Harnessing the Hybridization of a Metal-Organic Framework and Superbase-Derived Ionic Liquid for High-Performance Direct Air Capture of CO2

Direct air capture (DAC) of CO₂ has emerged as the most promising “negative carbon emission” technologies. Despite being state-of-the-art, sorbents deploying alkali hydroxides/amine solutions or amine-modified materials still suffer from unsolved high energy consumption and stability issues. In this work, composite sorbents are crafted by hybridizing a robust metal-organic framework (Ni-MOF) with superbase-derived ionic liquid (SIL), possessing well maintained crystallinity and chemical structures. The low-pressure (0.4 mbar) volumetric CO₂ capture assessment and a fixed-bed breakthrough examination with 400 ppm CO₂ gas flow reveal high-performance DAC of CO₂ (CO₂ uptake capacity of up to 0.58 mmol g⁻¹ at 298 K) and exceptional cycling stability. Operando spectroscopy analysis reveals the rapid (400 ppm) CO₂ capture kinetics and energy-efficient/fast CO₂ releasing behaviors. The theoretical calculation and small-angle X-ray scattering demonstrate that the confinement effect of the MOF cavity enhances the interaction strength of reactive sites in SIL with CO₂, indicating great efficacy of the hybridization. The achievements in this study showcase the exceptional capabilities of SIL-derived sorbents in carbon capture from ambient air in terms of rapid carbon capture kinetics, facile CO₂ releasing, and good cycling performance.     

Biomass derived 5-hydroxymethylfurfural as carbon precursor to form hollow carbon nanospheres for CO2 capture

We prepare the hollow carbon nanospheres (HCNs) by employing SiO₂ nanospheres as hard template, 5-Hydroxymethylfurfural (HMF) as carbon precursor under hydrothermal conditions. The HCNs show uniform spherical morphology copied from SiO₂ nanospheres and exhibit large cavity, thin shell structure with the surface area of 790 m² g^?1 and pore volume of 2.23 cm³ g^?1. Owing to their large internal voids and high surface area, the HCNs exhibit a promising prospect for CO₂ capture with the capacity of 3.04 mmol g^?1 at 1.0 bar and 298 K, as well as good recyclability for CO₂ after ten adsorption-desorption cycles.     

Controlled synthesis of mesoporous β-Ni(OH)2 and NiO nanospheres with enhanced electrochemical performance

Uniform mesoporous β-Ni(OH)₂ and NiO nanospheres with hierarchical structures were synthesized by a facile complexation–precipitation method. The effects of ammonia and citrate on the structure and morphology of the products were thoroughly investigated by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and nitrogen adsorption–desorption measurements. The results indicated that ammonia played an important role for the formation of flowerlike spheres assembled from nanosheets. The addition of citrate could remarkably reduce the particle sizes and increase the specific surface areas of flowerlike spheres. A possible formation mechanism based on the experimental results was proposed to understand their growing procedures. β-Ni(OH)₂ and NiO nanospheres prepared with the addition of citrate showed excellent capacitive properties due to their mesoporous structures and large surface areas, suggesting the importance of controlled synthesis of hierarchical nanostructures for their applications.     

Oxalate-Assisted Synthesis of Hollow Carbon Nanocage With Fe Single Atoms for Electrochemical CO2 Reduction

Metal single-atom catalysts are promising in electrochemical CO₂ reduction reaction (CO₂RR). The pores and cavities of the supports can promote the exposure of active sites and mass transfer of reactants, hence improve their performance. Here, iron oxalate is added to ZIF-8 and subsequently form hollow carbon nanocages during calcination. The formation mechanism of the hollow structure is studied in depth by controlling variables during synthesis. Kirkendall effect is the main reason for the formation of hollow porous carbon nanocages. The hollow porous carbon nanocages with Fe single atoms exhibit better CO₂RR activity and CO selectivity. The diffusion of CO₂ facilitated by the mesoporous structure of carbon nanocage results in their superior activity and selectivity. This work has raised an effective strategy for the synthesis of hollow carbon nanomaterials, and provides a feasible pathway for the rational design of electrocatalysts for small molecule activation.     

