Green synthesis of silver nanoparticles from anthocyanin extracts of purple cabbage ( brassica oleracea var capitata) and its characteristics for dye-sensitized solar cells (DSSC) application

Abstract

We extracted natural dye from purple cabbage (PCE) and green-synthesized the silver nanoparticle (AgNPs) from this extract for the light-harvesting material in DSSC. The anthocyanin was extracted with the maceration method for 24 hours with solvent variation (distilled water (DW), ethanol and methanol), followed by synthesized AgNPs. From FTIR, we found that the absorption area of anthocyanin at 1629 cm-1 correspond with stretch vibration of C=O shifted to 1608 cm-1 in AgNP, indicates the presence of amine group or flavanones group. The PCEs showed an amorphous non-Bragg diffraction peak at a range of (15-25)°. AgNP's diffractogram showed an intense peak at around 37.94° originates from Ag. Visible light range absorption observed, peaked at (421, 480, 550, and 966) nm, (415 and 544) nm, and (409 and 544) for PCEs in DW, ethanol, and methanol, respectively. The peak at 550 nm that comes from aglycone group in anthocyanin would be disappeared in the AgNPs that was made by dissolving AgNO3 in DW, ethanol, and methanol. The energy gap was (2.37, 3.00, and 3.03) eV for PCEs in DW, ethanol, and methanol, respectively, and (3.20, 3.30, and 3.31) eV for AgNPs. The reduction current originated from the Faradaic process (dark and irradiated condition) was detected in the extract with DW and ethanol as solvent, while it was not noticeable in methanol. This reduction current was detected for all solvents in AgNP positioned at a positive voltage of 0.2V. To be used as a light absorber in DSSC, one must choose the dye solution with the smallest energy gap without or small reduction current.