Flame retardant, superhydrophobic, and superoleophilic reduced graphene oxide/orthoaminophenol polyurethane sponge for efficient oil/water separation

Flame-retardant bamboo fiber-based films for high-performance fire sensors

Natural polymers play a non-negligible role in the development of green and sustainable sensors. However, their poor flame retardancy and deficient thermal stability inevitably restrict their application in sensors for monitoring the fire full-process. In this work, a facile and eco-friendly method for the large-scale preparation of flexible films composed of bamboo fiber (BF), carboxymethyl cellulose (CC), and graphene (GN) by solution casting was put forward. Iron ions and phytic acid (PA) self-assemble on its surface, eventually resulting in a film (referred to as BCGP) that exhibits high strength and high flame retardancy. Specifically, the strength of the film reaches 3.92 MPa, and reliable strength still be ensured even after long-term soaking. Furthermore, the limiting oxygen index of the film is as high as 33 %, the vertical burning test attains the V-0 level. As a sensor, the film promptly triggers an alarm within 3.6 s of contact with flames, and its response remains sensitive even after repeated scorching. The temperature response encompasses a wide range of 50 to 200 °C, and the gauge factor is as high as 1572.

Enhancing EMI Shielding Efficiency of Polyurethane Foam by Incorporating MWCNT-Decorated Hollow Glass Microspheres

This work explores the enhancement of EMI shielding efficiency of polyurethane (PU) foam by loading multiwall carbon nanotube (MWCNTs)-decorated hollow glass microspheres (HGMs). MWCNT was coated onto the HGM surface by a simple solution casting technique. The coated HGM particles were loaded in PU foams, resulting in an even dispersion of MWCNT in the foam struts, thereby forming an interconnected conductive network in the polymer matrix. The synthesized polymeric foam composites were characterized for bulk density, cellular morphology, Fourier transform infrared spectra, compression strength, electrical conductivity, and EMI shielding efficiency. The highest electrical conductivity, i.e., 15.75 × 10-3 S/cm, was achieved at 13 wt % loading, which resulted in the EMI shielding efficiency of -25.03 dB. Finally, we proposed a mechanism exploring the enhancement of EMI shielding of PU foam composite showing that the incident EMI radiations are being absorbed into the material due to the presence of interconnected MWCNTs and successive reflection via hollow glass spheres. The synthesized foam can be used as an EMI shielding material in such applications where flexibility and lightweight are the primary requirements.

A Review of Polyurethane Foams for Multi-Functional and High-Performance Applications

Polyurethane (PU) foams are cellular polymeric materials that have attracted much attention across various industries because of their versatile properties and potential for multifunctional applications. PU foams are involved in many innovations, especially in multi-functional and high-performance applications. Special attention is given to developing tailored PU foams for specific application needs. These foams have various applications including flame retardancy, sound absorption, radar absorption, EMI shielding, shape memory, and biomedical applications. The increasing demand for materials that can perform multiple functions while maintaining or enhancing their core properties has made PU foams a focal point of interest for engineers and researchers. This paper examines the challenges faced by the PU foam industry, particularly in developing multifunctional products, as well as the strategies for improving sustainability, such as producing PU foams from renewable resources and recycling existing materials.

Preparation of Superhydrophobic and Multifunctional Sponges for Oil/Water Separation and Oil Absorption

For settling the recycling problem of waste polyurethane sponges (PU) and environment pollution of oil spills simultaneously, this work exploited the multifunctional superhydrophobic PU materials via the dip-coating method, which were prepared by anchoring modified Fe3O4 and expandable graphite (EG) on PU sponges under the adhesion effect of polydimethylsiloxane (PDMS). The water contact angle and sliding angle of as-prepared PU sponges reached 154.1 ± 1.6 and 8°, respectively. Most importantly, the superhydrophobic PU sponges were endowed with the multipath oil treatment ability, which consisted of magnetically driven, gravity-driven, peristaltic pump-driven, and photothermally driven modes. Besides, the light oil absorption capacity, separation flux, and efficiency for superhydrophobic PU sponges reached 23.9 g/g, 27779 L m-2 h-1, and 99.5%, respectively. Owing to the photothermal conversion ability of Fe3O4 and EG, the temperature of superhydrophobic PU sponges was raised to 71.5 °C within 233 s under 1.2 solar irradiation (1200 W/m2), demonstrating its absorption potential for high-viscosity crude oils. In addition, the prepared sponges exhibited good chemical/mechanical stability, self-cleaning, and flame retardancy. In a nutshell, this article has evolved an environmentally benign and practical method for fabricating the multifunctional materials in oil spill treatment, which will efficiently accomplish the targets of low carbon and environmental management.

