The effect of a Gaussian distribution of chain-lengths on the phase-behaviour of a model system of rod-like macromolecules in solution

The calculations of Flory and co-workers for the formation and composition of isotropic, bi-phasic and anisotropic systems composed of rod-like macromolecules in solution have been extended to include a Gaussian distribution of rod-lengths. The critical concentrations for the beginning and end of the bi-phasic range $\text{v}{}^{\mathrm{<mtext>o</mtext><mtext>1</mtext>}}{}_{\mathrm{p}}$ and $\text{v}{}^{\mathrm{<mtext>o</mtext><mtext>7</mtext>}}{}_{\mathrm{p}}$ respectively, the volume fraction of anisotropic phase Φ_A, the compositions and average molecular weights of isotropic and anisotropic phases, and the order parameter S of the anisotropic phase are calculated as a function of polymer concentration v^o_p for rod-length x_o in the range 30 to 70 and for a Gaussian distribution half-width $\text{Δ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ in the range 10 to 70. The extent of the bi-phasic range and the composition of the two components is found to be strongly dependent on the breadth of the distribution and average rod-length. The applicability of the calculations to data for poly(alkylisocyanates) in solution is briefly considered.     

多孔碳结构调控及其在二氧化碳吸附领域的应用

CO_2大量排放引发的温室效应已成为当今世界面临的重要环境问题。燃煤发电厂是CO_2的集中排放源,其排放量约占总排放量的42%,因此,燃煤发电厂烟道气中CO_2的高效捕集迫在眉睫。吸附技术操作简便、能耗低,易于实际应用,被认为是最具前景的烟道气CO_2捕集技术。近年来,多孔碳吸附剂因原料来源广、理化特性可控性强以及目标吸附质适应性高等优点,成为当前CO_2捕集技术的研究热点。综述了近年来多孔碳的制备方法,物理活化法、化学活化法、炭气凝胶法和模板法等,以及制备方法对孔径结构、杂元素掺杂缺陷和多孔碳表面性能的调控;并阐述了孔径结构、元素掺杂和表面官能团改性对CO_2吸附量、循环稳定性、烟道气中CO_2吸附选择性的影响,归纳了多孔碳吸附在实际应用中亟需解决的问题和关键技术。可进一步深入研究机理,协同制备出更高效且适用于CO_2吸附的多孔碳。     

功能型配位聚合物在气体吸附方面的研究

作为潜在的新型功能材料,配位聚合物今年来得到科学家的普遍关注.本文主要对配位聚合物作为气体吸附材料的研究和潜在应用进行了描述和总结,并对其发展前景作出了展望.     

Effect of adsorption deformation on thermodynamic characteristics of a fluid in slit pores at sub-critical conditions

Solvation pressure due to adsorption of fluids in porous materials is the cause of elastic deformation of an adsorbent, which is accessible to direct experimental measurements. Such a deformation contributes to the Helmholtz free energy of the whole adsorbent-adsorbate system due to accumulation of compression or tension energy by the solid. It means that in the general case the solid has to be considered as not solely a source of the external potential field for the fluid confined in the pore volume, but also as thermodynamically noninert component of the solid-fluid system. We present analysis of nitrogen adsorption isotherms and heat of adsorption in slit graphitic pores accounting for the adsorption deformation by means of nonlocal density functional theory.     

The effect of substituents on the adsorption of alkenes on (111) Pt and Pd surfaces: a theoretical study

The coordination modes of ethylene, propene, 1- and 2-butenes, 2-methyl-2-butene, and styrene on a Pt(111) or a Pd(111) surface have been compared on the basis of extended Hückel calculations. The presence of methyl substituents induces a uniform decrease in the binding energies of the alkenes, both on Pt and on Pd. The phenyl group yields the same result on Pt but, on the contrary, gives a stronger adsorption mode on Pd. The interpretation of these results is based on the balance between attractive and repulsive interactions, the role of the latter being predominant. This trend in binding energy is related to the decrease of the hydrogenation reactivity of olefins upon substitutionin the case of a competitive reaction.     

