Sorption and Diffusion in Molecular Sieve Zeolites

Recent information concerning the kinetics and equilibria of sorption of various classes of molecule in four representative types of molecular sieve (4A/5A, 13X, natural erionite and H-chabazite) is reviewed. The general relationships between the crystal structure of the sieve, the molecular properties of the adsorbate (particularly the critical diameter and polar nature of the molecule) and the sorption/diffusion behaviour are emphasized.     

同位素示踪法测定稀土在土壤中的吸附,解吸和扩散

对９种不同性质土壤测定结果表明，ＲＥ的吸附或解吸均与Ｌａｎｇｍｕｉｒ方程有极好的拟合性。土壤ＲＥ吸附容量在１．５－１５ｍｇ／ｇ之间，它与土壤中伊利石的相对含量呈明显正相关土壤ＲＥ解吸量与吸附量之间呈显著指数曲线关系，曲线转折点的ＲＥ吸附量称为土壤特征吸附量，以它表征ＲＥ在土壤中运移难易，比土壤吸附容量表征更有意义。     

气相存在下CO在Pd上非线性脱附动力学的研究

利用同位素技术测定了预吸附在Pd表面上的CO在单一及混合同位素气氛下的脱附动力学．实验发现CO的脱附动力学是非线性的，在饱和表面上为一级加二级．在易位化学吸附模型和协同交换机理的基础上，对表面吸附物种的动态结构进行了深入分析讨论，并推导出了非线性脱附动力学的解析表达式．     

自然水体中3种固相物质吸附有机氯农药的动力学特征

研究了自然水体中生物膜、 悬浮颗粒物和表层沉积物3种典型固相物质对有机氯农药的吸附动力学特征. 研究结果表明, 有机氯农药在3种固相物质上的吸附动力学过程可分为快吸附阶段和慢吸附阶段. 准二级动力学模型较好地描述了三者对有机氯农药的吸附动力学过程. 吸附平衡时, 3种固相物质对有机氯农药吸附量的大小与它们的有机质含量顺序一致, 即, 生物膜>悬浮颗粒物>表层沉积物; 而在吸附初期阶段, 有机质含量最低的表层沉积物对有机氯农药的吸附速率最快, 吸附量的波动变化幅度最大, 其次为悬浮颗粒物和生物膜.     

Mechanism of Cations Suppressing Proton Diffusion Kinetics for Electrocatalysis

Proton transfer is crucial for electrocatalysis. Accumulating cations at electrochemical interfaces can alter the proton transfer rate and then tune electrocatalytic performance. However, the mechanism for regulating proton transfer remains ambiguous. Here, we quantify the cation effect on proton diffusion in solution by hydrogen evolution on microelectrodes, revealing the rate can be suppressed by more than 10 times. Different from the prevalent opinions that proton transport is slowed down by modified electric field, we found water structure imposes a more evident effect on kinetics. FTIR test and path integral molecular dynamics simulation indicate that proton prefers to wander within the hydration shell of cations rather than to hop rapidly along water wires. Low connectivity of water networks disrupted by cations corrupts the fast-moving path in bulk water. This study highlights the promising way for regulating proton kinetics via a modified water structure.     

13X分子筛上硫化促进剂的动态行为研究

采用TPD技术对13X分子筛的表面酸性及3种硫化促进剂在其表面上的动态行为进行了研究。结果表明,13X分子筛具有吸附能量高低不等的多种表面酸性吸附部位。对于吸附型缓释交联剂,有效的表面吸附部位为弱化学吸附位.表观脱附动力学计算结果表明,不同的硫化促进剂从13X分子筛表面有效部位脱出时,其动力学特征亦不同,但均与晶内扩散有关,表观脱附活化能(kJ/mol)分别为51.5(二乙胺)、68.6(环己胺)和78.3(乙二胺)。     

Effects of pH and Concentration on Cs Ions Sorption and Diffusion in Crushed Granite by Using Batch and Modified Capillary Method

