一种后交联大孔吸附树脂的合成及其对苯酚和维生素B_(12)吸附性能研究

工业二乙烯苯悬浮聚合制备的大孔树脂,在二氯乙烷溶剂中以无水三氯化铁为催化剂进行悬挂双键后交联反应,得到的后交联树脂的比表面积和孔容都有显著增加.低温氮气吸附/脱附等温线得到的孔径分布曲线证明初始共聚物PDT-55(polydivinylbenzene,toluene as porogen)和PDH-55(polydivinylbenzene,heptane andtoluene as porogen)经后交联反应,所形成的新孔以微孔为主.树脂对水溶液中苯酚和维生素B12(VB12)的静态吸附研究发现树脂经后交联后,对苯酚的吸附量有显著提高,但对VB12的吸附量增加不大,原因是分子尺寸较大的VB12无法进入由悬挂双键后交联反应所形成的微孔.树脂PDT-55pc对苯酚的吸附量大于商品树脂XAD-4;后交联前后树脂PDT-55、PDT-55pc(post-crosslinking of PDT-55)、PDH-55、PDH-55pc(post-crosslinking ofPDH-55)对VB12的吸附量均大于树脂XAD-4.在本研究的实验条件下,Langmiur和Freundlich吸附等温线方程能很好地拟合树脂对水溶液中苯酚和VB12的吸附,相关系数在0.99以上.静态吸附动力学实验结果表明后交联前后树脂对苯酚的吸附较VB12更容易达到吸附平衡.吸附动力学数据的拟合结果显示,McKay二级吸附动力学模型符合树脂对苯酚的吸附,而对VB12的吸附更符合Lagergren一级吸附动力学模型.     

光敏季铵盐Gemini表面活性剂a4-6-m在气/液界面的吸附

合成了3种不对称结构的季铵盐Gemini表面活性剂a4-6-m, 分子的一根疏水链是偶氮苯为端基的4个亚甲基链, 另一根是不同长度的脂肪链(m=12, 14, 16). 研究结果表明, 反式偶氮苯封端的a4-6-m在气/液界面上以直立方式排列, 偶氮苯端基间的π-π相互作用导致吸附分子较为紧密地排列, 但吸附层外表面含有偶氮苯成分使临界胶束浓度(cmc)时的表面张力(γcmc)较大. 紫外光激发使反式结构偶氮苯变为顺式结构, 这些极性较强的顺式偶氮苯夹杂在直立的烷烃链间, 增强的偶极-偶极相互作用促进了分子紧密排列, 使分子占据面积(Amin)略微减小. 增长脂肪链长度有助于降低临界胶团浓度和C20(使水的表面张力降低20 mN·m-1时所需的表面活性剂浓度), 但对γcmc影响不大.     

Ni(111)表面上N原子对C原子电子结构的影响

N是金刚石中的主要杂质之一, 为了研究金刚石生长过程中杂质N对C电子结构转化的影响, 用密度泛函理论研究了Ni(111)表面上C与N共吸附的三个不等价模型, 同时建立了三个C吸附模型作为比较. 计算结果表明, N原子的出现使得吸附体系相对不稳定, 吸附原子之间的相互作用不能忽略; 通过比较相互作用能可以看出, 相同的吸附位下C-C相互作用比C-N 相互作用强. 通过比较不同模型中C原子分波态密度可以看出, N-C相互作用一定程度上增加了Ni的催化活性, 但是与C-C自身的相互作用比较起来效果并不明显. 吸附几何结构和分波态密度还表明, 当吸附的原子过于紧密以致占有同一个Ni(111)-(1×1)晶胞表面时, 就会形成CN化合物或者类石墨杂质.     

吸附树脂和活性炭对气体中苯的吸附研究

采用了动态吸附实验方法研究了吸附树脂NDA-201和椰壳型活性炭C1对苯蒸汽的吸附行为.对吸附平衡数据采用Dubinill-Astakov方程进行了拟合分析,并根据吸附剂孔结构特征探讨了吸附机理.实验结果表明,两种吸附剂的苯吸附等温线存在交叉现象,对高浓度苯蒸汽吸附治理可采用NDA-201树脂,低浓度则采用椰壳型活性炭C1;Dubinin-Astakov方程能用来对两种吸附剂的等温线进行拟合,表明吸附剂的微孔区域对吸附起着重要作用.微孔体积计算值的比较和特征曲线叠合的程度说明了.Polanyi吸附势理论更适合于描述椰壳型活性炭C1对苯的吸附,这可能是由于椰壳型活性炭C1的孔分布集中于微孔区,而NDA-201树脂除了微孔外还有一定量的中孔和大孔.     

