Insights into the Critical Role of Abundant-Porosity Supports in Polyethylenimine Functionalization as Efficient and Stable CO2 Adsorbents

Improving the direct air capture capacity of grafted amines via thermal treatment

This study investigates the effects of elevated temperature thermal treatments on the direct air capture of CO2 by aminosilane-grafted SBA-15 silica sorbents. Exposing samples to high temperatures (200-250 °C compared to 80-120 °C) in an inert environment resulted in improved CO2 capacity (5-21%) that was sustained over multiple adsorption/desorption cycles.

Thickness Dependent CO2 Adsorption of Poly(ethyleneimine) Thin Films for Direct Air Capture

Mesoporous silica impregnated with polyethyleneimine (PEI) has been shown to be a suitable material for the direct air capture (DAC) of CO2. Factors such as CO2 concentration, temperature, and amine loading impact overall capture capacity and amine efficiency by altering diffusional resistance and reaction kinetics. When studied in the impregnated 3-dimensional sorbent material, internal diffusion impacts the evaluation of the reaction kinetics at the air/amine interface. In this work, we designed a novel tandem quartz crystal microbalance with dissipation (QCM-D) and polarization modulation infrared reflective absorption spectroscopy (PM-IRRAS) instrument. CO2 adsorption kinetics of the PEI-based amine layer in a 2-dimensional geometry were studied at a variety of film thicknesses (10 nm to 100 nm), temperatures (25 °C to 80 °C), and CO2 concentrations (5 % and 0.04 % by mole fraction). Total CO2 capture capacity increased with film thickness but decreased amine efficiency, as additional diffusional resistance for thicker films limits access to available amine sites. The capture capacity of thick films (>50 nm) is shown to be limited by amine availability, while capture of thin films (<50 nm) is limited by CO2 availability. A 50 nm PEI film was shown to be optimal for capture of 0.04 % (400 ppm) CO2. The adsorption profiles for these conditions were fitted to pseudo-first order and Avrami fractional order models. The reaction process switches between a diffusion limited reaction to a kinetic limited reaction at 80 °C when using 5 % CO2 and 55 °C when using 0.04 % CO2. These results offer accurate analysis of adsorption of CO2 at the air/amine interface of PEI films which can be used for the design of future sorbent materials.

Automated Parameterization of Coarse-Grained Polyethylenimine under a Martini Framework

As a versatile polymer in many applications, synthesized polyethylenimine (PEI) is polydisperse with diverse branched structures that attain pH-dependent protonation states. Understanding the structure-function relationship of PEI is necessary for enhancing its efficacy in various applications. Coarse-grained (CG) simulations can be performed at length and time scales directly comparable with experimental data while maintaining the molecular perspective. However, manually developing CG forcefields for complex PEI structures is time-consuming and prone to human errors. This article presents a fully automated algorithm that can coarse-grain any branched architecture of PEI from its all-atom (AA) simulation trajectories and topology. The algorithm is demonstrated by coarse-graining a branched 2 kDa PEI, which can replicate the AA diffusion coefficient, radius of gyration, and end-to-end distance of the longest linear chain. Commercially available 25 and 2 kDa Millipore-Sigma PEIs are used for experimental validation. Specifically, branched PEI architectures are proposed, coarse-grained using the automated algorithm, and then simulated at different mass concentrations. The CG PEIs can reproduce existing experimental data on PEI's diffusion coefficient and Stokes-Einstein radius at infinite dilution as well as its intrinsic viscosity. This suggests a strategy where probable chemical structures of synthetic PEIs can be inferred computationally using the developed algorithm. The coarse-graining methodology presented here can also be extended to other polymers.

