几种典型国产活性炭吸附各种烃类的NMR研究——Ⅱ.苯、环己烷、正戊烷和正己烷吸附的~1H NMR研究

活性炭吸附苯、环己烷、正戊烷和正已烷的测量表明,在同一种活性炭中各烃的饱和吸附体积相同,四种烃的吸附量与其摩尔体积成反比。同一种被吸附物在不同活性炭中的吸附量与各活性炭的比孔容和孔径分布有关。活性炭的比孔容大,且孔径小于30的微孔比例大时,其吸附和解吸容量也大。这些体系的~1H NMR研究进一步证实了孔径小于30的微孔中发生毛细管凝聚,导致吸附和解吸的容量增大。被吸附分子的自旋晶格弛豫时间几乎不随被吸附物的种类而异。他们与活性炭表面上酸性基团总量有较好的曲线关系。     

~(13)CNMR研究吡啶及2,6-二甲基吡啶在SiO_2、A1_2O_3、NaY及HY上的吸附

用NMR方法研究固体表面吸附可获得吸附分子活动性的动态信息,加深对吸附分子与固体表面相互作用力性质的了解。~13CNMR谱虽灵敏度低于~1H谱,但分辨率优于~1H谱,对吸附态分子可得中等分辨率的谱图。本文用~(13)CNMR方法研究吡啶(Py)和2,6-二甲基吡啶(DMPy)在SiO_2、Al_2O_3、NaY及HY上的吸附。比较NMR谱线的宽度,可知在不同吸附体系中处于吸附态的分子具有不同的活动性。推测了DMPy吸附时空间受阻情况及与表面相互作用力的性质。     

活性炭对蔗糖的吸附特性

活性炭吸附蔗糖是一种化学吸附过程，蔗糖是单分子铺展的形式被吸附于活性炭表面，其吸附速率由内扩散所控制。     

动力学、热力学和活化能在花生壳吸附铅离子实验中的应用

以花生壳为吸附剂、Pb2+为模拟污染物研究了物理化学中固体表面的吸附过程,考察了Pb2+的初始浓度、吸附温度的影响,研究了固体表面吸附反应动力学、热力学和活化能。结果表明:在不同Pb2+初始浓度下,Pb2+在花生壳表面的吸附动力学符合准二级动力学模型,表明该吸附过程是化学吸附为控制步骤的吸附过程。热力学结果表明Pb2+在花生壳表面的吸附是一个自发的放热过程,因为Pb2+由三维运动转变为二维运动导致系统熵减小。活化能Ea=31.35 kJ·mol-1再次证明Pb2+在花生壳表面的吸附是化学吸附过程,这些结果较好地验证了物理化学教学中固体表面的吸附行为。通过该拓展实验加深了学生对固体表面吸附过程的理解,同时,培养了学生的科技创新能力。     

活性炭对乙酸乙酯的吸附和再生

研究了活性炭的孔结构和表面化学性质及水蒸气存在对活性炭吸附乙酸乙酯的影响. 结果表明,活性炭的微孔(＜1.70 nm)结构特征是活性炭吸附乙酸乙酯的主要因素,其表面性质对乙酸乙酯的吸附没有明显影响. 40 ℃下,具有丰富微孔的椰壳活性炭AC和Y2在乙酸乙酯入口体积分数为0.30%时,对乙酸乙酯的饱和吸附量分别为0.31和0.28 g/g. 在相对湿度低于40%时,活性炭对乙酸乙酯的饱和吸附量仍可达干燥条件下相应值的90%. 在180 ℃加热时可将吸附在活性炭上的乙酸乙酯有效地回收. 活性炭的吸附性能不受再生气体中所含少量O2的影响. 活性炭经6次再生循环使用,未发现其对乙酸乙酯的吸附性能发生变化.     

几种典型国产活性炭吸附各种烃类的NMR研究——Ⅱ. 苯、环己烷、正戊烷和正己烷吸附的1H NMR研究

活性炭吸附苯、环己烷、正戊烷和正已烷的测量表明, 在同一种活性炭中各烃的饱和吸附体积相同, 四种烃的吸附量与其摩尔体积成反比。同一种被吸附物在不同活性炭中的吸附量与各活性炭的比孔容和孔径分布有关。活性炭的比孔容大, 且孔径小于3.0 nm的微孔比例大时, 其吸附和解吸容量也大。这些体系的~1H NMR研究进一步证实了孔径小于3.0 nm的微孔中发生毛细管凝聚, 导致吸附和解吸的容量增大。被吸附分子的自旋晶格弛豫时间几乎不随被吸附物的种类而异。他们与活性炭表面上酸性基团总量有较好的曲线关系。     

关于亚甲基蓝在活性炭表面吸附投影面积σA的探讨

溶液吸附法测定活性炭比表面积是大学本科基础物理化学实验中一个较重要的实验.亚甲基蓝在活性炭表面的吸附符合Langmuir单分子层吸附,但按照实验教科书及文献介绍的溶液吸附法测定活性炭比表面积的方法,大量学生实验的测定结果比活性炭实际比表面积偏低很多.本文以BET表面吸附装置测定活性炭比表面积,再以溶液吸附法测定了亚甲基蓝在活性炭表面的最大吸附量Γ∞,计算了亚甲基蓝在活性炭表面吸附投影面积σA.结果表明亚甲基蓝在活性炭表面可能不是端基吸附,而是平面吸附,分子的投影面积σA应为1.35×10-18 m2.     

