Post-combustion CO2 capture and air separation are integral parts of the energy industry, although the available technologies remain inefficient, resulting in costly energy penalties. Here we report azo-bridged, nitrogen-rich, aromatic, water stable, nanoporous covalent organic polymers, which can be synthesized by catalyst-free direct coupling of aromatic nitro and amine moieties under basic conditions. Unlike other porous materials, azo-covalent organic polymers exhibit an unprecedented increase in CO2/N2 selectivity with increasing temperature, reaching the highest value (288 at 323 K) reported to date. Here we observe that azo groups reject N2, thus making the framework N2-phobic. Monte Carlo simulations suggest that the origin of the N2 phobicity of the azo-group is the entropic loss of N2 gas molecules upon binding, although the adsorption is enthalpically favourable. Any gas separations that require the efficient exclusion of N2 gas would do well to employ azo units in the sorbent chemistry.
Carbon dioxide capture and separation requires robust solids that can stand harsh environments where a hot mixture of gases is often found. Herein, the first and comprehensive syntheses of porous sulfur-bridged covalent organic polymers (COPs) and their application for carbon dioxide capture in warm conditions and a wide range of pressures (0–200 bar) are reported. These COPs can store up to 3294 mg g−1 of carbon dioxide at 318 K and 200 bar while being highly stable against heating up to 400 °C. The carbon dioxide capacity of the COPs is also not hindered upon boiling in water for at least one week. Physisorptive binding is prevalent with isosteric heat of adsorptions around 24 kJ mol−1. M06–2X and RIMP2 calculations yield the same relative trend of binding energies, where, interestingly, the dimer of triazine and benzene play a cooperative role for a stronger binding of CO2 (19.2 kJ mol−1) as compared to a separate binding with triazine (13.3 kJ mol−1) or benzene (11.8 kJ mol−1).
High pressure CO2 absorption studies on imidazolium based ionic liquids: Experimental and simulation approaches
F. Karadas, B. Köz, J. Jacquemin, E. Deniz, D. Rooney, J. Thompson, C. T. Yavuz, M. Khraisheh, S. Aparicio, M. Atilhan
A combined experimental–computational study on the CO2 absorption on 1-butyl-3-methylimidazolium
hexafluophosphate, 1-ethyl-3-methylimidazolium bis[trifluoromethylsulfonyl]imide, and 1-butyl-3-
methylimidazolium bis[trifluoromethylsulfonyl]imide ionic liquids is reported. The reported results
allowed to infer a detailed nanoscopic vision of the absorption phenomena as a function of pressure
and temperature. Absorption isotherms were measured at 318 and 338 K for pressures up to 20 MPa
for ultrapure samples using a state-of-the-art magnetic suspension densimeter, for which measure-
ment procedures are developed. A remarkable swelling effect upon CO2 absorption was observed for
pressures higher than 10 MPa, which was corrected using a method based on experimental volumet-
ric data. The experimental data reported in this work are in good agreement with available literature
isotherms. Soave–Redlich–Kwong and Peng–Robinson equations of state coupled with bi-parametric
van der Waals mixing rule were used for successful correlations of experimental high pressure absorp-
tion data. Molecular dynamics results allowed to infer structural, energetic and dynamic properties of
the studied CO2 + ionic liquids mixed fluids, showing the relevant role of the strength of anion–cation
interactions on fluid volumetric properties and CO2 absorption
Noninvasive functionalization of polymers of intrinsic microporosity for enhanced CO2 capture
Modifying sorbents for the purpose of improving carbon dioxide capture often results in the loss of surface area or accessible pores, or both. We report the first noninvasive functionalization of the polymers of intrinsic microporosity (PIMs) where inclusion of the amidoxime functionality in PIM-1 increases carbon dioxide capacity up to 17% and micropore surface area by 20% without losing its film forming ability.
CO2 adsorption studies on prussian blue analogues
F. Karadas, H. El-Faki, E. Deniz, C. T. Yavuz, S. Aparicio, M. Atilhan
Carbon dioxide (CO2) adsorption capacities of several Prussian blue (PB) analogues have been studied using the state-of-the-art Rubotherm® sorption apparatus to obtain adsorption and desorption isotherms of these compounds up to 50 bar. The analogues were prepared by simply reacting a [M(CN)6]3− (Mdouble bondCo, Fe) solution with solutions of M2+ (Mdouble bondMn, Fe, Co, Ni, Cu) metal ions. Characterization of the studied samples has been performed by using a combination of powder XRD, TGA, FTIR, and CHN elemental analysis. Adsorption capacities of PB analogues calculated with theoretical calculations, using Monte Carlo approach, have also been compared with the experimental study, and used to discuss the molecular mechanism of adsorption.
Arsenic removal by magnetic nanocrystalline barium hexaferrite
Nanoscale magnetite (Fe3O4) (<15 nm) is known to remove arsenic efficiently but is very difficult to separate or require high magnetic fields to separate out from the waste water after treatment. Anisotropic hexagonal ferrite (BaFe12O19, BHF) is a well-known permanent magnet (i.e., fridge magnets) and attractive due to its low cost in making large quantities. BHF offers a viable alternative to magnetite nanocrystals for arsenic removal since it features surfaces similar to iron oxides but with much enhanced magnetism. Herein, we employ BHF nanocrystalline materials for the first time in arsenic removal from wastewater. Our results show better (75 %) arsenic removal than magnetite of the similar sizes. The BHF nanoparticles, 6.06 ± 0.52 nm synthesized by thermolysis method at 320 °C do not show hexagonal phase, however, subsequent annealing at 750 °C produced pure hexagonal BHF in >200 nm assemblies. By using BHF, we demonstrate that nanoparticle removal is more efficient and fixed bed type cartridge applications are more possible.
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