Mechanistic Investigation Of CO₂ Capture And Separation In Porous Carbon/boron Nitride Adsorbent Materials

The greenhouse effect caused by the massive uncontrolled CO₂ emission into atmosphere is becoming a huge threat to our global climate and environment.Carbon capture and storage（CCS）technology becomes one of the effective ways to relieve excessive greenhouse gases due to its huge potential of emission reduction and economy.At present,the inefficient adsorption materials are still one of the main bottlenecks that limit the development of CO₂capture and separation for CCS technology.Therefore,the design of novel adsorption materials with improved CO₂ capture and separation efficiency,low cost,and promoted stability have great scientific values and practical significance as the crucial content and task for CCS development.Porous carbonaceous materials have been widely utilized in CCS due to its light quality,ease of synthesis and preparation,low renewable energy and cost;similarly,hexgonal boron nitride（BN）nanometerials provide alternative candidates to CCS due to the high melting point,high resisrance to oxidation,low density,chemical inertness,excellent mechanical property,and the especially strong polarity.This thesis focuses on the influences of topological structure and morphology,chemical doping,and chemical functionalization on the adsorption and competitive adsorption mechanism of single and binary mixture of CO₂/CH₄ and CO₂/N₂ by using density functional theory（DFT）and grand canonical Monte Carlo（GCMC）simulations.Results of this project would provide theoretical prediction and scientific evidence for the design of novel absorbent materials and screening of conductive conditions for CO₂ capture and seperation.The effect of edge-functionalization on competitive adsorption of binary CO₂/N₂ mixture in nanoporous carbons（NPCs）have been investigated by using DFT and GCMC simulations.Our results showed that edge-functionalization has a positive effect on the adsorption capacity of CO₂ than N₂,and therefore enhancing the selectivity of CO₂ over N₂.The edge-functionalization provided a favorable environment for gas adsorption by extending the pore size and increasing the effective accessible surface area.For the functional groups,electronegativity and/or electropositivity was enhanced due to the large atomic local charge introduced,which had the large influence on the CO₂ selectivity.The adsorption performance of edge-functionalized NPCs was better than that of the unmodified NPC as reflected by the bigger isosteric heat of the former.This work highlighted the potential of edge-functionalized NPCs in competitive adsorption,capture,and separation for binary CO ₂/N₂ mixture,and provides an effective alternative strategy for design and screening of adsorbent materials for CCS.The effect of Li-modification on competitive adsorption of binary CO₂/CH₄ mixture inNPCs has been investigated by using DFT and GCMC simulations.O ur results showed that Li-doping could enhance the selectivity of CO₂ significantly because it inceased the electrostatic potential.This strategy could be used for adsorption and separation of the gas mixtures owing different dipole moment and quadrupole moment.The Li-modified NPCs provided a favorable environment for gas adsorption by extending the pore size and increasing the effective accessible surface area.The Li-modification had great influence on the adsorption,and the selectivity of CO₂ over CH₄ increased with the increase of added Li atom number.The ratio of gas mixture composition affected the selectivity to some extent,and the selectivity of CO₂ over CH₄ increased with the increase of CO₂/CH₄ ratio.The results highlighted the importance of the metal doping on CO₂ capture and separation performance for nanoporous carbon materials.The adsorption behavior of CO₂ and CH₄ in BN nanomaterials constructed with different sizes of nanosheet has been studied by combining DFT and GCMC methods.Our results showed that BN nanomaterials could create a beneficial environment with appropriate pore size and accessible surface area for gas adsorption on the basis of different sizes of nanosheet.Temperature had a negative effect on the gas adsorption and selectivity of CO₂ over CH₄,but no obvious influence on the electrostatic contribution.Under the low pressure condition,the selectivity of CO₂ over CH₄ decreased sharply and subsequently flattened out to a constant value with the increase of pressure,in good consistent with the electrostatic contribution along the adsorption processes.This work not only highlighted the potential of BN nanomaterials as a good candidate for CCS,but also provided an effective approach for understanding the synergetic effects of pore physical properties and electrostatic interactions.