The effect of the dehydration conditions of chitosan-based polymeric adsorbents on the adsorption of nickel cations

The structure and adsorption properties (with respect to water vapor and nickel cations) of chitosan samples dehydrated by either lyophilization after precipitation with NaOH or Na₂CO₃ or drying in air are investigated. IR spectroscopy and X-ray diffraction data testify that the lyophilization causes both changes in the conformation of chitosan macromolecules and a substantial rise in the crystallinity of the polymer to compare with the air dried one. Chitosan structure ordering resultant from the lyophilization noticeably increases its sorption ability with respect to both water vapor and nickel cations. For example, the sorption capacity of the lyophilized chitosan with respect to nickel cations is as high as 4.5 mmol/g and, thus, is threefold higher than that of air-dried chitosan. The comparative analysis of water adsorption isotherms in the region of low degrees of filling indicates that chitosan structure ordering resultant from the lyophilization changes the number and the energy of primary adsorption sites.     

Correlations between the adsorption and structural properties of SV-1 phytoadsorbent and its main components

The structural and morphological characteristics, as well as the adsorption properties with respect to benzene, methanol, and water vapors, were studied for the main components of SV-1 phytoadsorbent (lignin, cellulose, and melanin). Lignin and cellulose determine the capillary-porous structure of the material as a whole. The adsorption properties of the adsorbent are determined by the porous structure of its main constituents and by differences in the sensitivity of the adsorptives to the chemistry of the surface of the materials under study.     

Fluorous metal-organic frameworks with superior adsorption and hydrophobic properties toward oil spill cleanup and hydrocarbon storage

We demonstrate that fluorous metal-organic frameworks (FMOFs) are highly hydrophobic porous materials with a high capacity and affinity to C(6)-C(8) hydrocarbons of oil components. FMOF-1 exhibits reversible adsorption with a high capacity for n-hexane, cyclohexane, benzene, toluene, and p-xylene, with no detectable water adsorption even at near 100% relative humidity, drastically outperforming activated carbon and zeolite porous materials. FMOF-2, obtained from annealing FMOF-1, shows enlarged cages and channels with double toluene adsorption vs FMOF-1 based on crystal structures. The results suggest great promise for FMOFs in applications such as removal of organic pollutants from oil spills or ambient humid air, hydrocarbon storage and transportation, water purification, etc. under practical working conditions.     

Adsorption of benzene on dispersed polycrystalline fullerites

The sorption properties of dispersed polycrystalline C₆₀ and C_Σ (a mixture of fullerenes) fullerites were studied. The isotherms of adsorption of benzene on these sorbents were measured. Some data on the sorption of ethanol from gas and liquid phases, KOH from solutions in ethanol, and naphthalene in the solid and molten states and from its solutions in ethanol were obtained. The sorbability of the C_Σ samples with respect to benzene is as high as that of commercial activated carbons, while C₆₀ fullerites were found to be less efficient sorbents. It was concluded that dispersed polycrystalline fullerites are porous sorbents. Through porosity arises due to the presence of defects in the crystal structure; i.e., the less perfect the lattice, the higher its adsorption capacity.     

Effects of solution chemistry on the adsorption of ibuprofen and triclosan onto carbon nanotubes

Single-walled carbon nanotubes (SWCNTs), multiwalled carbon nanotubes (MWCNTs), and oxidized MWCNTs (O-MWCNTs) were studied for the adsorption of ibuprofen (IBU) and triclosan (TCS) as representative types of pharmaceutical and personal care products (PPCPs) under different chemical solution conditions. A good fitting of sorption isotherms was obtained using a Polanyi-Manes model (PMM). IBU and TCS sorption was stronger for SWCNTs than for MWCNTs due to higher specific surface area. The high oxygen content of O-MWCNT further depressed PPCP sorption. The sorption capacity of PPCPs was found to be pH-dependent, and more adsorption was observed at pHs below their pK(a) values. Ionic strength was also found to substantially affect TCS adsorption, with higher adsorption capacity observed for TCS at lower ionic strength. In the presence of a reference aquatic fulvic acid (FA), sorption of IBU and TCS was reduced due to the competitive sorption of FA on carbon nanotubes (CNTs). Sorption isotherm results with SWCNTs, MWCNTs and O-MWCNTs confirmed that the surface chemistry of CNTs, the chemical properties of PPCPs, and aqueous solution chemistry (pH, ionic strength, fulvic acid) all play an important role in PPCP adsorption onto CNTs.     