页岩孔隙结构及多层吸附模型的研究

页岩气是指主体位于暗色泥页岩或高碳泥页岩中,以吸附态或游离态为主要赋存方式的非常规天然气。页岩孔隙结构复杂,一般以纳米孔隙占优势,用常规储层孔隙的表征方法难以解释美国的高产页岩气系统。因此,页岩纳米孔隙的表征成为制约页岩气资源评价的关键因素。就浅谈页岩孔隙结构及多层吸附模型等方面的研究。     

功能化介孔材料吸附性能与机理的研究进展

综述了功能化介孔材料的孔径结构、改性基团和吸附条件对废水中的有机污染物、染料分子和重金属离子以及生物大分子、药物分子、CO2和挥发性有机气体污染物的吸附脱除效果的影响,还介绍了功能化介孔材料对液晶材料中的微量无机离子和大极性有机杂质的吸附脱除效果,指出了新型功能化介孔材料的开发和吸附环境的研究是未来的研究热点和发展趋势。     

A molecular mechanics study of the adsorption of ethane and propane on V2O5(001) surfaces with oxygen vacancies

Adsorption geometries and energies of ethane and propane physisorbed on the (001) surface of vanadium pentoxide with oxygen vacancies were determined by a molecular mechanics simulation. Three types of oxygen vacancies, built up by removal of vanadyl oxygen, two-fold and three-fold coordinated oxygen, respectively, have been modeled as defects. The energetically most favorable adsorption site is on top of a vacancy of two-fold coordinated oxygen for ethane and propane, respectively. The next favorable site for both alkanes is on top of a vacancy of vanadyl oxygen. Due to the generation of a “van der Waals cage” which traps the hydrocarbon the adsorption on the defect site is favored in comparison with the ideal surface for these two defect types. A vacancy of three-fold coordinated oxygen does not lead to an enhancement of adsorption and pushes the reactant towards the unperturbed surface areas due to the fact, that no energy minimum can be obtained in the vicinity of the defect. This revised version was published online in August 2006 with corrections to the Cover Date.     

Diffusion in liquid-filled pores of activated carbon. I. Pore volume diffusion

The adsorption isotherms on activated carbon were measured for the following six systems: benzaldehyde, phenol, and potassium chloride in water; benzene, isopropylbenzene, and phenol in cyclohexane. The systems isopropylbenzene and benzene each in cyclohexane and potassium chloride in water proved to be slightly adsorbing systems, whereas the benzaldehyde and phenol each in water were highly adsorbing systems. The rate of diffusion of the slightly adsorbing solutes was interpreted by assuming that the intraparticle diffusion was due to pore volume diffusion. The results indicated that the tortuosity factor for activated carbon is 3.5. The effective pore volume diffusivity and the tortuosity factor were not affected by the concentration of the solute, solute molecular size and the particle diameter. The external mass transfer resistance was negligible when pore volume diffusion was the controlling intraparticle diffusion mechanism.     

Theory of chromatography of complex cyclic polymers: eight-shaped and daisy-like macromolecules

A theory of chromatography of eight-shaped, trefoil-shaped and daisy-like polymers is developed. For a model of an ideal chain in a slit-like pore exact equations and a number of approximate formulae for the distribution coefficient K of these polymers are derived. All modes of chromatography of complex macrocycles of arbitrary molar mass in both narrow and wide pores are covered by the theory. It is shown that complex macrocycles always elute after linear polymers and rings of the same contour length. The effective chromatographic radius of eight-shaped and daisy-like macromolecules, which determines retention in size-exclusion chromatography are calculated. The increase in the retention with molar mass is predicted for all types of macrocycles at the critical interaction condition. Non-monotonous molar mass dependences of K are found at pre-critical interaction. We simulate separation of complex cyclic polymers from linear and ring precursors, discuss possibilities to separate symmetric and asymmetric eights, and speculates on the use of chromatography for separating knotted and unknotted polymer rings. According to the theory, the chromatography under the critical and pre-critical interaction conditions is expected to be especially efficient in these and similar problems. Boundary conditions for the theory and its applicability to real systems are discussed.     

