INTRODUCTION
Self-cleaning materials are considered the future of technology in the 21st century, with their origins tracing back to Thomas Young's 1805 report on material wettability The lotus leaf's remarkable wetting properties have inspired extensive research in this field To date, thousands of articles on self-cleaning materials have been published, highlighting their growing popularity worldwide These materials serve not only research purposes but also have diverse real-life applications, significantly contributing to advancements in science and technology beyond their self-cleaning capabilities.
Developing self-cleaning surfaces requires careful consideration of substrate properties and research objectives, making the selection of suitable fabrication techniques crucial Various methods can be employed to create substrates; for example, the hydrothermal process was utilized on glass by Haiyan Hi et al (Ji et al., 2013), while Satish explored alternative approaches.
Recent advancements in creating repellent surfaces have been achieved through various methods, including the sol-gel route (Mahadik et al., 2010) and laser processing (Lin et al., 2018; Nguyen et al., 2021) These techniques can be applied to a wide range of substrates, each requiring specific optimal conditions The sol-gel method is particularly versatile, demonstrating effectiveness on materials such as fabric (Yang et al., 2018), copper (Raimondo et al., 2017), glass (Mahadik et al., 2010), ceramic (Jamalludin et al., 2020), wood (Jia et al., 2018), and paper (Dimitrakellis et al., 2017) Additionally, integrating multiple methods within a single study offers a flexible approach to research (Li et al., 2015).
The self-cleaning feature has been effectively developed on various substrates, yet recent studies reveal ongoing challenges, including the use of toxic solvents like toluene and techniques that demand high energy consumption, such as plasma etching.
On the other hand, the research and application on this material has not been widely developed in Vietnam Superhydrophobic material is one of the economically,
The effective separation of oil and water is crucial for industrial waste oil recovery and marine oil spill cleanup While this technology is utilized in Vietnam, it is primarily imported from countries like Germany, Japan, and Taiwan Therefore, this study aims to explore the development of materials that can enhance oil recovery processes domestically.
Research on low-cost, eco-friendly self-cleaning materials is limited This study aims to promote sustainability by examining the entire product life cycle and minimizing waste The hydrothermal combined with dip-coating method was utilized to create superhydrophobic cotton fabric The properties of the resulting fabric were analyzed using various techniques, including Scanning Electron Microscope (SEM), Energy-dispersive X-ray spectroscopy (EDS), Fourier-Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), and Water Contact Angle (WCA) measurements Additionally, potential applications of this innovative fabric will be discussed in detail.
LITERATURE REVIEW
Theoretical basis
In 1805, Thomas Young first reported the contact angle between a liquid and a homogeneous solid surface, establishing a relationship between water contact angle (WCA) and surface energies based on mechanical theories Later, in the mid-20th century, Wenzel and Cassie-Baxter enhanced this understanding by exploring the effects of surface roughness on contact angle changes Today, the wettability of material surfaces continues to be a significant focus in both research and practical applications.
When a water droplet lands on a solid surface, the contact angle (θ) is formed between the liquid and the surface The Young’s equation is applicable exclusively to homogeneous solid surfaces.
Figure 2.1 Young theory (Young, 1805) Where, γsv, γsl, γlv are the interfacial tensions of the solid-vapor, solid-liquid and the liquid-vapor interface, respectively
The concept of heterogeneous surfaces is complex, as illustrated by the Wenzel and Cassie-Baxter models Wenzel's model describes a scenario where liquids fully penetrate rough surfaces, while the Cassie-Baxter model suggests that air trapped in the grooves of a rough surface keeps water droplets elevated, preventing direct contact with the surface.
Figure 2.2 Wenzel and Cassie-Baxter models (Wenzel, 1936),(B D Cassie and Baxter, n.d.)
The concept of superhydrophobic and superhydrophilic surfaces emerged from Onda et al.'s seminal papers on rough surface wettability in 1996 Since then, extensive research has been conducted on the water permeability of various materials A surface qualifies as superhydrophobic if it meets two criteria: a static water contact angle (WCA) of 150 degrees or greater, and a dynamic contact angle of less than 10 degrees.
Figure 2.3 Wetting state and static water contact angle of the solid surfaces
Table 2.1 The values of the WCA correspond to the solid surface states
States Water contact angle (WCA)
Methods to fabricate the superhydrophobic surface
To achieve superhydrophobicity, various methods are employed to modify substrate structures, primarily utilizing two approaches: TOP-DOWN, which involves creating nanoparticles from larger particles, and BOTTOM-UP, which forms nanoparticles from atoms or ions These methods can be combined in a sequential manner, typically starting with the TOP-DOWN approach followed by BOTTOM-UP restructuring, although alternative combinations have also been explored The goal of these techniques is to enhance surface roughness by attaching nanoparticles with crystalline structures, ultimately reducing the contact area between water and the solid surface, thus resulting in a high contact angle.
The top-down approach involves reshaping surfaces through techniques like carving, molding, and machining, often utilizing lasers or other tools This method is commonly employed to create superhydrophobic surfaces using processes such as electro-spinning, plasma etching, chemical etching, and electrochemical deposition.
Electro-spinning is a manufacturing technique that utilizes an electrostatic process to produce fibers with diameters ranging from tens of nanometers to a few micrometers One of its key advantages is its versatility, allowing for the creation of fibers in various arrangements and morphological structures This innovative approach has significantly advanced the development of new materials and applications.
In recent years, various technologies such as tissue engineering, regenerative medicine, and the encapsulation of bioactive molecules have significantly advanced For example, Nagrath et al (2019) combined sol-gel and electrospinning techniques to create bioactive glass fibers for biomedical applications, particularly in osteogenesis and hemostatic treatments Additionally, Linh et al (2011) successfully developed PVA-TiO2 composite polymer membranes for filtration purposes Furthermore, Nguyen et al (2010) synthesized PVA nanofibers containing silver nanoparticles with strong antibacterial properties using a combination of microwave irradiation and electrospinning methods.
