Superior Selective CO2 Adsorption and Separation over N2 and CH4 of Porous Carbon Nitride Nanosheets: Insights from GCMC and DFT Simulations

Recent Advances in Mesoporous Carbon Nitride-Based Materials for Electrochemical Energy Storage and Conversion and Gas Storage

Mesoporous carbon nitride (MCN) is a fascinating material with enhanced textural properties, tailored morphology and enriched surface functionalities. Hence, it demonstrates promising performance in various applications. Over the years, various methods such as hard template, soft template, template-free, etc. have been adopted toward the preparation of MCN with controlled structural properties. Furthermore, the exciting properties of MCN have been fine-tuned by controlling the morphology and tuning the textural properties and surface functionalities, including the type and amount of nitrogen, via simple adjustment of the precursors, the carbonization temperature and the nature of the structure-directing agents/hard template. Besides these, the integration of conductive carbon, heteroatoms, metal-based materials, organic molecules, etc. was found to not only enhance MCN's performance in the already existing applications but also open up more exciting applications. The present Review begins by providing a general overview of the salient features of MCN, which dictate its performance in the various applications. Then, the Review discusses the trends in the applications of MCN-based material in the areas of electrochemical energy storage and conversion and gas storage in the past decade. The structure-property relationships of MCN-based materials in the above-mentioned applications are also discussed in detail. Emphasis is given to the role of the synthetic approach adopted and the nature of the precursor(s) used toward controlling the textural, morphological properties and chemical composition of MCN-based materials in obtaining the final product with improved performance. Moreover, the effects of modifications of key features of MCN on its electrochemical performance are also discussed. Finally, the current challenges and perspectives are provided, thereby guiding future research in the field of MCN-based materials for electrochemical energy storage and conversion and gas storage.

Multiscale analysis of CO2 adsorption mechanisms on porous carbon: An investigation into the impact of intrinsic defects and pore size

Porous carbon adsorption represents a critical component of CCUS technologies, with microporous structures playing an essential role in CO2 capture. The preparation of porous carbon introduces intrinsic defects, making it essential to consider both pore size and these defects for a comprehensive understanding of the CO2 adsorption mechanism. This study investigates the mechanisms of CO2 adsorption influenced by intrinsic defects and pore size using multiscale methods, incorporating experimental validation, Grand Canonical Monte Carlo simulations, and Density Functional Theory simulations. Intrinsic defects increase structural disorder and microporous content in porous carbon by distorting the graphene framework, thereby creating additional spaces for CO2 adsorption. Moreover, atomic charge redistribution induced by intrinsic defects disrupts the balance of van der Waals and electrostatic potentials, generating more active adsorption sites and enhancing the strength of CO2 adsorption. This research aims to clarify the facilitative mechanisms of intrinsic defects and pore size on CO2 adsorption in porous carbons and to provide a theoretical basis for designing efficient carbon-based adsorbents.

Rational design of stable carbon nitride monolayer membranes for highly controllable CO2 capture and separation from CH4 and C2H2

CO2 capture and separation from natural and fuel gas are important industrial issues that refer to the control of CO2 emissions and the purification of target gases. Here, a novel non-planar g-C12N8 monolayer that could be synthesized via the supramolecular self-assembly strategy was identified using DFT calculations. The cohesive energy, phonon spectrum, BOMD, and mechanical stability criteria confirm the stability of the g-C12N8 monolayer. Our DFT calculations and MD simulations designate the g-C12N8 monolayer to perform as a superior CO2 separation membrane from CH4 and C2H2 gas owing to the high CO2 permeability and selectivity. Specifically, the CO2 permeability ranges from 1.21 × 107 to 1.53 × 107 GPU, while the selectivity of CO2/CH4 and CO2/C2H2 is 3.03 × 103 and 3.10 × 102 at 300 K, respectively, much higher than the Robeson upper bound and most of the reported 2D membranes, and even at high temperatures, the g-C12N8 monolayer-based CO2 separation membranes could operate with high performance. Further, at room temperature, the permeated CO2 gas can adsorb on the g-C12N8 surface with moderate adsorption energy and high capacity. These results indicate that the g-C12N8 membrane exhibits high performance for controlling CO2 capture and separation, which inevitably injects a new alternative of novel 2D membranes for CO2 separation and capture from CH4 and C2H2 in light of further experimental and theoretical research.

Analytical Techniques in Molecular Simulation and Its Application in Energetic Materials

Efficient design on the molecular and crystal levels is an urgent need to accelerate the development of energetic materials (EMs), and the performance analysis of microstructures is the most important thing in the research and design of EMs. Although molecular simulation methods are widely used in various research fields, there are few comprehensive reviews on analytical techniques. It is urgent to understand the basic principles of various analytical methods in the research of EMs. In this article, the characterization/analysis methods in quantum mechanics and molecular mechanics simulation technology are summarized, and their applications in the field of EMs are listed. At the molecular level, energy, composition, geometric structure, and electronic structure are all related to macroscopic properties, and most of them have been widely used as variables in numerical models to predict and compare the properties of EMs. In addition, this paper emphasizes that the correlation between theoretical calculation and confirmatory experiment needs to be further verified because the current experimental characterization can also be dealt with by molecular simulation, which is helpful to the popularization and application of theoretical research.

Adsorption Mechanisms of CO2 on Macroporous Ion-Exchange Resin Organic Amine Composite Materials by the Density Functional Theory

The adsorption mechanisms of CO2 on macroporous cation exchange resin (MCER), D001 ion-exchange resin, and macroporous ion-exchange resin organic amine composite materials (MCER-DEA and D001-PEI) were studied by density functional theory (DFT). The adsorption energies and Mulliken atomic charges in the adsorption process were analyzed, indicating that CO2 on MCER and D001 were physisorbed. The adsorption heat of the adsorption process of MCER-DEA and D001-PEI was calculated by the Monte Carlo method, and it was found that the adsorption process of CO2 by MCER-DEA and D001-PEI was both physical adsorption and chemical adsorption. Besides, the chemical adsorption mechanism of CO2 by MCER-DEA and D001-PEI was investigated by analyzing the free energy barrier and the Gibbs free energy change of the involved chemical reactions and the results showed that the free energy barrier required for MCER-DEA to generate zwitterion was 26.23 kcal/mol, which is 1.74 times that of D001-PEI (15.04 kcal/mol); meanwhile, the free energy barriers of the deprotonation process of zwitterions in MCER-DEA and D001-PEI were 16.23 and 9.89 kcal/mol, respectively, indicating that D001-PEI chemically adsorbs CO2 and requires more energy than MCER-DEA chemical adsorption of CO2. D001-PEI is more conducive to the chemical adsorption of CO2. In addition, H2O molecules were incorporated on the polymer models to study the influence of humidity on the CO2 adsorption mechanism. The analysis revealed that the adsorption of CO2 slowed under humid conditions.