Selective Oil Absorption Research Articles

Recent Progress in Modification Strategies of Nanocellulose-Based Aerogels for Oil Absorption Application.

Oil spills and oily wastewater have become a major environmental problem in recent years, directly impacting the environment and biodiversity. Several techniques have been developed to solve this problem, including biological degradation, chemicals, controlled burning, physical absorption and membrane separation. Recently, biopolymeric aerogels have been proposed as a green solution for this problem, and they possess superior selective oil absorption capacity compared with other approaches. Several modification strategies have been applied to nanocellulose-based aerogel to enhance its poor hydrophobicity, increase its oil absorption capacity, improve its selectivity of oils and make it a compressible and elastic magnetically responsive aerogel, which will ease its recovery after use. This review presents an introduction to nanocellulose-based aerogel and its fabrication approaches. Different applications of nanocellulose aerogel in environmental, medical and industrial fields are presented. Different strategies for the modification of nanocellulose-based aerogel are critically discussed in this review, presenting the most recent works in terms of enhancing the aerogel performance in oil absorption in addition to the potential of these materials in near future.

Investigation of Egyptian Chorisia spp. fiber as a natural sorbent for oil spill cleanup

Egyptian hollow fiber has been explored as natural feasible cellulosic materials that acquired great lumen and hydrophobic characteristics, which empower it to show high oil sorption capacity. The effect of solvent and sodium chlorite treatments and oil type on the sorption characteristics of Egyptian Chorisia spp. hollow fibers have been investigated. The outcomes demonstrate that with the exception of non-polar solvent, ether, Chorisia hollow fiber treated with other solvents show reduction of oil sorption capacity. NaClO2-treated fiber appears the highest and selective absorption of oil from oil/water mixtures and stayed stable after ten sorption/desorption cycles of reutilization with only 15% of sorption limit decrease. Besides, in view of SEM, NaClO2-treated fiber was retained its overall tubular and lumen structures after desorption of oils. These achievements will be reflected in the challenges for purification of other sources of water if there should arise an occurrence of water lack in Egypt.

Steamed bun-derived microporous carbon for oil-water separation

It is of great importance to develop inexpensive sustainable oil absorbent materials due to the frequent oil spill accidents and the increasing discharge of oil-containing waste water. In this work, through carbonization of steamed bun which was fabricated by steaming fermented flour dough, a low-cost microporous carbon material has been developed for oil removal from oil-water mixtures. Fermentation with yeasts produced plenty of interconnected micropores inside the dough, and this microporous structure was in the end inherited by microporous carbon after the dough was steamed and carbonized. Due to its hydrophobic/superoleophilic surface, the obtained microporous carbon showed affinity to oils while repellency to water. The combination of high porosity and special surface wettability provided this material with considerable oil absorption capacity as well as the capability of selective oil absorption from oil-water mixtures. This steamed bun-based microporous carbon could be a low-cost and sustainable material with great potential for remediation of water from oil pollutions.

Highly Stretchable Fully Biomass Autonomic Self-Healing Polyamide Elastomers and Their Foam for Selective Oil Absorption.

Renewable polymers with self-healing ability, excellent elongation, hydrophobicity, and selective oil absorption attributes are of interest for an extensive range of applications, such as e-skin, soft robots, wearable devices, and cleaning up oil spills. Herein, two fully renewable eco-friendly polyamide (PA)-based self-healing elastomers (namely, PA36,IA, and PA36,36) were prepared by a facile and green one-pot melt polycondensation of itaconic acid (IA), PripolTM 1009, and PriamineTM 1075 monomers. The molecular structures of these PAs were analyzed by FITR, 1H NMR, and 13C NMR. The distinct structure of these PAs shows superior strain values (above 2300%) and high ambient temperature autonomous self-healing ability. Interestingly, the synthesized renewable PA36,36 showed zero water absorption values and hydrophobic properties with a contact angle of θ = 91° compared to the synthesized PA36,IA and other previously reported PAs. These excellent attributes are due to the low concentration of amide groups, the highly entangled main chains, the intermolecular diffusion, the manifold dangling chains, and the numerous reversible physical bonds within the renewable PAs. Furthermore, the hydrophobic properties may aid in the selective oil absorption of the PA36,36-based foam, for which PA36,36 foam is produced by the green supercritical carbon dioxide (scCO2) batch foaming process. The PA36,36 foam with a microporous cellular structure showed better absorption capacity and high stability in repeated use. Due to these advantages, these bio-based PAs have potential for the production of eco-friendly self-healing materials, superabsorbent foams, and other polymeric materials.

