Study On The Effect Of Water Pressure Direction And Electric Field Direction On The Efficiency Of Nanochannel Filtration Membrane

Water is not only the foundation for the survival and development of all things on earth,but also an important strategic resource for economic development of a country.Although 75%of the earth's surface is covered by water,there are still many countries and regions in the world in which fresh water resources are very scarce.Seawater desalination and sewage purification are the main ways to effectively solve this major problem.There are a variety of technological methods to realize seawater desalination and sewage purifications,among which the most economical and efficient one is the membrane filtration technology.The carbon nanotube water channel has a natural hollow structure.According to a number of theoretical and experimental studies conducted in recent years,the transport speed of water in the carbon nanotube channel is up to 1000 times that under the condition of macroscopic non-slipping,therefore,there is no doubt that carbon nanotube is one of the ideal materials for manufacturing high permeability filter membrane.Confined in carbon nanotubes,water will have many unusual properties.In this case,it is of great theoretical significance and practical value for manufacturing efficient carbon nanotube filter membrane to explore these properties and set forth the internal physical mechanism.This thesis carries out a study mainly from the following three perspectives so as to further investigate relevant transport properties of carbon nanotubes:(1)The first is the impact of the direction of hydrostatic pressure on the water transport properties in carbon nanotubes.By virtue of molecular dynamics simulations,it is found that under the same hydrostatic pressure,different angles between the direction of the water pressure and the tube axis will lead to different water flow.Interestingly,when the angle between the direction of the water pressure and the tube axis is 45°,the water flow is the largest,which is about 3 times that when the angle is 0°.It is revealed that the angle between the direction of the water pressure and the tube axis affects the average number of water molecules and the number of hydrogen bonds in a tube,which are the largest when the angle is 45°,indicating that the system is the most stable and the water chain is not easy to break at this moment.Moreover,the direction of hydrostatic pressure affects whether it is easy or difficult for water molecules to enter and leave the tube.Considering the above factors,when the angle is45°,there is the maximum flux value(2)The second is the impact of the size and direction of the electrostatic field on the water transport properties in carbon nanotubes.By virtue of molecular dynamics simulations,it aims to explore the transport properties of water molecules in carbon nanotubes by applying electrostatic fields with different sizes and directions.The hydrostatic pressure of all simulated systems is 30 MPa,focusing on the impact of same and opposite directions of electrostatic field and axis z on the water transport properties in the case of the same field intensity.The research demonstrates that in the field intensity range of 0.01<E0<0.6 V/nm,if the field intensity is the same,the net water flow generated under the condition of the opposite direction E(-)of electrostatic field and water pressure is much larger than that generated under the condition of the same direction E(+),as high as 2.4 times larger.The analysis shows that when applying appropriate electrostatic field along the tube axis,as the water molecules are polar molecules,water molecules can be arranged in seriation along the direction of the electrostatic field,therefore,different directions of electrostatic field will lead to different orientation of water molecular chain in the tube,which will result in different barrier potential difference on both ends of the carbon nanotubes,accordingly,electrostatic field with E(-)direction can make the water molecules go through the carbon nanotubes more easily.(3)The third is the study on the preparation of carbon nanotube membranes and its application progress.The carbon nanotube membrane is a two-dimensional carbon nanotube network structure,which is made through filling a freely arranged carbon nanotube array with a physical or chemical method.This study has made a research overview of carbon nanotube membrane conducted in recent years.Based on the preparation of carbon nanotube membrane,this study briefly describes the chemical vapor deposition method,LB(Langmuir-Blodgett)membrane method and electrostatic layer-by-layer self-assembly technology,and introduces their applications in biological field,photoelectric nanometer devices,water treatment,seawater desalination and other fields.The research achievements of this paper are of great theoretical significance for operating nano water pumps,developing high permeability filter membranes,understanding biological nano-channels,and designing related nano sensors.