At room temperature, the elements in the material being etched interact with reactive species produced by plasma, causing the atoms to adhere to the object's surface and altering the physical properties of the substrates The plasma source, also known as etch species, can consist of charged ions or neutral atoms and radicals Despite the complexity of this technique, it offers the advantage of creating a uniform surface structure, which continues to be the focus of recent studies (Hou et al., 2020; Nguyen-Tri et al., 2019).
Chemical etching is an eco-friendly process that utilizes highly acidic or basic solutions to react with surface elements, allowing for high etching rates and selectivity with simple equipment This method produces corrosion-resistant products efficiently; however, it also presents challenges such as substrate contamination, poor process control, and a significant requirement for etchant chemicals Despite these drawbacks, numerous studies have explored the advantages of chemical etching (Yao et al., 2018; Huang et al., 2015).
Bottom-down approach is the process of adding or self-assembly material in nano or micro scale on initial surfaces Which includes some typical techniques as follow
Electrochemical deposition is a technique that constructs solid materials from molecules, ions, or complexes found in a solution, enabling the creation of patterned metal layers on top of other metals This process utilizes electrical energy to convert ions into atoms, often resulting in nano-scale thin films of metals such as zinc, copper, platinum, and gold Numerous studies have demonstrated the effectiveness of this method in producing durable thin metal films Notable research includes M.J Zheng et al.'s fabrication of nanowires using an alumina membrane and Yan Song et al.'s successful deposition of Au-Pt on an indium tin oxide surface through direct electrochemical methods, highlighting potential applications in electrocatalysis and sensing technologies.
The hydrothermal method is an effective technique for synthesizing superhydrophobic coatings by producing crystalline substances through the growth of crystals in an autoclave under high pressure and temperature, which enhances surface roughness Despite its inability to monitor the crystal growth process, this method is straightforward and yields high-quality crystals The properties of the crystal structures can be adjusted by altering experimental conditions such as temperature and reaction time, although initial equipment investment is required Numerous studies have highlighted the technique's effectiveness across various chemicals and substrates For instance, Shuhui Li et al (2015) developed flower-like hierarchical TiO2 micro/nanoparticles on cotton fabric, achieving a water contact angle (WCA) greater than 160° and a sliding angle below 5°, demonstrating superior anti-wetting and self-cleaning properties Similarly, Ruan Bing Hu et al (2013) created a superhydrophobic glass surface using a two-step method, first coating the glass with a carbon/silica composite and then applying carbon nanoparticles via hydrothermal synthesis, followed by surface modification with perfluordecyltrimethoxysilane to enhance the WCA.
In 2014, researchers successfully developed superhydrophobic ZnO micro/nanocrystals through a one-pot hydrothermal process, achieving a remarkable static contact angle of 167 degrees for water Additionally, Yanjing Tuo et al (2018) created a superhydrophobic surface on aluminum foil, showcasing excellent self-cleaning properties, along with numerous other studies in this field.
The dip coating technique, also known as the dip coating method, is a cost-effective and straightforward process that involves immersing a substrate in a coating solution After a designated dipping time, the substrate is withdrawn, allowing the solvent to evaporate and leaving a uniform coating on the surface This method is advantageous because it can coat both sides of the substrate simultaneously, is applicable to various materials, and produces a highly durable and stable coating layer Numerous studies have utilized dip coating; for instance, Liu et al (2011) created superhydrophobic wood using potassium methyl siliconate, Yao et al (2018) developed artificial superhydrophobic copper surfaces for anti-corrosion through wet chemical etching, and Raimondo et al (2017) conducted experiments with green-based flame retardants to produce flame-retardant superhydrophobic cotton.
The sol-gel technique is a widely used method in material science for creating superhydrophobic surfaces This process involves converting a monomer into a colloidal solution (sol), leading to the formation of a polymer or particle network (gel) with particle sizes ranging from 1 to 100 nm Despite challenges such as contraction during processing, extended processing times, fine pores, and residual hydroxyl or carbon groups, the advantages of the sol-gel method are substantial It allows for the production of thin, durable coatings that perform well at low temperatures, are cost-effective, and yield high-purity products Additionally, the composition is highly controllable, enabling application on various surfaces with a homogeneous coating Research by Hooda et al (2018) demonstrated the synthesis of Triethoxyoctylsilane-nanosilica on glass substrates via the sol-gel method, achieving a static water contact angle (WCA) of 162 ± 2° and a shedding angle (SA) of 3 ± 1°, showcasing its potential for self-cleaning surfaces and solar panel covers Similarly, Raimondo et al (2017) successfully deposited alumina nanoparticles on copper using two different preparation routes, further highlighting the versatility of the sol-gel approach.
In a study comparing the wettability of aqueous and alcoholic Al2O3 sol-gels, it was found that the alcoholic sol achieved water contact angles (WCA) close to 180°, indicating a highly hydrophobic state, while the aqueous sol produced coatings with different characteristics Research by Czyzyk et al (2020) investigated the effects of thermal, radiation, and dual curing processes on interfacial adhesion between silica nanoparticles, the sol-gel matrix, and the substrate The findings revealed that all three curing methods resulted in highly transparent superhydrophobic coatings with WCAs exceeding 150°.
Recent research by Nurul Pratiwi et al (2020) demonstrated the fabrication of a transparent superhydrophobic glass utilizing a TiO2 film combined with octadecyltrichlorosilane (OTS), achieving a static water contact angle (WCA) of 158 ± 2° and a sliding angle of 4 ± 1° This superhydrophobic glass exhibited excellent durability, maintaining its performance even after exposure to UV irradiation, chemical immersion, and physical abrasion Numerous studies have reported similar promising results, highlighting the effectiveness and applicability of objects produced through the sol-gel technique.
Various techniques can be employed to create superhydrophobic materials, including casting, phase separation, chemical vapor deposition, self-assembly, and lithography The choice of method depends on the intended application, the substrate's properties, and the allowable experimental conditions.
Applications of the superhydrophobic material
The diverse range of substrates leads to numerous applications, particularly in the development of superhydrophobic materials By modifying the wettability of these materials, we can unlock their potential beyond mere self-cleaning properties Superhydrophobic materials have significant implications across various fields, including everyday life, industrial processes, environmental protection, and medical treatments Below, we explore some of the prominent applications of these innovative materials.
