Direct Oil Recovery from Saturated Carbon Nanotube Sponges

Natural microfibrils/regenerated cellulose-based carbon aerogel for highly efficient oil/water separation

Cellulose-based carbon aerogels as biodegradable and renewable biomass materials have presented potential applications in oil/water separation. Herein, a novel carbon aerogel composed of natural microfibrils/regenerated cellulose (NM/RCA) was directly prepared by economical hardwood pulp as raw material using a novel co-solvent composed of deep eutectic solvent (DES) and N-methyl morpholine-N-oxide monohydrate (NMMO·H₂O). In addition, the morphology and structure of the filiform natural microfibers could be remained after carbonized at 400 ℃, which resulted in a low density (8-10 mg cm^-3), high specific surface area (768.89 m² g^-1) and high sorption capability. In addition, the aerogel exhibited high compressibility, outstanding elasticity, excellent fatigue resistance, and recyclability (80.5% height recovery after repeating 100 cycles at the strain of 80%). Due to the morphology and composition of the carbonized microfiber surface, the superhydrophobic materials with a water contact angle of 151.5°, could sorb various oils and organic solvents with 65-133 times its own weight and maintain 91.9% sorption capacity after 25 cycles. In addition, the aerogels could achieve the continuous separation of carbon tetrachloride (CCl₄) from water with a high flux rate of 11,718.8 L m^-2 h^-1. Therefore, our prepared NM/RCA aerogels are anticipated to have broad potential applications in oil purification and contaminant remediation.

Hydrophobic nanoporous carbon scaffolds reveal the origin of polarity-dependent electrocapillary imbibition

An engineered nanoporous carbon scaffold (NCS) consisting of a 3-D interconnected 85 nm nanopore network was used here as a model material to investigate the nanoscale transport of liquids as a function of the polarity and magnitude of an applied potential ('electro-imbibition'), all in 1 M KCl solution. A camera was used to track both meniscus formation and meniscus jump, front motion dynamics, and droplet expulsion, while also quantifying the electrocapillary imbibition height (H) as a function of the applied potential of the NCS material. Although no imbibition was seen over a wide range of potentials, at positive potentials (+1.2 V vs. the potential of zero charge (pzc)), imbibition was correlated with carbon surface electro-oxidation, as confirmed by both electrochemistry and post-imbibition surface analysis, with gas evolution (O₂, CO₂) seen visually only after imbibition was well underway. At negative potentials, vigorous hydrogen evolution reaction was observed at the NCS/KCl solution interface, well before imbibition began at -0.5 V_pzc, proposed to be nucleated by an electrical double layer charging-driven meniscus jump, followed by processes such as Marangoni flow, adsorption induced deformation, and hydrogen pressure driven flow. This study improves the understanding of electrocapillary imbibition at the nanoscale, being highly relevant in a wide range of multidisciplinary practical applications, including in energy storage and conversion devices, energy-efficient desalination, and electrical-integrated nanofluidics design.

Synthesis of hydrophilic carbon nanotube sponge via post-growth thermal treatment

Clean water is vital for healthy ecosystems, for human life and, in a broader sense, it is directly linked to our socio-economic development. Nevertheless, climate change, pollution and increasing world population will likely make clean water scarcer in the near future. Consequently, it becomes imperative to develop novel materials and more efficient ways of treating waste and contaminated water. Carbon nanotube (CNT) sponges, for example, are excellent in removing oleophilic contaminants; however, due to their super-hydrophobic nature, they are not as efficient when it comes to absorbing water-soluble substances. Here, by means of a scalable method consisting of simply treating CNT sponges at mild temperatures in air, we attach oxygen-containing functional groups to the CNT surface. The functionalized sponge becomes hydrophilic while preserving its micro- and macro-structure and can therefore be used to successfully remove toxic contaminants, such as pesticides, that are dissolved in water. This discovery expands the current range of applications of CNT sponges to those fields in which a hydrophilic character of the sponge is more suitable.

