聚酯/棕榈基多孔碳纤维杂化膜的结晶和力学性能

为提高静电纺丝聚酯纤维膜的力学性能,根据多孔碳纤维的高强度和高模量特性,在聚对苯二甲酸乙二醇酯(PET)溶液中添加自制棕榈基多孔碳纤维(PACF),制得PET/PACF杂化纤维膜,并研究了PACF含量对杂化纤维膜形貌、结晶行为和力学性能的影响。结果表明:添加PACF后,纤维牵伸效果明显改善,类竹节状纤维消失,纤维间黏连减少,直径更均匀;随PACF含量的增加,杂化纤维膜的玻璃化温度较纯PET提高约10℃,结晶度约提高6.7%,证明PACF的加入改善了电场对射流的牵伸效果,使得取向度提高;结晶温度提高约13.7℃,说明PACF异相成核作用促进了纤维膜的结晶。随取向度的提高,当PACF含量为2.5%时,纤维膜断裂强度达4.22 MPa,较纯PET静电纺膜提高了366.3%。     

壳聚糖改性静电纺聚砜纤维膜对染料的过滤性能

为提高静电纺聚砜(PSF)纤维膜的亲水性、力学性能及其对可溶性染料的过滤性能,采用戊二醛交联壳聚糖溶液浸轧处理静电纺PSF纤维膜。研究了纤维膜的表面润湿性、力学性能及其在0.1 MPa恒压死端过滤条件下对分散蓝2BLN和弱酸性蓝N-RL的过滤性能。研究结果表明:处理后的静电纺PSF纤维膜的表面润湿性和力学性能均得到显著改善;未经处理的静电纺PSF纤维膜和体积分数为0.4%戊二醛交联壳聚糖溶液处理纤维膜对分散蓝2BLN的截留率都能达到94%以上,对弱酸性蓝N-RL的截留率都小于35%,但都能保持较高的过滤通量;而体积分数为0.48%戊二醛交联壳聚糖溶液处理纤维膜对分散蓝2BLN和弱酸性蓝N-RL的过滤效率分别为99.5%和92.4%,但是过滤通量急剧下降。     

Research Watch: Analysis of PAHs in soils

Measurements.     

静电纺聚酰胺6/聚酰胺66纤维膜对染料的过滤性能

为将具有高表面吸附能和高孔隙率的静电纺纳米纤维膜作为一种新型膜材料应用于染料废水处理,以达到高效过滤染料的目的,研究了在0.1 MPa恒压死端过滤条件下静电纺聚酰胺6/聚酰胺66(PA6/PA66)纤维膜对质量浓度为0.1 g/L分散蓝2BLN悬浮液和弱酸性蓝N-RL水溶液的过滤效果,通过SEM、孔径分析测试仪、纳米粒径测试仪和紫外-可见分光光度仪观察及测试,分析了静电纺PA6/PA66纤维膜的表面形态、孔隙结构、染料粒径分布及对染料截留性能的影响。结果表明,连续过滤1 h后,静电纺PA6/PA66纤维膜的表面均沉积一层致密的滤饼,对分散蓝2BLN的截留率达95.6%,对弱酸性蓝N-RL的截留率仅为35.1%,但是对2类染料的过滤通量相差不大。     

静电纺聚酰胺6纳米纤维膜的制备及其性能

为制备功能性的聚酰胺6(PA6)纳米纤维膜,采用静电纺丝技术制备PA6/聚乙烯吡咯烷酮(PVP)共混纳米纤维膜,并对纤维膜的表面形貌、力学性能和亲水性能进行表征。结果表明,当PA6纺丝液质量分数为28%,PVP的加入量为0.5 g时,纤维膜的微观形貌较好,制备出的纤维直径为132 nm,断裂强度为9.68 MPa,断裂伸长率为31.89%,亲水角为(32.4±1.2)°。研究了不同纺丝时间对纤维膜空气过滤性能的影响,当纺丝时间为0.5 h时,纤维膜具有较好的过滤性能,过滤效率为99.5%,过滤压降为476 Pa。红外分析结果表明,在PA6中加入PVP,在搅拌的过程中二者均匀融合,PVP小分子填充在PA6大分子中,可使纤维膜的亲水性提高。制得的PA6纳米纤维膜可作为加湿器中的湿膜材料得到应用。     