活性炭纤维对铂离子的还原吸附特征

利用不同的活化工艺,制备了水蒸汽活化和磷酸或氯化锌活化活性炭纤维,并借助扫描电镜(SEM)、X-射线衍射(XRD)和光电子能谱(XPS)等技术,研究了这些活性炭纤维对铂的还原吸附特征。结果表明,各活性炭纤维均能还原吸附铂离子,吸附容量为30mgPt/gC至90mgPt/gC之间。依据活性炭纤维种类的不同,还原吸附的铂呈粒状或放射性簇状存在于活性炭纤维表面,铂颗粒的粒径为几十nm至1μm之间。对纤维表面铂的XRD分析表明,还原吸附的铂呈无定型结构,但经过400℃高温处理后,颗粒转化为金属铂结晶形态。还原吸附铂后,活性炭纤维表面的含氧基团相应增加,显示其表面被氧化为羟基和羰基。     

活性炭表面含氧基团对苯酚吸附平衡及动力学的影响

煤基活性炭分别用烧失处理和HNO3氧化处理后得到不同表面性质的活性炭,采用X射线光电子能谱(XPS)、N2吸附、酸碱滴定及零电荷点(pHPZC)对活性炭表面性质及孔结构进行表征,研究了活性炭表面性质对苯酚吸附平衡和吸附动力学影响.经HNO3氧化后,活性炭表面含氧基团显著增加,烧失处理后,表面含氧基团尤其是羧基显著减少.苯酚最大平衡吸附量随活性炭表面含氧基团的增多而减少,吸附速率常数与碳表面含氧基团的量呈正相关,而吸附活化能与活性炭在一定吸附条件下表面所带电荷多少相关.随着活性炭表面含氧基团增多,吸附活化熵增大(负值减小),苯酚在活性炭表面排列的有序性减小.静态吸附与动态吸附实验结果都表明:在含氧基团较少而碱性更强的活性炭上,发生化学吸附的程度更大.     

酪氨酸在活性炭/水界面上的吸附

研究了不同pH值介质中酪氨酸在活性炭上的吸附行为.结果表明,pH值4.2～6.1时吸附量较大,在酪氨酸的等电点时吸附量最大;酪氨酸被吸附的主要形式是兼性离子;酪氨酸离子靠VanderWaals力吸附在活性炭/水界面上.用介质pH值对酪氨酸溶解度的影响和活性炭的表面性质解释了实验结果     

吸附在活性炭上的苯和环己烷的NMR弛豫研究

被吸附分子的NMR弛豫测量可以提供该分子的运动和吸附状态等信息。近来证明,多孔固体中被吸附物的自旋晶格弛豫的测量(T_1)是孔径大小和孔结构分析及多孔物质渗透性能测量的有力工具这是基于靠孔壁近的分子比远离固体表面的分子自旋晶格弛豫     

十二烷基三甲基溴化铵在聚苯乙烯胶乳粒子上的吸附

实验测得C~1~2TAB在PS胶乳粒子表面的吸附等温线呈L型的二阶段吸附特征,这表明初始的C~1~2TA^+离子是将其季铵正电性头基吸引在PS链的负电性硫酸根端基上,并将碳氢链通过疏水相互作用吸附在PS链上。结合光子相关谱测得胶乳粒子流体力学半径R~H的变化,表明第I阶段围绕着这些初始吸附位的聚集吸附,产生平均聚集数为4.0的松散小聚集体,此时对应的浓度c/cmc=0.32是文献通常所指的临界表面胶团浓度csmc。其后的进一步聚集吸附最终生成了附着在PS链端基处且平均聚集数为19.5的球形吸附胶团。这一饱和吸附的结果增加了胶乳粒子在水溶液中的分散稳定性。     

可逆与不可逆吸附氢在合成甲醇反应中的作用

在自行设计和建立的加压动态分析装置上研究了合成甲醇催化剂上氢的吸附和反应行为。结果表明:在反应条件下催化剂上吸附的氢可分为可逆吸附氢和不可逆吸附氢;不可逆吸附氢又可分为能被CO顶替出来的和不能被CO顶替出来的两部分;能被CO顶替出来的不可逆吸附氢对CO的吸附起促进作用,不能被CO顶替出来的不可逆吸附氢是合成甲醇催化剂必不可少的“组分”或称“促进剂”;同时甲醇的生成是可逆吸附氢与一氧化碳作用的结果。     

