Resembling Graphene/Polymer Aerogel Morphology for Advancing the CO2/N2 Selectivity of the Postcombustion CO2 Capture Process

The separation of CO2 from N2 remains a highly challenging task in postcombustion CO2 capture processes, primarily due to the relatively low CO2 content (3-15%) compared to that of N2 (70%). This challenge is particularly prominent for carbon-based adsorbents that exhibit relatively low selectivity. In this study, we present a successfully implemented strategy to enhance the selectivity of composite aerogels made of reduced graphene oxide (rGO) and functionalized polymer particles. Considering that the CO2/N2 selectivity of the aerogels is affected on the one hand by the surface chemistry (offering more sites for CO2 capture) and fine-tuned microporosity (offering molecular sieve effect), both of these parameters were affected in situ during the synthesis process. The resulting aerogels exhibit improved CO2 adsorption capacity and a significant reduction in N2 adsorption at a temperature of 25 °C and 1 atm, leading to a more than 10-fold increase in selectivity compared to the reference material. This achievement represents the highest selectivity reported thus far for carbon-based adsorbents. Detailed characterization of the aerogel surfaces has revealed an increase in the quantity of surface oxygen functional groups, as well as an augmentation in the fractions of micropores (<2 nm) and small mesopores (<5 nm) as a result of the modified synthesis methodology. Additionally, it was found that the surface morphology of the aerogels has undergone important changes. The reference materials feature a surface rich in curved wrinkles with an approximate diameter of 100 nm, resulting in a selectivity range of 50-100. In contrast, the novel aerogels exhibit a higher degree of oxidation, rendering them stiffer and less elastic, resembling crumpled paper morphology. This transformation, along with the improved functionalization and augmented microporosity in the altered aerogels, has rendered the aerogels almost completely N2-phobic, with selectivity values ranging from 470 to 621. This finding provides experimental evidence for the theoretically predicted relationship between the elasticity of graphene-based adsorbents and their CO2/N2 selectivity performance. It introduces a new perspective on the issue of N2-phobicity. The outstanding performance achieved, including a CO2 adsorption capacity of nearly 2 mmol/g and the highest selectivity of 620, positions these composites as highly promising materials in the field of carbon capture and sequestration (CCS) postcombustion technology.

Metal-organic framework derived inverse opal type 3D graphitic carbon for highly stable lithium-ion batteries

Graphitic carbon-based anodes for lithium-ion batteries have seen remarkable development and commercial acceptance during the past three decades. Still, the performance of these materials is limited due to the low surface area, stacking of layers, poor porosity, and meager conductivity. To overcome these limitations, we propose using polystyrene as a core and small-sized zeolitic imidazolate framework-67 (ZIF-67) particles as decorators to develop a highly porous three-dimensional graphitic carbon material. The developed material is optimized with the carbonization temperature for the best anodic performance of LIBs. The pyridinic nitrogen content in the material carbonized at 700 °C makes it high performing and more stable than the samples treated at 600, 800, and 900 °C. The packed coin cell exhibited an initial discharge capacity of 775 mA h g-1 at a current density of 50 mA g-1, which increases to 806 mA h g-1 after testing the material at different current densities for 55 cycles. The packed half-cell exhibited a highly stable performance of about 96% even after testing for 2000 cycles at 1 A g-1.

Facile fabrication of N-doped hierarchical porous carbons derived from soft-templated ZIF-8 for enhanced adsorptive removal of tetracycline hydrochloride from water

N-doped hierarchical porous carbons (NHPCs) were successfully prepared from soft-templated zeolitic imidazolate framework-8 (ZIF-8) precursors using sodium dodecylbenzene sulfonate (SDBS) as a template through facile one-step carbonization and applied in tetracycline hydrochloride (TCH) adsorption. The NHPC synthesized at 1000 °C with an SDBS/Zn²⁺ molar ratio of 0.075 exhibited the highest TCH adsorption (q_m = 80.92 mg g^-1) owing to its relatively large BET surface area (1067.41 m² g^-1) and pore volume (1.22 cm³ g^-1) and the stronger surface interaction between TCH and NHPCs (HC1000-0.075). Compared with surfactant-free ZIF-8-derived carbon (HC), introduction of SDBS in the ZIF-8 precursor not only improved the pore structure of the carbon materials but also increased the nitrogen content and the number of surface functional groups. Adsorption kinetics and isotherms showed that the pseudo-second-order model and Sips model fit the TCH adsorption behavior on HC and HC1000-0.075 well. Adsorption experiments and characterizations revealed that the adsorption mechanism involved in TCH adsorption on HC1000-0.075 mainly depended on the synergistic effect of pore filling, H-bonding, π-π interactions, and weak electrostatic interactions. This study provides an effective and simple strategy for fabricating MOF-derived NHPCs as a promising adsorbent for the removal of antibiotics from water.