Icephobicity is a crucial property that prevents ice formation on surfaces, enhancing ease of removal due to reduced adhesion In the context of aircraft, ice accumulation can alter their shape and negatively affect aerodynamic performance, making anti-icing surfaces essential for ensuring reliability Additionally, surfaces exhibiting both superhydrophobicity and icephobicity have valuable applications in various industries, including ships, wind turbines, and air conditioning systems (Boinovich et al., 2013).
Fog occurs when particles are suspended in the air due to temperature changes and high humidity, impairing visibility and causing discomfort for individuals wearing glasses Anti-fogging surfaces enhance evaporation rates by providing a larger surface area compared to traditional materials, effectively reducing fog formation These surfaces can be designed to be either superhydrophobic or superhydrophilic For instance, research by Lai et al (2012) developed superhydrophobic/superhydrophilic layers with zero water contact angle on glass, showcasing significant potential for applications in eyewear, windshields, mirrors, and various industrial sectors.
Recent research into the creation of superhydrophobic surfaces on fibers has enabled the production of waterproof footwear and clothing, enhancing both everyday wear and protective apparel Additionally, these self-cleaning surfaces are effective in keeping solar panels free of dust, thereby maintaining their efficiency.
Superhydrophobic materials are increasingly utilized in biomedical applications to reduce platelet adhesion to artificial implants, thereby enhancing the success of organ transplants and artificial blood vessels Research by Sun et al (2005) exemplifies this innovative approach.
Superhydrophobic materials play a crucial role in environmental treatment by effectively separating oil from water and organic solvents, making them valuable for waste oil cleanup in marine environments and industrial applications For example, Shuhui Li et al (2015) developed hierarchical TiO2 micro/nanoparticles on cotton fabric, achieving a water contact angle (WCA) of 163° and a sliding angle (SA) below 5°, enabling efficient self-cleaning and oil-water separation Similarly, Tudu et al (2020) created superhydrophobic cotton fabric with a static WCA of 169.3 ± 2.1° and an SA of 6.3 ± 2.0°, demonstrating its capability to separate oil from water effectively over 140 cycles.
Aliasghar Parsaie et al (2020) successfully created a durable superhydrophobic/superoleophilic polyurethane sponge, demonstrating its potential for large-scale oil spill remediation Similarly, Dheeraj Ahuja et al (2021) developed a superhydrophobic sponge capable of absorbing motor oil and diesel oil across more than 10 cycles Numerous other studies have also reported promising results regarding the effectiveness of various substrates in filtering oil and water.
Analysis methodologies
Principles of Scanning Electron Microscopy
The Scanning Electron Microscope (SEM) utilizes a focused beam of electrons to scan the surface of a specimen, creating a highly magnified image When the electrons collide with the specimen's surface, they are reflected back, and a detector captures these signals to generate an image with nanometer-scale resolution The electron beam is focused using lenses located in the electron column, and the SEM must operate under vacuum conditions to prevent collisions between the electrons and gas molecules.
The main parts inside SEM directly involved in the process presented bellow
There are two types of electrons detected in electron microscopy: backscattered electrons (BSE) and secondary electrons (SE) BSE are reflected back from the surface of an object due to elastic interactions with the electron beam, while SE are emitted from the sample's atoms as a result of inelastic interactions These two types of electrons provide different information; BSE images reveal details from deeper regions of the object and are sensitive to variations in atomic number, making materials with higher atomic numbers appear brighter In contrast, SE imaging offers more intricate details of the object's surface, as SE originate from surface positions.
Figure 2.5 Electron beam and the different types of signals which are generated (T F
The electron column consists of an electron source and a series of lenses that focus the electrons The condenser lenses concentrate the electrons into a beam, which is then directed onto the sample surface by the objective lens, also referred to as the final lens.
Figure 2.6 Magnetic lens schematic (T F Scientific, n.d.)
Deflectors are essential for controlling the direction of electron flow, as electrons, which carry negative charges, travel through the electron column at high energy and speed When electrons pass through the column, they are deflected at an angle due to the influence of an electric field, which is determined by the electron's energy, the voltage applied between the plates (+U and -U), and the length of the plates, as illustrated in Figure 2.7.
Figure 2.7 Electron beam deflector (a) and lector-static lens (b) (T F Scientific, n.d.)
Electrostatic and magnetic lenses are essential components of Scanning Electron Microscopes (SEM) Magnetic lenses, constructed from ferromagnetic materials, feature two pole pieces at each end and operate based on the Lorentz force, which alters the velocity of electrons for deflection A coil situated atop the ferromagnetic circuit generates the necessary magnetic field, as illustrated in Figure 2.8 Adjusting the distance between the pole pieces influences the lens's performance.
14 pieces and electric flow in to the coils is the way of making the changing the strength of the lens
Figure 2.9 Different kinds of electrostatic lenses: single-aperture positive and negative lenses (a, b), two-aperture lens (c) and three aperture Einzel lens (d) (T F
Electrostatic lenses utilize metallic plates connected to high voltage to guide electron beams Single-aperture lenses, which consist of a single metallic plate, can effectively focus the beam when a positive voltage is applied.
In optical systems, the behavior of light beams can vary significantly depending on the type of lens used A negative lens causes the beam to diverge, while a positive lens directs the beam towards a specific point A two-aperture lens consists of two metallic plates with aligned apertures, creating a consistent electric field that directs the beam downward upon hitting the second plate In contrast, a three-aperture lens features three plates with either identical or varying diameters; the first and third plates are positively charged, while the second plate carries a negative charge This configuration results in a positive charge overall, guiding the beam to impact below the third plate.
Among them, the magnetic lens is most commonly used type due to their stability of the structure which generate the magnetic field
Figure 2.10 Michelson interferometer in configured for FTIR (Petergans, 2017)
FTIR (Fourier Transform Infrared Spectroscopy) detects functional groups on the surface of objects by measuring how different bonds absorb infrared radiation (IR) at various frequencies This technique analyzes the infrared region of the electromagnetic spectrum, which encompasses wavelengths longer and shorter than visible light.
