CO2 Diffusion Research Articles

Natural carbonation process in cement paste particles in different relative humidities

Finely ground hardened cement pastes (hcp) under 75 μm were carbonated at varying relative humidities (23–95 % RH) to determine the carbonation rate that minimized CO2 diffusion in the bulk paste. The amounts of portlandite (CH) and calcium carbonate (CC) polymorphs were quantified, and the decalcification and decomposition of C-A-S-H were analyzed using TGA, XRD, mass balance calculation, FTIR, and 29Si MAS NMR spectroscopy. A higher RH accelerated the reaction rate, and CH dissolution stopped midway at 58 % RH or below because of the loss of connectivity with the pore solution in the CC shell around CH. The precipitated CC phase included calcite at high RH, whereas all three polymorphs formed at 58 % or lower RH; amorphous CC were detected at low RH. The decalcification and decomposition of C-A-S-H were observed at 45 % or higher RH; it was rarely carbonated at 33 % or lower RH.

Experiment and numerical investigation on flow characteristics and near-field structure of dense phase CO2 pipeline leakage

Accidental leakage of high-pressure CO2 is not only a safety hazard, but also may have a great negative impact on the operating efficiency of some circulating systems. To analyze the accident hazards and improve the ability to predict the transient release flow behavior of high-pressure CO2, a set of small pipeline leakage test equipment was built. The changes of near-field pressure, temperature, and jet structure under different upstream pressure (6–12 MPa), temperature (280–300 K) and orifice diameter (5 mm, 10 mm, 20 mm, 40 mm) were analyzed. Secondly, as a supplement to the experiment, the near-field CO2 gas phase distribution and critical mass flow were studied by numerical model. The results show that the near field pressure peak is negatively correlated with the initial upstream pressure, but positively correlated with the release diameter. In addition, the increase of upstream initial pressure and release diameter will lead to the increase of radial development range of near-field jet cloud. Based on the numerical results, an empirical correlation of critical mass flow based on upstream initial conditions and RHP is established. The error between the experimental data and the predicted value within the range of the correlation is within ± 18%. The research data and results can help to enhance the understanding of the rapid release characteristics of high-pressure CO2 in the near field region and provide a basis for the study of CO2 diffusion in the far field region and the leakage risk assessment.

Exploring the responses of crop photosynthesis to CO2 elevation at the molecular, physiological, and morphological levels toward increasing crop production

Exploring the impact of elevated CO2 on photosynthesis is vital for understanding plant responses to climate change. In C3 plants, elevated CO2 concentrations generally enhance CO2 assimilation by increasing chloroplast CO2 concentration. However, the underlying mechanisms are complex since photosynthesis involves multiple physiological processes operating at different time scales and varying among plant species. In this review, we focused on the responses of key photosynthetic processes in crop, including CO2 diffusion conductances such as stomatal conductance (gs), mesophyll conductance (gm), photochemical reactions, the Calvin-Benson cycle, and related metabolic pathways. Short-term exposure to elevated CO2 often decreases gs and gm while increasing the electron transport rate. However, long-term exposure to elevated CO2 can decrease photosynthetic capacity due to coordinated downregulation of multiple processes, particularly when the sink‒source ratio declines. To enhance plant productivity under elevated CO2, it is crucial to maintain or enhance sink activity and understand the CO2 response mechanisms at the molecular, physiological, and morphological levels. This review provides an update on the short- and long-term responses of gs, gm, electron transport system, and carbon assimilation metabolism to elevated CO2. Furthermore, it offers a perspective on improving crop production in the future with elevated CO2 levels.

