Nitrogen-Containing Functional Groups-Facilitated Acetone Adsorption by ZIF-8-Derived Porous Carbon

The role of surface chemistry on CO2 adsorption in biomass-derived porous carbons by experimental results and molecular dynamics simulations

Biomass-derived porous carbons have been considered one of the most effective adsorbents for CO2 capture, due to their porous structure and high specific surface area. In this study, we successfully synthesized porous carbon from celery biomass and examined the effect of external adsorption parameters including time, temperature, and pressure on CO2 uptake in experimental and molecular dynamics (MD) simulations. Furthermore, the influence of carbon's surface chemistry (carboxyl and hydroxyl functionalities) and nitrogen type on CO2 capture were investigated utilizing MD simulations. The results showed that pyridinic nitrogen has a greater tendency to adsorb CO2 than graphitic. It was found that the simultaneous presence of these two types of nitrogen has a greater effect on the CO2 sorption than the individual presence of each in the structure. It was also revealed that the addition of carboxyl groups (O=C-OH) to the carbon matrix enhances CO2 capture by about 10%. Additionally, by increasing the simulation time and the size of the simulation box, the average absolute relative error for simulation results of optimal structure declined to 16%, which is an acceptable value and makes the simulation process reliable to predict adsorption capacity under various conditions.

Sago cycas-based hierarchical-structured porous carbon for adsorption of acetone vapour: preparation, characterization and performance

The porous structure and oxygen-containing functional groups of carbon materials play important roles in the adsorption of volatile organic compounds (VOCs). In this study, hierarchical-structured porous carbons (HSPCs) with a large specific surface area and abundant oxygen-containing functional groups were prepared from sago cycas without a template or post-processing for acetone (one of the most common VOCs) adsorption. The micropore volume (0.41-1.15 cm³ g^-1) and oxygen-containing functional groups (0.3-1.92 mmol g^-1) of HSPCs were manipulated by adjusting the activation temperature. Static adsorption data showed that the HSPC activated at 600 °C (HSPC-600) was superior for acetone adsorption, and a maximum adsorption capacity of 3.75 mmol g^-1 was achieved at 25 °C and 0.1 kPa. Breakthrough curves and cyclic adsorption-desorption tests demonstrated the dynamic adsorption capacity and regeneration performance of HSPC-600 were excellent as well. The adsorption isotherms were well described by Langmuir and Langmuir-Freundlich models, indicating the adsorption of acetone on HSPCs is a monolayer adsorption process. Due to electrostatic interaction, hydrogen bond and van der Waals forces between acetone molecules and oxygen-containing functional groups, the adsorption capacity of HSPCs for acetone was significantly improved at low relative pressure. This study may provide a peculiar insight into the development of high-performance acetone adsorbent.

Hierarchical porous polystyrene-based activated carbon spheres for CO2 capture

It is rather essential to design porous carbon adsorbents with high CO2 capture performance for improving global warming and climate change. Activated carbon spheres with high specific surface area and hierarchical porous texture were prepared from polystyrene-based macroreticular resin spheres due to their low ash and mechanical stability by air pre-oxidization and steam activation. The as-prepared carbon spheres had a specific surface area of 1274.95 m2 g-1, total pore volume of 1.09 cm3 g-1 and micropore volume of 0.47 cm3 g-1. Moreover, these carbon spheres showed a hierarchical porous texture composed of ultrafine micropores (0.5-1 nm), micropores (1-2 nm), mesopores (10-50 nm) and macropores (50-100 nm). A CO2 adsorption capacity of 2.82 mmol g-1 for carbon spheres can be obtained at 30 °C and 1 atm. Further, after introducing nitrogen-containing functional groups by gaseous ammonia at 600 °C, these carbon spheres (NPSRCSs) exhibited a high CO2 adsorption capacity of 3.2 mmol g-1. In addition, excellent cyclic stability, low hygroscopicity and regenerability temperature suggested these carbon spheres were favorable for CO2 capture.

