Zhixiang Zeng

A cellulose sponge with robust superhydrophilicity and under-water superoleophobicity for highly effective oil/water separation

We fabricate a cellulose sponge with stable superoleophobicity (θoil > 150°) under water and superhydrophilic wettability (θwater ≈ 0°) under oil without any further chemical modification for oil–water emulsion separation. The cellulose sponge shows superoleophobicity to various oils under water and possesses stable superoleophobicity in corrosive liquids like strong acid, alkali and salt solution. The sponge is made from the dissolution and regeneration of cellulose powder which is green, low cost, simple and easy to scale up. The natural hydrophilicity of the cellulose ensures its excellent under-water superoleophobicity and antifouling properties. The double layer construction of different pore sizes, which contains a top-layer with a pore size lower than 1 μm and a sub-layer with a pore size larger than 3 μm, ensures that the oil phase is resisted and the water phase easily and quickly permeates the sponge. Our cellulose sponge can separate oil–water mixtures, with >99.94% separation efficiency, solely using gravity and has excellent antifouling properties.

Excellent tribological and anti-corrosion performance of polyurethane composite coatings reinforced with functionalized graphene and graphene oxide nanosheets

In order to improve the mechanical durability, polyurethane (PU) needs to be modified to enhance the tribological and anti-corrosion properties. In this work, we fabricated a series of PU composite coatings reinforced with functionalized graphene (FG) and functionalized graphene oxide (FGO). The structural and morphological features of the composite coatings were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The results showed that the dispersion and compatibility of graphene and graphene oxide were improved via chemical modification. Moreover, they effectively enhanced the tribological and anti-corrosion properties of PU composite coatings, whose optimized additive range was between 0.25 wt% and 0.5 wt%. The effect depends on the balance of lubrication and barrier of fillers and cracks generated by them. Finally, in comparison with FG/PU coatings, the FGO/PU coatings exhibited a better tribological property but worse anti-corrosion property owing to the abundant oxygenated groups of GO. They led to stronger interfacial interactions between FGO and the PU matrix, but destroyed the graphene lattice structure to some extent.

Low Drag Porous Ship with Superhydrophobic and Superoleophilic Surface for Oil Spills Cleanup

To efficiently remove and recycle oil spills, we construct aligned ZnO nanorod arrays on the surface of the porous stainless steel wire mesh to fabricate a porous unmanned ship (PUS) with properties of superhydrophobicity, superoleophilicity, and low drag by imitating the structure of nonwetting leg of water strider. The superhydrophobicity of the PUS is stable, which can support 16.5 cm water column with pore size of 100 μm. Water droplet can rebound without adhesion. In the process of oil/water separation, when the PUS contacts with oil, the oil is quickly pulled toward and penetrates into the PUS automatically. The superhydrophobicity and low water adhesion force of the PUS surface endow the PUS with high oil recovery capacity (above 94%) and drag-reducing property (31% at flowing velocity of 0.38m/s). In addition, the PUS has good corrosion resistance and reusability. We further investigate the wetting behavior of water and oil, oil recovery capacity, drag-reducing property, and corrosion resistance of the PUS after oil absorbed. The PUS surface changes significantly from superhydrophobic to hydrophobic after absorbing oil. However, the oil absorbed PUS possesses better drag-reducing property and corrosion resistance due to the changes of the motion state of the water droplets.

Three-dimensional structured sponge with high oil wettability for the clean-up of oil contaminations and separation of oil–water mixtures

Oil spills not only result in extensive economic losses but also damage marine ecological environments. A series of materials with special wettability are investigated for the separation of oil–water mixtures. However, few studies have investigated the adsorption behaviors of sponges to crude oil (high viscosity). To solve the restrictions of high viscosity oil absorption, low oil absorption rate and oil–water emulsion separation of oil absorption materials, a superhydrophobic and superoleophilic polyurethane (PU) sponge was synthesized via an environmentally friendly surface grafting of a polymer molecular brush. This grafted sponge exhibited high oil absorption rate because of the expansion in oil and collapse in water of the polymer molecular brushes. The grafted PU sponge also possessed high absorption capacity (23 times of the self weight), high oil retention (93%), high mechanical strength and good recyclability (more than 400 times). We anticipate that the grafted sponge will have numerous applications and will show outstanding performance on a larger scale. A quick clean-up of marine spilled oil/organic solvents and the separation/recycling of an oil–water mixture/emulsion can also be achieved.

Simple and Green Fabrication of a Superhydrophobic Surface by One-Step Immersion for Continuous Oil/Water Separation.

In this paper, stainless steel meshes with superhydrophobic and superoleophilic surfaces were fabricated by rapid and simple one-step immersion in a solution containing hydrochloric acid and stearic acid. The apparent contact angles were tested by a video contact angle measurement system (CA). Field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) were conducted to characterize the surface topographies and chemical compositions. The SEM results showed that mesh surfaces were covered by ferric stearate (Fe[CH3(CH2)16COO]2) with low surface energy. The CA test results showed that the mesh had a maximum apparent contact angle of 160 ± 1.0° and a sliding angle of less than 5.0° for the water droplet, whereas the apparent contact angle for the oil droplet was zero. Ultrasound oscillation and exposure tests at atmospheric conditions and immersion tests in 3.5 wt % NaCl aqueous solution were conducted to confirm the mesh with excellent superhydrophobic and superoleophilic properties. On the basis of the superhydrophobic mesh, a miniature separation device pump was designed to collect pure oil from the oil/water mixture. It showed that the device was easier and convenient. The techniques and materials presented in this work are promising for application to wastewater and oil spill treatment.