CeY分子筛中有效脱硫物种活性位的构建及其吸附机理研究

以不同焙烧温度和Ce负载量的CeY分子筛为研究对象,运用XRD及N_2吸附表征其织构性质;运用吡啶吸附红外光谱法剖析了分子筛中活性位的化学属性;采用固定床评价其对噻吩模拟油的吸附脱硫性能及芳烃和烯烃对噻吩脱除的影响;并结合红外光谱和GC-SCD技术分析了其脱硫机制。结果表明,CeY样品经150℃焙烧后,其超笼中具备高含量的B酸和Ce羟基化物种活性位,两者协同增强了噻吩低聚反应能力,进而提高了其吸附穿透硫容量(18.45 mg (S)/g);而提升焙烧温度和Ce负载量会严重降低其有效活性位的数量,削弱了噻吩低聚反应能力,其吸附穿透硫容量显著减小(4.03 mg (S)/g)。当加入烯烃和芳烃后,CeY-12.3-150吸附剂对含低浓度(质量分数)1-己烯(1.0%)和苯(0.1%)的噻吩模拟油依旧保持较高吸附穿透硫容量;但随两者含量的持续增加,其硫容量急剧下降。其主要分别归因于噻吩烷基化反应的发生及“S-H”键的作用模式。     

Isotherm analysis of phenol adsorption on polymeric adsorbents from nonaqueous solution

Macroporous poly(methyl methacrylate-co-divinylbenzene) (PMMA), interpenetrating polymer adsorbent based on poly(styrene-co-divinylbenzene) (PS) and poly(methyl methacrylate-co-divinylbenzene) (PMMA/PS), and macroporous cross-linked poly(N-p-vinylbenzyl acetylamide) (PVBA) were prepared for the adsorption of phenol from cyclohexane. The sorption isotherms of phenol on the three polymeric adsorbents were measured and fitted to Langmuir and Freundlich isotherms. It is shown that the Langmuir isotherm, which is based on a homogeneous surface model, is unsuitable to describe the sorption of phenol on the adsorbents from nonaqueous solution and the Freundlich equation fits the tested three adsorption systems well. The isosteric enthalpy was quantitatively correlated with the fractional loading for the sorption of phenol onto the three polymeric adsorbents. The surface energetic heterogeneity patterns of the adsorbents were described with functions of isosteric enthalpy. The results showed that the tested three polymeric adsorbents exhibited different surface energetic heterogeneity patterns. The initial isosteric enthalpy of phenol sorption on polymeric adsorbent has to do with the surface chemical composition and is free from the pore structure of the polymeric adsorbent matrix. Forming hydrogen bonds between phenol molecules and adsorbent is the main driving force of phenol sorption onto PVBA and PMMA adsorbent from nonaqueous solution. When phenol is adsorbed on PMMA/PS, pi-pi interaction resulting from the stacking of the benzene rings of the adsorbed phenol molecules and the pendant benzene ring of adsorbent is involved.     

Modelling adsorption of a water molecule into various pore structures of silica gel

Silica gel is widely used in commercial applications as a water adsorbent due to its properties including hydrothermally stable, high water sorption capacity, low regeneration temperature, low cost and wide range of pore diameters. Since the water sorption capacity of silica gel strongly depends on the pore size and structure, which can be controlled during synthesis, this paper study the effect of pore shapes and dimensions of silica gel upon the adsorption of a water molecule aiming at maximising the water sorption capacity. In particular, we consider three types of pore structures, namely cylindrical, square prismatic and conical pores. On using the Lennard-Jones potential and a continuum approximation, we find that the minimum radii for a water molecule to be accepted into cylindrical, square prismatic and conical pores are 4.009, 3.7898 and 4.4575 Å, respectively. For cylindrical and square prismatic pores, the critical radii which maximise the adsorption energy are 4.5189 and 4.1903 Å, respectively. Knowledge of these critical pore sizes may be useful for the manufacturing process of silica gel that will maximise the water sorption capacity.     

Effect of solvent on the adsorption of benzene vapors by dicyclohexane-18-crown-6 thin films

The solvent effect on the stability of the zero signal of resonators with a dicyclohexane-18-crown-6 film was studied. The adsorption capacity and sensitivity of the film coatings to benzene vapors was estimated. The performance characteristics of the microweighing of benzene vapors were calculated. A model was proposed for benzene adsorption from the gas phase on thin films of crown ether.     

Selective gas sorption in a [2+3] 'propeller' cage crystal

A [2+3] organic cage compound based on the condensation reaction of 1,3,5-tri(4-formylphenyl)benzene with 1,5-pentanediamine was synthesized. The resulting porous molecular crystal demonstrates selective adsorption of hydrogen and carbon dioxide over nitrogen. As for porous polymer membranes, a trade-off between sorption capacity and selectivity is observed for materials in this class.     

