Yanji Zhu

A novel carbon nanotubes reinforced superhydrophobic and superoleophilic polyurethane sponge for selective oil–water separation through a chemical fabrication

Oil spillage and industrial oily wastewater have caused severe environmental concerns. A super absorbent material capable of separating oil–water mixtures, especially with a high absorption capacity and mechanical strength, is urgently desired. Here, a common and feasible approach to fabricate carbon nanotubes (CNTs) reinforced polyurethane (PU) sponge is presented that shows superhydrophobic and superoleophilic properties. The method involves the oxidative self-polymerization of dopamine and the reaction of hydrophilic polydopamine (PDA) with hydrophobic octadecylamine (ODA). The superhydrophobic stability of the as-prepared sponge with temperatures and in corrosive solutions of different pH is investigated. The as-prepared sponge could quickly and selectively absorb various kinds of oils up to 34.9 times of its own weight, and the absorbed oils can be collected by a simple squeezing process. More interestingly, the mechanical strength of the as-prepared sponge is improved due to the structural reinforcement of CNTs anchored on the sponge skeleton. Furthermore, the recovered sponge could be reused to separate oil–water mixture 150 times while maintaining its high absorption capacity. This promising multifunctional sponge exhibits significant potential as an efficient absorbent in large-scale oil–water separation applications.

Superhydrophobic polyaniline hollow spheres with mesoporous brain-like convex-fold shell textures

Novel hollow nano/microspheres of polyaniline (PANI) with mesoporous brain-like convex-fold shell structures were prepared via a new micelle-mediated phase transfer method, using perfluorooctanoic acid (PFOA)/aniline as a soft template. These self-assembled hollow spheres possess high specific surface areas (835.7 m2 g−1), and uniform particle morphology with narrowly distributed particle size can be controlled by adjusting the PFOA/aniline molar ratio and polymerization time. The conductive emeraldine state of PANI is also confirmed by FT-IR spectroscopy, UV-vis spectroscopy, X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry. In particular, these PANI spheres exhibit superhydrophobicity and high oleophobicity simultaneously, with contact angles of 165 ± 0.9°, 134 ± 0.8°, 131 ± 0.9° and 125 ± 0.7° towards water, glycerin, ethylene glycol and corn oil, respectively. Furthermore, the mechanisms of PANI structural evolution are proposed involving the formation, phase transfer and self-reassembly process of PFOA/aniline spherical micelles.

Preparation of high thermal stability polysulfone microcapsules containing lubricant oil and its tribological properties of epoxy composites

Abstract Polysulfone (PSF) microcapsules containing lubricant oil have been successfully prepared using solvent evaporation method. The results show that lubricant oil was successfully encapsulated and the encapsulation capacity of about 56.0 wt.% was achieved. The uniform microcapsules have nearly spherical shape and quite smooth outer surface. The mean diameter is approximately 156 and 169 μm by using different dispersant solutions. The wall material is porous in structure with wall thickness of about 20 μm. The initial decomposition temperature of PSF is 480 °C. It is higher than traditional poly(urea-formaldehyde) (PUF) and poly(melamine-formaldehyde) (PMF) wall materials with 245 °C and 260 °C initial decomposition temperature, respectively. High thermal stability of PSF microcapsules can be considered as additives in high temperature resistant polymer materials. The frictional coefficient and wear rate of epoxy composites decreased significantly by incorporating microcapsules containing lubricant oil into epoxy. When the concentration of microcapsules was 25 wt.%, the frictional coefficient and specific wear rate were reduced by 2.3 and 18.3 times, respectively, as compared to the neat epoxy.

Solar-driven thermo- and electrochemical degradation of nitrobenzene in wastewater: Adaptation and adoption of solar STEP concept.

