Versatile Fabrication of Ultralight Magnetic Foams and Application for Oil–Water Separation

Ultralow-density (<10 mg cm^–3) materials have many important technological applications; however, most of them were fabricated using either expensive materials or complicated procedures. In this study, ultralight magnetic Fe₂O₃/C, Co/C, and Ni/C foams (with a density <5 mg cm^–3) were fabricated on the centimeter scale by pyrolyzing commercial polyurethane sponge grafted with polyelectrolyte layers based on the corresponding metal acrylate at 400 °C. The ultralight foams consisted of 3D interconnected hollow tubes that have a diameter of micrometer and nanoscale wall thickness, forming hierarchical structures from macroscopic to nanometer length scales. More interesting was that the wall thickness and morphology of the microtubes could be tuned by controlling the concentrations of acrylic acid and metallic cations. After modification with low-surface-energy polysiloxane, the ultralight foams showed superhydrophobicity and superoleophilicity, which quickly and selectively absorbed a variety of oils from a polluted water surface under magnetic field. The oil absorption capacity reached 100 times of the foams’ own weight, exhibiting one of the highest values among existing absorptive counterparts. By controlling the composition and conformation of the grafted polyelectrolyte layers, the present approach is extendable to fabricate a variety of ultralow-density materials desirable for absorptive materials, electrode materials, catalyst supports, <i>etc</i>

Mussel-Inspired Direct Immobilization of Nanoparticles and Application for Oil–Water Separation

Immobilization of various nanoparticles onto complex 2D or 3D macroscopic surface is an important issue for nanotechnology, but the challenge remains to explore a facile, general and environmentally friendly method for achieving this goal. Taking inspiration from the adhesion of marine mussels, we reported here that oxide nanoparticles of different compositions and sizes were directly and robustly anchored on the surface of monolithic foams ranging from polymer to metals in an aqueous solution of dopamine. The effective immobilization of the nanoparticles was strongly dependent on the oxidation of dopamine, which could be tuned by either pH or by adding <i>n</i>-dodecanethiol. Interestingly, the thiol addition not only allowed the immobilization to take place in a wide pH range, but also led to superhydrophobicity of the resulting foams. Application of the superhydrophobic foams was illustrated by fast and selective collecting oils from water surface. Because catecholic derivatives exhibit high affinity to a variety of substances, the present strategy might be extendable to fabricate hybrid nanomaterials desirable for self-cleaning, environmental protection, sensors and catalysts, and so forth

Three-Dimensionally Macroporous Fe/C Nanocomposites As Highly Selective Oil-Absorption Materials

In this study, three-dimensionally macroporous Fe/C nanocomposites were investigated as highly selective absorption materials for removing oils from water surface. The macroporous nanocomposites were synthesized by sintering a mixture of closely packed polystyrene microspheres and ferric nitrate precursor. These nanocomposites exhibited superhydrophobic and superoleophilic properties without the modification of low-surface-energy chemicals. And the pore size of the nanocomposites, which is crucial for the oil-absorption capacity, was tuned by varying the diameter of polystyrene microspheres. The macroporous nanocomposites fast and selectively absorbed a wide range of oils and hydrophobic organic solvents on water surface, and the removal of the absorbed oils from the water surface was readily achieved under a magnetic field. Moreover, the nanocomposites still kept highly hydrophobic and oleophilic characteristics after repeatedly removing oils from water surface for many cycles. Because of frequently occurring environmental pollution arising from oil spills and chemicals leakage, the results of this study might offer a kind of efficient and selective absorbent materials for removing oils and nonpolar organic solvents from the surface of water

Mussel-Inspired Self-Healing of Ultralight Magnetic Frameworks

Ultralight materials have many important applications, but most of them are unable to spontaneously recover their microstructure and functions after physical damage or abuse. Here we report an ultralight magnetic framework that can repair its broken microstructure autonomously via a mussel-inspired strategy. The self-healable framework consists of three-dimensionally (3D) interconnected Fe₃O₄/C microtubes wrapped with nanoshells of nitrocatechol-substituted chitosan. The framework spontaneously recovers its configuration integrity and mechanical properties during all 6 breaking/healing cycles through pH-induced coordination between Fe³⁺ and catecholic moieties. On the basis of the self-healable property, the framework can even be tailored into complicated patterns. The investigation offers a strategy to fabricate multifunctional ultralight materials with a self-healable property and tailorability, which have potential applications in adsorption, energy-storage, and catalysis, and so on

Juncus Pith: A Versatile Material for Automatic and Continuous Separation of Various Oil–Water Mixtures

It is extremely important to develop a facile and versatile strategy for effectively separating various oil–water mixtures. Here we report that the pith of juncus (which is also known as common rushes) can serve as a versatile material for oil–water separation. Under the action of capillary force and gravity, a piece of pith automatically and continuously separates not only immiscible oil–water mixtures but also surfactant-stabilized water-in-oil emulsions with high selectivity and desirable flux. The separation strategy is cost-effective and energy-efficient because it avoids the switch of wettability, the input of additional energy, and the use of low-surface-energy chemicals or special equipment. The unique capability of the pith is mainly attributed to the presence of three-dimensionally (3D) reticular texture with highly hydrophobic and superoleophilic properties. Owing to its easy availability and high effectiveness, juncus might be a promising material aiming for oil–water separation, water treatment, and purification of solvent or fuel, and so on