Positron emission tomography dataset of [11C]carbon dioxide storage in coal for geo-sequestration application

Positron Emission Tomography (PET) imaging has demonstrated its capability in providing time-lapse fluid flow visualisation for improving the understanding of flow properties of geologic media. To investigate the process of CO2 geo-sequestration using PET imaging technology, [11C]CO2 is the most optimal and direct radiotracer. However, it has not been extensively used due to the short half-life of Carbon-11 (20.4 minutes). In this work, a novel laboratory protocol is developed to use [11C]CO2 as radiolabelled tracer to visualise and quantify in-situ CO2 adsorption, spreading, diffusion, and advection flow in coal. This protocol consists of generation and delivering of [11C]CO2, lab-based PET scanning, subsequent micro-CT scanning, and data processing. The lab-based PET scanning setup integrates in-situ core flooding tests with PET scanning. The real-time PET images are acquired under different storage conditions, including early gas production stage, depleted stage, and late storage stage. These datasets can be used to study across-scale theoretical and experimental study of CO2 flow behaviour in coal with the application to CO2 geo-sequestration.

Potential of nonionic polyether surfactant-assisted CO2 huff-n-puff for enhanced oil recovery and CO2 storage in ultra-low permeability unconventional reservoirs

Sequestering CO2 in oil reservoirs using CO2 huff-n-puff technology while maximizing oil recovery is critical for the efficient development of shale/tight reservoirs. In this work, intrinsic reasons for the limited EOR efficiency of CO2 huff-n-puff technology and the potential of a nonionic polyether surfactant C4(PO)3-assisted CO2 huff-n-puff process in further enhancing oil recovery and increasing CO2 storage capability in shale/tight reservoirs were investigated by physical modeling experiments combined with nuclear magnetic resonance techniques. The EOR performance, the mobilization of oil from different pore size ranges, and CO2 storage capability were analyzed in the CO2 huff-n-puff and CO2–C4(PO)3 mixed fluid huff-n-puff experiments. The results showed that the EOR efficiency of CO2 huff-n-puff was limited by the rapidly declining cyclic recovery and the meager recoveries from micropores and deep matrix regions. Applying CO2–C4(PO)3 mixed fluid with a surfactant concentration of 0.5 wt% resulted in a 9.7%–13.2% increase in the cumulative matrix oil recovery relative to CO2 under the same huff-n-puff cycles. Moreover, relative increases in oil recoveries from micropores, mesopores, and macropores reached 113.4%–142.2%, 14.2%–41.1%, and 0.8%–17.6%, respectively. When CO2 no longer enhanced production after the 4–5 huff-n-puff cycles, approximately 14%–19% of the residual oil was effectively recovered by applying the C4(PO)3-assisted CO2 huff-n-puff stimulation. Simultaneously, the ultimate CO2 storage capability in the examined cores increased by 22.3%–32.2% after the CO2–C4(PO)3 mixed fluid huff-n-puff process. The enhancement of CO2 injection and diffusion capabilities induced by the CO2–C4(PO)3 mixed fluid improved CO2 sweep and oil displacement efficiencies in shale/tight reservoirs, leading to a significant increase in the oil mobilization within micropores and an extended effective stimulation cycle, as well as achieving a higher CO2 storage capability. The increase of CO2 injection and diffusion amounts induced by nonionic polyether surfactants during the huff-n-puff process was attributed to the reduction in capillary resistance caused by the lowered CO2–oil interfacial tension and the increase of dissolved CO2 in oil resulting from the improved CO2–oil miscibility. This paper presents new strategies for advancing the sustainable and efficient development of shale/tight reservoirs with highly developed nanopores.

The influence of additive MgO and its content on the carbonation resistance of alkali-activated slag concrete with different activators

The influence of additive MgO and its content on both the compressive strength and carbonation depth of alkali-activated slag concrete (AASC) was investigated under an accelerated carbonation environment. Furthermore, the modification mechanism of MgO on the carbonation resistance of AASC was explored by multiple analytical techniques. Results showed that the incorporation of MgO effectively enhanced the post-carbonation compressive strength and diminished the carbonation depth of concrete. As the MgO content increased, there was a gradual reduction in carbonation depth. The incorporation of MgO promotes the hydration of slag, altering the Al environment, and promoting the formation of C-S-H and Mg-Al hydrotalcite phases. Moreover, the addition of MgO resulted in the emergence of magnesium carbonate and calcium magnesium carbonate in the carbonation products, which filled the pores and prevented the further diffusion of CO2 into the interior. In addition, the improvement effects are more pronounced in the water glass system compared to the NaOH system.

