In recent years the application of metal nanoparticles is gaining attention in various fields. The present study focuses on the additive effect of `green’ synthesized iron nanoparticles (FeNPs) on dark fermentative hydrogen (H₂) production by a mesophilic soil bacterium Enterobacter cloacae. The FeNPs were synthesized by a rapid green method from FeSO₄ using aqueous leaf extract of Syzygium cumini. The synthesized FeNPs showed a characteristic surface plasmon resonance peak at 267 nm. The transmission electron microscopy images confirm that the formation of FeNPs was mainly porous and irregular in shape, with an average particle size of 20–25 nm. The presence of iron (Fe) in the synthesized FeNPs was confirmed by energy-dispersive X-ray spectroscopy. The comparative effect of FeSO₄ and FeNPs on batch fermentative H₂ production from glucose was investigated. The fermentation experiments reveal that the percentage and yield of H₂ in FeNPs supplementation were increased significantly than the control (no supplementation) and FeSO₄ containing media. The maximum H₂ yield of 1.9 mol mol⁻¹ glucose utilized was observed in 100 mg l⁻¹ FeNPs supplementation, with two-fold increase in glucose conversion efficiency. Thus, the result suggests that FeNPs supplementation in place of FeSO₄ could improve the bioactivity of H₂ producing microbes for enhanced H₂ yield and glucose consumption.

Recently, the focus has been on the environment-friendly synthesis of nanoparticles (NPs) due to no chemical processing and generation of toxic and hazardous materials. Here, a novel method has been reported for the synthesis ofcerium oxide nanoparticles (CeO$_2$ NPs) through a green route using Dillenia indica aqueous extract. The physicochemical properties and morphological study of CeO$_2$ NPs were performed by using X-ray diffraction, field-emissions canning electron microscope imaging, energy dispersive X-ray analysis, Fourier transform infrared spectroscopy, RAMAN and ultraviolet-visible spectra. The nano-polycrystallinity of face cubic lattice structure is formed in CeO$_2$ NPssamples with an average particle size of 70 nm. The anti-oxidant property study of CeO$_2$ NPs was carried out using 2, 2-diphenyl-1-picrylhydrazyl (DPPH) scavenging assay. The CeO$_2$ NPs assure significant DPPH scavenging activity indicating excellent anti-oxidant property. This green synthesis method has the potential for mass production of CeO$_2$ NPs cost effectively without environmental pollution.