改性固体表面的吸附作用——甲基化硅胶的热稳定性和吸附性能

本文利用三甲基氯硅烷与硅胶表面羟基反应的方法制备了甲基化硅胶。测定了亲水硅胶和甲基化硅胶的热处理对其自四氯化碳中吸附乙酸的等温线的影响,并配合有热重分析(TG)和红外光谱(IR)的测定。结果表明:(1)甲基化后的硅胶对乙酸的吸附能力大大下降;(2)甲基化硅胶的热处理温度达500℃时吸附能力完全恢复到甲基化前的硅胶的水平,甲基化层明显开始破坏的温度为450℃;(3)甲基化硅胶高温处理后吸附能力得以恢复的主要原因是重新形成表面自由羟基。     

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。     

硅胶自环己烷中吸附含氧芳香化合物的研究

测定了15℃和30℃时硅胶自环己烷中吸附苯甲醇、苯甲醚、苯甲醛和苯甲酸的吸附等温线,这些等温线皆可用Langmuir公式表示。利用Langmuir常数n_m^s和b值计算了吸附过程的△G⁰、△H⁰和△S⁰;四种化合物的△S⁰皆为正值。测定了在较大复盖度时红外光谱图上硅胶表面自由羟基峰的移动值△v_OH。结果表明△H⁰和△v_OH及△v_OH^1/2间有线性关系。文中对所得结果做了初步的解释。     

聚乙二醇、聚丙二醇和环氧乙烷-环氧丙烷嵌段共聚物在固-液界面上的吸附 III:硅烷化活性炭/水和甲基化硅胶/水界面

测定了25℃时硅烷化不同时间(1至30天)的活性炭及甲基化硅胶自水溶液中吸附四种聚乙二醇(PEG)、三种聚丙二醇(PPG)和环氧乙烷(EO)-环氧丙烷(PO)嵌段共聚物pluronic-L64的等温线。结果表明, 在各活性炭样品上的等温线均为Langmuir型的; 同一炭样对不同PEG的极限吸附量(g·g^-^1)与分子量无关; 极限吸附时每个PEG分子所占面积(A)与分子中所含EO数(nEO)间有直线关系, 直线的斜率与硅烷化时间有关, 这一结果可用硅烷化时间延长时吸附分子的EO基可能以其氧原子向水, 碳氢链节靠近固体表面取向的模型解释。根据PPG的极限吸附量与分子量有关和极限吸附时的分子面积推断PPG分子不是以平躺方式吸附。甲基化硅胶对PEG的吸附量极小, 对PPG的吸附量随分子量减小急剧降低, 而对L64的吸附量明显大于在亲水硅胶上的。文中对所得结果给出了初步的解释。     

硅胶自环己烷中吸附环己酮和苯甲酸

用经不同温度处理的亲水硅胶(表面总羟基浓度不同)和甲基化硅胶(只含有缔合羟基或不同表面浓度的自由羟基的硅胶)为吸附剂, 测定了自环己烷中吸附环己酮和苯甲酸的等温线, 以及几种硅胶样品的红外光谱图, 探讨了表面自由羟基和缔合羟基在溶液吸附中的作用.     

苯基化硅胶的物理结构和表面性质的研究

本文利用苯基三氯硅烷和硅胶表面羟基反应制备了苯基化硅胶。测定了苯基化硅胶的物理结构、水蒸气吸附等温线、润湿热、差热分析(DTA)和红外光谱(IR)。结果表明,所有苯基化硅胶的真密度(dT)、比表面(S)和比孔体积(V)均减少, 而表观密度(dA)增加, 但苯基化对不同硅胶的平均孔半径(r)有不同的影响; 苯基化硅胶对水蒸气吸附, 对水、苯和环己烷的润湿热均显著减少; 苯基化硅胶的热稳定性大于甲基化硅胶, 甲基化硅胶的表面是高度憎水的, 但苯基化硅胶的憎水性则很弱。     

