THE EFFECT OF IRON ATOM IMPURITIES ON MONTMORILLONITE AS CO2 CATCHER

• Main Author: Ihsudha, Husni
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/73772
• Institution: Institut Teknologi Bandung

<p align="justify">Carbon dioxide is a greenhouse gas that naturally plays a role in keeping the Earth's surface temperature warm. However, in the current era of globalisation, much of it is produced from industrial processes that can cause environmental climate change. Carbon capture technology is built to reduce CO2 gas emissions by binding carbon dioxide molecules and then storing them or utilising them as more useful products. Montmorillonite, which is a clay material belonging to the smectite group and is widely found in nature, has the ability to bind molecules such as carbon dioxide in its interlayer region. Its characteristics that have cations to stabilise the charge on its structure open up the possibility of further material modification. In this study, simulations were carried out for the addition of iron (Fe) impurities as additional cations in montmorillonite to see the increase in the ability to bind carbon gas. Density Functional Theory calculations were carried out using the VASP program to see the reactions that occur between CO2 gas molecules and Fe montmorillonite material. The calculation process used the addition of van der Waals correction which represents the interaction between montmorillonite layers and Hubbard-U correction which improves the accuracy of the results for atoms that have d orbitals. By optimising the interlayer structure, the optimum vacuum distance between montmorillonite layers is obtained at a distance of 2.9Å judging from the optimum energy of the van der Waals force generated. From the 2.9Å interlayer structure, Fe atom impurities were added at several positions and obtained the tendency of Fe atoms to be trapped in the silicate void space and reduce the interlayer distance to about 2.5Å. This condition occurs because Fe atoms have a relatively small size than the silicate space and when trapped, Fe atoms also form bonds in the upper layer so that the interlayer distance decreases. In this condition, carbon dioxide gas will be placed on several sites with x and y orientations. The result of adsorption energy shows a non-spontanious reaction, therefore the interlayer is manually enlarged and the optimum distance to absorb carbon dioxide is about 4.6 Å. At the optimum distance, it is found that Fe atoms can increase the binding energy of carbon dioxide molecules, compared to sites without Fe atoms which only produce physical bonds or physisorption. It can also be compared with adsorption on monoxide gas which tends to have higher binding energy when Fe atoms bind to carbon atoms. If one of the optimum conditions is taken, it is obtained that carbon dioxide adsorption has a binding energy of -0.806eV while carbon monoxide produces a binding energy of -0.98eV. Described by charge density, under carbon monoxide binding conditions, the charge is mostly concentrated on carbon atoms which can be said to be the role of the more acidic Fe atoms donating charges on the more basic carbon side. It can be concluded, in the process of adsorbing carbon gas molecules on montmorillonite, an interlayer stretching process is needed which can be done by adding large cation atoms or generally using the help of water molecules. Fe atoms in this condition do not help adsorption by stretching the interlayer, but by providing an acidic side that more easily interacts with carbon dioxide and monoxide gas.