Molecular Layer Deposition-Modified 5A Zeolite for Highly Efficient CO2 Capture

Molecular recognition with resolution below 0.2 angstroms through thermoregulatory oscillations in covalent organic frameworks

Crystalline materials with uniform molecular-sized pores are desirable for a broad range of applications, such as sensors, catalysis, and separations. However, it is challenging to tune the pore size of a single material continuously and to reversibly distinguish small molecules (below 4 angstroms). We synthesized a series of ionic covalent organic frameworks using a tetraphenoxyborate linkage that maintains meticulous synergy between structural rigidity and local flexibility to achieve continuous and reversible (100 thermal cycles) tunability of "dynamic pores" between 2.9 and 4.0 angstroms, with resolution below 0.2 angstroms. This results from temperature-regulated, gradual amplitude change of high-frequency linker oscillations. These thermoelastic apertures selectively block larger molecules over marginally smaller ones, demonstrating size-based molecular recognition and the potential for separating challenging gas mixtures such as oxygen/nitrogen and nitrogen/methane.

Atomic/molecular layer deposition strategies for enhanced CO2 capture, utilisation and storage materials

Elevated levels of carbon dioxide (CO2) in the atmosphere and the diminishing reserves of fossil fuels have raised profound concerns regarding the resulting consequences of global climate change and the future supply of energy. Hence, the reduction and transformation of CO2 not only mitigates environmental pollution but also generates value-added chemicals, providing a dual remedy to address both energy and environmental challenges. Despite notable advancements, the low conversion efficiency of CO2 remains a major obstacle, largely attributed to its inert chemical nature. It is imperative to engineer catalysts/materials that exhibit high conversion efficiency, selectivity, and stability for CO2 transformation. With unparalleled precision at the atomic level, atomic layer deposition (ALD) and molecular layer deposition (MLD) methods utilize various strategies, including ultrathin modification, overcoating, interlayer coating, area-selective deposition, template-assisted deposition, and sacrificial-layer-assisted deposition, to synthesize numerous novel metal-based materials with diverse structures. These materials, functioning as active materials, passive materials or modifiers, have contributed to the enhancement of catalytic activity, selectivity, and stability, effectively addressing the challenges linked to CO2 transformation. Herein, this review focuses on ALD and MLD's role in fabricating materials for electro-, photo-, photoelectro-, and thermal catalytic CO2 reduction, CO2 capture and separation, and electrochemical CO2 sensing. Significant emphasis is dedicated to the ALD and MLD designed materials, their crucial role in enhancing performance, and exploring the relationship between their structures and catalytic activities for CO2 transformation. Finally, this comprehensive review presents the summary, challenges and prospects for ALD and MLD-designed materials for CO2 transformation.

Introducing a Pseudocapacitive Lithium Storage Mechanism into Graphite by Defect Engineering for Fast-Charging Lithium-Ion Batteries

The extreme fast-charging capability of lithium-ion batteries (LIBs) is very essential for electric vehicles (EVs). However, currently used graphite anode materials cannot satisfy the requirements of fast charging. Herein, we demonstrate that intrinsic lattice defect engineering based on a thermal treatment of graphite in CO₂ is an effective method to improve the fast-charging capability of the graphite anode. The activated graphite (AG) exhibits a superior rate capability of 209 mAh g^-1 at 10 C (in comparison to 15 mAh g^-1 for the pristine graphite), which is attributed to a pseudocapacitive lithium storage behavior. Furthermore, the full cell LiFePO₄||AG can achieve SOCs of 82% and 96% within 6 and 15 min, respectively. The intrinsic carbon defect introduced by the CO₂ treatment succeeds in improving the kinetics of lithium ion intercalation at the rate-determining step during lithiation, which is identified by the distribution of relaxation times (DRT) and density functional theory (DFT) calculations. Therefore, this study provides a novel strategy for fast-charging LIBs. Moreover, this facile method is also suitable for activating other carbon-based materials.

Keggin-type SiW12 encapsulated in MIL-101(Cr) as efficient heterogeneous photocatalysts for nitrogen fixation reaction

The incorporation of polyoxometalates (POMs) in metal-organic frameworks (MOFs) with host-guest structure have proven to be effective strategy to rational design of heterogeneous catalysis. In this study, the Keggin-type POM@MIL-101(Cr) composite catalysts (PMo₁₂, PW₁₂ and SiW₁₂) are synthesized for nitrogen fixation reaction without sacrificial agents at room temperature in the first time. The SiW₁₂ molecules are encapsulated in smaller cavities of MIL-101(Cr) by solvothermal method and in larger cavities by impregnation method, respectively. Solvothermal synthesized catalyst has a performance of 75.56 μmol·h^-1·g^-1_cat and TOF value of 1.95 h^-1, which are about 10 and 88 times than that of Na₄SiW₁₂O₄₀. The excellent performance is ascribed to the synergistic effect of SiW₁₂ and MIL-101(Cr). The MIL-101(Cr) adsorbs a large amount of N₂ and generates sufficiently photogenerated electrons under sunlight irradiation, and electrons quickly transfer to the SiW₁₂ through hydrogen bonds. Moreover, the agglomeration effect of the homogeneous catalyst SiW₁₂ is weakened due to encapsulation with more exposed active sites. This work provides a feasible route to design and synthesize nanocomposite materials with exceptional performance for photocatalytic nitrogen fixation.