Design of a Waste Paper-Derived Chemically 'Reactive' and Durable Functional Material with Tailorable Mechanical Property Following an Ambient and Sustainable Chemical Approach.

Controlled tailoring of mechanical property and wettability is important for designing various functional materials. The integration of these characteristics with waste materials is immensely challenging to achieve, however, it can provide sustainable solutions to combat relevant environmental pollutions and other relevant challenges. Here, the strategic conversion of discarded and valueless waste paper into functional products has been introduced following a catalyst-free chemical approach to tailor both the mechanical property and water wettability at ambient conditions for sustainable waste management and controlling the relevant environmental pollution. In the current design, the controlled and appropriate silanization of waste paper allowed to modulate both the a) porosity and b) compressive modulus of the paper-derived sponges. Further, the association of 1,4-conjugate addition reaction between amine and acrylate groups allowed to obtain an unconventional waste paper-derived chemically 'reactive' sponge. The appropriate covalent modification of the residual reactive acrylate groups with selected alkylamines at ambient conditions provided a facile basis to tailor the water wettability from moderate hydrophobicity, adhesive superhydrophobicity to non-adhesive superhydrophobicity. The embedded superhydrophobicity in the waste paper-derived sponge was capable of sustaining large physical deformations, severe physical abrasions, prolonged exposure to harsh aqueous conditions, etc. Further, the waste paper-derived, extremely water-repellent sponges and membranes were successfully extended for proof-of-concept demonstration of a practically relevant outdoor application, where the repetitive remediation of oil spillages has been demonstrated following both selective absorption (25 times) of oils and gravity-driven filtration-based (50 times) separation of oils from oil/water mixtures at different harsh aqueous scenarios.

Superhydrophobic Waste Cardboard Aerogels as Effective and Reusable Oil Absorbents.

As the main component of the municipal waste, waste cardboard has caused a host of environmental problems. Therefore, the reasonable disposal of waste cardboard is of great significance to global sustainable development and green economics. Herein, using waste cardboard as the raw material, a superhydrophobic aerogel has been developed with a unique three-dimensional porous network structure, which exhibits excellent selective oil absorption capacities. The aerogel was made by combining Ca2+ cross-links and postmodification with stearic acid. Superhydrophobic aerogels can absorb various organic solutions and its maximum absorption capacity can reach 47 times its own weight. Meanwhile, the size of aerogels has been further expanded, with a diameter of 21.2 cm and a height of 3.2 cm, which can absorb 34 times its own weight of kerosene. More importantly, the aerogel can also absorb oil droplets in oil/water emulsions with an adsorption efficiency of over 98.5%. Moreover, the aerogel can be employed multiple times without significantly reducing the adsorption capacity via distillation or squeezing, depending upon the type of pollutions. Consequently, we believe that these facile and inexpensive superhydrophobic aerogels can effectively adsorb oily wastewater, which matches well with the requirement for environmentally friendliness from the perspective of practical application.

Emulsion preparation of ultralight TiO2 foams for selective oil absorption

Ultralight TiO2 foams have been prepared by an emulsion route using mesoporous TiO2 microbeads (MTMs) as a raw material in water medium followed by mechanical frothing and calcination at elevated temperatures. The MTMs are modified by preferential adsorption of hexadecylamine in ethanol prior to the emulsion practice so that the surface became hydrophobic for facilitating formation of stable air-in-water bubbles. The TiO2 foams are featured with cellular spherical macropores with an interconnected pore structure in a pore-size range from ca. 10 to 400 μm and a porosity ranging from 85.8 to 95.6 % (corresponding to a bulk density of 0.06 to 0.24 g⋅ cm−3). The foams can float on oil/water mixtures and absorb oil selectively in short period of time without noticeable degradation under recycled use, e.g., absorption of soybean oil with up to 15 times of the foam weight has been obtained in less than 30 s after the third use.