Applications of graphene oxide (GO) in oily wastewater treatment: Recent developments, challenges, and opportunities

The treatment of oily wastewater has become a serious environmental challenge, for which graphene oxide has emerged as a promising material in solving the problem. The ever-growing utilization of graphene oxide (GO) in the treatment of oily wastewater necessitates a constant review. This review article employs a comprehensive literature survey methodology, systematically examining peer-reviewed articles, focusing on, but not entirely limited to, the last five years. Major databases such as EBSCOhost, Scopus, ScienceDirect, Web of Science and Google Scholar were searched using specific keywords related to GO and oily wastewater treatment. The inclusion criteria focused on studies that specifically address the application, efficiency, and mechanisms of GO in treating oily wastewater. The data extracted from these sources were then synthesized to highlight the most important developments, challenges, and prospects in this field. As far as oily wastewater treatment is concerned, the majority of the studies revolve around the use of GO in mitigating fouling in membrane processes, improving the stability, capacity and reusability of sorbents, and enhancing photodegradation by minimizing charge recombination.

Flame retardant and superoleophilic polydopamine/chitosan-graft (g)-octanal coated polyurethane foam for separation oil/water mixtures

The discharge of crude petroleum oils and their derivatives poses serious environmental challenges, which can be mitigated through oil/water separation. In this study, polyurethane (PU)/polydopamine (PDA)/chitosan-graft (g)-octanal foam was prepared by immersing of PU foam in PDA and chitosan-g-octanal solutions. The fabricated PU foam exhibited thermal stability, flame retardancy, and hydrophobicity/superoleophilicity. The coated PU foam can selectively absorb heavy and light oils from dynamic and static oil/water mixtures. The maximum sorption capacity for olive oil was found to be as high as 41.48 g/g. PU/PDA/chitosan-g-octanal foam also demonstrated excellent flame retardancy and the ability to quickly extinguish fire, as confirmed by the limiting oxygen index (LOI) test.

TDA/rGO@WS with Joule heat and photothermal synergistic effect: A promising adsorption material for all-weather recovery of viscous oil spills at sea

Oil spills are a global environmental protection challenge, and traditional adsorption materials have poor effect on low temperature and high viscosity marine oil spills. This article reports composite adsorption materials TDA/rGO@WS for viscous oil spills: loaded with rGO/TDA coating on a commercial biomass wood pulp sponge (WS), achieving Joule heating, photothermal effect and hydrophobic modification. The results showed that the TDA/rGO@WS has good photothermal conversion ability and Joule heating ability, and the temperature increased to 83.7 °C and 148 °C, respectively, under simulated solar irradiation and additional voltage at room temperature. The efficiency of adsorption at a low temperature of 5 °C increased by 22.41% at 1 sun and by 51.53% at 10 V. Temperature effectively reduced the viscosity of the offshore oil spill and ensures the efficient adsorption of oil spills at low temperatures promoted. The TDA/rGO@WS also showed good hydrophobicity (WCA=129°), excellent efficiency of water-oil separation (99.53%) and good adsorption capacity (9.4-13.68 g/g) for marine fuel oils. TDA/rGO@WS effectively solves the problem of cleaning up high-viscosity oil spills from ships in winter and polar waters, and proposes a new strategy for all-weather efficient treatment of oil spills at sea.

Coupling Carbon-Based Composite Phase Change Materials with a Polyurethane Sponge for Sustained and Efficient Solar-Driven Cleanup of Viscous Crude Oil Spill

The efficient cleanup of crude oil spills is a worldwide problem due to their high viscosity and low fluidity. Under the assistance of solar radiation, adsorbents with in situ heating function are becoming the ideal candidates to solve this problem. In this study, a new strategy coupling a polyurethane (PU) sponge with phase change materials (PCMs) is proposed to realize the efficient utilization of solar energy and crude oil cleanup. Wormlike carbon nanotubes/mesoporous carbon (CNTs/MC) with a core-shell structure was used to encapsulate polyethylene glycol (PEG), which was then introduced into the PU sponge for photothermal conversion and thermal storage. After coating with a polydimethylsiloxane (PDMS) layer, the sponge was further endowed with hydrophobic characteristics. Additionally, PDMS can function as a binder between PEG@CNTs/MC and sponge skeleton. The resulting PEG@CNTs/MC/PU/PDMS (named as PEG@CMPP) exhibited excellent photothermal conversion and high absorption capacity for high-viscosity crude oil. Most importantly, thanks to the heat storage properties of PEG, the stored heat can be sustainably transferred to the surrounding crude oil to promote its continuous absorption even under insufficient light intensity conditions. The crude oil absorption capacity of PEG@CMPP-3 reached approximately 0.96 g/cm3 even after the light source was removed, which manifested the distinctive advantages compared to the conventional photothermal adsorbent. The proposed approach integrates the high efficiency of solar-assisted heating and energy-conserving advantage, thereby providing a feasible strategy for highly efficient remediation of viscous crude oil spills.

