Reproduction Of Gas Uptakes And Cage-to-Framework Design For CC3 Based On First-principle Derived Force Field

Recent years,with the rapid development of the economy,the deepening of the industrialization process and the increasing scale of human production activities,the issue of energy and environmental pollution has become a major problem that threatens and affects human life.The storage and separation of gases has become a hot topic in the field of porous materials.For example,how to efficiently and cleanly separate and store the rare gases Kr and Xe in the treatment of nuclear waste,and the storage of carbon dioxide gas under conditions of increasing greenhouse effect,and the like.The design and synthesis of porous materials with advanced gas storage and separation properties has also become a top priority.In this field,in addition to traditional zeolites,activated carbon materials,and metal organic framework(MOF),porous organic materials,as a new class of functionalized nanomaterials with good properties,also show outstanding gas storage and separation,proton conduction or membrane,catalysis,sensing,photoelectron,magnetic and other properties.As an efficient way for material design,molecular modelling has attracted more and more scientist's attention,such as Materials Genome Initiative.The core problem of theoretically simulating gas adsorption in pore materials is the description of gas-framework weak interactions in the grand canonical Monte Carlo(GCMC).Traditional force fields cannot function in new or special adsorbent materials due to their inherent limitations,and density functional theory(DFT)methods cannot perform millions of Monte Carlo on large pore materials due to the expensive machine time.Therefore,the development of highprecision,high-efficiency force fields is the key and foundation for large-scale Monte Carlo simulation.As a result,this thesis starts with the development of high-precision force field,tries to reproduce the adsorption isotherm obtained by experiment,and strives to design porous materials with excellent gas adsorption and separation properties.Based on this,this thesis mainly carried out the following work:(1)In order to carry out theoretical calculations more accurately,we firstly developed first-principles force field,which is a parametric fit of the molecular force field model using the results of first-principles calculations.In the process of developing the force field,we have made two improvements on the basis of the existing method of the first-principles force field.First,we use the classical force field(UFF,Dreiding)to estimate the relative position of the gas and the segment configuration to replace the random position or fixed distance method in the existing method.The accuracy of the calculation can be enhanced accordingly.Secondly,the heuristic algorithm genetic algorithm is used to replace the original nonlinear fitting method,to make the calculation process more efficient and accurate.(2)The theoretical simulation method is used to calculate the effective gas adsorption value of porous materials,and this method is generalized to calculate the adsorption reproduction of the porous materials.Taking a series of DBA-COFs materials for nitrogen adsorption as an example,the problems of nitrogen adsorption and theoretical simulation values measured by six kinds of DBA-COFs materials were discussed,and the reasons for the non-reproduction were analyzed.The types,distributions,and mass-volume ratios of the impurities remaining in the channels are discussed,and the effects of these factors on the amount of gas adsorption are explained one by one.Theoretical calculations show that the quality of impurities involved in the pores is the most important factor affecting the amount of gas adsorption.In order to quantitatively analyze the influence of impurities on the amount of gas adsorption,two general theoretical formulas are defined to calculate the true effective adsorption volume and mass of porous materials,and the concept of activation rate and activation volume rate is proposed to evaluate the effective adsorption capacity of materials.And activation rate.Finally,this paper summarizes the methods of quantitative calculation,which is a general evaluation strategy that can be promoted.It is hoped that this strategy can be an effective method for high-throughput calculation and material screening in the future.(3)Based on the above work,taking the star molecule CC3 cage with intrinsic pores as the main body,the network structure is constructed by the connection of boric acid groups(BDBA and BBA).According to different molecular stacking methods,seven kinds of networks are designed.The calculation results show that the seven new materials are structurally stable.Moreover,at 298 K and 1 bar,these new materials demonstrate good adsorption properties for the rare gases Kr and Xe,and excellent Kr selectivity over Xe in 8?92 binary gases.It is worth noting that the adsorption capacity for Kr and Xe in the CC3 network has been significantly improved compared with the original CC3 molecular cage.Therefore,the networked molecular cage strategy is an effective method to improve gas adsorption performance.The way,it is worth the attention of the experimental researchers and try to synthesize.