N-doped porous carbons for CO2capture: Rational choice of N-containing polymer with high phenyl density as precursor

Review on CO2 Capture Using Amine-Functionalized Materials

CO₂ capture from industry sectors or directly from the atmosphere is drawing much attention on a global scale because of the drastic changes in the climate and ecosystem which pose a potential threat to human health and life on Earth. In the past decades, CO₂ capture technology relied on classical liquid amine scrubbing. Due to its high energy consumption and corrosive property, CO₂ capture using solid materials has recently come under the spotlight. A variety of porous solid materials were reported such as zeolites and metal-organic frameworks. However, amine-functionalized porous materials outperform all others in terms of CO₂ adsorption capacity and regeneration efficiency. This review provides a brief overview of CO₂ capture by various amines and mechanistic aspects for newcomers entering into this field. This review also covers a state-of-the-art regeneration method, visible/UV light-triggered CO₂ desorption at room temperature. In the last section, the current issues and future perspectives are summarized.

Efficient nitrogen doped porous carbonaceous CO2 adsorbents based on lotus leaf

In this work, the waste biomass lotus leaf was converted into N-doped porous carbonaceous CO₂ adsorbents. The synthesis process includes carbonization of lotus leaf, melamine post-treatment and KOH activation. For the resultant sorbents, high nitrogen content can be contained due to the melamine modification and advanced porous structure were formed by KOH etching. These samples were carefully characterized by different techniques and their CO₂ adsorption properties were investigated in detail. These sorbents hold good CO₂ adsorption abilities, up to 3.87 and 5.89 mmol/g at 25 and 0°C under 1 bar, respectively. By thorough investigation, the combined interplay of N content and narrow microporous volume was found to be responsible for the CO₂ uptake for this series of sorbents. Together with the high CO₂ adsorption abilities, these carbons also display excellent reversibility, high CO₂/N₂ selectivity, applicable heat of adsorption, fast CO₂ adsorption kinetics and good dynamic CO₂ adsorption capacity. This study reveals a universal method of obtaining N-doped porous carbonaceous sorbents from leaves. The low cost of raw materials accompanied by easy synthesis procedure disclose the enormous potential of leaves-based carbons in CO₂ capture as well as many other applications.

Carbon dioxide adsorption based on porous materials

Global warming due to the high concentration of anthropogenic CO2 in the atmosphere is considered one of the world's leading challenges in the 21st century as it leads to severe consequences such as climate change, extreme weather events, ocean warming, sea-level rise, declining Arctic sea ice, and the acidification of oceans. This encouraged advancing technologies that sequester carbon dioxide from the atmosphere or capture those emitted before entering the carbon cycle. Recently, CO2 capture, utilizing porous materials was established as a very favorable route, which has drawn extreme interest from scientists and engineers due to their advantages over the absorption approach. In this review, we summarize developments in porous adsorbents for CO2 capture with emphasis on recent studies. Highly efficient porous adsorption materials including metal-organic frameworks (MOFs), zeolites, mesoporous silica, clay, porous carbons, porous organic polymers (POP), and metal oxides (MO) are discussed. Besides, advanced strategies employed to increase the performance of CO2 adsorption capacity to overcome their drawbacks have been discoursed.

Constructing Hierarchically Porous N-Doped Carbons Derived from Poly(ionic liquids) with the Multifunctional Fe-Based Template for CO2 Adsorption

Nitrogen-doped hierarchical porous carbons with a rich pore structure were prepared via direct carbonization of the poly(ionic liquid) (PIL)/potassium ferricyanide compound. Thereinto, the bisvinylimidazolium-based PIL was a desirable carbon source, and potassium ferricyanide as a multifunctional Fe-based template, could not only serve as the pore-forming agent, including metallic components (Fe and Fe3C), potassium ions (etching carbon framework during carbonization), and gas generated during the pyrolysis process, but also introduce the N atoms to porous carbons, which were in favor of CO2 capture. Moreover, the hierarchically porous carbon NDPC-1-800 (NDPC, nitrogen-doped porous carbon) had taken advantage of the highest specific surface area, exhibiting an excellent CO2 adsorption capacity and selectivity compared with NDC-800 (NDC, nitrogen-doped carbon) directly carbonized from the pure PIL. Furthermore, its hierarchical porous architectures played an important part in the process of CO2 capture, which was described briefly as follows: the synergistic effect of mesopores and micropores could accelerate the CO2 molecules' transportation and storage. Meanwhile, the appropriate microporous size distribution of NDPC-1-800 was conducive to enhancing CO2/N2 selectivity. This study was intended to open up a new pathway for designing N-doped porous carbons combining both PILs and the multifunctional Fe-based template potassium ferricyanide with wonderful gas adsorption and separation performance.