Al2O3 atomic layer deposition on a porous matrix of carbon fibers (FiberForm) for oxidation resistance

Atomic layer deposition (ALD) was used to coat a porous matrix of carbon fibers known as FiberForm with Al2O3 to improve oxidation resistance. Static trimethylaluminum (TMA) and H2O exposures for Al2O3 ALD were used to obtain the uniform coating of this high porosity material. The carbon surfaces were initially functionalized for Al2O3 ALD by exposure to sequential exposures of nitrogen dioxide and TMA. A gravimetric model was developed to predict the mass gain per cycle under conditions when the ALD reactions reached saturation during each reactant exposure. The uniformity of the Al2O3 ALD coating on FiberForm was confirmed by scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) analysis. The SEM, EDS, and gravimetric models were all consistent with a uniform Al2O3 ALD coating on the porous carbon fiber network when the ALD reactions reached saturation on the entire surface area. In contrast, the profile of the Al2O3 ALD coating on the FiberForm was also characterized using undersaturation conditions when the ALD reactions did not reach saturation throughout the FiberForm sample. Based on comparisons with results from models for ALD in porous substrates, these Al2O3 coverage profiles were consistent with diffusion-limited Al2O3 ALD. Oxidation of the FiberForm and the Al2O3 ALD-coated FiberForm was also investigated by thermogravimetric analysis (TGA). TGA revealed that a 50 nm thick Al2O3 coating deposited using 400 Al2O3 ALD cycles enhanced the oxidation resistance. The Al2O3 ALD coating increased the oxidation onset temperature by ∼200 °C from 500 to 700 °C. The oxidation of the FiberForm removed carbon and left the Al2O3 ALD coating behind as a white “skeleton” that preserved the shape of the original FiberForm sample. The Al2O3 ALD coating also decreased the oxidation rate of the FiberForm by ∼30%. The oxidation rate of the Al2O3 ALD-coated FiberForm samples was constant and independent of the thickness of the Al2O3 ALD coating. This behavior suggested that the oxidation is dependent on the competing O2 diffusion into the FiberForm and CO2 diffusion out of the FiberForm.

Carbonation of a Synthetic CAF Compound by CO2 Absorption and Its Effect on Cement Matrix

In the field of construction materials, the development of fundamental technologies to reduce energy consumption and CO2 emissions, such as manufacturing process improvement and the expanded use of alternative materials, is required. Technologies for effectively reducing energy consumption and improving CO2 absorption and reduction that can meet domestic greenhouse gas reduction targets are also required. In this study, calcium–aluminate–ferrite (CAF), a ternary system of CaO·Al2O3·Fe2O3, was sintered at a low temperature (1100 °C) to examine the possibility of CO2 adsorption, and excellent CO2 absorption performance was confirmed, as the calcite content was found to be 11.01% after 3 h of the reaction between synthetic CAF (SCAF) and CO2. In addition, the physical and carbonation characteristics were investigated with respect to the SCAF substitution rate for cement (10%, 30%, 50%, 70%, and 100%). It was found that SCAF 10% developed a compressive strength similar to that of ordinary Portland cement (OPC 100%), but the compressive strength tended to decrease as the SCAF substitution rate increased. An increase in the SCAF substitution rate led to the rapid penetration of CO2, and carbonation was observed in all the specimens after 7 days. As carbonation time increased, the CO2 diffusion coefficient tended to decrease. This is because the diffusion of CO2 in the cement matrix follows the semi-infinite model of Fick’s second law. SCAF can contribute to reduced energy consumption and CO2 emissions because of the low-temperature sintering and can absorb and fix CO2 when a certain amount is substituted.

