Synthesis Of Silver Nanoparticles Using Pearl Millet (Pennisetum Glaucum ) Husk Extract And Its Application In Wastewater Treatment And Catalytic Oxidation Of Benzyl Alcohol

Abstract

Metal nanoparticles are endowed with optical, electrical physical and chemical properties and have become attractive materials for commercialization applications in optical spectroscopies, electrical devices and catalytic applications. Among them, silver nanoparticles (Ag-NPs) have distinctive physico-chemical and biological properties such as antimicrobial, chemical stability and catalytic properties. Namibia, a semi-arid country, relies on man-made dams to obtain water for potable use. However, these dams are periodically polluted by algal blooms that pose devastating effects on the water quality. On a separate but related note, there is limited research on the use of Ag-NP based catalysts with regard to the conversion of alcohols to aldehydes as opposed to other noble metals. The aim of this study was to biologically synthesize Ag-NPs and investigate their antimicrobial properties against algae and to further investigate the catalytic properties of Ag-NPs for oxidation of benzyl alcohol. Ag-NPs were formed under optimum conditions. The antimicrobial property of the Ag-NPs was tested by incubating freshwater algae in an Ag-NP solution and the chlorophyll concentration measured periodically. Catalytic properties of Ag-NPs were tested by oxidation of benzyl alcohol in the presence of hydrogen peroxide. The UV-Vis spectroscopic analysis of Ag-NPs revealed a surface plasmon resonance peak at 429 nm. Scanning and transmission electron microscopy showed spherical and polydispersed nanoparticles with an average size of 17 nm. Fourier transform infrared spectroscopy affirmed the role of Pearl Millet extract as a reducing and capping agent of silver ions. Incubation of algae with Ag-NPs resulted in a 41.31% reduction in chlorophyll concentration. High performance liquid chromatography confirmed the oxidation of benzyl alcohol to benzaldehyde, with 90% conversion. The study concluded that biologically synthesized Ag-NPs are toxic to algae and can be used for algae control in wastewater treatment, and furthermore, for catalytic oxidation of benzyl alcohol to form benzaldehyde. The study recommends the use of Ag-NPs as an antimicrobial against algae. In addition, further studies are recommended to investigate the effect of different calcination temperatures and time on the catalytic activity of Ag-NPs.