Green Synthesis of Zeolitic Imidazolate Frameworks: A Review of Their Characterization and Industrial and Medical Applications

Metal organic frameworks (MOF) are a class of hybrid networks of supramolecular solid materials comprising a large number of inorganic and organic linkers, all bound to metal ions in a well-organized fashion. Zeolitic imidazolate frameworks (ZIFs) are a sub-group of MOFs with imidazole as an organic linker to metals; it is rich in carbon, nitrogen, and transition metals. ZIFs combine the classical zeolite characteristics of thermal and chemical stability with pore-size tunability and the rich topological diversity of MOFs. Due to the energy crisis and the existence of organic solvents that lead to environmental hazards, considerable research efforts have been devoted to devising clean and sustainable synthesis routes for ZIFs to reduce the environmental impact of their preparation. Green chemistry is the key to sustainable development, as it will lead to new solutions to existing problems. Moreover, it will present opportunities for new processes and products and, at its heart, is scientific and technological innovation. The green chemistry approach seeks to redesign the materials that make up the basis of our society and our economy, including the materials that generate, store, and transport our energy, in ways that are benign for humans and the environment and that possess intrinsic sustainability. This study covers the principles of green chemistry as used in designing strategies for synthesizing greener, less toxic ZIFs the consume less energy to produce. First, the necessity of green methods in today's society, their replacement of the usual non-green methods and their benefits are discussed; then, various methods for the green synthesis of ZIF compounds, such as hydrothermally, ionothermally, and by the electrospray technique, are considered. These methods use the least harmful and toxic substances, especially concerning organic solvents, and are also more economical. When a compound is synthesized by a green method, a question arises as to whether these compounds can replace the same compounds as synthesized by non-green methods. For example, is the thermal stability of these compounds (which is one of the most important features of ZIFs) preserved? Therefore, after studying the methods of identifying these compounds, in the last part, there is an in-depth discussion on the various applications of these green-synthesized compounds.

Porous carbon nanoarchitectonics for the environment: detection and adsorption

As a post-nanotechnology concept, nanoarchitectonics has emerged from the 20th century to the 21st century. This review summarizes the recent progress in the field of metal-free porous carbon nanoarchitectonics.

Self-adjusted bimetallic zeolitic-imidazolate framework-derived hierarchical magnetic carbon composites as efficient adsorbent for optimizing drug contaminant removal

The construction of efficient and superior adsorbed materials for the precise removal of hazardous contaminants from water have gained significant attention by the scientific community. In this work, a facile bimetallic zeolitic-imidazolate framework (Co_xZn_y-JUC-160) by using self-adjusted strategy (SAS) was developed to synthesize various N-doped Co-based hierarchical porous carbon composites through sacrificial template route. A series of highly porous magnetic materials with well-dispersed or reduced Co particle size have been fabricated by fine tuning the ratio of Co and Zn in the precursors. For the first time the effect of the Co/Zn ratio on the textural properties and drug adsorption performance of the resultant porous carbon composites have been investigated systematically. Remarkably, the optimal Co@NC-1/4-900 possesses large specific surface area, hierarchical pore structures, and well-distributed Co adsorption sites which facilitates the exposure of active Co center and realizes fast diffusion of amodiaquine (ADQ) molecules with record-high adsorption capacities (890.23 mg g^-1). The presented synthetic strategy provides deep insights into the development of highly efficient recyclable magnetic adsorbent for the removal of contaminants.