Performance in microfluidic electrochemical cell with gradient or double-layers porous electrode for CO2 diffusion

To obtain better electrical behavior, the linear or double-layers porous electrode is set in microfluidic electrochemical cell for CO2 diffusion, which couples Tafel's law and Ohm's law with the flow equation and species transport equation for numerical calculations. This research analyzes the effects of linear or double-layer porosity, the thickness of double-layer porosity, and electrode structure in the electrode on current density, CO2 conversion, and Faraday efficiency under different working conditions. The higher current density and CO2 conversion occur in the case with smaller porosity in the electrode due to more reactive sites, and poor gas transport is observed simultaneously. Optimizing linear or double-layers porosity distribution results in higher current density, CO2 conversion, and Faraday efficiency. The Faraday efficiency can reach 91.54% in the case of stepwise increasing porosity from 0.3 to 0.9 in the electrode. Poor electrical behavior occurs as linear increasing porosity compared to stepwise porosity due to different porosity distributions, and the opposite is the case for decreasing linear porosity. Setting the double-layer porosity along the electrode thickness direction results in larger Faraday efficiency as a thickness ratio of 1:1 and larger current density and CO2 conversion as a thickness ratio of 4:1 in the case of porosity from 0.3 to 0.9. Better electrochemical behavior occurs with electrode thickness to length ratio of 10–20 and the CO2 gas channel to electrode thickness ratio of 1:1–4:1, and optimized electrode porosities tend to show higher Faraday efficiencies during electrode structural changes.

Divergences in leaf CO2 diffusion conductance and water use efficiency of soybean coping with water stress and its interaction with N addition

Drought and nitrogen (N) additions have been shown to affect plant photosynthesis, but the effect of their interaction on CO2 diffusion conductance (i.e., stomatal conductance, gsc, mesophyll conductance, gm) and water use efficiency (WUE) at the leaf level (i.e., instantaneous water use efficiency, WUEins; intrinsic water use efficiency, WUEint) has rarely been reported. Herein, we examined the interactive effects of drought and N addition on gsc and gm and WUE (i.e., WUEins and WUEint) in soybean (Glycine max (Linn.) Merr.) and analysed the interaction mechanisms mitigating water stress based on leaf anatomy and molecular activity. Drought decreased gsc,gm and WUEins, but N addition had a positive interactive effect with water stress on leaf physiological traits. The variables gsc, gm and WUEins were significantly increased by the additions of 7.5 and 15.0 g urea m−2 under moderate water stress (MW) conditions (P < 0.05), but they decreased under the interaction effect of SW and N addition. The decreased Tcw and increased Sm and Sc under the water stress × N addition interaction positively affected gm, and the increased SS dominated the gsc increase. In addition, these positive effects were further enhanced with increased AQP, CA and Rubisco activities and a decrease in the ABA content. Accordingly, moderate soil N additions of 7.5 and 15.0 g urea m−2 greatly mitigated the negative effects of droughts, especially the MW effects, by enhancing CO2 diffusion conductance and WUE.

Enhancing CO diffusion for selective acetate production via CO reduction on copper catalyst

The productivity of multi-carbon products in electrocatalytic CO reduction is greatly influenced by the local concentration of CO. Herein, we present a facile strategy for modulating the local concentration of CO under atmospheric pressure via polymer coating, which enables selective, active and stable production of acetate on a Cu model-catalyst. Specifically, we coat the Cu-catalyst with a fluorinated polymer, forming an optimized gas-involving reaction interface. This approach enhances the CO diffusion to catalyst surfaces and increases the hydrophobicity of the catalyst layer, resulting in enhanced acetate selectivity of over 50% with a high partial current density of −0.65 A cm−2 on Cu-catalyst. This represents an over 3 folders of enhancement compared to the pristine Cu-catalyst. Furthermore, this optimized reaction interface led to a stable COR electrolysis over a duration of 70 h. Our strategy offers valuable insights for designing efficient catalytic interface in various electrochemical reactions that involve gas diffusion.

