3D-Printed Anti-Fouling Cellulose Mesh for Highly Efficient Oil/Water Separation Applications

Lignin-Based Direct Ink Printed Structural Scaffolds

3D printing of lignocellulosic biomass (cellulose, hemicellulose, and lignin) has attracted increasing attention by using this abundant, sustainable, and ecofriendly material. While cellulose can be easily tailored into a highly viscous ink for 3D printing, after solvent evaporation, the final printed structures become highly porous, fragile, and easily fall apart in water due to its hydrophilic nature. Lignin, another crucial component of natural lignocellulose, has not yet been reported for ink printing due to its unfavorable rheological behavior. Herein, a low-cost direct ink printing strategy is developed to fabricate lignin-based 3D structures with lignin no further refined and a more compact microstructure as well as different functionalities compared with printed cellulose. By using a soft triblock copolymer as the crosslinking agent, the rheology of lignin-based inks can be adjusted from soft to rigid, and even enables vertical printing which requires stiff and self-supporting features. The lignin-based inks contain less water (≈40 wt%) and exhibit a much denser, stiffer structure, resulting in a wet tensile strength of ≈30 MPa, compared to only ≈0.6 MPa for printed cellulose. In addition, the unique macromolecular structure of lignin also demonstrates significantly improved stability in water and under heat, as well as UV-blocking performance.

Ultrafast Fabrication of Metal-Organic Framework-Functionalized Superwetting Membrane for Multichannel Oil/Water Separation and Floating Oil Collection

Traditional methods for oil/water separation suffer from many tricky problems such as low efficiency, high energy consumption, and difficulties in recycling and reusing. To address these hurdles, we developed a metal-organic framework-coated superwetting membrane for multichannel oil/water separation and collection of floating oils. The dip-coating method adopted in this paper is extremely flexible in manipulation and can be completed within 1 h under a low temperature without any assistance of high pressure. Interestingly, the strategy of fabricating superwetting membrane mainly includes introducing vital interlayers of Cu(OH)₂ nanowires, which not only construct the favorable hierarchical structures but also act as partly sacrificed templates for further growth of hydrophilic MOF nanowhiskers. In virtue of the high flexibility of the as-prepared mesh, this superwetting membrane can be applied for multichannel oil/water separation including gravity-driven oil/water separation, continuous oil/water separation, and floating oil collection. Moreover, the separation efficiency and flux of the superwetting membrane keep high and stable under multiple separation cycles. This study paves the way for a fast and facile preparation of a superwetting membrane with high applicability for multiple oil/water separation.

Superhydrophobic Nickel-Electroplated Carbon Fibers for Versatile Oil/Water Separation with Excellent Reusability and High Environmental Stability

Superhydrophobic filtrating materials have been widely developed for rapid removal or collection of oils from oil/water mixture due to the increasing water pollution caused by oil spills and oil-contaminated wastewater. However, poor reusability, superhydrophobic failure in harsh environments, and that only heavy oil or light oil was separated from water seriously restricted their practical application. Herein, superhydrophobic carbon fibers were first fabricated using a novel nickel electroplating for versatile oil/water separation with excellent reusability and high environmental stability. The interconnected nanometer-scale nickel grains formed on the micrometer-scale fibers and fluoroalkylsilane molecules enabled the fibers to be superhydrophobic with the water contact angle (CA) of ∼159.1° and superoleophilic with the oil CA of ∼0°. The nickel coating contributed to the improvement of the bonding strength, tensile strength, and oxidation resistance of the fibers. The as-prepared fibers could be applied for the separation of heavy or light oil/water mixtures with separation efficiencies above 99.1%, during which the oil content in the separated water all remained below 78 ppm. The fibers also realized the highly efficient separation of dichloromethane and various harsh environmental solutions such as hot water, acid, alkali, and salt. The superhydrophobicity of the fluorinated nickel-coated carbon fibers still remained even after 100 cycles of separation and 24 months of storage in air, demonstrating outstanding durability of the fibers. These novel superhydrophobic carbon fibers had promising potentials for versatile oil/water separation in practical applications.

Structure and properties of thermomechanically processed chitosan/carboxymethyl cellulose/graphene oxide polyelectrolyte complexed bionanocomposites

Bionanocomposites of chitosan and chitosan/carboxymethyl cellulose (CMC) polyelectrolyte complexed materials with graphene oxide (GO) or reduced graphene oxide (rGO) were prepared by thermomechanical processing with excellent levels of dispersion. While GO has a greater affinity with the chitosan polycation, rGO had a more pronounced effect on properties resulting in increased tensile strength, Shore D hardness, and thermal stability of both matrices. Although GO is more hydrophilic than rGO, the former increased more effectively the surface hydrophobicity of the biocomposites regardless of matrix type. GO and rGO changed the α-transition of the biocomposites in a similar manner. The electrochemical properties of the biocomposites were influenced by both nanofiller type and matrix. This research revealed that inclusion of 2D carbon nanomaterials can alter biopolymer interactions and that the phase structure of the biopolymer blend may play a more important role than nanofiller-matrix interactions in determining the overall properties of these bionanocomposites.

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.

