Potential of subcritical water hydrolyzed soybean husk as an alternative biosorbent to uptake basic Red 9 dye from aqueous solutions

Bioethanol produced from lignocellulosic sources still faces problems related to the feasibility of this technological route. Within the biorefinery concept and clean technology, subcritical water hydrolysis (SWH) is efficient for dissociating lignocellulosic biomass. The solid co-products can be used for other applications to become SWH a more feasible process. The potential use of subcritical water hydrolyzed soybean husks (SWHSH) as a biosorbent to remove basic Red 9 dye (BR9) from aqueous solutions was evaluated in this study. SWHSH was efficient in the uptake of BR9, mainly at a pH of 8.0. The Langmuir model satisfied the biosorption equilibrium profile with a biosorption capacity of 56.8 mg g-1. The thermodynamic parameters indicate that the biosorption is spontaneous, with the AG0 ranging from - 22.08 to - 24.88 kJ mol1, with an endothermic nature (AH0 = 5.59 kJ mol-1). The biosorption equilibrium was in 60 min for all the initial concentrations studied. The Linear Driving Force (LDF) model fitted the data well, furnishing diffusivity values from 1.41 to 2.00 x 10-8 cm2 s- 1. Desorption was also possible under acid conditions, and SWHSH could be effectively used 3 times. Last, the fixedbed biosorption showed that the SWHSH could remove the BR 9 dye up to 180 min without regeneration, presenting a biosorption capacity of 46.1 mg g1 for 900 mL of treated effluent with an initial concentration of 200 mg L1. The characterization and biosorption results indicate that the BR9 tends to be adsorbed by physical forces, possibly by hydrogen bonds, electrostatic interaction, nn interaction, and cation-n interaction. Overall, the SWHSH demonstrated potential application as a biosorbent for the removal of BR9.

Automated summary

In this study, the potential use of subcritical water hydrolyzed soybean husks as a biosorbent for the removal of basic Red 9 dye was evaluated. The biosorbent showed efficient uptake of the dye at a pH of 8.0, and the Langmuir model described the biosorption equilibrium well. The thermodynamic parameters indicated that the biosorption process was spontaneous and endothermic. The biosorption equilibrium was reached in 60 minutes, and the diffusivity values were calculated using the Linear Driving Force model.