Fireproof Nanocomposite Polyurethane Foams: A Review

First introduced in 1954, polyurethane foams rapidly became popular because of light weight, high chemical stability, and outstanding sound and thermal insulation properties. Currently, polyurethane foam is widely applied in industrial and household products. Despite tremendous progress in the development of various formulations of versatile foams, their use is hindered due to high flammability. Fire retardant additives can be introduced into polyurethane foams to enhance their fireproof properties. Nanoscale materials employed as fire-retardant components of polyurethane foams have the potential to overcome this problem. Here, we review the recent (last 5 years) progress that has been made in polyurethane foam modification using nanomaterials to enhance its flame retardance. Different groups of nanomaterials and approaches for incorporating them into foam structures are covered. Special attention is given to the synergetic effects of nanomaterials with other flame-retardant additives.

Magnetic, self-heating and superhydrophobic sponge for solar-driven high-viscosity oil-water separation

In this work, a novel oil-adsorption sponge with superhydrophobicity was fabricated using polymer-assisted electroless deposition and dip-coating techniques for depositing a rough polydopamine layer, magnetic particles, and low surface energy polydimethylsiloxane onto the surface of a sponge skeleton. The as-prepared superhydrophobic sponge (WCA > 150° and SA < 5°) exhibited rapid adsorption behavior, large adsorption capacity (up to 50.6 times its own dry weight or above 90% of its own volume), excellent durability (above 80% of the adsorption capacity after 80 recycles), and a self-cleaning property owing to sufficient open-cell pores and superelasticity provided by the melamine-formaldehyde host as well as the hierarchical roughness and convenient magnetic recovery enabled by the polymer-assisted electroless deposition approach. The pump-, gravity-, and solar-driven oil-water separation devices based on the fabricated cubic composites were also demonstrated, particularly the separation of high-viscosity oil-water mixtures via the solar-driven mode, demonstrating the broad prospects of such modified sponges in actual applications. This study provides a new avenue for rationally designing novel oil adsorption and separation materials.

Novel 3D carbon fibers derived from Luffa wastes for oil/water separation

In this study, the 3D structure of carbon fibers (CFs) was prepared from Luffa sponge wastes by H₃PO₄ impregnation with various ratios and a low-temperature carbonization process at 500 °C in a nitrogen atmosphere. The H₃PO₄-treated Luffa sponge had higher thermal stability and carbonic yield (∼60-70%) than neat-Luffa (∼21%). Characterization analyses exposed that the synthesized CFs derived from H₃PO₄-treated Luffa exhibited oleophilic and hydrophobic carbonic nature with 3D sponge skeletal, reflecting an ideal structure for oil sorption. The engine oil sorption properties on the CFs were studied by varying the contact time. The engine oil sorption equilibrium data for 3D CFs samples was explained by the pseudo-second-order and intraparticle diffusion models. The equilibrium oil sorption capacities of 3D CFs were as large as 23.1 ± 0.4 g/g for engine oil, 23.7 ± 1.0 g/g for gasoline, 28.1 ± 1.0 g/g for almond oil, and 29.2 ± 0.8 g/g for pomegranate seed oil in 20 min. Moreover, the optimized 3D CFs can be selectively for oil/water separation applications, such as high capacities for various oils, fast kinetic sorption, and reusability (>6 cycles). This research presented a facile and cost-effective process for the 3D CFs through recycling Luffa sponge wastes for rapid oil sorption.

A multifunctional heterogeneous superwettable coating for water collection, oil/water separation and oil absorption

Herein, inspired by desert beetles, we fabricated a multifunctional heterogeneous superwettable coating (MHSC) for water collection and oily wastewater cleanup. The selective modifications of 1-octadecanethiol (ODT) treated CoO and P25 TiO₂ nanoparticles (NPs) were prepared, so hydrophobic CoO NPs and superhydrophilic P25 NPs were combined on the MHSC, showing the water contact angle (WCA) of 156.5° and rolling-off angle (RA) of 6.4°. With the aid of waterborne polyurethane (WPU), five kinds of substrates (i.e., glass slide, dish, wood, fabric, sponge) spray-coated by MHSC displayed high-efficiency water collection rates (WCRs) of 18.1 ± 0.7 mg min^-1 cm^-2. Moreover, MHSC coated fabric manifested robust oil/water separations with separation efficiencies (SEs) > 99.7 % and fluxes ranged from 9.7 to 11.0 L m^-2 s^-1. Efficient oil sorption from oily water was obtained by MHSC coated sponge with oil absorption capacities (OACs) of 6.5-29.5 g g^-1. Further, even dealt with the treatments of mechanical destructions, extreme temperature and UV illumination, the coated materials remained stable performances.

