High permeability poly(vinylidene fluoride)ultrafiltration membrane doped with polydopamine modified TiO_(2) nanoparticles

In order to improve the water permeability of poly(vinylidene fluoride)(PVDF)ultrafiltration(UF)membranes with low molecular weight cut-off(MWCO),polydopamine(PDA)was employed in the membrane preparation process.Owing to itsmerits of material-independent adhesion,PDAwas coated on inorganic particles or added in coagulation bath to tailor the final membrane structure and property.The introduction of PDA broke through the permeability/selectivity trade-off of the PVDF membrane.By adding the PDA coated titaniumdioxide(PDA/TiO2)nanoparticles,water flux increased by 287% while MWCO kept similar with the pristine PVDF membrane.Thermodynamics and Kinetics of the PVDF/additives/non-solvent were analyzed and shown that nanoparticles reduced the thermodynamic stability and increased the phase separation speed,and the speed can be adjusted using different nanoparticles.Additionally,X-ray diffraction(XRD)test indicated that PVDF crystalline form changed fromαphase to β phase after adding different nanoparticles.Permeability/selectivity trade-offwas broken through by DA addition in coagulation bath.Compared with the original PVDF membrane,when the DA concentration of the coagulation bath was 2.0 g·L^−1,water flux increased by 312%,and MWCO of the PVDF membrane ranged in 10,000 to 20,000 Da as well as contact angle decreased from 81.4°to 45°.

Porous boronate affinity monolith for on-line extraction coupled to high-performance liquid chromatography for sensitive analysis of heterocyclic aromatic amines in food samples

A novel on-line solid-phase microextraction–high-performance liquid chromatography（SPME–HPLC）system was developed for the determination of heterocyclic aromatic amines（HAAs） in food samples. A poly（vinylphenylboronic acid-co-ethylene glycol dimethacrylate） polymer monolith was prepared for on-line efficient extraction and large-volume injection was used to increase the sensitivity of detection.The polymermonolith, based on a ternary porogen, was prepared by in situ polymerization of vinylphenylboronic acid（VPBA） and ethylene glycol dimethacrylate（EGDMA） in a fused-silica capillary column. It showed good permeability, high extraction capacity, and high selectivity. The column-tocolumn reproducibility was satisfactory, and the enrichment factors for HAAs were 3746–7414.Conditions influencing the on-line extraction efficiency, including p H of sample solutions, flow rate of extraction and desorption, and desorption volume, were investigated. The proposed method had low limit of detection（0.10–0.15 ng/L） and good linearity. Trace HAAs in roast beef and lamb samples were determined, and the amounts of 2-amino-3-methylimidazo[4,5-f]quinoline, 2-amino-3,4-dimethylimidazo[4,5-f]quinoline, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline, and 2-amino-3,4,7,8-tetramethyl-3H-imidazo[4,5-f]quinoxaline in these samples were 0.235–2.08 ng/g. The recoveries for the five HAAs ranged from74.3% to 119%, and the relative standard deviation（RSDs） were less than 8.2%. The results showed that the proposed on-line method was highly sensitive for monitoring HAAs in different food samples.

Remarkably Improved Gas Separation Performance of Polyimides by Forming“Bent and Battered”Main Chain Using Paracyclophane as Building Block

The design and development of highly permeable,selective and stable polymer membranes are great challenges in the gas separation industry.Herein,we constructed two intrinsic microporous polyimides(6FPCA and 6FMCA)derived from two isometric diamines(PCA and MCA),which were synthesized by palladium catalyzed C—N coupling reaction.The PCA and MCA diamines contain a hollow beaded structure of 2,2′-paracyclophane as a building block with a specified window size of 3.09Å.The chemical structures of monomers,polyimides were confirmed by NMR,FTIR,and elementary analysis.6FPCA and 6FMCA exhibit good solubility,excellent thermal stability,and mechanical properties.6FPCA exhibits much larger microporosity(434 versus 120 m2·g−1),FFV(0.22 versus 0.15),d-spacing(6.9 versus 5.9Å),and over 10 times higher permeability with a very little decrease in selectivity than the corresponding polyimide(6FpA)with a plane structure,which remarkably increased their separation performance from far below the 2008 Robeson Upper bounds to reach these limitations for O2/N2 and CO2/CH4.Additionally,the 6FPCA also demonstrates good plasticization resistance,moderate aging properties,and high CO2/CH4 mixed-gas separation performance.These results indicate that paracyclophane subunit can be successfully incorporated into polymers to enhance their ultra-microporosity and separation properties,which open a new avenue for developing high performance gas separation membranes with topological ultra-micropores.