Photocatalytic Activity of Gold and Silver Nanoparticles Synthesized by Using Coffee Flower Extract

Abstract

In this work, silver and gold nanoparticles (AgNPs and AuNPs) were synthesized via green synthesis using coffee flower (CF) extract as a source of reducing and stabilizing agents. The concentrations of HAuCl₄ and AgNO₃ were varied to be 2.5, 3, and 3.5 mM and 1.5, 2, and 2.5 mM, respectively, and five dilution ratios of CF extract to water were used. CF extract was analyzed for total phenolic content and reducing power. The obtained nanoparticles were characterized by UV-visible spectrophotometer and transmission electron microscope and were used as photocatalysts in colloidal form. The results showed that total phenolic content and reducing power of the extract were equivalent to 387.23 and 377.25 mg gallic acid/L. The optimum concentration of AgNO₃ was 3 mM and that of HAuCl₄•3H₂0 was 2 mM, and the ratio of CF extract to water was 20:80. The average diameters of AgNPs and AuNPs were 35.21 and 12.18 nm, corresponding to absorbance peaks at 449 and 532 nm, respectively. The photocatalytic activities of uncoated, PEG6000 coated and alginate-coated AgNPs and AuNPs were investigated by decomposing 10 ppm methylene blue (MB) in 4 mL under UV light (250 nm, 6W). The degradation percentage after 120 min reached maximum levels of 39.6% and 35.47% by using non-coated AgNPs and alginate-coated AuNPs at loading of 0.16 mg. It was found that 0.04 mg of reused AgNPs and 0.11 mg of reused AuNPs was able to remove MB up to 11.54% and 22.90%, respectively.