Characteristics of phenylalanine imprinted membrane prepared by the wet phase inversion method

A phenylalanine imprinted membrane without a sponge layer containing macrovoids was prepared by the wet phase inversion method. The structure of the phenylalanine imprinted membrane prepared by an in-situ implanting procedure was denser than that of the membrane prepared by post implanting. Consecutive washings with distilled water and acetic acid solution removed nearly all of the template molecules from the membrane prepared by the post implanting procedure, although much of the template molecules remained in the membrane prepared by in-situ implanting. The removal of the template molecules from the membrane increased the population of the free COOH groups but reduced that of the dimerized COOH groups in the membrane. A D-Phenylalanine imprinted membrane prepared by post implanting selectively adsorbed D-phenylalanine from a racemate solution, where the adsorption selectivity reached 4.79. A D-phenylalanine imprinted membrane prepared by in-situ implanting exhibited an inverse adsorption affinity.     

Enhanced adsorptive removal of Cr(VI) in aqueous solution by polyethyleneimine modified palygorskite

Polyethyleneimine (PEI) modified palygorskite (Pal) was used for the adsorption of Cr(VI) in aqueous solution. The absorbent was characterized by Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). Characterized results confirmed that the Pal has been successfully modified by PEI. The modification of PEI increased the Cr(VI) adsorption performance of the Pal by the adsorption combined reduction mechanism, and amino groups of the adsorbent play the main role in the enhanced Cr(VI) adsorption. The maximum adsorption capacity was 51.10 mg·g⁻¹ at pH 4.0 and 25 °C. The adsorption kinetics of Cr(VI) on the adsorbent conforms to the Langmuir isotherm model. The maximum adsorption occurs at pH 3, and then the adsorption capacity of PEI-Pal was decreased with the increase of pH values. The adsorption kinetics of Cr(VI) on PEI-Pal was modeled with pseudo-second-order model. The addition of Cl⁻, SO₄²⁻ and PO₄³⁻ reduced the Cr(VI) adsorption by competition with Cr(VI) for the active sites of PEI-Pal. The Cr(VI) saturated PEI-Pal can be regenerated in alkaline solution, and the adsorption capacity can still be maintained at 30.44 mg·g⁻¹ after 4 cycles. The results demonstrate that PEI-Pal can be used as a potential adsorbent of Cr(VI) in aqueous solutions.     

Alkylation of polyethyleneimine for homogeneous ligands in ATRP

Ethylated and butylated polyethyleneimine ligands were synthesized and employed in copper catalyzed atom transfer radical polymerization of styrene and methyl methacrylate with suitable initiators in order to obtain homogeneous polymerizations, resulting in well defined polymers with low polydispersities. Linear curves drawn from kinetics and conversion-molecular weight plots indicate that all the polymerizations were successfully controlled. In ATRP reactions of S and MMA, the apparent rate of polymerization, k_p^app, exhibits a plateau at [Ligand]/[CuBr] ≥ 0.5 ratio for both ligands. The apparent rate constant also decreases by increasing the alkyl chain length of the alkylated polyethyleneimine ligand. Ethylated and butylated polyethyleneimine ligands in ATRP of S and MMA were found to be faster than the existing ATRP ligands.     

季铵化聚乙烯亚胺的缓蚀与杀菌性能研究

制备了季铵化的聚乙烯亚胺(QPEI),采用静态挂片失重法研究了在0.5mol/L硫酸溶液中QPEI对低碳钢的缓蚀性能;以大肠杆菌(E.coli)为致病菌体,采用平板活菌记数法研究了QPEI的抗菌活性,并使用TTC-脱氢酶活性测定法,研究了QPEI的抗菌机理。结果表明,QPEI对低碳钢具有十分优良的缓蚀作用,同时具有很强的抗菌性能,其缓蚀作用抗菌作用基于杀菌过程,而不只是抑菌过程。     

Enhanced the dispersibility and permeability of silver nanoparticles over rGO grafted by positively-charged polyethyleneimine toward broad-spectrum sterilization

