膜流动电位测试中Ag-AgCl电极的制备及稳定性研究

膜的动电特性研究中,往往采用流动电位方法。该方法中,Ag-Ag Cl测试电极的质量是影响测试准确性的关键要素。本文采用正交试验设计和方差分析,着重考察电解法制备Ag-Ag Cl电极过程中,电流强度(I)、氯化时间(t)、电解质溶液浓度(CHCl)、电极来源(n)、烘烤温度(T)、活化电极溶液浓度(CKCl)等因素对Ag-Ag Cl电极稳定性的影响。得到Ag-Ag Cl电极的最优制备参数为:电流密度3.0m A/cm2,氯化时间50min,盐酸浓度0.1mol·L-1,烘烤温度120℃,活化电极溶液(KCl)浓度0.001mol·L-1;最显著影响因素为电极来源,显著影响因素为氯化时间和烘烤温度。对最优条件组合下制备的AgAg Cl电极,进行了稳定性实验,结果表明:制备的电极具有较好的稳定性,24h内电极电位漂移量小于0.10mv,7天内电极电位漂移量小于0.2mv;在聚偏氟乙烯中空纤维超滤膜流动电位测试中,流动电位与流动压差具有良好的线性和可重复性,回归曲线R20.99,变化规律符合Helmholtz-Smoluehowski公式,可以较好满足膜的流动电位测试要求。     

Expanded Analogs of Three-Dimensional Lead-Halide Hybrid Perovskites

Replacing the Pb−X octahedral building unit of A^IPbX₃ perovskites (X=halide) with a pair of edge-sharing Pb−X octahedra affords the expanded perovskite analogs: A^IIPb₂X₆. We report seven members of this new family of materials. In 3D hybrid perovskites, orbitals from the organic molecules do not participate in the band edges. In contrast, the more spacious inorganic sublattice of the expanded analogs accommodates larger pyrazinium-based cations with low-lying π* orbitals that form the conduction band, substantially decreasing the band gap of the expanded lattice. The molecular nature of the conduction band allows us to electronically dope the materials by reducing the organic molecules. By synthesizing derivatives with A^II=pyridinium and ammonium, we can isolate the contributions of the pyrazinium-based orbitals in the band gap transition of A^IIPb₂X₆. The organic-molecule-based conduction band and the inorganic-ion-based valence band provide an unusual electronic platform with localized states for electrons and more disperse bands for holes upon optical or thermal excitation.     

Synthesis and characterization of modular polyphosphonate homopolymers and copolymers

Linear polyphosphonates with the generic formula –[P(Ph)(X)OR′O]_n– (X = S or Se) have been synthesized by polycondensations of P(Ph)(NEt₂)₂ and a diol (HOR′OH = 1,4-cyclohexanedimethanol, 1,4-benzenedimethanol, tetraethylene glycol, or 1,12-dodecanediol) followed by reaction with a chalcogen. Random copolymers have been synthesized by polycondensations of P(Ph)(NEt₂)₂ and mixture of two of the diols in a 2:1:1 mol ratio followed by reaction with a chalcogen. Block copolymers with the generic formula –[P(Ph)(X)OR′O]_{(x + 2)} –[P(Ph)(X)OR′O]_{(x + 3)}– (X = S or Se) have been synthesized by the polycondensations of Et₂N[P(Ph)(X)OR′O]_{(x + 2)}P(Ph)NEt₂ oligomers with HOR′O[P(Ph)(X)OR′O]_{(x + 3)}H oligomers followed by reaction with a chalcogen. The Et₂N[P(Ph)(X)OR′O]_{(x + 2)}P(Ph)NEt₂ oligomers are prepared by the reaction of an excess of P(Ph)(NEt₂)₂ with a diol while the HOR′O[P(Ph)(X)OR′O]_{(x + 3)}H oligomers are prepared by the reaction of P(Ph)(NEt₂)₂ with an excess of the diol. In each case the excess, x is the same and determines the average block sizes. All of the polymers were characterized using ¹H, ¹³C{¹H}, and ³¹P{¹H} NMR spectroscopy, TGA, DSC, and SEC. ³¹P{¹H} NMR spectroscopy demonstrates that the random and block copolymers have the expected arrangements of monomers and, in the case of block copolymers, verifies the block sizes. All polymers are thermally stable up to ~300°C, and the arrangements of monomers in the copolymers (block vs. random) affect their degradation temperatures and T_g profiles. The polymers have weight average MWs of up to 3.8 × 10⁴ Da.     

