Sustainable HMF synthesis from waste cooked rice water using fly-ash based Al2SiO5 supported nano-photocatalyst under halogen-ultrasound synergistic-energy: LCA and DFT based simulation

Abstract

Innovative Fe3+/Fe2+/Al2SiO5/Ti4+ nano-photocatalyst (FA_NPC*) was successfully prepared employing fly ash (FA)-based unique nano-Al2SiO5 and nano-Fe3+/Fe2+ in an innovative assimilated energy-system comprising tungsten-halogen radiation and ultrasound (THUS). The energy-efficient THUS activated optimal FA_NPC* (FA_NPC*°) possessed favourably higher specific surface area (142.11 m2/g), finer nanoparticles (47.50 nm) and lower band gap energy (2.78 eV) compared (89.72 m2/g, 62.43 nm, 2.97 eV respectively) to its conventionally prepared analog (FA_NPCCO). The FA_NPC*° rendered a significantly higher HMF yield (38.37 mol%) from a kitchen waste viz., cooked rice water (CRW) under THUS at 70 °C in only 60 min compared to 21.67 mol% HMF yield provided by FA_NPCCO. The DFT based study revealed that the CRW conversion process to HMF occurred through water adsorption on FA_NPC* surface for H3O+ formation, followed by H3O+ induced CRW hydrolysis, subsequent glucose isomerization on -Ti active sites and finally fructose dehydration by H3O+. The LCA of the overall process confirmed that the FA_NPC*° catalysed CRW conversion process could appreciably alleviate harmful environmental parameters, viz. global warming, fossil depletion, human toxicity and metal depletion by 7.65%, 4.15%, 8.56% and 13.57% respectively in comparison with FA_NPCCO. Thus, the THUS stimulated system could favourably demonstrate the efficient and eco-friendly utilisations of two abundant waste resources, viz. fly ash and cooked rice water for a sustainable production of HMF.