低阶煤制备活性焦及其吸附性能研究

为解决煤化工废水处理难题,提高活性焦吸附性能,以5种典型低阶煤为原料,通过回转炉炭化和活化工序制备活性焦,研究活化温度、活化蒸气量和活化时间对活性焦吸附性能的影响,分析了不同活性焦对废水的吸附能力。结果表明:以褐煤为原料制备活性焦时,最佳活化温度为800℃,活化时间为3 h,活化蒸气量为1050 g;长焰煤最佳活化温度为850℃,活化时间为4 h,活化蒸气量为1200 g。在最佳条件下,褐煤活性焦的吸附值为36.32 mg/g,比长焰煤活性焦吸附值高10%。5种原煤制备的活性焦的比表面积与吸附值没有明显相关性。活性焦的孔容积越大,吸附值越高,造成不同活性焦吸附值差别的主要孔径为2~5 nm和5~20 nm。     

Pyridine adsorption reveals high-coordinated cationic centres at the surface of microcrystalline ZnO

The adsorption of pyridine at 300 K on microcrystalline ZnO has been investigated by FTIR spectroscopy. Besides an interaction by H-bonding with surface OH groups, evidence is found for the Lewis coordination of pyridine onto coordinatively unsaturated surface Zn²⁺ centres possessing a regular tetrahedral coordination, as well as onto some other surface Zn²⁺ centres, only slightly uncoordinated. The creation at the surface of the ZnO of cationic centres with an anomalous coordination higher than 4 (quasi-octahedral) is thus postulated. No such high-coordinated Zn²⁺ centres seem to form to an appreciable extent when ZnO is dispersed (at least at up to a 3% weight level) at the surface of other microcrystalline oxides such as, for instance, TiO₂.     

表面印迹聚合物的制备与吸附性能

以L-色氨酸作为模板分子,丙烯酰胺为功能单体,N,N'-亚甲基双丙烯酰胺为交联剂,通过在聚甲基丙烯酸甲酯多孔基质球表面复合印迹层,制备了L-色氨酸表面印迹聚合物微球(SMIPs),探索了不同比表面积基质球及添加丙烯腈对SMIPs吸附性能的影响,结果表明基质球比表面积为432.0m~2/g时,SMIPs对L-色氨酸的吸附量较高;当n(AN):n(L-trp):3:1时,SMIPs的综合吸附性能较好.     

压块净水活性炭的孔结构与吸附特性

研究分析了利用太西无烟超低灰纯煤生产的压块净水活性炭的技术指标、孔结构特征及其吸附特性;该活性炭内部以两种孔径范围的微孔为主,BET表面积高达764.83 m2/g,在P/P0为0.30时最大比表面积为809.776 m2/g,最大孔容积为0.412 cm3/g,是一种灰分低、强度高、吸附性能优良的净水活性炭。     

Determination of porosity in pillared clays by N2 adsorption isotherms

N₂ adsorption isotherms of various pillared montmorillonites (PILCs) were analyzed for evaluation of their porosities. The quantitative data of the total and micropore volumes were calculated using the B.J.H. method and the t-plot, respectively. The volume of mesopores is the difference between the total volume and the micropore volume. The linear branch above the P/P ₀ of 0.5 should be used for the calculations of the micropore volume and external surface area.The evaluation of the specific surface area (SA) of the PILCs and influences of the porosity on the calculations were discussed in detail. An upper limit of the monolayer capacity of a porous solid is proposed, based on the adsorption on a nonporous solid. Due to the space restriction in the fine slit-like pores of the PILCs, the specific surface areas calculated with the B.E.T. equation using the adsorption data in a relative pressure region ranging from 0.01 to 0.1 are more accurate.The mean micropore widths of the PILCs, derived from the data of the multi-point B.E.T. SA and micropore volume consist reasonably with the pore widths obtained by XRD diffraction.The step-like curves of the t-plot in low-pressure region and of the logarithmic plot reveal presence of pores of various sizes in the pillared clays. The micropore size distribution can be derived by a new method using the N₂ adsorption data.     

