Zhen-Liang Xu

Polypiperazine-amide Nanofiltration Membrane Modified by Different Functionalized Multiwalled Carbon Nanotubes (MWCNTs)

In this work, three modified multiwalled carbon nanotubes (MWCNTs) with carboxyl (MWCNT-COOH), hydroxyl (MWCNT-OH) and amino groups (MWCNT-NH), respectively, were added into the aqueous phase containing piperazine (PIP) to fabricate the nanocomposite nanofiltration (NF) membranes via interfacial polymerization. The influences of functional groups of MWCNTs on the performance of modified NF membrane were investigated. The MWCNTs were characterized by TEM, FT-IR and TGA; meanwhile, the properties of the membranes were evaluated by XPS, TEM, AFM and contact angle. The XPS results proved the successful incorporation of MWCNT in the active layer of modified NF membrane. When the MWCNT concentration is 0.01% (w/v), all the nanocomposite membranes possessed the optimal separation properties, among which the membrane incorporated with MWCNT-OH demonstrated the highest water flux of 41.4 L·m(-2)·h(-1) and the Na2SO4 rejection of 97.6% whereas the one with MWCNT-COOH had the relative lowest rejection of 96.6%. Furthermore, the increased hydrophilicity of functional groups in modified MWCNTs resulted in different nodular surface morphologies, thicknesses and hydrophilicities of the nanocomposite membranes. All the membranes possessed a molecular weight cutoff (MWCO) within 300 Da and good operation stability.

Superhydrophobic modification of PVDF–SiO2 electrospun nanofiber membranes for vacuum membrane distillation

Electrospun nanofiber membranes having a hierarchical structure with multilevel roughness were generated via electrospinning of poly(vinylidene fluoride) (PVDF)–SiO2 blend solutions. The composite PVDF–SiO2 nanofiber membranes were then endowed with superhydrophobicity by the fluorosilanization of the surface with low surface energy fluoroalkylsilane (FAS). The results showed that when the SiO2 content in the dope solutions increased from 0 wt% to 8 wt%, the water contact angles of the FAS modified nanofiber membranes increased significantly from 130.4° to 160.5°. The increment of the silica content in the dope solutions decreased the fiber diameters and pore sizes of the modified membranes, while the mechanical properties were enhanced with the silica addition. The liquid entry pressures of the membranes increased gradually from 84 kPa to 195 kPa with silica addition due to the increased contact angles and decreased pore size. Vacuum membrane distillation experiments were carried out for the modified nanofiber membranes to evaluate the anti-wetting properties. The optimal superhydrophobic nanofiber membrane maintained a stable flux of 31.5 kg m−2 h−1 with a permeate conductivity approximately 10 μs cm−1 over the entire test, while the fluxes and conductivities of the nanofiber membranes without superhydrophobicity showed a significant decrease and increase, respectively. The results indicated that the superhydrophobic modification process rendered the nanofiber membrane anti-wetting properties without compromising its excellent permeability.

FAS Grafted Electrospun Poly(vinyl alcohol) Nanofiber Membranes with Robust Superhydrophobicity for Membrane Distillation

This study develops a novel type of electrospun nanofiber membranes (ENMs) with high permeability and robust superhydrophobicity for membrane distillation (MD) process by mimicking the unique unitary microstructures of ramee leaves. The superhydrophobic ENMs were fabricated by the eletrospinning of poly(vinyl alcohol) (PVA), followed by chemical cross-linking with glutaraldehyde and surface modification via low surface energy fluoroalkylsilane (FAS). The resultant FAS grafted PVA (F-PVA) nanofiber membranes were endowed with self-cleaning properties with water contact angles of 158° and sliding angles of 4° via the modification process, while retaining their high porosities and interconnected open structures. For the first time, the robust superhydrophobicity of the ENMs for MD was confirmed by testing the F-PVA nanofiber membranes under violent ultrasonic treatment and harsh chemical conditions. Furthermore, vacuum membrane distillation experiments illustrated that the F-PVA membranes presented a high and stable permeate flux of 25.2 kg/m2 h, 70% higher than those of the commercial PTFE membranes, with satisfied permeate conductivity (<5 μm/cm) during a continuous test of 16 h (3.5 wt % NaCl as the feed solution, and feed temperature and permeate pressure were set as 333 K and 9 kPa, respectively), suggesting their great potentials in myriad MD processes such as high salinity water desalination and volatile organiccompounds removal.

