Poly(vinylpyrrolidone) (PVP) is most widely used in the process of preparing a drug carrier by subcritical or supercritical fluids impregnation technology, and the design and operation conditions of the subcritical or supercritical fluids impregnation technology are based on the equilibrium solubility of PVP in subcritical or supercritical fluids. In this work, the solubility of PVP with molecular weights of 24 000 and 58 000 in subcritical 1,1,1,2-tetrafluoroethane (R134a) was measured at temperatures from 313 to 333 K and at pressures of 5.0, 7.0, 9.0, 11.0, 13.0, 15.0, and 18.0 MPa. The solubility of PVP in SCCO2 and subcritical R134a at the same experimental temperature and pressure conditions was also compared by calculating the enhancement factor (δ), finding that the solubility of PVP in subcritical R134a is much higher than that in SCCO2. Six semiempirical models (Chrastil, Adachi and Lu, Kumar and Johnston, Sung and Shim, Mendez-Santiago and Teja, and Bartle) were used to correlate PVP solubility in subcritical R134a, and the enthalpy values of PVP, including ΔHtotal, ΔHsub, and ΔHsol, were estimated through the Chrastil’s and the Bartle’s models.

In this paper, a high-gravity technology was described to prepare two-dimensional molybdenum disulfide nanosheets from bulk materials. This high-gravity field, producing by a rotating packed bed, provides shear force and collision force to exfoliate layered bulk molybdenum disulfide into nanosheets. The effects of rotational speed, surfactant concentration, exfoliation time, packing volume fraction, and exfoliation time on the concentration were systematically studied. The results showed that the concentration of the as-prepared suspension could be easily controlled. The concentration is 0.37 mg/mL under optimum conditions. Moreover, the dispersion of two-dimensional molybdenum disulfide nanosheets could be stabile for a long time. The lateral size of as-produced molybdenum disulfide nanosheets ranged from 50 to 800 nm, and the mean lateral size was 380 nm. Almost 84% of nanosheets were less than five layers. We also demonstrated that high-gravity technology also can be applied to tungsten disulfide. This technology provides a facile, efficient, and universal approach to prepare two-dimensional materials from layered bulk precursors.

•High gravity and hydrothermal technologies were used to prepare nitrogen-doped graphene.•Graphene oxide reduction and nitrogen doping were accomplished with hydrothermal method.•The nitrogen-doped graphene had better ORR catalytic properties.•The mechanisms of nitrogen doping and graphene oxide reduction were proposed.Electrochemical oxygen reduction is key to many clean and sustainable energy technologies, including proton exchange membrane fuel cells and metal–air batteries. However, the high activation barriers in the oxygen reduction reaction often make it the bottleneck of energy conversion processes; thus, high-performance oxygen reduction electrocatalysts are desired. At present, the best commercially available oxygen reduction catalyst is based on the precious metal Pt. However, it suffers from resource scarcity and unsatisfactory operational stability, hindering its widespread and large-scale application in clean and sustainable technologies. Nitrogen-doped graphene has excellent electrocatalytic properties for oxygen reduction. In this paper, a scalable method to prepare nitrogen-doped graphene with high quality was introduced, in which the graphene oxide prepared by high-gravity technology and urea was reacted under hydrothermal conditions. Accompanying the hydrothermal reaction, graphene oxide reduction and nitrogen doping were accomplished at the same time. The effect of the content of nitrogen on the performance of nitrogen-doped graphene was investigated. When the mass ratio (graphene oxide/urea) was 1:400, the nitrogen-doped graphene had the best oxygen reduction performance. Compared with the undoped samples, the initial reduction voltage of the nitrogen-doped samples distinctly shifted 45 mV to the right. When the voltage was −1.0 V, the electron transfer number was 4.1, indicating good oxygen reduction activity. The preparation method is feasible, simple, and can be easily scaled up.Download high-res image (143KB)Download full-size image

•A multicomponent mathematical model for hydrogen recycling membrane process.•The mathematical software MATLAB was used to solve the model.•Effects of various parameters on the hydrogen recovery.In methanol synthesis, hydrogen from purge gas is commonly recycled. In order to recycle hydrogen in a methanol synthesis loop effectively, multicomponent mathematical model for a hydrogen recycling process using membrane separation is established. With the help of L’Hopital’s rule, we get the boundary conditions easily, which greatly simplified the calculation. The mathematical software MATLAB was used to solve the model. Various operating conditions and membrane separator parameters were considered to investigate the effects of various parameters on the hydrogen recovery. Results from the model are in good agreement with literature values. This model can therefore be used in the analysis of operating conditions for hydrogen recovery from purge gas and in the analysis of other gas separation processes. It can be a significant guide to industrial applications of gas separation process.