Preparation of cellulose-coated cotton fabric and its application for the separation of emulsified oil in water

Cellulose is a natural material with dissolution-regeneration property and numerous hydrogen bonds in the molecule. By utilizing these properties, this paper reported the development of a multi-functional fabric consisting of cellulose and commercial cotton fabric. The morphology, mechanical and thermal properties along with the oil-water separation performance of the developed material were studied. The results showed that the cellulose dissolved in NaOH/urea solution was regenerated in a salt solution, and attached tightly onto the cotton fabric, forming a sandwich structure for the material. Such modification significantly enhanced the strength, thermal stability and hydrophilic performance of the fabrics. Interestingly, the prepared material exhibited a unique underwater oleophobic performance, and had the capability to separate highly emulsified oil-water mixtures. The relatively low cost for the material preparation, enhanced mechanical property and high separation performance distinguished the developed material a suitable candidate for the separation of emulsified oil from water in practical applications.

Robust Nacrelike Graphene Oxide-Calcium Carbonate Hybrid Mesh with Underwater Superoleophobic Property for Highly Efficient Oil/Water Separation

Inspired by the mastoid structure of the lotus leaf and the robust layered structure of the nacre, a novel nacrelike graphene oxide-calcium carbonate (GO-CaCO₃) hybrid mesh with superhydrophilic and underwater superoleophobic property was prepared for the first time, via a facile, economical, and environmentally friendly layer-by-layer (LBL) self-assembly method using commercially available stainless steel mesh (SSM) as a ready-made mask. Interestingly, GO nanosheets played a threefold role, regulating the growth of CaCO₃ nanocrystals between the GO interlamination for constructing a "brick-and-mortar" structure, improving the interface stability via coordination assembly onto SSM, and creating strong hydration derived from rich oxygen-containing functional groups. The surface hydrophilicity and hierarchically micro/nanoscale structure of GO-CaCO₃ artificial pearls imbed on the SSM, contributing to outstanding superhydrophilicity and underwater superoleophobicity. The biomimetic hybrid mesh exhibited a strong mechanical property with a Young's modulus of 25.4 ± 2.6 GPa. The optimized hybrid mesh showed a high separation efficiency of more than 99% toward a series of oil/water mixtures with high flux. The low oil-adhesion force, high fatigue-resistance, chemical stability (acid/alkali/salt resistance), and excellent recycling performance enlighten the great prospects of GO-based nacrelike material for application in oily wastewater treatment.

3D printing of biomass-derived composites: application and characterization approaches

Biomass-derived 3D printing has attracted interests because of its developing technology and availability with renewable materials as well as compatible characteristics for many applications.

Durable and Multifunctional Superhydrophobic Coatings with Excellent Joule Heating and Electromagnetic Interference Shielding Performance for Flexible Sensing Electronics

Superhydrophobic coatings have wide applications in many fields. However, superhydrophobic and smart coatings with multifunctionality and their applications in flexible sensing electronics are seldom reported. In this work, durable, superhydrophobic, and anticorrosive coatings with excellent Joule heating and electromagnetic interference (EMI) shielding performance are prepared on the basis of Ag precursor reduction and synchronous nonsolvent induced phase separation. Silver nanoparticles (AgNPs) coated with the copolymer (polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene: SEBS) are uniformly distributed on the target substrate, forming mechanically durable conductive network. SEBS could not only endow the surface coating with superhydrophobicity but also improve the interaction among individual Ag nanoparticles and the interfacial adhesion between AgNPs and the substrate. The multifunctional coating possesses excellent anticorrosive, self-cleaning, and deicing properties. The high conductivity endows the coatings with excellent Joule heating and EMI shielding performance. The multifunctional coating can be applied to a variety of different substrates with outstanding surface stability and reliability. The conductivity for the smart coating can reach as high as 107 S/cm with the EMI shielding effectiveness up to 37.8 dB. At a low applied voltage of 1 V, the conductive fabric can be heated up to over 80 °C in 60 s and displays good recyclability during dozens of heating and cooling cycles. The Joule heating-induced temperature increase could be used for efficient surface deicing. When used for the flexible and wearable strain sensors, the multifunctional coating has a very low strain detection limit of 0.5% and large sensitivity (with the gauge factor as high as 1075) and excellent repeatability. In addition, it can be used for precisely monitoring different body motions, including both large and subtle joint movement.

Green Construction of an Oil-Water Separator at Room Temperature and Its Promotion to an Adsorption Membrane

Underwater superoleophobic membranes as an effective means of resisting oil stains are often subjected to cumbersome modification procedures, limited stability, and difficult expansion of assembly. To develop simple, green, stable, and scalable underwater superoleophobic films, herein, cellulose-based oil-water separators with high-efficiency oil purification were constructed by using commercial carboxymethocel (CMC) as a solute and a dimethyl sulfoxide-modified ionic liquid as a solvent. Owing to the superior dissolution, regenerability, and gelation of CMC, the metal mesh and gauze can be imparted with an excellent oleophobic ability through simple dipping, spraying, and coating of the CMC solution. As a result, these modified functionalized devices exhibit a purification capacity of more than 99.5% for various oil-water mixtures. Unexpectedly, the CMC gel coating also shields the gloves from organic solvents. Significantly, when the CMC solution is applied to an adsorption membrane, it not only endows the film with excellent oil-water separation characteristics but also enhances the adsorption amount and rate of the adsorbent. Therefore, CMC-based oleophobic materials can be widely developed and applied to a variety of fields that require oleophobic properties.