酚酞基聚芳醚砜非对称超滤膜凝胶动力学研究

采用耐高温工程塑料——含酚酞侧基的聚芳醚砜(PES-C)为膜材料,草酸和聚乙二醇为添加剂,N,N-二甲基乙酰胺为溶剂,并利用改进的凝胶动力学实验装置和方法,使之能真实地再现不同膜孔结构生长及发展演化的过程,借助相关软件对图像进行处理,考察了添加剂、聚合物浓度对铸膜液凝胶速度的影响,对酚酞基聚芳醚砜非对称膜的凝胶过程的动力学进行研究.结果表明,动力学图像与最终膜结构有很好的一致性,凝胶动力学方面得到了与Strathman等不同的研究结果,发现凝胶前锋位移的平方与时间不是线性关系,凝胶动力学过程不能简单地用Fick扩散定律来描述.     

TiO2颗粒表面包覆SiO2纳米膜的动力学模型

针对液相法二氧化钛颗粒表面包覆氧化硅纳米膜的过程,提出包覆过程是溶胶凝胶机制,研究了表面成膜的动力学方程,考察了成膜剂浓度和成膜过程中温度对成膜速度的影响,并通过实验对氧化硅膜形成的动力学方程进行了验证.     

BPU/PLLA/DO体系的热力学性质对成膜过程及共混膜结构的影响

利用浸沉凝胶相转化法制备医用聚氨酯(BPU)/聚乳酸(PLLA)微孔膜,讨论了BPU/PLLA不同配比时聚合物/1,4-二氧六环/水三元体系的凝胶特性及其对共混膜结构和性能的影响,并初步探讨成膜机理.研究结果表明,随着BPU/PLLA质量比例由90/10变为75/25、50/50、25/75、10/90,聚合物/溶剂/非溶剂三元体系的热力学稳定性增强,凝胶值增大,但是共混溶液的黏度增大;并且,共混膜的孔隙率、膜厚、平均孔径、水蒸汽透过速率及吸水率先增加后降低.这主要是由于随着BPU/PLLA质量比例的变化,动力学扩散过程控制成膜速度转变为成膜体系热力学性质控制成膜速度;成膜过程由延时分相转变为瞬时分相,后又转变为延时分相.     

草酸对酚酞基聚芳醚砜超滤膜性能和结构的影响

以新型耐高温工程塑料一含酚酞侧基的聚芳醚砜（PES-C）为膜材料,N,N-二甲基乙酰胺（DMAc）为溶剂,通过改变铸膜液中添加荆草酸的含量,采用相转化法在平板刮膜机上制备了一系列超滤膜,考察了添加荆草酸含量对铸膜液粘度、凝胶速度、膜性能和结构的影响,研究了PES-C／DMAC体系中添加荆草酸作用的规律。     

溶剂及凝胶浴对硝酸纤维素膜结构的影响

利用丙酮(AC)、二甲基乙酰胺(DMAc)和二甲基亚砜(DMSO)三种不同溶剂制备硝酸纤维素铸膜液。考察了溶剂的性质及凝胶浴组成对膜结构的影响,利用扫描电镜表征了膜的表面及截面结构,通过成膜过程的热力学和动力学分析解释了不同膜结构的形成原因。结果表明:溶剂的种类及凝胶浴中溶剂的含量对膜结构的影响很大,其变化规律也是不同的。     

非对称结构的CO2分离膜成膜过程的研究

采用干/湿相转化法制备了一系列非对称结构的气体分离膜。动态监测成膜过程的不同阶段,用傅立叶变换红外光谱仪来研究干相转化的蒸发过程,采用数码相机连续照相的方法,用光学显微镜来研究湿相转化的凝胶过程,并探讨成膜动力学过程对膜的最终结构及性能的影响。结果表明,对流蒸发和凝胶过程溶剂/非溶剂的交换速率对形成非对称结构的高渗透性能气体分离膜有着重要的影响。     

脱溶剂速度对聚砜/磺化聚砜合金膜结构和性能的影响

介绍了铸膜液温度、成膜过程中的蒸发时间、环境湿度、凝胶浴温度对聚砜/磺化聚砜合金膜的渗透、分离性能的影响.随环境相对湿度、凝胶浴温度增大,合金膜的水通量增大,截留率下降;蒸发时间延长,合金膜的水通量通过一个极大值,截留率呈现下降趋势.     