Infrared light from a source passes through a Michelson interferometer, which consists of a beam splitter, a mobile mirror, and a fixed mirror The beam splitter divides the light beam into two paths, reflecting off the two mirrors before recombining As the mobile mirror adjusts along the optical path, it creates variations in phase differences over time The resulting light beams are collected to produce an infrared spectrum, displayed as a graph with infrared light absorbance on the vertical axis and wavelength on the horizontal axis (PerkinElmer, 2009).
Operating the FTIR process is straightforward: first, position the sample in the FTIR spectrometer, where infrared beams interact with its surface to measure absorption at various frequencies The sample must be thin enough for the infrared light to penetrate effectively Subsequently, a mathematical technique known as Fourier transformation is employed to decode the obtained signals, resulting in the generation of spectra.
16 database references help to recognize substances on samples Interestingly, particular molecular identities can be determined
X-ray diffraction (XRD) is a technique used as a tool to determine the crystallographic structure of a solid material XRD principle is irradiating an incident X-rays to the sample the measure the intensities and scattering angles of the X-rays that reflect the sample
The XRD device operates by having crystal atoms in a sample scatter incident X-rays through interactions with the electrons of the atoms, resulting in an elastic scattering phenomenon This process generates a regular array of spherical waves due to the orderly arrangement of the crystals While most of these waves cancel each other out through destructive interference in various directions, certain waves constructively interfere in specific directions as dictated by Bragg's law.
The distance between diffracting planes (d), the incident angle (θ), an integer (n), and the wavelength of the incident ray (λ) are key factors in the diffraction process, which produces distinct spots in a diffraction pattern By utilizing the Crystallography Open Database (COD), we can identify the chemical compositions of various objects X-rays are particularly effective for generating diffraction patterns due to their wavelengths, which typically range from 1 to 100 angstroms, aligning closely with the distances between crystal planes.
Contact angle measurement is a widely utilized method for assessing surface properties The static water contact angle (WCA) is determined under static conditions, where the solid, liquid, and gas phases remain motionless.
Figure 2.11 Contact angle measurement (image cut from video) (B Scientific, n.d.)
When capturing an image of a liquid droplet, typically water, resting on a solid surface, the droplet's volume is approximately 10 µL The static contact angle can be determined using the Young equation applied around the droplet, with alternative fitting methods such as circular and polynomial approaches also available.
Superhydrophobic material studies in Viet Nam
Research and development of superhydrophobic materials in Vietnam has been limited, with only a few studies emerging in recent years Notable works include Vu Manh Tuong et al., who utilized nanotechnology to create superhydrophobic TiO2 and ZnO coatings on Acacia mangium x auriculiformis wood, achieving impressive contact angles of 152.6° and 151.8°, respectively Additionally, Phan The Anh and Dang Kim Hoang developed a sorbent material for oil spill cleanup by modifying melamine formaldehyde foam, which demonstrated a high sorption capacity of 15-61 g/g for oils and organic solvents Despite these advancements, the exploration of superhydrophobic materials across diverse substrates and applications remains underdeveloped in Vietnam, necessitating imports to meet the high industrial demand This study aims to lay the groundwork for further research in this crucial area.
18 development of superhydrophobic materials in general, and their self-cleaning and oil filtration application in particular.
Oil pollution situation in Vietnam in recent years and treatment methods
A recent report by Nguyen and Chung (2020) from Ho Chi Minh City University of Transport highlights that Vietnam ranks among the top three countries, alongside China and the United States, for oil spills from 2005 to 2014, according to the International Association of Oil Tankers These oil spills pose severe threats to the marine environment, disrupting ecosystems, harming marine life, and contaminating coastal waters and land, which ultimately damages the fishing industry and the economy Moreover, oil pollution is not limited to maritime incidents; waste oil from inland industries also poses significant environmental risks if not properly managed A notable recent incident involved the theft of waste oil in the Da River basin, which supplies domestic water to several districts in Hanoi, severely impacting the health and daily lives of residents Exposure to contaminated water, especially for children, increases the risk of digestive, ocular, and skin diseases Consequently, oil pollution has emerged as a critical environmental challenge in Vietnam.
Various methods are employed to manage oil spills effectively Oil booms, designed for specific marine environments, help contain the spill In situ burning is another technique that must be executed promptly to prevent the spread of oil, although it releases toxic emissions harmful to ocean air Oil dispersants, which are mixtures of surface-active chemicals, enhance the separation of oil particles to prevent clumping Skimming involves using specialized tools to remove oil from the water's surface, while manual labor can also play a role, with individuals using basic tools like pickaxes and shovels to clean up oil on shores Additionally, oil absorbers utilize materials that can absorb several times their weight in oil, facilitating effective cleanup.
19 and can be reused plenty of times Also, it easy to performance, efficient and economical method
The limited development of superhydrophobic materials in Vietnam, particularly for environmental applications, highlights the need for research focused on creating effective oil-absorbent materials This study aims to develop a material that can efficiently remove oil from water, addressing a significant environmental challenge.
MATERIALS AND METHODOLOGIES
Materials
The chosen substrate for this project is 100% cotton fabric, which is composed of long-chain cellulose molecules featuring hydroxyl groups (–OH) in their structure The cotton fabric was sourced from a local store.
Main chemicals for coating are TiO2 and 1H,1H,2H,2H- Perfluorodecyltrimethoxysilane (FTDS) In which, TiO2 is prepared from Ti(SO4)2; FTDS was used as received
Figure 3.1 Cellulose, TiO2 and FDTS structures
The experiment utilized absolute ethanol sourced from Duc Giang Chemical Company and involved the use of NaOH Key equipment included a stainless steel reactor, a furnace, a hot-air oven, and a magnetic stirrer to facilitate the production process.
Methodologies
Prior to treatment, cotton fabric must undergo pre-treatment, which involves cutting the fabric into 6x6 cm pieces, each weighing approximately 0.5 grams These pieces are then gently hand washed three times with distilled water and once with 70% ethanol to effectively eliminate impurities from the fibers, ensuring they are thoroughly clean.
