Advanced interpretation of CO2 adsorption thermodynamics onto porous solids by statistical physics formalism

Three different activated carbons, namely Aquacarb 207EA (AQ), Organosorb-10 (OR-10) and Organosorb-10AA (OR10-AA) are investigated for carbon dioxide (CO2) adsorption from simulated flue-gas, which is one of the promising approaches to mitigate global warming. Adsorption isotherms are determined at three temperatures (303 K, 323 K and 353 K) and over a wide CO2 partial pressure range (0.03–0.3 bar), in a dynamic lab-scale experimental apparatus. Experimental results show that CO2 adsorption capacity is affected by micropore volume, while the chemical properties (mainly pHPZC and acid functional groups) seem to play a secondary role. The CO2 adsorption isotherms are interpreted by three advanced models derived from statistical physics. The selected model allows retrieving useful information about the sorption process by determining the number of captured CO2 molecules per site (nms), the density of receptor sites (Dsr), the total number of adsorbed layers (Nc) and the energetic parameters (−ε1) and (−ε2). The modeling analysis suggests that the captured CO2 molecules aggregate upon adsorption and are anchored with a perpendicular position on the adsorbents surface. The total numbers of adsorbed layers range from 3.12 to 5.56 for the three adsorption systems, and the value increases with temperature as if the diminution of active sites available for CO2 capture on adsorbent surface was partially counterbalanced by a multilayer adsorption mechanism. The adsorption energies retrieved from data analysis are in the range from −11.39 to −21.10 kJ/mol, confirming that, for the investigated systems, adsorption is exothermic and based on physisorption. Finally, the site energy distribution is also estimated to corroborate the surface heterogeneity and the physical nature of the adsorbate/adsorbent interactions

Adaptation of advanced physical models to interpret the adsorption isotherms of lead and cadmium ions onto activated carbon in single-compound and binary systems

The work reports a modeling analysis of single-compound and binary adsorption of Pb2+ and Cd2+ ions from polluted water onto the activated carbon at room temperature. The homogeneous model for single adsorption (HM) and the exclusive extended monolayer model for binary adsorption (EEMM) are applied for the interpretation of the experimental data set. The adopted models correlate the entire set of adsorption data, allowing a thorough description of the occurring phenomena. The overall objective of the study is to determine the adsorption mechanisms, also through a comparative analysis between the single-compound and binary modeling data. The parameters of both models are used for to retrieve useful indications about the adsorption of these two ions. In particular, the number of ions adsorbed per single functional groups changed from single-compound to binary adsorption, allowing to explain the competitive behavior of the investigated system. The adsorption energy values vary between 21.39 (Pb2+) and 24.06 kJ/mol (Cd2+), and 27.17 (Pb2+) and 32.59 kJ/mol (Cd2+) in single-compound and binary systems, respectively, indicating that adsorption is a physisorption process

Theoretical analysis of the removal mechanism of Crystal Violet and Acid Red 97 dyes on Agaricus bisporus residue

In this paper, the Agaricus bisporus residue (ABR) is employed as an adsorbent to study the adsorption mechanism of two relevant dyes, namely Crystal Violet (CV) and Acid Red 97 (AR97). The adsorption mechanism is theoretically analyzed by application of models derived from statistical physics and the model parameters derived from the best fitting are used for the interpretation of the experimental results. A double-layer model best fitsboth CV and AR97 experimental data,showing that AR97 molecules aggregate only at high temperature forming a dimer (n = 2.55 at T = 328 K). Similarly, CV dye tends to form a monomer with a slight tendency to a dimer at high temperature.AR97 dye is adsorbed through a non-parallel orientation on the ABR surface at most of the investigated temperatures (T = 298, 318 and 328 K), while CV dye is removed via both parallel and non-parallel orientations. The analysis of the adsorption capacity suggests that ABR adsorbent has a stronger affinity to remove AR97. The calculation of the adsorption energies indicated that the adsorption process is a physisorption