•Prussian blue nano-layer was in-situ prepared on porous polymer membranes.•Immobilization of PB on membrane surface does not deteriorate in adsorption performance.•The membrane showed high adsorption capacity and selectivity for cesium and rubidium.Ion-exchange adsorption is an effective method for separating cesium and rubidium from other alkaline metal ions in aqueous solutions. Herein, we developed a novel and facile method for in-situ preparation of Prussian blue (PB) nano-layer on porous polyacrylonitrile (PAN) membranes by heterogeneous nucleation in potassium ferrocyanide solution and then growth in FeCl3 solution, or potassium ferrocyanide solution as single precursor. The effects of reactant concentrations and reaction time on the PB layer, the static adsorption, dynamic adsorption, desorption and reuse of PB membranes were investigated. The results showed that the maximum adsorption capacity of PB nano-layer for cesium attains 0.714 mmol g−1 (25 °C), and the ideal selectivity factor of Cs+ vs. Li+, K+, and Na+ is found to be 41.76, 35.50, and 23.67 respectively. Compared with the PB powder, the immobilized PB on membrane surface does not deteriorate in the adsorption performance. NH4Cl aqueous solution exhibits excellent eluting effect, and the membrane can be reused for 5 times without apparent deterioration, indicating practical perspective in adsorption of cesium and rubidium from aqueous solutions.Download high-res image (139KB)Download full-size image

•Graphene oxide was modified by pyridine derivatives with SOCl2 activation method for adsorption of Cu(II).•The adsorption capacity of modified GO is related to the molecular structure of pyridine derivatives.•The adsorption capacity of 4′-carboxy-2,2′:6′,2″-terpyridine modified GO reaches up to 119.6 mg g−1.Graphene oxide (GO) was covalently modified by series of pyridine derivatives with SOCl2 activation method for adsorption of Cu(II) for the first time. The effects of pyridine derivatives structure, adsorption thermodynamics, kinetics and adsorbents reusability were investigated. The adsorption capacity of modified GO is related to the number of pyridine groups, and substituent position. The maximum adsorption capacity of 4′-carboxy-2,2′:6′,2″-terpyridine modified GO (GO-CTPy) reaches 119.6 mg g−1, which is much higher than that of other modified GO. The adsorption can be well described by the Langmuir isotherm model and pseudo-second-order kinetic model. GO-CTPy exhibited excellent regeneration and reusability.Download high-res image (116KB)Download full-size image

•Sandwich PES-SPES/amino-MIL-53(Al)/PTFE adsorptive membranes were prepared.•The membrane showed higher adsorption capacity than that of mixed matrix membrane.•The static and dynamic adsorption capacities increased with amino-MIL-53(Al) content.Novel sandwich PES-SPES/amino-MIL-53(Al)/PTFE adsorptive membranes were prepared by a filtration/immersion precipitation method and employed for the removal of p-nitrophenol (PNP) from water. The static adsorption thermodynamics, kinetics, dynamic adsorption/desorption and membrane reusability were investigated. The results showed that, amino-MIL-53(Al) displays very high saturation adsorption capacity towards PNP (297.85 mg g−1). The sandwich membranes showed much higher adsorption performance (static adsorption capacity, breakthrough volume, saturation volume, dynamic adsorption capacity) and lower pressure drop than those of blank and mixed matrix membranes. With increased amino-MIL-53(Al) content, the maximum static adsorption capacity, saturation volume and dynamic adsorption capacity significantly increased. The sandwich membranes exhibited excellent reusability even after four recycles.

In the fabrication of zeolitic imidazolate frameworks (ZIFs) thin films and membranes, the preparation of stable ZIFs dispersions is crucial. Herein, ultra-stable ZIF-8 aqueous dispersions were obtained successfully for the first time. It was found that, after the synthesis of ZIF-8, with the increased washing times, the positive surface potentials of ZIF-8 particles decrease, resulting in increased aggregate size. The ZIF-8 dispersions washed for zero times are very stable in water, and there is no settlement even after centrifuging at 8000 rpm for 6 min. The aggregate size of ZIF-8 dispersions in ethanol aqueous solutions decreases with increased ethanol content, and there is no apparent settlement in absolute ethanol even after 13 days. The ultra-stable ZIF-8 dispersions display great potentials in fabrication of thin films and membranes.