Advances in Post-Combustion CO2 Capture by Physical Adsorption: From Materials Innovation to Separation Practice

The atmospheric CO₂ concentration continues a rapid increase to its current record high value of 416 ppm for the time being. It calls for advanced CO₂ capture technologies. One of the attractive technologies is physical adsorption-based separation, which shows easy regeneration and high cycle stability, and thus reduced energy penalties and cost. The extensive research on this topic is evidenced by the growing body of scientific and technical literature. The progress spans from the innovation of novel porous adsorbents to practical separation practices. Major CO₂ capture materials include the most widely used industrially relevant porous carbons, zeolites, activated alumina, mesoporous silica, and the newly emerging metal-organic frameworks (MOFs) and covalent-organic framework (COFs). The key intrinsic properties such as pore structure, surface chemistry, preferable adsorption sites, and other structural features that would affect CO₂ capture capacity, selectivity, and recyclability are first discussed. The industrial relevant variables such as particle size of adsorbents, the mechanical strength, adsorption heat management, and other technological advances are equally important, even more crucial when scaling up from bench and pilot-scale to demonstration and commercial scale. Therefore, we aim to bring a full picture of the adsorption-based CO₂ separation technologies, from adsorbent design, intrinsic property evaluation to performance assessment not only under ideal equilibrium conditions but also in realistic pressure swing adsorption processes.

In Silico Screening of Zeolites for High-Pressure Hydrogen Drying

According to the ISO 14687-2:2019 standard, the water content of H₂ fuel for transportation and stationary applications should not exceed 5 ppm (molar). To achieve this water content, zeolites can be used as a selective adsorbent for water. In this work, a computational screening study is carried out for the first time to identify potential zeolite frameworks for the drying of high-pressure H₂ gas using Monte Carlo (MC) simulations. We show that the Si/Al ratio and adsorption selectivity have a negative correlation. 218 zeolites available in the database of the International Zeolite Association are considered in the screening. We computed the adsorption selectivity of each zeolite for water from the high-pressure H₂ gas having water content relevant to vehicular applications and near saturation. It is shown that due to the formation of water clusters, the water content in the H₂ gas has a significant effect on the selectivity of zeolites with a helium void fraction larger than 0.1. Under each operating condition, five most promising zeolites are identified based on the adsorption selectivity, the pore limiting diameter, and the volume of H₂ gas that can be dried by 1 dm³ of zeolite. It is shown that at 12.3 ppm (molar) water content, structures with helium void fractions smaller than 0.07 are preferred. The structures identified for 478 ppm (molar) water content have helium void fractions larger than 0.26. The proposed zeolites can be used to dry 400-8000 times their own volume of H₂ gas depending on the operating conditions. Our findings strongly indicate that zeolites are potential candidates for the drying of high-pressure H₂ gas.

Polyvinyl Chloride-Derived Carbon Spheres for CO2 Adsorption

Polyvinyl chloride (PVC) is the world's third-most widely produced plastic polymer. Directly transforming PVC to carbonaceous materials for CO₂ capture provides an environmentally friendly and attractive strategy to recycle plastics. In this work, a simple and effective method was developed to prepare PVC-derived carbon spheres. In this method, the classical "spheroidization" process shaped the original PVC powders into millimeter spheres, and a special dehalogenation and cross-linking process in the presence of a phase-transfer catalyst transferred the thermoplasticity of the PVC-spheres into thermosetting, which stabilized the shape. Furthermore, by rationally adjusting the activation conditions, the porous structure of the carbon spheres was well optimized. With a specific surface area up to 1738 m²  g^-1 and the developed microporous structure, the as-prepared carbon spheres showed not only excellent performance in pure CO₂ adsorption (8.93 mmol g^-1 , 39.3 wt% at 0 °C and 5.47 mmol g^-1 , 24.1 wt% at 25 °C), but also outstanding adsorption capacity and recyclability in low-concentration CO₂ capture, even superior to conventional molecular sieves.

