Adsorpsion and Dissociation of Water at the alpha-Al2O3 (110) Surface by 2-dimensional Density-Functional Based Tight-Binding/Molecular Mechanics Molecular Dynamics (2d-DFTB/MM MD)

AHYA AULIA OKTARINI, Dr. Aulia Sukma Hutama, S.Si., M.Si.; Mokhammad Fajar Pradipta, S.Si., M.Eng.

2021 | Skripsi | S1 KIMIA

Penelitian ini dilakukan dengan tujuan untuk membandingkan struktur dan reaksi pada permukaan alpha-Al2O3 (001) yang telah dibuat sebelumnya dan juga untuk mensimulasikan permukaan alpha-Al2O3 (110) dengan menggolongkan sistem pada level atom. Adsorpsi dan disosiasi antarmuka molekul air pada permukaan alpha-Al2O3 (110) disimulasi dengan strategi simulasi 2-dimensi density-functional tight-binding/molecular mechanics molecular dynamics (2d-DFTB/MM MD). Kristal alpha-Al2O3 (110) pertama-tama disimulasi dengan classical molecular dynamics menggunakan Potensial Buckingham. Ekuilibrasi α-Al2O3 (110) disimulasi menggunakan DFTB/MM selama 30 ps pada suhu 298.15 K. Potensial Lennard-Jones digunakan saat air ditambahkan di bagian atas Kristal dengan beberapa variasi sistem, yakni single, dimer, dan monolayer molekul air. Permukaan alpha-Al2O3 (110) kurang reaktif dibandingkan dengan alpha-Al2O3 (001) yang telah dibuat sebelumnya karena tidak ada protonasi yang teramati. Kecenderungan yang diamati dari ketiga system air tidak menunjukkan perubahan yang signifikan, namun system dimer mengalami perubahan struktur dan sifat dinamis adsorpsi air pada permukaan antarmuka dibuktikan dengan terjadinya disosiasi yang ditunjukkan dengan adanya pemutusan ikatan molekul air. Strategi simulasi 2d-DFTB/MM MD dapat digunakan untuk mempelajari adsorpsi dan disosiasi antarmuka molekul air pada permukaan alpha-Al2O3 (110).

This study was conducted to compare the structure and reaction at the surface with the well-established alpha-Al2O3 (001) crystal as well as to simulate the alpha-Al2O3 (110) surface by characterizing the system at the atomic level. The interfacial adsorption and dissociation of water molecules at the alpha-Al2O3 (110) surface was simulated using 2-dimensional density-functional tight-binding/molecular mechanics molecular dynamics (2d-DFTB/MM MD) strategy. Crystal alpha-Al2O3 (110) was firstly simulated by classical molecular dynamics with Buckingham Potential. Equilibration of alpha-Al2O3 (110) was done using DFTB/MM simulation for 30 ps at temperature of 298.15 K. Lennard-Jones potential was used when the water was added on top of the crystal surface with several variation of systems, such as single, dimer, and monolayer of water molecules. The alpha-Al2O3 (110) is less reactive than the well-established alpha-Al2O3 (001) crystal since no protonation occurred. The tendency observed at three water systems was showing no significant differences, yet the dimer water system was assessing structural and dynamical behaviour of adsorbed water at the interface region indicated by dissociation which shown by bond breaking of water molecule. The 2d-DFTB/MM MD strategy is suitable to study the interfacial adsorption and dissociation of water molecule in the alpha-Al2O3 (110) surface.

Kata Kunci : Dissociation of alpha-Al2O3 (110), molecular dynamics simulation, 2D-DFTB/MM MD.