The fabrication process has divided into 2 stage corresponding to two layers of coating as follow
The fabrication process has divided into two stages corresponding to two layers of coating as follow
Step 1: Preparation of TiO 2 @cotton fabric
The TiO2@cotton fabric was synthesized through a hydrothermal reaction involving two solutions Solution A was created by dissolving 0.84g of titanium sulfate in 40mL of distilled water, while Solution B consisted of 0.56g of NaOH in 30mL of distilled water, both stirred separately for 30 minutes at 25°C Subsequently, Solution B was gradually added to Solution A under continuous magnetic stirring at 300 rpm for 12 hours The resulting mixture was then transferred into a Teflon-lined stainless steel vessel for further processing.
A cotton pad was immersed in a solution of TiO2 nanoparticles (100 mL) and subjected to specific heating conditions This process facilitated the attachment of TiO2 nanoparticles to the cotton fibers under elevated temperature and pressure Once the reaction was complete, the cotton pad was removed and directly dried in an oven at 60°C without any washing.
Step 2: Preparation of TiO 2 -FDTS@cotton fabric
The TiO2-FDTS@cotton fabric was created using a dip-coating method, where a coating solution was prepared by adding 108 µL of FDTS to 50 mL of 0.005M absolute ethanol The mixture was stirred at 60°C for 30 minutes, after which the TiO2@cotton fabric was immersed in the solution and stirred continuously for 3 hours to ensure uniform deposition of functional groups on both sides of the cotton fabric.
22 fibers Finally, cotton pads were dried in hot-air oven at 60 o C until the mass unchanged then the superhydrophobic TiO2-FDTS@cotton fabric were achieved
The study focused on optimizing the fabrication process by examining the effects of experimental conditions such as pH, heating temperature, heating time, and the number of coating layers This investigation specifically targeted the first layer of coating.
The effects of various pH conditions were initially examined across a range of values from 2 to 11, specifically in increments of 1 (2-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, and 10-11) pH adjustments were made after thoroughly mixing the coating solution to prevent any unintended reactions between the acid or base and Ti(SO4)2.
Second, different temperature conditions from 100 o C to 160 o C were carried out with the optimum pH value obtained during pH checked experiment
In this study, hydrothermal reactions were conducted for durations of 2, 3, 4, 5, and 6 hours to identify the shortest time that yields the best results The experiments were carried out under optimal pH and temperature conditions determined from prior investigations.
The TiO2 coating will be applied between one to four times, ensuring optimal conditions of pH, temperature, and reaction time are maintained The minimum number of TiO2 coatings required to achieve superhydrophobicity after applying both layers will be utilized for all subsequent samples.
The JSM-IT100 InTouchScope™ Scanning Electron Microscope from JEOL Ltd was utilized to capture images of the surface morphology of cotton samples Additionally, Energy-Dispersive X-Ray Spectrometry (EDS) analysis was conducted to identify the elemental composition present on the cotton surfaces.
Fourier transform infrared (FTIR) spectroscopy analysis reveals essential information about titanium oxide and the functional groups present on surfaces The JASCO FT/IR 4600 device was utilized to identify the functional groups on cotton fabrics.
X-Ray Diffraction (XRD) is used to analyze the chemical composition of the sample XRD works by irradiating a sample with incident X-rays and then measuring the intensities and scattering angles of the X-rays that leave the sample, thereby give the
This study utilized the MiniFlex 600 device from Rigaku Corporation alongside the Crystallography Open Database (COD) to analyze the chemical composition of cotton fabric samples.
The SmartDrop water contact angle meter from Femtofab Co Ltd is utilized to measure the static water contact angle by placing a 10 µL droplet of water on the sample surface and capturing its image The static contact angle is determined by applying the Young-Laplace equation around the droplet, with the water contact angle (WCA) calculated as the average of the left and right WCAs This measurement process is repeated three times at random positions on the sample to ensure accuracy.
Figure 3.6 WCA measurement device (Femtobiomed, 2021)
TiO2-FDTS@cotton fabric is attached to a glass sheet slide when placed on a flat inclined to the floor at a maximum angle of 10 o
To determine the shedding angle of water on a cotton surface, water was dropped perpendicularly and the angle was gradually decreased until the droplet could no longer roll off The shedding angle, defined as the smallest angle at which a water droplet remains on the surface, was measured using a protractor, with all measurements conducted manually.
3.2.3 Applications of fabricated superhydrophobic fabric
A self-cleaning test was conducted using a simple experiment with superhydrophobic fabric adhered to transparent slide sheets positioned at a slight angle Intentional dust, represented by crushed shrimp shells and sand, was applied to the surface, and water was then dropped perpendicularly to wash away all the dirt Photographs were taken at various stages of the process to document the results.
RESULTS AND DISCUSSION
Results
4.1.1 Optimization condition for fabrication of superhydrophobic fabric
(i) Effect of pH condition on the first coating of TiO 2
Figure 4.1 SEM images of TiO2 coated samples (a) pH = 2~3; (b) pH = 3~4; (c) pH 4~5; (d) pH= 5 ~6; (e) pH= 6~7; (f) pH = 7~8; (g) pH = 8~9; (h) pH = 9~10; (i) pH 10~11
SEM images in Figure 4.1 illustrate the surface structure of TiO2@cotton samples across various pH levels Most samples exhibit plaque-like structures, particularly under acidic and basic conditions In contrast, at neutral pH, a significantly lower amount of TiO2 adheres to the fibers, indicating that neutral pH does not facilitate effective coating Between pH 5 and 6, particles appear minimal and scattered on the fibers, while a pH range of 4–5 is notable for producing a distinct crystal structure, as depicted in Figure 4.1 (c).
30 roughness on the fabric surface Thus, pH value of 4 -5 is chosen as optimize pH for the fabrication process
(ii) Effect of heating temperature on the first coating of TiO 2
SEM images reveal that at 100 °C, a coating forms around the cotton yarn At 120 °C, the crystal structure begins to develop, as illustrated in the images However, when the reaction temperature is raised to 140 °C and 160 °C, the particles struggle to adhere to the cotton fibers.
