Recent developments in usage of fluorine-free nano structured materials in oil-water separation: A review
Introduction
Mixing oil-water is more common than the world expects and can happen in various ways. There are tons of oil spills in Asian waters last year. The majority of these leaks are minor, for example, when a ship refueled with diesel. These Oil spills can bring the chance of being disastrous, mainly when they happen in fragile areas such as wetlands, seashores, and waterbeds near mangroves.
Colossal oil spills are potentially deadly disasters. These usually occur when pipelines collapse, massive oil tanker ships drown, or fracking activities go wrong. Following an oil spill, the effects on habitats and economies are usually lasting for decades. The bionic surfaces, which have unique surface wettability, are being researched for the last two decades. These surfaces are developed by doing reverse engineering with material science already seen in nature. The Superhydrophobic Surfaces usually have a high-water contact angle on the surface when the WCA is more significant than 150 o and considers the sliding angle on the surface below, less than 10o. These have piqued the attention of scientists and industry alike [1,2].
The super-hydrophobic surfaces mainly piqued industrial attention as they can be successfully used to determine an artificial self-cleaning surface. They can also be used as an anti-icing agent and anti-corrosion applications. Drag elimination and oil-water separation are other critical applications of this material science. Microfluidics, oil modulation, protein adhesion control on surfaces, and oil-water separation benefit from a solid surface's wettability to oils in an aqueous phase environment. These can be developed by integrating the material's surface roughness with nano structural factors such as Low-energy Surface [3]. This material science is characterized by two separate wetting states known as the Wenzel state and the Casie-Baxter state. Scholars worldwide agree on these details, which have culminated in the production of various chemical coatings. With the vast volume of oily wastewater and the rising frequency of oil spill incidents, oil/water separation has become a critical and urgent concern. The spilling leading to the oil-water mix wastes petroleum products and causes considerable pollution of water bodies and the nearby shores by making the ephemerality of ocean creatures difficult due to a shortage of oxygen. Traditional technology has poor performance and high operating costs. Then introduced a new form of technology for separating the oil from the Oil-Water solutions very efficiently. Many methods have been investigated, and super-hydrophobic materials have piqued the attention of researchers due to their high separation ability of oils or organic solvents from water, as well as their low cost and environmental friendliness.
The particular reason for the circumstance of their immense low surface free energy is due to the presence of hydrophobic agents, such as fluoroalkyl silanes (FAS), is often used to alter coatings to achieve hydrophobic or super-hydrophobic surfaces. However, these compounds are expensive and hazardous to the environment as they can release highly toxic substances such as perfluoroalkyl carboxylates or sulfonates to the ecosystem. As they can be a renewable source by offering eco-friendly applications in new, modern world technology, the fundamental purpose is to increase the material science of fluorine-free super-hydrophobic coating in the industry [4].
Superhydrophobicity is prevalent in an environment in which many plants and animals have acquired distinct superhydrophobic surfaces via evolutionary development, including leaves and stems, rice leaves, and butterfly wings [6]. Inspired by the naturally occurring superhydrophobic surfaces, numerous artificial coverings with nanostructures have been created. These superhydrophobic coatings seem to be of tremendous value in the anti-icing protective layer for aircraft, anti-corrosion layer for chemical engineering, anti-fogging layer for the windscreen of automotive, and oil-water segregation for environmental sustainability. Different functional chemical groups considered during fabrication process, plays an important role in altering the surface energy and its superhydrophobic nature (Fig. 1). Fluorinated chemicals are the most widely utilized in manufacturing superhydrophobic coatings. The smooth surface organized with the -CF3 group has a shallow surface energy of 6.7 MJ/m2. Nevertheless, the fluorinated compounds are potentially hazardous to ecosystems since the long-chain fluorinated alkyl molecules have been persistent, bio accumulative and poisonous. The rising awareness of environmental protection and completing the Sustainable development goals had motivated researchers to build fluorine-free nanostructured surfaces utilizing non-fluorinated hydrophobic substances [7]. These fluorine-free hydrophobic surfaces include various organic compounds such as polydimethylsiloxane (PDMS) and silicon nanoparticles. Apart from these organic waxes, various long-chain alkanes and carbon nanomaterials are taken into consideration. This study mainly concentrated on oil-water separation, an actual application of fluorine-free nanostructured material surface [2,8].
Section snippets
Traditional oil-water separation technologies
Several traditional technologies (Fig. 2) for oil-water separation were reviewed in this section. The major types of treatment in diverse municipal and industrial sectors are physical, chemical, and biological oil-water separation techniques. The chemical processes generally have higher running costs, need trained operators, and require reliable monitoring and control of the process.