Characterization and Optimization of Injectable In Situ Crosslinked Chitosan-Genipin Hydrogels

In recent years, there has been an increased interest in injectable, in situ crosslinking hydrogels due to their minimally invasive application and ability to conform to their environment. Current in situ crosslinking chitosan hydrogels are either mechanically robust with poor biocompatibility and limited biodegradation due to toxic crosslinking agents or the hydrogels are mechanically weak and undergo biodegradation too rapidly due to insufficient crosslinking. Herein, the authors developed and characterized a thermally-driven, injectable chitosan-genipin hydrogel capable of in situ crosslinking at 37 °C that is mechanically robust, biodegradable, and maintain high biocompatibility. The natural crosslinker genipin is utilized as a thermally-driven, non-toxic crosslinking agent. The chitosan-genipin hydrogel's crosslinking kinetics, injectability, viscoelasticity, swelling and pH response, and biocompatibility against human keratinocyte cells are characterized. The developed chitosan-genipin hydrogels are successfully crosslinked at 37 °C, demonstrating temperature sensitivity. The hydrogels maintained a high percentage of swelling over several weeks before degrading in biologically relevant environments, demonstrating mechanical stability while remaining biodegradable. Long-term cell viability studies demonstrated that chitosan-genipin hydrogels have excellent biocompatibility over 7 days, including during the hydrogel crosslinking phase. Overall, these findings support the development of an injectable, in situ crosslinking chitosan-genipin hydrogel for minimally invasive biomedical applications.     

Terpyridine Based Heteroleptic Ruthenium Complexes: Influence of Donor and Acceptor Ligands in Photosensitization

We report heteroleptic ruthenium complexes of terpyridine (tpy) ligands with directly linked carboxylic acid anchors. These complexes feature methyl or methoxy-substituted ^4′−Phtpy as donor ligands. We prepared these heteroleptic complexes from the ruthenium (II) precursor via a milder route to preclude the homoleptic complex formation. The donor−acceptor arrangement of tpy ligands in these ruthenium complexes renders visible light absorption giving metal and ligand-to-ligand charge transfer excitations at c.a. 490 nm. We evaluate the effect of the tpy donor substituents on the light-harvesting ability in Dye-Sensitized Solar Cells (DSSCs) and compare their photosensitizing ability with heteroleptic complexes bearing phenyl spacer at the acceptor end. Further, scrutinizing their photovoltaic performance, we studied their electron transfer kinetics in DSSCs using electrochemical impedance spectroscopy. This paper presents the structure-photosensitization relationship of these heteroleptic ruthenium complexes through a combined experimental and computational approach.     

Quantitative determination of fucoidan using polyion-sensitive membrane electrodes

The use of polyanion and polycation-sensitive membrane electrodes to detect five different preparations of fucoidan is described. Unlike linear polyanionic molecules previously measured with polymer membrane-based electrochemical sensors, fucoidans from marine brown algae are all highly branched, sulfated polysaccharides with varying charge densities and structures, depending on the species of seaweed, method of extraction used and extent of purification. When tridodecylmethylammonium (TDMA) was used as the ion-exchanger, a large, non-equilibrium EMF response was observed over a concentration range of 0.5–50 μg mL⁻¹ fucoidan. Fucoidan was also measured by titration with polycationic protamine, using a dinonylnaphthalene sulfonate (DNNS)-doped membrane electrode as the potentiometric endpoint detector. Potentiometric titration was used to determine the binding ratio between protamine and fucoidan at the neutralization endpoint for each fucoidan preparation. This binding ratio was then used to successfully determine the fucoidan content of commercially available nutritional supplements. Fucoidan was also measured in undiluted blood serum, demonstrating that this method may be applicable for measuring fucoidan for clinical applications.