Polymer/reduced graphene oxide functionalized sponges as superabsorbents for oil removal and recovery

Preparation of the graphene-based smart hydrophobic nanocomposite and its application in oil/water separation

Designing and synthesizing materials with smart hydrophobicity against an external magnetic field for efficient oil/water separation is of great importance due to the increasing problems caused by oil pollution. Here, the nanocomposites were fabricated based on graphene and different iron oxides exhibit smart hydrophobicity against an external magnetic field and they are in powder form eliminating the requirement for a substrate employing a facile and echo friendly method. The results prove that autoclaving of graphene leads to its ferromagnetic property; then it is attached to iron oxides by magnetic attraction and a nanocomposite is produced. The magnetic property of the resulting nanocomposite is higher than the magnetic property of its individual components. In addition, following nanocomposite formation, its hydrophobicity and surface area also change. FESEM images were taken from the nanocomposites to study their surface morphology, and EDS-MAP analysis to observe the elemental distribution uniformity of the nanocomposites. Also, to measure the surface area and pore size, BET analysis has been performed on pure materials and graphene-black iron oxide nanocomposite (graphene@black iron oxide). The results show that the specific surface area of black iron oxide increases after being composited with graphene dispersed at 5000 rpm. Indeed, graphene forms a composite by binding to iron oxide, and therefore, its specific surface area increases compared to iron oxide and graphene alone. These results show an increase in oil sorption and better separation of oil from water by the prepared nanocomposite. Also, to measure the magnetic properties of pure materials, graphene@black iron oxide, and ferromagnetic graphene at 3000 and 5000 rpm, the Vibrating Sample Magnetometer analysis has been performed. The results have proven that the nanocomposite powder prepared by a simple method obtained from cost-effective and available materials is hydrophobic and becomes more hydrophobic by applying an external magnetic field. Due to the ease with which oil can be readily removed from the nanocomposite by eliminating the external magnetic field, this nanocomposite is an excellent choice for the separation of oil from water.

Solar-Assisted Superhydrophobic MoS2/PDMS/MS Sponge for the Efficient Cleanup of Viscous Oil

Industrialization releases many high-viscosity oil pollutants into the environment, requiring a hydrophobic recyclable oil-absorbing material. Therefore, a self-heating and superhydrophobic melamine sponge (MS) by connecting polydimethylsiloxane (PDMS) was coated with functionalized molybdenum disulfide (MoS₂) nanosheets on a three-dimensional microstructure of a commercial MS (MoS₂/PDMS/MS) via a simple and low-cost dip-coating method. The prepared sponge showed a water contact angle of 151.8°, indicating that the modified sponge exhibited superhydrophobicity. Due to the addition of MoS₂, the modified sponge can convert light into heat, and its surface could be heated to 59.7 °C within 30 s. Because of the excellent MoS₂/PDMS/MS photothermal performance, the sponge could decrease the viscosity of the high-viscosity oil, absorbing the high-viscosity oil efficiently. After simultaneous thermal analysis and repeated compression tests, the modified sponge exhibited high thermochemical stability, mechanical property, and reusability. This superhydrophobic multifunctional sponge shows excellent potential for high-viscosity oil absorption.

Recent progress in nanomaterial-functionalized membranes for removal of pollutants

Membrane technology has gained tremendous attention for removing pollutants from wastewater, mainly due to their affordable capital cost, miniature equipment size, low energy consumption, and high efficiency even for the pollutants present in lower concentrations. In this paper, we review the literature to summarize the progress of nanomaterial-modified membranes for wastewater treatment applications. Introduction of nanomaterial in the polymeric matrix influences membrane properties such as surface roughness, hydrophobicity, porosity, and fouling resistance. This review also covers the importance of functionalization strategies to prepare thin-film nanocomposite hybrid membranes and their effect on eliminating pollutants. Systematic discussion regarding the impact of the nanomaterials incorporated within membrane, toward the recovery of various pollutants such as metal ions, organic compounds, dyes, and microbes. Successful examples are provided to show the potential of nanomaterial-functionalized membranes for regeneration of wastewater. In the end, future prospects are discussed to develop nanomaterial-based membrane technology.

