Silica surface controversies,strong adsorption sites,their blockage and removal. Part II

Summary In this second part of the review heterogeneity of the silica surface is described and evidence is presented for the existence of a low population of strong adsorption sites. Methods of detection and determination of these strongly interacting sites are discussed. The last part of the review is devoted to the suppression of unwanted adsorption activity. Methods of blockage and special methods for the preparation of HPLC packings are described.     

PEI/SiO2复合型吸附材料对脲酸吸附特性的研究

通过γ-氯丙基三甲氧基硅烷的偶联, 将聚乙烯亚胺(PEI)偶合接枝在硅胶微粒表面, 制得了对脲酸有强吸附性能的复合型医用吸附材料PEI/SiO₂. 静态吸附实验结果表明, 凭借强烈的氢键相互作用, 硅胶表面的聚胺大分子PEI对脲酸的互变异构体三羟基嘌呤具有很强的吸附能力, 等温吸附满足Freundlich吸附方程, 饱和吸附量可达84.9 mg/g; 介质的pH值对吸附作用有很大的影响, 在中性溶液中(pH＝6～7), 复合吸附材料PEI/SiO₂对脲酸具有强吸附能力, 而在酸性与碱性溶液中吸附能力都较弱; 温度对吸附性能也有影响, 升高温度吸附量增大.     

Efficient Removal of Pb(II) from Aqueous Medium Using Chemically Modified Silica Monolith

The adsorptive removal of lead (II) from aqueous medium was carried out by chemically modified silica monolith particles. Porous silica monolith particles were prepared by the sol-gel method and their surface modification was carried out using trimethoxy silyl propyl urea (TSPU) to prepare inorganic–organic hybrid adsorbent. The resultant adsorbent was evaluated for the removal of lead (Pb) from aqueous medium. The effect of pH, adsorbent dose, metal ion concentration and adsorption time was determined. It was found that the optimum conditions for adsorption of lead (Pb) were pH 5, adsorbent dose of 0.4 g/L, Pb(II) ions concentration of 500 mg/L and adsorption time of 1 h. The adsorbent chemically modified SM was characterized by scanning electron microscopy (SEM), BET/BJH and thermo gravimetric analysis (TGA). The percent adsorption of Pb(II) onto chemically modified silica monolith particles was 98%. An isotherm study showed that the adsorption data of Pb(II) onto chemically modified SM was fully fitted with the Freundlich and Langmuir isotherm models. It was found from kinetic study that the adsorption of Pb(II) followed a pseudo second-order model. Moreover, thermodynamic study suggests that the adsorption of Pb(II) is spontaneous and exothermic. The adsorption capacity of chemically modified SM for Pb(II) ions was 792 mg/g which is quite high as compared to the traditional adsorbents. The adsorbent chemically modified SM was regenerated, used again three times for the adsorption of Pb(II) ions and it was found that the adsorption capacity of the regenerated adsorbent was only dropped by 7%. Due to high adsorption capacity chemically modified silica monolith particles could be used as an effective adsorbent for the removal of heavy metals from wastewater.     

二氧化硅气凝胶对挥发性有机污染物的吸附性能研究

以TEOS为前驱体,乙醇为溶剂,氢氟酸为催化剂,一步法合成了常规二氧化硅气凝胶。经乙醇超临界干燥后,通过SEM,FTIR和N2吸脱附分析仪等仪器对二氧化硅气凝胶样品进行表征,以更好地了解吸附机理与性质的关系。结果表明,样品的比表面积高达519 m2/g,孔体积为1.9 cm3/g,平均孔径为15.15 nm,是一种优良的吸附材料。制备的样品用作测试甲苯、对二甲苯和苯三种挥发性有机化合物的吸附效果。结果表明,二氧化硅气凝胶对三种污染物都具有很高的吸附量,其高吸附能力归因于气凝胶的三维纳米网络结构。样品对甲苯,对二甲苯和苯的最大吸附能力分别为1422.8 mg/g,707.4 mg/g和1299.4 mg/g。综上所述,二氧化硅气凝胶是一种很有前景的处理挥发性有机化合物的吸附剂,具有优异的吸附性能。     

