Metal-organic framework hybrid adsorbents for carbon capture - A review

Metal-organic frameworks (MOFs) are three-dimensional network structures synthesized by the assembly of organic ligands with metal ions or clusters. They currently constitute one of the most promising adsorbent categories for CO2 capture given their high specific surface area and porosity, chemical versatility, and facile chemistry supporting strategic structural modifications. Indeed, many thousands of MOFs are referenced in various structural databases. Within this wide family of materials, many experience certain challenges, which often limit their use for practical applications, including their relatively poor thermal and chemical stability, cyclability, and sensitivity to trace contaminants. One promising approach to address these drawbacks lies with the hybridization of MOFs with other material counterparts to design combinatorial hybrid adsorbents exhibiting superior performance and enhanced properties, benefiting from synergetic effects from each component and interfacial properties engineering. The purpose of this work is to critically review hybridized MOF adsorbents for CO2 capture, with a prime focus on the different opportunities offered by hybridizing materials and additives to MOFs. The engineering, properties, and performance of hybridized MOFs are systematically reviewed, and opportunities and challenges are discussed. This work provides key parameters of the application of hybridized MOF adsorbents and presents recommendations for further research, thereby providing a roadmap for the synthesis and usage of these types of adsorbents for practical CO2 capture applications

Hybrid salt-enriched micro-sorbents for atmospheric water sorption

Water shortage severely impacts drought-stricken regions, with estimates indicating that almost half a billion people are affected yearly. Composites of Salt and Porous Matrix (CSPMs) are promising functional materials for water vapor sorption. Here, CSPMs were synthesized by loading SAPO-34 porous crystals with highly hygroscopic salts, namely LiCl and CaCl2, individually (mono-salt systems) or combined (binary salt systems) to enhance water sorption capacity and cyclability. The LiCl and CaCl2 content in the impregnation solution impacted the sorption behavior and equilibrium capacity of the resulting composites. Physicochemical, morphological, textural, and sorption properties were evaluated showing that the confinement of binary salts yielded the highest water uptake (0.88 gw/gads at 25 °C and 90 % RH), which was four times higher than that of the parent SAPO-34. The shape of the obtained water vapor isotherms revealed that the salts introduced into the porous structure led to significant changes in the sorption mechanism, with SAPO-34 following a Langmuir behavior (type I isotherm) and the composites a type II isotherm with associated multilayer formation due to the presence of the salts. Kinetic studies also revealed that the materials follow a PSO model dominated by water-surface interactions. Embedding different salts into the same hosting pores to support atmospheric water harvesting was therefore found to enhance capacity and cyclability compared to single inorganic porous structures toward more efficient water sorption processes