Thermally Conductive and Superhydrophobic Polyurethane Sponge for Solar-Assisted Separation of High-Viscosity Crude Oil from Water

The rapid and effective separation of high-viscosity heavy crude oil from seawater is a worldwide challenge. Herein, an ultralow density, photothermal, superhydrophobic, and thermally conductive polyurethane/polyaniline/hexagonal boron nitride@Fe₃O₄/polyacrylic-oleic acid resin sponge (PU/PANI/h-BN@Fe₃O₄/AR) was fabricated with a water contact angle (WCA) of 158°, thermal conductivity of 0.76 W m^-1 K^-1, density of 0.038 g cm^-3, limited oxygen index (LOI) of 28.82%, and porosity of 97.97% and used for solar-assisted separation of high-viscosity crude oil from water. Photothermal components were composed of PANI and Fe₃O₄, while h-BN particles were used as thermally conductive and flame retardant fillers. Therefore, the illuminated sunlight irradiation on the modified sponge was converted to heat due to the activity of photothermal components. The produced heat was rapidly transferred to the environment due to the presence of h-BN for increasing the temperature of the high-viscosity crude oil and reducing oil viscosity that helped to promote its fluidity and effective absorption. The crude oil absorption capacity of this sponge increased from 4 to 57 g g^-1 under irradiation of a sunlight simulator (power: 1 sun: 1 kW m^-2) for 17 min due to oil viscosity reduction from 2.46 × 10⁴ to below 100 mPa s followed by an increase in the surface temperature from 26 to 89 °C. Also, the oil absorption capacity was evaluated in a static state (172 g g^-1 for chloroform), under different external magnetic fields (140.7 g g^-1 for gasoline), and in a continuous state, which was 65,100 times of its own weight in the gasoline filtration process. The PU/PANI/h-BN@Fe₃O₄/AR sponge exhibited excellent stability against 20 times of reusing, mechanical compression, abrasion, immersing in various pH solutions, seawater, and high temperature. In all, the results confirmed that the prepared sponge is an excellent absorbent for organic solvents and highly viscous crude oil in the absence and presence of sunlight irradiation.

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.

Polystyrene-Fe3O4-MWCNTs Nanocomposites for Toluene Removal from Water

In this research, multi-walled carbon nanotubes (MWCNTs) were functionalized by oxidation with strong acids HNO₃, H₂SO₄, and H₂O₂. Then, magnetite/MWCNTs nanocomposites were prepared and polystyrene was added to prepare polystyrene/MWCNTs/magnetite (PS:MWCNTs:Fe) nanocomposites. The magnetic property of the prepared nano-adsorbent PS:MWCNTs:Fe was successfully checked. For characterization, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and BET surface area were used to determine the structure, morphology, chemical nature, functional groups, and surface area with pore volume of the prepared nano-adsorbents. The adsorption procedures were carried out for fresh MWCNTs, oxidized MWCNTs, MWCNTs-Fe, and PS:MWCNTs:Fe nanocomposites in batch experiments. Toluene standard was used to develop the calibration curve. The results of toluene adsorption experiments exhibited that the PS:MWCNTs:Fe nonabsorbent achieved the highest removal efficiency and adsorption capacity of toluene removal. The optimum parameters for toluene removal from water were found to be 60 min, 2 mg nano-sorbent dose, pH of 5, solution temperature of 35 °C at 50 mL volume, toluene concentration of 50 mg/L, and shaking speed of 240 rpm. The adsorption kinetic study of toluene followed the pseudo-second-order kinetics, with the best correlation (R²) value of 0.998, while the equilibrium adsorption study showed that the Langmuir isotherm was obeyed, which suggested that the adsorption is a monolayer and homogenous.

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.

A facile approach to ultralight and recyclable 3D self-assembled copolymer/graphene aerogels for efficient oil/water separation

In this paper, a facile approach was developed for highly effective oil/water separation by incorporating of the dimethyldiallylammonium chloride acrylamide polymer (P(AM-DMDAAC)) into graphene aerogels. The functionalized 3D graphene aerogel integrated a series of excellent physical properties, including low density (11.4 mg/cm³), large specific surface area (206.591 m²/g), and great hydrophobicity (contact angle of 142.7°). The modified aerogel showed excellent adsorption capacity for oils and organic solvents (up to 130 g/g). The saturation can be reached in a short time and the adsorption capacity remained nearly unchanged after repeated heating cycles. Meanwhile, we found a simple method to achieve controlled wettability transition of P(AM-DMDAAC)/graphene aerogels (PGAs) by changing the pH values. The hydrophobic PGA prepared at pH 2.03 showed outstanding oil/water separation performance (130 g/g). As the pH increased, the oil adsorption capabilities of PGAs decreased slightly, but the adsorption performance for the hydrophilic organic dye was significantly improved. Therefore, as a recyclable and efficient water purification material, the sustainable and environment-friendly polymer-modified graphene aerogel has great application potential.

