One-step fabrication of highly stable, superhydrophobic composites from controllable and low-cost PMHS/TEOS sols for efficient oil cleanup

Porous lignin-based composites for oil/water separation: A review

Frequent oceanic oil spill incidents and the discharge of industrial oily wastewaters have caused serious threats to environments, food chains and human beings. Lignin wastes with many reactive groups exist as the byproducts from bioethanol and pulping processing industries, and they are either discarded as wastes or directly consumed as a fuel. To make full use of lignin wastes and simultaneously deal with oily wastewaters, porous lignin-based composites have been rationally designed and prepared. In this review, recent advances in the preparation of porous lignin-based composites are summarized in terms of aerogels, sponges, foams, papers, and membranes, respectively. Then, the mechanisms and the application of porous lignin-based adsorbents and filtration materials for oil/water separation are discussed. Finally, the challenges and perspectives of porous lignin-based composites are proposed in the field of oil/water separation. The utilization of abundant lignin wastes can replace fossil resources, and meanwhile porous lignin-based composites can be used to efficiently treat with oily wastewaters. The above utilization strategy opens an avenue to the rational design and preparation of lignin wastes with high-added value, and gives a possible solution to use lignin wastes in a sustainable and environmentally friendly way.

Up to Date Review of Nature-Inspired Superhydrophobic Textiles: Fabrication and Applications

In recent years, with the rapid development of the economy and great progress in science and technology, people have become increasingly concerned about their quality of life and physical health. In order to pursue a higher life, various functional and biomimetic textiles have emerged one after another and have been sought after by people. There are many animal and plant surfaces with special wettability in nature, and their unique "micro-nano structures" and low surface energy have attracted extensive attention from researchers. Researchers have prepared various textiles with superhydrophobic features by mimicking these unique structures. This review introduces the typical organisms with superhydrophobicity in nature, using lotus, water strider, and cicada as examples, and describes their morphological features and excellent superhydrophobicity. The theoretical model, commonly used raw materials, and modification technology of superhydrophobic surfaces are analyzed. In addition, the application areas and the current study status of superhydrophobic surfaces for textiles are also summarized. Finally, the development prospects for superhydrophobic textiles based on bionic technology are discussed.

Evaporation Dynamics of Surfactant-Laden Droplets on a Superhydrophobic Surface: Influence of Surfactant Concentration

Surfactant-laden sessile droplet evaporation plays a crucial role in a variety of omnipresent natural and technological applications, such as drying, coating, spray, and inkjet printing. Surfactant molecules can adsorb easily on interfaces and, hence, destructively ruin the useful gas-trapping wetting state (i.e., Cassie-Baxter, CB) of a drop on superhydrophobic (SH) surfaces. However, the influence of surfactant adsorption or concentration on evaporation modes has been rarely investigated so far. Here, we investigate the evaporation dynamics of aqueous didodecyldimethylammonium bromide (DDAB) sessile droplet on SH surfaces made of regular hydrophobic micropillars, with various dimensionless surfactant concentrations (C_S), primarily using experiments. We find that all drops initially form a CB state with a pinned base radius and evaporate in a mode of constant contact radius (CCR). Water and low-C_S (=0.02) drop subsequently evaporate with a constant contact angle (CCA) mode, followed by a CCR mode and, eventually, a mixed-mode. By contrast, high-C_S (of 0.25-1) droplets undergo a complex mixed mode, with rapidly increasing base radius, and finally a mixed mode, with slowly decreasing base radius and contact angle. The experimental data reveal that contact-angle-dependent evaporative mass flux, ṁ, collapses onto a nearly universal curve depending on C_S. For the low-C_S (of 0-0.25) drops, ṁ is lower and consistent with an evaporative cooling model, whereas high-C_S (of 0.5-1) droplets are consistent with a pure vapor-diffusive model. We further show that the critical C_S delineating these two evaporative models correlates with saturated surfactant adsorption on both liquid-solid and liquid-vapor interfaces.

