Adsorption of ferulic acid from an alkali-pretreated hydrolysate using a new effective adsorbent prepared by a thermal processing method

A new adsorbent (AEPA₂₅₀) was prepared using the enzymatic hydrolyzed residue of rice straw in an air environment at 250 ℃ by a thermal processing method. Compared to the commercial adsorbent, AEPA₂₅₀ possessed a larger specific surface area of 277.680 m² g⁻¹, and the maximum adsorption efficiency of ferulic acid from alkali-pretreated hydrolysate of rice straw achieved 70.33 % at the optimum conditions. Adsorption kinetics and isotherm studies showed that the pseudo second-order (PSO) (0.997 ≤ R² ≤ 0.999) and Liu models (0.931 ≤ R² ≤ 0.997) exhibited better fitting results, which indicated that chemical and saturable adsorption existed between ferulic acid and AEPA₂₅₀. An adsorption thermodynamics study revealed the spontaneous and endothermic adsorption process (ΔH^o > 0 and ΔS^o< 0). Micropore diffusion was defined as the major adsorption rate-limiting step according to the analysis of Webber-Morris and Bangham's model. Additionally, π-π*, ion exchange, hydrogen bonding and precipitation were recognized as the four main mechanisms of ferulic acid removal by AEPA₂₅₀ through SEM/EDX, EDX mapping, XPS, FTIR and XRD analysis. These results indicated that AEPA₂₅₀ was effective for adsorbing inhibitors in pretreated rice straw hydrolysates, and it has high potential for application in establishing the self-sufficient production process of bioethanol.