The excessive emission of greenhouse gases, which leads to global warming and alarms the world, has triggered a global campaign for carbon neutrality. Carbon capture and sequestration (CCS) technology has aroused wide research interest as a versatile emission mitigation technology. Metal-organic frameworks (MOFs), as a new class of high-performance adsorbents, hold great potential for CO2 capture from large point sources and ambient air due to their ultra-high specific surface area as well as pore structure. In recent years, MOFs have made great progress in the field of CO2 capture and separation, and have published a number of important results, which have greatly promoted the development of MOF materials for practical carbon capture applications. This review summarizes the most recent advanced research on MOF materials for carbon capture in various application scenarios over the past six years. The strategies for enhancing CO2 selective adsorption and separation of MOFs are described in detail, along with the development of MOF-based composites. Moreover, this review also systematically summarizes the highly concerned issues of MOF materials in practical applications of carbon capture. Finally, future research on CO2 capture by MOF materials is prospected.

In this study, an innovative and cost-effective ionic polymer for CO2 capture and utilization for the first time, using abundant and nonfood-based biomass lignin is reported. The modified ionic polymer synthesizes through the reaction of glycidyltrimethylammonium chloride with lignin under alkaline conditions to yield quaternary ammonium ionic functionality. Subsequently, the hydroxide-based pure ionic lignin polymer is employed for CO2 capture from both direct air and concentrated CO2 sources at room temperature and atmospheric pressure. Structural characterization of the polymers is accomplished through 1H, 13C, and 2D-heteronuclear single quantum coherence (HSQC) NMR, and FT-IR spectroscopy. The CO2 capture process is established through the formation of bicarbonate ions alongside the presence of CO2. The captured CO2 is precisely quantified by using inverse-gated proton decoupled 13C NMR with an internal standard (trioxane). Remarkably, the captured-CO2 amounts of ionic lignin polymer are 1.06 mmol g-1 (47 mg g-1) from concentrated-CO2 source and 0.60 mmol g-1 (26 mg g-1) from direct-air. The captured-CO2 in ionic lignin polymer is released in controlled manner and utilized in the synthesis of cyclic carbonate, showcasing the productive application of the captured carbon. Moreover, the fully controlled recovering of ionic lignin polymer achieves via repeated CO2 release ↔ CO2 capture.

This work studied the low-temperature sorption of carbon dioxide on impregnated silica gel. An impregnating agent was used polyethyleneimine. The content of the impregnating agent in the silica gel matrix was 33.4 wt.%. Material properties such as the Brunauer-Emmett-Teller (BET) surface area, pore distribution, total pore volume, and thermal stability of the impregnated material were determined for the sample. During the measurement of the adsorption-desorption cycles, the loss of the impregnating agent in the material matrix was also determined. Due to the decrease in the content of polyethyleneimine, the sorption capacity of the adsorbent for CO2 also decreased. It was found that after the 20th adsorption-desorption cycle, the content of the impregnating agent in the adsorbent dropped by 3.15 wt.%, and, as a result, the adsorption capacity for CO2 dropped to almost half.

Porous metal-organic frameworks (MOFs), also known as porous coordination polymers, represent a new class of porous materials, and one of their striking features lies in their tunable, designable, and functionalizable nanospace. This nanospace within MOFs provides virtually plenty of room for imagination, allowing designed incorporation of different size, shape, and functionalities for targeted gas storage and separation applications. Furthermore, the features of high porosities, tunable framework structures and pore sizes, and immobilized functional sites enable MOF materials to fully make use of their nanopore space for gas storage, to optimize their sieving effects, and to differentiate their interactions with gas molecules for gas separation. In this review article, we highlight some recent significant advances in developing microporous MOFs for some of the most important gas storage and separation applications.

The use of powered activated carbon is often limited by inconsistent particle sizes and porosities, leading to reduced adsorption efficiencies. In this study, we demonstrated a practical and environmentally friendly method for creating a 3D graphene nanostructure with highly uniform ultramicropores from wood-based biomass through a series of delignification, carbonization, and activation processes. In addition, we evaluated the capture characteristics of this structure for CO2, CH4, and N2 gases as well as its selectivity for binary-mixture gases. Based on textural and chemical analyses, the delignified monolith had a lamellar structure interconnected by cellulose-based fibers. Interestingly, applying the KOH vapor activation technique solely to the delignified samples led to the formation of a monolithic 3D network composed of interconnected graphene sheets with a high degree of crystallinity. Especially, the Act. 1000 sample exhibited a specific surface area of 1480 m2/g and a considerable pore volume of 0.581 cm3/g, featuring consistently uniform ultramicropores over 90% in the range of 3.5-11 Å. The monolithic graphene-based samples, predominantly composed of ultramicropores, demonstrated a notably heightened capture capacity of 6.934 mol/kg at 110 kPa for CO2, along with favorable selectivity within binary gas mixtures (CO2/N2, CO2/CH4, and CO2/CH4). Our findings suggest that this biomass-derived 3D structure has the potential to serve as a monolithic adsorbent in gas separation applications.