First principle-based rate equation theory for the carbonation kinetics of CaO with CO2 in calcium looping

Calcium oxide (CaO), a CO2 sorbent and key ingredient in the process of making cement, exhibits excellent potential for carbon capture, utilization, and storage (CCUS) applications through calcium looping and integrated carbon capture and utilization, owing to its outstanding kinetic properties and high recyclability. From a fundamental standpoint, it is important to establish a comprehensive and precise carbonation kinetic model for CaO. In the present study, a density functional theory (DFT)-based rate equation was developed to predict the gas–solid reaction kinetics of CaO carbonation with CO2 in calcium looping. The reaction pathway of CaO carbonation, including surface reactions and structural transformations, was obtained by a transition state search of DFT calculations, and the transition state theory was used to calculate the reaction rate constants. The nucleation model was implemented in the mean-field surface reaction model to describe the nucleation of the CaCO3 product at the gas–solid interface. A grain model was developed to couple the surface reaction and CO2 diffusion through the product layer. The developed theory was validated using a wide range of experimental data, and the negative activation energy of CaO carbonation close to equilibrium was accurately predicted. The developed first principle-based rate equation provides a detailed theoretical framework for predicting CaO performance and optimizing the microstructure of Ca-based sorbents.

Long Time CO2 Storage Under Ambient Conditions in Isolated Voids of a Porous Coordination Network Facilitated by the "Magic Door" Mechanism.

A coordination network containing isolated pores without interconnecting channels is prepared from a tetrahedral ligand and copper(I) iodide. Despite the lack of accessibility, CO2 is selectively adsorbed into these pores at 298K and then retained for more than one week while exposed to the atmosphere. The CO2 adsorption energy and diffusion mechanism throughout the network are simulated using Matlantis, which helps to rationalize the experimental results. CO2 enters the isolated voids through transient channels, termed "magic doors", which can momentarily appear within the structure. Once inside the voids, CO2 remains locked in limiting its escape. This mechanism is facilitated by the flexibility of organic ligands and the pivot motion of cluster units. In situ powder X-ray diffraction revealed that the crystal structure change is negligible before and after CO2 capture, unlike gate-opening coordination networks. The uncovered CO2 sorption and retention ability paves the way for the design of sorbents based on isolated voids.

Synergistic promotions of K doping on CO2 capture and in situ conversion

AbstractThe integrated CO2 capture and conversion (iCCC) technology has been recognized as a promising strategy for upcycling the emitted CO2 into artificial carbon sequestration but still demands highly efficient dual functional materials (DFMs). We develop an efficient iCCC process of the integrated lithium‐looping (LiL) and reverse water gas shift reaction through deeply understanding K doping in the novel Kx‐Li4SiO4@Niy DFMs. The appropriate K doping enables the fast diffusion of CO2 and H2 into the bulk DFMs through forming LiKCO3 surface eutectic layer as well as strongly interacts with catalyst Ni to generate new medium basic sites for synergistic promotions of CO2 capture and in situ conversion. More importantly, after the pelletization, the LP‐K0.2‐Li4SiO4@Ni10 DFM (20–40 mesh) avoids the agglomeration and achieves an excellent and stable iCCC cycle performance, with CO2 capture capacity of 3.8 mmol/g, CO2 conversion efficiency of 90%, and CO selectivity close to 100% at 550°C in one fixed‐bed column.

Ultra-strong and ductile amorphous-crystalline Ti-Zr-Hf-Nb-Ta/Co-Ni-V nanolaminate thin films

Films with a combination of high strength, large ductility, and high thermodynamic stability are always pursued for industrial applications. Here, we prepared the amorphous-crystalline Ti-Zr-Hf-Nb-Ta/Co-Ni-V nanolaminate with hardness and yield strength of 7.4 GPa and 3.8 GPa, and large deformability of ∼70%. The ductility is attributed to two aspects. One is the Ti-Zr-Hf-Nb-Ta/Co-Ni-V layer interfaces acted as barriers to obstruct the propagation of nanocracks at the heavily deformed stage. Another is that amorphous layers acted as dislocation sinks promoting the dislocations to get annihilated when undergoing plastic flow, maintaining the plastic deformability of the crystalline layers. After annealing at 873 K for 1 h, the Co-Ni-V layer changes to a V-rich amorphous layer with minor nanocrystals, while the Ti-Zr-Hf-Nb-Ta layer transforms to a Ni-rich amorphous layer, due to the diffusion of Co and Ni. This chemical partitioning and consequent amorphization lead to the enhanced hardness and yield strength of 9.4 GPa and 4.5 GPa, but low ductility. In addition, the microstructure and mechanical properties of the nanolaminate can be further optimized by adjusting substrate temperature, layer thickness, and annealing process. The findings provide a new avenue for improving the mechanical properties of nanolaminates in a controllable manner.

