Theoretical Calculations Of Carbon Nanotubes Adsorbed With Chloride Salts In The Seawater

Among all the nanomaterials, CNTs attract very great attentions due to unique geometricalstructure properties. The adsorption property is of importance to the material modificationapplications of the carbon nanotubes. In this thesis, first-principles calculations are performedon an armchair (5,5) single-walled carbon nanotube or a zigzag (9,0) single-walled carbonnanotube with clorides salts. Conclusions are as follows:1. Alkali-earth metals adsorption on carbon nanotubes. The characteristics of the metalsadsorption on carbon nanotubs depends on the chirality of CNTs, adsorption position andproperty of the metals. The adsorption energy of all the (9,0) carbon nanotube is lager thanthat of them on the (5,5) carbon nanotube. Calculations of adsorption energy, geometry,density of states, charge transfer, dipole moment, and work function give a consistent pictureof bonding for the adatoms considered. Charge transfer is analyzed quantitatively based onBader theory. Whatever the case, there is significant charge-transfer and work-function shiftsfor Ca and Sr adsorption. However, variation of Mg adsorption on PCNTs is little. The workfunction can be understood to have two main contributions coming from dipole potential andfrom Fermi-level shift and a vacancy defect increased the values of CNTs. Ca and Mg withmore complicate empty orbital exhibit stronger interaction with CNTs. Though Mg, Ca and Srbelong to the same group, they are transition from alkaline metals to transition metals, and theadsorption law varies as greatly as their crystal form. We can use different alkaline earthmetals to modulate CNTs2. Chloride salts adsorption on carbon nanotubes. The direct adsorption mechanism ofchlorides (LiCl, NaCl, CsCl, MgCl2, CaCl2and SrCl2) on carbon nanotubes (CNTs) wasinvestigated with first-principles calculations. The adsorption energy is less than600meVand belongs to physisorption. The dipole moment, the adsorption energy and the Coulomb interaction energy were calculated. The value of the adsorption energy ranges from0.2to0.6eV. Considering the structure change of chlorides before and after adsorption, we find that theadsorption energy is proportional to the ratio of chloride’s dipole moment to the square ofadsorption distance. So, we conclude that the direct adsorption of chlorides on CNTs occursmainly through dipolar interactions.3. The influence of water on chloride salt adsorption on carbon nanotubes. Carbon nanotubebasically does not adsorb water molecule, so carbon nanotube adsorb chlorides salt to be apriority under water solution. After carbon nanotube adsorbing chloride, the adsorption energyof water molecule on carbon nanotube becomes larger, this may be explained the interactionbetween carbon nanotube and water is enhanced after carbon nanotube modified by chlorides.In aqueous solution, the selective adsorption behavior of carbon nanotube to chloride salts canprovide theoretical basis for utilization of seawater resources.