Theoreticaland Practical Study On Nano-microscale Interface Interaction In Chemical Engineering

In the typical chemical engineering process of multiphase flow across space and time,industrial practice is usually manifested as"macro-solvable but micro-unclear".The transport/reaction laws at nano-and microscales often play vital roles.Driven by the innovative achievements of computational science and instrument science,chemical engineering has ushered in a historical opportunity for in-depth development from the macroscopic reactor-unit（droplet/bubble/particle）level to the microscopic molecular-atomic level.With the continuous reduction of the research size,the contribution of surface-interface interaction is increasing,so the interface-related issues are particularly critical in the study of nanoscale and microscale transport/reaction laws.In view of this,starting from the multi-scale theoretical calculation,this thesis focuses on several chemical reactions and transport processes related to interface interaction at the scale of 1-100 nm.The mechanism of interface interaction in solid wetting,nanoconfined flow and heterogeneous catalysis has been deeply studied,and the theoretical study of interface interaction has been applied to guide the design of meltblown materials for respirators,the design of anode materials for lithium metal batteries and the design of MnO₂catalysts for the catalytic oxidation of benzyl alcohol.The main research contents and innovations of this thesis are as follows:1.Taking the wetting transparency of two-dimensional materials as a typical case,the wetting behavior of solid surfaces related to interfacial affinity has been studied.Molecular dynamics simulations provide an explanation for the long-standing controversy in the study of the wettability of graphene（Gr）and boron nitride（BN）.First,both 2D materials exhibit wetting translucency in non-extreme environments.In addition,BN generally has a larger wetting transparency than Gr（BN:～32.4%,Gr:～17.3%）,and the wetting transparency of both is affected by the polarity of the substrate.The wetting transparency is mainly affected by the change of the substrate dipole moment in the z direction,and the dipole moment in the+z direction has a greater effect on the wettability of 2D materials than in the-z direction.Further,it is found that the+z direction dipole has a greater influence on the orientation of the interfacial water molecules.At this time,the O atoms in the water molecules are close to the surface and the H atoms are far away from the surface,thus forming more hydrogen bonds with the bulk water molecules and making the supported 2D material appear more hydrophilic.By comparing the polarized Gr model and BN,it is found that the dipole of BN induced by the substrate dipole is much lower than that of polarized Gr,indicating the shielding effect on coulomb interaction of BN is smaller,which is the reason for its greater wetting transparency.2.The filtration performance of the respirator has been studied by establishing an improved numerical model of the meltblown filter layer filtration efficiency and pressure drop.It is found that reducing the fiber diameter can reduce the areal density of the filter layer while ensuring the filtration efficiency,and is beneficial to reduce pressure drop,thereby reducing the use of polypropylene material.With the increase of the filtered particle size,the filtration efficiency shows a trend of first decreasing and then increasing.Nano-microfiber network in meltblown cloth generally has the worst filtration performance on particles with a size of 0.1～0.2μm（which just matches the size of virus）.In addition,the influence of the interfacial affinity between the material and different particulates（water-based,oily,etc.）on the adsorption and trapping of particulates should be considered,so that the meltblown cloth can achieve the best performance.For example,in order to capture and intercept water-based particles with viruses,a design scheme of a respirator filter layer with a hydrophilic-hydrophobic-hydrophilic three-layer structure is proposed to improve the protective performance.3.Taking the Poiseuille flow between nanoconfined plates as a case,the effect of different interface interaction on the transport behavior has been studied.MD simulations are used to analyze the interfacial water structure,velocity distribution,and boundary conditions of the nanoconfined fluid.The relationship between transport performance and interface interaction（or confined space size）has great significance for the study of species diffusion and transport in typical nano-confinement spaces such as catalyst pores.In addition,a high-density Li transport anode material for lithium metal batteries based on bulk diffusion is designed using the interface affinity theory,which guides the experimental synthesis of materials and fabricated high-performance devices.A high areal capacity and～100%capacity retention is achieved over 370 cycles,and the devices can suppress the growth of lithium dendrites.4.The tandem catalyst of Ti-doped graphene（Ti Gr）and Co-doped graphene（Co Gr）has been found to be an efficient and stable low-temperature CO selective catalytic reduction of NO_x（CO-SCR）catalyst by density functional theory（DFT）calculations combined with microkinetic simulations.The predicted turnover frequencies（TOFs）of Ti Gr for NO reduction and Co Gr for N₂O reduction can,respectively,reach 1.85×10^-2and 3.46×10^-4s^-1at 450 K.By analyzing the DFT calculation results,it is found that the interfacial affinity associated with the active site charge can be used to construct a catalytic reaction activity descriptor,which provides important guidance for the experimental and theoretical design of new green and efficient denitrification catalysts.5.Under the guidance of the interfacial affinity theory,the morphologies and exposed crystal facets of the experimentally synthesizedα-,β-,γ-andδ-MnO₂crystals have been successfully predicted by using the crystal surface energy calculation.Based on the related terms（such as adsorption energy,number of active sites,etc.）of O₂adsorption on the exposed crystal facets of MnO₂,as well as structural characteristic parameters such as the area ratio of crystal facets and oxygen vacancy（OV）formation energy,an activity descriptor for the catalytic oxidation performance of MnO₂is proposed.Based on the activity descriptor related to the gas-solid interface affinity,the guided experiments successfully synthesizedβ-MnO₂catalysts with a high specific surface area（25.41 m²/g）,achieving the highest catalytic oxidation conversion（89.1%）in this study.The mechanism of MnO₂-catalyzed oxidation of BA to benzaldehyde（BAD）by O₂has been revealed by ab initio molecular dynamics（AIMD）simulations,which is different from the typical Mars-van Krevelen（Mv K）mechanism.Thereby a generalized Mv K mechanism mediated by the Langmuir-Hinshelwood（LH）process is proposed,in which the catalytic process does not require the participation of OV.