二组分气体在固体上吸附的研究(Ⅳ)

测定了丙酮－正己烷、甲苯－正己烷、苯－正己烷、正戊烷－正己烷四个二组分气体在部分石墨化的灯黑上的吸附等温线，并测定了单组分气体吸附等温线．对比了上述四个二组分气体，分别在硅胶、硅烷化硅胶和灯黑上吸附的十二个吸附体系的吸附规律．结果表明，二组分气体在吸附剂上的竞争吸附的强弱，基本上可以通过它们的纯组分气体在吸附剂上第一层吸附热Q1数值的大小加以预测．     

氨基酸在固/液界面的吸附作用

本文介绍了氨基酸在固/液界面吸附等温线的特点,氨基酸液相吸附热力学和活性炭、硅胶、二氧化钛、氧化铝、蒙脱土等自水中吸附氨基酸的机制。     

Apparent and partial specific adsorption of 1,10-phenanthroline on mixtures of Ca-montmorillonite, activated carbon, and silica gel

The process of 1,10-phenanthroline adsorption at pH 5 on Ca-montmorillonite, activated carbon, and silica gel mixtures was studied as a function of the equilibrium concentration and the composition of the mixture. A model is presented for determining adsorption of the main component (the variable in the system) of the mixture, based on the thermodynamic concept of apparent and partial quantities, in combination with an equation representing total adsorption of the other two adsorbents as a function of the weight fraction of one of them and introducing the concept of mean total adsorption. The partial specific adsorption of orthophenanthroline (OP) on Ca-montmorillonite is strongly influenced by the presence of activated carbon and silica gel. Owing to a phenomenon of cationic exchange, adsorption on the clay is higher at low proportions in the mixture, but the strong effect of carbon and silica gel becomes apparent at increasing amounts of clay in the mixture. The partial specific adsorption of orthophenanthroline on activated carbon and silica gel was determined using a total adsorption equation for the two adsorbents as a function of the weight fraction of one of them and shows behavior inverse to that of adsorption on clay.     

阳离子型聚氨酯-脲-胺在二氧化硅水溶胶听吸咐行为

研究了水溶性阳离子聚氨酯-脲-胺乙酸盐在球形、单分散的纳米二氧化硅水分 散注保的吸附行为。PUUA分子链在烯溶液中呈较舒展的构象，分子尺寸小于纳米氧 化硅的粒径。PUUA通过van der Waals作用力和氢键吸附在氧化硅表面。在稳喧吸 附后，等温吸附线呈线性上升，且没有极限值。吸附量随纳米氧化硅粒径的增大、 胶粒表面电荷的减少和电解质乙酸钢加入量的变化均以相同的斜率线性下降。 PUUA分子量增加，吸附量增加，且分子量大的PUUA优先吸附于氧化硅胶粒表面，静 电吸引是PUUA吸附至氧化硅溶胶粒表面的主要作用力。PUUA在氧化硅胶粒上的吸咐 使体系表现粘度下降，敏化作用使体系呈假塑性，而保护作用使体系呈胀流型。     

几种树脂对芦荟苦素的吸附性能

研究硅胶H和三种不同极性的大孔吸附树脂对芦荟苦素的吸附与洗脱性能，用静态实验筛选树脂、动态实验考察芦荟苦素提取液浓度、上样流速和温度对GD-10大孔吸附树脂吸附能力影响。结果表明GD-10吸附树脂对芦荟苦素的吸附能力较强，洗脱能力最好，且易于再生。     

Adsorption of Nitrogen on Silica Gel Over a Large Range of Temperatures

To study the mechanism of physical adsorption of supercritical gases, the adsorption equilibria of N₂ on silica gel for 103–298 K using 20 K increments and pressures up to 10 MPa were measured. A transition of the adsorption mechanism was proven on crossing the critical temperature, but the transition way observed is different from that observed with activated carbon. This causes a difference in the locations of the linear section of the n- _g isotherm at the near-critical temperature. Although the isotherm type is different on silica gel and on activated carbon in the sub-critical region, all isotherms in the supercritical region can be well modeled by a single model. It leads to the argument that the adsorption mechanism of supercritical gases is identical no matter what kind of adsorbent is used.     