用23Na和27Al固体核磁共振研究Na+在γ-Al2O3上的吸附状态

The adsorption of Na~+ on γ-alumina surface at four coverages of Na_2CO_3 (5%, 10%, 15%, and 20% wt/wt) was characterized by solid-state ~(23)Na and ~(27)Al NMR spectroscopy. The experimental results suggest that two distinct adsorbed species are present on alumina surface: surface species and surface salts. At lower coverages of Na_2CO_3 (5% and 10%), a surface species is predominant, in which the Na~+ cations are associated with the oxygen atoms of γ-alumina. With increasing the loading level to 15%, a second adsorbed species begins to appear which is attributed to the surface salt, Na_2CO_3, deposited on the solid surface. Further adsorption of Na_2CO_3 leads to an increase in the amount of surface salt while the amount of surface species remains unchanged. ~1H-~(27)Al CP/MAS experiments give the evidence that some Na~+ cations in the form of surface species are coordinated with the Br~(‥)onsted acid sites of γ-alumina. This may be the main driving force that improves appreciably the catalytic efficiency of Na_2CO_3/γ-Al_2O_3 catalyst.     

Mixing in adsorbed monolayers: perfluorinated alkanes

The mixing behavior of binary combinations of perfluoroalkanes in the bulk and in solid monolayers adsorbed at the graphite/liquid interface, determined by calorimetry and powder diffraction, is reported. The perfluoroalkanes are found to generally have a smaller excess enthalpy of mixing on the surface than in the bulk, and their relative size ratio is a good parameter to predict the mixing behavior. The excess enthalpy of mixing for perfluoroalkanes is found to be significantly smaller than that of the closely related hydrocarbons. The preferential adsorption of longer homologues over shorter ones is observed. Interestingly, the extent of preferential adsorption with relative size ratio is very similar to that of the hydrocarbons. These results can be understood in terms of the increased compressibility and lower polarizability of the perfluoroalkanes compared to hydrocarbons.     

Special features of methanol interaction with adsorbed oxygen at platinized platinum electrode: Transients of the open-circuit potential

Open-circuit potential transients are measured under the conditions of methanol interaction with the pre-adsorbed oxygen at platinized platinum electrode. The time necessary for complete removal of the adsorbed oxygen monolayer appeared being shorter by a factor of ～1.5 as compared with smooth polycrystalline platinum. The dependence of platinum surface coverage with adsorbed oxygen on the potential during its decay is found. It was shown that the reaction of methanol with the adsorbed oxygen is most slow at a high coverage (1–0.8). It is suggested that at these coverages, like the case of polycrystalline platinum, the adsorbed oxygen directly interacts with the methanol molecules from the solution. At moderate coverages (0.8–0.2), the reaction of the adsorbed oxygen with methanol at the platinized platinum is better described by the “conjugated reactions” mechanism. The specific rates of the methanol dissociative adsorption at the platinized platinum turned out to be close to those observed earlier for the polycrystalline platinum.     

吸附在活性炭上的二氧六环类固相和类液相性质的NMR研究

物理吸附在活性炭上的有机分子的性质,一直是人们感兴趣的问题。近年来,人们开始用NMR梯度场和核弛豫的方法,研究活性炭上吸附分子的扩散运动和分子交换运动.由于吸附分子在活性炭上处于不同的状态,其核弛豫表现出快、慢两个过程。通过拟合磁化矢量随时间变化的曲线,可以得到不同状态分子的百分含量。本文采用核弛豫的方法,研究活性炭的表面酸性基团及孔径对被吸附的二氧六环(DO)类固相和类液相形成的影响.并对不同吸附量下,DO在活性炭上的吸附行为进行讨论。     

Impedance Spectroscopic Measurements of Pure Gas Adsorption Equilibria on Zeolites

Physisorption equilibria of gases on inert porous solids like activated carbon or molecular sieves can be characterized by measuring the (frequency dependent) capacitance of a capacitor filled with a sample adsorbent. This quantity strongly depends not only on the physico-chemical structure of the empty adsorbent in vacuum, but also on the permanent or induced dipole moments of the molecules adsorbed and of the fluid phase. Consequently, it should be possible to determine the excess mass being adsorbed on the internal surface of a highly porous solid by measurements of the dielectric constant. The aim of this work is to show for various pure gases and adsorbents that the change of the capacitance of an adsorption system depends on the adsorbed mass. Therefore, this effect can be used to characterize porous solids and their adsorbates and, for example, to check the state or the quality of industrial adsorbents during a process on site if calibration measurements have been taken (Staudt et al., 1994, 1998).