The hydrophobically modified ceramic membranes have great potential for energy-efficient membrane distillation. In this work, flat-sheet ceramic membranes with a superhydrophobic surface were fabricated by grafting 1H,1H,2H,2H-perfluorooctyltrichlorosilane or 1H,1H,2H,2H-perfluorodecyltriethoxysilane and followed by ultraviolet irradiation. The surface water contact angle was improved from 46° of original ceramic membrane to 159°, which exhibited a stable and excellent superhydrophobic effect. The modified membranes showed a high flux of 27.28 kg·m− 2·h− 1 and simultaneously maintained an excellent retention rate of 99.99%, when used in vacuum membrane distillation process for treatment of a 1 wt% NaCl (75 °C) aqueous solution. These results suggested that superhydrophobic modification of ceramic surface is a facile and cost-effective way to achieve higher membrane distillation performance. The superhydrophobically-modified ceramic membrane with an excellent desalination capacity would show considerable potential in practical membrane distillation utilizations.

•Solubilities of rutin in SCCO2 and subcritical R134a were determined.•Extract rutin by SCCO2 or R134a above or below transition pressure, respectively.•Solubility data were satisfactorily correlated by Chrastil and m-ER&HV model.•Solubility data were tested to be thermodynamically consistent.Rutin is a common dietary flavonoid that has been widely consumed in pharmaceutical industry. To facilitate the extraction of rutin from plant tissues, we determined the solubility of rutin in supercritical carbon dioxide by dynamic method at 313.2–343.2 K over the pressures range of 9.0–18.0 MPa and in subcritical 1,1,1,2-tetrafluoroethane (R134a) by static method at 313.2–343.2 K over the pressures rang of 7.0–18.0 MPa. The experimental results indicate that the extraction of rutin should be operated by subcritical R134a or supercritical CO2 below or above the transition pressure (the pressure at which the rutin solubilities in subcritical R134a and supercritical CO2 are the same), respectively. Furthermore, the solubility data were satisfactorily correlated by Chrastil model and m-ER&HV model (modified Esmaeilzadeh–Roshanfekr equation of state combined with Huron–Vidal mixing rule), and the thermodynamic consistency of the solubility data was confirmed by the thermodynamic consistency test.

•An utra-thin graphene oxide (GO) intermediate layer was successfully prepared by a atomizing spray assembly technique.•An optimal voltage obtained from GO-based bipolar membrane was only 1.85 V at 100 mA/cm2.•GO was an effective catalyst for water dissociation and could significantly reduce the energy consumption of such a bipolar membrane.Bipolar membranes have interesting applications because they allow to produce an acid and a base from a neutral salt feed stream. Water dissociation occurred in intermediate layer plays a very important role for efficient bipolar membrane processes. Development of a strong hydrophilic and low resistance intermediate layer is crucial to further improve bipolar membrane efficiency. In this work, an utra-thin graphene oxide (GO) intermediate layer was successfully prepared by an atomizing spray assembly technique, which has greatly improved the water dissociation capacity. An optimal voltage obtained from GO-based bipolar membrane was only 1.85 V at 100 mA/cm2, which was far lower than those previously reported. An electrodialysis test also showed that the H+ concentration was higher than that in a bipolar membrane without GO as an intermediate layer. These clearly indicated that GO was an effective catalyst for water dissociation and could significantly reduce the energy consumption of such a bipolar membrane. The preliminary performances suggested the great prospect of these GO-based membranes for bipolar membrane electrodialysis.Download high-res image (169KB)Download full-size image

Bipolar membrane processes have evolved as one of the most promising technologies in the field of acid and base production as well as many interesting separation applications. Herein, we report a rapid spray-crosslinked assembly for fabricating a high-performance polyelectrolyte bipolar membrane. Polyvinyl alcohol (PVA), glutaricdialdehyde (GA) and polyethyleneimine (PEI) are alternatively and successively sprayed onto a supporting cation-exchange membrane. GA crosslinked PVA and PEI are responsible for the interlayer and anion-exchange layer, respectively. Under optimal conditions, at a current density of 100 mA cm−2, the cell voltage of the BPM was as low as 1.79 V. Moreover, it has been demonstrated that the spray crosslinked membrane has good stability in acid and alkali harsh conditions. In contrast to the traditional casting method, spray assembly combined with chemical cross-linking can tune the membrane thickness at the nanoscale and microscale levels, as well as increase its charge density and ion-exchange capacity. This facile approach might open a new way to efficiently and flexibly produce various bipolar membranes with different polyelectrolytes.