Catalyst-free development of N-doped microporous carbons for selective CO2 separation

Owing to their catalyst-free development, high yield, notable CO₂ uptake performance, and excellent CO₂/CH₄ selectivity, the fabricated N-doped microporous carbons (NMCs) are highly suitable for selective CO₂ separation.

Superior CO2 uptake on nitrogen doped carbonaceous adsorbents from commercial phenolic resin

In this study, N-doped porous carbons were produced with commercial phenolic resin as the raw material, urea as the nitrogen source and KOH as the activation agent. Different from conventional carbonization-nitriding-activation three-step method, a facile two-step process was explored to produce N-incorporated porous carbons. The as-obtained adsorbents hold superior CO₂ uptake, i.e. 5.01 and 7.47 mmol/g at 25 °C and 0 °C under 1 bar, respectively. The synergistic effects of N species on the surface and narrow micropores of the adsorbents decide their CO₂ uptake under 25 °C and atmospheric pressure. These phenolic resin-derived adsorbents also possess many extremely promising CO₂ adsorption features like good recyclability, quick adsorption kinetics, modest heat of adsorption, great selectivity of CO₂ over N₂ and outstanding dynamic adsorption capacity. Cheap precursor, easy preparation strategy and excellent CO₂ adsorption properties make these phenolic resin-derived N-doped carbonaceous adsorbents highly promising in CO₂ capture.

Biowaste-derived 3D honeycomb-like N and S dual-doped hierarchically porous carbons for high-efficient CO2 capture

Considering the characteristics of abundant narrow micropores of <1 nm, appropriate proportion of mesopores/macropores and suitable surface functionalization for a highly-efficient carbon-based CO₂ adsorbent, we proposed a facile and cost-effective strategy to prepare N and S dual-doped carbons with well-interconnected hierarchical pores. Benefiting from the unique structural features, the resultant optimal material showed a prominent CO₂ uptake of up to 7.76 and 5.19 mmol g⁻¹ at 273 and 298 K under 1 bar, and importantly, a superb CO₂ uptake of 1.51 mmol g⁻¹ at 298 K and 0.15 bar was achieved, which was greatly significant for CO₂ capture from the post-combustion flue gases in practical application. A systematic study demonstrated that the synergetic effect of ultramicroporosity and surface functionalization determined the CO₂ capture properties of porous carbons, and the synergistic influence mechanism of nitrogen/sulfur dual-doping on CO₂ capture performance was also investigated in detail. Importantly, such as-prepared carbon-based CO₂ adsorbents also showed an outstanding recyclability and CO₂/N₂ selectivity. In view of cost-effective fabrication, the excellent adsorption capacity, high selectivity and simple regeneration, our developed strategy was valid and convenient to design a novel and highly-efficient carbonaceous adsorbent for large-scale CO₂ capture and separation from post-combustion flue gases.

We proposed a facile and cost-effective strategy to prepare N/S dual-doped carbons with abundant micropores of <1 nm, appropriate proportion of meso/macropores and suitable surface functionalization for highly efficient CO₂ capture.

