Saponin-intercalated organoclays for adsorptive removal of β-carotene: Equilibrium, reusability, and phytotoxicity assessment

Abstract

Acid-activated clays play an essential role in the edible oil refining industry to remove colored pigments and impurities to meet consumer demands and specific purposes. Despite its high bleaching activity, the use of highly corrosive acids in significant quantities for producing the activated clay raises safety and environmental concerns. Herein, we demonstrate an environmentally friendly and low-cost preparation of organoclay-type bleaching earth via aqueous phase intercalation of bentonite with natural surfactant (rarasaponin) under microwave irradiation. The influence of the rarasaponin concentrations on the textural and chemical characteristics of the resultant organoclays was investigated with relevant techniques, including SEM, XRD, FTIR, and N2 sorption. The results revealed that the intercalation of rarasaponin causes a basal spacing increase to 1.50 nm, surface area to 99.5 m2/g, and pore volume to 0.85 cm3/g, while the cation exchange capacity (CEC) value decreased to 19.1 ± 4.4 meq/100 g; where the untreated bentonite has a basal spacing of 1.39 nm, a surface area of 86.8 m2/g, a pore volume of 0.69 cm3/g, and a CEC value of 30.1 ± 3.6 meq/100 g. The RSB-2 organoclay exhibits the best bleaching activity, with ~91% β-carotene removal efficiency achieved in degummed palm oil compared to the untreated bentonite (72% efficiency). The equilibrium behavior of β-carotene adsorption onto RSB-2 organoclay) was best fit with the Redlich–Peterson isotherm model, giving the theoretical maximum sorption capacity (qmax) 78.09 mg g−1, which represents the best-reported values among the investigated samples. A reusability study of the spent bleaching clay demonstrates that the adsorptive removal of β-carotene remained greater than 90% after five consecutive cycles. The spent RSB-2 organoclays also showed no appreciable phytotoxicity toward Arabidopsis seed germination but a slight inhibitory activity on the root development, suggesting environmentally friendly behavior and allowing for the landfill disposal.