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

N-doped carbon nanospheres synthesized from a newly designed eco-friendly sustainable polymer for highly selective CO2 capture

N-doped carbon nanospheres and porous carbon were produced by a hydrothermal template and the activation of hexamethylenetetramine (HMTA as a nitrogen source and activator) and ZnCl2 (only as an activator) from a poly(Ri-S-ε-CL-PDMS) multiblock/graft copolymer produced using a renewable resource and eco-friendly autoxidation. N-doped carbon nanospheres (PPiSiHMTA) exhibited excellent CO2 adsorption (2.73 mmol/g at 0 °C and 0.15 atm, 1.72 mmol/g at 25 °C and 0.15 atm) and CO2/N2 selectivity (344-512). Despite the higher BET surface area and pore volume, porous carbon (PPiSi) showed low CO2 adsorption (1.21 and 0.71 mmol/g, 0.15 atm) and CO2/N2 selectivity (57 and 112). PPiSiHMTA and PPiSi have low isosteric heats of adsorption (Qst, 18-33 kJ/mol) and stability in humid environments. In addition, PPiSiHMTA exhibited an excellent CO2 recycling performance. The experimental data on CO₂ adsorption was evaluated using various isotherm models, including Freundlich, Langmuir, Sips, and Temkin. The results demonstrated a nearly perfect fit between the Freundlich isotherm and the experimental data, indicating the heterogeneous nature of the adsorbent surfaces. Our study is promising for industrial applications, offering excellent CO2 adsorption, CO2/N2 selectivity, moisture stability, and porous material fabrication strategies.

Solvent-Free Synthesis of Hollow Carbon Nanostructures for Efficient Sodium Storage

The structural characteristics of hollow carbon nanostructures (HCNs) result in intriguing physicochemical properties and various applications, especially for electrochemical energy storage applications. However, the currently solvent-based template methods to prepare HCNs are still far from meeting the facile, environment-friendly, and scalable demand. Herein, we explored a general and facile solvent-free block copolymer self-assembly approach to prepare various hollow hard carbon nanostructures, including hollow carbon nanofibers, hollow carbon Janus nanotadpoles, hollow carbon spheres, etc. It was found that the obtained HCNs possess abundant active sites, fast pathways for electrons/ions transport, and superior electronic conducting connectivity, which are promising for efficient electrochemical energy storage. Typically, the resultant hollow carbon nanofibers with a thick-walled tube deliver a high reversible capacity (431 mAh g-1) and excellent rate performance (259 mAh g-1 at 800 mA g-1) for sodium ion storage. This intelligent solvent-free block copolymer self-assembly method would inspire the design of hollow hard carbon-based nanostructures for advanced applications in various energy conversion and storage.

Design of biomass-based N, S co-doped porous carbon via a straightforward post-treatment strategy for enhanced CO2 capture performance

Biomass-based adsorbents are considered to have great potential for CO₂ capture due to their low cost, high efficiency and exceptional sustainability. The aim of this work is to design a simple method for preparing biomass-based adsorbents with abundant active sites and large numbers of narrow micropores, so as to enhance CO₂ capture performance. Herein, N, S co-doped porous carbon (NSPC) was created utilizing walnut shell-based microporous carbon (WSMC) as the main framework and thiourea as N/S dopant through physical grinding and post-treatment process at a moderate temperature without any other reagents and steps. By altering the post-treatment parameters, a series of porous carbons with varying physico-chemical properties were prepared to discuss the roles of microporosity and N/S functional groups in CO₂ adsorption. NSPC with narrow micropore volume of 0.74 cm³ g^-1, N content of 4.89 % and S contents of 0.71 % demonstrated the highest CO₂ adsorption capacity of 7.26 (0 °C) and 5.51 mmol g^-1 (25 °C) at 1 bar. Meanwhile, a good selectivity of binary gas mixture CO₂/N₂ (15/85) of 29.72 and outstanding recyclability after ten cycles of almost 100 % adsorption capacity retention were achieved. The proposed post-treatment method was beneficial in maintaining the narrow micropores and forming N/S active sites, which together improve the CO₂ adsorption performance of NSPC. The novel NSPC displays amazing CO₂ adsorption characteristics, and the practical, affordable synthetic approach exhibits significant potential to produce highly effective CO₂ adsorbents on a broad scale.