Silver nanoparticles (Ag NPs) are used as antimicrobial agents due to their high-efficiency, broad-spectrum disinfection activity. However, the agglomeration and stability problems caused by excessive release of silver ions (Ag⁺) have severely restricted their developments. Herein, a novel silver/polyethyleneimine/reduced graphene oxide (Ag/PEI/rGO) antibacterial material featuring good dispersibility and permeability was rationally designed, thus benefiting for the capture of bacteria due to the introducing of highly-cationic PEI modifier and controllable release of biocidal agents (Ag⁺). Compared with Ag/rGO, the Ag/PEI/rGO has excellent stability and shows a more efficient sterilization efficacy against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) with 100% germicidal efficiency with low orders of dozens of ppm. In addition, the outstanding biocompatibility of this Ag/PEI/rGO antibacterial material endows it with promising potential in sterilization applications, which is expected to solve the infection problem caused by bacterial biofilm formation.     

Adsorption behaviour of functional grafting particles based on polyethyleneimine for chromate anions

Polyethyleneimine (PEI) was first grafted on the surfaces of micro-sized silica gel particles in the manner of the coupling graft, forming the grafting particles PEI/SiO₂. Afterward, for the grafted PEI, two polymer reactions, tertiary amination reaction and quaterisation, were allowed to be carried out in turn, and a kind of functional composite particles, QPEI/SiO₂, was obtained. QPEI/SiO₂ particles were used as solid adsorbent in the removal of chromate anions from aqueous solution. The static adsorption experiments (batch method) were performed, the effects of various factors on the adsorption capacity of QPEI/SiO₂ were examined, and the dynamic desorption experiments were also carried out. The experimental results show that QPEI/SiO₂ particles have strong adsorption ability for CrO₄²⁻ ions by right of electrostatic interaction, and the saturated adsorption amount actually reach up to 0.14 g/g. The isothermal adsorption behaviour is fitted to Langmuir model. The adsorption ability of QPEI/SiO₂ particles for CrO₄²⁻ ions is affected greatly by the quaterisation degree of the grafted PEI macromolecules. The QPEI/SiO₂ particles with higher quaterisation degrees have greater adsorption capacities. The adsorption ability of QPEI/SiO₂ particles for CrO₄²⁻ ions is nearly independent of pH values of the medium. QPEI/SiO₂ particles have excellent eluting and regenerating property as a mixed solution of NaOH and NaCl is used as eluent.     

Effect of pH on the removal of Cr(III) and Cr(VI) from aqueous solution by modified polyethyleneimine

A novel flocculant with the capacities of reduction and chelation was prepared in this paper. The flocculant, called polyethyleneimine–sodium xanthogenate (PEX), was synthesized by modifying polyethyleneimine with carbon disulfide and sodium hydroxide. The effect of pH on the removal of Cr(III) and Cr(VI) from aqueous solution with PEX was investigated by using flocculation experiments. The results showed that in the single-ion system (only including Cr(III) or Cr(VI) in the solution), the final Cr(III) decreased with the increase in pH from 2.0 to 10.0, while the final Cr(VI) increased at first and then decreased with the increase in this pH range studied. The removal of Cr(III) was not desirable at pH lower than 7.0, whereas the final Cr(VI) concentration reached the minimum value of 0.145 mg/L at pH 2.0. In the mixture system of Cr(III) and Cr(VI), the variation tendency for the removal of Cr(III) or Cr(VI) was very similar to that obtained in the single-ion system. The oxidation–reduction potential, zeta potential, and final pH in the supernatant were also measured to analyze the above results. Furthermore, FTIR spectra revealed that dithiocarboxylic acid groups on the macromolecular chains of PEX played a major role in the Cr(VI) reduction and Cr(III) chelation.     

Enzyme kinetics of kinetic resolution of racemic ibuprofen ester using enzymatic membrane reactor

An ultrafiltration hollow fiber enzymatic membrane reactor was employed to study the kinetics of lipase-catalyzed kinetic resolution of racemic ibuprofen ester. Lipase from Candida rugosa was employed in the hydrolysis reaction both in free form in a batch system and in immobilized form in an enzymatic membrane reactor (EMR). The half life (t_1/2) of immobilized lipase on spongy layer was 105 h at reaction temperature of and 62 h at . This value was 94 h for lipase immobilized on the inner lumen and 45 h for free lipase in batch system at . Excessive substrate was found to inhibit the reaction as an uncompetitive inhibitor. The by-product 2-ethoxyethanol was found to be non-competitive inhibitor to the reaction when it was present in an excess. Michaelis constant (K_m) and maximum reaction rate (V_max) for immobilized lipase were and , respectively; and that for free lipase were and h^-1, respectively.     