硅胶自溶液中吸附胆固醇和卵磷脂

卵磷脂和胆固醇是细胞膜的主要组成,它们在不同界面上的定向排列方式对细胞膜的结构与功能起着重要的作用。用固体物质自非水溶剂中吸附类脂化合物形成类脂单层,再自水溶液中吸附蛋白质,可制成固体载体上的模拟生物膜。在固体表面上的类脂单层膜中类脂分子的定向方式与溶剂和固体表面性质有关。这些研究大多数是以非孔性物质为吸附剂(如aerosil,石墨化炭黑,carbochrom.等)自有机溶剂中吸附类脂化合物(主要是胆固醇和卵磷脂),根据单层饱和吸附时分子占据的面积推算单层中类脂化合物分子的取向。实际应用的吸附剂大多是孔性的,因此研究类脂化合物在孔性吸附剂(如,硅胶、活性炭等)上的吸附机理更有实际意义。     

ZnCl2、KOH和HNO3改性MWCNT对苯酚的吸附行为研究

通过扫描电子显微镜、X射线衍射仪、N₂吸附分析仪及Boehm滴定法获得ZnCl₂、KOH和HNO₃化学处理对高纯多壁碳纳米管的结构和表面含氧官能团的影响,通过批处理实验考察吸附条件（吸附时间、初始浓度、温度）对处理前后的碳纳米管吸附苯酚行为的影响,并采用准一级、准二级、Evolich动力学模型和热力学方程拟合其吸附数据,分析其动力学行为、热力学行为和吸附机理。结果表明,虽然ZnCl₂、KOH和HNO₃化学处理法均未对碳纳米管BET比表面积产生显著影响,但会影响其表面化学性质（即,对于ZnCl₂和KOH化学处理降低表面羧基、内酯基含量和增大碱性官能团量,而对于HNO₃化学处理可以增大表面羧基、内酯基含量,而碱性官能团略有增加）;改性处理影响碳纳米管去除苯酚效率：由于ZnCl₂和KOH改性处理降低碳纳米管表面羧基量,故其提高了苯酚去除率,而HNO₃处理则略减小碳纳米管的苯酚去除率,可能是由于碳纳米管结构和表面化学性质共同影响所致;碳纳米管的苯酚去除率均随苯酚溶液初始浓度的增大而减小;高温不利于吸附;热力学研究发现碳纳米管吸附苯酚过程是自发的和放热的,属于物理吸附;动力学研究表明,吸附过程符合准二级动力学方程。通过ZnCl₂和KOH化学处理,可以显著提高碳纳米管对苯酚的吸附性能。     

氨基功能化SBA-16对CO_2的动态吸附特性

采用浸渍法将四乙烯五胺(TEPA)负载到介孔分子筛SBA-16的孔道内,形成功能化的介孔材料用于CO2的吸附.利用X射线衍射(XRD)、透射电镜(TEM)、氮气物理吸附-脱附和热重分析(TGA)等方法对样品进行了表征.通过动态吸附对不同TEPA浸渍量的SBA-16的CO2吸附性能和再生性能进行研究.结果表明:修饰后的SBA-16仍然保持有序的孔道结构,但样品的孔道有序度降低,比表面积、孔容、平均孔径都减小.样品对CO2的饱和吸附容量和穿透吸附容量随着TEPA浸渍量的增加而增加.60℃时,30%TEPA浸渍量的样品的穿透吸附容量和饱和吸附容量达到最大,分别为0.625和0.973mmol·g-1.在60-80℃,样品的动态吸附性能稳定.经过20次吸附-脱附循环后,样品的饱和吸附容量仅降低了6.45%.采用失活模型对CO2的吸附穿透曲线进行模拟,该模型能够很好地模拟样品对CO2的吸附过程.     

