Zheng-Hong Luo

Smart Fiber Membrane for pH-Induced Oil/Water Separation

Wastewater contaminated with oil or organic compounds poses threats to the environment and humans. Efficient separation of oil and water are highly desired yet still challenging. This paper reports the fabrication of a smart fiber membrane by depositing pH-responsive copolymer fibers on a stainless steel mesh through electrospinning. The cost-effective precursor material poly(methyl methacrylate)-block-poly(4-vinylpyridine) (PMMA-b-P4VP) was synthesized using copper(0)-mediated reversible-deactivation radical polymerization. The pH-responsive P4VP and the underwater oleophilic/hydrophilic PMMA confer the as-prepared membrane with switchable surface wettability toward water and oil. The three-dimensional network structure of the fibers considerably strengthens the oil/water wetting property of the membrane, which is highly desirable in the separation of oil and water mixtures. The as-prepared fiber membrane accomplishes gravity-driven pH-controllable oil/water separations. Oil selectively passes through the membrane, whereas water remains at the initial state; after the membrane is wetted with acidic water (pH 3), a reverse separation is realized. Both separations are highly efficient, and the membrane also exhibits switchable wettability after numerous cycles of the separation process. This cost-effective and easily mass-produced smart fiber membrane with excellent oil-fouling repellency has significant potential in practical applications, such as water purification and oil recovery.

1,2,4-Triazolium perfluorobutanesulfonate as an archetypal pure protic organic ionic plastic crystal electrolyte for all-solid-state fuel cells

1,2,4-Triazolium perfluorobutanesulfonate (1), a novel, pure protic organic ionic plastic crystal (POIPC) with a wide plastic crystalline phase, has been explored as a proof-of-principle anhydrous proton conductor for all-solid-state high temperature hydrogen/air fuel cells. Its physicochemical properties, including thermal, mechanical, structural, morphological, crystallographic, spectral, and ion-conducting properties, as well as fuel cell performances, have been studied comprehensively in both fundamental and device-oriented aspects. With superior thermal stability, 1 exhibits crystal (phase III), plastic crystalline (phase II and I) and melt phases successively from −173 °C to 200 °C. Differential scanning calorimetry and temperature-dependent powder X-ray diffraction (XRD) measurements together with polarized optical microscopy and thermomechanical analysis reveal the two solid–solid phase transitions of 1 at 76.8 °C and 87.2 °C prior to the melting transition at 180.9 °C, showing a wide plastic phase (87–181 °C). Scanning electron microscopy displays the morphology of different phases, indicating the plasticity in phase I. Single-crystal XRD studies reveal the molecular structure of 1 and its three-dimensional N–H⋯O hydrogen bonding network. The influence of the three-dimensional hydrogen bonding network on the physicochemical properties of 1 has been highlighted. The temperature dependence of hydrogen bonding is investigated by variable-temperature infrared spectroscopy. The sudden weakening of hydrogen bonds at 82 °C seems to be coupled with the onset of orientational or rotational disorder of the ions. The temperature dependence of ionic conductivity in the solid and molten states is measured via impedance spectroscopy and current interruption technique, respectively. The Arrhenius plot of the ionic conductivity assumes a lower plateau region (phase I, 100–155 °C) with a low activation energy of ∼36.7 kJ mol−1 (i.e. ∼0.38 eV), suggesting likely a Grotthuss mechanism for the proton conduction. Variable-temperature infrared analysis, optical morphological observations, and powder XRD patterns further illustrate the structural changes. Electrochemical hydrogen pumping tests confirm the protonic nature of the ionic conduction observed in the lower plateau region. Finally, measurements of the open circuit voltages (OCVs) and the polarization curves of a dry hydrogen/air fuel cell prove the long-range proton conduction. At 150 °C, a high OCV of 1.05 V is achieved, approaching the theoretical maximum (1.11 V).

