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A novel nanofiber composite nano-filtration membrane was prepared by combination of grafting, electrospinning and surface coating. First, carboxyl multi-walled carbon nanotubes were grafted onto bacterial cellulose molecular chains by solution reaction. The grafting products were characterized by TEM, FTIR, Raman, XPS and TGA measurements. Then, they were electrospun into nanofibers to be the supporting layer, and a coating of denser chitosan hydrogel thin film was used as the barrier layer. The morphology of the electrospun nanofibers and composite membrane were observed by SEM. The mechanical behavior of the composite membrane was investigated in dry and wet state. The filtration properties were evaluated in term of the pure water flux (PWF), dye rejection rate and anti-fouling properties. Results showed that the chitosan hydrogel coated electrospun nanofiber composite membrane had higher tensile strength and Young’s Modulus with the value of 11.75, 10.11 and 244, 211 MPa in dry and wet state, respectively. The PWF was increased from 52.1 to 140.7 L/m² h with the operation pressure increasing from 0.1 to 0.6 MPa. Direct Orange S, Procion Red mx-5B, Stilbene Yellow and Methylene Blue with molecular weight ranged from 300 to 800 g/mol were selected for dye removal test. The rejection rate could maintain over 90% for dyes with the molecular weight larger than 600 g/mol under 0.5 MPa. The chitosan hydrogel coated electrospun nanofiber composite membrane exhibited good anti-fouling properties for both oil and protein. These results indicate that these membranes are efficient for dye removal from wastewater, with high flux and rejection rate at high pressure.

A novel nanofiber composite nanofiltration membrane was fabricated through coating calcium alginate hydrogel on electrospun polyhydroxybutyrate/carbon nanotubes (CaAlg-c-PHB/CNT) nanofiber membrane. The CaAlg-c-PHB/CNT nanofiber composite membrane was investigated by means of SEM, FTIR, Raman, XRD, DSC, TGA, zeta potential and water contact angle (WCA) measurements. The tensile tests of the CaAlg-c-PHB/CNT nanofiber composite membrane were performed in dry and wet state. The filtration properties of the CaAlg-c-PHB/CNT nanofiber composite membrane were measured in term of flux and rejection rate at operation pressure ranged from 0.1 to 0.7 MPa. The antifouling properties were investigated by emulsified oil–water and BSA solution separation. Results showed that the CaAlg-c-PHB/CNT nanofiber composite membrane with 1 wt% CNT had the highest tensile strength and initial Modulus with the value of 6.14, 5.12 and 142.64, 127.5 MPa in dry and wet state, respectively. The water contact angle was decreased remarkably from 83.6° to 17.8° after calcium alginate hydrogel coating. The pure water flux (PWF) was increased from 68.61 to 150.72 L/m2 h with operation pressure increased from 0.1 to 0.7 MPa. Five dyes with different molecular weight ranged from 400 to 900 g/mol were selected for filtration test. The rejection rate could maintain over 90% for dyes with the molecular weight higher than 600 g/mol under 0.5 MPa. The CaAlg-c-PHB/CNT nanofiber composite membrane showed good antifouling performance for both oil and protein. These results indicated that the CaAlg-c-PHB/CNT composite nanofiber membrane can be used as an effective nanofiltration membrane operated at high pressure for dye removal.

Electrospun polyhydroxybutyrate (PHB)/carboxyl multi-walled carbon nanotubes grafted polyhydroxybutyrate (CMWCNT-g-PHB) composite nanofibers scaffolds were fabricated by electrospinning technology. The grafted product CMWCNT-g-PHB was prepared by condensation reactions between the carboxyl groups of CMWCNT and hydroxyl groups of PHB molecules and characterized by FTIR, XRD, XPS, TG and TEM measurements. The surface morphology, hydrophilicity and tensile mechanical properties of the electrospun PHB/CMWCNT-g-PHB composite nanofibers membrane scaffolds were investigated. The values of tensile strength, breaking elongation rate, initial modulus and fracture energy of the composite nanofibers scaffolds can reach to 4.64 MPa, 255.59%, 88 MPa and 109.73 kJ/m2, respectively. The biodegradability and cytocompatibility of the electrospun composite nanofibers scaffolds were preliminarily evaluated. The as-prepared electrospun PHB/CMWCNT-g-PHB composite nanofibers scaffolds with the characteristics of large specific area, high porosity, good biodegradability and cytocompatibility as well as sufficient mechanical properties should be more promising in the field of tissue engineering scaffolds and biological medicine.

Calcium alginate (CaAlg) hydrogel filtration membrane was prepared using urea as pore-forming agent. The effects of preparation and operating conditions on the removal rate of Cd 2+ were researched. The removal mechanism of Cd 2+ and the anti-fouling property of CaAlg membrane were investigated. The removal rate of the CaAlg filtration membrane reached over 99.5% within 120 min when 20 mg/L Cd 2+ was used, and the flux was 15.5 L/m 2 h at 0.1 MPa when the thickness of the membrane was 0.28 ± 0.08 mm. However, the removal rate of Cd 2+ was below 10.0% when the same concentration Cd 2+ solution was adsorbed by CaAlg membrane with the same size. Energy dispersive spectroscope analysis demonstrated that the removal of Cd 2+ depended on the adsorption and ion exchange of Ca 2+ by Cd 2+ . CaAlg membrane exhibited a higher removal rate for Cd 2+ (almost 100%). It was the filtration process that promoted the adsorption and ion exchange of Cd 2+ in CaAlg hydrogel.

Kaolin/calcium alginate (kaolin/CaAlg) free-standing membranes were prepared by adding different amounts of Kaolin into the sodium alginate (NaAlg) casting solution and crosslinked by Ca2+ using urea as porogen agent. The morphology of the kaolin/CaAlg filtration membrane was characterized by scanning electron microscope (SEM). Then the kaolin/CaAlg membrane was used for the removal of dyes and Cd2+. The kaolin significantly improved the mechanical behavior and flux of the kaolin/CaAlg membrane. The flux reached 17.53 L/m2&middot, h at 0.1 MPa and when the content of Kaolin in NaAlg was 70 wt.%. The filtration of BSA solution and oil-water emulsion indicated that the kaolin/CaAlg composite filtration membrane exhibited good anti-fouling properties. The rejection of Brilliant Blue G250, Congo red, and methylene blue by the kaolin/CaAlg filtration membrane was 100%, 95.22%, and 62.86%, respectively. The removal rate of Cd2+ reached 99.69%, with a flux of 17.06 L/m2&middot, h at 0.1 MPa.