Properties of Mitragyna Speciosa (Ketum) extracted in water as organic dye molecular sensitizer

Abstract

Generally, dye sensitizers make use of inorganic elements such as ruthenium or osmium. However, these elements were toxic and hard to be produced due to its rarity. Alternatively, organic and natural sensitizer derived from various organic sources were studied. In this research, a natural dye which is chlorophyll b (Chl-b) extracted from Mitragyna Speciosa or ketum leaf pigment is used as the dye sensitizer. The geometry, optical properties and electronic properties were observed by the computational method using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) with B3LYP/6-31G with Gaussian-03 and Gaussview-03 software. Here, properties of bulk Chl-b were firstly obtained from databank as a control experiment. It was to be compared with the properties of Chl-b extracted using water as solvent. It can be observed that, UV-Vis of Chl-b showed peak absorbance at 430 nm at the blue light region of the visible light. The highest occupy molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were calculated by DFT ground state level. Bandgap of Chl-b without and with water extraction are 2.12 eV and 2.10 eV respectively, while excitation state of LUMO to conduction band are 1.21 eV and 1.27 eV respectively. It shows that the bandgap is lower when extracted using water as the solvent. Therefore, water extracted Chl-b tends to give a better result for HOMO/LUMO energy and voltage open circuit, Voc, HOMO and LUMO energy resulted in higher energy than the bulk Chl-b in Mitragyna leaves. This lower bandgap is attributed to the addition of electrons contents in the extracted molecules which is beneficial for dye-sensitize solar cells, DSSC.