Facile and selective separation of anthraquinones by alizarin-modified iron oxide magnetic nanoparticles

Anthraquinones are widely distributed in higher plants and possess broad biological activities. The conventional separation procedures for isolating anthraquinones from the plant crude extracts require multiple extraction, concentration, and column chromatography steps. In this study, we synthesized three alizarin (AZ)-modified Fe₃O₄ nanoparticles (Fe₃O₄@AZ, Fe₃O₄@SiO₂-AZ, and Fe₃O₄@SiO₂-PEI-AZ) by thermal solubilization method. Fe₃O₄@SiO₂-PEI-AZ showed strong magnetic responsiveness, high methanol/water dispersion, good recyclability, and high loading capacity for anthraquinones. To evaluate the feasibility of using Fe₃O₄@SiO₂-PEI-AZ for separating various aromatic compounds, we employed molecular dynamics simulations to predict the adsorption/desorption effects of PEI-AZ for various aromatic compounds in different methanol concentrations. The results showed that the anthraquinones could be efficiently separated from the monocyclic and bicyclic aromatic compounds by adjusting the methanol/water ratio. The Fe₃O₄@SiO₂-PEI-AZ nanoparticles were then used to separate the anthraquinones from the rhubarb extract. At 5% methanol, all the anthraquinones were adsorbed by the nanoparticles, thus allowing their separation from other components in the crude extract. Compared with the conventional separation methods, this adsorption method has the advantages of high adsorption specificity, simple operation, and solvent saving. This method sheds light on the future application of functionalized Fe₃O₄ magnetic nanoparticles to selectively separate desired components from complex plant and microbial crude extracts.

Characteristics, application and modeling of solid amine adsorbents for CO2 capture: A review

In recent years, global warming has become an important topic of public concern. As one of the most promising carbon capture technologies, solid amine adsorbents have received a lot of attention because of their high adsorption capacity, excellent selectivity, and low energy cost, which is committed to sustainable development. The preparation methods and support materials can influence the thermal stability and adsorption capacity of solid amine adsorbents. As a supporting material, it needs to meet the requirements of high pore volume and abundant hydroxyl groups. Industrial and biomass waste are expected to be a novel and cheap raw material source, contributing both carbon dioxide capture and waste recycling. The applied range of solid amine adsorbents has been widened from flue gas to biogas and ambient air, which require different research focuses, including strengthening the selectivity of CO₂ to CH₄ or separating CO₂ under the condition of the dilute concentration. Several kinetic or isotherm models have been adopted to describe the adsorption process of solid amine adsorbents, which select the pseudo-first order model, pseudo-second order model, and Langmuir isotherm model most commonly. Besides searching for novel materials from solid waste and widening the applicable gases, developing the dynamic adsorption and three-dimensional models can also be a promising direction to accelerate the development of this technology. The review has combed through the recent development and covered the shortages of previous review papers, expected to promote the industrial application of solid amine adsorbents.

Chitosan-based nanocomposites for removal of Cr(VI) and synthetic food colorants from wastewater

Current study aims to synthesize chitosan/polyvinyl alcohol (CS/PVA), poly(ethyleneimine), and Fe₃O₄ impregnated beads for co-removal of Cr(VI) and toxic azo-dyes from wastewater. The mesoporous PEI@AC@Fe₃O₄ exhibits magnetism and enhanced physisorption by higher specific-porosity (2.1 nm) from Cr(VI) radii (0.044 nm). Moreover, surface functional groups (-OH, -NH, -NH₂, -COOH etc.), especially amines enhance ionic bonding due to positive zeta potential. Hence, it is unique for anionic dyes removal under a wide pH range. It showed maximum adsorption capacity 98, 85.5, 85.8, and 91%, or 199.8, 148, 167, 176.5 mg g^-1 respectively for Cr(VI), tartrazine, sunset yellow, and erythrosine. Surface adsorption of Cr(VI) and its transition into Cr(III) was confirmed by EDX. Langmuir isotherm and pseudo-first-order kinetics best fit the adsorption of Cr(VI) and azo-dyes confirming their monolayer physisorption on adsorbent surface. Synthesized adsorbent examined in wastewater purification prototype for efficient removal of different simulated wastewaters confirms its potential for real-world applications.