanometers, allowing the magnification to be adjusted

be emitted by thermal emission, which is then accelerated The acceleration potential

of the SEM is from 10kV to 50kV The magnetic lens emits and concentrates electrons into a focused electron beam and then scans over the sample surface by electrostatic scanning coils The focused electron beam size decides the resolution of the SEM The interaction between the material on the specimen surface and the electron also affects the study of the radiations does the resolution of SEM Imaging in the SEM analysis is generated when electrons interact with the sample’s surface (Mohammed & Abdullah, 2018) For example, SEM can be used to analyze the microstructure of a metal sample The electron beam is scanned over the surface of the metal, and the resulting radiation supplies information about the crystal structure and size distribution These details can

be used to assess the metal's strength and ductility, among other mechanical characteristics

This study measured SEM images of the fabricated materials using a TM4000Plus (Hitachi High-Technologies Corp., Japan) scanning electron microscope at VNU KLAMG, Hanoi University of Science

Figure 3.2 SEM TM4000Plus (Hitachi Corp., Japan)

3.3.2 Energy-dispersive X-ray (EDX)

X-ray energy scattering spectroscopy is a method for deciding the chemical makeup of solids based on capturing the X-ray spectrum that the solid emits due to its interaction with radiation Microstructure pictures of solids were captured using a high-energy electron beam that interacts with the solid atom and penetrates deep into the solid atom

to interact with the inner electron layers of the atom

The chemical elements contained in the sample and their quantities can be decided by seeing the X-ray spectrum that a solid emits The accuracy of EDX is in the order of a few percent, with elements that make up a ratio of 3 - 5% or more However, EDX is inefficient with light elements, and there is often a superposition effect of X-ray peaks

of different elements because an element often emits many characteristic peaks Kα,

Kβ , and the peaks of different elements can overlap, making analysis difficult (Cardell & Guerra, 2016)

This research measured the EDX spectrum of the material samples on an EDX MisF+ instrument (Oxford Instruments plc., UK) at VNU KLAMG, Hanoi University of Science

Figure 3.3 EDX MisF+ instrument (Oxford Instruments plc., UK)

3.3.3 X-ray Diffraction (XRD)

According to the theory of crystal structure, a crystal lattice is built from atoms or ions evenly distributed in space in a particular order When the X-ray beam contacts the surface and penetrates deeply into the crystal, the crystal’s lattice exhibits a specific diffraction pattern Atoms and ions will form centers after being stimulated by the X-ray radiation, producing reflected photons On the other hand, these atoms and ions are distributed in parallel planes Consequently, the X-ray beam is diffracted in a particular pattern that can be used to find the crystal structure and makeup This method, called X-ray crystallography, is frequently used in many disciplines, including chemistry, biology, and materials science, to investigate the atomic and molecular structure of various substances (Bunaciu et al., 2015)

Bragg's equation, which is the basic equation for measuring the wavelength of X-rays

or for studying the structure of a crystal lattice:

(4)

In the equation, n is the diffraction order, λ is the wavelength of the incoming X-ray

beam, d is the separation between parallel crystal surfaces, and θ is the reflection angle

(Bunaciu et al., 2015)

Figure 3.4 XRD MiniFlex 600 (Rigaku Corp., Japan)

In this study, XRD MiniFlex 600 (Rigaku Corp., Japan) was used under emission source conditions using CuKα radiation (λ = 0.154 nm) and a 0.02° scan step between

10 - 80° (2θ) at a scan speed of 10 ° min-1 at VNU KLAMG, Hanoi University of Science

3.3.4 Fourier-transform infrared spectroscopy (FTIR)

The Fourier transform infrared spectroscopy method is based on the interaction between the analyte and monochromatic rays with wavelengths in the infrared range (400 - 4000 cm-1) Each peak in the IR spectrum characterizes a functional group’s presence or a bond’s oscillation Therefore, it is possible to rely on these characteristic frequencies to infer the presence of bonds or functional groups in the molecule of the studied substance (Mohamed et al., 2017) For example, FTIR spectroscopy can be used to find the composition of a plastic material By analyzing the IR spectrum, researchers can decide what functional groups are in plastic They can use this information to find the type of polymer, which can be especially helpful in sectors like packaging Understanding the material composition is critical in ensuring products can

be safely used with food or other delicate items

This study analyzed the sample by FTIR 4600 (Jasco Corp., Japan) at KLAMG, Hanoi University of Science

Figure 3.5 FTIR-4600 (Jasco Corp., Japan)