静电纺PA6纳米纤维膜的过滤性能

用98%甲酸溶解聚酰胺6(PA 6)制备质量浓度为13%纺丝液,经静电纺丝获得厚度31～60μm、纤维平均直径217 nm、表面平均孔径为234 nm的纳米纤维非织造膜.由于该纤维膜的断裂强度仅为8.06 MPa,实验以普通聚酯纤维织物为支撑基布,测试了不同样品的过滤性能.结果发现:在气流速度为2.83 L/min时,...     

Modeling maximum adsorption capacities of soot and soot-like materials for PAHs and PCBs

Recent studies have shown that not partitioning but adsorption is the main mechanism for sorption of hydrophobic organic compounds to soot and soot-like materials. For compounds that adsorb by van derWaals forces only, variation in soot-water distribution coefficients will result from differences in these forces for adsorption, as well as the maximum number of accessible sites. This maximum number of accessible sites may a priori be expected to vary due to differences in both sorbent characteristics and sorbate dimensions. In this modeling study, variation in maximum adsorption capacities is explained from sorbent and sorbate properties. Maximum adsorption capacities were calculated using (a) literature values for soot-water distribution coefficients for polycyclic aromatic hydrocarbons and polychlorobiphenyls on 10 different soot and soot-like materials and (b) Langmuir affinities for adsorption at a carbonaceous surface estimated using a recently reported method. The variation in maximum adsorption capacities could be explained by the variation in sorbent specific surface area, sorbent organic carbon content, and the sorbent-sorbate contact area. Furthermore, increasing sorbate thickness was related to a decrease in maximum adsorption capacities, which points to adsorption in micropores. Maximum adsorption capacities decreased by 1-2 orders of magnitude as the contact area increased by 50%. This points to adsorption sites being hardly larger than sorbates.     

静电纺PA6/CS复合纤维膜的过滤性能研究

采用自制单喷头静电纺丝设备,以聚丙烯熔喷非织造布为基布,制备静电纺聚酰胺6/壳聚糖(PA 6/CS)复合纤维膜,研究了静电纺丝时间对复合膜表面形貌、孔径和过滤性能的影响。结果表明:随着静电纺丝时间增加,复合纤维膜对Na Cl气溶胶的过滤效率显著增加,过滤阻力明显增加,品质因子先增加后减小;连续纺丝90 min后,复合纤维膜的过滤效率达到99%以上。     

静电纺锡/聚丙烯腈纳米纤维膜制备与表征

将纳米锡(Sn)与聚丙烯腈(PAN)共混,采用静电纺丝法制备Sn/PAN纳米纤维膜并进行炭化处理。使用扫描电子显微镜、透射电子显微镜和X射线衍射法对纤维平均直径、直径分布、Sn在纤维上的存在情况以及Sn加入到PAN中静电纺丝后的结晶程度进行表征,将炭化后的纤维膜直接制成锂离子电池负极,测试其电化学性能。结果表明:随着纺丝电压升高或固化距离增大,纤维直径减小;当静电纺丝电压为14 kV,固化距离为14 cm时,纤维平均直径较小,分布最均匀;炭化后纤维变细;Sn加入到PAN中静电纺丝后发生团聚,结晶程度明显下降;Sn/PAN作为锂离子电池负极材料,具有良好的储能性能。     

Nitrogen and carbon dioxide adsorption by soils

High-resolution nitrogen (77 K) and carbon dioxide (273 K) adsorption at subatmospheric pressures has been studied for a range of model soils of various origins with different organic matter (OM) contents. It is demonstrated that N2 and CO2 molecules probe different regions of soil particles. Nitrogen is adsorbed primarily on the outer surface of soil particles, while CO2 has a higher affinity to OM domains. Low-pressure nitrogen adsorption reveals that soil particle surfaces consist of clay/mineral domains with discrete patches of OM. A linear correlation has been found between the CO2 uptake and the amount of organic carbon reduced per unit of the external surface area. A new method for discriminating the microporosity of soil particles and accessibility of OM has been proposed.     

