Green Synthesis of Iron Oxide Nanoparticles for Biohydrogen Production using Plant Extract

Abstract

Hydrogen is an outstanding source of energy that is free from any hostile carbon footprint as it produces only water during combustion. The application of nanotechnology is one of the recent advanced technologies used to enhance the rate of hydrogen production from biomass fermentation. Researchers have proved that nanoparticles including those of metal oxides have shown a significant improvement in the biohydrogen yield and productivity. However, their hydrogen production efficiencies have been found to vary significantly with the type of nanoparticles and their concentration. Therefore, this study aimed to investigate the effect of adding green synthesized magnetic iron oxide nanoparticles in biohydrogen production in terms of bacterial growth and kinetic study. Magnetic iron oxide nanoparticles were fabricated using the green route by utilizing the plant extract that is rich with phenolic compound to produce uniformly distributed nanoparticles with an average size of 75 nm. Extraction of phenolic compound from biomass waste was done using deep eutectic solvent (DES) method. In this study, the best biomass waste chosen was coconut shell, and the best DES combination was choline chloride and ascorbic acid at 1:2 molar ratio. It was found that there were about four types of phenolic compounds extracted from this waste which represented about 3715.67 mg GAE/L of total phenol. Then, this extract was used in fabrication of magnetic iron oxide nanoparticles under hydrothermal method. Characterization of the fabricated magnetic iron oxide nanoparticles were made using fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscope (FESEM), gas chromatography-mass spectrometry (GC-MS), x-ray powder diffraction (XRD) and vibrating sample magnetometer (VSM). The characterization analysis found that the fabricated iron oxide nanoparticle assembles the properties of magnetite iron oxide (Fe3O4) with superparamagnetic properties at 44.025 emu/g magnetic moment. The magnetic iron oxide nanoparticles were then applied in anaerobic fermentation of biohydrogen in order to enhance the biohydrogen yield and productivity of the fermentation process. The concentration of magnetic iron oxide nanoparticles used was varied from 0 to 300 mg/L during the fermentation process as to determine its efficiency in improving biohydrogen production. It was found that the biohydrogen yield was increased up to 75 % when there was a presence of 200 mg/L of magnetic iron oxide nanoparticles in the fermentation media with 0.7865 mol H2/mol sugar respectively and this result was much better than control experiment. Kinetic study was then conducted using the optimum concentration of magnetic iron oxide nanoparticles and it showed that for Gompertz model, the maximum hydrogen production potential (Pmax) and hydrogen production rate (Rm) increased to 50.69 mL and 3.30 mL/h respectively and the lag phase time reduced about 7.12 h as compared with the control experiment (0 mg/L). On the other hand, analysis of the bacterial growth with the presence of magnetic iron oxide nanoparticles using Monod model gave the specific growth rate, ?max of -0.006 h-1 with cell growth saturation coefficient, Ks of -10.09 g/L. In conclusion, the positive results of magnetic iron oxide nanoparticles supplementation on fermentative biohydrogen production of mixed thermophilic bacteria proved the feasibility of adding this nanoparticle as micronutrient for enhancement of such hydrogen production system.