Application of green synthetic iron oxide nanocatalyst in biohydrogen production from domestic wastewater

Hydrogen (H₂) is considered to be an energy carrier with high yields in future. Using green nanoparticles as the catalyst to produce H₂ from organic wastes is an environmentally friendly and cost-effective approach. This study specifically addresses H₂ production biologically from domestic wastewater using dark fermentation process with green nanoparticles in anaerobic condition. In this investigation, acid, alkaline, and heat pre-treated wastewater were utilized as the feedstock and identified that the alkaline pre-treated wastewater was an efficient feedstock for H₂ production. The reaction conditions such as pH, time, and nanocatalyst dosage were optimized for the enhancement of H₂ production. In addition, the green iron oxide nanoparticles (Fe₃O₄-NPs) were prepared by sustainable way using Murraya koenigii (curry leaves) with FeSO₄ and characterized it using Fourier-transform infrared spectroscopy (FT-IR), ultraviolet-visible spectrophotometer (UV-vis), power X-ray diffraction (pXRD), and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDX), further tested for their 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging performance via in vitro antioxidant activities. This study demonstrates that a maximum production of bio-H₂ was obtained (72.8 mL/L) with 20 mg of nanocatalyst load at alkaline condition (pH 9). The correlation coefficient value was highly significant for biohydrogen production with increasing pH (r = 0.9026) and catalyst dosage (r = 0.9962). The characterization studies confirmed the existence of iron oxide nanoparticles in the green synthesized nanoparticles. The in vitro antioxidant assay showed that Fe₃O₄-NPs effectively reduces the DPPH radical by significantly releasing H-atoms, thereby confirming that the plant extract functions as reducing/oxidizing agents. The high yield under the dark fermentation method has clearly been attributed to the enhancement in bio-H₂ production by using the green Fe₃O₄-NPs based on M. koenigii.