Bio-Based Aerogel Based on Bamboo, Waste Paper, and Reduced Graphene Oxide for Oil/Water Separation

In recent years, the discharge of industrial waste oil has increased and offshore oil leakage has occurred frequently, and thus water pollution has become a worldwide problem that attracts much attention. In this regard, a kind of oil-absorbing material with high oil-absorbing property and good mechanical property is urgently needed. Here, we reported a new type of aerogels with three-dimensional layered voids using natural bamboo powder, waste paper (WP), and graphene oxide (GO) as raw materials. The obtained aerogel had high adsorption capacity (87-121 g/g), compressibility, and high elasticity, which can separate oil from water and selectively absorb oil. This study provides not only a new treatment in agricultural waste treatment but also a facile, green, and low-cost approach to synthesize high-performance graphene-based oil absorbers, which might give us an effective solution for oil pollution of water resources worldwide.

The Era of Nanomaterials: A Safe Solution or a Risk for Marine Environmental Pollution?

In recent years, the application of engineered nanomaterials (ENMs) in environmental remediation gained increasing attention. Due to their large surface area and high reactivity, ENMs offer the potential for the efficient removal of pollutants from environmental matrices with better performances compared to conventional techniques. However, their fate and safety upon environmental application, which can be associated with their release into the environment, are largely unknown. It is essential to develop systems that can predict ENM interactions with biological systems, their overall environmental and human health impact. Until now, Life-Cycle Assessment (LCA) tools have been employed to investigate ENMs potential environmental impact, from raw material production, design and to their final disposal. However, LCA studies focused on the environmental impact of the production phase lacking information on their environmental impact deriving from in situ employment. A recently developed eco-design framework aimed to fill this knowledge gap by using ecotoxicological tools that allow the assessment of potential hazards posed by ENMs to natural ecosystems and wildlife. In the present review, we illustrate the development of the eco-design framework and review the application of ecotoxicology as a valuable strategy to develop ecosafe ENMs for environmental remediation. Furthermore, we critically describe the currently available ENMs for marine environment remediation and discuss their pros and cons in safe environmental applications together with the need to balance benefits and risks promoting an environmentally safe nanoremediation (ecosafe) for the future.

Superhydrophobic Self-Supporting BiOBr Aerogel for Wastewater Purification

This research was focused on the raw material level construction of bismuth oxybromide (BiOBr) catalysis-loaded 3D cross-linked network polyurethane (PU) foam via the in situ polymerization method. After modification of superhydrophobic polydivinylbenzene nanoparticles, the PU foam possessed excellent superhydrophobic stability. The larger selective absorption oil phase capacity depended on its macroporous structure, and the existence of catalyst BiOBr (the band gap energy was about 2.57 eV) among the PU foam played a crucial role in degrading water-soluble contaminants under visible light irradiation. In this article, the photocatalytic experiment results verify that it has remarkable recycle degradation ability (the degradation efficiency can reach ∼97%) and the capture experiments indicate that the uppermost active species is h⁺.

Robust Bifunctional Compressed Carbon Foam for Highly Effective Oil/Water Emulsion Separation

In this study, we report the pure compressed carbon foam (CCF) that offers a brand-new solution for separating emulsified oil/water mixtures. The CCF was fabricated by low-temperature carbonization of three-dimensional commercial melamine foam, which was then compressed without any further chemical modification. The CCF has amphiphilicity in air, underwater superoleophobicity, and underoil superhydrophobicity; therefore, it has been proved to be successfully utilized in highly emulsified oil-in-water and water-in-oil emulsions with excellent separation efficiencies, and it merely relies on gravity in the absence of external force. The CCF can also maintain its superwetting property under different harsh conditions, including strong acid, alkali, and salt solution conditions; this property offers great opportunities for widespread applications. Importantly, the CCF exhibits excellent permeability, separation efficiency, antifouling, and reusability performance. This novel CCF material has great potential application in handling oily wastewater owing to its low-cost raw materials, easily scaled-up preparation process, excellent antifouling property, and high separation capacity of materials.

Smart Sponge for Fast Liquid Absorption and Thermal Responsive Self-Squeezing

Liquid absorption and recycling play a crucial role in many industrial and environmental applications, such as oil spill cleanup and recovery, hemostasis, astronauts' urine recycling, and so on. Although many liquid absorbing materials have been developed, it still remains a grand challenge to achieve both fast absorption and efficient recycling in a cost-effective and energy-saving manner, especially for viscous liquids such as crude oil. A smart polyurethane-based porous sponge with aligned channel structure is prepared by directional freezing. Compared to common sponges with random porous structure, the as-prepared smart sponge has larger liquid absorption speed due to its lower tortuosity and stronger capillary ("tortuosity effect"). More importantly, the absorbed liquid can be remotely squeezed out due to a thermally responsive shape memory effect when the sponge is heated up. Such smart sponges with well-defined porous structure and thermal responsive self-squeezing capability have great potential in efficient liquid absorption and recycling.