Solar-heating superhydrophobic modified melamine sponge for efficient recovery of viscous crude oil

Developing self-heating sorbents for rapid clean-up of viscous oil spills by using clean solar energy is attracting attention. Still, simple and scalable fabrication approaches of solar-heating sorbents remain challenging. Herein, a facile and practical modification strategy was presented to develop a solar-heating modified melamine sponge (rGO/CNT/MS) by dip-coating layer-by-layer (LBL) electrostatic assembly of GO and CNT with opposite charges onto MS skeleton followed by thermal reduction, without any complicated microfabrication and hydrophobic modification processes. Based on the intercalation of CNT into rGO layers and strong conjugation/hyperconjugation synergy of rGO and CNT, the light sorption ability, photothermal conversion, hydrophobicity and mechanical properties of the rGO/CNT/MS sorbent were further improved compared to rGO/MS and CNT/MS. The surface temperature could reach 75 ℃ in 100 s under 1 sun radiation (1 kW m^-2), which would effectively absorb crude oil by in-situ sunlight-heating to reduce its viscosity. The sorption speed increased by about 30 times compared with no sunlight irradiation, and the continuous sorption capacity was up to 1.71 g/cm² at 610 s driven by pump force. The easily-prepared solar-assisted rGO/CNT/MS with high photothermal performance, corrosion resistance, mechanical compressibility, coating firmness and oil sorption ability showed huge potential application in oil spill recovery.

Nanohybrid of Co3O4 Nanoparticles and Polyphosphazene-Decorated Ultra-Thin Boron Nitride Nanosheets for Simultaneous Enhancement in Fire Safety and Smoke Suppression of Thermoplastic Polyurethane

Thermoplastic polyurethane (TPU) is widely used in daily life due to its characteristics of light weight, high impact strength, and compression resistance. However, TPU products are extremely flammable and will generate toxic fumes under fire attack, threatening human life and safety. In this article, a nanohybrid flame retardant was designed for the fire safety of TPU. Herein, Co₃O₄ was anchored on the surface of exfoliated ultra-thin boron nitride nanosheets (BNNO@Co₃O₄) via coprecipitation and subsequent calcination. Then, a polyphosphazene (PPZ) layer was coated onto BNNO@Co₃O₄ by high temperature polymerization to generate a nanohybrid flame retardant named BNNO@Co₃O₄@PPZ. The cone calorimeter results exhibited that the heat release and smoke production during TPU combustion were remarkably restrained after the incorporation of the nanohybrid flame retardant. Compared with pure TPU, the peak heat release rate (PHRR) decreased by 44.1%, the peak smoke production rate (PSPR) decreased by 51.2%, and the peak CO production rate (PCOPR) decreased by 72.5%. Based on the analysis of carbon residues after combustion, the significant improvement in fire resistance of TPU by BNNO@Co3O4@PPZ was attributed to the combination of quenching effect, catalytic carbonization effect, and barrier effect. In addition, the intrinsic mechanical properties of TPU were well maintained due to the existence of the PPZ organic layer.

Durable 3D Porous Superhydrophobic Composites for Versatile Emulsion Separation in Multiple Environments

Polydopamine as a multifunctional biomimetic polymer with nonselective strong adhesion properties has become a hot research topic in recent years. However, there are a few reports on the durable and effective emulsion separation of polydopamine composites from other materials. Therefore, it is necessary to construct durable polydopamine composites to achieve selective adsorption of materials. In this work, polypyrrole (PPy)-PDA was obtained on sponges by an in situ polymerization reaction, followed by the attachment of SiO₂ nanoparticles to the surface by polydimethylsiloxane to achieve superhydrophobicity. As a result, previously unreported selective superhydrophobic adsorbents for PPy-PDA coatings were obtained. The prepared sponges have an excellent adsorption capacity for oils and organic solvents. Not only can the sponges absorb 19-39 g of organic solvents per gram but they can also absorb oil from oil-in-water emulsions. The chemical oxygen demand value of the emulsion can be reduced to 219 mg/L after separation. More importantly, the performance remains good in the cycle test, and due to the construction of a durable superhydrophobic sponge, it can still maintain its relatively good performance in artificial seawater, acid-base environments, and can achieve relatively stable emulsion separation. At the same time, the potential of the polymer material composited with PDA in lasting and stable emulsion separation was also verified.