Porous Organic Polymers for Post‐Combustion Carbon Capture

One of the most pressing environmental concerns of our age is the escalating level of atmospheric CO₂. Intensive efforts have been made to investigate advanced porous materials, especially porous organic polymers (POPs), as one type of the most promising candidates for carbon capture due to their extremely high porosity, structural diversity, and physicochemical stability. This review provides a critical and in‐depth analysis of recent POP research as it pertains to carbon capture. The definitions and terminologies commonly used to evaluate the performance of POPs for carbon capture, including CO₂ capacity, enthalpy, selectivity, and regeneration strategies, are summarized. A detailed correlation study between the structural and chemical features of POPs and their adsorption capacities is discussed, mainly focusing on the physical interactions and chemical reactions. Finally, a concise outlook for utilizing POPs for carbon capture is discussed, noting areas in which further work is needed to develop the next‐generation POPs for practical applications.     

Space‐Confined Synthesis of ZIF‐67 Nanoparticles in Hollow Carbon Nanospheres for CO2 Adsorption

Herein, the design and synthesis of ZIF‐67 nanoparticles (NPs) with tunable size grown inside hollow carbon nanospheres (ZIF‐67@HCSs) via a space‐confined strategy is reported. HCSs are first prepared via pyrolysis of polystyrene@polypyrrole (PS@PPy) composite nanospheres. Further infiltration of 2‐methylimidazole (MI) into the HCSs (MI@HCSs) using a melting‐diffusion strategy, followed by immersing MI@HCSs into Co(NO₃)₂ solution through the pores and channels of HCSs results in the formation of ZIF‐67@HCSs. The as‐synthesized ZIF‐67@HCSs with tunable ZIF‐67 size is achieved by changing the amount of MI. Due to the high pore volume provided by nanoscale ZIF‐67 NPs, the as‐prepared core–shell ZIF‐67@HCSs exhibit outstanding adsorption capacity for CO₂.     

Porous liquids as solvents for the economical separation of carbon dioxide from methane

Current CO₂ separation technologies by liquid solvents suffer from either high regeneration costs or low selectivity/capacity of the solvent. Dispersing ca. 12.5 wt% CO₂-selective zeolite rho solid into the commercial CO₂ capture solvent Genosorb® converts it into a porous liquid with at least 2.5 times greater CO₂ capacity and CO₂/CH₄ selectivity compared to Genosorb® itself. This is predicted to result in more economical separation processes, particularly for biogas upgrading.     

Valuing Metal–Organic Frameworks for Postcombustion Carbon Capture: A Benchmark Study for Evaluating Physical Adsorbents

The development of practical solutions for the energy‐efficient capture of carbon dioxide is of prime importance and continues to attract intensive research interest. Conceivably, the implementation of adsorption‐based processes using different cycling modes, e.g., pressure‐swing adsorption or temperature‐swing adsorption, offers great prospects to address this challenge. Practically, the successful deployment of practical adsorption‐based technologies depends on the development of made‐to‐order adsorbents expressing mutually two compulsory requisites: i) high selectivity/affinity for CO₂ and ii) excellent chemical stability in the presence of impurities. This study presents a new comprehensive experimental protocol apposite for assessing the prospects of a given physical adsorbent for carbon capture under flue gas stream conditions. The protocol permits: i) the baseline performance of commercial adsorbents such as zeolite 13X, activated carbon versus liquid amine scrubbing to be ascertained, and ii) a standardized evaluation of the best reported metal–organic framework (MOF) materials for carbon dioxide capture from flue gas to be undertaken. This extensive study corroborates the exceptional CO₂ capture performance of the recently isolated second‐generation fluorinated MOF material, NbOFFIVE ‐1‐Ni, concomitant with an impressive chemical stability and a low energy for regeneration. Essentially, the NbOFFIVE ‐1‐Ni adsorbent presents the best compromise by satisfying all the required metrics for efficient CO₂ scrubbing.     