Solvent-Free Synthesis of Polymer Spheres and the Activation to Porous Carbon Spheres for Advanced Aluminum-Ion Hybrid Capacitors

Porous carbon spheres (PCSs) characteristic of perfect symmetry and ideal rheological property have great potential in electrochemical energy storage (EES). However, conventional synthesis of PCSs heavily relies on solution-based methods that may lead to environmental issues. Herein, an environment-friendly solvent-free method toward the facile and mass production of m-phenylenediamine-formaldehyde (MPF) resin spheres, which can be converted into PCSs after carbonization and activation is reported. An ultrahigh productivity of 25.89 g in a 100-mL container and an impressive percent yield of 98.89% can be achieved for the MPF resin spheres, which are further converted into carbon spheres with a reasonable yield of 14.5% after carbonization. When employed as the cathode material for aluminum-ion hybrid capacitors, the obtained PCSs afford a double-layer capacity of ≈200 mAh g^-1 , the highest value among reported porous carbon materials for Al-based EES devices. It is anticipated that the solvent-free synthesis method for PCSs developed here may play a significant role in other EES devices, such as magnesium-ion and calcium-ion hybrid capacitors.

Directed Stabilization by Air-Milling and Catalyzed Decomposition by Layered Titanium Carbide Toward Low-Temperature and High-Capacity Hydrogen Storage of Aluminum Hydride

AlH₃ is a metastable hydride with a theoretical hydrogen capacity of 10.01 wt % and is very easy to decompose during ball milling especially in the presence of many catalysts, which will lead to the attenuation of the available hydrogen capacity. In this work, AlH₃ was ball milled in air (called "air-milling") with layered Ti₃C₂ to prepare a Ti₃C₂-catalyzed AlH₃ hydrogen storage material. Such air-milled and Ti₃C₂-catalyzed AlH₃ possesses excellent hydrogen storage performances, with a low initial decomposition temperature of just 61 °C and a high hydrogen release capacity of 8.1 wt %. In addition, 6.9 wt % of hydrogen can be released within 20 min at constantly 100 °C, with a low activation energy as low as 40 kJ mol^-1. Air-milling will lead to the formation of an Al₂O₃ oxide layer on the AlH₃ particles, which will prevent continuous decomposition of AlH₃ when milling with active layered Ti₃C₂. The layered Ti₃C₂ will grip on and intrude into the AlH₃ particle oxide layers and then catalyze the decomposition of AlH₃ during heating. The strategy employing air-milling as a synthesis method and utilizing layered Ti₃C₂ as a catalyst in this work can solve the key issue of severe decomposition during ball milling with catalysts economically and conveniently and thus achieve both high-capacity and low-temperature hydrogen storage of AlH₃. This air-milling method is also effective for other active catalysts toward both reducing the decomposition temperature and increasing the available hydrogen capacity of AlH₃.

Fluorine-Induced Electric Field Gradient in 3D Porous Aromatic Frameworks for Highly Efficient Capture of Xe and F-Gases

The development of robust and efficient porous adsorbents is essential for capturing xenon (Xe) and perfluorinated electron specialty gases (F-gases) in semiconductor exhaust gases, as toxic and corrosive gases coexist in high-temperature plasma degradation off-gases. Herein, two three-dimensional (3D) fluorinated porous aromatic frameworks (PAFs) with abundant fluorine (labeled PAF-4F and PAF-8F) were synthesized. The two PAFs exhibit high IAST selectivity in capturing Xe and F-gases from semiconductor off-gases, as well as excellent physicochemical stability and reusability, which have been collaboratively verified by single-component gas adsorption and regeneration tests, etc. Density functional theory (DFT) simulation revealed that the entry of strongly electronegative fluorine atoms into PAFs causes localized charge separation on the polymer pore surface, resulting in the preferential adsorption of high-polarizability Xe and F-gases via induced electric field gradients. Systematic studies have sufficiently manifested the great potential of fluorine-functionalized porous materials to effectively capture Xe and F-gases, which provides practical insights into the fabrication of highly stable porous adsorbents for harsh operating conditions.