Ordered hollow nanofiber aerogel with revivability for efficient oil absorption

Abstract Efficient, convenient, economical and environmentally friendly materials have always been the first choice for solving environmental problems. In this work, stable carbonized and ordered hollow nanofiber aerogels were obtained under the action of directional freezing and calcination. The benzoxazine monomer (BA) in the nanofiber was polymerized in situ under the action of high temperature to crosslink the nanofibers, thereby further stabilizing the aerogel structure. The plastic deformation of the carbonized aerogel after oil absorption with 100 cycles of compression was 30%. The carbonized hollow nanofiber aerogels were superhydrophobic and oleophilic, which allowed selective absorption of oil upon contact with oily wastewater. As a similar density, the oil absorption performance of the hollow nanofiber aerogels was higher than that of the normal nanofiber aerogels, implying high efficiency of the hollow nanofiber aerogels. After compression, the dry sample could recover its shape in oil, indicating the resilience of the hollow nanofiber aerogel. Moreover, the cycle absorption experiment illustrated that low-toxicity ethanol could remove most of the oil adsorbed in the aerogels, and ensure stable performance during recycling. After five cycles, the hollow nanofiber aerogel still retained its the original shape without fiber falling off, reducing the secondary pollution to the environment. The present study provides a strategy for the design and fabrication of ordered hollow nanofiber aerogels for wastewater treatment and other potential applications.

Superefficient and robust polymer coating for bionic manufacturing of superwetting surfaces with “rose petal effect” and “lotus leaf effect”

Mimicking the superwetting behaviors of nature creatures is advantageous for the development of multifunctional surfaces. Superhydrophobic surfaces are desired for applications such as self-cleaning, drag reduction, anti-staining, anti-corrosion, oil-water separation, etc. Herein, a superefficient approach is proposed to produce a robust ultrahigh molecular weight polyethylene (UHMWPE) coating on various substrates by dripping and drying UHMWPE solutions. The superhydrophobic surfaces can be tuned between Cassie impregnating state and Cassie state, which resembles the “rose petal effect” and “lotus leaf effect”, respectively, by simply adjusting the quenching temperature and the solvent system. UHMWPE/ortho-xylene biphasic solution resulted in a wrinkled morphology with a high-adhesion superhydrophobic surface, while the UHMWPE/ortho-xylene/cyclohexanone triple-phase solution led to a highly porous morphology with a low-adhesion superhydrophobic surface. The micro-nano structured surfaces displayed promising applicability in droplet transportation, selective oil absorption, anti-staining, and self-cleaning. They also possess superior stability and durability against various liquids and mechanical impact. This work provides a highly efficient approach to produce versatile bionic superhydrophobic coatings with tunable superwetting states.

Assembly of Ultralight Dual Network Graphene Aerogel with Applications for Selective Oil Absorption.

High-performance graphene aerogels with well-developed internal structures are generally obtained by means of introducing additive materials such as carbon nanotubes, cellulose, and lignin into the aerogel network, which not only enhances the cost but also complicates the preparation process. Therefore, tailoring the internal structure of pristine graphene aerogel in a feasible way to achieve high performance is of great significance to the practical applications. Herein, a novel cysteamine/l-ascorbic acid graphene aerogel (CLGA) was fabricated by a simple one-step hydrothermal method followed by freeze-drying. Through the creative combination of the reducing agent l-ascorbic acid and cross-linking agent cysteamine, a dual-network structure was constructed by both layered physical stacking and vertical chemical cross-linking. The addition of cysteamine not only enhanced the reduction degree but also assisted the formation of more vertical connections between graphene nanosheets, resulting in more abundant pores with smaller sizes compared with graphene aerogels prepared by the traditional hydrothermal reduction method. CLGA possessed an ultra-low density of 4.2 mg/cm3 and a high specific surface area of 397.9 m2/g. As expected, this dual-network structure effectively improved the absorption capacity toward a variety of oil and organic solvents, with an outstanding oil absorption capacity up to 310 g/g. Furthermore, CLGA possessed good mechanical properties and oil/water selectivity. The absorbed oil could be recovered by both continuous absorption-removal process and mechanical squeezing, making the as-prepared aerogel superior absorbent material for a variety of applications, such as selective oil absorption and water treatment.