Polyethyleneimine functionalised nanocarbons for the efficient adsorption ofcarbon dioxide with a low temperature of regeneration

Polyethyleneimine (PEI) conjugates with a range of nanocarbons (NCs) have been prepared, and their performances with regard to carbon dioxide absorption and liberation are compared. PEI-functionalised multi-walled carbon nanotubes (PEI-MWNTs) prepared by the reaction of branched PEI (25,000 Da) with F-MWNTs in the presence of pyridine, showed a lower CO₂ capacity at 25 °C (5 wt%, 1.1 mmol CO₂/g adsorbent) as compared to PEI-SWNTs (9.2 wt%, 2.1 mmol CO₂/g adsorbent), consistent with the interior layers of the MWNTs adding weight to the base NC without adding functionality. PEI-functionalised graphite/graphene was prepared by three routes: fluorinated graphite intercalation compounds, prepared from natural graphite powder, were reacted with PEI in EtOH with pyridine; exfoliated natural graphite powder was reacted with Boc–Phe(4-N₃)–OH, and subsequently PEI to give PEI-Phe(4-N-G); graphite oxide (GO) was reacted with PEI in the presence of NEt₃ to give PEI-GO. The CO₂ capacity of PEI-GO at 25 °C (8 wt%, 1.8 mmol CO₂/g adsorbent) was comparable to that of PEI-SWNTs making GO a valid and cheaper alternative to the SWNT scaffold. The temperature of CO₂ desorption of the PEI-NCs was 75 °C, providing a lower energy load for regeneration compared to current amine-based scrubbing units. The rate of CO₂ uptake is seen to depend on the curvature of the NC substrate.     

Electrolysis Synthesis of Carbides and Carbon Dioxide Capture in Molten Salts

The application of carbides in catalysis, batteries, aerospace fields, etc. has been continuously expanded and deepened, which is attributed to the diversified physicochemical properties of carbides via a tune-up of their morphology, composition, and microstructure. The emergence of MAX phases and high entropy carbides with unparalleled application potential undoubtedly further stimulates the research upsurge of carbides. The traditional pyrometallurgical or hydrometallurgical synthesis of carbides inevitably faces the shortcomings of complex process, unacceptable energy consumption, extreme environmental pollution, and beyond. The molten salt electrolysis synthesis method with the superiorities of straightforward route, high efficiency, and environmental friendliness has demonstrated its validity in the synthesis of various carbides, which naturally initiates more research. In particular, the process can achieve CO₂ capture while synthesizing carbides based on the excellent CO₂ capture capability of some molten salts, which is of great significance for carbon neutralization. In this paper, the synthesis mechanism of carbide by molten salt electrolysis, the process of CO₂ capture and carbides conversion, the latest research progress in the synthesis of binary, ternary, multi-component, and composite carbides are reviewed. Finally, the challenges, development perspectives, and research directions of electrolysis synthesis of carbides in molten salts are featured.     

Catalytic Hydrogenation of CO2 to Formate Using Ruthenium Nanoparticles Immobilized on Supported Ionic Liquid Phases

Ruthenium nanoparticles (NPs) immobilized on imidazolium-based supported ionic liquid phases (Ru@SILP) act as effective heterogeneous catalysts for the hydrogenation of carbon dioxide (CO₂) to formate in a mixture of water and triethylamine (NEt₃). The structure of the imidazolium-based molecular modifiers is varied systematically regarding side chain functionality (neutral, basic, and acidic) and anion to assess the influence of the IL-type environment on the NPs synthesis and catalytic properties. The resulting Ru@SILP materials contain well-dispersed Ru NPs with diameters in the range 0.8–2.9 nm that are found 2 to 10 times more active for CO₂ hydrogenation than a reference Ru@SiO₂ catalyst under identical conditions. Introduction of sulfonic acid groups in the IL modifiers results in a greatly increased turnover number (TON) and turnover frequency (TOF) at reduced metal loadings. As a result, excellent productivity with TONs up to 16 100 at an initial TOF of 1430 h⁻¹ can be achieved with the Ru@SILP(SO₃H-OAc) catalyst. H/D exchange and other control experiments suggest an accelerated desorption of the formate species from the Ru NPs promoted by the presence of ammonium sulfonate species on Ru@SILP(SO₃H-X) materials, resulting in enhanced catalyst activity and productivity.     

