Distribution of basic centres on Yb 2O 3 surfaces

Based upon the adsorbate–adsorbent interactions due to pore size distribution and surface heterogeneity, as characterized by the adsorption isotherms, the adsorption phenomenon has many industrial and environmental applications. These adsorption isotherms are very important to define the information related to the equilibrium uptake of adsorbate–adsorbent pair. Due to the presence of different energy distribution of adsorption sites, pore size distribution, surface area availability and surface heterogeneity, of each of the adsorbent–adsorbate pair, these isotherms are categorized into six types by the International Union of Pure and Applied Chemistry and so far, in the literature, there is no generalized adsorption isotherm model available that can define and predict the behavior of all adsorption isotherm types. In this study, a universal adsorption isotherm model is developed based upon the energy distribution function of the available adsorption sites and the pore size. The proposed model is able to define all adsorption isotherm characteristics, irrespective of their multi- or monolayer formations and micro- or meso-pore distribution.

Physical adsorption on heterogeneous surfaces: The effect of the topography of surfaces on the evaluated adsorption energy distribution

The reversible adsorption process occurring on patchwise heterogeneous bivariate surfaces is studied by Monte Carlo simulation and mean-field approximation. These surfaces are characterized by a collection of deep and shallow adsorbing patches with a typical length scale l. Patches can be either arranged in a deterministic chessboard structure or in a random way. Previous studies showed that the topography of a given surface can be obtained from the knowledge of the corresponding adsorption isotherm and a reference curve. In the present work, we discuss the advantages and disadvantages of using different reference curves. One of the main consequences of this analysis is to provide an improved method for the determination of the energetic topography of the surface from adsorption measurements.

A new general-purpose Type–I adsorption isotherm is proposed to improve standard adsorption Gibbs energy estimation. This new isotherm stems from considering a functional dependence of various adsorption models on the c/θ vs. c plot, where θ is the fractional surface coverage and c the concentration. It can accurately describe many adsorption isotherms, implying that it is flexible enough to describe various adsorption scenarios. Among the tested adsorption models that the new isotherm can describe are those that consider lateral inter-adsorbate interactions, molecular size, surface heterogeneity, and mobile adsorption.

Calorimetric determination of the acidic character of amorphous and crystalline aluminosilicates

We study and describe-from the point of view of the interactions of the adsorbed particles-three types of the adsorption isotherms, namely, Langmuir type adsorption isotherms, phase transition type adsorption isotherms, and adsorption limited type adsorption isotherms, which are observed by experiments. By introducing and using a one dimensional statistical occupancy model, we derived analytical adsorption isotherms for the no force, the attractive force, and the repulsive force exerted on the other adsorbed particles. Our derived adsorption isotherms qualitatively pretty well agree with the experimental results of the adsorption isotherms. To specify each adsorption type, Langmuir type adsorption is a phenomenon that occurs with no forces between the adsorbed particles, phase transition type adsorption is a phenomenon that occurs with the strong attractive forces between the adsorbed particles, and adsorption limited type adsorption is a phenomenon that occurs with the repulsive forces between the adsorbed particles. The theoretical analysis-only using fundamental thermodynamics and occupancy statistics though-qualitatively quite well explains the experimental results.

A model study has been undertaken to elucidate the interplay between vertical and lateral interaction effects in the physical adsorption of gases on heterogeneous solid surfaces. The surface model employed is a square lattice with a random distribution of adsorption sites of different energies on which adsorbed molecules interact only with their nearest neighbours. Isotherms are generated by simulating the system in the grand canonical ensemble by Monte Carlo methods. These isotherms are subsequently subjected to analysis by the adsorption integral equation using various local isotherm models, in an attempt to recover the adsorption energy distributions. When lateral interactions are ignored, the analysis yields an adsorption energy distribution which (a) is centred on a mean value which is too high and (b) has a 'spread' which is too small. These effects are correlated with the magnitude of the neglected lateral interactions and a possible physical interpretation of the mean energy calculated by such means is given. Differential heats of adsorption as well as isotherm 'data' are presented for the model system considered.

On the thermodynamics of adsorption on heterogeneous surfaces

Ways of satisfying the condition for the self-consistent description of adsorption and desorption rates of non-dissociated molecules on a rough aerosol surface are considered. The rates are calculated with allowance for the interaction between nearest neighbors in the quasi-chemical approximation. Four types of models are analyzed. One describes the initial distributed heterogeneous surface, while the other three are variants averaged over the number of monolayers (with a transition to a single-layered heterogeneous surface) and different types of adsorption centers with different Henry constants (with a transition to an effective homogeneous monolayer in a multilayered transition region), or over the number of monolayers and types of adsorption centers (with a transition to the single-layered homogeneous surface) simultaneously. Types of models are distinguished for which the self-consistency condition is strictly satisfied and for which it is violated. Observed discrepancies are explained. The dependence of the degree of discrepancy (if there is one) on the density of the gas in the system, the energy of interaction of the activated complex, and the radius of adsorbent particles is established.