Figure 4.2 (c) and (d) Thus, heating temperature of 120 o C is chosen as optimize temperature for the fabrication process
Figure 4.2 SEM images of TiO2 coated samples (a) T 0 o C; (b) T 0 o C; (c) T
(iii) Effect of heating time on the first coating of TiO 2
According to Collazzo et al (2011), heating time has minimal impact on crystallite size SEM images (Figure 4.3) indicate that reaction time slightly affects structural morphology and the quantity of particles adhered to the fabric A reaction time of 3 hours (Figure 4.3(b)) is optimal for achieving a well-defined crystal structure, while a 2-hour reaction (Figure 4.3(a)) results in an irregular distribution of particles across the sample Conversely, extending the reaction to 6 hours (Figure 4.3(e)) can lead to a decline in quality as it surpasses the optimal point.
31 reduce the amount of particles attachment Thus, heating time of 3h is chosen as optimize heating time for the fabrication process
Figure 4.3 SEM images of TiO2 coated samples (a) t =2h; (b) t=3h; (c) t=4h; (d) t=5h;
(iv) Effect of number of coating on the first coating of TiO 2
To achieve a superhydrophobic state through the fabrication process, a minimum number of TiO2 coatings is required, as evidenced by water contact angle (WCA) measurements As shown in Table 4.1, the WCA increases with the number of TiO2 coatings applied, while the FTDS layer coating remains constant.
Table 4.1 WCA of TiO2-FDTS@cotton samples with different number TiO2 coating
The results show that, the TiO2 coating layer is should be repeated at least 3 times to obtain the final product reaches the WCA greater than 150 o a b c d e
Figure 4.4 WCA of TiO2-FDTS@cotton
The elevated water contact angle (WCA) is attributed to the rough texture created by the TiO2 crystal particles deposited on cotton fibers, combined with the presence of superhydrophobic functional groups Consequently, applying three layers of TiO2 coating has been identified as the optimal condition for the fabrication process.
After examining the influencing factors, the final optimal conditions of the first coating with TiO2 is in Table 4.2
Table 4.2 Optimal conditions in the first layer coating with TiO2
The water contact angle (WCA) on cotton fabric is determined by averaging the left and right WCAs of a water droplet, which typically has a volume of around 10 µL The TiO2-FDTS-coated cotton has achieved a superhydrophobic state, exhibiting a remarkable WCA of 152.9° ± 1° and a shedding angle of 7°.
The SEM image illustrates the smooth structure of cotton fibers, while EDS spectra confirm the presence of carbon and oxygen, key components of cellulose fibers Following the application of the initial TiO2 layer, the TiO2 crystal structure began to develop across the fabric surface, as evidenced by the appearance of Ti element peaks in the EDS spectra Additionally, the presence of roughness on the fiber surfaces, characterized by sharp crystal-like tips, facilitates water interaction, creating valleys with air pockets that elevate water droplets.
The presence of silicon (Si) and fluorine (F) on the TiO2-FDTS@cotton indicates that a particle film has been successfully applied to the raw cotton surfaces This process was achieved under optimal conditions of 120 °C for a duration of 3 hours.
Figure 4.6 SEM images, EDS spectrum of the cotton (a1, b1) raw cotton, (b1, b2)
TiO2@cotton and (c1, c2) TiO2-FTDS@cotton
Figure 4.7 shows the FTIR spectra of raw cotton (blue line) and TiO2- FDTS@cotton (red line) in the wavenumber range of 400 4000 cm -1 Initial cotton has
The analysis reveals that the hydroxyl group (–OH) is indicated at a wavenumber of 3381 cm⁻¹, while the presence of C-O is noted at 1070 cm⁻¹ Additionally, the superhydrophobic cotton exhibits a wavenumber of 532 cm⁻¹, which corresponds to Ti-O-Ti bonding, while Ti-OH vibrations are observed in the range of 1622 to 1725 cm⁻¹ The Si-O bonds are represented by the designations a1, a2, b1, b2, c1, and c2.
35 represented by the 1396 cm -1 ; 1199 cm -1 correspond to C-F functional groups This results was demonstrated that both two layers successfully prepared on cotton fibers
Figure 4.7 FTIR spectra of the cotton samples
In figure 4.8, the raw sample X-ray diffraction (black line) has the peaks
The X-ray diffraction analysis revealed distinct peaks at 15.3598°, 23.0695°, 28.2344°, and 29.2894°, indicating the presence of cellulose fibers In contrast, the TiO2-FDTS@cotton fabric showed peaks at 32.3385°, 34.2591°, and 49.1235°, confirming the presence of TiO2 particles Additionally, the slight decrease in the peak at 23.0695° suggests the binding of TiO2 to the -OH groups in cellulose fibers, thereby demonstrating the successful coating of TiO2 micro-particles on the cotton fabric surface.
Figure 4.8 XRD spectra of TiO2-FTDS@cotton
4.1.3 Applications of fabricated superhydrophobic fabric
Figure 4.9 The water droplets carry dirt (Shrimp sell powder) and roll off the cotton fabric surface with shedding angle = 7 o
A self-cleaning experiment using shrimp shell powder demonstrated that dust on a superhydrophobic cotton surface is effectively washed away by water, which drips off naturally without any external force This process effortlessly removes dirt, leaving the cotton fabric's surface as clean as it was initially, with no change in the fabric's weight.
37 and after the test, indicating that the cotton surface is capable of completely self-cleaning from solid dust
The second experiment used sand to be sprinkled on the surface of superhydrophobic cotton pad that had been glued to a flat transparent sheet slide in SA
In the process of cleaning, water droplets laden with sand accumulate on a round dish, as depicted in Figure 4.10 The weight of the sand particles necessitates that the water droplets exert a spray force to effectively remove the sand Ultimately, this results in a thoroughly cleaned fabric surface.
Figure 4.10 The water droplets carry dirt (Sand) and roll off the cotton fabric surface with shedding angle = 7 o
The TiO2-FDTS@cotton exhibits superhydrophobic properties, making it effective for separating organic solvents from both underwater and water surface environments This specialized fabric selectively absorbs red-dyed toluene droplets on the water's surface while also quickly removing chloroform droplets submerged in water, resulting in pristine, uncontaminated water.
Toluene and chloroform droplets can be quickly absorbed by cotton from water; however, the limited space capacity of cotton fabric may hinder the effectiveness of superhydrophobic cotton in absorbing oil from water.
