Phytofabrication of bimetallic Co–Ni nanoparticles using Boerhavia diffusa leaf extract: analysis of phytocompounds and application for simultaneous production of biohydrogen and bioethanol

Abstract

Boerhavia diffusa mediated synthesis of bimetallic cobalt—nickel nanoparticles (Co–Ni NPs) was developed using optimized process parameters including pH, precursor (mixture of Co and Ni salts) concentration (mM) and volume ratio of precursor solution to leaf extract. Foureir Transform Infra Red spectroscopy (FTIR) studies revealed that the protein, phenolic and alcoholic compounds were mainly accountable for the formation and stabilization of Co–Ni NPs. Gas Chromatograpgy—Mass Spectrometric (GC-MS) results showed that the presence of alcoholic (1,3-dioxolane-2-methanol), phenolic (phenol,2-(1,1-dimethylethyl)-4-(1-methyl-1-phenylethyl)-, ketone (4H-1-benzopyran-4-one, 2-(2, 6-dimethoxyphenyl)-5, 6-dimethoxy-), ester (9-octadecenoic acid, (2-phenyl-1,3-dioxolan-4-yl) methyl ester, cis-) and oxygenated monoterpenes (1-(2-methoxyethoxy)-2-methyl-2-propanol, methyl ether) were mainly responded for the formation and stabilization of bimetallic Co–Ni NPs. High Resolution—Transmission Electron Microscopic (HR-TEM) images exhibit that the size of the Co–Ni NPs was observed to be less than 10 nm. The effect of the Co–Ni NPs as cofactor on simultaneous production of biohydrogen and bioethanol from glucose using Citrobacter freundii NCIM No. 2489 was investigated at different concentrations from 250 to 1250 μg l−1. The yields of biohydrogen and bioethanol were 0.26 mol H2/mol glucose and 3307 ± 238 mg l−1, respectively at 1000 μg l−1 Co–Ni NPs. The Co–Ni NPs supplemented fermentation system yielded high production of bioethanol and low production of biohydrogen. The volatile fatty acids (VFAs) in the Co–Ni NPs supplemented system were also noticed in the following order: propionate > butyrate > acetate.