The Adsorption of Methanol Vapors on Silica Gel Si-100 and Its Surface Containing Different Concentrations of Chemically Bonded Fluoride Ions

Synthesis of two types Si-100 silica gel with different concentrations of chemically bonded surface fluoride ions (2 and 4 μmol m⁻² ) was performed. Using gravimetric methods, adsorption isotherms of methanol as a function of its pressure in gas phase were measured for these adsorbents. It was found the strong surface deactivation of silica gel in relation to methanol with the increase of bonded fluoride ions concentration. This revised version was published online in August 2006 with corrections to the Cover Date.     

在线固相氧化物吸附-火焰原子吸收法测定痕量银

基于硅胶表面对碱性体系中新生成的氧化银(Ag2O)的有效吸附, 建立了流动注射-固相氧化物分离富集-火焰原子吸收法测定痕量银的方法. 当银以氧化物的形式被滞留在硅胶固相表面时, 硅胶表面的硅醇基和表面电荷有利于反应体系中新生成的Ag2O胶状沉淀的吸附, 将收集的沉淀用HNO3(10%, 体积分数)洗脱后用火焰原子吸收测定. 当进样体积为5.4 mL时, 测得的富集系数为25.5, 检出限为0.6 μg/L, 采样频率为50次/h, 线性范围为2~150 μg/L, 相对标准偏差(RSD)为2.0%(40 μg/L, n=11). 将该法用于自来水、河水、井水、雪水和山泉水中银含量的测定, 加标回收率分别为93.3%, 89.5%, 96.6%, 108.4%和102.8%.     

Selective separation behavior of silica gel for zirconium in simulated high level radioactive liquid waste

Zirconium in simulated high level radioactive liquid waste (HLLW) was selectively adsorbed and separated by self-made high adsorption activity silica gel. The selective adsorption mechanism was analyzed according to the structure character of self-made silica gel and performance of zirconium in acid simulated HLLW. The results show that the adsorption selectivity of self-made silica gel for zirconium is strong, because zirconium has higher positive charge and zirconium ion hydrolyzes easily. Distribution coefficient of self-made silica gels for zirconium is 53.5 ml/g. There are 6.5 (OH)/nm² on the surface on self-made silica gels which provide more adsorption activity places, thus self-made silica gels have higher adsorption capacity for zirconium (31.4 mg/g). The elution rate of the adsorption of zirconium on self-made silica gel by 0.2 mol/l H₂C₂O₄ is more than 99%. The solubility of the self-made silica gel in nitric acid is low, the chemical stability of self-made silica gel is very strong.     

热处理对憎水硅胶吸附水蒸气的影响

用甲基氯硅烷蒸气或溶液处理硅胶,均可制成憎水硅胶。关于憎水硅胶的吸附性能和热稳定性的研究,文献中时有报道。本文主要探讨以下3个问题:(1)在水蒸气吸附中,硅胶表面自由羟基和缔合羟基究竟哪种起主要作用;(2)从吸附水蒸气等数据讨论硅胶表面有机基团—OSi(CH_3)_3的热稳定性;(3)用二甲基二氯硅烷(DMCS)和三甲基氯硅烷(TMCS)处理的憎水硅胶,哪种硅胶的热稳定性较高。这些基本问题,不仅具有学术意义,对研究氧化物表面改性也有参考价值。     

Adsorption of toluene, methylcyclohexane and neopentane on silica MCM-41

Adsorption-desorption isotherms of toluene, methylcyclohexane and neopentane were determined on a silica MCM-41 material of pore diameter ∼3.4 nm over the temperature range 258 K to 308 K (278 K for neopentane). The isosteric enthalpies of adsorption were determined from the isotherms at the various temperatures. It was found that the isotherms of toluene and methylcyclohexane have a similar variation with the temperature, exhibiting hysteresis at 268 K and at lower temperature, while the adsorption of neopentane is reversible at all temperatures. The three organic adsorptives interact differently with the silica surface and the isosteric enthalpies of adsorption indicated that methylcyclohexane has the weakest interaction and toluene the strongest. A slight increase in the adsorption enthalpy at the beginning of the capillary condensation step is observed with methylcyclohexane and neopentane but not with toluene.     