Ellipsometry studies of fibronectin adsorption

The adsorption of fibronectin on a series of different surfaces was investigated with in situ ellipsometry. For silica and methylated silica, the adsorbed amount (Γ), the adsorbed layer thickness (δ_el) and the mean adsorbed layer refractive index (n_f) were obtained by a procedure involving studies of the bare substrate at two different ambient refractive indices, as well as four-zone averaging. It was found that the adsorbed amount of fibronectin was the same (1.9 ± 0.1 mg m⁻²) on both silica and methylated silica surfaces. However, the adsorbed layers formed on methylated silica were more extended and had a lower average protein concentration than those formed on silica. Furthermore, on both silica and methylated silica, an increasing adsorbed amount is achieved both by a denser packing of the fibronectin molecules and by a growth of the adsorbed layer normal to the surface. Furthermore, the adsorption of fibronectin on lipid surfaces was investigated. It was found that the adsorption of fibronectin on phosphatidic acid was quite significant (2.2 ± 0.2 mg m⁻²), while that on phosphatidylcholine, phosphatidylinositol and phosphatidylserine was much smaller (all 0.1 ± 0.05 mg m⁻²). These results are correlated to findings on the adsorption of fibrinogen on these surfaces, as well as on the opsonization of lipid-stabilized colloidal particles.     

Micellization and adsorption of a zwitterionic surfactant: N-dodecyl betaine-effect of salt

Time-resolved fluorescence quenching, self-diffusion measurements and calorimetric investigations have been used in order to investigate the effect of salt on aggregation in aqueous solutions and the adsorption onto silica gel of the zwitterionic surfactant N-dodecyl betaine (NDB).

The micelle aggregation number of NDB stays constant when the NDB or salt concentration increases but decreases with an increase of temperature. Evidence is presented for the binding of cations and anions to micellar aggregates. The degree of binding has been obtained for Na⁺, Ca²⁺ and Cl⁻ ions; it is always larger for the anion.

Enthalpies of micellization were obtained directly from calorimetric curves of NDB in dilution experiments. The observed decrease of the endothermic enthalpies of micellization with increasing temperature or salinity is attributed to a structural change in the water molecules around the alkyl chain of the free monomers.

The adsorption isotherms of NDB onto silica gel depend very little on temperature, and a plateau is reached near the CMC. At saturation, the adsorbed amount of NDB depends on the salt and follows the sequence NDB < (NDB + NaCl) < (NDB + CaCl₂).

The exothermic differential molar enthalpies of adsorption demonstrate the same behaviour as the enthalpies of micellization with varying temperature or salinity. Adsorption onto silica gel depends on the NDB concentration, the salt concentration and temperature.     

硅烷化活性炭的吸附性质

本工作测定了25℃和35℃时硅烷化活性炭自水溶液中吸附苯甲酸和苯甲醛的等温线;计算了吸附过程的ΔGⅲ,ΔHⅲ和ΔSⅲ;用Hill-deBoer方程处理了实验结果。所得结果表明:(1)随硅烷化时间延长,苯甲酸和苯甲醛的吸附量(mol.m^-^2)明显增加;-ΔGⅲ和-ΔHⅲ略有升高,ΔSⅲ为正值;(2)吸附分子之间的相互作用很弱,吸附分子与活性炭表面间的作用随硅烷化程度增加而加大;(3)芳香化合物可能是以苯环吸附在炭表面上的。     

负载型氨基酸离子液体的制备及其对二氧化碳的吸附性能

采用浸渍蒸发法将四甲基铵甘氨酸([N1111][Gly])和四甲基铵赖氨酸([N1111][Lys])两种离子液体分别负载到硅胶(SG)表面,利用EA、TGA、BET和FT-IR等技术对所得到的吸附剂进行表征,考察了离子液体种类、离子液体负载量和温度等条件对其CO_2吸附性能的影响。结果表明,离子液体成功负载到硅胶表面,所制得的负载型氨基酸离子液体对二氧化碳具有良好的吸附性能。在所考察的温度范围(303.15-323.15 K)内,温度越高,平衡吸附量越小;在负载量为10%-60%,随着负载量的增加,平衡吸附量先增加后减小。对于[N1111][Gly]/SG,当负载量为22.4%(质量分数)、吸附温度为30℃、压力为0.1 M Pa时,二氧化碳的平衡吸附量可达到41 mg/g(相对于1 mol AAILs吸附0.62 mol CO_2),而且,吸附20 min即可达到平衡吸附量的90%。吸附剂在循环使用六次之后,其结构与性能均保持良好。     

Grafting of Polymers onto Activated Carbon Surface: Graft Polymerization of Vinyl Monomers Initiated by Azo Groups That Were Introduced onto the Surface