Mass transfer in liquid phase is the rate-limiting step for carbon dioxide capture by ammonia water, which results in a low total mass transfer coefficient and thus a poor carbon dioxide removal efficiency. For this issue, this study established a venturi reactor with an excellent mass transfer performance to promote mass transfer rate during carbon dioxide capture, and investigated the effect of operating parameters of the venturi reactor on carbon dioxide removal efficiency and overall mass transfer coefficient. The results showed that with an increasing flow rate of the jet from 8.31 to 12.73 L/min, the carbon dioxide removal efficiency decreased due to the increase of flow rate of flue gas, and the changing trend of overall mass transfer coefficient gradually transited from increasing to decreasing with the extension of reaction time. The carbon dioxide removal efficiency and the overall mass fraction coefficient increased upon the increase of ammonia concentration from 0.1 wt% to 0.75 wt%. With the increase of inlet carbon dioxide concentration from 7% to 19%, the carbon dioxide removal efficiency and the overall mass transfer coefficient decreased. Venturi reactor was of a fast mass transfer rate during carbon dioxide capture, and the maximum CO2 removal efficiency was 96.4% at ammonia concentration of 0.75 wt%, CO2 volume concentration of 15%, flow rate of jet of 8.36 L/min. This study provided a theoretical value for the development of venturi reactor for carbon dioxide capture.

Carbonic anhydrase (CA) has a promising application as a green and efficient biocatalyst for CO2 capture, and many successful cases of immobilizing CA have been reported. However, CA antifouling coatings on metal for CO2 sequestration have rarely been reported. Herein, dimeric CA from Sulfurihydrogenibium azorense (SazCA) with a ferritin tag, which was prepared by low-speed centrifugation with high yield, was adopted as a free enzyme and encapsulated in the sol-gel silica. The silica-immobilized CAs were dispersed into the commercialized metal-antifouling epoxy resin paint to obtain CA coated nickel foams, which had excellent stability, with 90 % and 67 % residual activity after 28 days of incubation at 30 °C and 60 °C, respectively. The CA coated nickel foams remained 60 % original activity after 6 cycles of use within 28 days. Then, a CA-microalgae carbon capture device was constructed using the CA coated nickel foams and Chlorella. The growth rate of Chlorella was significantly increased and the biomass of Chlorella increased by 29 % compared with control after 7 days of incubation. Due to the simple and cost-effective preparation process, sustainable and efficient CO2 absorption, this easy-to-scale up CA coated nickel foam has great potential in CA assisted microalgae-based CO2 capture and carbon neutrality.

Activated carbon is an attractive adsorbent for capturing various environmental pollutants, including CO2. Herein, an optimal synthesis and impressive performance of activated carbon made from Balanites aegyptiaca (Desert date) seed shells is reported, which is an abundant agricultural waste in the Middle East and Africa. The synthesis route involved pretreating the biomass with KOH and heating it under a suitable temperature profile. An optimal KOH-to-biomass ratio and multi-stage carbonization yielded activated carbon with a surface area above 3000 m2/g and an average pore size of nearly 4.1 nm. At 0 °C, this activated carbon exhibited CO2 uptake of 11.3 mmol g-1 that surpassed the uptake capacity of previously reported activated carbons. The selectivity towards CO2 was also found to be significantly higher compared to other gases. Thus, the present approach demonstrates an efficient conversion of agricultural waste to activated carbon for capturing CO2 and other environmental contaminants.

Covalent organic frameworks are a novel class of crystalline porous polymers that enable molecular design of extended polygonal skeletons to attain well-defined porous structures. However, construction of a framework that allows remote control of pores remains a challenge. Here we report a strategy that merges covalent, noncovalent, and photo chemistries to design photoresponsive frameworks with reversibly and remotely controllable pores. We developed a topology-guided multicomponent polycondensation system that integrates protruded tetrafluoroazobenzene units as photoresponsive sites on pore walls at predesigned densities, so that a series of crystalline porous frameworks with the same backbone can be constructed to develop a broad spectrum of pores ranging from mesopores to micropores. Distinct from conventional azobenzene-based systems, the tetrafluoroazobenzene frameworks are highly sensitive to visible lights to undergo high-rate isomerization. The photoisomerization exerts profound effects on pore size, shape, number, and environment, as well as molecular uptake and release, rendering the system able to convert and switch pores reversibly and remotely with visible lights. Our results open a way to a novel class of smart porous materials with pore structures and functions that are convertible and manageable with visible lights.

Non-aqueous absorbents (NAAs) have attracted increasing attention for CO2 capture because of their great energy-saving potential. Primary diamines which can provide high CO2 absorption loading are promising candidates for formulating NAAs but suffer disadvantages in regenerability. In this study, a promising strategy that using tertiary amines (TAs) as proton-transfer mediators was proposed to enhance the regenerability of an aminoethylethanolamine (AEEA, diamine)/dimethyl sulfoxide (DMSO) (A/D) NAA. Surprisingly, some employed TAs such as N,N-diethylaminoethanol (DEEA), N,N,N\',N\'\',N\'\'-pentamethyldiethylenetriamine (PMDETA), 3-dimethylamino-1-propanol (3DMA1P), and N,N-dimethylethanolamine (DMEA) enhanced not only the regenerability of the A/D NAA but also the CO2 absorption performance. Specifically, the CO2 absorption loading and cyclic loading were increased by about 12.7% and 15.5%-22.7%, respectively. The TA-enhanced CO2 capture mechanism was comprehensively explored via nuclear magnetic resonance technique and quantum chemical calculations. During CO2 absorption, the TA acted as an ultimate proton acceptor for AEEA-zwitterion and enabled more AEEA to form carbamate species (AEEACOO-) to store CO2, thus enhancing CO2 absorption. For CO2 desorption, the TA first provided protons directly to AEEACOO- as a proton donor; moreover, it functioned as a proton carrier and facilitated the low-energy step-wise proton transfer from protonated AEEA to AEEACOO-. Consequently, the presence of TA made it easier for AEEACOO- to obtain protons to decompose, resulting in enhanced CO2 desorption. In a word, introducing the TA as a proton-transfer mediator into the A/D NAA enhanced both the CO2 absorption performance and the regenerability, which was an efficient way to \"kill two birds with one stone\".