Potassium Tethered Carbons with Unparalleled Adsorption Capacity and Selectivity for Low-Cost Carbon Dioxide Capture from Flue Gas

Carbons are considered less favorable for postcombustion CO₂ capture because of their low affinity toward CO₂, and nitrogen doping was widely studied to enhance CO₂ adsorption, but the results are still unsatisfactory. Herein, we report a simple, scalable, and controllable strategy of tethering potassium to a carbon matrix, which can enhance carbon-CO₂ interaction effectively, and a remarkable working capacity of ca. 4.5 wt % under flue gas conditions was achieved, which is among the highest for carbon-based materials. More interestingly, a high CO₂/N₂ selectivity of 404 was obtained. Density functional theory calculations evidenced that the introduced potassium carboxylate moieties are responsible for such excellent performances. We also show the effectiveness of this strategy to be universal, and thus, cheaper precursors can be used, holding great promise for low-cost carbon capture from flue gas.

Potassium-incorporated mesoporous carbons: strong solid bases with enhanced catalytic activity and stability

Through chemical activation combined with the hard-templating strategy, potassium-incorporated mesoporous carbons were fabricated which showed strong basicity and enhanced catalytic performance.

Probing the role of O-containing groups in CO2 adsorption of N-doped porous activated carbon

Porous activated carbons (PACs) are promising candidates to capture CO₂ through physical adsorption because of their chemical stability, easy-synthesis, cost-effectiveness and good recyclability. However, their low CO₂ adsorption capacity, especially low CO₂/N₂ selectivity, has limited their practical applications. In this work, an optimized PAC with a large specific surface area, a small micropore size, and a large micropore volume has been synthesized by one-step carbonization/activation of casein using K₂CO₃ as a mild activation agent. It showed a remarkably enhanced CO₂ adsorption capacity as high as 5.78 mmol g^-1 and an excellent CO₂/N₂ selectivity of 144 (25 °C, 1 bar). Based on DFT calculations and experimental results, the coexistence of adjacent pyridinic N and -OH/-NH₂ species was proposed for the first time to make an important contribution to the ultra-high CO₂ adsorption performance, especially CO₂/N₂ selectivity. This work provides effective guidance to design PAC adsorbents with high CO₂ adsorption performance. The content of pyridine N combined with -OH/-NH₂ was further elevated by additional nitrogen introduction, resulting in a further enhanced CO₂ adsorption capacity up to 5.96 mmol g^-1 (25 °C, 1 bar). All these results suggest that, in addition to the well-defined pore structure, pyridinic N with neighboring OH or NH₂ species played an important role in enhancing the CO₂ adsorption performance of PACs, thus providing effective guidance for the rational design of CO₂ adsorbents.

Metal-Organic Frameworks for Heterogeneous Basic Catalysis

Great attention has been given to metal-organic frameworks (MOFs)-derived solid bases because of their attractive structure and catalytic performance in various organic reactions. The extraordinary skeleton structure of MOFs provides many possibilities for incorporation of diverse basic functionalities, which is unachievable for conventional solid bases. The past decade has witnessed remarkable advances in this vibrant research area; however, MOFs for heterogeneous basic catalysis have never been reviewed until now. Therefore, a review summarizing MOFs-derived base catalysts is highly expected. In this review, we present an overview of the recent progress in MOFs-derived solid bases covering preparation, characterization, and catalytic applications. In the preparation section, the solid bases are divided into two categories, namely, MOFs with intrinsic basicity and MOFs with modified basicity. The basicity can originate from either metal sites or organic ligands. Different approaches used for generation of basic sites are included, and each approach is described with representative examples. The fundamental principles for the design and fabrication of MOFs with basic functionalities are featured. In the characterization section, experimental techniques and theoretical calculations employed for characterization of basic MOFs are summarized. Some representive experimental techniques, such as temperature-programmed desorption of CO₂ (CO₂-TPD) and infrared (IR) spectra of different probing molecules, are covered. Following preparation and characterization, the catalytic applications of MOFs-derived solid bases are dealt with. These solid bases have potential to catalyze some well-known "base-catalyzed reactions" like Knoevenagel condensation, aldol condensation, and Michael addition. Meanwhile, in contrast to conventional solid bases, MOFs show some different catalytic properties due to their special structural and surface properties. Remarkably, characteristic features of MOFs-derived solid bases are described by comparing with conventional inorganic counterparts, keeping in mind the current opportunities and challenges in this field.