Optimisation of photo-fermentative biohydrogen production from corn stover through the synergetic effect of ultrafine grinding and SnO2 nanomaterials

Abstract The synergetic effect of ultrafine grinding coupled with the incorporation of an appropriate amount of nanomaterials (NMs) on biohydrogen (bioH2) production from corn stover (CS) was studied. The changes in the physicochemical and optical characteristics of CS pretreated with various ultrafine grinding times were comprehensively studied. High-quality SnO2 NMs with high defect concentrations (e.g., oxygen vacancies (OVs)) were successfully synthesised. The physio-optical structures of pretreated CS and synthesised NMs were analysed using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy, and diffuse reflectance spectroscopy. SEM measurements confirmed that the morphology of the CS changed with the increase in grinding time and the particle size was reduced to the submicron range with increased surface roughness. The biomass particle size changed considerably from micron to submicron with an increase in grinding time. The intensities of the diffracted peak 22° decreased and the full width at half maximum increased with the increase in grinding time, which confirmed the considerable modification of biomass crystalline structure. The SEM analysis revealed that the synthesised SnO2 NMs were spherical in nature with a uniform size distribution. XRD analysis confirmed that the synthesised NMs had a stable rutile structure without any secondary phases. Hydrogen production tests were performed by utilising a mixed consortium of photosynthetic bacteria HAU-M1 as the inoculum. Hydrogen production rates of 120, 123, and 145 mL/h were observed for samples pretreated with 2, 4, and 6 h of ultrafine grinding, respectively. Owing to the synergetic effect of ultrafine grinding and nanomaterial loading, the hydrogen production rate increased considerably to 143, 144, and 163 mL/h after 2, 4, and 6 h of ultrafine grinding and nanomaterial loadings of 200, 150, and 150 mg/L, respectively. The highest cumulative bioH2 production of 425 mL was recorded after ultrafine grinding for 6 h and nanomaterial loading of 150 mg/L, 49% higher than that achieved with the standard sample (285 mL). Furthermore, the synergetic effect reduced not only the lag time (from 36 to 24 h) but also the amount of SnO2 NMs loading required to achieve the highest hydrogen production rate (150 mg/L) as compared with the standard sample (200 mg/L). Our results highlight that an appropriate combination of pretreatments can present a potential roadmap to enhance bioH2 production from lignocellulosic biomass, which can be a prospective sustainable energy supply.