Multilayer adsorption in liquid chromatography – The surface heterogeneity below an adsorbed multilayer

The present work was designed to synthesize a Chitosan (CS) - Cerium oxide (CeO2)nanobiosorbent and study the adsorption of Indigo Carmine. The adsorption equilibrium data were better fitted in the Freundlich isotherm model, indicating that adsorption is occurring on a heterogeneous surface in the multilayer pattern. Low pH values (3 and 4), low initial Indigo Carmine concentration (50 mg/L), high adsorbent concentration (500 mg/L) and relatively high temperatures (50 °C) exhibited the highest removal efficiency towards the examined dye. The pseudo-second order kinetic model described better the adsorption process;thus, it can be stated that chemisorption between the adsorbent and the adsorbate is occurring. According to the thermodynamic analysis, adsorption process is spontaneous, exothermic and more favorable at high temperatures. FTIR analysis confirmed the adsorption of the dye onto the CS/CeO2nanobiosorbent.

Chemically demethoxylated and Ca-cross-linked orange-peel waste was engineered as a biosorbent for Mn(II) removal from water. A three-factor Box–Behnken design (biosorbent dose 3–10 g L−1, initial Mn2+ 100–300 mg L−1, contact time 3–8 h; pH 5.5 ± 0.1, 25 °C) required only 16 runs to locate the optimum (10 g L−1, 100 mg L−1, 8 h), at which the material removed 94.8% ± 0.3% manganese removal under the optimized conditions (10 g L−1, 100 mg L−1, 8 h, pH 5.5) of dissolved manganese and reached a Langmuir capacity of 29.7 mg g−1. Equilibrium data fitted the Freundlich (R2 = 0.968) and Sips (R2 = 0.969) models best, indicating a heterogeneous surface, whereas kinetic screening confirmed equilibrium within 6 h. FTIR and SEM–EDX verified abundant surface –COO−/–OH groups and showed Mn deposits that partially replaced residual Ca, supporting an ion-exchange component in the uptake mechanism. A preliminary cost analysis (<USD 10 kg−1) and > 90% regeneration efficiency over three cycles highlight the economic and environmental promise of this modified agro-waste for polishing Mn-laden effluents.

Nitrate has been identified as a major source of water pollution and eutrophication. The use of modified chicken feathers (MCFs) as an adsorbent has not been fully explored. The study therefore assessed the use of MCFs for the adsorption of nitrate. Fresh chicken feathers, obtained from a commercial poultry farm, were first hydrolyzed with sodium hydroxide and activated with HCl aq to give modified chicken feathers, MCFs. Experimental constraints were varied in a series of batch tests including concentration, pH, adsorbent dosage and contact time. FTIR was used to monitor the adsorption processes (before and after) of the polluted water. The outcome showed increase in specific surface area and the favorable formation of adsorption sites of MCFs. For the understanding of adsorption mechanism, experimental data were assessed by Langmuir, Freundlich, Temkin and Sips isotherm equations. Pseudo-first and pseudo-second order models were used to evaluate time characteristics of adsorption. The optimum parameters for adsorption are found to be initial ion concentration, initial pH, adsorbent dosage and contact time 300 mg/L, 8, 10 and 480 min, respectively. This study also reveals adsorption fit the chosen isotherm models in the following order: (Sips >Langmuir > Freundlich > Temkin). Sips isotherm having the best fit infers adsorption took place on heterogeneous surface. Pseudo-second-order is suited for explaining nitrate removal based on statistical R2 coefficient. The use of MCFs as an eco-friendly, cost-effective and renewable bio-sorbent for wastewater treatment is very possible due to its adsorption ability in the removal of nitrate.

A functional food as a matrix based on a blend of carbohydrate polymers (25% maltodextrin and 75% inulin) with quercetin and Bacillus claussi to supply antioxidant and probiotic properties was prepared by spray drying. The powders were characterized physiochemically, including by moisture adsorption isotherms, X-ray diffraction (XRD), scanning electron microscopy (SEM), and modulated differential scanning calorimetry (MDSC). The type III adsorption isotherm developed at 35 °C presented a monolayer content of 2.79 g of water for every 100 g of dry sample. The microstructure determined by XRD presented three regions identified as amorphous, semicrystalline, and crystalline-rubbery states. SEM micrographs showed variations in the morphology according to the microstructural regions as (i) spherical particles with smooth surfaces, (ii) a mixture of spherical particles and irregular particles with heterogeneous surfaces, and (iii) agglomerated irregular-shape particles. The blend’s functional performance demonstrated antioxidant activities of approximately 50% of DPPH scavenging capacity and viability values of 6.5 Log10 CFU/g. These results demonstrated that the blend displayed functional food behavior over the complete interval of water activities. The equilibrium state diagram was significant for identifying the storage conditions that promote the preservation of functional food properties and those where the collapse of the microstructure occurs.

Adsorption isotherm, kinetic modeling and mechanism of tetracycline on Pinus taeda-derived activated biochar