Oxygenated Surface of Carbon Nanotube Sponges: Electroactivity and Magnetic Studies

We report the synthesis of nitrogen-doped carbon nanotube sponges (N-CNSs) by pyrolysis of solutions of benzylamine, ferrocene, thiophene, and isopropanol-based mixture at 1020 °C for 4 h using an aerosol-assisted chemical vapor deposition system. The precursors were transported through a quartz tube using a dynamic flow of H₂/Ar. We characterized the N-CNSs by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and thermogravimetric analysis. We found that isopropanol, isopropanol-ethanol, and isopropanol-acetone as precursors promote the formation of complex-entangled carbon fibers making knots and junctions. The N-CNSs displayed an outstanding oxygen concentration reaching a value of 9.2% for those synthesized with only isopropanol. We identified oxygen and nitrogen functional groups; in particular, the carbon fibers produced using only isopropanol exhibited a high concentration of ether groups (C-O bonds). This fact suggests the presence of phenols, carboxyl, methoxy, ethoxy, epoxy, and more complex functional groups. Usually, the functionalization of graphitic materials is carried out through aggressive acid treatments; here, we offer an alternative route to produce a superoxygenated surface. The understanding of the chemical surface of these novel materials represents a huge challenge and offers an opportunity to study complex oxygen functional groups different from the conventional quinone, carboxyl, phenols, carbonyl, methoxy, ethoxy, among others. The cyclic voltammetry measurements confirmed the importance of oxygen in N-CNSs, showing that with high oxygen concentration, the highest anodic and cathodic currents are displayed. N-CNSs displayed ferromagnetic behavior with an outstanding saturation magnetization. We envisage that our sponges are promising for anodes in lithium-ion batteries and magnetic sensor devices.

Flame-Synthesis of Carbon Nanotube Forests on Metal Mesh Structure: Dependence, Morphology, and Application

Multi-walled carbon nanotubes (MWCNTs) in the form of “forests” were synthesized directly on the surface of stainless steel (SS) mesh from ethanol flame volume. The growth dependence of the MWCNT forests on the porosity of SS mesh substrate and the morphologies and growth mechanism of the MWCNT forests were investigated in detail by a combination of turbulent flow simulation, scanning electron microscopy (SEM), transmission electron microscope (TEM), and Raman and X-ray diffraction (XRD) spectroscopy. The growth height of the MWCNT forests exhibited a strong dependence on the flame gas flow rate controlled by the porosity of SS mesh substrate, and the maximum averaged height of the MWCNT forests reached 34 μm. Most MWCNTs grew perpendicularly on the surface of SS wires, and some branch, welded, and spiral structures were observed by SEM and TEM. The MWCNT-decorated mesh was used as a novel heating element to weld glass-fabric-reinforced polyetherimide (GF/PEI) thermoplastics. We found that the maximum tensile lap-shear strength (LSS) of the welded joints could reach 39.21 MPa, an increase of 41% in comparison with that of conventional SS mesh-based joints.

Tailoring the Performance of Graphene Aerogels for Oil/Organic Solvent Separation by 1-Step Solvothermal Approach

Ultra-light eco-friendly graphene oxide (GO)-based aerogels are reported by simple one-step solvothermal self-assembly. The effect of varying parameters such as C/O ratio of GO; reducing agent amount; temperature; and duration on the properties of the aerogels was studied. The structural and vibrational features and hydrophobic surface properties of the obtained aerogels were obtained by XRD; FTIR; XPS; Raman; SEM; and contact angle measurements. The effect of synthesis conditions on the engine oil and organic solvent absorption properties was assessed. The results indicated that the lower the C/O ratio of GO, the better the absorption properties, with the best performance for oil uptake reaching 86 g g⁻¹. The obtained results indicate the approach based on ice-templating and the tailoring of oxygen content in GO make the resulting aerogels potential candidates for use in oil spill and organic solvent treatments.