Preparation and properties of PVDF-fabric composite membrane for membrane distillation

The flat sheet PVDF-fabric composite membrane used for membrane distillation was prepared by coating and wet phase inversion process. The composite membrane consisted of a PVDF porous membrane layer and a fabric layer. The thin polyester filament woven fabric with water-and-oil repellent finish was used as the support of composite membrane. The effects of fabric texture, PVDF concentration in casting solution and functional finishing of fabric on the preparation and properties of the composite membrane were investigated. The experimental results showed that fabric texture, PVDF concentration and functional finishing of fabric had great influence on the preparation and properties of the composite membrane. When the PVDF concentration in casting solution was 10-12% and the support fabric, with 435 warps/10 cm and 273 wefts/10 cm and the area weight of 79 g/m², was finished with 2 g/L water-and-oil repellent agent FK-501, the prepared composite membrane exhibited better performance in tensile strength, peeling strength and water vapor permeability, with mean pore size of 0.63 μm and overall porosity of 57.6%.     

Gas permeation properties in a composite mesoporous alumina ceramic membrane

In this study, the effect of different chemical interactions on the gas permeation properties were investigated in the composite mesoporous ceramic membrane prepared with γ-alumina on the surface of a macroporous ceramic membrane. In the permeation results, the gas permeance of the strongly adsorbing gas species increased in the mesoporous ceramic membranes. It is considered that the permeation of the adsorbing gas species increased through preferential adsorption on the membrane pore surface. It was shown in this study that the modified mesoporous ceramic membrane could increase the permeation performance in the presence of the adsorbing gas species due to the surface diffusion mechanism.     

Characterization of membrane distillation membranes prepared by phase inversion

In this paper, flat membrane distillation membranes have been successfully manufactured from PVDF/DMAc and PVDF/DMF blends by using phase inversion induced by an immersion precipitation technique. The structure of the membranes is asymmetric with a porous top layer and macrovoids, as assessed by SEM. The existence of MD fluxes in these membranes is established by performing various pure water flux experiments. A maximum in the MD fluxes for a particular value of the polymer content in the casting solution from which the membrane is manufactured has been observed. The dependence of the magnitude of the fluxes on the membrane thickness is also discussed and the influence of temperature polarization evaluated.     

Polyurethane-SAPO-34 mixed matrix membrane for CO2/CH4 and CO2/N2 separation

SAPO-34 nanocrystals (inorganic filler) were incorporated in polyurethane membranes and the permeation properties of CO₂, CH_4, and N₂ gases were explored. In this regard, the synthesized PU-SAPO-34 mixed matrix membranes (MMMs) were characterized via SEM, AFM, TGA, XRD and FTIR analyses. Gas permeation properties of PU-SAPO-34 MMMs with SAPO-34 contents of 5 wt%, 10 wt% and 20 wt% were investigated. The permeation results revealed that the presence of 20 wt% SAPO-34 resulted in 4.45%, 18.24% and 40.2% reductions in permeability of CO_2, CH_4, and N₂, respectively, as compared to the permeability of neat polyurethane membrane. Also, the findings showed that at the pressure of 1.2 MPa, the incorporation of 20 wt% SAPO-34 into the polyurethane membranes enhanced the selectivity of CO₂/CH₄ and CO₂/N₂, 14.43 and 37.46%, respectively. In this research, PU containing 20 wt% SAPO-34 showed the best separation performance. For the first time, polynomial regression (PR) as a simple yet accurate tool yielded a mathematical equation for the prediction of permeabilities with high accuracy (R² > 99%).     