Focusing in Liquid Thermal Adsorption Systems

Focusing can be obtained in liquid thermal cycling zone adsorption by significantly increasing the temperature of the hot feed. To prevent boiling column pressure is raised. This method for concentrating dilute fluids was studied using the simulation package ADSIM. The systems studied were ethanol-water on silicalite and toluene-n-heptane on silica gel. Substantial concentration of dilute feeds while producing a pure solvent product were obtained. This research highlights the need for equilibrium data for liquid adsorption systems at elevated temperatures and pressures.     

气相色谱法测定气固表面的吸附停留时间

提出了一个用气相色谱测定气体在固体表面上吸附停留时间的方法. 经推导, 得到了测定公式.用八种烷烃及苯在硅胶上的吸附实验数据进行验证和研究, 得到了满意的结果.     

Adsorption of three selected flavonoids with humic fraction-modified silica gel in hexane: A mechanism study

Three selected flavonoids, commonly found in spices, red-purple fruits, and vegetables, were adsorbed on humic fraction-modified silica gel in hexane. The percentage of adsorption in hexane for all examined analytes was nearly 100% after 1 hr, as a result of the strong dipole–dipole interaction. The increasing amount of adsorbent involved in the process improved the percentage of adsorption, which in turn shortened the time needed to reach the maximum by providing more binding sites. However, adsorption was not observed in other liquid phases under the same conditions, such as acetonitrile and ethyl ether. The mechanism leading to the adsorption was explored chromatographically, as well as by fourier transform infrared spectroscopy (FTIR) and theoretical simulations.     

NPE在有序介孔炭上的吸附行为研究

采用有序介孔硅为硬模板制备了具有不同孔径的有序介孔炭(OMCs). 氮气吸附测试表明, 有序介孔炭具有丰富的介孔表面和集中的介孔分布. 以壬基酚聚氧乙烯醚(NPE)为探针分子, 研究了大分子酚类在有序介孔炭上的吸附行为. 吸附研究表明, NPE在有序介孔炭上的吸附满足Langmuir吸附模型. 孔结构分析表明, 大于1.5 nm的孔的表面积是决定NPE吸附量的关键因素, 而有序介孔炭的最可几孔径决定吸附速率的大小. 与吸附量相比, 吸附速率更容易受环境温度的影响. 动力学研究表明, NPE在有序介孔炭上的吸附满足准二级动力学方程.     

Wetting of β-casein layers adsorbed at the solid–aqueous interface

The wetting by water of the adsorbed layer of β-casein on hydrophobised silica and pure (hydrophilic) silica surface was investigated by dynamic contact angle measurements based on the Wilhelmy plate principle. The results are discussed in relation to adsorption data obtained for the protein on similar surfaces by in situ ellipsometry. β-casein adsorption on a hydrophobic surface leads to a significant decrease of the contact angle, in particular in terms of the receding contact angle, which decreased by about 70°. This indicates a strong shielding of the hydrophobic surface by the hydrophilic domain of β-casein. Adding a specific enzyme, endoproteinase Asp-N, which previously has been proposed to remove a large fraction of the hydrophilic segments, results in a significantly decreased wettability of the solid surface. The layer is now more hydrophobic and the hysterises is much smaller. The receding contact angle after the proteolysis is roughly 70°. The results are consistent with the hypothesis that β-casein adsorbs at the hydrophobic surface to form a monolayer with the hydrophobic part of the protein anchored at the surface, leaving the hydrophilic segments dangling into the solution. Less dramatic effects are observed in terms of changes of the wettability on the hydrophilic surface. The surface is still quite hydrophilic both after adsorbing β-casein and exposing the layer to endoproteinase Asp-N. These results confirm the differences in the structure of β-casein layers on the hydrophobic and hydrophilic surface.