Gas Capture and Storage

Porous polymers. For an effective CO₂ capture and separation, we built over 200 nanoporous
network polymers (Covalent Organic Polymers, COPs). COP-1 recorded the highest CO₂ capacity ever measured in any materials to date (128 mmol/g, J. Mater. Chem. 2012, 22, 8431). Targeting the pre-combustion conditions, COP-2 shows a near infinite selectivity for CO₂ over hydrogen gas. COPs-68-81 (Azo-COPs) shows a unique, previously unknown, N₂-phobic behavior (Nature Commun., 2013, 4, 1357 and two subsequent papers in Chem. Eur. J.) and COP-40 is easily made into membranes for continuous CO₂ separation. COP-83 has a capacity of 5 mmol/g at 298 K and 1 bar (J. Mater. Chem. A 2014, 2, 12507), and COP-97 shows an uptake of 8 % (w/w) CO₂ in 2 minutes from a simulated flue gas mixture (CO₂ 15%, H₂O 3.8%, He 81.2%, 40 ^oC, flow rate: 80 mL/min) (Faraday Disc. 2015, 183, 401-412). Box-COPs (COPs 93-95) are stable up to a staggering 600 oC and could be formed into films (Chem. Mater. 2014, 26, 6729). Using COPs 114 and 115 we controlled the amine amount and chain length to observe a concerted CO₂ binding mechanism (Phys. Chem. Chem. Phys. 2016, 18, 14177-14181). COPs with ester and amide functionalities also found to favor CO₂ adsorption, particularly at high pressures (ACS Appl. Mater. Interfaces, 2016, 8, 20772–20785). Our results point to an ideal nanoporous structure to be made from a highly porous, inexpensive, physisorptive solid, which is chemically modified with chemisorptive functionalities such as amines (see our tutorial review at ChemSusChem, 2017, 10, 1303).

Amidoximes. We have discovered CO₂-philic properties of amidoxime functional groups for the first time. Our initial studies focused on the proof of the concept, where molecular amidoximes are found to capture CO₂ better than the industrial standard, monoethanolamine, MEA (Energy Environ. Sci., 2011, 4, 4528). Introducing amidoxime functionality to porous polymeric membranes enhanced CO₂ capture and selectivity significantly (Chem. Comm., 2012, 48, 9989).

Inorganic sorbents. Layered double hydroxides (hydrotalcites) are effective high temperature CO₂ sorbents with poor stability and recyclability. Trivalent cations (Al³⁺) are substituted with gallium for a reversible and robust CO₂ sorbent (Chem. Mater., 2009, 21, 3473). Lithium silicate was promoted with TiO₂ nanotubes for a reusable high temperature CO₂ sorbent with fast kinetics of adsorption – desorption cycles (Ind. Eng. Chem. Res., 2017, 56, 3413).