Porous Carbon Nanofibers with Heteroatoms Doped by Electrospinning Exhibit Excellent Acetone and Carbon Dioxide Adsorption Performance: The Contributions of Pore Structure and Functional Groups

Rich chemical properties and a well-developed pore structure are the key factors of porous materials for gas storage. Herein, rich heteroatom-doped porous carbon nanofibers (U₁K₂-X) with a large surface area were prepared by electrospinning followed by potassium hydroxide (KOH) activation. Low-cost urea was chosen as the nitrogen source and structural guiding agent. U₁K₂-X have a high specific surface area (628-2688 m² g^-1), excellent pore volume (0.468-1.571 cm³ g^-1), and abundant nitrogen (2.5-12.8 atom %) and oxygen (4.5-12.5 atom %) contents. Acetone and carbon dioxide were used as target adsorbents to evaluate the adsorption properties of U₁K₂-X by experiments. These U₁K₂-X exhibit excellent adsorption performance (260.03-955.74 mg g^-1, 25 °C, 18 kPa) and multilayer adsorption (the adsorption layer number n > 2) for acetone, which is mainly attributed to the large specific surface area and pore volume. Besides this, the carbon dioxide uptake reached 2.73-3.34 mmol g^-1 at 25 °C. This was attributed to the combination of high nitrogen-oxygen contents and microporous structure. Furthermore, U₁K₂-X show the desirable repeatability. This study provides a new direction for the preparation of heteroatom-doped porous carbon nanofibers, which will be a promising material for gas adsorption.

R-Silsesquioxane-Based Network Polymers by Fluoride Catalyzed Synthesis: An Investigation of Cross-Linker Structure and Its Influence on Porosity

Silsesquioxane-based networks are an important class of materials that have many applications where high thermal/oxidative stability and porosity are needed simultaneously. However, there is a great desire to be able to design these materials for specialized applications in environmental remediation and medicine. To do so requires a simple synthesis method to make materials with expanded functionalities. In this article, we explore the synthesis of R-silsesquioxane-based porous networks by fluoride catalysis containing methyl, phenyl and vinyl corners (R-Si(OEt)₃) combined with four different bis-triethoxysilyl cross-linkers (ethyl, ethylene, acetylene and hexyl). Synthesized materials were then analyzed for their porosity, surface area, thermal stability and general structure. We found that when a specified cage corner (i.e., methyl) is compared across all cross-linkers in two different solvent systems (dichloromethane and acetonitrile), pore size distributions are consistent with cross-linker length, pore sizes tended to be larger and π-bond-containing cross-linkers reduced overall microporosity. Changing to larger cage corners for each of the cross-linkers tended to show decreases in overall surface area, except when both corners and cross-linkers contained π-bonds. These studies will enable further understanding of post-synthesis modifiable silsesquioxane networks.

High-Energy Efficiency Membraneless Flowless Zn-Br Battery: Utilizing the Electrochemical-Chemical Growth of Polybromides

Aqueous Zn-Br batteries (ZBBs) offer promising next-generation high-density energy storage for energy storage systems, along with distinctive cost effectiveness particularly in membraneless and flowless (MLFL) form. Unfortunately, they generally suffer from uncontrolled diffusion of corrosive bromine components, which cause serious self-discharge and capacity fade. An MLFL-ZBB is presented that fundamentally tackles the problem of bromine crossover by converting bromine to the polybromide anion using protonated pyridinic nitrogen doped microporous carbon decorated on graphite felt (NGF). The NGF electrodes efficiently capture bromine and polybromide anions at the abundant protonated nitrogen dopant sites within micropores and facilitate effective conversion of bromine into polybromides through electrochemical-chemical growth mechanism. The MLFL-ZBBs with NGF exhibit an extraordinary stability over 1000 charge/discharge cycles, with an energy efficiency over 80%, the highest value ever reported among membraneless Zn-Br batteries. Judicious engineering of an atomistically designed nanostructured electrode offers a novel design platform for low cost, high voltage, long-life cycle aqueous hybrid Zn-Br batteries.

