Carbon Capture Membranes Based on Amorphous Polyether Nanofilms Enabled by Thickness Confinement and Interfacial Engineering

Nanofilm Composite Membranes of Bottlebrush Poly(1,3-Dioxolane) Plasticized by Poly(Ethylene Glycol) for CO2/N2 Separation

Poly(1,3-dioxolane) has emerged as a leading membrane material for post-combustion CO2 capture due to its high ether oxygen content and strong affinity toward CO2. However, they are often cross-linked to inhibit crystallization, which makes them impossible to fabricate into industrial thin-film composite membranes. Herein, soluble and high molecular weight bottlebrush polymers (bPDXLA) are synthesized using reversible addition-fragmentation chain transfer polymerization and demonstrate the feasibility of fabricating nanofilm (≈100 nm) composite membranes (NCMs). Furthermore, bPDXLA can be plasticized using a miscible additive of poly(ethylene glycol) dimethyl ether (PEGDME) to improve CO2 permeability while retaining good CO2/N2 selectivity. For example, adding 20 mass% PEGDME improves CO2 permeance from 930 to 1300 GPU and decreases CO2/N2 selectivity from 74 to 53 at 25 °C; the membrane exhibits stable separation performance competitive with state-of-the-art commercial membranes. This work unveils a practical approach to designing uncross-linked, highly polar polymers for practical membrane gas separation and highlights a facile way to enhance performance by incorporating miscible plasticizers using industrial manufacturing processes.

Polymer-MOF Network Enabling Ultrathin Coating for Post-Combustion Carbon Capture

Permeance-selectivity trade-off and high temperature resilience are key challenges in development of membranes for post-combustion carbon capture. While mixed matrix membranes (MMMs) consisting of polymers and metal-organic frameworks (MOFs) offer the potential to address the challenges, they are limited by the low loading of MOFs in the thin film layer. Herein, we propose an inverse synthesis strategy to form polymer-MOF networks by copolymerizing monomers with functionalized UiO-66 nanoparticles. This process yields a finely dispersed, easily processable solution, enabling defect-free, thin polymer-MOF coatings with up to 40 wt % MOF loading within the polyethylene oxide-based polymers on polyacrylonitrile supports. The membrane with 40 wt % MOF demonstrated a 212 % increment in CO2 permeance at 25 °C and maintained a selectivity of 20 at 60 °C, which is attributed to the stable diffusivity selectivity of MOFs at high temperature. Furthermore, the membrane was evaluated with mixed gas and 83 % relative humidity (RH) at 60 °C, achieving a CO2 permeance up to 2793 GPU and a CO2/N2 selectivity of 21.6. This work offers insights into the design of practical mixed matrix membranes, which not only paves the way towards energy efficient carbon capture from flue gas, but also provides more possibilities for other applications.

Template-Assisted Growth of High-Quality α-Phase FAPbI3 Crystals in Perovskite Solar Cells Using Thiol-Functionalized MoS2 Nanosheets

Formamidinium lead iodide (FAPI) has gained attention for hybrid perovskite solar cell (PSC) applications due to its enhanced stability and narrow bandgap. However, a significant challenge remains in inducing and stabilizing the elusive perovskite "black phase"─photoactive cubic α-FAPI─as the relatively bulky FA+ cations tend to favor the thermodynamically stable nonphotoactive "yellow phase". In this study, we present a templated growth strategy employing thiol-functionalized MoS2 nanosheets as templates. By introduction of 3-mercaptopropionic acid (MPA)-functionalized MoS2 as a growth template, precise control over crystal formation was achieved, favoring the growth of high-quality α-FAPI films. These advanced templated films exhibited substantial improvements in charge transport properties, efficient light absorption, and enhanced charge extraction. As a result, the PSCs achieved a significantly enhanced power conversion efficiency (PCE) compared to the nontemplated control device, increasing from 20.6 to 22.5%. The MoS2-incorporated device also demonstrated excellent shelf stability, maintaining 91% of the initial PCE even after 1600 h of storage without device encapsulation.

Insect tracheal systems as inspiration for carbon dioxide capture systems

Membrane technology advancements within the past twenty years have provided a new perspective on environmentalism as engineers design membranes to separate greenhouse gases from the environment. Several scientific journals have published articles of experimental evidence quantifying carbon dioxide (CO2), a common greenhouse gas, separation using membrane technology and ranking them against one another. On the other hand, natural systems such as the respiratory system of mammals also accomplish transmembrane transport of CO2. However, to our knowledge, a comparison of these natural organic systems with engineered membranes has not yet been accomplished. The tracheal respiratory systems of insects transport CO2at the highest rates in the animal kingdom. Therefore, this work compares engineered membranes to the tracheal systems of insects by quantitatively comparing greenhouse gas conductance rates. We demonstrate that on a per unit volume basis, locusts can transport CO2approximately ∼100 times more effectively than the best current engineered systems. Given the same temperature conditions, insect tracheal systems transport CO2three orders of magnitude faster on average. Miniaturization of CO2capture systems based on insect tracheal system design has great potential for reducing cost and improving the capacities of industrial CO2capture.

Scalable and Highly Porous Membrane Adsorbents for Direct Air Capture of CO2

Direct air capture (DAC) of CO2 is a carbon-negative technology to mitigate carbon emissions, and it requires low-cost sorbents with high CO2 sorption capacity that can be easily manufactured on a large scale. In this work, we develop highly porous membrane adsorbents comprising branched polyethylenimine (PEI) impregnated in low-cost, porous Solupor supports. The effect of the PEI molecular mass and loading on the physical properties of the adsorbents is evaluated, including porosity, degradation temperature, glass transition temperature, and CO2 permeance. CO2 capture from simulated air containing 400 ppm of CO2 in these sorbents is thoroughly investigated as a function of temperature and relative humidity (RH). Polymer dynamics was examined using differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS), showing that CO2 sorption is limited by its diffusion in these PEI-based sorbents. A membrane adsorbent containing 48 mass% PEI (800 Da) with a porosity of 72% exhibits a CO2 sorption capacity of 1.2 mmol/g at 25 °C and RH of 30%, comparable to the state-of-the-art adsorbents. Multicycles of sorption and desorption were performed to determine their regenerability, stability, and potential for practical applications.

Low-Loading Mixed Matrix Materials: Fractal-Like Structure and Peculiarly Enhanced Gas Permeability

Mixed matrix materials (MMMs) containing metal-organic framework (MOF) nanoparticles are attractive for membrane carbon capture. Particularly, adding <5 mass % MOFs in polymers dramatically increased gas permeability, far surpassing the Maxwell model's prediction. However, no sound mechanisms have been offered to explain this unusual low-loading phenomenon. Herein, we design an ideal series of MMMs containing polyethers (one of the leading polymers for CO2/N2 separation) and discrete metal-organic polyhedra (MOPs) with cage sizes of 2-5 nm. Adding 3 mass % MOP-3 in a polyether increases the CO2 permeability by 100% from 510 to 1000 Barrer at 35 °C because of the increased gas diffusivity. No discernible changes in typical physical properties governing gas transport properties are detected, such as glass transition temperature, fractional free volume, d-spacing, etc. We hypothesize that this behavior is attributed to fractal-like networks formed by highly porous MOPs, and for the first time, we validate this hypothesis using small-angle X-ray scattering analysis.