From metal-organic frameworks to porous carbon materials: recent progress and prospects from energy and environmental perspectives

Metal-organic frameworks (MOFs) have emerged as promising materials in the areas of gas storage, magnetism, luminescence, and catalysis owing to their superior property of having highly crystalline structures. However, MOF stability toward heat or humidity is considerably less as compared to carbons because they are constructed from the assembly of ligands with metal ions or clusters via coordination bonds. Transforming MOFs into carbons is bringing the novel potential for MOFs to achieve industrialization, and carbons with controlled pore sizes and surface doping are one of the most important porous materials. By selecting MOFs as a precursor or template, carbons with heteroatom doping and well-developed pores can be achieved. In this review, we discussed the state-of-art study progress made in the new development of MOF-derived metal-free porous carbons. In particular, the potential use of metal-free carbons from environmental and energy perspectives, such as adsorption, supercapacitors, and catalysts, were analyzed in detail. Moreover, an outlook for the sustainable development of MOF-derived porous carbons in the future was also presented.

Porous, flexible, and core-shell structured carbon nanofibers hybridized by tin oxide nanoparticles for efficient carbon dioxide capture

HYPOTHESIS

Carbon based nanofibrous materials are considered to be promising sorbents for the CO₂ capture and storage. However, the precise control of porous structure with flexibility still remains a challenging task. In this research, we report a simple strategy to develop tin oxide (SnO₂) embedded, flexible and highly porous core-shell structured carbon nanofibers (CNFs) derived from polyacrylonitrile (PAN)/polyvinylidene fluoride (PVDF) core-shell nanofibers.

EXPERIMENT

PAN/PVDF core-shell solutions were electrospun using co-axial electrospinning process. The as spun PAN core, and PVDF shell, with an appropriate amount of SnO₂, fibers were stabilized followed by carbonization to develop SnO₂ embedded highly porous and flexible core-shell structured CNFs.

FINDINGS

The optimized CNFs membrane shows a prominent CO₂ capture capacity of 2.6 mmol g^-1 at room temperature, excellent CO₂ selectivity than N₂, and a remarkable cyclic stability. After 20 adsorption-desorption cycles, the CO₂ capture capacity retains >95% of the preliminary value showing the long-term stability and practical worth of the final product. The loading of SnO₂ nanoparticles in the carbon matrix not only enhanced the thermal stability of the precursor nanofibers, their surface characteristics, and porous structure to capture CO₂ molecules, but also improves the flexibility of the CNFs by serving as a plasticizer for single-fiber-crack connection. Meaningfully, the flexible SnO₂ embedded core-shell CNFs with excellent structural stability can prevail the limitations of annihilation and collapse of structures for conventional adsorbents, which makes them strongly useful and applicable. This research introduces a new route to produce highly porous and flexible materials as solid adsorbents for CO₂ capture.

Development and Applications of MOFs Derivative One-Dimensional Nanofibers via Electrospinning: A Mini-Review

Metal organic frameworks (MOFs) have been exploited for various applications in science and engineering due to the possibility of forming different mesoscopic frameworks and pore structures. To date, further development of MOFs for practical applications in areas such as energy storage and conversion have encountered tremendous challenge owing to the unitary porous structure (almost filled entirely with micropores) and conventional morphology (e.g., sphere, polyhedron, and rod shape). More recently, one-dimensional (1D) MOFs/nanofibers composites emerged as a new molecular system with highly engineered novel structures for tailored applications. In this mini-review, the recent progress in the development of MOFs-based 1D nanofibers via electrospinning will be elaborated. In particular, the promising applications and underlying molecular mechanism of electrospun MOF-derived carbon nanofibers are primarily focused and analyzed here. This review is instrumental in providing certain guiding principles for the preparation and structural analysis of MOFs/electrospun nanofibers (M-NFs) composites and electrospun MOF-derived nanomaterials.

From ZIF nanoparticles to hierarchically porous carbon: toward very high surface area and high-performance supercapacitor electrode materials

A high-performance capacitive energy storage material was derived from a new nanoscale ZIF precursor by using the activating reagent KOH, exhibiting a high surface area of 3253 m² g⁻¹ and an ultra-high specific capacitance.

Fe/N-doped carbon nanofibers with Fe3O4/Fe2C nanocrystals enchased as electrocatalysts for efficient oxygen reduction reaction

A Fe-based carbon material with multi active sites of Fe–N_x, Fe₃O₄ and Fe₂C for oxygen reduction was synthesized through facile pyrolysis of a Fe–porphyrin conjugated microporous polymer.

