Biogenic silver nanoparticles: synthesis, characterization, and degradation of congo red

Senna leaves have been used in traditional folk medicine for the treatment of colon infections. Silver nanoparticles (AgNPs) were fabricated by using an aqueous extract of Senna leaf extract as a reducing agent with cetyltrimethylammonium bromide (CTAB). Morphology of AgNPs was determined with transmission electron microscope (TEM), scanning electron microscope (SEM), energy-dispersive X-ray spectroscope (EDX), Fourier transform infrared spectroscope (FTIR), and X-ray diffraction patterns (XRD). The Ag+ ions were reduced into metallic silver (Ag-0) by the primary -OH groups of water-soluble constituent of Senna leaf extract. The aggregation number (= 2.4 x 10(4)) and molar concentration (= 4.4 x 10(-5) mol/L) of AgNPs were calculated from the TEM data. CTAB concentrations have significant impact on the color of AgNPs and position of surface plasmon resonance (SPR) band. The AgNPs were used as an activator for potassium persulfate (K2S2O8) to the oxidative degradation of Congo red (CR). The degradation of CR was promoted with increasing concentrations of K2S2O8 and decreasing concentrations of CR. The results showed that the CR degradation increased with increasing temperature. The maximum CR degradation was observed at pH 6.7, whereas at pH above and below 6.7, the efficiency of CR degradation was decreased.