The design and tailoring of membrane permeation channels is crucial for precise separation of ions or molecules. Herein, a method for tuning the permeation channels of graphene oxide (GO) membranes is developed, in which the basal planes and edges of GO flakes are simultaneously crosslinked by dicarboxylic acid and diamine. By altering the chain length of the crosslinkers, the size, structure and properties of the permeation channels are successfully tuned. In the permeation of single metal salt solution, the fluxes of metal ions are related to the swelling degree of GO membranes. In the separation of mixed salt solutions, the fluxes are determined by the radii of hydrated cations, and the crosslinked GO membranes display outstanding size-selectivity. This is the first report about the distinct orders of permeation fluxes of single salt solution and mixed salt solution. With the increasing hydrophobicity of diamines, the permeation fluxes of aqueous solution decrease. The optimized crosslinked GO membranes display excellent fluxes and separation factor, which are more than 2 times and 3 times that of the pristine membranes, respectively. The elastic modulus of the crosslinked GO membranes is double that of the pristine one, and the swelling degree in water is 75 times lower.

•Metal-organic frameworks/based mixed matrix membranes for pervaporation are reviewed.•Progress in polymer, MOFs, mass transfer, and applications are given.•Perspectives and suggestions of mixed matrix membranes are provided.Metal-organic frameworks (MOFs)/polymer mixed matrix membranes (MMMs) have great potential in pervaporation separation due to the ease of design and modification of MOFs, along with the compatibility between MOFs and polymer matrix. This article reviews the current status of MOFs MMMs for pervaporation, including polymer (hydrophobicity/hydrophilicity, structure stability), MOFs (stability, hydrophobicity/hydrophilicity, surface functional structure, particles morphology and pores size), mass transfer, and applications (dehydration of organic solvents, removal of dilute organic compounds from aqueous streams, separation of organic-organic mixtures, and membrane reactor). The perspectives and suggestions of MOFs MMMs are given.

•Graphene oxide membranes were covalently crosslinked by dicarboxylic acids.•The pyrolysis temperature of crosslinked membranes increased while the swelling degree decreased.•The fluxes of single salt solutions are positively correlated to swelling degree of GO membranes.Graphene oxide (GO) membranes were crosslinked by dicarboxylic acids in order to improve the mechanical strength, stability and permeation performance. The effects of crosslinking conditions (temperature, catalyst concentration, time, crosslinker concentration) on the mechanical performance, along with the influences of crosslinker molecular structure on the thermal stability and swelling degree of GO membranes, were studied. The thermal pyrolysis temperature of crosslinked GO membranes increased about 2–8 °C while the swelling degree averagely decreased about 66% in DI water and 40% in 0.05 mol L−1 of KCl solution in comparison with those of pristine one. In the permeation of single salt solutions, the fluxes are positively correlated to the swelling degree of GO membranes. The effects of swelling degree on the permeation fluxes were firstly noticed. The crosslinked GO membranes show high permeation fluxes (more than 2 times) along with low swelling degree, demonstrating its potential application in ion dialysis.

We present a method to prepare covalently crosslinked graphene oxide (GO) membranes with adjustable intersheet spacing by esterification reactions, using dicarboxylic acids, diols or polyols as the crosslinker and hydrochloric acid as the catalyst. For dicarboxylic acids, with the increased length of the molecular chain, the intersheet spacing, the elastic moduli and permeation fluxes of GO membranes generally increases. The elastic modulus of the hexanedioic acid crosslinked membrane is 15.6 times as that of pristine, and the selectivity of K+/Mg2+ attains to 6.1. There exists an optimum chain length of crosslinkers. For diols or polyols, the hydrophobic substituents (–CH3) tend to enlarge the intersheet spacing of GO membranes, while the hydrophilic substituents (–OH) favor the penetration of hydrated ions. The elastic moduli, permeation fluxes and selectivity of diols or polyols crosslinked membranes are relatively lower than those of dicarboxylic acids crosslinked ones.

Hydroxide ions play a crucial role in the reduction of Ag+ ions with alcohol. In this paper, Ag nanoparticles were prepared with triethanolamine (TEA) serving as reducing agent and alkali for the first time. The effects of stabilizer, mole ratio of AgNO3/TEA, temperature and AgNO3 concentration on the particles, as well as the antibacterial performance of the particles, were studied. The results showed that, PEG and PVP are effective for inhibiting the growth of particles, and Ag particles about 40 nm in size were obtained. The effects of TEA amount on the particles are negligible. On rising temperature, the particles size increase and the particles become more regular. With the increased AgNO3 concentration, the particles tend to large and poly-dispersed. The Ag nanoparticles show excellent antibacterial property.Highlights► Ag nanoparticles were prepared with triethanolamine as reducing and alkaline agent. ► Particles about 40 nm in size were obtained. ► Effects of stabilizer, temperature and concentration on particles were studied.

In this paper, particles of calcium tungstate as a model compound were prepared by a reverse micelle’s method. The morphology of particles was tuned from rod to spindle-like and spherical by altering the temperature and concentration of reactants. A volume per single particle and a total number of particles were calculated to explain quantitatively the mechanism of influence of reaction conditions on the process. It was found that the reactant concentration had no effect on the number of particles. With increasing temperature or reaction time, the number of particles decreased, whereas the particle volume increased. The bulk water in the micelles seemed actually affect the size of particles.