Ultrathin Nitrogen-Doped Carbon Encapsulated Ni Nanoparticles for Highly Efficient Electrochemical CO2 Reduction and Aqueous Zn-CO2 Batteries

Electrochemical CO₂ reduction reaction (CO₂RR), powered by renewable electricity, has attracted great attention for producing high value-added fuels and chemicals, as well as feasibly mitigating CO₂ emission problem. Here, this work reports a facile hard template strategy to prepare the Ni@N-C catalyst with core–shell structure, where nickel nanoparticles (Ni NPs) are encapsulated by thin nitrogen-doped carbon shells (N-C shells). The Ni@N-C catalyst has demonstrated a promising industrial current density of 236.7 mA cm⁻² with the superb FE_CO of 97% at −1.1 V versus RHE. Moreover, Ni@N-C can drive the reversible Zn-CO₂ battery with the largest power density of 1.64 mW cm⁻², and endure a tough cycling durability. These excellent performances are ascribed to the synergistic effect of Ni@N-C that Ni NPs can regulate the electronic microenvironment of N-doped carbon shells, which favor to enhance the CO₂ adsorption capacity and the electron transfer capacity. Density functional theory calculations prove that the binding configuration of N-C located on the top of Ni slabs (Top-Ni@N-C) is the most thermodynamically stable and possess a lowest thermodynamic barrier for the formation of COOH^* and the desorption of CO. This work may pioneer a new method on seeking high-efficiency and worthwhile electrocatalysts for CO₂RR and Zn-CO₂ battery.     

Highly Enhancing CO2 Photoreduction by Metallization of an Imidazole-linked Robust Covalent Organic Framework

Converting CO₂ into value-added chemicals to solve the issues caused by carbon emission is promising but challenging. Herein, by embedding metal ions (Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺) into an imidazole-linked robust photosensitive covalent organic framework (PyPor-COF), effective photocatalysts for CO₂ conversion are rationally designed and constructed. Characterizations display that all of the metallized PyPor-COFs (M-PyPor-COFs) display remarkably high enhancement in their photochemical properties. Photocatalysis reactions reveal that the Co-metallized PyPor-COF (Co-PyPor-COF) achieves a CO production rate as high as up to 9645 µmol g⁻¹ h⁻¹ with a selectivity of 96.7% under light irradiation, which is more than 45 times higher than that of the metal-free PyPor-COF, while Ni-metallized PyPor-COF (Ni-PyPor-COF) can further tandem catalyze the generated CO to CH₄ with a production rate of 463.2 µmol g⁻¹ h⁻¹. Experimental analyses and theory calculations reveal that their remarkable performance enhancement on CO₂ photoreduction should be attributed to the incorporated metal sites in the COF skeleton, which promotes the adsorption and activation of CO₂ and the desorption of generated CO and even reduces the reaction energy barrier for the formation of different intermediates. This work demonstrates that by metallizing photoactive COFs, effective photocatalysts for CO₂ conversion can be achieved.     

Solvent‐Free Self‐Assembly to the Synthesis of Nitrogen‐Doped Ordered Mesoporous Polymers for Highly Selective Capture and Conversion of CO2

A solvent‐free induced self‐assembly technology for the synthesis of nitrogen‐doped ordered mesoporous polymers (N‐OMPs) is developed, which is realized by mixing polymer precursors with block copolymer templates, curing at 140–180 °C, and calcination to remove the templates. This synthetic strategy represents a significant advancement in the preparation of functional porous polymers through a fast and scalable yet environmentally friendly route, since no solvents or catalysts are used. The synthesized N‐OMPs and their derived catalysts are found to exhibit competitive CO₂ capacities (0.67–0.91 mmol g^?1 at 25 °C and 0.15 bar), extraordinary CO₂/N₂ selectivities (98–205 at 25 °C), and excellent activities for catalyzing conversion of CO₂ into cyclic carbonate (conversion >95% at 100 °C and 1.2 MPa for 1.5 h). The solvent‐free technology developed in this work can also be extended to the synthesis of N‐OMP/SiO₂ nanocomposites, mesoporous SiO₂, crystalline mesoporous TiO₂, and TiPO, demonstrating its wide applicability in porous material synthesis.     

