Sustainable fermentable sugar production using a glass fiber supported gallium–molybdenum photocatalyst towards bioethanol production: LCA analysis

Abstract

For the first time, a cost-effective glass fiber (GF) support derived from waste printed circuit boards (W-PCBs) was utilized to synthesize a reusable GF-supported gallium–molybdenum photocatalyst (GaMo–GF) for generating fermentable sugar (FS) from delignified corncob (DCC) in a quartz halogen solar batch reactor (QHSR). Additionally, this paper presents a comparative detoxification investigation and subsequent fermentation of the resulting FS using Pichia stipitis. The optimum Ga⁴Mo-GF (with a gallium precursor loading of 4 wt%) photocatalyst exhibited impressive characteristics, including a high specific surface area (28.01 m² g⁻¹), high pore volume (0.04198 cc g⁻¹) and lower band gap energy (2.3 eV), providing a maximum 78.35 mol% FS yield under mild reaction conditions (100 °C and 20 min) with mild energy consumption (12 kJ mL⁻¹). The comparative hydrolysate detoxification study highlighted the superior efficacy of the Amberlite IRP69 cation resin, achieving maximum removal rates of 86% for furfural, 92% for formic acid, and 95% for levulinic acid compared to other methods. Furthermore, the hydrolysate detoxified using Amberlite IRP69 resulted in a higher bioethanol concentration (4.32 mmol mL⁻¹) compared to NaOH neutralization (3.06 mmol mL⁻¹), Ca(OH)₂ over-liming (2.88 mmol mL⁻¹), and ethyl acetate solvent extraction (3.73 mmol mL⁻¹) when fermented with Pichia stipitis. Additionally, the overall environmental impact assessment indicated that utilizing the Amberlite IRP69 cation resin not only enhanced bioethanol yield but also reduced environmental impacts. Remarkably, the optimized Ga⁴Mo-GF catalyst demonstrated reusability for up to 7 cycles in the DCC hydrolysis process, showcasing its stability and the consequential reduction in environmental impacts throughout the corncob to bioethanol conversion process.