Quo Vadis Dry Reforming of Methane?—A Review on Its Chemical, Environmental, and Industrial Prospects

In recent years, the catalytic dry reforming of methane (DRM) has increasingly come into academic focus. The interesting aspect of this reaction is seemingly the conversion of CO2 and methane, two greenhouse gases, into a valuable synthesis gas (syngas) mixture with an otherwise unachievable but industrially relevant H2/CO ratio of one. In a possible scenario, the chemical conversion of CO2 and CH4 to syngas could be used in consecutive reactions to produce synthetic fuels, with combustion to harness the stored energy. Although the educts of DRM suggest a superior impact of this reaction to mitigate global warming, its potential as a chemical energy converter and greenhouse gas absorber has still to be elucidated. In this review article, we will provide insights into the industrial maturity of this reaction and critically discuss its applicability as a cornerstone in the energy transition. We derive these insights from assessing the current state of research and knowledge on DRM. We conclude that the entire industrial process of syngas production from two greenhouse gases, including heating with current technologies, releases at least 1.23 moles of CO2 per mol of CO2 converted in the catalytic reaction. Furthermore, we show that synthetic fuels derived from this reaction exhibit a negative carbon dioxide capturing efficiency which is similar to burning methane directly in the air. We also outline potential applications and introduce prospective technologies toward a net-zero CO2 strategy based on DRM.

Transforming Porous Silica Nanoparticles into Porous Liquids with Different Canopy Structures for CO2 Capture

Porous liquids (PLs) have both liquid fluidity and solid porosity, thereby offering a variety of applications, such as gas sorption and separation, homogeneous catalysis, energy storage, and so forth. In this research, canopies with varying structures were utilized to modify porous silica nanoparticles to develop Type I PLs. According to experimental results, the molecular weight of canopies should be high enough to maintain the porous materials in the liquid state at room temperature. Characterization results revealed that PL_1_M2070 and PL_1_AC1815 displayed low viscosity and good fluidity. Both low temperature and high pressure positively influenced CO₂ capacity. The cavity occupancy resulted in poorer sorption capacity of PLs with branched canopies in comparison with that with linear canopies. Furthermore, the sorption capacity of PL_1_M2070 was 90.5% of the original CO₂ sorption capacity after 10 sorption/desorption cycles, indicating excellent recyclability.

Hypercrosslinked Ionic Polymers with High Ionic Content for Efficient Conversion of Carbon Dioxide into Cyclic Carbonates

The effective conversion of carbon dioxide (CO2) into cyclic carbonates requires porous materials with high ionic content and large specific surface area. Herein, we developed a new systematic post-synthetic modification strategy for synthesizing imidazolium-based hypercrosslinked ionic polymers (HIPs) with high ionic content (up to 2.1 mmol g−1) and large specific surface area (385 m2 g−1) from porous hypercrosslinked polymers (HCPs) through addition reaction and quaternization. The obtained HIPs were efficient in CO2 capture and conversion. Under the synergistic effect of high ionic content, large specific surface area, and plentiful micro/mesoporosity, the metal-free catalyst [HCP-CH2-Im][Cl]-1 exhibited quantitative selectivities, high catalytic yields, and good substrate compatibility for the conversion of CO2 into cyclic carbonates at atmospheric pressure (0.1 MPa) in a shorter reaction time in the absence of cocatalysts, solvents, and additives. High catalytic yields (styrene oxide, 120 °C, 8 h, 94% yield; 100 °C, 20 h, 93% yield) can be achieved by appropriately extending the reaction times at low temperature, and the reaction times are shorter than other porous materials under the same conditions. This work provides a new strategy for synthesizing an efficient metal-free heterogeneous catalyst with high ionic content and a large specific surface area from HCPs for the conversion of CO2 into cyclic carbonates. It also demonstrates that the ionic content and specific surface area must be coordinated to obtain high catalytic activity for CO2 cycloaddition reaction.

A lamellar structure zeolite LTA for CO2 capture

Two-dimensional zeolite LTA with a special structure can be used in gas separation.