Template‐Free Fabrication of Mesoporous Alumina Nanospheres Using Post‐Synthesis Water‐Ethanol Treatment of Monodispersed Aluminium Glycerate Nanospheres for Molybdenum Adsorption

This work reports the template‐free fabrication of mesoporous Al₂O₃ nanospheres with greatly enhanced textural characteristics through a newly developed post‐synthesis “water‐ethanol” treatment of aluminium glycerate nanospheres followed by high temperature calcination. The proposed “water‐ethanol” treatment is highly advantageous as the resulting mesoporous Al₂O₃ nanospheres exhibit 2–4 times higher surface area (up to 251 m² g^?1), narrower pore size distribution, and significantly lower crystallization temperature than those obtained without any post‐synthesis treatment. To demonstrate the generality of the proposed strategy, a nearly identical post‐synthesis “water treatment” method is successfully used to prepare mesoporous monometallic (e.g., manganese oxide (MnO₂)) and bimetallic oxide (e.g., CuCo₂O₄ and MnCo₂O₄) nanospheres assembled of nanosheets or nanoplates with highly enhanced textural characteristics from the corresponding monometallic and bimetallic glycerate nanospheres, respectively. When evaluated as molybdenum (Mo) adsorbents for potential use in molybdenum‐99/technetium‐99m (⁹⁹Mo/^99mTc) generators, the treated mesoporous Al₂O₃ nanospheres display higher molybdenum adsorption performance than non‐treated Al₂O₃ nanospheres and commercial Al₂O₃, thereby suggesting the effectiveness of the proposed strategy for improving the functional performance of oxide materials. It is expected that the proposed method can be utilized to prepare other mesoporous metal oxides with enhanced textural characteristics and functional performance.     

Optimal Bidding and Operation of a Power Plant with Solvent-Based Carbon Capture under a CO2 Allowance Market: A Solution with a Reinforcement Learning-Based Sarsa Temporal-Difference Algorithm

In this paper, a reinforcement learning (RL)-based Sarsa temporal-difference (TD) algorithm is applied to search for a unified bidding and operation strategy for a coal-fired power plant with monoethanolamine (MEA)-based post-combustion carbon capture under different carbon dioxide (CO₂) allowance market conditions. The objective of the decision maker for the power plant is to maximize the discounted cumulative profit during the power plant lifetime. Two constraints are considered for the objective formulation. Firstly, the tradeoff between the energy-intensive carbon capture and the electricity generation should be made under presumed fixed fuel consumption. Secondly, the CO₂ allowances purchased from the CO₂ allowance market should be approximately equal to the quantity of CO₂ emission from power generation. Three case studies are demonstrated thereafter. In the first case, we show the convergence of the Sarsa TD algorithm and find a deterministic optimal bidding and operation strategy. In the second case, compared with the independently designed operation and bidding strategies discussed in most of the relevant literature, the Sarsa TD-based unified bidding and operation strategy with time-varying flexible market-oriented CO₂ capture levels is demonstrated to help the power plant decision maker gain a higher discounted cumulative profit. In the third case, a competitor operating another power plant identical to the preceding plant is considered under the same CO₂ allowance market. The competitor also has carbon capture facilities but applies a different strategy to earn profits. The discounted cumulative profits of the two power plants are then compared, thus exhibiting the competitiveness of the power plant that is using the unified bidding and operation strategy explored by the Sarsa TD algorithm.     

2D Transition Metal Carbides (MXenes) for Carbon Capture

Global warming caused by burning of fossil fuels is indisputably one of mankind's greatest challenges in the 21st century. To reduce the ever‐increasing CO₂ emissions released into the atmosphere, dry solid adsorbents with large surface‐to‐volume ratio such as carbonaceous materials, zeolites, and metal–organic frameworks have emerged as promising material candidates for capturing CO₂. However, challenges remain because of limited CO₂/N₂ selectivity and long‐term stability. The effective adsorption of CO₂ gas (≈12 mol kg^?1) on individual sheets of 2D transition metal carbides (referred to as MXenes) is reported here. It is shown that exposure to N₂ gas results in no adsorption, consistent with first‐principles calculations. The adsorption efficiency combined with the CO₂/N₂ selectivity, together with a chemical and thermal stability, identifies the archetype Ti₃C₂ MXene as a new material for carbon capture (CC) applications.     

