A polypropylene melt-blown strategy for the facile and efficient membrane separation of oil-water mixtures

Porous materials with selective wettability and permeability have significant importance in oil-water separation, but complex fabrication processes are typically required to obtain the desired structures with suitable surface chemistry. In this work, an industrial melt-blown strategy that utilized commercially available polypropylene (PP) was used for the large-scale fabrication of superhydrophobic/superoleophilic membranes with staggered fabric structures. These membranes could readily separate different oils including pump oil and crude oil from various aqueous solutions such as strongly acidic, alkaline, and saline media. In addition, the separation efficiencies of these membranes exceeded 99%, and they could remain functional even after exposure to corrosive media. We anticipate that this work will further the design of membranes and enhance their applicability in oil-water separation, and provide researchers and engineers with a more effective tool for performing challenging separations and mitigating pollution.     

Tailored surface properties of semi-fluorinated block copolymers by electrospinning

Diblock copolymers based on polystyrene (PS) macroinitiators and four different fluorinated monomers (perfluorooctyl ethyl methacrylate (FMA), pentafluorostyrene (FS), perfluorooctyl-ethylene oxymethyl styrene (EMS), 2,3,5,6-tetrafluoro-4-(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecaoxy)styrene (FSF)) were synthesized via atom transfer radical polymerization (ATRP). The lengths of the PS and fluorinated blocks were altered and the surface and self-assembling properties of the polymers were compared with respect to the fluorinated monomer used and the fluorine content. The surface properties, contact angles and surface tension, were enhanced by the existence of the CF₃ groups at the end of the alkyl chains compared with poly(pentafluorostyrene). Hydrophobicity of the surfaces was further enhanced by electrospinning the polymer solutions, which yielded superhydrophobic surfaces with water contact angles >150° for polymers having CF₃ groups.     

Inside Front Cover: Towards Understanding Why a Superhydrophobic Coating Is Needed by Water Striders (Adv. Mater. 17/2007)

Gold threads modified with superhydrophobic or normal hydrophobic coatings are used as model system in the study of the contribution of a superhydrophobic coating of water striders to their floating and movement on water surfaces. After depositing Pt aggregates on one of its ends, the gold threads are able to move in the H₂O₂ aqueous solution. The superhydrophobic coating is proven to be able to decrease fluidic drag during motion, as described by Xi Zhang and co‐workers on p. 2257.     

Cover Picture: Conducting and Superhydrophobic Rambutan‐like Hollow Spheres of Polyaniline (Adv. Mater. 16/2007)

Conductive and superhydrophobic rambutan‐like hollow spheres of polyaniline are formed through self‐assembly by using perfluorooctane sulfonic acid as a dopant, soft template, and superhydrophobic agent at the same time, as reported by Meixiang Wan and Lei Jiang on p. 2092. The results show that the approach used is not only simple, but also that the hollow spheres have a large specific area and exhibit physical properties that are required for many applications in nanotechnology.     

The effect of superhydrophobicity of prickly shape carbonyl iron particles on the oil-water adsorption

The separation of oil spillage from marine environments has been discussed as a global concern. Recyclable superhydrophobic magnetic particles with micro-nano structures have been considered as a potential providing a safe, practical, and easy method for removing the oil from oil-water. In this research, the hydrophobicity of magnetic particles was enhanced to achieve the maximum adsorption capacity. For this purpose, reacted carbonyl iron (CI) with glucose was reacted with stearic acid under different condition of temperature, time, and concentration. Analytical tests were performed to confirm the reaction of stearic acid with CI@glucose. The prickly shape created on the surfaces of magnetic particles led to achieving the maximum superhydrophobicity. In this connection, the optimized superhydrophobic particles based on the maximum obtained water contact angle (WCA) of 169° at 75 °C, and 3.5 h and 10% concentration of stearic acid were selected for the oil-water separation. The results revealed that the superhydrophobic particles had acceptable stability within pH range of 2–12. The adsorption capacity of the modified particles for hexane, silicone oil, gasoline, and kerosene was 4.1, 2.5, 3.1, and 3.7 g/g, respectively, with a high adsorption efficiency ( > 99.7%) in the oil-water mixture. After ten cycles of using these particles, the adsorption capacity range was 2 to 4 g/g regardless of the number of recycling times, and no significant change was observed in the contact angle.     