Comparison of adsorption equilibrium of fructose, glucose and sucrose on potassium gel-type and macroporous sodium ion-exchange resins

Adsorption equilibrium of fructose, glucose and sucrose was evaluated on sulfonated poly(styrene-co-divinylbenzene) cation-exchange resins. Two types of resins were used: potassium (K⁺) gel-type and sodium (Na⁺) macroporous resins. Influence of the cation and effect of the resin structure on adsorption were studied. The adsorption isotherms were determined by the static method in batch mode for mono-component and multi-component sugar mixtures, at 25 and 40 °C, in a range of concentrations between 5 and 250 g L⁻¹. All adsorption isotherms were fitted by a linear model in this range of concentrations. Sugars were adsorbed in both resins by the following order: fructose > glucose > sucrose. Sucrose was more adsorbed in the Na⁺ macroporous resin, glucose was identically adsorbed, and fructose was more adsorbed in the K⁺ gel-type resin. Data obtained from the adsorption of multi-component mixtures as compared to the mono-component ones showed a competitive effect on the adsorption at 25 °C, and a synergetic effect at 40 °C. The temperature increase conducted to a decrease on the adsorption capacity for mono-component sugar mixtures, and to an increase for the multi-component mixtures. Based on the selectivity results, K⁺ gel-type resin seems to be the best choice for the separation of fructose, glucose and sucrose, at 25 °C.     

Thermodynamics, adsorption kinetics and rheology of mixed protein-surfactant interfacial layers

Depending on the bulk composition, adsorption layers formed from mixed protein/surfactant solutions contain different amounts of protein. Clearly, increasing amounts of surfactant should decrease the amount of adsorbed proteins successively. However, due to the much larger adsorption energy, proteins are rather strongly bound to the interface and via competitive adsorption surfactants cannot easily displace proteins. A thermodynamic theory was developed recently which describes the composition of mixed protein/surfactant adsorption layers. This theory is based on models for the single compounds and allows a prognosis of the resulting mixed layers by using the characteristic parameters of the involved components. This thermodynamic theory serves also as the respective boundary condition for the dynamics of adsorption layers formed from mixed solutions and their dilational rheological behaviour. Based on experimental studies with milk proteins (β-casein and β-lactoglobulin) mixed with non-ionic (decyl and dodecyl dimethyl phosphine oxide) and ionic (sodium dodecyl sulphate and dodecyl trimethyl ammonium bromide) surfactants at the water/air and water/hexane interfaces, the potential of the theoretical tools is demonstrated.The displacement of pre-adsorbed proteins by subsequently added surfactant can be successfully studied by a special experimental technique based on a drop volume exchange. In this way the drop profile analysis can provide tensiometry and dilational rheology data (via drop oscillation experiments) for two adsorption routes — sequential adsorption of the single compounds in addition to the traditional simultaneous adsorption from a mixed solution. Complementary measurements of the surface shear rheology and the adsorption layer thickness via ellipsometry are added in order to support the proposed mechanisms drawn from tensiometry and dilational rheology, i.e. to show that the formation of mixed adsorption layer is based on a modification of the protein molecules via electrostatic (ionic) and/or hydrophobic interactions by the surfactant molecules and a competitive adsorption of the resulting complexes with the free, unbound surfactant. Under certain conditions, the properties of the sequentially formed layers differ from those formed simultaneously, which can be explained by the different locations of complex formation.     