Liquid-in-Aerogel Porous Composite Allows Efficient CO2 Capture and CO2/N2 Separation

The pursuit of efficient CO₂ capture materials remains an unmet challenge. Especially, meeting both high sorption capacity and fast uptake kinetics is an ongoing effort in the development of CO₂ sorbents. Here, a strategy to exploit liquid-in-aerogel porous composites (LIAPCs) that allow for highly effective CO₂ capture and selective CO₂/N₂ separation, is reported. Interestingly, the functional liquid tetraethylenepentamine (TEPA) is partially filled into the air pockets of SiO₂ aerogel with left permanent porosity. Notably, the confined liquid thickness is 10.9–19.5 nm, which can be vividly probed by the atomic force microscope and rationalized by tailoring the liquid composition and amount. LIAPCs achieve high affinity between the functional liquid and solid porous counterpart, good structure integrity, and robust thermal stability. LIAPCs exhibit superb CO₂ uptake capacity (5.44 mmol g⁻¹, 75 °C, and 15 vol% CO₂), fast sorption kinetics, and high amine efficiency. Furthermore, LIAPCs ensure long-term adsorption–desorption cycle stability and offer exceptional CO₂/N₂ selectivity both in dry and humid conditions, with a separation factor up to 1182.68 at a humidity of 1%. This approach offers the prospect of efficient CO₂ capture and gas separation, shedding light on new possibilities to make the next-generation sorption materials for CO₂ utilization.     

Geometric and Electronic Structural Engineering of Isolated Ni Single Atoms for a Highly Efficient CO2 Electroreduction

Tuning the coordination environment and geometric structures of single atom catalysts is an effective approach for regulating the reaction mechanism and maximize the catalytic efficiency of single-atom centers. Here, a template-based synthesis strategy is proposed for the synthesis of high-density NiN_x sites anchored on the surface of hierarchically porous nitrogen-doped carbon nanofibers (Ni-HPNCFs) with different coordination environments. First-principles calculations and advanced characterization techniques demonstrate that the single Ni atom is strongly coordinated with both pyrrolic and pyridinic N dopants, and that the predominant sites are stabilized by NiN₃ sites. This dual engineering strategy increases the number of active sites and utilization efficiency of each single atom as well as boosts the intrinsic activity of each active site on a single-atom scale. Notably, the Ni-HPNCF catalyst achieves a high CO Faradaic efficiency (FE_CO) of 97% at a potential of −0.7 V, a high CO partial current density (j_CO) of 49.6 mA cm⁻² (−1.0 V), and a remarkable turnover frequency of 24 900 h⁻¹ (−1.0 V) for CO₂ reduction reactions (CO₂RR). Density functional theory calculations show that compared to pyridinic-type NiN_x, the pyrrolic-type NiN₃ moieties display a superior CO₂RR activity over hydrogen evolution reactions, resulting in their superior catalytic activity and selectivity.     

Harnessing the Beneficial Attributes of Ceria and Titania in a Mixed-Oxide Support for Nickel-Catalyzed Photothermal CO2 Methanation

Solar-powered carbon dioxide (CO₂)-to-fuel conversion presents itself as an ideal solution for both CO₂ mitigation and the rapidly growing world energy demand. In this work, the heating effect of light irradiation onto a bed of supported nickel (Ni) catalyst was utilized to facilitate CO₂ conversion. Ceria (CeO₂)-titania (TiO₂) oxide supports of different compositions were employed and their effects on photothermal CO₂ conversion examined. Two factors are shown to be crucial for instigating photothermal CO₂ methanation activity: ① Fine nickel deposits are required for both higher active catalyst area and greater light absorption capacity for the initial heating of the catalyst bed; and ② the presence of defect sites on the support are necessary to promote adsorption of CO₂ for its subsequent activation. Titania inclusion within the support plays a crucial role in maintaining the oxygen vacancy defect sites on the (titanium-doped) cerium oxide. The combination of elevated light absorption and stabilized reduced states for CO₂ adsorption subsequently invokes effective photothermal CO₂ methanation when the ceria and titania are blended in the ideal ratio(s).