Differential superhydrophobicity and hydrophilicity on a thin cellulose layer

Here we have developed cellulosic materials (cotton fabric or paper) with differential superhydrophobicity and hydrophilicity on each side of the surfaces by coating with polyvinylidene fluoride and fluorinated silane molecules using electro-spraying. Such materials are advantageous in various textile and medical applications.Analysis of surface morphology indicated that, not only surface chemical property and roughness, but also particle diameter affects surface superhydrophobicity. Smaller particle diameter enhances superhydrophobicity, if the surface roughness and surface chemical property remain constant. By controlling these three factors, superhydrophobicity with a water contact angle of more than 160° can be achieved at one side of a thin cellulosic material while maintaining the hydrophilicity (contact angle is 0°) at the opposite side.     

Reversibly light-switchable wettability between superhydrophobicity and superhydrophilicity of hybrid ZnO/bamboo surfaces via alternation of UV irradiation and dark storage

Functional bamboo surfaces with reversibly tunable wettability have become much sought after because of their usefulness in sustainable material protection strategies and industrial applications. In this paper, the hybrid ZnO/bamboo surfaces with reversibly light-switchable wettability between superhydrophobicity and superhydrophilicity were successfully prepared via a hydrothermal method at low temperature. The bamboo substrates served as adhesion, and the well-aligned ZnO nanosheet arrays (WZNA) were deposited on the bamboo surfaces after a hydrothermal process. A subsequent chemical treatment with octadecyltrichlorosilane (OTS) led to a superhydrophobic surface with a water contact angle (WCA) up to 153°. Under UV irradiation, the WCA decreased gradually, and the surface eventually became superhydrophilic because of hydroxyl absorption on the ZnO surfaces. The wetting behavior of the WZNA can be reversibly switched between superhydrophilic and superhydrophobic via alternation of UV exposure for 12 h and dark storage for 10 days.     

Role of silane grafting in the development of a superhydrophobic clay-alumina composite membrane for separation of water in oil emulsion

Hydrophobic composite kaolin-coated clay-alumina membranes are unique choices for water in oil emulsion separation. In this work, a membrane fabrication approach is presented using kaolin clay coating in the clay-alumina tubular composite support tube and subsequently grafting by different concentrations of fluoroalkyl silane (FAS: 1H, 1H, 2H, 2H, -Perfluorooctyltriethoxysilane) on the membrane surface. Different concentrations of fluoroalkyl silane formed distinctive hierarchical structures which exhibited hydrophobicity of the membrane surface. The pore property, surface roughness properties, and thermogravimetric properties can be suitably tailored by tuning the silane concentration in the grafting solution. The surfaces of comparatively higher silane content grafted (M50 and M100) composite membranes were found to be superhydrophobic. Comparably, our optimal composite membrane (M100) displayed a moderate steady flux rate of 80-100LMH (Lm^?2h ^?1) and excellent water rejection (>99%) properties during the separation of water in hexane and toluene emulsion at a cross-flow transmembrane pressure of 1 bar. The role of silane concentration on permeated hexane and toluene flux rate, water rejection rate, surface wettability, microstructure, and hydrophobic stability reveals new distinguishing insights into the hydrophobic clay-alumina composite membrane fabrication.     

Inside Front Cover: Superhydrophobic Surfaces Generated from Water‐Borne Dispersions of Hierarchically Assembled Nanoparticles Coated with a Reversibly Switchable Shell (Adv. Mater. 1/2008)

On p. 200, Sergiy Minko and co‐workers report on the fabrication of a superhydrophobic coating from aqueous dispersions of hybrid responsive nanoparticles with no application of surfactants and organic solvents. A suspension of the particles forms a textured hydrophilic coating upon casting. Heating above the glass transition temperature of polystyrene, or treatment in acidic water, resulted in backward and forward switching between the superhydrophobic and the hydrophilic material, respectively.