Comparative analysis of the electrostatics of the binding of cationic proteins to vesicles: Asymmetric location of anionic phospholipids

The role of electrostatics is studied in the adsorption of cationic proteins to zwitterionic phosphatidylcholine (PC) and anionic PC/phosphatidylglycerol (PG) mixed small unilamellar vesicles (SUVs). For model proteins the interaction is monitored vs. PG content at low ionic strength. The adsorption of lysozyme and myoglobin (isoelectric point, pI 7-11) is investigated in SUVs, along with changes of the fluorescence emission spectra of the cationic proteins, via their adsorption on SUVs. In the Gouy-Chapman formalism, the activity coefficient goes with the square of charge number. Deviations from the ideal model could indicate the asymmetric location of the anionic phospholipid in the bilayer inner leaflet, in mixed zwitterionic/anionic SUVs for both lysozyme- and myoglobin-PC/PG systems, in agreement with experiments and molecular dynamics simulations. Fitted effective SUV charge stays constant. Effective—formal difference increases 0.417 e.u. Effective protein charge increases as PC/PG < PC being greater for myoglobin. The molar free energies of the protein in aqueous and lipid phases increase as PC < PC/PG. Both free-energy changes are greater for myoglobin. Effective interfacial charge stays constant for anionic PC/PG SUVs being greater for myoglobin.     

Enantioseparation of flurbiprofen on amylose-derived chiral stationary phase by supercritical fluid chromatography

The separation of the enantiomers of flurbiprofen on an amylose-derived chiral stationary phase, Chiralpak AD-H, by supercritical fluid chromatography (SFC) under both linear and non-linear conditions is studied. Pulse injections were implemented using supercritical CO₂modified with methanol as a mobile phase at a temperature of 30 °$°$C. At linear conditions, the isotherm is determined directly from the chromatogram. Under overload conditions, the elution profiles were described by competitive Langmuir and bi-Langmuir isotherm. Isotherm parameters were estimated using the inverse method and the effects of operation variables such as pressure and modifier composition were studied. The value of selectivity is from 1.9 to 2.1 while the value of resolution is from 5.3 to 11.8. The number of theoretical plates is always greater than 5000 indicating high efficiency of SFC.     

In situ ATR-IR investigation of L-lysine adsorption on montmorillonite

The adsorption behavior of lysine on montmorillonite in aqueous solution was investigated by in situ attenuated total reflectance infrared (ATR-IR) spectroscopy. To distinguish the protonation states of α-amino group, side-chain amino group and carboxyl group in lysine structure using ATR-IR spectra (i.e., NH₂ versus and COO⁻ versus COOH), pH-induced spectral changes of dissolved lysine were firstly measured and correlated with the thermodynamically calculated dissociation states of lysine (di-cationic, cationic, zwitterionic and anionic states). The obtained result was applied to interpret the ATR-IR spectra of lysine adsorbed on montmorillonite. We found that the adsorbed lysine was dominantly present as cationic state over the whole range of tested pH (pH = 4.9–9.7). This indicates that the adsorption is mainly driven by electrostatic interaction between the negatively charged montmorillonite surface and positively charged cationic lysine. We also found that lysine interacts with montmorillonite surface through the protonated side-chain amino group. This result suggests that lysine has a preferred vertical orientation, with the side-chain amino group pointing toward the surface.     

Macroscopic and spectroscopic characterization of selenate, selenite, and chromate adsorption at the solid–water interface of γ-Al2O3

The interaction of selenate, selenite, and chromate with the hydrated surface of γ-Al₂O₃ was studied using a combination of macroscopic pH edge data, electrophoretic mobility measurements, and X-ray absorption spectroscopic analyses. The pH edge data show generally increased oxyanion adsorption with decreasing pH, and indicate ionic strength-(in)dependent adsorption of chromate and selenate across the pH range 4–9, and ionic strength-(in)dependent adsorption of selenite in this pH range. The adsorption of chromate peaks at pH 5.0, whereas for selenate and selenite no pH adsorption maxima are observed. Electrophoretic mobility measurements show that all three oxyanions decrease the zeta potential of γ-Al₂O₃ upon adsorption; however, only selenite decreased the pH_PZC of the γ-Al₂O₃ sorbent. EXAFS data indicate that selenite ions are coordinated in a bridging bidentate fashion to surface AlO₆ octahedra, whereas no second-neighbor Al scattering was observed for adsorbed selenate ions. Combined, the results presented here show that pH is a major factor in determining the extent of adsorption of selenate, selenite, and chromate on hydrated γ-Al₂O₃. The results point to substantial differences between these anions as to the mode of adsorption at the hydrated γ-Al₂O₃ surface, with selenate adsorbing as nonprotonated outer-sphere complexes, chromate forming a mixture of monoprotonated and nonprotonated outer-sphere adsorption complexes, and selenite coordinating as inner-sphere surface complexes in bridging configuration.