Showing papers by "Francisco Rodríguez-Reinoso published in 2019"

Characterization of the adsorption site energies and heterogeneous surfaces of porous materials

Abstract: Characterization of the guest–host interactions and the heterogeneity of porous materials is essential across the physical and biological sciences, for example for gas sorption and separation, pollutant removal from wastewater, biological systems (protein–ligand binding) and molecular recognition materials such as molecularly imprinted polymers. Information about the guest–host interactions can be obtained from calorimetric experiments. Alternatively, more detailed information can be obtained by properly analysing the experimentally acquired adsorption equilibrium data. Adsorption equilibrium is usually interpreted using theoretical adsorption isotherms that correlate with the equilibrium concentration of the adsorbate in the solid phase and in the bulk fluid at a constant temperature. Such theoretical isotherms or expressions can accurately predict the adsorbent efficiency (at equilibrium) as a function of process variables such as the initial adsorbate concentration, adsorbent mass, reactor volume and temperature. Detailed analysis of the adsorption isotherms permits the calculation of the number density of the adsorbent sites, their binding energy for the guest molecules and information about the distribution of adsorption site binding energies. These analyses are discussed in this review. A critical evaluation of the analytical and numerical methods that can characterize the heterogeneity and guest–host interactions involved in terms of discrete or continuous binding site affinity distribution was performed. Critical discussion of the limitations and the advantages of these models is provided. An overview of the experimental techniques that rely on calorimetric and chromatographic principles to experimentally measure the binding energy and characteristic properties of adsorbent surfaces is also included. Finally, the potential use of site energy distribution functions and their potential to provide new information about the binding energy of adsorbents for a specific guest molecule application is discussed.

Structural Flexibility in Activated Carbon Materials Prepared under Harsh Activation Conditions.

Abstract: Although traditionally high-surface area carbon materials have been considered as rigid structures with a disordered three dimensional (3D) network of graphite microdomains associated with a limited electrical conductivity (highly depending on the porous structure and surface chemistry), here we show for the first time that this is not the case for activated carbon materials prepared using harsh activation conditions (e.g., KOH activation). In these specific samples a clear structural re-orientation can be observed upon adsorption of different organic molecules, the structural changes giving rise to important changes in the electrical resistivity of the material. Whereas short chain hydrocarbons and their derivatives give rise to an increased resistivity, the contrary occurs for longer-chain hydrocarbons and/or alcohols. The high sensitivity of these high-surface area carbon materials towards these organic molecules opens the gate towards their application for sensing devices.

Methane Storage on Nanoporous Carbons

Abstract: This chapter reviews the requirements for a nanoporous carbon material to be used as an adsorbent for methane storage. Due to the necessity to achieve a large gravimetric and volumetric storage capacity in real applications (e.g., onboard storage for transportation vehicles), a proper carbon material must fulfill certain requirements in terms of porous structure, pore geometry, pore size distribution, and packing density. The effect of these parameters on the methane adsorption/storage capacity will be revised both from a theoretical and experimental perspective. State-of-the-art values for excess and storage capacity for the best performing carbon materials will be summarized. Last but not least, heat and mass transfer limitations will be revised due to the dramatic effect that these scarcely explored variables can have in the performance of the final prototype.

Adsorption of hydrogen on activated carbons prepared by thermal activation : Hydrogen storage

Abstract: Microporous activated carbons were prepared from date pits using thermal activation with CO2 or steam. The adsorbents were characterized by N2 and CO2 adsorption at 77 K and 273K, respectively. The H2 adsorption was measured at 298K and 100 bar using a volumetric equipment. To increase the hydrogen storage, activated carbons are doped by metals. The results show that the H 2 adsorption capacity is influenced by the size and volume of micropores in the activated carbon adsorbent. A relationship between hydrogen adsorption capacity calculated using Langmuir isotherm and the volume of narrow micropores deduced from the CO2 adsorption isotherm at 273 K was found. A correlation was also found between both micropore volumes and the amount of hydrogen adsorbed at 298 K and 100 bar. Additionally, vanadium doping of activated carbons could positively influence hydrogen adsorption.