CFD-DEM modeling of gas-solid flow and catalytic MTO reaction in a fluidized bed reactor

National Natural Science Foundation of China [201076171]; National Ministry of Science and Technology of China [2012CB21500402]; State-Key Laboratory of Chemical Engineering of Tsinghua University [SKL-ChE-13A05]

Poly(ionic liquid)s-based nanocomposite polyelectrolytes with tunable ionic conductivity prepared via SI-ATRP

In this study, a novel kind of organic–inorganic core–shell SiO2-poly(p-vinylbenzyl) trimethylammonium tetrafluoroborate (SiO2–P[VBTMA][BF4]) nanoparticle was well designed and successfully synthesized via surface-initiated atom transfer radical polymerization (SI-ATRP). Fourier transform infrared spectroscopy (FT-IR), 1H nuclear magnetic resonance (1H NMR), X-ray photoelectron spectroscopy (XPS), dynamic light scattering (DLS) and scanning electron microscopy (SEM) were used to confirm the formation of the core–shell nanoparticles and the surface modification. In order to overcome the challenge of the characterization of the number average molecular weight of poly(ionic liquid)s, “sacrificial initiator” method was used here employing a trimethylsilyl (TMS)-labeled initiator as the NMR marker for integration. In addition, good thermal stability of the new hybrid polyelectrolyte was proved by thermogravimetric analysis. The electrochemical impedance measurements revealed that the room temperature conductivity reached 10−4 S cm−1, which is much higher than that of the pure poly(ionic liquid)s and varies with the amount of the grafted polymer and the test temperature. The X-ray diffraction (XRD) tests further investigated the crystal structure of the nanocomposite and pure P[VBTMA][BF4]. The temperature dependence of ionic conductivity conforms to Arrhenius behavior for both of the nanocomposites and the pure polymer. The results indicated that the SI-ATRP approach provided a simple and versatile route to tune the ionic conductivity of the hybrid nanoparticles by changing the chain length of the grafted polymer, which can be potentially used in a variety of electrochemical devices.

Facile synthesis of gradient copolymers via semi-batch copper(0)-mediated living radical copolymerization at ambient temperature

In this work, we report an example of the facile synthesis of methyl methacrylate/tert-butyl acrylate (MMA/tBA) gradient copolymers (poly(MMA-grad-tBA) using the Cu(0) and conventional ATRP ligands as catalysts in DMF solvent at 25 °C. Semi-batch copper(0)-mediated living radical copolymerization technique (Cu(0)-mediated LRP) was used for achieving the chain gradient microstructure of the resulting copolymers. We also compared copolymerizations with two different ATRP ligands at ambient temperature allowing control over the molecular weight and polydispersity with a quarter of catalyst concentration versus a conventional ATRP in dipolar protic solvent (i.e. DMF), while the reaction temperature up to 80 °C in a non-polar medium (i.e. toluene) in order to reach the above polymerization efficiency. The addition of a small amount of reducing agent (i.e. hydrazine hydrate) into the reaction system allows the reaction proceeding in the oxygen tolerant system without losing control and decreasing total conversion such as using the reagents without deoxygenating.

Light-Responsive Smart Surface with Controllable Wettability and Excellent Stability

Novel fluorinated gradient copolymer was designed for smart surface with light-responsive controllable wettability and excellent stability. The switchable mechanism and physicochemical characteristics of the as-prepared surface decorated by designed polymeric material were investigated by ultraviolet-visible (UV-vis) spectrum, scanning electron microscope (SEM), atomic force microscope (AFM), and X-ray photoelectron spectroscopy (XPS). Thanks to the functional film and surface roughening, etched silicon surface fabricated by copolymer involving spiropyran (Sp) moieties possesses a fairly large variation range of WCA (28.1°) and achieves the transformation between hydrophilicity (95.2° < 109.2°) and hydrophobicity (123.3° > 109.2°) relative to blank sample (109.2°). The synthetic strategy and developed smart surface offer a promising application in coating with controllable wettability, which bridge the gap between chemical structure and material properties.