Tunable bulk material with robust and renewable superhydrophobicity designed via in-situ loading of surface-wrinkled microparticles

Superhydrophobic surfaces possess susceptibility towards mechanical and chemical damages as well as oil fouling, which limits their widespread use in practical applications. Here, we demonstrate a straightforward approach to fabricate tunable bulk material with robust and renewable superhydrophobicity by in-situ loading of interconnected surface-wrinkled microparticles. The bulk material shows mechanochemically robust superhydrophobicity across its whole 3D volume, features renewable superhydrophobicity after extremely chemical corrosion, and could regenerate its water repellency after oil contamination. The bulk material also features ultrahigh efficiency (~98%) in oil-water mixtures separation, due to its selective oil absorption capability from water. Notably, the mechanical performances, microstructures and density of the bulk material can be adjusted on demand by simply changing the amount of loaded microparticles. Compared to the pristine commercial melamine-formaldehyde based porous substrate (MFPS), the achieved bulk material shows up to ~230 folds increase in Young’s modulus, ~145 folds increase in flexure stress and ~25 folds increase in tensile stress. This strategy features great potential for designing lightweight structural materials with robust waterproof functionality as well as materials with efficient oil recovery capability from wastewater.

Hollow three-dimensional graphene reinforced with poly (methyl methacrylate) for selective absorption of oil

Removal of oil from water through absorbent materials such as graphene proves to be an excellent technique due to its simplicity and recoverability. However, there are several issues encountered such as poor structural integrity and complexity of the fabrication process. In this study, the hollow three-dimensional graphene (H3DG) grown using chemical vapor deposition technique is strengthened by infusing poly(methyl methacrylate) (PMMA) for structural robustness and better recovery process. The overall porous nature of the H3TG and the gaps created within the graphene layers after the nickel etching provides an excellent absorption capacity of up to 48.132 g g−1. Besides, the polymeric reinforcement gives additional flexibility and improved mechanical properties such as reduced elastic modulus and ultimate tensile strength at 452.41 MPa and 19.05 kPa, respectively, as compared to the standalone H3TG. The presence of PMMA is also advantageous as the absorbed oil is recoverable by compression and reused with only 3.616% reduction in oil absorption performance after 10 cycles.

Superhydrophobic cellulose nanofibril/silica fiber/Fe3O4 nanocomposite aerogel for magnetically driven selective oil absorption

The development of superabsorbent materials with high absorption capacity, selectivity, and stable performance is needed for oil recovery. Remote-controlled oil absorption is highly favorable for oil absorption in harsh environment. In this study, a novel ultralight superhydrophobic nanocomposite aerogel composed of organic cellulose nanofibrils (CNFs), inorganic silica fiber, and magnetic Fe3O4 nanoparticles was developed through a simple freeze drying and surface modification method as a magnetically driven superabsorbent material. The aerogel has a highly porous and fibrous structure that contains hierarchical micro-nano surface topography. Low surface energy carbon–fluorine chains were grafted on aerogel surface which rendered the aerogel superhydrophobic. The addition of Fe3O4 nanoparticles significantly improved the surface area, compressive property, water contact angle, and the separation efficiency of the aerogel, but reduced the absorption capacity due to the increase of bulk density. The developed nanocomposite aerogel has a high absorption capacity (weight gain of 3420–5837%), separation efficiency ~ 100%, and a water contact angle of 150°. It also demonstrated high elasticity and performance stability in repetitive use. Given its magnetic property, the CNF/silica/Fe3O4 nanocomposite aerogel is a promising candidate for selective oil removal from open water, especially for remotely controlled applications.