The STEP concept has successfully been demonstrated for driving chemical reaction by utilization of solar heat and electricity to minimize the fossil energy, meanwhile, maximize the rate of thermo- and electrochemical reactions in thermodynamics and kinetics. This pioneering investigation experimentally exhibit that the STEP concept is adapted and adopted efficiently for degradation of nitrobenzene. By employing the theoretical calculation and thermo-dependent cyclic voltammetry, the degradation potential of nitrobenzene was found to be decreased obviously, at the same time, with greatly lifting the current, while the temperature was increased. Compared with the conventional electrochemical methods, high efficiency and fast degradation rate were markedly displayed due to the co-action of thermo- and electrochemical effects and the switch of the indirect electrochemical oxidation to the direct one for oxidation of nitrobenzene. A clear conclusion on the mechanism of nitrobenzene degradation by the STEP can be schematically proposed and discussed by the combination of thermo- and electrochemistry based the analysis of the HPLC, UV-vis and degradation data. This theory and experiment provide a pilot for the treatment of nitrobenzene wastewater with high efficiency, clean operation and low carbon footprint, without any other input of energy and chemicals from solar energy.

Polysulfone/SiO2 hybrid shell microcapsules synthesized by the combination of Pickering emulsification and solvent evaporation technique and their application in self-lubricating composites

Lubricant oil-filled polysulfone/SiO2 (PSF/SiO2) hybrid shell microcapsules are prepared by the combination of Pickering emulsification and the solvent evaporation technique. Silica particles are used as stabilizers. The structure and properties of the microcapsules are influenced by the silica particle concentration, agitation speed, and encapsulation temperature. The formation of PSF/SiO2 hybrid microcapsules is confirmed by a scanning electron microscope, Fourier transform infrared spectroscopy, and thermal gravimetric analysis. The resulting microcapsules prepared at the optimum synthetic parameters show a spherical, ideal structure with a rough outer surface, mean diameter of 5.0 ± 0.6 μm, shell thickness of 0.83 μm, core content of 50.5 wt %, and excellent thermal stability with an initial evaporating temperature of 250 °C. The synthesized microcapsules are embedded into epoxy for application in self-lubricating composites. Investigated by friction and wear tests, the tribological properties of the self-lubricating microcapsule-incorporated epoxy composites attain a significant improvement.

Corrosion-resistant engineering superhydrophobic and superoleophilic bulk materials with oil–water separation property

A corrosion-resistant superhydrophobic and superoleophilic modified poly(vinylidene fluoride)-based bulk material with oil–water separation ability is fabricated through a facile method of molding and sintering process. Fluorinated ethylene propylene was added as the one of the cross-linking agents. Nanometer silica (SiO2) and carbon nanotubes (CNTs) were added into the bulk material to construct the necessary reticulate papillae structures for superhydrophobic surface. NH4HCO3 was added as a pore-forming reagent in order to realize porous structure and oil–water separation. The bulk material can be designed to different appearances, such as cuboids, cylinder and sealing rings. The resulting bulk material shows excellent superhydrophobic and superoleophilic with a water contact angle of 164° and oil contact angle of almost 0°. As the SiO2 and CNTs filled the entire bulk material, any section of the bulk material shows excellent superhydrophobicity. The thermal resistance of the bulk material was improved due to the introduction of nanoparticles. The corrosion resistance of the superhydrophobic bulk material was investigated in an aqueous NaCl solution (3.5%). The results show that the prepared composite bulk material is effective in corrosion resistance, primarily due to the barrier effect of Cassie–Baxter model of superhydrophobic surface. It is believed that this bulk material would be an engineering material for large-scale application.

Mechanical and tribological characteristics of carbon nanotube-reinforced polyvinylidene fluoride (PVDF)/epoxy composites

In this study, epoxy (EP) composites filled with different contents of polyvinylidene fluoride (PVDF) and carbon nanotubes (CNTs) were fabricated by the solvent evaporation and curing method. FT-IR and XRD analysis were performed to explore the discolorment mechanism of the PVDF/EP composites before and after curing. The effects of the PVDF and CNT content on the mechanical and tribological properties of the composites were investigated. Results revealed that 1.0% CNT/30% PVDF/EP composites exhibited a 36.2% and 10.1% increase in flexural strength and hardness, as compared to those of the 30% PVDF/EP composites. The wear rates of 1.0% CNT/30% PVDF/EP composites and 30% PVDF/EP composites were 92.1% and 86.8% lower than that of pristine EP under 1.0 MPa and 0.76 m s−1, respectively. Meanwhile, the fractured and worn surfaces of specimens were both analyzed by the observations of SEM. In addition, wear tests under various applied loads were conducted for pristine EP, 30% PVDF/EP and 1.0% CNT/30% PVDF/EP composites. The results showed that the wear properties of the two composites were both superior to those of pristine EP due to the formation of a transfer film as revealed by SEM-EDS analysis, which could effectively protect the worn surface from direct abrasion during the wear testing.