Tuning Electro-Magnetic Interference Shielding Efficiency of Customized Polyurethane Composite Foams Taking Advantage of rGO/Fe3O4 Hybrid Nanocomposites

Electromagnetic interference (EMI) has been recognized as a new sort of pollution and can be considered as the direct interference of electromagnetic waves among electronic equipment that frequently affects their typical efficiency. As a result, shielding the electronics from this interfering radiation has been addressed as critical issue of great interest. In this study, different hybrid nanocomposites consisting of magnetite nanoparticles (Fe₃O₄) and reduced graphene oxide (rGO) as (conductive/magnetic) fillers, taking into account different rGO mass ratios, were synthesized and characterized by XRD, Raman spectroscopy, TEM and their magnetic properties were assessed via VSM. The acquired fillers were encapsulated in the polyurethane foam matrix with different loading percentages (wt%) to evaluate their role in EMI shielding. Moreover, their structure, morphology, and thermal stability were investigated by SEM, FTIR, and TGA, respectively. In addition, the impact of filler loading on their final mechanical properties was determined. The obtained results revealed that the Fe₃O₄@rGO composites displayed superparamagnetic behavior and acceptable electrical conductivity value. The performance assessment of the conducting Fe₃O₄@rGO/PU composite foams in EMI shielding efficiency (SE) was investigated at the X-band (8-12) GHz, and interestingly, an optimized value of SE -33 dBw was achieved with Fe₃O₄@rGO at a 80:20 wt% ratio and 35 wt% filler loading in the final effective PU matrix. Thus, this study sheds light on a novel optimization strategy for electromagnetic shielding, taking into account conducting new materials with variable filler loading, composition ratio, and mechanical properties in such a way as to open the door for achieving a remarkable SE.

Phytic acid and graphene oxide functionalized sponge with special-wettability and electronegativity for oil-in-water emulsion separation in single-step

Developing an emulsion separation material with one-step in-situ purifying capability and improved security in applications, especially for subsequent scale-up, is valuable but remains a challenge. Herein, the amphiphilic sponge (PA@RGO@MS) was prepared via impregnation and in-situ growth of the negatively charged hydrophilic phytic acid (PA) and the hydrophobic reduced graphene oxide (RGO) on the surface of the melamine sponge (MS) and applied in emulsion purification. The mechanics, wettability, absorption performance of the PA@RGO@MS were analyzed to identify its potential for stable demulsification. Results show that the PA@RGO@MS could purify emulsions (turbidity removal rate = 99.7%; TOC removal rate = 94.14%) in-situ in one step by simple shock absorption, profited from the hydrophilic and demulsification capability of PA, oil absorption of RGO, and wide reaction and storage space of MS. Targeting the emulsion with distinct properties (density, viscosity, and concentration) of the oil phase, the PA@RGO@MS could efficiently enable the purification. Meanwhile, the powerful flame-retardant granted from PA ensures the safe shipment and storage of sponges. The favorable cyclability (turbidity removal rate > 98.5% and TOC removal rate > 89.5% after 10 cycles) and diversified operating modes enhance the practical value of the PA@RGO@MS.

Electrospun composites nanofibers from cellulose acetate/carbon black as efficient adsorbents for heavy and light machine oil from aquatic environment

The feasibility of preparing cellulose acetate/carbon black (CA/CB) composite nanofiber in one step through electrospinning process and investigating its potential oil absorbability and application for machine oil removal from aquatic environment was reported. Different CA/CB composite nanofibers were fabricated by electrospinning of cellulose acetate (CA) solution containing different loads of 0.7, 1.5, and 2.2% CB relative to the weight of CA and labeled as CA/CB0.7, CA/CB1.5, and CA/CB2.2. The scanning electron microscope (SEM) images showed continuous and smooth fiber with submicron diameter ranging from 400–900 nm with good adhering of CB into CA nanofiber. Furthermore, the CA/CB composite nanofibers exhibited high surface area compared with CA nanofiber, which reached 3.057, 2.8718 and 8.244 m2/g for CA/CB0.7, CA/CB1.5 and CA/CB2.2, respectively. Oil adsorption tests were performed with heavy and light machine oils. The CA/CB composite nanofibers showed higher affinity for oil removal from an aqueous solution than pure CA nanofiber. The CA/CB1.5 composite nanofiber has an exceptional performance for the adsorption of both oils, and the maximum oil adsorbed reached 10.6 and 18.3 g/g for light and heavy machine oils, respectively. The kinetic of machine oils adsorption was fitted well by the pseudo-second-order model. Besides, CA/CB composite nanofiber exposed good adsorption properties and respectable reusability after regeneration for four consecutive cycles. The results advocate the excellent potential of as-fabricated CA/CB composite nanofiber as a promising reusable oil adsorbent for oil spill cleanup applications.

