Chemisorbent materials, based on porous aminosilicas, are amongst the most promising adsorbents for direct air capture applications, one of the key technologies to mitigate carbon emissions. Herein, a critical survey of all reported chemisorbed CO2 species, which may form in aminosilica surfaces, is performed by revisiting and providing new experimental proofs of assignment of the distinct CO2 species reported thus far in the literature, highlighting controversial assignments regarding the existence of chemisorbed CO2 species still under debate. Models of carbamic acid, alkylammonium carbamate with different conformations and hydrogen bonding arrangements were ascertained using density functional theory (DFT) methods, mainly through the comparison of the experimental 13 C and 15 N NMR chemical shifts with those obtained computationally. CO2 models with variable number of amines and silanol groups were also evaluated to explain the effect of amine aggregation in CO2 speciation under confinement. In addition, other less commonly studied chemisorbed CO2 species (e.g., alkylammonium bicarbonate, ditethered carbamic acid and silylpropylcarbamate), largely due to the difficulty in obtaining spectroscopic identification for those, have also been investigated in great detail. The existence of either neutral or charged (alkylammonium siloxides) amine groups, prior to CO2 adsorption, is also addressed. This work extends the molecular-level understanding of chemisorbed CO2 species in amine-oxide hybrid surfaces showing the benefit of integrating spectroscopy and theoretical approaches.

Solid-state NMR and molecular modeling provide structural insights on the influence of water upon CO2 chemisorption on primary and tertiary amine-grafted mesoporous silica sorbent materials.

Gas storage and gas separation using porous solids are important technologies that have attracted great attention because of their environmental and energetic applications. Highly porous materials, such as zeolites, silicate, and carbonbased materials, [1] have long-established specific applications. The key for new applications is the development of new frameworks. Advances in gas sorption capacities were achieved through the synthesis of materials such as metalorganic frameworks (MOFs), organic polymers, and microporous organic crystals.[2] Recently, crystals formed by dipeptides were tested as adsorbents [3] with significant results in hydrogen absorption and methane purification from carbon dioxide.

Among the greatest challenges in the field of microporous solids is the development of ''smart'' materials, displaying environment-triggered property tuning. These could be used both in traditional and new applications of microporous materials. In this context, supramolecular peptide-based solids have recently emerged as interesting alternatives to standard microporous solids, such as zeolites and carbon molecular sieves. They possess framework and conformational flexibility, are kinetically stable and reasonably thermally resistant. Important properties such as pore size and inner wall chemistry can be controlled through appropriate chemical modification of the peptide molecules. Peptide-based porous solids have permanent microporosity, often with molecularly sized cavities created by removal of co-crystallised solvent. Some have already been successfully tested as adsorbents and permselective materials, confirming their potential. This review covers the identification, synthesis, characterization techniques and properties of peptide-based microporous solids, discussing their most unique functionalities.

The Langmuir equation is one of the most successful adsorption isotherm equations, being widely used to fit Type I adsorption isotherms. In this article we show that the kinetic approach originally used by Langmuir for 2D monolayer surface adsorption can also be used to derive a 1D analogue of the equation, applicable in ultramicropores with singlefile diffusion systems. It is hoped that such a demonstration helps dispel the idea that the 2 Langmuir isotherm equation cannot apply to some micropores as more than a mathematical correlation. We furthermore seek to extend the intuitive insight provided by the simple kinetic derivation of the Langmuir equation to other isotherm equations capable of modelling Type I isotherms. The kinetic approach is thus also used to derive the Volmer, Fowler-Guggenheim and Hill-de Boer equations, both for surface (2D adsorbed phase) and micropore adsorption (1D and 3D adsorbed phases). It is hoped that this will help make it more intuitively clear that these equations can be used as phenomenological models in some instances of adsorption in micropores.