Yunxiang Bai

Graphene Oxide Quantum Dots Incorporated into a Thin Film Nanocomposite Membrane with High Flux and Antifouling Properties for Low-Pressure Nanofiltration

Graphene oxide quantum dots (GOQDs), novel carbon-based nanomaterials, have attracted tremendous research interest due to their unique properties associated with both graphene and quantum dots. In the present study, thin film nanocomposite (TFN) membranes comprising GOQDs dispersed within a tannic acid (TA) film were fabricated by an interfacial polymerization reaction for low-pressure nanofiltration (NF). The resultant TA/GOQDs TFN membranes had measurably smoother and more hydrophilic, negatively charged surfaces compared to the similarly formed TA thin film composite (TFC) membrane. Owing to the loose active layer structure and the combination of Donnan exclusion and steric hindrance, the TA/GOQDs TFN membrane showed a pure water flux up to 23.33 L/m2·h (0.2 MPa), which was 1.5 times more than that of pristine TA TFC membrane, while high dye rejection to Congo red (99.8%) and methylene blue (97.6%) was kept. In addition, the TA/GOQDs TFN membrane presented better antifouling properties, which was ascribed to the favorable changes in membrane hydrophilicity, ζ-potential, and surface roughness. These results indicated the great potential of such membranes in wastewater treatment, separation, and purification in many industrial fields.

Improving CO2/N2 separation performance using nonionic surfactant Tween containing polymeric gel membranes

Polymeric gel membranes containing 0 to 65 wt% of Tween20, Tween21 and Tween80 in PEBA2533 were prepared using a solvent casting method. The effect of Tween with different lengths of alkyl chain on the properties and performance of the gel membranes was discussed. The results showed a better compatibility of PEBA2533 with Tween21 than Tween20 and Tween80. Both the pure CO2 permeability and CO2/N2 selectivity increased with the increase in the number of N-alkyl groups in Tween. On the other hand, with the increase of Tween content, CO2 permeability and CO2/N2 selectivity simultaneously increased. The best separation performance was achieved for the PEBA2533/Tween80-65 gel membrane, which had CO2 permeability of 289 Barrer and CO2/N2 selectivity of 40.70, at 0.6 atm and 25 °C. This suggests a potential application in gas separation membranes, for instance for CO2 capture.

ZIF-8 Filled Polydimethylsiloxane Membranes for Pervaporative Separation of n-Butanol from Aqueous Solution

ZIF-8-filled polydimethylsiloxane (PDMS) membranes, PDMS/ZIF-8, were prepared by a two-step polymerization process and were used to recover n-butanol from an aqueous solution by pervaporation (PV). Compared with pure PDMS membrane, PDMS/ZIF-8 membranes demonstrated an obviously higher n-butanol permselectivity. As an increase of ZIF-8 content, n-butanol/water selectivity increased initially and then decreased, while the n-butanol and water permeability decreased monotonously. PDMS/ZIF-8 membrane containing 2 wt% ZIF-8, that is, PDMS/ZIF-8-2 showed the highest selectivity. On the other hand, selectivity and permeability for n-butanol and water of PDMS/ZIF-8-2 membrane decreased with the increase of operating temperature. The selectivity and permeability for n-butanol reached 7.1 and 3.28 × 105 barrer, respectively, at 30°C when the feed concentration of n-butanol was 0.96 wt%.

High performance polydimethylsiloxane pervaporative membranes with hyperbranched polysiloxane as a crosslinker for separation of n-butanol from water

Hyperbranched polysiloxane (HPSiO) was successfully synthesized by a three-step process. The result of 29Si Nuclear Magnetic Resonance (NMR) measurement indicates that the degree of branching (DB) of HPSiO is 0.73. Then, novel polysiloxane membranes, HPSiO-c-PDMS, were prepared by the cross-linking reaction between HPSiO and α,ω-dihydroxypolydimethylsiloxane (H-PDMS) with different molecular weights. HPSiO-c-PDMS membranes were first used as membrane materials for recovering n-butanol from an aqueous solution by pervaporation (PV). The HPSiO-c-PDMS membranes demonstrated high n-butanol/water selectivity as well as high permeability. As the molecular weight of H-PDMS increased, the selectivity increased and the n-butanol permeability of HPSiO-c-PDMS-2 (with moderate H-PDMS molecular weight) membrane showed the highest value. The effects of temperature and feed concentration on the PV performances were also investigated. The PV performance, n-butanol permeability and n-butanol/water selectivity of the HPSiO-c-PDMS-2 membrane, reached 4.3 × 105 Barrer and 8.75, respectively, with a feed concentration of 1.0 wt% at 30 °C.