Abstract

We examined the grafting of polymers onto an activated carbon powder surface by polymerization that was initiated by azo groups that were introduced onto the surface as well as the effects of grafted polymers on the adsorption of acetic acid. The introduction of azo groups onto the surface was achieved by the following methods: (1) a reaction of 4,4′-azobis(4-cyano-pentanoic acid) (ACPA) with surface isocyanate groups that were introduced beforehand by treatment with tolylene 2,4-diisocyanate (AC-Azo 1) and (2) the direct condensation of ACPA with surface phenolic hydroxyl groups by using N,N'-dicyclohexylcarbodiimide (AC-Azo 2). The radical polymerizations of styrene, methyl methacrylate, N,N-diethylacrylamide (DEAM), and N-isopropylacrylamide (NIPAM), were successfully initiated by the azo groups on the surface and the corresponding polymers were grafted onto the surface. There was a significant decrease in the adsorption of the acetic acid of the activated carbons when polymers were grafted onto them, particularly in regards to the grafting of hydrophobic polymers. On the other hand, a decrease in the adsorbability of the polyDEAM-grafted and polyNIPAM-grafted activated carbon was barely observed. In addition, polyDEAM-grafted and polyNIPAM-grafted activated carbons showed temperature-dependent adsorption of acetic acid: the adsorbability of these activated carbon decreased above lower critical solution temperature of these polymers, which is about 32°C.     

Phenol adsorption on active carbon by means of thin-layer chromatography

Summary The effect of the acidity of the media on the adsorption of phenol and creasols was investigated using TLC and using the R_F-values as a measure of the adsorption ability of active carbon. Three types of chromatographic layers were employed: silica gel, silica gel containing 3% of active carbon and silica gel containing 6% of active carbon. Standard solutions of phenol, m-cresol and o-cresol were used as the samples. The acetic acid content of the solvent mixture significantly influences the adsorption of phenol and cresols on the active carbon layer. An increase in the acetic acid content results in a decrease of the adsorption of phenols. However, under specific conditions [81∶5∶7 hexane-diethyl ether-acetic acid, and 48∶2∶8 benzene-acetone-acetic acid developers] the competitive adsorption of phenols and acetic acid may take place, which has been observed by a steep increase in the adsorption of phenol and cresols.     

Theoretical Study About Effects of H2O and Na+ on Adsorption of CO2 on Kaolinite Surfaces

The density functional theory(DFT) was used to investigate the adsorptions of carbon dioxide(CO₂) on kaolinite surfaces and the influences of Na⁺ and H₂O on the adsorption. Both cluster and periodic models of kaolinite were considered. The calculated results indicate that stable complexes can be formed between adsorbed CO₂ and the surfaces of kaolinite in the presence or absence of sodium cation and water molecule. The Al-O octahedral surface has a larger adsorption affinity for CO₂ than the Si-O tetrahedral surface of kaolinite because the hydroxyl groups of kaolinite Al-O surface present more activity than the basal O atoms of the Si-O tetrahedral surface in the inter-molecular interactions. The existence of exchangeable sodium cations exerts the significant effect on the adsorption of CO₂ with the dramatic increase of the adsorption energy, while the presence of water molecule decreases the adsorption strength insignificantly. The calculated Gibbs free energies of the adsorption reveal that the adsorptions of CO₂ on all the investigated kaolinite surfaces are feasible thermodynamically in the gas phase. Surface free energy was calculated to provide the predictions of the surface stability as a function of temperature.     