The techniques of gases flotation, such as sparking or dissolved gas floatation, can be used in a continuum of
Superhydrophobic surfaces in nature
The natural superhydrophobic surfaces are found from a variety of plants and animals in our natural environment [9], [10], [11]. Different experiments on super-hydrophobic artificial surfaces show that surface roughness is an essential factor determining that reducing the surface roughness usually affects the contact area by increasing when the droplet approaches a surface. This reduces its hydrophobicity by disturbing the hydrophobic surface and causes instability or an unacceptable increase
Rudiments of nanostructured surfaces
The properties of super hydrophobic substances are based on two major forces, adhesive force and cohesive force [42]. Cohesive force is the force, which keeps the fluid molecules attached to one another whereas the adhesive force is which keeps a fluid attached to the surface. If the adhesive force exceeds the cohesive force, the fluid tends to stick to the surface, if the fluid is water, the surface is called hydrophilic [43]. When the cohesive force is greater than the adhesive force, the
Role of nanotechnology in oil-water separation
We began studying the nanostructures found in nature as a result of advancements in the field of nanotechnology [88]. As we all know, the majority of nature's marvels occur at the subatomic level, which can only be observed with multipurpose methods such as scanning tunneling microscopy (STM) [89] and atomic force microscopy (AFM) [90]. These approaches enable us to have a better understanding of how these materials operate. For example, after studying their nanostructure spatulae, we were able
Different methods for altering surface wettability
Repelling surfaces for water is usually differentiated based on various characteristics. Among that micro-roughness of the surface and the complex morphology are the main characteristics. Another significant feature is the repetition of multi-scaled roughness, which can describe as nano micro-level morphology of various nano projections seen on the surface [89,90]. As a result, many deposition techniques are used to create the above facets on pseudo surfaces. Some of the most widely used
Fabrication of nano structured oil-water separation materials
Zhiguang Xu et al. [107], introduced a model for preparing a super-hydrophobic layer with pH-effective and ammonia-induced vapor-based wettability transfer, used decanoic acid (DA), an inexpensive and non – toxicity by nature [107]. They are also naturally occurring chemical, which is Fluorine-free for the ecosystem. The coating is made from a silicone-nanoparticle formulation and TiO2 solution compounded with DA using a primary dip-coating method (Fig. 11 [i]). The layer was super-hydrophobic
Advantages of fluorine-freebased nano structured oil-water separation material
In recent decades, hydrophobic surfaces have been of great interest for materials we have discussed earlier and their applicability in everyday life and some industrial operations.
Their composition, texture, and roughness significantly affect the surface's hydrophobicity. Many techniques have been created in this regard to raise the WCA of surfaces, such as the deposition of layers of different fluoride or hydrocarbon compounds, certain kinds of wax inorganic and organic materials displaying
Challenges and future perspective of nano structured oil-water separation membrane
Superhydrophobic nanostructured and superhydrophilic surfaces have found practical applications in oil-water separation, such as oil spill cleanup and oily waste management. They do, however, have little capability for segregating volatile components and so risk fouling systems. Additionally, the membrane's durability in harsh working conditions, such as strong acids, bases, oxidants, and saline solutions, is unknown [171]. Hydrophobicity may diminish at elevated temperatures. The effect of
Conclusion
This review gives an in-depth knowledge of the latest techniques in separating oil-water mixtures, which includes the usage of fluorine free-based chemicals for surface characteristic modifications, adsorption/filtration materials like SS meshes, cotton fabric and sponges. The latest research for sustainable and environmentally friendly Fluorine Free super-hydrophobic coverage and its use in oil-water separation has been decided in this study. The most efficient technology for fluorine-free
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
References (172)
- et al.
A review of the recent advances in superhydrophobic surfaces and the emerging energy-related applications
Energy
(2015) - et al.
Replication of rose-petal surface structure using UV-nanoimprint lithography
Mater. Lett.
(2014) - et al.
Biomimetic Superhydrophobic Surfaces with Transition Metals and Their Oxides: A Review
J. Bionic Eng.
(2017) - et al.
Lotus effect in wetting and self-cleaning
Biotribology
(2016) - et al.
Developments in smart anticorrosive coatings with multifunctional characteristics
Prog. Org. Coatings.
(2017) - et al.
Superhydrophobic and superoleophobic properties in nature
Mater. Today.
(2015) - et al.
Mosquito eyes inspired surfaces with robust antireflectivity and superhydrophobicity
Surf. Coatings Technol.
(2017) - et al.
Gene reconstruction spandex with intrinsic antimicrobial activity
Chem. Eng. J.
(2021) - et al.
Reduction in the contact time of impacting droplets by decorating a rectangular ridge on superhydrophobic surfaces
Int. J. Heat Mass Transf.
(2019) - et al.
Synthesis of ultrahydrophobic and thermally stable inorganic–organic nanocomposites for self-cleaning foul release coatings
Chem. Eng. J.
(2017)