Synthesis and pH-responsive micellization of brush copolymers poly(methyl methacrylate-co-2-(2-bromoisobutyryloxy)ethyl methacrylate-graft-acrylic acid): role of composition profile

A series of brush copolymers (i.e. poly(methyl methacrylate (MMA)-co-2-(2-bromoisobutyryloxy)ethyl methacrylate (BIEM)-graft-acrylic acid (AA))) having three backbone composition profiles, i.e. random, gradient and block, were synthesized via the combination of atom transfer radical polymerization (ATRP)/model-based semibatch ATRcoP and the “grafting from” method. These samples allowed us to systematically investigate the effects of the composition profile (including the grafting density corresponding to the composition profile) on the micelle formation and pH responsivity of the brush copolymers in solution. FTIR, 1H NMR and GPC were used to provide evidence for the formation of the well-defined brush copolymers. TEM, light transmittance and DLS were used to investigate the self-assembly and pH responsivity of the resulting copolymers. It was found that the micelles formed by these copolymers underwent a different conformational transition caused by the change from acidic to basic in the solution. These transitions were mainly influenced by pH and composition profile since the composition profile also had a strong effect on the acid-dissociation degree of the brush copolymer.

An improved kinetic model for cellulose hydrolysis to 5-hydroxymethylfurfural using the solid SO42−/Ti-MCM-41 catalyst

5-Hydroxymethylfurfural (5-HMF) which can be produced from cellulose is considered as one of the promising green platform chemicals. In this work, the conversion of cellulose to 5-HMF was carried out through hydrolysis in a batch reactor using the SO42−/Ti-MCM-41 catalyst at a temperature of 463–503 K. Two analytical techniques including the 3,5-dinitrosalicylic acid (DNS) method and high performance liquid chromatography (HPLC) were employed to track the time evolution of the main reagents, i.e., cellulose, 5-HMF and reducing sugar. Based on the typical kinetic experiments for the cellulose hydrolysis, a comprehensive hydrolysis mechanism was introduced to describe the heterogeneous hydrolysis of cellulose to 5-HMF. A corresponding kinetic model was proposed on the basis of the hydrolysis mechanism and the mass balance law. The results show that the predicted data obtained via the suggested model agree well with the experimental results. In addition, some data from the open reports were referred for further model verification in this work. The kinetic model suggested in this work is a mechanism model for the heterogeneous catalytic cellulose hydrolysis process, which is different from the previous first-order kinetic model.

Multi-scale product property model of polypropylene produced in a FBR: From chemical process engineering to product engineering

Abstract A multi-scale product model has been built to characterize the polypropylene (PP) formation dynamics in a catalytic FBR. For the first time, the gas–solid flow field, the morphological and molecular properties of particles, as well as their dynamics can be simultaneously obtained by solving the unique model that couples a CFD model, a population balance model (PBM) and moment equations. The quantitative relationships between the operating conditions and the multi-scale particle properties have been further established. The results demonstrate that the product model can be used to guide a multi-scale generalization of the polymer product from chemical process to product engineering.

A two-phase CFD modeling approach to investigate the flow characteristics in radial flow moving-bed reactors

Abstract Based on a complete CFD Eulerian–Eulerian two-fluid approach, a comprehensive three-dimensional (3D) two-phase reactor model was suggested to describe the flow behavior in radial flow moving-bed reactors (RFMBRs). A porous media model was incorporated into the reactor model in order to describe the flow resistance provided by the porous walls of the center and annular pipes. Compared with these previous reactor models, the reactor model considers the solid-phase movement instead of immobilization, which benefits for predicting the formation of cavity practically. The simulation results are agreement with the published experimental data. By employing the verified model, the flow field parameters in the reactors such as pressure drop and flow velocity were obtained. Besides, the simulations were then carried out to investigate the effect of the bed voidage on the flow behavior and to understand the phenomenon of cavity in the RFMBRs. The simulation results showed that both the centripetal and the centrifugal flow configurations have the inhomogeneous flow distribution and the phenomenon of cavity. Furthermore, the inhomogeneous distribution increases with the increase of the bed voidage, whereas the phenomenon of cavity is more obvious with the increase of gas inlet velocity. As a whole, this work provided a realistic modeling and a useful approach for the understanding of RFMBRs.