Advanced Functional Hierarchical Nanoporous Structures with Tunable Microporous Coatings Formed via an Interfacial Reaction Processing

It is challenging, but constructing hierarchical nanoporous structures with microporous coatings for various important applications, such as entrapment of homogeneous catalysts, size/shape selective catalysis, and so forth, is an urgent need. Moreover, microporous inorganic coatings are particularly desirable because of their excellent stability in organic solvents and at elevated temperatures and pressures. In this study, we design a novel liquid phase interfacial reaction process to form a defect-free, hybrid coating, which can be subsequently converted into microporous coatings, with tunable pore size, on nanoporous materials. As an example to entrap functional materials, tetrakis(triphenylphosphine) palladium (Pd(PPh₃)₄) was in situ synthesized in the mesoporous channels and encapsulated by the microporous coating shell. The encapsulated Pd(PPh₃)₄ catalyst exhibited negligible Pd leaching, providing a promising solution for the challenging catalyst separation problem in homogeneous catalysis. These results suggest that this novel strategy might be an effective way of forming microporous inorganic coatings on nanoporous materials for entrapping functional materials for wide applications.

Spherical amine grafted silica aerogels for CO2 capture

The objective of this research was to develop a novel spherical amine grafted silica aerogel for CO₂ capture. A spherical silica gel was synthesized by dropping a sodium silicate based silica sol into an oil bath. Amine grafting was achieved by bonding 3-aminopropyltriethoxysilane onto the framework of the silica gel. The spherical amine grafted silica gels were dried using vacuum drying to prepare the spherical amine grafted silica aerogels (SASAs). The synthetic mechanism of the SASAs was proposed. The structures and the CO₂ adsorption performances of SASAs were researched. The amine loading of the SASAs increased with the grafting time, however, the specific surface area and pore volume sharply decreased owing to the blockage of the pore space. Excess amine loading led to the decrease of the CO₂ adsorption capacity. The optimal CO₂ adsorption capacity was 1.56 mmol g⁻¹ with dry 1% CO₂ and at 35 °C. This work provides a low-cost and environmentally friendly way to design a capable and regenerable adsorbent material.

The objective of this research was to develop a novel spherical amine grafted silica aerogel for CO₂ capture.

Emerging trends in porous materials for CO2 capture and conversion

This review highlights the recent progress in porous materials (MOFs, zeolites, POPs, nanoporous carbons, and mesoporous materials) for CO₂ capture and conversion.

Industrial carbon dioxide capture and utilization: state of the art and future challenges

This review covers the sustainable development of advanced improvements in CO₂ capture and utilization.

Trends in Solid Adsorbent Materials Development for CO2 Capture

A recent report from the United Nations has warned about the excessive CO₂ emissions and the necessity of making efforts to keep the increase in global temperature below 2 °C. Current CO₂ capture technologies are inadequate for reaching that goal, and effective mitigation strategies must be pursued. In this work, we summarize trends in materials development for CO₂ adsorption with focus on recent studies. We put adsorbent materials into four main groups: (I) carbon-based materials, (II) silica/alumina/zeolites, (III) porous crystalline solids, and (IV) metal oxides. Trends in computational investigations along with experimental findings are covered to find promising candidates in light of practical challenges imposed by process economics.

Controlling Pore Shape and Size of Interpenetrated Anion-Pillared Ultramicroporous Materials Enables Molecular Sieving of CO2 Combined with Ultrahigh Uptake Capacity

The separation of carbon dioxide (CO₂) from hydrocarbons is a critical process for the production of clean energy and high-purity chemicals. Adsorption based on molecular sieving is an energy-saving separation process; however, most of molecular sieves with narrow and straight pore channels exhibit low CO₂ uptake capacity. Here, we report that a twofold interpenetrated copper coordination network with a consecutive pocket-like pore structure, namely, SIFSIX-14-Cu-i (SIFSIX = hexafluorosilicate, 14 = 4,4'-azopyridine, i = interpenetrated) is a remarkable CO₂/CH₄ molecular sieving adsorbent which completely blocks the larger CH₄ molecule with unprecedented selectivity, whereas it has excellent CO₂ uptake (172.7 cm³/cm³) under the ambient condition. The exceptional separation performance of SIFSIX-14-Cu-i is attributed to its unique pore shape and functional pore surface, which combine a contracted pore window (3.4 Å) and a relatively large pore cavity decorated with high density of inorganic anions. Dispersion-corrected density functional theory calculation and neutron powder diffraction were performed to understand the CO₂ binding sites. The practical feasibility of SIFSIX-14-Cu-i for CO₂/CH₄ mixtures separation was validated by experimental breakthrough tests. This study not only demonstrates the great potential of SIFSIX-14-Cu-i for CO₂ separation but also provides important clues for other gas separations.

A lithium-modified zirconium-based metal organic framework (UiO-66) for efficient CO2 adsorption

The adsorption mechanism of carbon dioxide (CO₂) on Li/UiO-66 was studied by an in situ DRIFTS study.