One-pot construction of nitrogen-rich polymeric ionic porous networks for effective CO2 capture and fixation

Facile preparation of ionic porous networks (IPNs) with large and permanent porosity is highly desirable for CO₂ capture and transformation but remains a challenge. Here we report a one-pot base-mediated construction of nitrogen-rich IPNs through a combination of nucleophilic substitution and quaternisation chemistry from H-imidazole. This strategy, as proven by the model reactions of 1H-imidazole or 1-methyl-1H-imidazole with cyanuric chloride, allows for fine regulation of porosity and physicochemical properties, leading to nitrogen-rich IPNs featuring abundant ionic units and radicals. The as-prepared networks, termed IPN-CSUs, efficiently capture CO₂ (80.1 cc g^-1 at 273 K/1 bar) with an ideal CO₂/N₂ selectivity of 139.7. They can also effectively catalyse the cycloaddition reaction between CO₂ and epoxides with high yields of up to 99% under mild conditions (0.1 MPa, 298 K), suggesting their possible applications in the fields of both selective molecular separation and conversion. Unlike the previously known strategies generally involving single coupling chemistry, our strategy combining two coupling routes in one pot appears to be unique and potentially applicable to other building blocks.

Different functional groups modified porous organic polymers used for low concentration CO2 fixation

Through a facile post-synthetic method, different kinds of polar group-functionalized ionic liquid porous organic polymers (POP-PA-COOH, POP-PA-OH, and POP-PA-NH₂) were obtained. The materials can be used as efficient heterogeneous catalysts in the cycloaddition reaction of CO₂ with epoxides under mild and co-catalyst-free conditions. It is demonstrated that POP-PA-NH₂ possesses much higher catalytic activity than POP-PA-OH and POP-PA-COOH. Interestingly, this activity difference can further be amplified when the reaction is carried out under low CO₂ concentration, and POP-PA-NH₂ possesses a conversion of 84.7% with a selectivity of 99.0% in 96 h. It is noteworthy to mention that research focusing on the transformation of CO₂ under low concentration using heterogeneous catalysts is rare and still a challenge. The excellent activities of POP-PA-NH₂ under low CO₂ concentration make this material a good candidate for CO₂ elimination under mild conditions.

Mechanochemical Process to Construct Porous Ionic Polymers by Menshutkin Reaction

The synthesis of porous ionic polymers (PIPs) via the Menshutkin reaction is intriguing because the reaction works smoothly in catalyst-free condition with 100 % atom utilization. However, the rotation of methane site, nonrigid knots, and charge interaction all may cause collapses of the channel, which is detrimental to the synthesis PIP in solid-state conditions. In this work, an inorganic salt (NaBr, NaCl: pollution-free and easy to recycle) was rationally chosen as the hard template and effectively prevented the intermolecular packing. Moreover, the increased surface area dramatically promoted the catalytic activity of PIP for cyclic carbonate synthesis. This work provides a green and efficient strategy to construct PIPs via the Menshutkin reaction.

Developing Eco-Friendly and Cost-Effective Porous Adsorbent for Carbon Dioxide Capture

To address the issue of global warming and climate change issues, recent research efforts have highlighted opportunities for capturing and electrochemically converting carbon dioxide (CO₂). Despite metal doped polymers receiving widespread attention in this respect, the structures hitherto reported lack in ease of synthesis with scale up feasibility. In this study, a series of mesoporous metal-doped polymers (MRFs) with tunable metal functionality and hierarchical porosity were successfully synthesized using a one-step copolymerization of resorcinol and formaldehyde with Polyethyleneimine (PEI) under solvothermal conditions. The effect of PEI and metal doping concentrations were observed on physical properties and adsorption results. The results confirmed the role of PEI on the mesoporosity of the polymer networks and high surface area in addition to enhanced CO₂ capture capacity. The resulting Cobalt doped material shows excellent thermal stability and promising CO₂ capture performance, with equilibrium adsorption of 2.3 mmol CO₂/g at 0 °C and 1 bar for at a surface area 675.62 m²/g. This mesoporous polymer, with its ease of synthesis is a promising candidate for promising for CO₂ capture and possible subsequent electrochemical conversion.