Biomass poplar catkin fiber-based superhydrophobic aerogel with tubular-lamellar interweaved neurons-like structure

Superhydrophobic aerogels are attractive candidates in controlling oil spills. The major challenges for existing aerogels are the construction of mechanical endurance as well as accessible of building materials. Herein, a newfangled biomass superhydrophobic aerogel (M-PCF/CS) with both superior compressibility and oil caption speed is fabricated by assembling poplar catkin fiber (PCF) hollowed-out shell of 330 nm and chitosan (CS) into tubular-lamellar interweaved neurons-like structure. The resultant aerogels (porosity ~ 96.12%), with flexuous PCF as the elastic buffer and second-pore capillaries, exhibit large longitudinal and transverse compressibility, endurable fatigue tolerance, fast oil sorption rate with a capacity of 28.8-78.1 g/g at 5-25 s. In parallel, the aerogels are tolerant of NaCl, UV radiation, and organic solvents without superhydrophobic variation and a case of oil spill remediation via pump-supported experiment shows that the aerogels facilely achieve continuous oil recycling from seawater by 23052-43956 L·m^-2·h^-1. Furthermore, the resultant M-PCF/CS, with assistance of an oscillator, can be applied to separate oil/water emulsions with efficiency of 98.07-99.11%. The successful fabrication of this material provides a new design strategy for the construction of mechanically robust aerogels for speedy and economical cleanup of oil pollutants from water.

Superhydrophobic nanohybrid sponges for separation of oil/ water mixtures

The industrial revolution has led to different types of environmental pollution, including frequent leakage of crude oil to marine waters and the contamination of wastewater with immiscible or emulsified oils and organic liquids from various industrial residues. Hence, developing multifunctional materials for oil/water separation is a field of high significance for the remediation of oil-polluted water. Recently, advanced superwetting materials have been employed for oily wastewater treatment. This review summarizes the recent development in fabricating superhydrophobic/superoleophilic nanohybrid polyurethane, melamine, and cellulose sponges for oil/water separation. The use of organic and/or inorganic nanohybrid materials opens the horizon for designing a diverse and wide range of superhydrophobic sponges due to the synergistic effect between the surface roughness and chemical composition. The discussion is organized based on different classes of low surface energy materials including thermoplastics, thermosets, elastomers, fluorinated polymers, conductive polymers, organosilanes, long alkyl chain compounds, and hydrophobic carbon-based materials. Recent examples for the separation of both immiscible and emulsified oil/water mixtures are presented, with a focus on fabrication strategies, separation efficiency, recyclability, mechanical performance, and durability. Currently, most studies did not focus on the mechanical/chemical stability of the fabricated sponges, and hence, future research directions shall address the fabrication of robust and long-term durable superhydrophobic sponges with proper guidelines. Similarly, more research focus is required to design superhydrophobic sponges for the separation of emulsified oil/water mixtures and heavy crude oil samples. Superhydrophobic sponges can be employed for treatment of oily wastewater, emulsion separation, and cleanup of crude oil spills.

A Modified Porous Sponge with Selective Ability for Oil Removal from Oil-Water Mixtures

As oil and chemical spills pose a significant threat to the water environment, the need to develop efficient sorbent materials to remove oil and organic pollutants from water has arisen. This study aimed to develop a simple modification scheme to impart oil and water selective absorption capacity to a common three-dimensional porous material. Commercially available polyurethane sponges were used as the base material, and vinyl silica aerogel particles were loaded onto the sponges using polydimethylsiloxane as an adhesion agent. As a result, the water contact angle of the modified sponge increased from 118° to 149.2°, and the water absorption decreased from 106.5 g/g to 0.2 g/g; it could absorb oil in oil-water mixtures without absorbing water and maintain an excellent level of selective absorption ability after 20 cycles. This modification scheme is easy to operate and robust and is a scheme of practical application.

3D graphene-based adsorbents: Synthesis, proportional analysis and potential applications in oil elimination

The suitability and efficacy of three-dimensional (3D) graphene, including its derivatives, have garnered widespread attention towards the development of novel, sustainable materials with ecological amenability. This is especially relevant towards its utilization as adsorbents of wastewater contaminants, such as heavy metals, dyes, and oil, which could be majorly attributed to its noteworthy physicochemical features, particularly elevated chemical and mechanical robustness, advanced permeability, as well as large specific surface area. In this review, we emphasize on the adsorptive elimination of oil particles from contaminated water. Specifically, we assess and collate recent literature on the conceptualization and designing stages of 3D graphene-based adsorbents (3DGBAs) towards oil adsorption, including their applications in either batch or continuous modes. In addition, we analytically evaluate the adsorption mechanism, including sorption sites, physical properties, surface chemistry of 3DGBA and interactions between the adsorbent and adsorbate involving the adsorptive removal of oil, as well as numerous effects of adsorption conditions on the adsorption performance, i.e. pH, temperature, initial concentration of oil contaminants and adsorbent dosage. Furthermore, we focus on the equilibrium isotherms and kinetic studies, in order to comprehend the oil elimination procedures. Lastly, we designate encouraging avenues and recommendations for a perpetual research thrust, and outline the associated future prospects and perspectives.