The investigation of transition metal doped CuGaS2 for promising intermediate band materials

Here, we have systematically investigated the electronic structure and optical properties of transition metal (M) doped CuGaS2 (M = Fe, Co, and Ni) systems, using a density functional theory by considering a non-local interaction. Isolated intermediate bands (IBs), with the potential of achieving the efficiency of photovoltaic materials, are introduced in the main band gap of the host CuGaS2 by doping Fe or Ni with a favorable position and width. Therefore, extra absorption peaks appear in the optical spectrum of the Fe and Ni doped CuGaS2 compounds, accompanied with a greatly enhanced light absorption intensity and a largely broadened light absorption energy range. Whereas for Co doped CuGaS2, the material turns into a half-metal. Consequently, Fe and Ni doped CuGaS2 could be potential materials for future applications in the photovoltaic area.

Fabrication and Investigation the Microtribological Behaviors of Ionic Liquid–Graphene Composite Films

A novel thin composite film, which contained both ionic liquids (ILs) and graphene, was fabricated successfully on silicon substrate using a dip-coating method. The formation and surface properties of the films were analyzed using scanning electron microscopy (SEM) and multifunctional X-ray photoelectron spectroscopy. A ball-on-plate tribometer was used to evaluate the influence of graphene content on the microtribological performance of the thin composite films. The results showed that compared to the single IL film deposited directly on the silicon surface, the as-prepared IL–graphene (IL-G) film showed improved friction reduction properties, which was attributed to the synergistic effect of IL and graphene. The composite IL-G film also exhibited decreasing wear resistance compared to the single IL film. We postulate that this is due to the fact that IL films become more discontinuous with the incorporation of graphene powder. This was verified by SEM imaging, which showed that the film was not continuous enough to prevent direct contact between the steel ball counterpart and Si surface.

Preparation of anticorrosion hybrid silica sol–gel coating using Ce(NO3)3 as catalyst

In this report, hybrid silica sol–gel coating was prepared using Ce(NO3)3 (Sol-Ce) as catalyst. Structure, surface morphology and anticorrosion ability of Sol-Ce solution/coating were studied by infrared spectroscopy (IR), scanning electron microscopy, energy dispersive spectrometer (EDS), potentiodynamic scan (PDS) and electrochemical impedance spectroscopy (EIS). IR results showed that Ce(NO3)3 had a stronger influence on reactivity of alkoxysilane. EDS results revealed that the fraction of Fe in Sol-Ce coating was significantly lower than regular acid-catalyzed hybrid silica sol–gel coating (Sol-Ac) and Sol-Ac with Ce(NO3)3-doped coating (Sol-Ac/Ce). The results of PDS and EIS demonstrated that Sol-Ce coating had better anticorrosion ability than Sol-Ac and Sol-Ac/Ce on carbon steel. The enhanced anticorrosion performance of the Sol-Ce coating might result from the following two reasons: (a) Ce(NO3)3 as a catalyst could alleviate the negative effects of low pH with using acid catalyst (dissolution of carbon steel) and (b) Ce(NO3)3 could impede corrosion of carbon steel as corrosion inhibitor.

Negatively charged polysulfone membranes with hydrophilicity and antifouling properties based on in situ cross-linked polymerization

Polysulfone (PSf) membrane has been widely used in water separation and purification, although, membrane fouling is still a serious problem limiting its potential. We aim to improve the antifouling of PSf membranes via a very simple and efficient method. In this work, antifouling PSf membranes were fabricated via in situ cross-linked polymerization coupled with non-solvent induced phase separation. In brief, acrylic acid (AA) and vinyltriethoxysilane (VTEOS) were copolymerized in PSf solution, then directly casted into membranes without purification. With the increase of monomers concentration, the morphology of the as-cast membranes changed from a finger-like morphology to a fully sponge-like structure due to the increased viscosity and decreased precipitation rate of the polymer solutions. Meanwhile, the hydrophilicity and electronegativity of modified membranes were highly improved leading to inhibited protein adsorption and improved antifouling property. Furthermore, in order to further find out the different roles player by AA and VTESO, the modified membrane without VTEOS was prepared and characterized. The results indicated that AA is more effective in the membrane hydrophilicity improvement, VTEOS is more crucial to improve membrane stability. This work provides valuable guidance for fabricating PSf membranes with hydrophilicity and antifouling property via in situ cross-linked polymerization.

Ultra low water adhesive metal surface for enhanced corrosion protection

A superhydrophobic surface with ultra low water adhesive force is fabricated on various metals for enhanced corrosion protection. The superhydrophobic surface is constructed by passivated zinc oxide (ZnO) and low surface energy poly(dimethylsiloxane) (PDMS). The process of wettability transformation and corrosion are evaluated by a salt spray test and electrochemical measurement. The superhydrophobic surface is separated layer-by-layer to reveal the function of each layer in corrosion protection. The surface adhesive force is applied as a novel metric for precisely determining the wettability state on the substrate surface. The results reveal that the ultra low water adhesive force of the superhydrophobic surface can effectively suppress water condensation on the metal surface which can suppress the transformation from the Cassie to Wenzel state. The superhydrophobic surface can effectively inhibit corrosion because of the synergistic effect of the triple layered protection system of air, PDMS and ZnO.