Ultrahigh Metal-Organic Framework Loading and Flexible Nanofibrous Membranes for Efficient CO2 Capture with Long-Term, Ultrastable Recyclability

In the global transition to a sustainable low-carbon economy, CO₂ capture and storage technology plays a key role in reducing emissions. Metal-organic frameworks (MOFs) are crystalline materials with ultrahigh porosity, tunable pore size, and rich functionalities, holding the promise for CO₂ capture. However, the intrinsic fragility and depressed processability of MOF crystals make the fabrication of the flexible MOF nanofibrous membrane (NFM) rather challenging. Herein, we demonstrate an effective strategy for the versatile preparation of self-supported and flexible HKUST-1 NFM with ultrahigh HKUST-1 loading (up to 82 wt %) and stable and uniform HKUST-1 growth through the combination of electrospinning, multistep seeded growth, and activation process. The loading rate of MOF is the highest level among the reported analogues. Significantly, the HKUST-1 NFM exhibits a prominent CO₂ adsorption capacity of 3.9 mmol g^-1, good CO₂/N₂ selectivity, and remarkable recyclability. The CO₂ capacity retains ∼95% (3.7 mmol g^-1) of the initial value after 100 adsorption-desorption cycles, indicating that the HKUST-1 NFM has long-term and ultrastable recyclability and a significant practical value. Thus, the low-cost and scalable production pathway is able to convert MOF particles into self-supported and flexible NFMs, and thereby, they are better applied to the efficient postcombustion CO₂ capture.

Metal-organic framework-derived metal-free highly graphitized nitrogen-doped porous carbon with a hierarchical porous structure as an efficient and stable electrocatalyst for oxygen reduction reaction

Nitrogen-doped carbon materials are promising oxygen reduction reaction (ORR) electrocatalysts owing to high performance and stability. Herein, a three-dimensional porous bio-MOF-1, Zn₈(Ad)₄(Bpdc)₆O·2Me₂NH₂ (Ad = adeninate; Bpdc = biphenyldicarboxylate), was used as precursor to fabricate N-doped porous carbon materials (NPC-1000-ts, where 1000 stands for the carbonization temperature and t represents the carbonization time, t = 2, 3 and 4 h) by simple carbonization under Ar atmosphere. The porous carbon materials had different contents of graphitic N and graphitization degrees of carbon. The catalytic activities of NPCs as metal-free ORR electrocatalysts were studied. The obtained NPC-1000-4 (pyrolysis under 1000 °C for 4 h) displayed outstanding ORR performance, with a positive onset potential (-0.012 V), a higher half-wave potential (E_1/2) (-0.13 V) and a larger limiting current density (-5.76 mA/cm²) at -0.8 V (vs. Ag/AgCl) in KOH solution (0.1 M) than those of commercial Pt/C (20 wt%) catalyst (E_onset = -0.014 V, E_1/2 = -0.14 V and -5.08 mA/cm² at -0.8 V vs. Ag/AgCl). Obviously, the onset potential of NPC-1000-4 surpassed that of Pt/C, which was rare among currently available studies on metal-free nitrogen-doped porous carbon materials. Graphitic N significantly affected ORR catalytic performance besides graphitization degree of carbon. Meanwhile, NPC-1000-4 allowed an effective 4e^--dominant ORR process, and most importantly, coupled with much higher long-term stability (89.5%) than that of commercial Pt/C (20 wt%, 65.8%) catalyst and higher resistance to methanol poisoning. The remarkable ORR activity of NPC-1000-4 can be ascribed to large surface area, considerable hierarchical porosity, high graphitization degree and synergism between enriched active sites and high portion of graphitic N. Overall, the findings guide the development of MOF-derived metal-free N-doped carbon materials as high-activity non-precious electrocatalysts for ORR.

Facile synthesis of oxidized activated carbons for high-selectivity and low-enthalpy CO2 capture from flue gas

The oxidized activated carbon obtained using a facile synthetic approach shows high-capacity and low-enthalpy CO₂ capture with a selectivity of 48.5 toward flue gas, which is double that of the pristine activated carbon.