Competitive Adsorption of Methanol-Acetone on Surface Functionalization (-COOH, -OH, -NH2, and -SO3H): Grand Canonical Monte Carlo and Density Functional Theory Simulations

The capture and separation properties of surface-functionalized activated carbons (AC-Rs, R= -COOH, -OH, -NH₂, and -SO₃H) for the methanol-acetone mixture were investigated for the first time by grand canonical Monte Carlo simulation (GCMC) and density functional theory (DFT). The effects of surface functional groups and structural characteristics of AC-Rs on the adsorption and separation behaviors of methanol and acetone were clarified. The surface functional group with strong electron-donating or electron-accepting capacity (i.e., -NH₂, -OH, and -SO₃H) was a crucial factor for the methanol-acetone capture and separation performance at the lower pressure range, and the accessible surface area was found to be another determinative factor. AC-NH₂ with the relatively large accessible surface area (4497 m²/g) exhibited an efficient capture performance for the single component (15.7 mol/kg for methanol and 6.7 mol/kg for acetone) and the highest methanol/acetone selectivity (∼23) at 0.02 kPa. At high pressures, the surface functionalization and available pore volume of AC-Rs played pivotal roles in the adsorptive separation process. This study provided mechanistic insights on how the surface functional groups affected the capture and separation properties of ACs, which would further provide a rational alternative strategy in the preparation and synthesis of ACs for the effective gas mixture separation.

Acetone adsorption capacity of sulfur-doped microporous activated carbons prepared from polythiophene

Sulfur-doped activated carbons (SACs) with high sulfur content and large specific surface area were synthesized from polythiophene for acetone removal. The sulfur content of carbons (3.10-8.43 at.%) could be tunable by adjusting the activation temperature. The BET surface area and pore volume of the obtained samples were 916-2020 m² g^-1 and 0.678-1.100 cm³ g^-1, with a significant proportion of microporosity (up to 84% and 72% for BET surface area and pore volume, respectively). The resulting SACs show a superior acetone adsorption capacity (i.e., 716.4 mg g^-1 at 15 °C and 705 mg g^-1 at 25 °C for SAC700). In terms of the adsorption behavior of acetone on the activated carbons, compared to the Langmuir model, the Langmuir-Freundlich model showed better agreement with the adsorption amount. The results reveal that the surface area and micropore volume are the key factors for acetone adsorption, while the sulfur-doped functional groups, especially oxidized sulfur functional groups, can enhance the acetone adsorption capacity at a certain low pressure. Temperature programmed desorption (TPD) experiments were performed to get desorption activation energy of acetone on SAC samples, and the results ranged from 23.54 to 38.71 kJ mol^-1. The results of the molecular simulation show that the introduction of sulfur element can increase the binding energy between acetone molecule and carbon surface, and the tri-oxidized sulfur (sulfonic acid) functional group has the highest binding energy of - 0.4765 eV. Graphical abstract.

A Facile Approach To Improve Electrochemical Capacitance of Carbons by in Situ Electrochemical Oxidation

A facile approach of in situ electrochemical oxidation has been utilized to modify carbons, including activated carbon, mesoporous few-layer carbon, graphite, carbon fiber, and carbon nanotube, which induces oxygen-containing functional groups on its surface and simultaneously enhances its wettability, contributing to the improvement of capacitance. By this approach, the capacitance of commercialized activated carbon is increased by 86% in an acidic electrolyte, reaching 320 F g^-1, of which more than 96% was maintained after 10 000 cyclic tests. The huge improvement stems from electrochemical redox reactions enabled by oxygen-associated groups, which do not adversely affect the porous structure and electrical conductivity. Such improvement will put carbon-based electrochemical capacitors into more practical application areas.