Estimating the pore size distribution of activated carbons from adsorption data of different adsorbates by various methods

Experimental adsorption isotherms of four adsorbates (N2, Ar, C6H6, and CCl4) as well as adsorption enthalpy (C6H6 and CCl4) measured on two strictly microporous carbons are used to evaluate the porosity of adsorbents (i.e., pore size distributions (PSDs) and average pore diameter (Lav)). The influence of the diameter of adsorbates (dA) as well as of the temperature (T) is analyzed in order to explain the differences or similarities between the above-mentioned quantities for all systems. Proposed previously, the general relationships between the parameters of the Dubinin-Astakhov (DA) isotherm equation (the characteristic energy of adsorption (E0) and the exponent of this equation (n)) and the average slit-width of carbon micropores are investigated. Moreover, the thermodynamic verification of the Horvath-Kawazoe (HK) theory and the ND model is presented based on data of the adsorption and enthalpy of adsorption of benzene and carbon tetrachloride on two carbons. Finally, the pore diameters calculated from calorimetry data using the Everett and Powl method and those calculated applying the recently developed equations are compared. In our opinion the change of apparent PSD should be monitored by performing a series of isotherm measurements from high (equal and higher than room temperature) to low temperatures (ca. 77.5 K) as was presented in the current study. Moreover, the analysis of the experimental data leads to the conclusion that the entropy of C6H6 and CCl4 can approach to the values characteristic of quasi-solid (a partially ordered structure). Therefore, this behavior of the adsorbate should be taken into consideration in the theoretical assumptions of model and its thermodynamic verification

Effect of the Carbon Surface Layer Chemistry on Benzene Adsorption from the Vapor Phase and from Dilute Aqueous Solutions

Wepresent a complex study of benzene adsorption on chemically modified commercial activated carbons. The porosity of studied carbons is almost the same, whereas the chemical composition and the acid-base properties of surface layers differ drastically from amphoteric (initial de-ashed carbon D43/1, Carbo-Tech, Essen, Germany) and acidic (carbon modified with concentrated HNO3 and fuming H2SO4) to strongly basic (carbon modified with gaseousNH3). Benzene adsorption isotherms measured from aqueous solution at three temperatures (298, 313, and 323 K) and at the neutral pH level are reported. They are supported by studies of water and benzene adsorption from the gaseous phase (volumetric and calorimetric data) and the data of benzene temperature-programmed desorption (TPD). Moreover, the data of the enthalpy of immersion in water and benzene are also presented. Obtained data of benzene adsorption from the gaseous phase are approximated by applying the method of Nguyen and Do (ND) and the Dubinin-Astakhov (DA) equation. The data of adsorption from solution are described by the hybrid DA-Freundlich (DA-F) model. We show that there are similarities in the mechanisms of benzene adsorption from the gaseous phase and from aqueous solutions and that the pore-blocking effect is the main stage of the adsorption mechanism. This effect strongly depends on the polarity of the carbon surface. The larger the ratio of the enthalpy of carbon immersion in water to the enthalpy of immersion in benzene, the larger the reduction in adsorption from solution, compared to that in the gaseous phase, that is observed

Benzene adsorption on carbonaceous materials: The influence of pore structure on the state of the adsorbate

Experimental nitrogen (T = 77 K) and as benzene (T = 298 K) adsorption isotherms measured on eight carbons possessing various porous structure are used to evaluate the parameters characterizing the geometric heterogeneity. Additionally, the experimental energetic measurements, i.e. the enthalpy and adsorption and related entropy of adsorbed benzene, are taken into considerations. The analysis of experimental data leads to the conclusion that the entropy of C6H6 adsorbed in strictly microporous materials approaches the value characteristic of quasi-solid (a partially ordered structure). On the other hand, for adsorbents possessing wider pores (i.e. the contribution of mesopores to the total porosity is significant) the differential entropy approaches to the value characteristic of liquid. We test a key assumption of the theoretical models describing the mechanism of adsorption, that the adsorbed phase is considered as liquid. This verification leads to the conclusion that the various orientation of the adsorbate in the pore space should be taken into consideration in the theoretical assumptions of a model and in its thermodynamic verification. The significant improvement in the description of benzene experimental data for microporous adsorbents is observed if the ‘‘correction term’’ in the enthalpy of adsorption is considered. This term is correlated with the average pore diameter of studied solids. Our results of the critical pore diameter where the system undergoes an order-disorder transition are very close to obtained by Chakrabarti and Kerkhof via the computer simulation experiments

Giles' classification of solute adsorption isotherms for binary non-electrolyte solutions via lattice DFT supported by experimental sorption data from aqueous solutions on carbonaceous materials

Abstract not availabl

Cyclodextrins in drug delivery: An updated review

The purpose of this review is to discuss and summarize some of the interesting findings and applications of cyclodextrins (CDs) and their derivatives in different areas of drug delivery, particularly in protein and peptide drug delivery and gene delivery. The article highlights important CD applications in the design of various novel delivery systems like liposomes, microspheres, microcapsules, and nanoparticles. In addition to their well-known effects on drug solubility and dissolution, bioavailability, safety, and stability, their use as excipients in drug formulation are also discussed in this article. The article also focuses on various factors influencing inclusion complex formation because an understanding of the same is necessary for proper handling of these versatile materials. Some important considerations in selecting CDs in drug formulation such as their commercial availability, regulatory status, and patent status are also summarized. CDs, because of their continuing ability to find several novel applications in drug delivery, are expected to solve many problems associated with the delivery of different novel drugs through different delivery routes