VTOS Cross-Linked PDMS Membranes for Recovery of Ethanol from Aqueous Solution by Pervaporation

PDMS membranes were prepared by cross-linking with vinyltriethoxysilane (VTOS) on polyacrylonitrile (PAN) substrate to increase hydrophobicity and improve pervaporation (PV) performance. It was shown that the membranes had high ethanol permselectivity and flux. The effects of cross-linking temperature, the content of cross-linking agent, and feed temperature on PV performance of VTOS cross-linked PDMS membranes were investigated. For 6 wt% ethanol aqueous solution, the PDMS membrane had the high separation factor of 15.5 and total flux 573.3 g·m−2·h−1, respectively, when the feed temperature was 40°C, H-PDMS : VTOS : DBTDL = 1 : 0.2 : 0.02 and cross-linking temperature was 80°C.

Efficient CO2 capture by metallo-supramolecular polymers as fillers to fabricate a polymeric blend membrane

Novel fillers based on metallo-supramolecular polymers were incorporated into PEBA2533 to obtain gas separation membranes, which exhibit excellent CO2 permeability and CO2/N2 selectivity.

ZSM-5 Filled Polyether Block Amide Membranes for Separating EA from Aqueous Solution by Pervaporation

ZSM-5 filled polyether block amide membranes (PEBA), PEBA/ZSM-5, were prepared and used to recover aroma, ethyl acetate (EA), from aqueous solution by pervaporation (PV). The membranes demonstrated high EA permselectivity, and with the increase of ZSM-5 loading, the separation factor increased initially and then decreased, while the total flux demonstrated the similar variation until the ZSM-5 loading was 10 wt%, at which it reached the lowest value. After that, it began to increase again. On the other hand, the separation factor, and total flux of the PEBA/ZSM-5 membrane containing 10 wt% ZSM-5, PEBA/ZSM-5-10, increased with the increase of feed concentration and temperature. The best PV performance, separation factor and total flux of PEBA/ZSM-5-10 membrane were 185.5 and 199.5 gm−2h−1, respectively, with feed concentration of 5 wt% EA at 50°C.

Preparation of jujube-cake structure membranes through in situ polymerization of hyperbranched polysiloxane in ethylene-vinyl acetate matrix for separation of ethyl acetate from water

Ethylene-vinyl acetate (EVA)/hyperbranched polysiloxane (HPSiO) hybrid pervaporative membranes for separation of ethyl acetate (EA) from water with a “jujube-cake” structure were prepared by in situ polymerization. The morphology of the EVA/HPSiO membranes was characterized by using a scanning electron microscope (SEM) and transmission electron micrographs (TEM). The mechanical properties, contact angle, density, void volume and swelling behavior of the membranes were investigated. We also studied the effect of HPSiO content, operating temperature and feed concentration on the separation properties of EA/water mixtures. The results show that the addition of appropriate HPSiO could improve the hydrophobicity of the membranes, which is helpful to recover EA from water. The membrane, loading 20 wt% HPSiO, exhibited the highest separation factor and permeability for a feed concentration of 1 wt% at 30 °C.

Poly(ether-b-amide)/Tween20 Gel Membranes for CO2/N2 Separation

Poly(ether-b-amide) (PEBA)/Tween20 gel membranes containing from 0 wt% to 65 wt% of Tween20 in PEBA2533, PEBA3533, and PEBA4033 were prepared by solvent casting method for CO2/N2 separation. The gas separation properties of the polymeric gel membranes were tested for single gases of CO2 and N2 at 25°C with the feed pressure of 0.6 atm. For all pure PEBA membranes, CO2 and N2 permeability decreased as the amount of polyamide block increased, but CO2/N2 selectivity increased. For PEBA/Tween20 gel membranes, both the CO2 permeability and CO2/N2 selectivity were greatly enhanced with the increase of Tween20 content. For the membrane of PEBA4033/Tween20-65, CO2/N2 selectivity, and CO2 permeability reached 54 and 146 Barrer, respectively, which is very interesting for potential application in CO2 removal from flue gas.

Tuning the size and morphology of zeolitic imidazolate framework-8 in a membrane dispersion reactor

Zeolitic imidazolate framework-8 (ZIF-8) with different sizes and morphologies were successfully synthesized using a membrane dispersion reactor (MDR). The MDR synthesis applied in this paper was expected to be an efficient and economical way to synthesize ZIF materials.