One-step facile fabrication of PVDF/graphene composite nanofibrous membrane with enhanced oil affinity for highly efficient gravity-driven emulsified oil/water separation and selective oil absorption

Highly efficient separation of emulsified oily wastewater, especially for surfactant-stabilized water-in-oil emulsions is urgently demanded and still worldwide challenge. Herein, a superoleophilic and under oil superhydrophobic Poly (vinylidene fluoride) (PVDF)/graphene (GE) composite nanofibrous membrane (GPNM) was fabricated through a simple one-step electrospinning strategy for highly efficient gravity-driven surfactant-stabilized water-in-oil emulsions separation. The resultant membrane possessed water contact angel of 140.1°±1.1°, oil contact angel of nearly 0°, as well as under oil ultralow water adhesion ability. Furthermore, the morphology, pore size and surface wettability of as-prepared nanofibrous membranes were simply tuned by adjusting the concentration of GE in electrospinning solution. Thanks to the narrow pore size distribution, high porosity (＞92.8%), and the intrinsic strong oil affinity of GE nanosheet, the composite membrane showed outstanding Span 80 surfactant-stabilized water-in-oil emulsions separation efficiency as high as 99.8% with corresponding permeation flux up to 23794 ± 928 L m−2 h−1 bar−1 during gravity-driven separation process. The exceptional oil absorption performance was also displayed by collecting floated oils on water surface. The results would make our composite nanofibrous membranes a great promise of dealing with practical oily wastewater remediation.

Elastic nanocellulose/graphene aerogel with excellent shape retention and oil absorption selectivity

In this work, a simple preparation method is developed to synthesize aerogels with great shape retention for oil absorption application. First, an elastic aerogel is prepared by ice-templating an aqueous suspension of cellulose nanocrystal (CNC) with polyethyleneimine (PEI) and epoxy cross-linker. After the lyophilization process, the prepared CNC aerogel shows highly porous structures and allows rapid absorption of solvents, including water, through capillary forces. In particular, the aerogel after compression recovers to its original shape without any deformation. To realize selective oil absorption, chemically modified graphene sheets are attached to the aerogel pore surface via a dip coating process. SEM images show that the graphene sheets form a uniform and dense monolayer on the pore surfaces of the CNC aerogel. This graphene coating improves hydrophobicity without compromising the overall porosity and elasticity of the aerogel. After surface modification, the CNC/graphene aerogel can selectively absorb organic solvents with a weight ratio ranging from 25 to 58 g/g. The CNC/graphene aerogel can be squeezed dried into a compact size, and retains its original shape rapidly in contact with liquids. The absorbed liquids can be collected by mechanical squeezing, and the absorption performance of this aerogel remains unchanged after 100 squeezing-swelling cycles. Several examples are also demonstrated to show the feasibility of applying this aerogel in oil spill control.

Facile preparation of superhydrophobic melamine sponge for efficient underwater oil-water separation

When oil spills occur at sea, surface oil can be collected or dispersed using methods that are now routine in the industry. However, a significant proportion of the oil may reside sub-surface, as discrete droplets, undispersed bulk oil or water-in-oil emulsion ‘mousses’, which may not be responsive to the conventional procedures. Therefore, the topic of the present paper is the preparation of an oil-selective absorbent sponge, surface modified using biowaxes, of potential use for the selective absorption of oil in the presence of water. In this work, stable, surfactant-free biowax-in-water emulsions have been prepared as a low-cost and non-toxic method for the production of superhydrophobic absorbent surfaces of commercial melamine sponge. Different pre- and post-treatment methods have been investigated to improve the selective oil absorption performance of the sponge in the presence of water. The results of this study suggest that an economic and efficient melamine-based sponge exhibiting efficient underwater oil absorbency can be produced by treating the sponge with a beeswax-in-ethanol/water “Ouzo” emulsion, followed by annealing.

Cellulosic sponges with pH responsive wettability for efficient oil-water separation

To obtain efficient oil-water separation materials with responsiveness, cellulosic porous materials with switchable wettability in response to pH changes were developed by reacting cellulose acetoacetate sponges with alkylamines of varying carbon chain length via dynamic covalent enamine bonds. The resulting sponges reversibly changed between being superhydrophilic (θwater = 0°) and highly hydrophobic (maximal θwater = 146°) under suitable pH conditions while maintained the favorable porous structures. Notably, the functionalized sponges exhibited high and selective oil absorption capacity (40–80 g/g) and satisfying desorption ability of 80%, and could efficiently separate oil-water mixtures and emulsions with extremely high efficiency (> 99%) in a controllable manner. With the three-dimensional micro/nano porous structure, switchable wettability and intrinsic environmentally friendliness, the pH responsive cellulosic sponges developed here hold great potential in controllable oil-water separation and oily wastewater purification.