Balsam-Pear-Skin-Like Porous Polyacrylonitrile Nanofibrous Membranes Grafted with Polyethyleneimine for Postcombustion CO2 Capture

Amine-containing sorbents have been extensively studied for postcombustion carbon dioxide (CO₂) capture because of their ability to chemisorb CO₂ from the flue gas. However, most sorbents are in the form of powders currently, which is not the ideal configuration for the flue gas separation because of the fragile nature and poor mechanical properties, resulting in blocking of the flow pipes and difficult recycling. Herein, we present a novel approach for the facile fabrication of flexible, robust, and polyethyleneimine-grafted (PEI-grafted) hydrolyzed porous PAN nanofibrous membranes (HPPAN-PEI NFMs) through the combination of electrospinning, pore-forming process, hydrolysis reaction, and the subsequent grafting technique. Excitingly, we find that all the resultant porous PAN (PPAN) fibers exhibit a balsam-pear-skin-like porous structure due to the selective removal of poly(vinylpyrrolidone) (PVP) from PAN/PVP fibers by water extraction. Significantly, the HPPAN-PEI NFMs retain their mesoporosity, as well as exhibit good thermal stability and prominent tensile strength (11.1 MPa) after grafting, guaranteeing their application in CO₂ trapping from the flue gas. When exposed to CO₂ at 40 °C, the HPPAN-PEI NFMs show an enhanced CO₂ adsorption capacity of 1.23 mmol g^-1 (based on the overall quantity of the sample) or 6.15 mmol g^-1 (based on the quantity of grafted PEI). Moreover, the developed HPPAN-PEI NFMs display significantly selective capture for CO₂ over N₂ and excellent recyclability. The CO₂ capacity retains 92% of the initial value after 20 adsorption-desorption cycle tests, indicating that the resultant HPPAN-PEI NFMs have good long-term stability. This work paves the way for fabricating NFM-based solid adsorption materials endowed with a porous structure applied to efficient postcombustion CO₂ capture.

Solvent-Induced Cadmium(II) Metal-Organic Frameworks with Adjustable Guest-Evacuated Porosity: Application in the Controllable Assembly of MOF-Derived Porous Carbon Materials for Supercapacitors

In this work, five new cadmium metal-organic frameworks (Cd-MOFs 1-5) have been synthesized from solvothermal reactions of Cd(NO₃ )₂ ⋅4 H₂ O with isophthalic acid and 1,4-bis(imidazol-1-yl)-benzene under different solvent systems of CH₃ OH, C₂ H₅ OH, (CH₃ )₂ CHOH, DMF, and N-methyl-2-pyrrolidone (NMP), respectively. Cd-MOF 1 shows a 3D diamondoid framework with 1D rhombic and hexagonal channels, and the porosity is 12.9 %. Cd-MOF 2 exhibits a 2D (4,4) layer with a 1D parallelogram channel and porosity of 23.6 %. Cd-MOF 3 has an 8-connected dense network with the Schäfli symbol of [4²⁴ ⋅6⁴ ] based on the Cd₆ cluster. Cd-MOFs 4-5 are isomorphous, and display an absolutely double-bridging 2D (4,4) layer with 1D tetragonal channels and porosities of 29.2 and 28.2 %, which are occupied by DMF and NMP molecules, respectively. Followed by the calcination-thermolysis procedure, Cd-MOFs 1-5 are employed as precursors to prepare MOF-derived porous carbon materials (labeled as PC-me, PC-eth, PC-ipr, PC-dmf and PC-nmp), which have the BET specific surface area of 23, 51, 10, 122, and 96 m²  g^-1 , respectively. The results demonstrate that the specific surface area of PCs is tuned by the porosity of Cd-MOFs, where the later is highly dependent on the solvent. Thereby, the specific surface area of PCs could be adjusted by the solvent used in the synthese of MOF precusors. Significantly, PCs have been further activated by KOH to obtain activated carbon materials (APCs), which possess even higher specific surface area and larger porosity. After a series of characterization and electrochemical investigations, the APC-dmf electrode exhibits the best porous properties and largest specific capacitances (153 F g^-1 at 5 mV s^-1 and 156 F g^-1 at 0.5 Ag^-1 ). Meanwhile, the APC-dmf electrode shows excellent cycling stability (ca. 84.2 % after 5000 cycles at 1 Ag^-1 ), which can be applied as a suitable electrode material for supercapacitors.

Synthesis and application of a MOF-derived Ni@C catalyst by the guidance from an in situ hot stage in TEM

Metal–organic frameworks (MOFs) as a class of crystalline porous solids have attracted considerable attention due to their promising potential performance.

Simple coordination complex-derived Ni NP anchored N-doped porous carbons with high performance for reduction of nitroarenes

N-doped hierarchical porous carbons anchored with nickel nanoparticles were prepared by using the simple coordination complex Ni(dmg)₂ as a precursor.