Conductive 3D sponges for affordable and highly-efficient water purification

Effective, affordable and low energy water purification technologies are highly desirable to address the current environmental issues. In this study, we developed a low-cost method to achieve efficient organic pollutants degradation by incorporating conductive nanomaterials (i.e., carbon nanotubes, CNTs) to assist electro-oxidation, leading to an efficient conductive nano-sponge filtration device. The integration of electrochemistry has significantly improved the performance of the sponge-based device to adsorb and oxidize organic compounds in aqueous solution. In particular, CNT materials could serve as both high-performance electro-catalysts for pollutant degradation and conductive additives that make polyurethane sponges highly conductive. On the other hand, the polyurethane sponge could work as a low-cost and highly porous matrix that could effectively host these CNT conductors. The conductive sponge can be easily fabricated by a simple dying based approach. The as-fabricated gravity fed device could effectively oxidize two model organic compounds (i.e., >92% antibiotic tetracycline and >94% methyl orange) via a single pass through the conductive sponge under the optimized experimental conditions (e.g., [Na₂SO₄] = 10 mmol L^-1, [CNT] = 0.3 mg mL^-1, and [SDBS] = 2.0 mg mL^-1). We have achieved >88% degradation efficiency for the antibiotic tetracycline within 6 h of continuous operation with an average electro-oxidation flux of 0.82 ± 0.05 mol h^-1 m^-2 and an energy requirement of 1.0 kW h kg^-1 COD or <0.02 kW h m^-3. These promising data make our CNT-sponge filtration device attractive for affordable and effective water purification.

Bioinspired Assembly of Carbon Nanotube into Graphene Aerogel with "Cabbagelike" Hierarchical Porous Structure for Highly Efficient Organic Pollutants Cleanup

Nowadays, physical absorption has become a feasible method offering an efficient and green route to remove organic pollutants from the industrial wastewater. Inspired by polydopamine (PDA) chemistry, one-dimensional PDA-functionalized multiwalled carbon nanotubes (MWCNT-PDA) were creatively introduced into graphene aerogel framework to synthesize a robust graphene/MWCNT-PDA composite aerogel (GCPCA). The whole forming process needed no additional reducing agents, significantly reducing the contamination emissions to the environment. The GCPCA exhibited outstanding repeatable compressibility, ultralight weight, as well as hydrophobic nature, which were crucial for highly efficient organic pollution absorption. The MWCNTs in moderate amounts can provide the composite aerogels with desirable structure stability and extra specific surface area. Meanwhile, the eventual absorption performance of GCPCAs can be improved by optimizing the microporous structure. In particular, a novel "cabbagelike" hierarchical porous structure was obtained as the prefreezing temperature was decreased to -80 °C. The miniaturization of pore size around the periphery of GCPCA enhanced the capillary flow in aerogel channels, and the super-absorption capacity for organic solvents was up to 501 times (chloroform) its own mass. Besides, the GCPCAs exhibited excellent reusable performance in absorption-squeezing, absorption-combustion, and absorption-distillation cycles according to the characteristic of different organic solvents. Because of the viable synthesis method, the resulting GCPCAs with unique performance possess broad and important application prospects, such as oil pollution cleanup and treatment of chemical industrial wastewater.

Selective surface tension induced patterning on flexible textiles via click chemistry

A solid surface commonly forms two wetting modes by alternating the type of the liquids, i.e. wetting and nonwetting. Here we report that a textile can be programmed to exhibit three wetting modes by simply alternating the surface tension of the liquids, they are in turn, wetting, selective wetting and nonwetting. The hidden patterns are prepared via a combination of wet chemical etching and two-step UV-induced thiol-ene click chemistry to graft low-surface-tension thiols and high-surface-tension thiols, respectively, on the textile surface. The as-prepared flexible textiles possess the nonwetting and wetting properties of the high-surface-tension liquids, such as water and glycerol, and the low-surface-tension liquids, such as decane and ethanol, respectively. Furthermore, the selective wetting behavior can be revealed only if the surface tension of the liquids is within a narrow range of approximately 44.8 mN m^-1 to 28.1 mN m^-1, such as N,N-dimethylformamide and acetonitrile. In addition, the as-patterned textiles demonstrated high mechanical and chemical stability with long-term and repeated usage, which implies their high potential to act as novel encoded information carrier materials for flexible and textile-based devices.