Multifunctional Edge-Activated Carbon Nitride Nanosheet-Wrapped Polydimethylsiloxane Sponge Skeleton for Selective Oil Absorption and Photocatalysis.

Developing green 3D porous materials integrating multitasking environmental remediation with high efficiency and reusability is considered to be a promising sustainable approach and is urgently required. Herein, we have successfully prepared a facile, ecofriendly, and robust multifunctional composite sponge of carbon nitride (CN) nanosheets wrapping an elastomer polydimethylsiloxane (PDMS) skeleton without harsh treatments. The composite sponge (CN@PDMS) exhibits excellent hydrophobic and superoleophilic properties with a water contact angle of 133.2°. This sponge also shows high selective absorption of organic solvents and oils with high recyclability after 10 absorption cycles. Furthermore, the CN@PDMS sponge has a high ability for demulsification of the oil-in-water emulsion as well. The as-prepared sponge displays high thermal stability, retaining 82.16% of its original weight up to 550 °C, and extraordinary prolonged stability in harsh corrosive solutions over 35 h compared with the pristine PDMS sponge. Additionally, the CN@PDMS sponge exhibits a high ability for adsorption and photodegradation of rhodamine B under visible light irradiation with self-cleaning and high reusability over 5 runs. Such a sustainable strategy would provide new ways for broad environmental applications.

Robust superhydrophobic fluorinated fibrous silica sponge with fire retardancy for selective oil absorption in harsh environment

Water pollution caused by oil leaks is a global environmental problem, calling for high-performance superabsorbent materials for the selective removal and recovery of oil from water. Herein, a robust fluorinated silica fibrous sponge (Silica-GA-F) was developed as an efficient superabsorber for selective oil absorption in harsh environments. Silica fibrous sponge was fabricated by self-assembly electrospinning and calcination. Superhydrophobic Silica-GA-F was obtained after crosslinking and fluorination using glutaraldehyde (GA) and perfluorodecyltriethoxysilane (PDTS). The fluffy microscale fibrous structure and low surface energy of Silica-GA-F contributed to its low bulk density of 16 mg/cm3, relatively high surface area of 6.5 m2/g, and high water contact angle of 151°. The sagging of water interface along silica fiber profile led to an impregnated Cassie-Baxter wetting sate and a “rose petal” effect. The Silica-GA-F possesses an extraordinary absorption capacity of ~122 times of its weight toward various oils, excellent separation efficiency, and promising stability in harsh environments and repetitive use. The oil absorbed can be combusted due to the fire retardancy of Silica-GA-F. Moreover, the GA crosslinking renders the silica sponge with high dimensional stability and recoverability. These properties make the Silica-GA-F sponge an ideal selective superabsorbent material with superior robustness and stability for water remediation, especially in harsh environments.

White Graphene-Cobalt Oxide Hybrid Filler Reinforced Polystyrene Nanofibers for Selective Oil Absorption.

In this work, stable hydrophobic nanocomposites are made from electrospun fibers of polystyrene (PS) containing a hybrid filler combination of (i) hexagonal boron nitride (hBN) and (ii) cobalt oxide (Co3O4) nanomaterials. Good synergistic interaction is observed between the nanomaterials, since the growth of Co3O4 was carried out in presence of white graphene nanosheets. Filler synergy modifies the PS surfaces, by enhancing the filler-polymer interfacial interactions and provides good tensile strength. The hydrophobic films are gamma irradiated to improve crosslinking within the polymer nanocomposites. Since gamma irradiation enhances the surface roughness, its hydrophobicity/oleophilicity increases much and the final nanofibers show good oil-water separation efficiency. The nanofibers act as sponge clothing to skim the oil from a mixture of oil and water. Durability of the fibers in hot water and in presence of ultrasonic waves is also tested and good response is achieved. Contact angle studies are performed to investigate the surface properties and to check the influence of gamma irradiation on the surface wettability. The gamma-irradiated PS nanocomposite fiber shows a contact angle of 152° ± 2° compared to the 140° ± 1° of the neat PS fiber, evidencing the superhydrophobicity. Both the effects of crosslink density enhancement and hybrid filler distribution make the composite fibers stronger in oil absorption application even at higher operation temperatures. The fibers are reported to be robust and durable, in addition.