Physicochemical properties, equilibrium adsorption performance, manufacturability, and stability of TIFSIX-3-Ni for direct air capture

21 March 2024, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


The use of adsorbents for direct air capture (DAC) is regarded as a promising and essential carbon dioxide removal technology to help meet the goals outlined by the 2015 Paris Agreement. A class of adsorbents that has gained significant attention for this application is ultramicroporous metal organic frameworks (MOFs). However, the necessary data needed to facilitate process scale evaluation of these materials is not currently available. Here, we investigate TIFSIX-3-Ni, a previously reported ultramicroporous MOF for direct air capture, and measure several physicochemical and equilibrium adsorption properties. We report its crystal structure, textural properties, thermal stability, specific heat capacity, CO2, N2, and H2O equilibrium adsorption isotherms at multiple temperatures, and Ar and O2 isotherms at a single temperature. For CO2, N2, and H2O, we also report isotherm model fitting parameters and calculate heats of adsorption. We assess the manufacturability and process stability of TIFSIX-3-Ni by investigating the impact of batch reproducibility, binderless pelletization, humidity, and adsorption-desorption cycling (50 cycles) on its crystal structure, textural properties, and CO2 adsorption. For pelletized TIFSIX-3-Ni, we also report its skeletal, pellet, and bed density, total pore volume, and pellet porosity. Overall, our data enable initial process modelling and optimization studies to evaluate TIFSIX-3-Ni for DAC at the process scale. They also highlight the possibility to pelletize TIFSIX-3-Ni and the limited stability of the MOF under humid and oxidative conditions as well as upon multiple adsorption-desorption cycles.


direct air capture
metal organic framework

Supplementary materials

Supporting Information
Chemicals used; additional information on specific heat capacity, humidity, cyclic measurements; comparison of XRD patterns to literature; images of synthesized NiTiF6, TIFSIX-3-Ni precursor, and final TIFSIX-3-Ni powder; check for achievement of equilibrium in isotherm measurements; theoretical CO2 and H2O loading calculations; XPS analysis; fitting of the SSL isotherm model to CO2 isotherms; bounds for isotherm fitting parameters; N2, Ar, and O2 desorption isotherm data; H2O adsorption potentials; alternative fitting of the UNIV6 isotherm model for H2O; additional information on calculations of limiting and isosteric heats of adsorption; N2 adsorption isotherms at -196 °C in log-log scale of loading and pressure; CO2 adsorption isotherms at 0 °C and textural properties; in-situ XRD patterns for powder and pellet samples; images of color changes of samples after exposure to humidity; XPS analysis of samples exposed to humidity; pellet mass change after a “long-cycle”; air adsorption comparison of pellet before and after cyclic testing.


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