Design of ultrathin cross-linked poly(ethylene oxide) selective layer for high-performance CO2 capture

Cross-linked poly(ethylene oxide) (PEO) is a highly promising membrane material for CO2 capture, as it allows fast and selective CO2 transport. However, the facile fabrication of an ultrathin cross-linked PEO selective layer for thin-film composite (TFC) membrane to achieve high CO2 separation performance remains challenging. To address this issue, we reported the design of a soluble high-permeability cross-linked PEO polymer and the fabrication of it into an ultrathin CO2-selective layer through a simple coating technique. The as-synthesized cross-linked PEO polymer contains abundant poly(dimethylsiloxane) (PDMS) segments, leading to highly improved free volume and affinity towards CO2, which result in high CO2 diffusivity, solubility, and consequently high CO2 permeability (528 Barrer). TFC membranes with an ultrathin selective layer (∼128 nm) were successfully fabricated using the PEO polymer, leading to superior CO2 capture performance (CO2 permeance = 2650 GPU, CO2/N2 = 20) for CO2/N2 mixture separation in a long-term stability test, exceeding the target performance for carbon capture. Given their high separation performance, excellent stability, and scalable fabrication route, our PEO-based membranes hold great promise for post-combustion CO2 capture.

CO2 diffusion in shale oil based on molecular simulation and pore network model

Field practices show that CO2 huff and puff can effectively promote the exploitation of shale resources, and CO2 diffusion is noteworthy as a crucial mechanism of enhanced oil recovery (EOR). Understanding the confinement effect on CO2 diffusion is imperative to accurately characterize the fluid transport in shale nanopores and further upscaling. We integrate molecular simulation and pore network model (PNM) to study CO2 diffusion behavior at the nanoscale and pore scale. We first explored CO2 diffusion into heptane in kerogen and calcite pores using molecular dynamics, and analyzed the impacts of pore size, molar fraction, temperature, and pore pressure on the confined Fick diffusion. Based on the molecular simulation results, a model characterizing the ratio of the confined diffusion coefficient to that of the bulk phase is constructed for further upscaling. Based on the PNM containing organic and inorganic pores, we established a model to simulate the CO2 diffusion at the pore scale by introducing the characterization model at the nanoscale into the convective diffusion equation. Considering the microscale effects and the influence of CO2 concentration on diffusion is beneficial to improve the simulation accuracy at the pore scale. The estimated CO2 diffusion coefficients are in good agreement with the experimental results. This work provides better insight into CO2 diffusion behavior in shale oil, which can afford effective support for industrial exploitation and the breakthrough of the technical bottleneck of shale oil production.

High-temperature oxidation-wear properties of Ru-doped cermet

The oxidation-wear properties of WC-Co cermet at high temperatures were remarkably enhanced by Ru addition for increasing life expectancy of cermet tools in high-speed cutting processes. The oxidation-resistant mechanisms of Co with substitutional Ru were disclosed by calculating the energy barrier for oxygen adsorption and diffusion in Co with and without Ru doping. Particularly, the oxidation of WC was effectively inhibited due to the suppression of reactions between cobalt oxides and WO3. Thus less cracking occurred in the Ru-containing cermet as its tribolayer contained fewer oxides with low shear resistance, which in turn protected the subsurface materials from further oxidation.

The Structure-Function Relationship of Branched Polyethylenimine Impregnated over Mesoporous Carbon Aerogels: An In-Depth Thermogravimetric Insight.

