ADSORPTION OF AIR POLLUTANT HEAVY METAL Pb ON Ca-MONTMORILLONITE USING DENSITY FUNCTIONAL THEORY

• Main Author: Rifqi Al Fauzan, Muhammad
• Format: Theses
• Language: Indonesia
• Subjects: Ilmu alam dan matematika
• Online Access: https://digilib.itb.ac.id/gdl/view/37140
• Institution: Institut Teknologi Bandung

The increasing number of vehicles as a result of population growth impact on increasing the amount of pollutants in the air. One of the most dangerous vehicle exhaust pollutant are heavy metals lead (Pb) since it cannot be degraded or destroyed. Pb considered as the most signicant air contaminant in recent use. Therefore, an eort to reduce Pb contamination is needed. A way that can be done to reduce Pb contamination is to use a material that has the ability to adsorb pollutants. One material that can be used is montmorillonite, particularly Ca-montmorillonite, which is montmorillonite with cation Ca2+ addition. Related to the above statements, the purpose of this study is to analyze the mechanism of adsorption of Pb on Ca-montmorillonite and investigate the structure and electronic properties of Pb/Ca-montmorillonite. In this study, montmorillonite structure is modeled as an innite slab with a thickness of 6.834A which consist of silica tetrahedral and alumina octahedral layers. The structure of Ca-montmorillonite obtained by applying isomorphic substitution in the pyrophyllite structure. Those isomorphic substitution is applied in two layers, one Al3+ ion replaces one Si4+ ion in the tetrahedral layer and one Mg2+ ion replaces one Al3+ ion in the octahedral layers. The method used in this calculation is Density Functional Theory (DFT) using Vi- enna Ab Initio Simulation Package (VASP). One unit cell of Ca-montmorillonite consisting of 41 atoms. The valence electrons for each atom used is as follows: H, 1s1; O, 2s22p4; Al, 3s23p1; Si, 3s23p2; Mg, 3s2; Ca, 4s2; Pb, 6s26p2 with GGA-PBE exchange correlation type. According to our calculation results Ca-montmorillonite unit cell has lattice constants a = 5; 18A; b = 8; 98A; c = 13; 24A with lattice iv v angle = 90; 50; = 99; 20; = 89; 70. With addition of Pb atom in Camontmorillonite we get energy adsorption Eads????Pb of -0,734 eV. The type of adsorption that occurs is chemisorption, this is evidenced by changes in band gap value of Ca-montmorillonite material. In other words adsorption of Pb changes the electronic properties of Ca-montmorillonite from insulator into a metallic. In this study we have carried out further investigations on the interaction between Pb atom and Ca-montmorillonite. Charge dierence distribution of Pb/Ca-montmorillonite showed the existence of charge between Pb and Ca atom indicates there has occurred a charge transfer between those two atoms. The charge transfer process is conrmed by the results of Bader calculation which showed the decreasing of electron charge of Ca and the increasing of electron charge of Ca neighboring atoms including Pb. We also perform supercell calculation of Pb/Ca-montmorillonite with three dierent sizes of Ca-montmorillonite: 1 2 1, 2 2 1, and 3 2 1 then varying the percentage of Pb atoms. We get lower total energy system and higher energy of each atom in higher percentage of Pb atoms and vice versa. We also found that the addition of Pb atom would change the electronic properties of Ca-montmorillonite both on unit cell and supercell although only by adding one Pb atom. In actual case, element of lead in vehicle exhaust is in the form of Pb atoms that have been oxidized to PbO. Therefore we also perform calculations of PbO/Camontmorillonite to determine the adsorption energy of PbO molecule on Ca-montmorillonite. Our calculation result shows addition of O atom on Pb signicantly decrease the adsorption energy becomes -2.616 eV.