A comprehensive evaluation of Cs ions sorption to and diffusion in crushed granite was conducted in this study. The sorption capacity of crushed granite suggested by the Langmuir model was 5.48 × 10^?6 mol‐Cs/g‐granite. The distribution coefficient (Kd) was around 7.5 mL/g and pH independent. By using an in‐diffusion method with a modified capillary column, some diffusion relevant parameters of Cs ions in crushed granite were derived. The apparent diffusion coefficient (Da) seemed unaffected by Cs concentration (1.15 × 10^?10 to 2.82 × 10^?10 m²/s, at 10^?7 and 10^?3 M, respectively). The determined effective diffusion coefficients (De) were located in the window from 8.59 × 10^?10 (10^?7 M) to 1.69 × 10^?9 (10^?3 M) m²/s. Under various pH environments, pH independent Da (9.0 × 10^?9 m²/s) and De (1.0 × 10^?9 m²/s) values were observed. Under current systems, consistently higher De than Da implied the diffusion of Cs ions was governed by surface diffusion phenomenon. Whereas the pH insensitive feature indicated the Cs sorption to crushed granite was mainly through ion‐exchange reaction. Moreover, further SEM/EDS mapping clearly showed the adsorbed Cs ions were highly concentrated on the fracture surface of biotite.     

Impact of Mineralizing Agents on Aluminum Distribution and Acidity of ZSM-5 Zeolites

Intensive research on improving the catalytic properties of zeolites is focused on modulating their acidity and the distribution of associated Al sites. Herein, by studying a series of ZSM-5 zeolites over a broad range of Al content, we demonstrate how the nature of the mineralizing agent (F⁻ or OH⁻) used in hydrothermal syntheses directly impacts Al sites distribution. The proportions of Al sites, probed by ²⁷Al NMR, depend on the Si/Al ratio for F⁻, but remain identical for OH⁻ (from Si/Al=30 to 760). This leads to contrasting variations in weak and strong acidities. Such opposite effect of mineralizers is explained by the spatial location of negative charges and the resulting balance between short- and long-range electrostatic interactions. This understanding paves the way for additional and simple opportunities to control zeolites’ acidity.     

Sorption of dissolved galactoglucomannans and galactomannans to bleached kraft pulp

Sorption of mannans onto bleached kraft pulp (BKP) was investigated withreference to other interactions of mannans in mechanical pulping andpapermaking. O-Acetyl galactoglucomannans (GGM) isolated from thermomechanicalpulp (TMP), as well as enzymatically modified guar gum galactomannans (GM) wereused in the study. The results showed that deacetylation of TMP GGMs, alsooccurring during peroxide bleaching of TMP, dramatically increased thesorption.A higher sorption was also achieved after salt addition, while temperature hadno effect. Sorption of guar gum GMs onto BKP fibres was, on the other hand,quite unaffected by external conditions such as temperature, pH and saltaddition. The degree to which the pulp was beaten did not notablyinfluence the sorption either – only unbeaten pulp gave a clearly lower mannansorption. A lower number of galactose side groups, however, strongly affectedsorption – the lower the number of side groups, the higher the sorption.The molar mass did not seem to affect the rate of sorption to any higher extentat ambient temperature. At higher temperatures the rate of sorption of smallerGM polymers was, nevertheless, slightly increased. Low-molar-mass GMs alsosorbed at a higher rate onto unbeaten pulp compared to high-molar-mass mannans.GM sorption appeared to be virtually irreversible.     

Sorption and transport behavior of gasoline components in polyethylene glycol membranes

Desulphurization mechanism of polyethylene glycol (PEG) membranes has been investigated by the study of solubility and diffusion behavior of typical gasoline components through PEG membranes with various crosslinking degrees. The sorption, diffusion and permeation coefficients were calculated by the systematic studies of dynamic sorption curves of gasoline components such as thiophene, n-heptane, cyclohexane, cyclohexene and toluene in PEG membranes. Furthermore, the temperature dependence of diffusion and solubility coefficients and the influence of crosslinking degree on sorption and diffusion behaviors were conducted to elucidate the mass-transfer mechanism. According to the discussions on dynamic sorption curves, transport mode, activation energy and thermodynamic parameters, thiophene species were the preferential permeation components. Crosslinking is an effective modification way to improve the overall performance of PEG membranes applied in gasoline desulphurization. The pervaporation (PV) and gas chromatography (GC) experiments results corresponded to the conclusions. All these investigations will provide helpful suggestions for the newly emerged membrane desulphurization technology and complex organic mixture separation by pervaporation.     

