Investigating the quantum size effects of multi-walled carbon nanotubes (MWCNTs) in photocatalytic fermentative biohydrogen production

Nanocatalysts' quantum size impacts their catalytic activity, hence surface area in nanomaterials plays a key role in controlling the charge transferring. Since multi-walled carbon nanotubes (MWCNTs) possess a large surface area as compared to bulk activated carbon (AC), thus their role in photo fermentative biohydrogen production (PFHP) from corn stover has been investigated. The physio-optical characteristics of the studied MWCNTs, and AC were characterized through the Brunauer Emmett Teller (BET), scanning electron microscope (SEM), and Raman spectroscopy. The experimental finding revealed that MWCNTs has a larger specific surface area (SSA) of 227.69 m²/g than activated carbon (AC) (126.26 m²/g). SEM and Raman results confirmed that MWCNTs have smaller sizes and more defects due to surface dangling bonds. The incorporation of MWCNTs in a photo fermentative medium showed a pronounced effect on hydrogen production. The optimal concentration of 20 mg/L MWCNTs increased the hydrogen production rate to 132.96 mL/h, 46.66% and 17.85% greater than the control group (CG) and AC, respectively, and reduced the lag period by 12 h. At 20 mg/L loading concentration, total hydrogen production was 293.84 mL, 2-fold and 16.24% greater than CG. The 44.85%, 100.39%, and 126.49% increase in byproducts, energy conversion efficiency (ECE), and light conversion efficiency (LCE), respectively compared to CG indicated an increase in metabolic processes, which increased total hydrogen production, suggesting that catalyst surface area is the key parameter affecting fermentative biohydrogen production catalytic efficiency.