Effect of a Cationic Surfactant on Droplet Wetting on Superhydrophobic Surfaces

We experimentally and theoretically examine the influence of a double-chain cationic surfactant, didodecyldimethylammonium bromide (DDAB), on the wetting states and contact angles on superhydrophobic (SH) surfaces made of hydrophobic microcylinders. We use two types of micropatterns of different surface roughness, r, and packing fraction, ϕ, and vary nine dimensionless surfactant concentrations (C_S), normalized by the critical micelle concentration (CMC), in the experiments. At low C_S, some of the surfactant-laden droplets are in a gas-trapping, Cassie-Baxter (CB) state on the high-roughness microstructures. In contrast, some droplets are in a complete-wetting Wenzel (W) state on the low-roughness microtextures. We found that the contact angle of CB drops can be well predicted using a thermodynamic model considering surfactant adsorption at the liquid-vapor (LV) and solid-liquid (SL) interfaces. At high C_S, however, all of the DDAB drops wet in a Wenzel mode. Based on a Gibbsian thermodynamic analysis, we find that for the two types of superhydrophobic surfaces used, the Wenzel state has the lowest thermodynamic energy and thus is more favorable theoretically. The CB state, however, is metastable at low C_S due to a thermodynamic energy barrier. The metastable CB wetting state becomes more stable on the SH microtextures with greater ϕ and r, in agreement with our experimental observations. Finally, we generalize this surface-energy analysis to provide useful designs of surface parameters for a DDAB-laden surfactant droplet on the SH surface with a stable and robust CB state.

A less harmful system of preparing robust fabrics for integrated self-cleaning, oil-water separation and water purification

Although the development of constructing oil-water separation materials is quick, the defects of using harmful regents, weak stability and single function still exist. Here, we report an effective and less-harmful system with poly-dimethylsiloxane (PDMS)/ZnO composite solution to fabricate robust superhydrophobic surfaces for oil-water separation and removal of organic pollutant. The obtained samples were characterized by a range of instruments. The water contact angle (WCA) of coated cotton was 155.6°, which attributed to the synergetic effect of low surface energy of PDMS and roughness of ZnO nanoparticles. The coated cotton was tolerant to mechanical damage, various corrosive solvents and temperature conditions. The emphasis of this study is the combination of superhydrophobicity and photocatalysis, resulting in multifunctional cotton with dual self-cleaning properties, outstanding oil-water separation ability and efficient water purification property. When utilized a simple laboratory facility, the cotton could separate water from oil-water mixture with a high efficiency (99.3%). Furthermore, the dyed water could be purified with coated cotton through photocatalysis under UV light and became colorless. Meanwhile, this mild and facile method could also be utilized to modify other porous substrates, such as PET, silk, non-woven and sponge. Therefore, the characteristics of environmental protection and easy operation make this cotton a desirable candidate for extensive applications in self-cleaning, oil-water separation and water purification.

One-pot fabrication of superhydrophobic and flame-retardant coatings on cotton fabrics via sol-gel reaction

Waterproof and flame-retardant fabrics are widely utilized in many fields, such as automotive interiors, indoor decorations, outdoor clothing and tents. Herein, a facile one-pot sol-gel approach was developed to construct superhydrophobic and flame-retardant (SFR) coatings on cotton fabrics. The cotton fabric was activated by O₂ plasma and then immersed into the ethanol suspension containing tetraethoxysilane (TEOS), hydroxyl-terminated polydimethylsiloxane (HPDMS) and ammonium polyphosphate (APP). The hydrogen bonding interaction between APP and cellulose motivated the APP to attach to the cotton fibers during the initial stirring process. After the addition of ammonia, the in situ sol-gel reaction of TEOS and HPDMS was initiated to generate polydimethylsiloxane-silica hybrid (PDMS-silica). The micro-nano structured composite coating on cotton fabric was successfully fabricated by the PDMS-silica and APP. The SFR cotton fabric showed outstanding durability and self-cleaning ability with a water contact angle (WCA) above 160°. When exposed to fire, the SFR cotton fabric quickly charred to extinguish the fire by generating a dense intumescent char layer under the physical barrier effect of PDMS-silica and the intumescent flame-retardant effect of APP. This one-pot approach for fabricating SFR cotton fabric is simple, cost-effective and timesaving, demonstrating significant advantages in practical production.