Processing–Structure–Property Correlations of Polyethersulfone/Perfluorosulfonic Acid Nanofibers Fabricated via Electrospinning from Polymer–Nanoparticle Suspensions

Polyethersulfone (PES)/perfluorosulfonic acid (PFSA) nanofiber membranes were successfully fabricated via electrospinning method from polymer solutions containing dispersed calcium carbonate (CaCO(3)) nanoparticles. ATR-FTIR spectra indicated that the nanoparticles mainly existed on the external surface of the nanofibers and could be removed completely by acid treatment. Surface roughness of both the nanofibers and the nanofiber membranes increased with the CaCO(3) loading. Although FTIR spectra showed no special interaction between sulfonic acid (-SO(3)) groups and CaCO(3) nanoparticles, XPS measurement demonstrated that the content of -SO(3) groups on external surface of the acid-treated nanofibers was enhanced by increasing CaCO(3) loading in solution. Besides, the acid-treated nanofiber membranes were performed in esterification reactions, and exhibited acceptable catalytic performance due to the activity of -SO(3)H groups on the nanofiber surface. More importantly, this type of membrane was very easy to separate and recover, which made it a potential substitution for traditional liquid acid catalysts.

Fabrication and characterization of a novel nanofiltration membrane by the interfacial polymerization of 1,4-diaminocyclohexane (DCH) and trimesoyl chloride (TMC)

This study focuses on the preparation and nanofiltration properties of a novel thin-film composite polyamide membrane formed by the interfacial polymerization of 1,4-diaminocyclohexane (DCH) and trimesoyl chloride (TMC) on a porous polysulfone supporting membrane. At the same time, we found that the introduction of sodium N-cyclohexylsulfamate (SCHS) can improve to a degree the water flux and salt rejection. The active surface of the membrane was characterized by employing SEM and AFM. The performance of the nanofiltration membrane was optimized by considering the preparation conditions, including the monomer concentration, reaction time, curing conditions and SCHS concentration. The resulting NF membrane prepared under the optimum conditions exhibited a Na2SO4 rejection of 98.1% and a water flux of 44.6 L m−2 h−1 at 0.6 MPa. The pore size of the NF membrane was about 0.33–0.42 nm, which was calculated from the rejection of PEG and carbohydrates, respectively.

A Novel Seeding Method of Interfacial Polymerization-Assisted Dip Coating for the Preparation of Zeolite NaA Membranes on Ceramic Hollow Fiber Supports

A novel seeding method combining interfacial polymerization (IP) technique with dip-coating operation was designed for directly coating nanosized NaA seed crystals (150 nm) onto the micrometer-sized α-Al2O3 hollow fiber support, in which the polyamide (PA) produced by IP acted as an effective medium to freeze and fix seed crystals at the proper position so that the controlled seed layer could be accomplished. While a coating suspension with only 0.5 wt % seed content was used, a very thin seed layer with high quality and good adhesion was achieved through dip coating twice without drying between, and the whole seeding process was operated at ambient conditions. The resulting zeolite NaA membranes not only exhibited high pervaporation (PV) performance with an average separation factor above 10000 and flux nearly 9.0 kg/m(2)·h in dehydration of 90 wt % ethanol aqueous solution at 348 K but also demonstrated great reproducibility by testing more than eight batches of zeolite membranes. In addition, this seeding strategy could be readily extended to the preparation of other supported zeolite membranes for a wide range of separation applications.

