Improving CO2 Separation Performance of MIL-53(Al) by Incorporating 1-n-Butyl-3-Methylimidazolium Methyl Sulfate

1-n-Butyl-3-methylimidazolium methyl sulfate is incorporated into MIL-53(Al). Detailed characterization is done by X-ray fluorescence, Brunauer-Emmett-Teller surface area, scanning electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. Results show that ionic liquid (IL) interacts directly with the framework, significantly modifying the electronic environment of MIL-53(Al). Based on the volumetric gas adsorption measurements, CO2, CH4, and N2 adsorption capacities decreased from 112.0, 46.4, and 19.6 cc (STP) gMIL-53(Al) -1 to 42.2, 13.0, and 4.3 cc (STP) gMIL-53(Al) -1 at 5 bar, respectively, upon IL incorporation. Data show that this postsynthesis modification leads to more than two and threefold increase in the ideal selectivity for CO2 over CH4 and N2 separations, respectively, as compared with pristine MIL-53(Al). The isosteric heat of adsorption (Qst) values show that IL incorporation increases CO2 affinity and decreases CH4 and N2 affinities. Cycling adsorption-desorption measurements show that the composite could be regenerated with almost no decrease in the CO2 adsorption capacity for six cycles and confirm the lack of any significant IL leaching. The results offer MIL-53(Al) as an excellent platform for the development of a new class of IL/MOF composites with exceptional performance for CO2 separation.

Relevance of hydrogen bonding in CO2 capture enhancement within InOF-1: an energy and vibrational analysis

DFT and experimental in situ results postulate four plausible CO₂ adsorption mechanism for MeOH-functionalised InOF-1.

Adsorption and correlations of selected aromatic compounds on a KOH-activated carbon with large surface area

Knowledge of adsorption mechanism and behavior of organic compounds by KOH-activated carbons (KOH-ACs) from wastewater is crucial to its environmental application in wastewater treatment as adsorbent. A superior adsorbent, KOH-activated carbon (KOH-AC), with large surface area (3143m²/g), total pore volume of 2.03cm³/g, relatively low micropore fraction of 53.2%, and having adsorption capacities of organic compounds up to >1000mg/g, was prepared. It is an adsorbent significantly different with common ACs because the molecular sieving effect, widely observed for common ACs, is insignificant for KOH-AC. This difference could be attributed to the lower micropore fraction of KOH-AC than common ACs. A negative relationship of adsorption capacity of 25 aromatic compounds (including phenols, anilines, nitrobenzenes and polycyclic aromatic hydrocarbons) with chemical melting point was observed, suggesting that adsorption is dependent on the packing efficiency and stacking density of molecules on KOH-AC. A linear solvation energy relationships of adsorption affinity of 25 aromatic compounds with solute solvatochromic parameters was also observed, that can be used to quantify the contributions of π-π interaction, hydrogen-bonding interaction and hydrophobic effect to adsorption on KOH-AC. Combined with the reported results of adsorption of organic compounds on carbon nanotubes and biochars, it was also observed that external surface area of adsorbents is controlling the packing efficiency and stacking density of molecules on adsorbents and thus affecting adsorption capacity of organic compounds. Moreover, micropore surface area and the fraction of micropores are the adsorbent properties mainly affecting adsorption affinity of organic compounds. The observations and the developed correlations in this study would be helpful in the application of KOH-AC as superior adsorbent by enhancing the understanding of adsorption mechanisms of organic compounds on KOH-AC and by giving a method to predict the adsorption behaviors.

Solvent-free nanofluid with three structure models based on the composition of a MWCNT/SiO2 core and its adsorption capacity of CO2

A series of core/shell nanoparticle organic/inorganic hybrid materials (NOHMs) with different weight ratios of two components, consisting of multi-walled carbon nanotubes (MWCNTs) and silicon dioxide (SiO₂) as the core were synthesized. The NOHMs display a liquid-like state in the absence of solvent at room temperature. Five NOHMs were categorized into three kinds of structure states based on different weight ratio of two components in the core, named the power strip model, the critical model and the collapse model. The capture capacities of these NOHMs for CO₂ were investigated at 298 K and CO₂ pressures ranging from 0 to 5 MPa. Compared with NOHMs having a neat MWCNT core, it was revealed that NOHMs with the power strip model show better adsorption capacity toward CO₂ due to its lower viscosity and more reactive groups that can react with CO₂. In addition, the capture capacities of NOHMs with the critical model were relatively worse than the neat MWCNT-based NOHM. The result is attributed to the aggregation of SiO₂ in these samples, which may cause the consumption and hindrance of reactive groups. However, the capture capacity of NOHMs with the collapse model was the worst of all the NOHMs, owing to its lowest content of reactive groups and hollow structure in MWCNTs. In addition, they presented non-interference of MWCNTs and SiO₂ without aggregation state.

Improving the hydrogen selectivity of graphene oxide membranes by reducing non-selective pores with intergrown ZIF-8 crystals

The large defects of graphene oxide membranes were reduced by the intergrown ZIF-8 crystals, affording dramatically increased gas separation performance.