沥青/树脂基活性炭的制备及其吸脱附性能研究

以高软化点煤沥青、热塑性酚醛树脂为原料,在机械混合条件下,制备出比表面积大、吸脱附时间短、机械强度高的沥青/树脂基活性炭。通过偏光显微镜(OM)、N2物理吸脱附、TEM及苯的静态吸脱附实验对不同复合比沥青/树脂基复合颗粒进行对比研究。实验结果表明:沥青基活性炭吸脱附时间短,酚醛树脂基活性炭的静态饱和吸附值大、机械强度高;而沥青/树脂基活性炭则兼具沥青基活性炭与酚醛树脂基活性炭的优点,在机械强度为6.5 N(CP/PF-50/50)、静态苯吸附值达到472 mg/g时,仅需60 min进行脱附。结构及性质变化的原因在于:两种前躯体分子结构的不同导致两者在高温煅烧过程中由于所受热应力的不同而产生一定程度的界面剥离,进而形成一定量的孔道结构。     

Study of H2O adsorption on sulfides surfaces and thermokinetic analysis

Adsorption of water on mineral surfaces was studied using density functional theory and microcalorimetry technique. The calculation results show that galena and molybdenite are hydrophobic, while pyrite and sphalerite is hydrophilic. Thermokinetic analysis shows that the heat of adsorption is in decreasing order of pyrite, sphalerite, galena and molybdenite, which is in good agreement with the calculation results. The adsorption kinetics parameters of hydrophobic galena and molybdenite surfaces are close, while those of hydrophilic pyrite and sphalerite surfaces are very different. The adsorption rate of water on the sphalerite surface is larger than that of water on the pyrite surface.     

Size exclusion and adsorption column chromatographic studies on functionality distribution of HTPB

Adsorption column chromatography and size exclusion chromatography have been used to determine the functionality distribution of hydroxyl terminated polybutadiene (HTPB), a modern solid propellant binder. The resin after conversion to 3,5-dinitrobenzoyl ester was separated into various fractions on a silica column. The fractions were analysed using a dual detector (UV and differential refractive index) analytical gel permeation chromatograph. The functionality of each fraction calculated from the chromatogram showed a continuous increase with increase in the molecular weight. The adsorption chromatography method is unable to fractionate the polymer into fractions with specific functionality. All the fractions have molecules ranging from monofunctional to multifunctional ones and therefore the apportionment method followed in the conventional adsorption chromatography method yields conflicting results.     

吸附树脂极性的高效液相色谱法测定及表征

建立了测定及表征吸附树脂极性的高效液相色谱法。DA-201极性树脂、AB-8弱极性树脂和D-101非极性树脂分别填充高效液相色谱柱,以去离子水为流动相,葡聚糖为示踪剂,流速1.0 mL/min,柱温30℃,测定树脂的极性。结果表明,正丁醇、乙醇均可作为单一探针分子,流出顺序可定性表征吸附树脂极性:DA-201极性树脂AB-8弱极性树脂D-101非极性树脂;采用乙醇/甲醇作为探针分子组,通过相对极性法计算,得到3种吸附树脂的定量极性值:DA-201极性树脂极性值100,AB-8弱极性树脂极性值18,D-101非极性树脂极性值0,相对标准偏差(RSD)均小于1.50%。方法稳定可靠,可以有效表达吸附树脂的极性。