Liquid-phase adsorption on metal-organic frameworks

This work is focusing on the potential application of metal-organic frameworks as porous materials in heterogeneous catalysis where the substrate is in solution. The understanding of such a liquid-phase heterogeneous catalytic process requires adsorption equilibrium data in solution. For this purpose several metal-organic frameworks were synthesized as reference materials and tested as adsorbents for the adsorption of substrate molecules such as styrene or ethylcinnamate from the liquid phase. The adsorption capacity strongly depends on the polarity of the substrate with respect to the solvent. In several instances solvent and polarity effects are heavily superimposed on the pore size effects. Adsorption isotherms, rates and hydrogenation of the substrates are reported and discussed.     

Isotherms of adsorption of aromatic compounds on cellulose from heptane-isopropanol solutions

The isotherms of adsorption of benzene, anisole, benzyl alcohol, and benzaldehyde on the surface of microspherical mesoporous crosslinked cellulose were calculated from the chromatographic peaks of these compounds with consideration given to the longitudinal smearing of the analyte zone under the action of adsorption forces. The solvents were n-heptane-isopropanol mixtures containing various amounts of isopropanol (up to 2 vol %). The adsorption isotherms were described using equations of the displacement adsorption theory. The mechanism of the sorption of aromatic compounds and the physical meaning of the constants entering into the adsorption isotherm equation were discussed.     

Effect of pH, ionic strength, and temperature on the phosphate adsorption onto lanthanum-doped activated carbon fiber

Phosphate removal from polluted water is crucial to preventing eutrophication. Herein, we present the investigation on phosphate adsorption in aqueous solutions by using lanthanum-doped activated carbon fiber (ACF-La). Various batch sorption conditions, e.g., pH, ionic strength, and temperature were tested, and the adsorption mechanisms were discussed. The sorption capacity of ACF-La was higher in acidic solutions than that in basic ones, suggesting that the Lewis acid-base interaction gradually dominated the adsorption process with the increase in pH values. The degree of phosphate removal decreased with the enhancement of the ionic strength of the solution, meaning that the adsorption of phosphate on ACF-La was strongly dependent on ionic strength. Employing the pseudo first- and second-order, and intra-particle diffusion models to evaluate the adsorption kinetics of phosphate onto ACF-La indicated that the second-order model best fits the experimental data. The presence of chloride ion in solutions increased the effect of intra-particle diffusion on the adsorption of phosphate onto ACF-La but reduced the overall rate of the adsorption. The thermodynamic parameters were determined which revealed the feasibility, spontaneity, and endothermic nature of adsorption.     

Mesoporous Molecular Sieves Modified with Carbonaceous Deposits

There were investigated aluminosilicate MCM-41 samples in the as-prepared form and those modified by the deposition of carbonaceous compounds during conversion of cyclohexene for 12 h. The amount of the deposits decreased with the rising reaction temperature and increased with the Al content of the samples. The cyclohexene conversion followed mainly two mechanisms: cyclohexene skeletal isomerization and hydrogen transfer. The products with 6 carbon atoms in a molecule prevailed in all cases. The process of conversion, proceeding on the Brønsted acid sites, resulted in formation of both coke deposits and volatile products. The creation of coke caused a decrease in the effective concentration of both the Brønsted and the Lewis acid sites. Thermodesorption of pyridine showed that (i) the concentration of these sites before and after the conversion differed only slightly and (ii) the acidic strength of the Brønsted sites was practically independent of their concentration and the sample Si/Al ratio. The chemical composition of the deposits was insignificantly affected by the Al content of the materials and depended mostly on the temperature and duration of the reaction. At relatively low temperatures, both aliphatic and aromatic compounds were formed, being rather weakly bound to the surface of the material. After a longer (55 h) reaction period, some deposits appeared that were strongly bound to the surface. Isotherms of adsorption of water, benzene, and nitrogen were determined, from which a mechanism of this process was derived. It included most probably multilayer adsorption at lower relative pressures, followed by capillary condensation. The sorption capacities of the uncoked samples for benzene and nitrogen were relatively high and independent of the sample Al content. In the case of water, however, an observed reduction in the sorption capacity with the increasing Al content suggested that clusters of the adsorbed molecules formed around the Al centers and caused partial clogging of the material pores. The deposited coke strongly decreased both the surface area and the sorption capacity of the materials.     