自溶液中的吸附 VII: 硅胶自环己烷中吸附醇,酮和酯

The adsorption isotherms of some monofunctional alcohols, ketones and esters from cyclohexane onto silica gel have been determined at 30`C and 10`C. The silica gel used bad a BET area of 417 m2/g and an average pore radius of 45A. The concentrations of free and associated hydroxyls on the silica gel were 1.4 and 4.1/100A^2 respectively. The adsorption order is cyclohexanol>n-octyl alcohol>cyclohexanone>methyl isobutyl ketone>n-propyl acetate=n-amyl acetate. The adsorption decreases with increasing temperature as normal. Except at very low concentrations, the isotherms can be represented by the Langmuir equation. The limiting adsorption, nms, on the silica gel does not accord with the stoichiometric ratio (1:1) between the free surface hydroxyl groups of the adsorbent and the adsorbate. In addition to surface conditions and the functional group of the adsorbate, it seems that the limiting adsorption is also controlled by the other factors, including temperature, solvent, and, sometimes the chain length of the adsorbate. The standard free energy (ΔG0) and standard enthalpy (ΔH0) of the adsorbates in adsorptien processes have been determined from the Langmuir parameters. The results indicate that the absolute value of ΔH0 is higher than that of ΔG0 (in other words, standard entropy ΔS0 is negative), as in the case of the adsorption of gases. Since there is practically no difference in ΔG0 or ΔH0 of adsorption between alcohols or esters, it is suggested that in dilute solution only the polar groups take part in adsorption, and the hydrocarben chains remain in solution during the adsorption process. For ketones, the absolute values of ΔG0 and ΔH0 are somewhat lower for methyl isobutyl ketone than that for cyclohexanone. A possible explanation is that in the adsorbed state the isobutyl chain of the methyl isobutyl ketone may somewhat close to the surface and thus decreases the adsorption and changes the ΔG0 and ΔH0.     

水蒸气对高岭土高温吸附铅的影响

使用沉降炉开展了水蒸气对高岭土高温吸附铅影响的实验研究，其中铅的形态为PbO和PbCl₂两种。首先研究了0-20%水蒸气对高岭土吸附PbO（1100-1300 ℃）和PbCl₂（800-1300 ℃）的影响规律，然后基于XRD、SEM和残余羟基率等分析，掌握了水蒸气影响高岭土高温吸附的机理。结果表明，水蒸气可以减少高岭土表面羟基的高温脱落，从而阻碍了PbO吸附、促进了PbCl₂吸附。综合高温下惰性莫来石的出现和高岭土孔隙结构的坍塌等因素，PbO和PbCl₂的最佳吸附温度分别为1200和1000 ℃。     

Analytical investigation of the chemical reactivity and stability of aminopropyl-grafted silica in aqueous medium

Various samples of aminopropyl-functionalized silica (APS) have been prepared by grafting an organosilane precursor 3-aminopropyl-triethoxysilane (APTES) onto the surface of silica gel. The amine group content of the materials has been adjusted by varying the amount of APTES in the reaction medium (toluene). The grafted APS solids have been characterized with using several analytical techniques (N₂ adsorption, X-ray photoelectron spectroscopy, infrared spectrometry) to determine their physico-chemical properties. Their reactivity in aqueous solutions was studied by acid-base titration, via protonation of the amine groups, and by way of complexation of these groups by Hg^II species. APS stability in aqueous medium was investigated at various pH and as a function of time, by the quantitative analysis of soluble Si- or amine-containing species that have been leached in solution upon degradation of APS. The chemical stability was found to increase when decreasing pH below the pK_a value corresponding to the RNH₃⁺/RNH₂ couple, but very low pH values were necessary to get long-term stability because of the high local concentration of the amine groups in the APS materials. Adsorption of mercury(II) ions on APS was also performed to confirm the long-term stability of the grafted solid in acidic medium. Relationship between solution pH and APS stability was discussed. For sake of comparison, the stability of APS in ethanol and that of mercaptopropyl-grafted silica (MPS) in water have been briefly considered and discussed with respect to practical applications of silica-based organic–inorganic hybrids, e.g., in separation science or in the field of electrochemical sensors.     

表面含氧基团对AuCl3-CuCl2/C双组分非汞催化剂催化性能的影响

采用HNO₃氧化及在He气氛围经不同温度焙烧处理椰壳活性炭, 以此活性炭为载体, 通过浸渍法制得AuCl₃-CuCl₂/C双组分非汞催化剂, 并用于乙炔氢氯化反应评价. 结果表明, 分别以HNO₃处理、 未处理和400 ℃焙烧处理活性炭为载体的催化剂乙炔转化率最高分别可达98%, 96%和90%; 而以700和1000 ℃焙烧的活性炭为载体的催化剂反应4 h后乙炔转化率急剧下降为30%. 考察了活性炭表面的含氧基团(尤其是羟基)对Au基催化剂的催化性能的影响.