Ultraviolet-Durable Superhydrophobic Nanocomposite Thin Films Based on Cobalt Stearate-Coated TiO2 Nanoparticles Combined with Polymethylhydrosiloxane

Ultraviolet (UV)-durable superhydrophobic nanocomposite thin films have been successfully fabricated on aluminum substrates by embedding cobalt stearate (CoSA)-coated TiO₂ nanoparticles in a hydrophobic polymethylhydrosiloxane (PMHS) matrix (PMHS/TiO₂@CoSA) using the sol-gel process. When compared to the sharp decrease of water contact angle (WCA) on the superhydrophobic PMHS/TiO₂ thin films, the PMHS/TiO₂@CoSA superhydrophobic thin films exhibited a nearly constant WCA of 160° under continuous UV irradiation for more than 1 month. The designed scheme of the TiO₂@CoSA core-shell structure not only increased the hydrophobic properties of the TiO₂ nanoparticle surface but also confined the photocatalytic efficiency of TiO₂ nanoparticles. A plausible model has been suggested to explain the UV-durable mechanism of the superhydrophobic nanocomposite thin films based on PMHS/TiO₂@CoSA. Furthermore, the elongated lifetime in the exposure of the solar light imparts this superhydrophobic nanocomposite thin film with potential practical applications where UV-resistant properties are emphasized including corrosion-resistant building walls, anti-icing airplanes, self-cleaning vehicles, and so forth.

Recyclable Cu(i)/ZrSBA-15 prepared via a mild vapor-reduction method for efficient thiophene removal from modeled oil

Recyclable Cu(i)/ZrSBA-15 composites prepared via a controllable and effective methanol vapor-reduction method exhibited excellent adsorption capacity for the removal of thiophene (29.9 mg g⁻¹).

Advanced Sorbents for Oil-Spill Cleanup: Recent Advances and Future Perspectives

Oil sorbents play a very important part in the remediation processes of oil spills. To enhance the oil-sorption properties and simplify the oil-recovery process, various advanced oil sorbents and oil-collecting devices based on them have been proposed recently. Here, we firstly discuss the design considerations for the fabrication of oil sorbents and describe recently developed oil sorbents based on modification strategy. Then, recent advances regarding oil sorbents mainly based on carbon materials and swellable oleophilic polymers are also presented. Subsequently, some additional properties are emphasized, which are required by oil sorbents to cope with oil spills under extreme conditions or to facilitate the oil-collection processes. Furthermore, some oil-collection devices based on oil sorbents that have been developed recently are shown. Finally, an outlook and challenges for the next generation of oil-spill-remediation technology based on oil-sorbents materials are given.

Monolithic magnetic carbonaceous beads for efficient Cr(vi) removal from water

Alginate-derived magnetic monolithic carbonaceous beads were synthesized for the first time, aiming for efficient Cr(vi) removal, easy recovery and reusability.

Simple and eco-friendly fabrication of superhydrophobic textile for oil/water separation

Superhydrophobic and superoleophilic material was successfully prepared by the coating of Polyvinyl alcohol (PVA) onto the surface of cotton textile and subsequent hydrophobic modification. The formation of PVA with rough structure and hydrophobicity was confirmed with scanning electron microscopy and investigation of the wetting behavior of water on the textile. The coated textile is water repellant and can be used as a material for separating various oil/water mixture with a high separation efficiency up to 91%. Due to its simple fabrication process, low cost, excellent recyclability and durability, and high separation efficiency, the as-prepared textile can be considered as promising material for practical oil/water separation.

Sodium alginate-based magnetic carbonaceous biosorbents for highly efficient Cr(vi) removal from water

A novel magnetic alginate-based biosorbent, aiming for efficient removal of Cr(vi) from aqueous system, was successfully synthesized.