Elsevier

Surfaces and Interfaces

Volume 27, December 2021, 101455
Surfaces and Interfaces

Recent developments in usage of fluorine-free nano structured materials in oil-water separation: A review

https://doi.org/10.1016/j.surfin.2021.101455Get rights and content

Abstract

In recent years, significant oil spills and organic solvent contamination are harming ocean habitats and endangering aquatic species. Separating the toxic oil substances from water using a type of coating that is sustainable and easily safe is the main aim of researchers. The superhydrophobic coating without flourine is the alternative approach that is being developed since several years as fluorine is harmful to nature. It resulted in substantial endeavors in constructing a substance with a higher oil adsorption power, a straightforward implementation in oil-water segregation, and excellent stability in oil-water with outstanding recycling. The two main aspects while fabricating a superhydrophobic coating on a substrate are wettability and the oil-water separation performance. The whole analysis summarizes the material for oil-water segregation in recent times which are sustainable, including their adsorption performance and filtering, and has manoeuvrable wettable segregation technology. The chemical element fluorine is one of the microelements needed to develop living organisms when absorbed in tiny quantities properly and it is toxic when present in an excessive amount. Fluorine is considered an environmental pollutant with adverse effects in people and animals on diverse organisms. Fluoride elements in living organism functions as an enzyme poison that inhibits enzyme activity and eventually breaks down critical metabolic functions. However, most of the techniques documented so far include high prices or complex procedures and severe environments, limiting the processing of flexible substrates. Therefore, easy, quick, low-cost, environmentally friendly methods for hydrophobic surfaces having controlled morphology continue to be developed to extend their industrial uses. We report herein on the production of hydrophobic coatings based chiefly on the deposition of biocompatibility products with various nanoparticles to overcome this gap and meet the green requirements. Consequently, this fabrication process has been thought to be necessary, practical, and achievable for the manufacturing of superhydrophobic surfaces for use in commercial processes. This review paper also mentions the simple hypothesis that has already developed which would help to understand the surface-specific wettability.

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.

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