Advances in the applications of graphene adsorbents: from water treatment to soil remediation

Graphene, a novel carbon allotrope, is single-layered graphite with honeycomb lattice. Its unique structure endows graphene many outstanding physical/chemical properties and a large surface area, which are beneficial to its applications in many areas. The potential applications of graphene in pollution remediation are adsorption, membrane separation, catalysis, environmental analysis, and so on. The adsorption efficiency of graphene adsorbents largely depends on its surface area, porous structure, oxygen-containing groups and other functional groups, adsorption conditions, and also the properties of adsorbates. With appropriate modifications, graphene materials are mostly efficient adsorbents for organic pollutants (e.g. dyes, pesticides, and oils) and inorganic pollutants (e.g. metal ions, nonmetal ions, and gas). Since our first report of graphene adsorbents in 2010, plenty of studies have been dedicated to developing various graphene adsorbents and to evaluating their performance in treating contaminated water. Recently, there is a growing trend in graphene adsorbents that could be applied in soil remediation, where the situation is much more complicated than in aqueous systems. Herein, we review the design of graphene adsorbents for water treatment and analyze their potential in soil remediation. Several suggestions to accelerate the research on graphene-based soil remediation technology are proposed.

Temperature-triggered sensitive resistance transition of graphene oxide wide-ribbons wrapped sponge for fire ultrafast detecting and early warning

Fire prevention and safety of combustible materials is a global challenge. To reduce their high fire risk, traditional smoke detectors are widely used indoor via detecting smoke product after combustion; however, they usually show a long response time and limitation for outdoor use. Herein, we report a temperature-induced electrical resistance transition of graphene oxide wide-ribbon (GOWR) wrapped sponges to reliably monitor fire safety of the combustible materials. Novel rectangle-like GOWR sheets are synthesized from unzipping carbon nanofibers and used to fabricate GOWR wrapped melamine formaldehyde sponges with multi-functionalities, e.g. lightweight, good hydrophobicity, reversible compressibility, excellent acidic/alkaline tolerance and flame resistance. The GOWR sheets on the sponge skeleton can be in-situ thermally reduced once encountering a flame attack or abnormal high temperature, inducing a distinct transition in electrical resistance. Consequently, an ultrafast alarm response of ∼2 s to flame attack is triggered, and rapid fire early warning signals to abnormal high temperatures, e.g. ∼33 s at 300 °C, are achieved below ignition temperature of most combustible materials. This method drives substantial motivation and opportunity to develop advanced fire detection and early warning sensors for reducing the high fire risk of various combustible materials in outdoor applications.

ZnO-pHEMA Nanocomposites: An Ecofriendly and Reusable Material for Water Remediation

The design of new hybrid nanocomposites based on poly(2-hydroxyethylmethacrylate) (pHEMA) graphene oxide (GO) cryosponges, wherein ZnO nanolayers have been deposited to induce photocatalytic properties, is reported here. Atomic layer deposition at low temperature is specifically selected as the deposition technique to stably anchor ZnO molecules to the pendant polymer OH groups. Furthermore, to boost the pHEMA cryogel adsorption capability versus organic dyes, GO is added during the synthetic procedure. The morphology, the crystallinity, and the chemical composition of the samples are deeply investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction analyses, Fourier transform infrared spectroscopy, and thermogravimetric analysis. Swelling properties, mechanical performance, and adsorption kinetics models of the hybrid materials are also evaluated. Finally, the adsorption and photocatalytic performance are tested and compared for all of the samples using methylene blue as a dye. Particularly, the adsorption efficiency of ZnO/pHEMA and ZnO/pHEMA-GO nanocomposites, as well as their in situ regeneration via photocatalysis, renders such devices very appealing for advanced wastewater treatment technology.

Recycle of oil waste via hydrophobic sponge prepared from toner waste

In this paper a hydrophobic sponge was prepared by solvent free coating of thermosetting toner from a laser printer via simple heating. The sponge was used for oil-water mixture and emulsion separation. The sponge had good separation performance for the oil-water mixture. In dynamic oil recovery study, the sponge had a flux up to thousands L/(m²·h) for kerosene and n-hexane. For the water-in-petroleum emulsion with 60% water content, the final water content could be brought down to 1.7-5.0% after 2 cycles of operation. While for the water-in-kerosene emulsion with low water content of 10%, the recovered oil had water content below 1.0%. The study revealed a potential industrial utilization of toner waste, which was beneficial to the emission reduction, and a facile way for fast separation of light oil from water, which was beneficial to the oil waste treatment.

Surface modification of polymeric foams for oil spills remediation

In the last decade, a continuous increasing research activity is focused on the surface functionalization of polymeric porous materials for the efficient removal of oil contaminants from water. This work reviews the most significant recent studies on the functionalization of polyurethane and melamine foams, materials commonly reported for oil-water separation applications. After the identification of the key features of the foams required to optimize their oil removal performance, a wide variety of physicochemical treatments are described together with their effect on the oil absorption selectivity and oil absorption capacity, both critical parameters for the application of the foams in the remediation of oil spills. The efficiencies of the different functionalization processes on the same type of foams are compared, determining the main advantages and potentialities of each treatment and remediation procedure.