Water-Dispersible Nanocatalysts with Engineered Structures: The New Generation of Nanomaterials for Energy-Efficient CO2 Capture

Catalytic Membrane Vacuum Regeneration: Enhancing Energy Efficiency and Renewable Compatibility in Direct Air Capture

Liquid-based CO2 direct air capture (DAC) is a pivotal technology for mitigating climate change. Energy-intensive CO2 desorption, high regeneration temperatures, and solvent degradation are key challenges. Here, low-temperature catalytic membrane vacuum regeneration (C-MVR) as a promising approach for sustainable and energy-efficient DAC is developed and evaluated. Noncatalytic experiments are conducted using three commercial membrane modules and four green amino acid salts under varying conditions (e.g., temperatures and flowrates). Based on CO2 transfer rates, ultra-thin dense composite membranes and aqueous potassium taurinate (TauK) are the most promising for MVR in DAC applications. For C-MVR trials, commercial ion-exchange resin improves CO2 desorption fluxes by up to 64.4% and reduces thermal energy requirements by up to 39.1%. TauK demonstrates the highest CO2 flux and lowest thermal energy consumption. Parametric analysis of catalyst performance for varying temperatures, catalyst amount, and solvent concentrations is also performed. To minimize any potential precipitation in TauK, potassium carbonate (K2CO3) is added, showing minimal impact on CO2 desorption kinetics and catalyst improvement. The findings of this study highlight the practical applicability of C-MVR using green amino acid salts as a sustainable approach to boost CO2 desorption rate and reduce thermal energy input.

Assembly of Silicate-Phenolic Network Coatings with Tunable Properties for Controlled Release of Small Molecules

Engineered coatings are pivotal for tailoring the surface properties and release profiles of materials for applications across diverse areas. However, developing robust coatings that can both encapsulate and controllably release cargo is challenging. Herein, a dynamic covalent coordination assembly strategy is used to engineer robust silicate-based coatings, termed silicate-phenolic networks (SPNs), using sodium metasilicate and phenolic ligands (tannic acid, gallic acid, pyrogallol). The coatings are pH-responsive (owing to the dynamic covalent bonding), and their hydrophobicity can be tuned upon their post-functionalization with hydrophobic gallates (propyl, octyl, lauryl gallates). The potential of the SPN coatings for the controlled release of small molecules, such as urea (a widely used fertilizer), is demonstrated-controlled release of urea in soil is achieved in response to different pHs (up to 7 days) and different hydrophobicity (up to 14 days). Furthermore, leveraging the presence of silicon (within the coating) and post-functionalization of the SPN coatings with metal ions (Fe3+, Cu2+, Zn2+) generates a multipurpose delivery system for the sustained release of micronutrient fertilizers, and silicon and metal ions, over 28 and 14 days, respectively. These SPN coatings have potential applications beyond agriculture, including nutrient delivery, separations, food packaging, and medical device fabrication.

Synergistic Catalysis of SO42-/TiO2-CNT for the CO2 Desorption Process with Low Energy Consumption

To address the issue of high energy consumption associated with monoethanolamine (MEA) regeneration in the CO2 capture process, solid acid catalysts have been widely investigated due to their performance in accelerating carbamate decomposition. The recently discovered carbon nanotube (CNT) catalyst presents efficient catalytic activity for bicarbonate decomposition. In this paper, bifunctional catalysts SO42-/TiO2-CNT (STC) were prepared, which could simultaneously catalyze carbamate and bicarbonate decomposition, and outstanding catalytic performance has been exhibited. STC significantly increased the CO2 desorption amount by 82.3% and decreased the relative heat duty by 46% compared to the MEA-CO2 solution without catalysts. The excellent stability of STC was confirmed by 15 cyclic absorption-desorption experiments, showing good practical feasibility for decreasing energy consumption in an industrial CO2 capture process. Furthermore, associated with the results of experimental characterization and theoretical calculations, the synergistic catalysis of STC catalysts via proton and charge transfer was proposed. This work demonstrated the potential of STC catalysts in improving the efficiency of amine regeneration processes and reducing energy consumption, contributing to the design of more effective and economical catalysts for carbon capture.

Facile Fabrication of Monodispersed Carbon Sphere: A Pathway Toward Energy-Efficient Direct Air Capture (DAC) Using Amino Acids

Direct removal of carbon dioxide (CO₂ ) from the atmosphere, known as direct air capture (DAC) is attracting worldwide attention as a negative emission technology to control atmospheric CO₂ concentrations. However, the energy-intensive nature of CO₂ absorption-desorption processes has restricted deployment of DAC operations. Catalytic solvent regeneration is an effective solution to tackle this issue by accelerating CO₂ desorption at lower regeneration temperatures. This work reports a one-step synthesis methodology to prepare monodispersed carbon nanospheres (MCSs) using trisodium citrate as a structure-directing agent with acidic sites. The assembly of citrate groups on the surface of MCSs enables consistent spherical growth morphology, reduces agglomeration and enhances water dispersibility. The functionalization-assisted synthesis produces uniform, hydrophilic nanospheres of 100-600 nm range. This work also demonstrates that the prepared MCSs can be further functionalized with strong Brønsted acid sites, providing high proton donation ability. Furthermore, the materials can be effectively used in a wide range of amino acid solutions to substantially accelerate CO₂ desorption (25.6% for potassium glycinate and 41.1% for potassium lysinate) in the DAC process. Considering the facile synthesis of acidic MCSs and their superior catalytic efficiency, these findings are expected to pave a new path for energy-efficient DAC.

Aqueous 2-Ethyl-4-methylimidazole Solution for Efficient CO2 Separation and Purification

Carbon capture and storage (CCS) technology is considered as one of the most effective short-term solutions in reducing atmospheric CO2 concentrations. A key of CCS technology is to seek the absorbent with low cost, fast absorption rate, and high stability. In this study, we show that 2-ethyl-4-methylimidazole is particularly suitable for efficient CO2 capture. The aqueous solution of 2-ethyl-4-methylimidazole displays a maximum CO2 molar absorption capacity of 1.0 mol∙mol−1 and the absorbed CO2 can be completely released through heating the solution at a relatively low temperature (<100 °C). Stability tests show that the aqueous system is quite stable, with less than 10% loss of the molar absorption capacity after eight absorption–desorption cycles. Time-related in-situ attenuated total reflection infrared absorption spectroscopy and 13C nuclear magnetic resonance spectroscopy studies reveal that the intermediates are HCO3− and H2CO3 in the process of CO2 absorption–desorption. These intermediates are easily decomposed, which are responsible for the low CO2 desorption temperature and high desorption efficiency of the system. Moreover, the aqueous solution of 2-ethyl-4-methylimidazole is able to separate and purify CO2 from flue gas and even ambient air. Consequently, 2-ethyl-4-methylimidazole is a promising low-cost CO2 absorbent for industrial implementation.