We present a comprehensive thermogravimetric analysis (TGA) of polyethylenimine (PEI)-impregnated resorcinol-formaldehyde (RF) aerogels. While numerous studies focus on PEI-impregnated SBA, RF materials have been less examined, despite their interest and specificities. As most articles on PEI-impregnated porous materials follow typical experimental methods defined for SBA, particularities of RF-PEI materials could remain unheeded. The design of nonisothermal TGA protocols, completed with nitrogen isotherms, based on the systematic filling of the matrix delivers a fundamental understanding of the relationship between the structure and function. This study demonstrates (i) the competition between the matrix and PEI for CO2-physisorption (φ) and CO2-chemisorption (χ), (ii) the hysteresis ([Formula: see text]) of CO2 capture at low temperature attributed to the kinetic (K) hindrance of CO2 diffusion (D) through PEI film/plugs limiting the chemisorption, and (iii) the thermodynamic (θ) equilibrium limiting the capture at high temperature. At variance with SBA-PEI materials, the first layers of PEI in RF are readily available for CO2 capture given that this matrix does not covalently bind PEI as SBA. A facile method allows the discrimination between physi- and chemisorption, exhibiting how the former decreases with PEI coverage. The CO2 capture hysteresis, while seldom introduced or discussed, underlines that the commonly accepted operating temperature of the "maximum capture" is based on an incomplete experiment. Through isotherm adsorption analysis, we correlate the evolution of this maximum to the morphological distribution of PEI. This contribution highlights the specificities of RF-PEI and the advantages of our TGA protocol in understanding the structure/function relationship of this kind of material by avoiding the typical direct applications of SBA-specific protocols. The method is straightforward, does not need large-scale facilities, and is applicable to other materials. Its easiness and rapidness are suited to high-volume studies, befitting for the comprehensive evaluation of interacting factors such as the matrix's nature, pore size, and PEI weight.

Direct air CO2 capture using coal fly ash derived SBA-15 supported polyethylenimine

Designing an amine modified silica derived from coal fly ash (CFA) towards direct air CO2 capture (DAC) provides an economic way to manage increasing atmospheric CO2 concentration utilizing solid wastes. In this work, rod-like SBA-15 (SBA-15-R) and wheat-like SBA-15 (SBA-15-W) with distinct pore lengths are synthesized from CFA by controlling the synthesis conditions and then modified by PEI via the wet impregnation method. Their CO2 adsorption behaviors under sub-ambient conditions are investigated to explore their feasibility under aggressive conditions. The adsorbents with various silica morphologies exhibit distinctive CO2 adsorption performance under ambient and sub-ambient conditions. At 35°C under dry conditions, the CO2 adsorption capacity increases with amine loading. The CO2 adsorption capacity (qe) of SBA-15-W-PEI with long channels reaches the highest qe of 1.92 mmol/g with 70 wt.% PEI loading due to a large amount of strong chemisorption sites. Under the sub-ambient conditions (-20°C, 400 ppm), SBA-15-R-PEI30 with short channels having weaker CO2 diffusion resistance exhibits promising CO2 uptake of 0.83 mmol/g. These findings indicate that the ultra-dilute CO2 adsorption at ambient temperature requires an adsorbent with large amounts of adsorption sites, whereas the adsorbents for cold temperature application should reconcile amine loading with CO2 diffusion resistance inside pores. The co-adsorption of H2O and CO2 significantly improves CO2 capacity from 0.83 mmol/g and 1.92 mmol/g to 1.81 mmol/g and 3.48 mmol/g for SBA-15-R-PEI30 (-20°C, 400 ppm) and SBA-15-W-PEI70 (35°C, 400 ppm), respectively. Furthermore, the CFA derived SBA-15-PEI shows good cyclic stability during five consecutive TSA cycles. Preparing the amine silica adsorbents from coal fly ash potentially reduces the adsorbent cost of DAC devices. Moreover, the systematic exploration of amine silica adsorbents at a wide range of temperatures guides the design of high-performance CO2 adsorbents employed under various climatic conditions.