小分子醇对PVDF／PFSA共混膜凝胶动力学、膜结构及膜性能的影响

以小分子醇为添加剂,研究了小分子醇对聚偏氟乙烯(PVDF)/全氟磺酸(PFSA)共混超滤膜凝胶动力学、结构与渗透性能的影响.结果表明:在PVDF/PFSA铸膜液中添加乙醇时,其凝胶速率随乙醇浓度的增加而加快,超滤膜通量随乙醇浓度的增加而增大;而当添加相同浓度的4种小分子醇时,初始凝胶速率差别不大,20 s后添加乙醇的铸膜液的凝胶速率最大;添加小分子醇后超滤膜的水通量大小顺序为:异丙醇<甲醇<乙醇<正丁醇.SEM照片显示在铸膜液中添加5%乙醇所制备的共混超滤膜具有较为圆整的内腔结构与均匀的孔结构.     

添加剂对PVDF相转化过程及膜孔结构的影响

研究了PVP、PEG及LiCl 3种成孔添加剂下PVDF DMAc H2 O 添加剂体系的成膜机理 .无论那种添加剂的铸膜液相转换成膜过程中都存在凝胶分相和液液分相两种相变方式 ,在 30～ 6 0℃时凝胶分相在较低的非溶剂浓度下先于液液分相发生 ,LiCl作为添加剂较PEG、PVP对铸膜液有较强的致凝胶作用 ,成膜过程中凝胶分相段时间依PVP、PEG、LiCl的顺序延长 ,导致液液分相初始分相点处聚合物浓度增大 ,阻止了大孔结构的充分发展 .制得的膜依PVP、PEG、LiCl的顺序有效孔隙率和通量降低 ,结晶度升高 .以LiCl为添加剂制得的膜几乎不改变PVDF膜的疏水性 ,而以PVP或PEG为添加剂的膜隔水压差降低约 2 0kPa .     

扩散致相转化法制备结晶性聚合物多孔膜

介绍了扩散致相转化法制备结晶性聚合物多孔膜的研究现状。其三元等温成膜体系的相图包含液-液分相和固-液分相两种相分离方式,是理解成膜过程的重要工具,总结了成膜机理和膜的结构形貌：单纯S-L相分离生成粒子状对称膜结构;单纯L-L相分离生成蜂窝状非对称膜结构;两种相分离方式竞争发生将生成多样的混合膜结构。铸膜液浓度、非溶剂种类、铸膜溶剂组成、凝胶浴组成、制膜温度是影响膜结构形貌的主要因素。     

Oxalic acid cross-linked sodium alginate and carboxymethyl chitosan hydrogel membrane for separation of dye/NaCl at high NaCl concentration

Dye desalination is a challenge in the treatment of textile wastewater with high salt concentration. It is imperative to develop salt resistance membrane that is from sustainable materials to effectively treat dye/salt mixtures. And most polymer membrane materials are non-renewable petrochemical resources.In this paper, a green hydrogel membrane(CMCS-OA-Na Alg) was prepared by non-metallic ions of oxalic acid(OA) cross-linking of two natural macromolecules of sodium alginate(Na Alg) and carboxym...     

A Thermochemical Study on the Formation of Oxalato-Titanium(III) Complex

The thermometric titration of titanium(III) chloride with oxalic acid was carried out at 25°C. The molar ratio of titanium (III): oxalate was found to be 1:2, which indicates the formation of Ti(C₂O₄)₂⁻ ion in acid media. The limiting value of the heat of reaction between Ti(III) ion and oxalic acid in hydrochloric acid solution was found to be −1.5 Kcal mole⁻¹ at 25°C.     