Constructing Robust Liquid Marbles for Miniaturized Synthesis of Graphene/Ag Nanocomposite

Miniaturized synthesis is attracting much attention due to many potential applications; a challenge remains in exploring versatile microreactors capable of producing pure products. In this study, we reported a kind of thermally robust liquid marbles and their application for miniaturized synthesis of graphene/Ag nanocomposite. The liquid marbles were constructed by using superhydrophobic Fe₃O₄/C microsheets as encapsulating agents. Results revealed that the morphology of the encapsulating agent as well as the humidity of atmosphere strongly affected the robustness of liquid marbles at elevated temperature. The resulting graphene/Ag nanocomposite showed one of the best catalytic characteristics for 4-nitroaniline reduction among the reported catalysts. The findings of this study not only offer an alternative insight into the stability of liquid marbles at elevated temperature but also provide a facile strategy for miniaturized synthesis

Why Superhydrophobicity Is Crucial for a Water-Jumping Microrobot? Experimental and Theoretical Investigations

This study reported for the first time a novel microrobot that could continuously jump on the water surface without sinking, imitating the excellent aquatic locomotive behaviors of a water strider. The robot consisted of three supporting legs and two actuating legs made from superhydrophobic nickel foam and a driving system that included a miniature direct-current motor and a reduction gear unit. In spite of weighing 11 g, the microrobot jumped 14 cm high and 35 cm long at each leap. In order to better understand the jumping mechanism on the water surface, the variation of forces exerted on the supporting legs was carefully analyzed and calculated based on numerical models and computational simulations. Results demonstrated that superhydrophobicity was crucial for increasing the upward force of the supporting legs and reducing the energy consumption in the process of jumping. Although bionic microrobots mimicking the horizontal skating motions of aquatic insects have been fabricated in the past years, few studies reported a miniature robot capable of continuously jumping on the water surface as agile as a real water strider. Therefore, the present finding not only offers a possibility for vividly imitating and better understanding the amazing water-jumping capability of aquatic insects but also extends the application of porous and superhydrophobic materials to advanced robotic systems

A Smart “Strider” Can Float on Both Water and Oils

Aquatic devices that can work on both water and oils have great scientific and practical significance, but the challenge remains in developing novel materials with excellent repellence to both water and oils. Here, we report that an artificial “strider” can float on both water and oils by using supporting legs with ultraviolet (UV) switchable wettability. The legs were fabricated by immobilizing TiO₂ nanoparticles and <i>n</i>-dodecanethiol onto copper foams via a simple mussel-inspired process. At ambient conditions, the strider floated freely on a water surface, but it dived in water and then stood stably at the interface of water/CHCl₃ after UV illumination for 2 h. The reason for this unique behavior is that the legs changed their wettability from superhydrophobicity to underwater superoleophobicity after the illumination. It was revealed that the micro/nanohierarchical structures and photosensitivity of the immobilized TiO₂ nanoparticles accounted for the switchable wettability and large supporting force of the legs. The findings of this study offer an alternative strategy for fabricating smart aquatic devices that might be used for water environment protection, water resource surveillance, oil spill cleanup, and so on

Remote Manipulation of a Microdroplet in Water by Near-Infrared Laser

Facile manipulation of a tiny liquid droplet is an important but challenging issue for many miniaturized chemical and biological systems. Here we report that a microdroplet can be readily and remotely manipulated in aqueous environments under ambient conditions. The droplet is encapsulated with photothermal nanoparticles to form a liquid marble, and subsequently irradiated with a near-infrared (NIR) laser. The marble is able to ascend, shuttle, horizontally move, and even suspend in water by simply controlling the laser irradiation. Moreover, filling and draining of the marble can also be conducted on the water surface for the first time. This facile manipulation strategy does not use complicated nanostructures or sophisticated equipment, so it has potential applications for channel-free microfluidics, smart microreators, microengines, microrobots, and so on

Stabilizing Li Metal Anodes through a Novel Self-Healing Strategy

Poor stability is a long-standing problem preventing the practical application of Li metal anodes, which is fundamentally attributed to their fragile solid electrolyte interphase (SEI) layers that are intrinsically neither adaptable to the dynamic volume change nor self-healable after breakage. Here a Li metal anode is effectively stabilized by in situ integrating its SEI layer into a self-healable polydimethylsiloxane (PDMS) network cross-linked via imine bonding. The self-healing network enables the integrated SEI layer to readily accommodate the volume change but also to repair itself after breaking. Consequently, the resulting anode exhibits excellent cycling stability and a dendrite-free morphology. In a Li/LiFePO₄ full cell, this strategy leads to capacity retention up to 99% and a Coulombic efficiency >99.5% after 300 cycles. Our investigation provides a novel self-healing strategy for developing stable Li-metal anodes aiming at high energy-density batteries