Removal of CO2 from high-temperature flue gas using PDMS/IL composite membranes

The physical-crosslinking interaction between PDMS and an IL enables the membrane to separate CO2 from high-temperature flue gas.

Dual modulation steering electron reducibility and transfer of bismuth molybdate nanoparticle to boost carbon dioxide photoreduction to carbon monoxide

Owing to the exorbitant CO₂ activation energy and unsatisfactory photogenerated charge separation efficiency, CO₂ photoconversion still faces enormous challenges. In this study, a directional electron transfer channel has been established by decorating N-doped carbon quantum dots (N-CQDs) on the surface of Bi₄MoO₉ nanoparticles to ensure that more active electrons can participate in the CO₂ reduction. The conduction band of Bi₄MoO₉ nanoparticles is calculated to be -1.55 eV versus the normal hydrogen electrode (NHE), pH = 7, which is negative enough to attain the photocatalytic CO₂ reduction potential of -0.53 eV versus NHE, pH = 7. CO₂ adsorption curves and in situ Fourier transform infrared spectra reveal that N-CQDs facilitate surface CO₂ adsorption and activation, as well as CO desorption. In addition, steady-state photoluminescence and photoelectrochemical tests prove that the charge separation efficiency can be greatly enhanced by constructing N-CQDs/Bi₄MoO₉ composites. In the presence of pure water, N-CQDs/Bi₄MoO₉-2 composite achieved a CO yield of 16.22 μmol g^-1 after 5 h Xe light illumination, which was 3.24 times higher than that of pure Bi₄MoO₉ (4.98 μmol g^-1). This study offers a distinctive approach to the optimization of Bi₄MoO₉ photocatalysts and their application in energy conversion.

Guanidine as a strong CO2 adsorbent: a DFT study on cooperative CO2 adsorption

Among the various carbon capture and storage (CCS) technologies, the direct air capture (DAC) of CO2 by engineered chemical reactions on suitable adsorbents has attained more attention in recent times. Guanidine (G) is one of such promising adsorbent molecules for CO2 capture. Recently Lee et al. (Phys. Chem. Chem. Phys., 2015, 17, 10925-10933) reported an interaction energy (ΔE) of -5.5 kcal mol-1 for the GCO2 complex at the CCSD(T)/CBS level, which was one of the best non-covalent interactions observed for CO2 among several functional molecules. Here we show that the non-covalent GCO2 complex can transform to a strongly interacting G-CO2 covalent complex under the influence of multiple molecules of G and CO2. The study, conducted at M06-2X/6-311++G** level density functional theory, shows ΔE = -5.7 kcal mol-1 for GCO2 with an NC distance of 2.688 Å while almost a five-fold increase in ΔE (-27.5 kcal mol-1) is observed for the (G-CO2)8 cluster wherein the N-C distance is 1.444 Å. All the (G-CO2)n clusters (n = 2-10) show a strong N-CO2 covalent interaction with the N-C distance gradually decreasing from 1.479 Å for n = 2 to 1.444 Å for n = 8 ≅ 9, 10. The N-CO2 bonding gives (G+)-(CO2-) zwitterion character for G-CO2 and the charge-separated units preferred a cyclic arrangement in (G-CO2)n clusters due to the support of three strong intermolecular OHN hydrogen bonds from every CO2. The OHN interaction is also enhanced with an increase in the size of the cluster up to n = 8. The high ΔE is attributed to the large cooperativity associated with the N-CO2 and OHN interactions. The quantum theory of atoms in molecules (QTAIM) analysis confirms the nature and strength of such interactions, and finds that the total interaction energy is directly related to the sum of the electron density at the bond critical points of N-CO2 and OHN interactions. Further, molecular electrostatic potential analysis shows that the cyclic cluster is stabilized due to the delocalization of charges accumulated on the (G+)-(CO2-) zwitterion via multiple OHN interactions. The cyclic (G-CO2)n cluster formation is a highly exergonic process, which reveals the high CO2 adsorption capability of guanidine.

Ultrastable and Efficient Visible-light-driven CO2 Reduction Triggered by Regenerative Oxygen-Vacancies in Bi2 O2 CO3 Nanosheets

Herein, we first design a fast low-pressure ultraviolet light irradiation strategy for easily regenerating the nearly equivalent surface vacancies. Taking the defective Bi₂ O₂ CO₃ nanosheets as an example, nearly equal amount of oxygen vacancies can be regenerated under UV light irradiation. Synchrotron-radiation quasi in situ X-ray photoelectron spectra disclose the Bi sites in the O-defective Bi₂ O₂ CO₃ nanosheets can act as the highly active sites, which not only help to activate CO₂ molecules, but also contribute to stabilizing the rate-limiting COOH* intermediate. Also, in situ Fourier transform infrared spectroscopy and in situ mass spectrometry unravel the UV light irradiation contributes to accelerating CO desorption process. As a result, the O-defective Bi₂ O₂ CO₃ nanosheets achieve a stability up to 2640 h over 110 cycling tests and a high evolution rate of 275 μmol g^-1  h^-1 for visible-light-driven CO₂ reduction to CO.

CO2 capture enhancement in MOFs via the confinement of molecules

This review focuses on exploring a new approach to improve the CO₂ adsorption properties of MOFs by confining small amounts of molecules with different nature, such as: water, alcohols, amines, and even aromatic molecules.

Dissociative detachment of the fluoroformate anion

3D fragment imaging of the fluoroformate anion (FCO₂⁻) dissociative photodetachment products shows reductive fragmentation, forming FCO + O, as well as a dominant cleavage of the CF bond.