Novel polyamide thin-film composite nanofiltration membrane modified with poly(amidoamine) and SiO2 gel

Recently, poly(amidoamine) (PAMAM) has emerged as a novel material due to its high density of functional groups, hyper-branched structure and hydrophilic nature. PAMAM has been used as a monomer during an interfacial polymerization process for the fabrication of nanofiltration membranes. Previous work has focused on the low generation of PAMAM (G0, G1 and G2), however, the high generation of PAMAM (G4 and G5) still lacks investigation. This work focuses on the preparation of nanofiltration membranes, which are made of PAMAM–NH2 G4 and PAMAM–NH2 G5. By optimizing the concentration of PIP and SiO2 gel in the aqueous solution, the pure water flux improved by 106% while separation properties are kept at the same level. XPS, EDS, SEM, AFM and contact angle were used to characterize the NF membrane properties. The PAMAM/PIP/SiO2 membrane prepared under the optimum conditions exhibited a pure water flux of 38.5 L m−2 h−1 and Na2SO4 rejection of 92.0% under 0.6 MPa. The PAMAM/PIP/SiO2 membrane’s robust long-time running performance showed its good potential in practical applications.

A Novel Composite Nanofiltration Membrane Prepared by Interfacial Polymerization of 2,2′-Bis(1-Hydroxyl-1-trifluoromethyl-2,2,2-trifluoroethyl)-4,4′-methylenedianiline and Trimesoyl Chloride

A novel composite nanofiltration (NF) membrane was prepared by interfacial polymerization of 2,2′-bis(1-hydroxyl-1-trifluoromethyl-2,2,2-trifluoroethyl)-4,4′-methylenedianiline (BHTTM) and trimesoyl chloride (TMC) on polyethersulfone (PES) supporting membrane. Different preparation conditions and NF membrane performances were discussed. The membrane structures of composite NF membranes were characterized by attenuated total reflectance infrared (ATR-IR), scanning electron microscope (SEM), and atomic force microscopy (AFM). The results showed that the NF membrane prepared under the optimum condition exhibited Na2SO4 rejection of 85.3% and the water flux of 10.1 l.m−2.h−1. The NF membrane was treated by 5000 ppm chlorine solution for 1 h. The salt rejection and water flux of the treated membrane reached to 94.5% and 94.8 l.m−2.h−1. The rejection of two NF membranes for inorganic electrolyte solutions decreased in the order of Na2SO4, MgSO4, MgCl2, and NaCl, which were typical characteristics of negatively charged membranes.

Formation of microporous polymeric membranes via thermally induced phase separation: A review

A review of recent research related to microporous polymeric membranes formed via thermally induced phase separation (TIPS) and the morphologies of these membranes is presented. A summary of polymers and suitable diluents that can be used to prepare these microporous membranes via TIPS are summarized. The effects of different kinds of polymer materials, diluent types, cooling conditions, extractants and additive agents on the morphology and performance of TIPS membranes are also discussed. Finally new developments in TIPS technology are summarized.

Preparation of MFI zeolite membranes on coarse macropore stainless steel hollow fibers for the recovery of bioalcohols

Hydrophobic MFI zeolite membranes are considered suitable for the recovery of bioalcohols (bioethanol and biobutanol) from fermentation broths. Stainless steel (SS) hollow fibers (HF) are more appropriate Al-free supports for MFI membranes due to their high mechanical strength and easily-sealing property as compared to other Al-free HF such as silica or yttria-stabilized zirconia HF. High-quality MFI membranes on coarse macropore SS HF were fabricated via secondary growth with a simple dip-coating seeding method. The synthesis conditions (composition, time, temperature) were systematically investigated in this study. Considering the separation performance and time saving demand, the membranes synthesized at 175 °C for 6 h exhibited the optimal ethanol or butanol permselectivity with a flux of 1.68 kg (m2 h)−1 and a separation factor of 65 for 5 wt% ethanol/water pervaporation (PV) at 80 °C, and with a flux of 218 g (m2 h)−1 and a separation factor of 207 for 1.5 wt% butanol/water PV at 80 °C. The separation performance for ethanol or butanol permselectivity was comparable to that reported in the literature. The MFI membranes together with the intrinsic advantages of SS HF displayed promising prospects in the field of bioethanol or biobutanol recovery.