Carbon dioxide adduct from polypropylene glycol grafted polyethyleneimine as a climate-friendly blowing agent for polyurethane foams

A novel CO₂ adduct has been synthesised from a branched polyethyleneimine with polypropylene glycol (PPG) side chains and can serve as an alternative to traditional polyurethane blowing agents, such as hydrochloroflourocarbons and hydrofluorocarbons, which cause ozone depletion and/or global warming. The CO₂ adduction trapped 13.8 wt% of CO₂, forming alkylammonium carbamates in the main chains. Therefore, the prepared blowing agent is amphophilic, and can form micellae-like spheres in the mixture of polyurethane raw materials called the white component. Once this mixture is blended with isocyanate or the black component like in conventional foaming processes, the consequent exothermic polymerisation drives the release of the captured CO₂ from the micelles, serving as the foaming gas. Meanwhile, the blowing agent gradually restores its original polyamine structure, whose bulky PPG side chains can sterically inhibit the reaction between the restored amine groups and the isocyanate groups in the growing polyurethane chains. The resulting foam displays uniform cellular morphology with a much lower density than the control sample blown by trances of water from the raw materials. This is the first report using thermally instable CO₂ adduct to blow polyurethanes, which could pave the way for the next generation of climate-friendly polyurethane blowing agents.     

A Selective Silicon-Based Membrane Formed by Pyrolysis of Silicon Resin

Abstract

A new, highly selective silicon-based membrane was developed by pyrolyzing a thermosetting silicon resin precursor in two steps. The pyrolysis step was performed under an inert gas in the range of 800 to 950°C. The activation step was conducted at the same temperature as the first step. Oxygen content in the activation gas was located between 0.5 and 1.0%. The crosslinking density and the matrix structure of the polymeric precursor were important factors for the permeable characteristics of the resulting pyrolysis membrane. The average selectivity was 5 to 10 times those of a pyrolysis membrane from silicon rubber. Additives in the precursor had significant effects on toughness and stability of the resulting membrane. By varying the additive content in the precursor, silicon-based pyrolysis membranes with different stabilities in air were obtained.     

Desalination by membrane distillation adopting a hydrophilic membrane

Direct contact membrane distillation (MD) by means of composite membranes with a PVA/PEG hydrophilic layeron a hydrophobic PVDF substrate has been developed for desalination. The effects of brine temperature, salt concentration, running time and the addition of ethanol on the flux of composite membranes have been investigated. Results showed that the flux of the composite membrane did not deteriorate by adopting an additional hydrophilic membrane although durability was obviously improved. More than 99% of the separation coefficient in one run was achieved with the conductivity of the produced fresh water in the range of 6-10 μs/cm. The flux of the composite membrane retained 91% flux of substrate at 70°C, being 23.7 kg/h·m². When the brine temperature rose to 70°C, the composite membrane showed a declined concentration polarisation, with a smaller C_mb/C_b (3.89) than that of the substrate (5.79). Although the flux decreased with the increase of brine concentration, it retained 64% flux of pure water at brine solution containing 20% NaCl and was kept almost constant until 25% NaCl. In the continuous running experiments, there was no obvious drop of flux, even after adding 25% ethanol to the brine and running overnight. It is expected that adopting a hydrophilic layer can prohibit the wetting problem that faced traditional MD with hydrophobic membranes.     

Microstructures and properties of solid-state-sintered silicon carbide membrane supports

Porous solid-state-sintered SiC (S–SiC) membrane supports were successfully fabricated by pressureless sintering at 2150 °C in argon, using fine and coarse graded SiC powders as the main starting material. There were uniformly distributed and fully interconnected pores in as-acquired S–SiC membrane supports, accompanied with similar apparent porosities for all of them. When increasing the size of coarse SiC powder, their average pore sizes were distinctly enlarged from ∼1.6 μm to ∼2.3 μm, which significantly enhanced their nitrogen permeability from 0.9 × 10⁻¹³ m² to 2.6 × 10⁻¹³ m². Moreover, S–SiC membrane supports possessed outstanding flexure strengths of 134.1 ± 21.3 MPa at room temperature and 88.7 ± 8.4 MPa at 1000 °C owing to strong interface bonding between SiC grains. Compared with the traditional SiO₂ -bonded and mullite-bonded SiC supports, S–SiC membrane supports presented their great superiority in high-temperature flexure strength as well as acid and alkali corrosion resistance, which permitted them to be potentially applied in high-temperature and strongly corrosive environments.     

膜参数对乳化过程的影响

膜乳化法是近年来提出的一种新的乳化方法,可以制备出单分散性非常好的乳液,在各领域都有广泛的应用。但生产率低是制约该方法工业化的一个主要因素。对影响乳液形成的膜参数进行了讨论,并对膜的优化设计进行了探讨。