Temporal evolution of the composition of mixed monolayers on TiO2 surfaces: evidence for a dimerization-induced chelate effect

Mixed monolayers of octanoic acid (OA) and 16-mercaptohexadecanoic acid (MHDA) were adsorbed to nanocrystalline TiO(2) films from mixed solutions in tetrahydrofuran. For a range of solution compositions, the mole fraction of MHDA within the mixed monolayers (chi (MHDA,surf)) exceeded that of the coadsorption solution. In addition, chi (MHDA,surf) increased with time, while the sum of the surface coverages of MHDA and OA remained constant. To account for these effects, we propose a mechanism involving disulfide formation between the terminal thiol groups of surface-adsorbed MHDA molecules. Disulfide formation leads to an increase in the surface adduct formation constant ( K(ad)) of dimeric MHDA, causing the gradual displacement of OA from the surface. The mechanism is supported by spectroscopic evidence and desorption kinetics. These are the first examples of mixed monolayers that undergo time-dependent compositional changes as a result of covalent bond formation between surfactants. Our findings illustrate that dimerization and other intermolecular interactions between surfactants may dramatically influence the composition and terminal functionalization of a wide range of mixed monolayer systems.     

氧化钴纳米管的制备和模板剂多孔氧化铝的孔洞结构

以草酸电解液制备的多孔氧化铝作为模板,采用硝酸钴溶液浸润法,合成出氧化钴纳米管．通过对分叉氧化钴纳米管成因研究,指出氧气气泡的作用是形成多孔氧化铝纳米孔洞结构的主要驱动力．     

Electrocatalytic formation of polymolecular products at the cathodic polarization of polycrystalline chromium in sulfuric acid solutions of formic and oxalic acids

The cathodic behavior of polycrystalline Cr electrodes in sulfuric acid solutions of oxalic (OA) and formic (FA) acids is studied by cyclic voltammetry. These organic substances not only chemisorb on the electrode surface thus severely hindering the hydrogen evolution on the metal but also take active part in the electrocatalytic reactions that occur under these conditions. The use of methods of chromatography mass spectrometry and photon-correlation spectroscopy demonstrates that long-term cathodic polarization of Cr in the potential range of active hydrogen evolution (in the vicinity of ?1.0 V) in sulfuric acid solutions containing FA and OA leads to the formation of polymolecular compounds. Among the latter, linear hydrocarbons and carboxylic acids containing 12–27 carbon atoms are isolated and identified.     

Effect of chelating agents on catalytic performance of Cr/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> dehydrogenation catalysts

Chromia/alumina (Cr₂O₃/γ-Al₂O₃) catalysts with addition of chelating agents (citric acid or oxalic acid) were prepared by the incipient impregnation method. The resulting catalysts with different citric acid (CA) or oxalic acid (OA) contents were applied to the dehydrogenation of isobutane to isobutene. The influence of chelating agents on the catalysts was investigated by means of BET, SEM, H₂-TPR, NH₃-TPD, and TG-DTG. The results showed that the Cr₂O₃/γ-Al₂O₃ catalysts with addition of CA or OA exerted slightly increase on specific surface area. The addition of the chelating agents as expected, determined a general decrease in the surface acidity. The catalysts with CA or OA have a better anti-coking ability by inhibiting the side reaction of cracking and carbon formation. The addition of CA or OA for preparing these catalysts resulted in a beneficial effect on the reducibility of the Cr species to diminish the reduction temperature. The appropriate content of chelating agents could improve dispersion of metal species in the γ-Al₂O₃ support. The catalytic activity showed an important enhancement when the metal species was impregnated in the presence of CA or OA.     

Electrodeposition of PdAu Alloy Nanoparticles on Ionic Liquid Functionalized Graphene Film for the Voltammetric Determination of Oxalic Acid

An ionic liquid functionalized graphene film was prepared and PdAu nanoparticles (NPs) were electrodeposited on it. The PdAu NPs were characterized by various methods and they showed the features of alloys. In 0.2 M H₂SO₄ solution, oxalic acid (OA) exhibited a sensitive anodic peak at the resulting electrode at about 1.1 V (vs. SCE), and the peak current was linear to OA concentration in the range of 5–100 µM with a sensitivity of 45.5 µA/mM. The detection limit was 2.7 µM (S/N=3). The electrode was successfully applied to the determination of OA in real sample.