Cellulose acetate hollow fiber nanofiltration membrane with improved permselectivity prepared through hydrolysis followed by carboxymethylation

Enzyme mimics based membrane reactor for di(2-ethylhexyl) phthalate degradation

Di(2-ethylhexyl) phthalate (DEHP), the most abundantly used plasticizer, was considered to be a hazardous chemical that was difficult to be degraded naturally. In this study, inspired by the "catalytic triad'' in serine proteases, an enzyme mimic material was developed by combining the proteases's active sites of serine, histidine and aspartate (S-H-D) with the self-assembling sequence of LKLKLKL and the aromatic group of fluorenylmethyloxycarbonyl (Fmoc). By mixing the monomer of peptides containing separate S, H and D residues with a ratio of 2:1:1, the enzyme mimics were found to co- assemble into nanofibers (Co-HSD) and showed the highest activity towards DEHP degradation because of the synergistic effects of active sites, orderly secondary structure and stable molecular conformation. To further improve ability and applicability, the high active mimetic enzyme was immobilized onto regenerated cellulose (RC) membranes for DEHP degradation in a continuous recycling mode. The RC membranes were first functionalized by the NaIO₄ oxidation method to form aldehyde groups and then conjugated with the enzyme mimics via Schiff-base reaction. As a biocatalytic membrane, this membrane could not only effectively degrade DEHP, but also showed good stability, thus establishing a promising biomaterial for large scale biodegradation of DEHP in water decontamination and liquid food depollution.

Fabrication and evaluation of carboxymethylated diethylaminoethyl cellulose microcarriers as support for cellular applications

Cellulose based microcarriers can be used in biomedical science as supports for cell adhesion and proliferation. However, to facilitate cell attachment to their surface, they require appropriate functional surface charge. Cell function such as adhesion and growth is increased on the modified surfaces with cationic and anionic groups. In this research, diethylaminoethyl cellulose was carboxymethylated to produce soluble multifunctional cellulose with simultaneous presence of cationic and anionic functional groups. Then, carboxymethylated diethylaminoethyl cellulose (CM-DEAEC) were produced by ionic crosslinking. Various instrumental techniques were applied to characterize the microcarriers. Biological tests were also performed to determine cell seeding efficiency, proliferation and attachment on microcarriers. Fabricated CM-DEAEC microcarriers had 1500-1800 μm diameter, +26.0 surface potential, 376% swelling behavior and 233 °C glass transition temperature respectively. The findings showed that CM-DEAEC microcarriers support cellular attachment and proliferation very well and hence are promising materials for cell therapy and tissue engineering applications.

Fractionation and Concentration of High-Salinity Textile Wastewater using an Ultra-Permeable Sulfonated Thin-film Composite

A sulfonated thin-film composite (TFC) nanofiltration membrane was fabricated using 2,2'-benzidinedisulfonic acid (BDSA) and trimesoyl chloride (TMC) on a polyether sulfone substrate by conventional interfacial polymerization. Due to a nascent barrier layer with a loose architecture, the obtained TFC-BDSA-0.2 membrane showed an ultrahigh pure water permeability of 48.1 ± 2.1 L^-1 m^-2 h^-1 bar^-1, and a considerably low NaCl retention ability of <1.8% over a concentration range of 10-100 g L^-1. The membrane, which possesses a negatively charged surface, displayed an excellent rejection of over 99% toward Congo red (CR) and allowed the fast fractionation of high-salinity textile wastewater. The prepared membrane required only 3-fold water addition to accomplish the separation of multiple components, whereas the commercial NF270 (Dow) membrane required 4-fold water addition and almost double the length of time. Furthermore, the TFC-BDSA-0.2 membrane was subsequently tested for the dye concentration process. It maintained a high flux of 8.2 L^-1 m^-2 h^-1 bar^-1 and a negligible dye loss, even when the concentration factor reached ∼10. Finally, by using a 20% alcohol solution as a back-washing medium, a flux recovery ratio (FRR) of 95.6% was achieved with TFC-BDSA-0.2, and the CR rejection ability remained the same. These results prove the outstanding antifouling and solvent-resistant properties of the membrane.

Preparation and Characterization of Antibacterial Cellulose/Chitosan Nanofiltration Membranes

Abstract: Presently, most nanofiltration membranes are prepared with non-biodegradable petrochemical materials. This process is harmful to the ecosystem and consumes a large amount of non-renewable energy. In this study, biodegradable and biocompatible antibacterial cellulose/chitosan nanofiltration membranes (BC/CS-NFMs) were fabricated and characterized for their mechanical strength, antimicrobial activity, salt and dye filtration performance, and polyethylene glycol (PEG) retention using Thermal gravimetric analysis (TGA), Field emission scanning electron microscopy(FE-SEM), Fourier transform infrared spectroscopy(FT-IR), and X-ray diffraction (XRD). The BC/CS-NFMs were obtained by the hydrolysis and carboxymethylation of dense cellulose/chitosan membranes (BC/CSMs). The tensile strength of the BC/CS-NFMs decreased as the chitosan content increased. In addition, the thermal stability and antibacterial ability of the BC/CS-NFMs improved. The pore size is less than 1 nm, and a spongy, layered structure is observed in the cross-sectional FE-SEM images. FT-IR analysis shows that a part of the hydroxyl in cellulose transforms to carboxymethyl during the hydrolysis and carboxymethylation of the BC/CSMs. No obvious changes can be observed in the cellulose and chitosan after the blend membrane formation from the XRD measurements. Based on the experimental results on the permeation and rejection of BC/CS-NFMs, different proportions of cellulose and chitosan nanofiltration membranes almost did not affect the water flux and rejection rate. The BC/CS-NFMs showed better water flux and a higher rejection rate in aqueous dye-salt solutions.

Dissolution control of Mg by cellulose acetate-polyelectrolyte membranes

Cellulose acetate (CA)-based membranes are used for Mg dissolution control: the permeability of the membrane is adjusted by additions of the polyelectrolyte, poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA). Spin-coated films were characterized with FT-IR, and once exposed to an aqueous solution the film distends and starts acting as a membrane which controls the flow of ions and H2 gas. Electrochemical measurements (linear sweep voltammograms, open-circuit potential, and polarization) show that by altering the CA:PDMAEMA ratio the dissolution rate of Mg can be controlled. Such a control over Mg dissolution is crucial if Mg is to be considered as a viable, temporary biomedical implant material. Furthermore, the accumulation of corrosion products between the membrane and the sample diminishes the undesirable effects of high local pH and H2 formation which takes place during the corrosion process.