Synthetic Porous Melanin

Commonly known as a skin pigment, melanin has a vital role in UV radiation protection, primarily acting as a radical scavenger. However, a lesser known natural property of melanin, observed in some melanized organisms, is its capacity to adsorb toxins, including metals and organic molecules. Inspired by this, we set out to generate a synthetic porous melanin that would pave the way to enhancing the natural adsorbent properties of melanin and melanin-like materials. Here, we developed a method for the synthesis of porous polydopamine-based melanin utilizing a mesoporous silica (MS) nanoparticle template and characterized its physical properties. Through the oxidative polymerization of dopamine, followed by the etching of silica, we generated synthetic porous melanin (SPM) with the highest measured surface area of any known polydopamine-based material. The prepared SPM was effective for the uptake of various gases and organophosphate toxins, with the material exhibiting high selectivity for CO₂ over CH₄ and high potential for ammonia capture. Given the demonstrated advantages provided by synthetic porous melanin and melanin's role as an adsorbent in nature, we anticipate the discovery of porous analogues in biological systems.

Sustainable method towards magnetic ordered mesoporous polymers for efficient Methylene Blue removal

The difficulty in achieving high removal efficiency for contaminants in textile wastewater over a wide range of pH impedes the progress of its treatment technique greatly. Herein, a facile and sustainable strategy was adopted for constructing magnetic ordered mesoporous polymers (M-OMPs) without the assistance of organic solvent and catalyst. The prepared M-OMPs were endowed with high special surface area and good superparamagnetism simultaneously, and exhibited high removal efficiency (>99%) for Methylene Blue (MB) within a short time (10 min) at a concentration of 50 mg/L. What's more, high removal efficiency was achieved over a wide range of pH 2-12 and the adsorption capacity for MB on M-OMPs was substantially retained even after 5 adsorption-desorption cycles, further demonstrating the application potential of M-OMPs in the decontamination of textile wastewater.

Flower-like cobalt carbide for efficient carbon dioxide conversion

Catalytic conversion of carbon dioxide (CO₂) to value-added chemicals under mild conditions is highly desired, albeit with significant challenges. Here, in terms of exposure of abundant active sites and excellent photo-to-thermal conversion properties, flower-like Co₂C has been firstly used for effectively catalysing the cycloaddition of CO₂ with epoxides to produce cyclic carbonates with yields of up to 95% under solar light. Density functional theory (DFT) calculations reveal that Lewis acid sites of the surface Co atoms can activate both CO₂ and epoxide, thus opening up the possibility of a CO₂-epoxide cycloaddition reaction.

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.

A Mechanochemical-Assisted Synthesis of Boron, Nitrogen Co-Doped Porous Carbons as Metal-Free Catalysts

A green and convenient solid-state method assisted by mechanical energy is employed for the synthesis of boron (B) and nitrogen (N) co-doped porous carbons (B,N-Cs). Glutamic acid (Glu) and boric acid (H₃ BO₃ ) are used as the N-containing carbon precursor and boron source, respectively. This method is easy to perform and proved to be efficient towards co-doping B and N into the carbon matrix with high contents of B (7 atom %) and N (10 atom %). By adjusting the molar ratio of H₃ BO₃ to Glu, the surface chemical states of B and N could be readily modulated. When increasing H₃ BO₃ dosage, the pore size of B,N-Cs could be tuned ranging from micropores to mesopores with a Brunauer-Emmett-Teller (BET) surface area up to 940 m²  g^-1 . Finally, the B,N-Cs were applied as metal-free catalysts for the cycloaddition of CO₂ to epoxides, which outperform the N-doped carbon catalyst (NC-900) and the physically mixed catalyst of NC-900/B₄ C. The enhanced activity is attributed to the cooperative effect between B and N sites. X-ray photoelectron spectroscopy (XPS) analysis reveals that BN₃ in the B,N-Cs serves as a critical active site for the cooperative catalysis.

Facile fabrication of a heterogeneous Co-modified pyridinecarboxaldehyde-polyethylenimine catalyst for efficient CO2 conversion under mild conditions

A heterogeneous Co-modified pyridinecarboxaldehyde-polyethylenimine catalyst with active metal sites and amine groups exhibited high catalytic activity for CO₂ conversion under mild conditions, even at ambient temperature.