Approaches for the assembly of molecularly imprinted electrospun nanofibre membranes and consequent use in selected target recognition

Molecular recognition plays an indispensable role in nature for the recognition of antibodies, enzymes and nucleic acids. Biomimetic fibrous non-woven materials are being developed to act as highly sensitive and selective artificial receptors based on molecular recognition sites in the constituent fibres. Molecular imprinting technologies (MITs) with specific recognition abilities are currently being developed to produce versatile materials for the recognition of diverse species in various applications, but specifically in membrane separation to express permselectivity. Conventionally, the production of molecularly imprinted polymers (MIPs) involves introducing binding sites where highly cross-linked copolymers are formed around the analyte molecules that act as cavity-creating templates. Subsequent removal of the template molecule provides recognition sites in the polymer that ideally resemble the template in terms of shape, size and functionality. Rebinding of the target molecule within these pre-formed sites can occur when the polymer is incubated in the presence of the template molecule. However, removing of template after polymerization is difficult because cross-linked polymer materials tend to be insoluble. This review paper describes work on new non-covalent molecular imprinting technologies applied to fibrous materials and electrospun fibres that are suitable for selected target recognition. This method has the potential of becoming a tool for producing truly simple, rapid and robust receptors on membranes of the type in regular use in the food industry, making the in-process simultaneous removal of undesirable co-product chemicals and microbial toxins a commercial possibility.     

A WHAM-based kinetics model for Zn adsorption and desorption to soils

A novel model has been developed to describe the kinetics of Zn adsorption and desorption to soils. The model incorporates the mechanistic-based equilibrium model WHAM (Windermere humic aqueous model) to account for the chemical variation during the reaction (e.g., pH and Zn2+ concentration), the heterogeneity of binding sites of soil organic matter (SOM), and the nonlinear binding of Zn to SOM. To test the model, kinetic experiments were conducted using a stirred-flow method. Six soils, with low clay fractions and covering a wide range in SOM concentrations, and various Zn concentrations and pHs were studied. Under these experimental conditions, SOM is found to be the major adsorbent for Zn binding. The fast and slow Zn reactions with soils were associated, respectively, with the monodentate and bidentate binding sites of humic substances in WHAM. The model has only three fitting parameters, the two desorption rate coefficients for the fast (monodentate) and slow (bidentate) reaction sites which are constant and independent of soil type, and the reactive organic matter fraction of the total SOM in each soil. All other parameters are derived from WHAM. The model is able to predict Zn release from spiked soils including the effects of Ca competition.     

Quantifying the availability of clay surfaces in soils for adsorption of nitrocyanobenzene and diuron

Coverage of clay surfaces by soil organic matter (SOM) may limitthe efficacy of the soil mineral fractions for adsorption of organic contaminants and pesticides. Two methods were scrutinized for quantitatively assessing the availability of clay surfaces in a smectitic Webster A-horizon soil for sorption of p-nitrocyanobenzene (p-NCB) and diuron. One method, described previously, involves the summation of independent contributions of SOM and swelling clays to sorption of organic solutes. For this method, several assumptions must be made and/or procedural difficulties overcome in the determination of certain terms in the equation proposed for calculating the fractional availability of mineral surfaces (fa). To alleviate the methodological limitations, we developed an alternative approach for determining fa. Good agreement between fa values was obtained from both methods for p-NCB but not diuron. For p-NCB sorption, fa values varied between 0.55 and 0.71. For diuron sorption, our alternative equation estimated fa values varied between 0.41 and 0.61; the other approach yielded negative values. The results demonstrate that SOM does reduce the availability of clay surfaces, hence, suppressing sorption by the Webster A-horizon soil. Our newly developed method provides more reasonable estimates of the availability of soil-clay surfaces for sorption than an earlier published approach.     