Recent Developments and Advancements in Graphene-Based Technologies for Oil Spill Cleanup and Oil-Water Separation Processes

The vast demand for petroleum industry products led to the increased production of oily wastewaters and has led to many possible separation technologies. In addition to production-related oily wastewater, direct oil spills are associated with detrimental effects on the local ecosystems. Accordingly, this review paper aims to tackle the oil spill cleanup issue as well as water separation by providing a wide range of graphene-based technologies. These include graphene-based membranes; graphene sponges; graphene-decorated meshes; graphene hydrogels; graphene aerogels; graphene foam; and graphene-coated cotton. Sponges and aerogels modified by graphene and reduced graphene oxide demonstrated effective oil water separation owing to their superhydrophobic/superoleophilic properties. In addition, oil particles are intercepted while allowing water molecules to penetrate the graphene-oxide-coated metal meshes and membranes thanks to their superhydrophilic/underwater superoleophobic properties. Finally, we offer future perspectives on oil water separation that are hindering the advancements of such technologies and their large-scale applications.

A Robust Superhydrophobic Polyurethane Sponge Loaded with Multi-Walled Carbon Nanotubes for Efficient and Selective Oil-Water Separation

The influence of different coupling agents and coupling times on the wettability of a polyurethane (PU) sponge surface were optimized. Octadecyltrichlorosilane (OTS) was selected as the optimal coupling agent to prepare the superhydrophobic sponge. The superhydrophobic sponge was prepared in one step, which has the advantages of simple operation and enhanced durability. The superhydrophobic sponge was characterized by scanning electron microscopy, Teclis Tracker tensiometry, and Fourier transform infrared (FT-IR) spectrophotometry. The water contact angle increased from 64.1° to 151.3°, exhibiting ideal superhydrophobicity. Oils and organic solvents with different viscosities and densities can be rapidly and selectively absorbed by superhydrophobic sponges, with an absorption capacity of 14.99 to 86.53 times the weight of the sponge itself, without absorbing any water. Since temperature affects the viscosity and ionic strength of oil, and influences the surface wettability of the sponges, the effect of temperature and ionic strength on the oil absorption capacity of the superhydrophobic sponges was measured, and its mechanism was elucidated. The results showed that the absorptive capacity retained more than 90% of the initial absorptive capacity after repeated use for 10 times. Low-cost, durable superhydrophobic sponges show great potential for large-scale oil-water separation.

A Mechanically Flexible Superhydrophobic Rock Wool Modified with Reduced Graphene Oxide-Chloroperene Rubber for Oil-Spill Clean-Up

The leakage of industrial oil and organic wastewater discharge has caused serious damage to the natural environment and ecology. Therefore, implementation of a low-cost and high-performance adsorbent material is of great significant. This work reports the preparation of superhydrophobic rock wool (RW) for efficient clean-up of oil and organic solvents. The modified RW is prepared by coating a commercial RW with reduced graphene oxide (RGO) nanosheets under hydrothermal treatment. To improve the adhesion between the RGO nanosheets and RW, a film of chloroperene rubber is deposited on the RW surface followed by modification with RGO. The modified RW possesses superhydrophobicity and superoleophilicity with a water contact angle of 152.4°, and it is used for separation of oil-water mixture. The modified RW exhibits excellent mechanical elasticity and durability when compared with commercial one, and the adsorbed oils are recycled by simple squeezing. Its oil adsorption capacities are maintained above 95%, after several compression cycles. Importantly, the modified RW exhibits excellent photothermal properties which are beneficial for the separation of high-viscosity oils. Owing to low costs, versatility, and scalability in production, the modified RW can be regarded as a suitable choice for large-scale oil/water separation.

Insight on açaí seed biomass economy and waste cooking oil: Eco-sorbent castor oil-based

The reuse of açaí seeds is an organic approach for valorizing biomass, encouraging the public policies of circular economy, which reduces the human impact on the production chain processes. This research proposes an alternative for açaí seed as a filler in castor oil-based polyurethane, obtaining eco-sorbent to evaluate the sorption capacity for another impactful food industry by-product: waste cooking oil (WCO). Eco-sorbents were obtained with castor oil based-polyol and isocyanate (MDI) by mass mixing equal to 1:1 (OH:NCO), reinforced with açaí seed residue (5-20 wt%). The samples were characterized by techniques scanning electron microscopy (SEM), optical microscopy (OM), apparent density, contact angle, infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). Sorption capacity and efficiency were evaluated as a function of the fiber content, with tests performed in times of 30-180 s in two systems: oil and oil/water. The results showed that the eco-sorbents had a hydrophobic nature (θ > 98.3°) and macroporous morphology (pore size from 152 to 119 μm), which allowed the adsorption of residual cooking oil by the porous structure. The kinetics study showed that the sample with greater fiber content (15% wt.) reached the equilibrium in a short time compared to the neat PU for the oil system, with a sorption capacity of 9.50 g g^-1 in the first 30 s. For the oil/water system, an opposite behavior could be observed, with a sorption capacity of 9.98 g g^-1 in the 150 s equilibrium time. The Langmuir isotherm model presented a maximum adsorption capacity of 10.42 g g^-1. However, the Freundlich isotherm model had a better fit to the experimental data with R² (0.97) and lower chi-square (0.159), showing favorable adsorption (n = 1.496). Thus, it was proved that the weak interactions (connection H) and the binding energy of the predominant physisorption for the oil/water system. Thus, developed eco-sorbents are an excellent option for the sorption of WCO.