等级孔分子筛的可控合成、扩散研究及催化应用

等级孔分子筛是一类具有两种或多种以特定形式排布的孔结构的分子筛材料. 多层等级的孔结构使得分子筛孔道内的分子扩散得到显著改善, 进而提升了其在吸附和非均相催化等领域的应用性能. 等级孔分子筛的制备策略通常有两种, 即“自上而下”后处理法(如对母样分子筛进行脱铝、 脱硅产生介孔)和“自下而上”合成法(如软模板、 硬模板法). 本文主要对近20年来等级孔分子筛的合成方法进行了梳理, 并着重介绍了具有较高应用潜力的“自上而下”制备法. 鉴于合成等级孔分子筛的主要目的是提高分子的晶内扩散, 对近年来客体分子在等级孔分子筛内扩散的实验研究也进行了简要综述. 此外, 本文还综合评述了等级孔分子筛与传统分子筛在催化应用中的对比, 以展示前者在提升催化性能方面(如活性、 选择性等)的独特优势.     

Dissolution Behavior and Varied Mesoporosity of Zeolites by NH4F Etching

The mesopores formation in zeolite crystals has long been considered to occur through the stochastic hydrolysis and removal of framework atoms. Here, we investigate the NH₄F etching of representative small, medium, and large pore zeolites and show that the zeolite dissolution behavior, therefore the mesopore formation probability, is dominated by zeolite architecture at both nano- and sub-nano scales. At the nano-scale, the hidden mosaics of zeolite structure predetermine the spatio-temporal dissolution of the framework, hence the size, shape, location, and orientation of the mesopores. At the sub-nano scale, the intrinsic micropore size and connectivity jointly determine the diffusivity of reactant and dissolved products. As a result, the dissolution propensity varies from removing small framework fragments to consuming nanodomains and up to full digestion of the outmost part of zeolite crystals. The new knowledge will lead to new understanding of zeolite dissolution behavior and new adapted strategies for tailoring hierarchical zeolites.     

Equilibrium,kinetics and thermodynamics studies of Cd sorption onto a dithizone-impregnated Amberchrom CG-300m polymer resin

Amberchrom CG-300m, a styrene acrylic ester polymer resin, was studied for the first time as sorbent for metal ion sorption in a solid-phase extraction system. The polymer sorbent was modified via impregnation with dithizone to improve its efficiency. Efficiency of the modified sorbent improved by more than 47%. The loading capacity of the resin is 3.2 mg dithizone per gram of sorbent. The mechanisms of Cd(II) sorption from aqueous solutions are presented. Capacity of the modified resin for Cd(II) was investigated in batch experiments as a function of pH, initial metal ion concentration, temperature and time. Maximum capacity of 0.551 mg Cd(II) per gram of sorbent was achieved. The dimensionless separation factor, 0 < R_L < 1, associated with the Langmuir isotherm (at T = 294 K) signifies sorption of Cd(II) was favorable, as do negative values of free energy of sorption (ΔG) at temperatures exceeding 293 K. Sorption was endothermic (ΔH > 0) while ΔS > 0 reflects the affinity of the sorbent towards Cd(II). The pseudo-second order model proved to be the best fit model for Cd(II) sorption kinetics data. Particle-diffusion models suggest sorption follows film as well as pore diffusion mechanisms.     

Sorption and diffusion of ethanol vapor in polybutadiene/acrylonitrile, polybutadiene/styrene and polybutadiene based polyurethanes

The sorption and diffusion behavior of ethanol vapor in series of polyolefine based polyurethanes (PU) made from hydroxyl-terminated polybutadiene/acrylonitrile (HTBN), hydroxyl-terminated polybutadiene/styrene (HTBS) and hydroxyl-terminated polybutadiene (HTPB) were investigated by using the quartz-spring, DSC, FTIR and AFM. The equilibrium absorption reduced with increasing content of hard segments for all the three types of PUs. The values of the maximum absorption were in the order of HTBN > HTBS > HTPB based PU and related to their composition. The non-Fickian diffusion was confirmed and the sorption was discovered mainly in the hard segments. The HTBN based PU revealed different sorption and diffusion behavior from the other two, which was resulted from its hydrogen bonding not only between ethanol and hard segments but also soft segments. The morphologies of PUs before and after ethanol absorption were also compared. The HTBN based PU showed the most evident phase re-congregation after ethanol absorption.     