Lead adsorption onto "red soils" as function of environmental conditions

The adsorption characteristics of the "Red Soil" with respect to lead were studied as function of different experimental conditions. Lead adsorption was investigated as function of the complexing capacity of the liquid phase (background electrolyte NaClO4, NaCl, CH3COONa e EDTA), pH (experimental range 4-7) and ionic strength (experimental range 0.001-0.35 M), by determining the adsorption isotherms at the different conditions. Experimental results allowed to identify the presence of different sorption sites, acting on lead removal through different mechanisms (ion exchange and surface complexation). These sorption sites are differently affected by changing the experimental conditions. Adsorption representation in terms of free metal was not able to describe the experimental behaviour, especially when different charged species can be formed and might be sorbed at the surface with different affinities. Particular attention was given to the optimisation of the experimental system based on the flow-through reactor set-up, in order to carry out adsorption tests more representative of the field situation.     

Ultrahigh CO2 adsorption capacity on carbon molecular sieves at room temperature

Although metal-organic framework (MOF) materials have been postulated as superior to any other sorbent for CO(2) adsorption at room temperature, here we prove that the appropriate selection of the raw material and the synthesis conditions allows the preparation of carbon molecular sieves (CMSs) with adsorption capacity, on a volumetric basis, highly exceeding those reported in the literature for MOFs. Furthermore, the excellent sorption properties of CMSs over the whole pressure range (up to 50 bar) are fully reversible after different adsorption/desorption cycles.     

Comments on surface structure analysis by water and nitrogen adsorption

Specific surface area and pore size distribution are determined usually from adsorption isotherms at low temperatures using nitrogen or noble gases. These are not absolute parameters and the measuring methods are fraught with serious difficulties. General problems of sorption measurements and recent developments are discussed. To obtain information for practical purposes these measurements need to be supplemented by investigations of the sorbate/sorbent system used in practice. Results of the measurement of nitrogen and water vapour adsorption on different materials are compared. This revised version was published online in July 2006 with corrections to the Cover Date.     

Enhanced adsorption of arsenate on the aminated fibers: sorption behavior and uptake mechanism

Novel aminated polyacrylonitrile fibers (APANFs) were prepared through the reaction of polyacrylonitrile fibers (PANFs) with four multinitrogen-containing aminating reagents, and the best adsorbent was obtained after the optimization of preparation experiments. The APANFs were effective for arsenate removal from aqueous solution, and the sorption behaviors including kinetics, isotherms, effect of pH, and competitive anions were investigated. Experimental results show that the equilibrium of arsenate sorption on the fibers was achieved within 1 h, and Langmuir equation described the sorption isotherms well with a high sorption capacity of 256.1 mg/g obtained. The thermodynamic parameters calculated show that the sorption was spontaneous and exothermic under the condition applied. The zero point of zeta potential of the APANFs was at about pH = 8.2, in contrast with that of the PANFs at pH = 3.6. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) for the APANFs before and after arsenate adsorption revealed that the amine groups on the fiber surface played an important role in the removal of arsenate from water, attributed to the electrostatic interaction between the positive protonated amine groups and negative arsenate ions.     

The adsorption of phosphate from an aquatic environment using metal-loaded orange waste

Phosphate removal from an aquatic environment was investigated using La(III)-, Ce(III)- and Fe(III)-loaded orange waste. The adsorption isotherm, the kinetics of adsorption and the effect of pH on the removal of phosphate have been examined. The % removal of phosphate using La(III)- and Ce(III)-loaded orange waste gel increases with increasing pH within the range of 5-7 but decreases when the pH is increased beyond this range. The equilibrium sorption was observed to be in accordance with Langmuir type adsorption and the maximum adsorption capacity was evaluated as 13.94 mg P/g of dry gel for all the three types of gels. Kinetic studies revealed that 15 h is enough to reach equilibrium in batch experiments. Fixed bed sorption experiments confirmed the continuous phosphate adsorption and elution capability of such simply modified gels. Due to their low cost, availability and significantly high adsorption capability, metal-loaded SOW gels can be effectively employed for the removal of phosphate from water.     

Investigation of the factors affecting organic cation adsorption on some silicate minerals

In this study, the effects of some factors on the adsorption of a basic dye (methylene blue) on bentonite and sepiolite samples were studied. These factors are cation (Na(+) and Ca(2+)) saturation of the samples and pH and ionic strength of the dye solution. The adsorption data were found to conform to the Langmuir equation within the concentration range studied and Langmuir constants were determined for each of the samples. The adsorption capacities of the samples were found to increase with cation saturation. Changes in the pH of the dye solution had no significant influence on the adsorption capacity and adsorption capacities were found to decrease with increasing ionic strength. The maximum sorption capacity of methylene blue exceeded the cation exchange capacity of bentonite and sepiolite.