This study was conducted to investigate the effect of inorganic salts on the mass-transfer coefficient of O3 and decolorization of azo dye (Acid Red 14, AR14) solution through ozonation in a microporous tube-in-tube microchannel reactor (MTMCR). The overall volumetric mass-transfer coefficient (KGa) of O3 in the MTMCR was deduced by material balance. The effects of different salts on the KGa of O3 and decolorization efficiency of the AR14 solution were studied, and results show that both were significantly affected by the inorganic salts. Although the KGa of O3 and the decolorization efficiency of AR14 increased with increasing salt concentration and pH, the effect of NaNO3 was much weaker than that of NaCl, Na2SO4, Na2CO3, and NaHCO3. The enhanced KGa of O3 and decolorization could be due to the generation of species with high oxidizing ability in the presence of the salts.

•Copper acetate adsorbed graphene oxide sheet as precursor to prepare composites.•RGO intensified effective charge transfer, specific surface area and reaction sites.•Cu2O-RGO nanocomposites were originally used as photocatalyst to reduce CO2.•Nanocomposites showed better photo-reduction CO2 activity than Cu2O nanoparticles.The composites of cuprous oxide (Cu2O)/reduced graphene oxide (RGO) were prepared with copper acetate adsorbed graphene oxide (GO) sheets as precursors followed by in-situ reduction in the presence of ethylene glycol. The as-synthesized nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, UV–Vis spectroscopy (UV), fluorescence spectroscopy (FL) and electrochemical impedance spectroscopy (EIS). The graphene sheets were decorated by spherical Cu2O particles with an average diameter of 200 nm. Such combination not only alleviates the agglomeration of Cu2O particles but also restrains the restacking of graphene. A preliminary study on the photo-catalytic activities of the Cu2O/RGO nanocomposites including photo-degradation of Rhodamine B dye and photo-reduction of CO2 under the illumination of simulated sunlight was carried out. The as-synthesized nanocomposites showed better photo-catalytic activity than the conventional Cu2O particles. The photo-degradation efficiency increased about 52% and the methanol yield improved about 53%. The enhancements of the photo-catalytic activities were attributed to the effective charge transfer from Cu2O to RGO, enhanced specific surface area and increased reaction sites.

•PAM/SiO2 composite microcapsules were prepared by inverse Pickering emulsion polymerization.•Synthesized capsules consisted of a SiO2 nanoparticle shell and a polymer inner layer.•Size and rigidity of the capsules depended on concentrations of SiO2 and AM during preparation.•Composite capsules exhibited high adsorption capacity and rate to Hg(II) ions.Polyacrylamide/silica (PAM/SiO2) composite capsules were synthesized by inverse Pickering emulsion polymerization. Silica nanoparticles modified with methacryloxypropyltrimethoxysilane (MPS) were used as a stabilizer. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and thermal gravimetric analysis (TGA) were used to characterize the morphology and composition of the composite capsules. SEM and TEM images showed that capsules consisted of a particle shell and a polymer inner layer. The capsule size depends on the nanoparticle concentration in the continuous phase. The composite rigidity largely depends on the acrylamide concentration. FTIR and TGA results indicated the existence of polyacrylamide and SiO2 in the composite particles. Aqueous Hg(II) removal testing by the PAM/SiO2 composite capsules indicated promising potential for removing heavy metal ions from wastewater.

•A green one-step hydrothermal approach to synthesize ZnO-RGO nanocomposites.•The nanocomposites alleviate the agglomeration of ZnO nanoparticles.•The nanocomposites also restrain the restacking of RGO.•The ZnO-RGO nanocomposites were originally used as photocatalyst to reduce CO2.•The nanocomposites showed better photo-reduction CO2 activity than ZnO nanoparticles.The zinc oxide (ZnO)-reduced graphene oxide (RGO) nanocomposites were greenly synthesized by one-step hydrothermal reaction with ZnCl2 and graphite oxide (GO) as precursors without extra reductant. The photo-catalytic performances consisting of the photo-degradation of Rhodamine B (RhB) and the photo-reduction of CO2 under the illumination of simulated solar light at ambient temperature were investigated. It was validated that the ZnO spherical particles assembled by ZnO nanorods with an average diameter of 150 nm are uniformly deposited on the RGO sheets. Meanwhile, due to the introduction of RGO, the light adsorption scope of ZnO is enlarged, the size of ZnO is decreased, the degree of crystallinity is improved and the self-aggregation of the ZnO particles is effectively prevented. Comparing with the pure ZnO particles, the efficiency of the nanocomposites for the photo-degradation of RhB is increased by 39% and the yield of methanol from the reduction of CO2 is improved by 75%. The mechanisms that may explain the enhanced properties of as-synthesized ZnO-RGO for both the photo-degradation of RhB and the reduction of CO2 were also proposed.