Figure 4.11 Organic solvents removal test Time sequence of (a-c) toluene dyed red on water surface, and (d-f) underwater chloroform dyed red with superhydrophobic cotton pad
TiO2-FTDS@cotton fabric effectively separates oil from oil-water mixtures, specifically when kerosene-water (50% v/v) is gradually introduced into a glass filter holder The red-dyed oil passes through into the flask, while water is retained on the cotton fabric, thanks to its anti-wet properties This filtration process occurs naturally without the need for a pump, resulting in a minimal absorption of oil within the cotton fabric.
Figure 4.12 Oil-water separation test Table 4.3 Oil recover efficiency
(ml) Oil (ml) Recovered oil (ml)
Oil recover efficiency in average (%)
Discussion
Figure 4.16 Water dropt on cotton fabric (a) only TiO2 coated, (b) TiO2-FDTS coated,
The test proves that the combination of two coatings in order is important, only TiO2 or FTDS layer is not changes the wettability significantly
The Wenzel theory experiment shows that the wettability contact angle (WCA) is influenced by surface patterns; a rough hydrophilic surface becomes even more hydrophilic, while a rough hydrophobic surface increases its hydrophobicity Consequently, when cotton, known for its hydrophilicity, is coated, its hydrophilic properties are enhanced Conversely, FDTS introduces hydrophobic functional groups, indicating that the sequence of coating layers is crucial and that both modification techniques are essential for achieving superhydrophobicity.
Based on the characterization analysis data, the mechanism of forming superhydrophobic surface can be proposed as following (Figure 4.17)
Cotton fiber contains hydroxyl groups, which during hydrothermal reactions at high temperature and pressure, allow hydrogen atoms to be replaced by TiO2 particles Subsequently, TiO2@cotton undergoes further coating; when immersed in a coating solution with FTDS in ethanol, the less stable bond between Ti and O is disrupted, enabling the functional group from FTDS to replace it at the CH3 position.
Figure 4.17 Mechanism of the attachment TiO2 and FTDS on cotton fiber
Two effective techniques for creating superhydrophobic materials are hydrothermal and dip-coating, both of which operate at low temperatures and are easy to implement These methods offer significant advantages, making them the ideal choice for developing energy-efficient superhydrophobic surfaces without the need for complex equipment.
The optimal conditions for the TiO2 coating process have been established, requiring a reaction temperature of 120°C for three consecutive hours with a solution pH between 4 and 5 This initial process must be repeated at least three times before applying the second layer, which involves using FTDS at an immersion temperature of 60°C for three hours.
TiO2-FDTS@cotton fabric achieved superhydrophobic state with WCA = 152.9 o
The SEM image reveals a crystalline structure forming on the fabric's surface, while FTIR and XRD spectra confirm the presence of TiO2 and superhydrophobic functional groups The material exhibits successful self-cleaning properties, effectively repelling water and remaining dry Furthermore, the superhydrophobic cotton fabric demonstrates reliable separation of oil-water and organic solvent-water, both on the surface and underwater, highlighting its advanced functional capabilities.
1 Ahuja, D., Dhiman, S., Rattan, G., Monga, S., Singhal, S., Kaushik, A., 2021 Superhydrophobic modification of cellulose sponge fabricated from discarded jute bags for oil water separation J Environ Chem Eng 9, 105063 https://doi.org/10.1016/j.jece.2021.105063
2 B D Cassie, B.A., Baxter, S., n.d OF POROUS SURFACES
3 Boinovich, L.B., Emelyanenko, A.M., Ivanov, V.K., Pashinin, A.S., 2013 Durable icephobic coating for stainless steel ACS Appl Mater Interfaces 5, 2549–2554 https://doi.org/10.1021/am3031272
4 Collazzo, G.C., Jahn, S.L., Carreủo, N.L.V., Foletto, E.L., 2011 Temperature and reaction time effects on the structural properties of titanium dioxide nanopowders obtainedvia the hydrothermal method Brazilian J Chem Eng 28, 265–272 https://doi.org/10.1590/S0104-66322011000200011
5 Czyzyk, S., Dotan, A., Dodiuk, H., Kenig, S., 2020 Processing effects on the kinetics morphology and properties of hybrid sol-gel superhydrophobic coatings
Prog Org Coatings 140, 105501 https://doi.org/10.1016/j.porgcoat.2019.105501
6 Dimitrakellis, P., Travlos, A., Psycharis, V.P., Gogolides, E., 2017 Superhydrophobic Paper by Facile and Fast Atmospheric Pressure Plasma
Etching Plasma Process Polym 14, 1–8 https://doi.org/10.1002/ppap.201600069
7 Femtobiomed, 2021 SmartDrop [WWW Document] URL https://www.smartdrop.co.kr/
8 Hoàng, T.P.T.A.T.Đ.K., 2019 Modification of melamine formaldehyde foam by graphene for oil sorption Univ Danang J Sci Technol
9 Hooda, A., Goyat, M.S., Kumar, A., Gupta, R., 2018 A facile approach to develop modified nano-silica embedded polystyrene based transparent superhydrophobic coating Mater Lett 233, 340–343 https://doi.org/10.1016/j.matlet.2018.09.043
10 Hou, W., Shen, Y., Tao, J., Xu, Y., Jiang, J., Chen, H., Jia, Z., 2020 Anti-icing performance of the superhydrophobic surface with micro-cubic array structures fabricated by plasma etching Colloids Surfaces A Physicochem Eng Asp 586,
