In this work, CO 2 adsorption on a laboratory-synthesized polymeric copper(II) benzene-1,3,5-tricarboxylate (Cu-BTC) metal-organic framework was modeled by means of the semiempirical Sips equation in order to obtain parameters of engineering interest. Produced Cu-BTC samples were characterized by X-ray diffraction, thermogravimetry, and microporosimetric analysis; high crystallinity and very high specific surface area and pore volume were found. CO 2 adsorption isotherms on Cu-BTC were evaluated at T ) (283, 293, 318, and 343) K for p e 1 bar by means of a volumetric technique. In order to establish a comparison, CO 2 adsorption isotherms on samples of commercial 13X zeolite were determined under the same experimental conditions and then modeled in the same way as those for Cu-BTC. The modeling and experimental results indicated that relative to 13X zeolite, Cu-BTC showed higher CO 2 adsorption capacities at near-ambient temperature and a lower heat release during the adsorption phase.

This review highlights the recent advances in the development of functionalized nanoporous adsorbents for CO2 capture. Three main classes of materials are taken into account: zeolites, mesoporous silicates, and metal organic frameworks (MOFs). Proper modification of the cation content of zeolites, as well as the introduction of functional groups such as amine groups into ordered mesoporous silicates and MOFs, greatly enhance the CO2 adsorptive properties of these substrates. Specifically, cation-exchanged zeolites can be currently considered the benchmark for ordered nanoporous CO2 adsorbents, finding application also on a plant scale. Amino-functionalized mesoporous silicates tend to show a high affinity toward CO2: while this could be an advantage when pushed purification is needed, it also implies that full regeneration of the adsorbent can be achieved only by putting its surface in contact with a completely CO2-free environment. On the contrary, similarly modified MOFs show higher CO2 adsorption working capacities: this potentially makes them even better candidates than their mesoporous inorganic homologues for a plant scale use. However, the persisting lack of reliable methods for the pelletization of both ordered mesoporous silicates and MOFs creates a care for further development efforts in the next future.

SBA-15 mesoporous silica was functionalized with polyethylenimine and was used as a substrate for CO 2 adsorption. The synthesized material, denoted SBA-15-PEI, was characterized by means of X-ray diffraction, thermogravimetric analysis, and N 2 adsorption/desorption at 77 K, in order to prove that polymer chains efficiently filled the pores of functionalized samples. CO 2 adsorption isotherms on SBA-15-PEI were evaluated at T = (298, 313, 328, and 348) K for pressures up to 100 kPa by means of a volumetric technique. The experimental data showed a significant dependence of the CO 2 adsorption capacity on temperature, with the highest capacity encountered at the highest temperature explored. Despite this unusual behavior, CO 2 adsorption on SBA-15-PEI was satisfactorily modeled by means of the Sips isotherm. The modeling effort allowed to evaluate the isosteric heat of adsorption as a function of the fractional coverage of SBA-15-PEI. The comparison between the results obtained in the present work and those relative to CO 2 adsorption on "benchmark" microporous substrates, such as 13X zeolite and Cu-BTC metal organic framework, allowed us to highlight significant analogies and differences with those other solids, giving interesting hints on the possible applications of SBA-15-PEI.

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