静电纺PA 6纳米纤维膜的力学性能研究

利用静电纺丝可形成由纳米级纤维组成的纳米纤维膜,由于该膜孔径小并具有高比表面积和高孔隙率,可用作组织工程支架、传感器感知膜、过滤材料和防护材料等。静电纺纳米纤维膜的力学性能对其适用性和耐用性有重要影响。以PA 6甲酸溶液进行静电纺丝,研究了纺丝液喂入速度和纺丝距离对静电纺PA 6纳米纤维膜力学性能的影响。结果表明:纺丝液喂入速度较低时,形成的纳米纤维膜力学性能差;纺丝距离增大时,纳米纤维膜的断裂强度降低;PA 6溶解于98%甲酸中配制成13%(质量分数)纺丝液,在喷嘴口径0.9 mm、电压30 kV下进行静电纺丝,纺丝液喂入速度在0.2～0.3 ml/h、纺丝距离为8～10 cm时可获得具有良好力学性能的PA 6纳米纤维膜。     

Uptake of trace elements and PAHs by fruit and vegetables from contaminated soils

The aims of this study were to investigate the uptake of seven trace elements and five PAHs in crop plants in order to establish advice regarding consumption of fruit and vegetables grown in soils contaminated by trace elements and PAHs. In a field experiment, vegetables were grown in two contaminated soils and in a reference soil, whereas fruits were collected from uncontaminated and contaminated private gardens. The results showed elevated levels of several trace elements and PAHs in the vegetables from contaminated soil. Bioconcentration factors (BCF values), based on dry weight, were below 1, except for those of Cd in lettuce and carrot with peel from uncontaminated soil. In most cases, BCF values were decreasing with increasing concentrations in soil. From the heavily contaminated soil, BCF values for Pb in lettuce, potato, and carrot with peel were 0.001, 0.002, and 0.05, respectively, and those for benzo[a]pyrene were 0.004, 0.002, and 0.002, respectively. For most metals in most vegetables, linear regression showed good correlation between soil and crop concentrations. For PAHs, such good correlation was generally not found. The contents of contaminants in fruits were generally low and no correlation with the level of contamination in the soils was found.     

沥青和PAN的静电纺碳纳米级纤维膜的制备及表征

利用N,N-二甲基甲酰胺(DMF)为溶剂、滚轴为接收装置,通过静电纺丝法制备聚丙烯腈(PAN)和可纺沥青(SP)共混前驱体纳米级纤维膜,再对其进行预氧化和碳化,制备碳纳米级纤维膜,以有效降低碳纤维生产成本.结果 表明:在保持纺丝液质量浓度不变的条件下,纤维直径随SP质量分数的增大而减小.制得的纳米级纤维膜具有一定取向度...     

Ochratoxin degradation and adsorption caused by astaxanthin-producing yeasts

Ochratoxin degrading and adsorbing activities of Phaffia rhodozyma and Xanthophyllomyces dendrorhous isolates were tested. P. rhodozyma CBS 5905 degraded more than 90% of ochratoxin A (OTA) in 15 days at 20 degrees C. The data presented indicate that P. rhodozyma is able to convert OTA to ochratoxin alpha, and this conversion is possibly mediated by an enzyme related to carboxypeptidases. Chelating agents like EDTA and 1,10-phenanthroline inhibited OTA degradation caused by P. rhodozyma indicating that the carboxypeptidase is a metalloprotease, similarly to carboxypeptidase A. The temperature optimum of this enzyme was found to be above 30 degrees C, which is much higher than the temperature optimum for growth of P. rhodozyma cells, which is around 20 degrees C. The enzyme responsible for ochratoxin degradation was found to be cell-bound. Besides, both viable and heat-treated (dead) P. rhodozyma cells were also able to adsorb significant amounts (up to 250 ng ml(-1)) of OTA. Heat treatment enhanced OTA adsorbing activities of the cells. Further studies are in progress to identify the enzyme responsible for OTA degradation in P. rhodozyma.