A superrobust superhydrophobic PSU composite coating with self-cleaning properties, wear resistance and corrosion resistance

In this study, a superhydrophobic polysulfone (PSU) composite coating with a high water contact angle (WCA) of 159° and a low slide angle (SA) of only 3.5° has been fabricated through a simple thermal spraying method. The ductility and mechanical properties of the PSU composite coating were improved effectively through the combination of the cross-linking ability of PVDF and the special multilayer structure of MMT. The wear resistance of the prepared coating is approximately 14.3 times longer than that of commercial fluorocarbon coating. Simultaneously, the prepared superhydrophobic coating also possesses outstanding corrosion resistance; the corrosion current and corrosion potential decreased from 10−0.9 to 10−3.6 μA cm−2 and from −803 to −218 mV, respectively. Furthermore, the prepared coating demonstrated superb self-cleaning, anti-fouling and durability properties. It is believed that this robust superhydrophobic PSU/PVDF/MMT–PDMS composite coating may provide the possibility to realize large-scale fabrication and applications in industry.

A simple drop-casting approach to fabricate the super-hydrophobic PMMA-PSF-CNFs composite coating with heat-, wear- and corrosion-resistant properties

A novel super-hydrophobic poly(methyl methacrylate) (PMMA)-polysulfone (PSF)-carbon nano-fibers (CNFs) composite coating was prepared by a simple drop-casting method. Heat-induced phase separation contributed to the formation and evolution of coatings morphology. These coatings could spread on various substrates of glass, aluminum plate, and steel plate with the water contact angle up to 165° and the slide angle only 5°, especially. Providing the coating with good heat-, wear-, and corrosion-resistant properties was urgently desired for industrial applications. Simultaneously, CNFs modified by fluoro-groups as the mechanical low-surface-energy nano-elements benefited to enhance the coating surface roughness during the process of phase separation which had a positive effect on hydrophobicity. The morphologies and structures of the coatings annealed under different temperatures had been investigated through the scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. The possible mechanism of heat-induced phase separation to construct the nano-micro-structure PMMA-PSF-CNFs composite coating had been discussed that high temperature provided the kinetic energy to make CNFs aggregate to the surface of polymer (PMMA-PSF) phase and formed the cross-linked network structure. The enhancement in these preliminary results will guide the design and fabrication of the low-cost and high-performance commercial super-hydrophobic coatings.

Fabrication of superhydrophobic fiber fabric/epoxy composites coating on aluminum substrate with long-lived wear resistance

A superhydrophobic coating with long-lived wear resistance was successfully prepared by integrating the hydrophobization of cotton fiber fabric and the curing of epoxy composites consisting of polyurethane (PU), polyfluoroalkoxy (PFA) and hydrophobic SiO2 nanoparticles. Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) were employed to investigate the chemical compositions and morphologies of the modified cotton fiber fabric and the prepared coating. When the epoxy solution containing 35 wt% PFA and 25 wt% PU, the obtained coating exhibited superhydrophobic behavior with a water contact angle (WCA) of 153.5 ± 1°. Tribological tests indicated that this fiber fabric/epoxy composites coating had stable friction coefficient and excellent wear-resistance under the harsh conditions with the applied load of 2.8 MPa and the sliding velocity of 0.51 m s−1. After 240000 cycles of abrasion, the coating just showed the decrease in thickness of 80 μm without apparent damage and could retain high hydrophobicity with the WCA of 142°. Simultaneously, the coating was resistant to the acid or alkali solution. This wear-resistant superhydrophobic fiber fabric/epoxy composites coating may be a good candidate for the practical industrial applications under harsh working conditions.