Mesopores in USY Zeolites II

Microporous zeolites Na‐Y and K‐Y were converted into the NaNH₄‐Y and KNH₄‐Y modifications by ion exchange being active in dealumination. Removal of framework aluminium and silicon is accompanied by formation of secondary mesopores. Internal mesopores are formed in the centre of zeolite crystals and external pores at their surface. Formation of mesopores changes the sorption behaviour.Residual alkali metal cations as Na⁺ or K⁺ stabilise, however, the framework ≡Si‐O‐Al≡ bonds. Because of inhomogeneous distribution of sodium ions, in NaNH₄‐Y less internal but more external mesopores are formed. Potassium ions of KNH₄‐Y are more homogeneous distributed over the framework why a more balanced formation of secondary pores takes place.     

Sorption Kinetics and Intracrystalline Diffusion of Methanol in Ferrierite: An Example of Disguised Kinetics

Sorption kinetics of methanol in large crystals of ferrierite have been studied in detail by interference microscopy (IFM) and infra-red microscopy (IRM). The IFM measurements yield the transient concentration profiles, thus providing a direct measurement of both the surface resistance to mass transfer and the internal diffusion resistance. It is shown that, for this system, the uptake rate is controlled by the combined effects of surface resistance and diffusion through the 8-ring channels (in the y-direction). Transport through the 10-ring channels (in the z-direction) appears to be blocked by surface resistance. Although the overall uptake curves conform well to the “root t law” the diffusivity values derived from the uptake curves vary widely depending on the assumed direction of diffusion. Even if the correct direction of diffusion is assumed, the diffusivity values derived from the uptake curves are seriously in error as a result of the intrusion of surface resistance. The existence of transport resistances at the crystal surface is clearly apparent from the transient concentration profiles but is not obvious from the uptake curves.     

Mesopores in USY Zeolites

Zeolites of type NaY synthesised by use of seed‐solution and zeolite X‐seeds to initialise the crystallisation were compared. A different homogeneity of the internal framework structure related to the Si/Al ratio was expected. Thus, the formation of closed bulk mesopores should be influenced during treatment of NH₄NaY modification for 7 hours at 450 °C and 600 °C, respectively, in the water steam of 1 bar. Occurrence of different mesopores was actually observed in obtained ultra‐stable USY zeolites using nitrogen adsorption. Whereas USY prepared by use of seed‐solution contains only open mesopores at the crystal surface, the X‐seed synthesised material contains open and closed mesopores at the surface and in the nuclei of samples, respectively.     

Deposition of Phosphate Nanoparticles onto Textile Fabrics via Sol-gel Method and Their Kinetics Desorption Studies

In this paper, phosphate nanoparticles were coated on cotton(CO) and polyester(PES) textile surfaces by sol-gel method using tetraethylorthosilicate(TEOS) and chloropropyltriethoxysilane(CPTS) as silica precursors. The deposited nanoparticles were observed with scanning electronic microscopy energy-dispersive X-ray spectroscopy (SEM-EDX). The release kinetics of phosphorus(P) from these textiles into the aqueous medium(Aq), acid(Ac), and basic(Ba) artificial sweats were then studied. The released amount of phosphorus was evaluated by the inductively coupled plasma(ICP) according to ISO NF EN 16711-2 procedure. The results revealed that the release of P into the aqueous medium is lower than in the artificial sweat. The kinetics data[the phosphorus desorption amount(mg/g) as a function of time] were modeled according to five models:the first order, the second order, the third order, simple Elovich and parabolic diffusion. The suitable model was chosen based on the coefficient of determination(R²) and the calculation of the sum of the absolute errors(EABS), which describes the error between the theoretical and experimental values. SEM observations were also carried out on the fabrics after desorption in order to show the impact of desorption on their morphology. Furthermore, the impact of P release on the tensile strength of CO and PES fabrics was investigated using a uniaxial tensile test. The thermal stability of all samples before and after desorption was assessed by thermogravimetric analysis(ATG).