Solar-assisted isotropically thermoconductive sponge for highly viscous crude oil spill remediation

Efficiently cleaning up high-viscosity crude oil spills is still a serious global problem. In this paper, a composite filler PPy-polydopamine/BN (PPB) with high photothermal effect and high thermal conductivity was first prepared. Then the polyurethane sponge is decorated with polydimethylsiloxane and PPB to obtain a solar-assisted isotropically thermoconductive adsorbent (PPB@PU), which exhibits remarkable stability and durable mechanical properties. Meanwhile, the PPB@PU sponge has good thermal conductivity, and its surface temperature rises to 91°C in just 1 min under irradiation (1 sun). Therefore, the PPB@PU sponge can quickly heat and adsorb the crude oil contacted by the surface, significantly speed up the crude oil recovery process, and the adsorption capacity is as high as about 45 g/g. Finally, the oil adsorption method of the three-dimensional adsorbent is demonstrated, which provides a new idea for the subsequent development of advanced oil spill adsorbent.

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PPB@PU sponge exhibits good superhydrophobic/lipophilicity and mechanical stability

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PPB@PU sponge has outstanding photothermal conversion and thermal conductivity

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PPB@PU sponge can efficiently recover heavy oil for large-scale oil spill cleanup

Durable super-hydrophobic PDMS@SiO2@WS2 sponge for efficient oil/water separation in complex marine environment

The robust and eco-friendly super-hydrophobic sponge with remarkable performances has been potential adsorption material for the treatment of offshore oil spills. In this work, the durable PDMS@SiO₂@WS₂ sponge was fabricated via a green and facile one-step dipping method. The mixed tungsten disulfide (WS₂) microparticles and hydrophobic SiO₂ nanoparticles were immobilized on the sponge by non-toxic polydimethylsiloxane (PDMS) glue tier, which featured the hierarchical structure and extreme water repellency with the water contact angle of 158.8 ± 1.4°. The obtained PDMS@SiO₂@WS₂ sponge exhibits high oil adsorption capacity with 12-112 times of its own weight, and oil/water selectivity with separation efficiency over 99.85%. Notably, when subjected to the complex marine environment including high temperature, corrosive condition, insolation, and strong wind and waves, the modified sponge can maintain sable super-hydrophobicity with water contact angle over 150°. Moreover, it possesses superior mechanical stability for sustainable reusability and oil recovery. The sponge fabricated by non-toxic modifiers along with its sable super-hydrophobicity in complex marine environment makes it a potential material for practical applications.

In situ self-foaming preparation of hydrophobic polyurethane foams for oil/water separation

Polyurethane foams with excellent oil–water separation performance were prepared using hydrophobic raw materials with the assistance of a physical cooling agent.

A Green Approach to Modify Surface Properties of Polyurethane Foam for Enhanced Oil Absorption

The non-selective property of conventional polyurethane (PU) foam tends to lower its oil absorption efficiency. To address this issue, we modified the surface properties of PU foam using a rapid solvent-free surface functionalization approach based on the chemical vapor deposition (CVD) method to establish an extremely thin yet uniform coating layer to improve foam performance. The PU foam was respectively functionalized using different monomers, i.e., perfluorodecyl acrylate (PFDA), 2,2,3,4,4,4-hexafluorobutyl acrylate (HFBA), and hexamethyldisiloxane (HMDSO), and the effect of deposition times (1, 5 and 10 min) on the properties of foam was investigated. The results showed that all the modified foams demonstrated a much higher water contact angle (i.e., greater hydrophobicity) and greater absorption capacities compared to the control PU foam. This is due to the presence of specific functional groups, e.g., fluorine (F) and silane (Si) in the modified PU foams. Of all, the PU/PHFBA_i foam exhibited the highest absorption capacities, recording 66.68, 58.15, 53.70, and 58.38 g/g for chloroform, acetone, cyclohexane, and edible oil, respectively. These values were 39.19–119.31% higher than that of control foam. The promising performance of the PU/PHFBA_i foam is due to the improved surface hydrophobicity attributed to the original perfluoroalkyl moieties of the HFBA monomer. The PU/PHFBA_i foam also demonstrated a much more stable absorption performance compared to the control foam when both samples were reused for up to 10 cycles. This clearly indicates the positive impact of the proposed functionalization method in improving PU properties for oil absorption processes.