11 Hu, R., Jiang, G., Wang, X., Xi, X., Wang, R., 2013 Facile preparation of superhydrophobic surface with high adhesive forces based carbon/silica composite films Bull Mater Sci 36, 1091–1095 https://doi.org/10.1007/s12034-013-0577-6
12 Huang, Y., Sarkar, D.K., Grant Chen, X., 2015 Superhydrophobic aluminum alloy surfaces prepared by chemical etching process and their corrosion resistance properties Appl Surf Sci 356, 1012–1024
13 Jamalludin, M.R., Hubadillah, S.K., Harun, Z., Othman, M.H.D., Yunos, M.Z., Ismail, A.F., Salleh, W.N.W., 2020 Facile fabrication of superhydrophobic and superoleophilic green ceramic hollow fiber membrane derived from waste sugarcane bagasse ash for oil/water separation Arab J Chem 13, 3558–3570 https://doi.org/10.1016/j.arabjc.2018.12.007
14 Ji, H., Chen, G., Yang, J., Hu, J., Song, H., Zhao, Y., 2013 A simple approach to fabricate stable superhydrophobic glass surfaces Appl Surf Sci 266, 105–
15 Jia, S., Chen, H., Luo, S., Qing, Y., Deng, S., Yan, N., Wu, Y., 2018 One-step approach to prepare superhydrophobic wood with enhanced mechanical and chemical durability: Driving of alkali Appl Surf Sci 455, 115–122 https://doi.org/10.1016/j.apsusc.2018.05.169
16 Lai, Y., Tang, Y., Gong, J., Gong, D., Chi, L., Lin, C., Chen, Z., 2012 Transparent superhydrophobic/superhydrophilic TiO 2-based coatings for self- cleaning and anti-fogging J Mater Chem 22, 7420–7426 https://doi.org/10.1039/c2jm16298a
17 LĐO, 2019 Toàn cảnh vụ đổ trộm dầu thải khiến người dân lao đao ‘khát’ nước sạch Lao Động
18 Li, S., Huang, J., Ge, M., Cao, C., Deng, S., Zhang, S., Chen, G., Zhang, K., Al- Deyab, S.S., Lai, Y., 2015 Robust Flower-Like TiO2@Cotton Fabrics with Special Wettability for Effective Self-Cleaning and Versatile Oil/Water
Separation Adv Mater Interfaces 2, 1–11 https://doi.org/10.1002/admi.201500220
19 Lin, Y., Han, J., Cai, M., Liu, W., Luo, X., Zhang, H., Zhong, M., 2018 Durable and robust transparent superhydrophobic glass surfaces fabricated by a femtosecond laser with exceptional water repellency and thermostability J Mater Chem A 6, 9049–9056 https://doi.org/10.1039/c8ta01965g
20 Linh, N.T.B., Lee, K.H., Lee, B.T., 2011 Fabrication of photocatalytic PVA- TiO2 nano-fibrous hybrid membrane using the electro-spinning method J Mater Sci 46, 5615–5620 https://doi.org/10.1007/s10853-011-5511-y
21 Liu, C., Wang, S., Shi, J., Wang, C., 2011 Fabrication of superhydrophobic wood surfaces via a solution-immersion process Appl Surf Sci 258, 761–765 https://doi.org/10.1016/j.apsusc.2011.08.077
22 Mahadik, S.A., Kavale, M.S., Mukherjee, S.K., Rao, A.V., 2010 Transparent superhydrophobic silica coatings on glass by sol-gel method Appl Surf Sci
23 Nagrath, M., Alhalawani, A., Rahimnejad Yazdi, A., Towler, M.R., 2019 Bioactive glass fiber fabrication via a combination of sol-gel process with electro-spinning technique Mater Sci Eng C 101, 521–538 https://doi.org/10.1016/j.msec.2019.04.003
24 Nguyen-Tri, P., Altiparmak, F., Nguyen, N., Tuduri, L., Ouellet-Plamondon, C.M., Prud’Homme, R.E., 2019 Robust Superhydrophobic Cotton Fibers Prepared by Simple Dip-Coating Approach Using Chemical and Plasma-Etching
Pretreatments ACS Omega 4, 7829–7837 https://doi.org/10.1021/acsomega.9b00688
25 Nguyen, H.H., Tieu, A.K., Wan, S., Zhu, H., Pham, S.T., Johnston, B., 2021 Surface characteristics and wettability of superhydrophobic silanized inorganic glass coating surfaces textured with a picosecond laser Appl Surf Sci 537,
26 Nguyen, M.H., Chung, N., 2020 Oil spill in maritime field : An urgent problem in Vietnam 6, 1–5
27 Nguyen, T.H., Lee, K.H., Lee, B.T., 2010 Fabrication of Ag nanoparticles dispersed in PVA nanowire mats by microwave irradiation and electro-spinning Mater Sci Eng C 30, 944–950 https://doi.org/10.1016/j.msec.2010.04.012
28 Parsaie, A., Mohammadi-Khanaposhtani, M., Riazi, M., Tamsilian, Y., 2020 Magnesium stearate-coated superhydrophobic sponge for oil/water separation: Synthesis, properties, application Sep Purif Technol 251, 117105 https://doi.org/10.1016/j.seppur.2020.117105
30 Petergans, 2017 Fourier-transform infrared spectroscopy [WWW Document] URL https://en.wikipedia.org/wiki/Fourier-transform_infrared_spectroscopy
31 Pratiwi, N., Zulhadjri, Arief, S., Admi, Wellia, D.V., 2020 Self-cleaning material based on superhydrophobic coatings through an environmentally friendly sol–gel method J Sol-Gel Sci Technol 96, 669–678 https://doi.org/10.1007/s10971- 020-05389-7
32 Raimondo, M., Veronesi, F., Boveri, G., Guarini, G., Motta, A., Zanoni, R., 2017 Superhydrophobic properties induced by sol-gel routes on copper surfaces Appl Surf Sci 422, 1022–1029 https://doi.org/10.1016/j.apsusc.2017.05.257
33 Scientific, B., n.d Contact angle measuremment [WWW Document] URL https://www.biolinscientific.com/measurements/contact-angle
34 Scientific, T.F., n.d Principles of Scanning Electron Microscopy [WWW Document] URL https://www.thermofisher.com/sg/en/home/materials- science/learning-center/applications/scanning-electron-microscope-sem- electron-column.html
35 Shibuichi, S., Onda, T., Satoh, N., Tsujii, K., 1996 Super water-repellent surfaces resulting from fractal structure J Phys Chem 100, 19512–19517 https://doi.org/10.1021/jp9616728
36 Song, Y., Ma, Y., Wang, Y., Di, J., Tu, Y., 2010 Electrochemical deposition of gold-platinum alloy nanoparticles on an indium tin oxide electrode and their electrocatalytic applications Electrochim Acta 55, 4909–4914 https://doi.org/10.1016/j.electacta.2010.03.089