Metal complexes are often employed as precursors for the preparation of nanocrystals. Prussian Blue nanocrystals were prepared as a model product with Fe(III)–oxalic acid complexes as precursors. The particles size was easily tuned by varying the molar ratio of oxalic acid to FeCl3. Quantitative calculation of the species distribution was investigated to interpret the experimental results for the first time. The theoretical estimation is well consistent with the experimental results. The calculation is useful for selection of ligand and ligand-to-metal molar ratios, as well as for prediction of precipitation process. This method can be expanded to other ligands and reactions.Graphical abstractHighlights► Prussian Blue nanocrystals were prepared with Fe3+–oxalic acid complexes. ► Quantitative calculation of species distribution was investigated. ► The calculation is useful for ligand selection and prediction of particles size.

Nanosized calcium carbonate was prepared as a model product in a continuous gas–liquid membrane contactor for the first time. The effects of Ca(OH)2 concentration, CO2 partial pressure and liquid flow velocity on the absorption rate were estimated according to the gas–liquid reaction theory. The results showed that, with the increase in Ca(OH)2 concentration, CO2 partial pressure and liquid flow velocity, the absorption rate increased. The theoretical predictions were in agreement with the experimental data.

Nanosized calcium carbonate, strontium carbonate, aluminium hydroxide and alumina particles, about 50 nm in size, were prepared with a gas–liquid membrane contactor for the first time. The contactor provided large and constant interfacial area, as well as symmetrical supersaturation profile in the radial direction of the membrane fibers. Furthermore, all the gas could be absorbed in the non-disperse contacting mode, which was especially important for the expensive or hazardous gases. The effects of the reactant concentrations on the pH evolution and the particles morphology were studied.

Nanosized calcium carbonate particles were prepared with a continuous gas-liquid membrane contactor. The effects of Ca(OH)2 concentration, CO2 pressure and liquid flow velocity on the particles morphology, pressure drop and membrane fouling were studied. With rising Ca(OH)2 concentrations, the average size of the particles increased. The effects of Ca(OH)2 concentration and CO2 pressure on particles were not apparent under the experimental conditions. When the Ca(OH)2 concentration and liquid flow velocity were high, or the CO2 pressure was low, the fouling on the membrane external surface at the contactor entrance was serious due to liquid leakage, whereas the fouling was slight at exit. The fouling on the membrane inner-surface at entrance was apparent due to adsorption of raw materials. The membrane can be recovered by washing with dilute hydrochloric acid and reused for at least 6 times without performance deterioration.

•PVDF membranes were modified by photografting and quaternization.•Lysozyme was employed as a model alkaline protein.•Effects of grafting and quaternization conditions were studied.PVDF microfiltration membranes were modified by photografting of 4-vinylpyridine and then quaternized with n-butyl chloride. Lysozyme was employed as a model alkaline protein to investigate the antifouling performance of quaternized membranes. The effects of grafting and quaternization conditions on modification were studied. The results show that, the percent of initiator grafted and grafting density increase with the irradiation time, whereas the grafted chain length and grafting degree rise initially and then reach plateau. The optimal concentrations of initiator and 4-vinylpyridine are 5 wt.% and 20 wt.%, respectively. The ion exchange capacity increases with quaternization temperature and time, and the optimal concentration of n-butyl chloride is 30 wt.%. When the solution pH is at the isoelectric point of lysozyme, the saturated adsorption capacity of membranes reaches maximum. When the solution pH is lower than isoelectric point, the saturated adsorption capacity of quaternized membranes is the lowest due to electrostatic repulsion and hydrophilicity of membranes. The modified membranes exhibit excellent antifouling performance to alkaline proteins.Download full-size image

We present a method to prepare covalently crosslinked graphene oxide (GO) membranes with adjustable intersheet spacing by esterification reactions, using dicarboxylic acids, diols or polyols as the crosslinker and hydrochloric acid as the catalyst. For dicarboxylic acids, with the increased length of the molecular chain, the intersheet spacing, the elastic moduli and permeation fluxes of GO membranes generally increases. The elastic modulus of the hexanedioic acid crosslinked membrane is 15.6 times as that of pristine, and the selectivity of K+/Mg2+ attains to 6.1. There exists an optimum chain length of crosslinkers. For diols or polyols, the hydrophobic substituents (–CH3) tend to enlarge the intersheet spacing of GO membranes, while the hydrophilic substituents (–OH) favor the penetration of hydrated ions. The elastic moduli, permeation fluxes and selectivity of diols or polyols crosslinked membranes are relatively lower than those of dicarboxylic acids crosslinked ones.