Bentonite-ionic liquid composites for Congo red removal from aqueous solutions

Clay-organic composites have attracted great interest due to their ability to remove various contaminants from wastewater. The surfactants are the most commonly used organic compounds for clay modification. However, cationic surfactants are toxic and can be environmentally hazardous. Ionic liquids are a new promising alternative to the cationic surfactants due to lesser toxicity and appropriate thermal stability. The research aim is to prepare an environmentally friendly new class of clay sorbents modified with ionic liquids for potential applications in wastewater treatment from the textile industry. Imidazolium-based ionic liquids with different lengths of alkyl chains were intercalated in the interlayer space of sodium bentonite via an ion exchange reaction. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric (TG) analysis, and Brunauer-Emmett-Teller (BET) method for the specific surface area (SSA) analysis provided evidence of successful modification of the bentonite. The removal of model organic contaminant, Congo red dye, from aqueous solutions was investigated using the modified clays under different experimental conditions, i.e., reaction time, pH and sorbate concentration. Detailed isotherm studies showed that the modified clays have much higher Congo red sorption capacity compared to unmodified bentonite. The maximum Congo red sorption capacity of 150 mg/g was observed for bentonite modified with 1-dodecyl-3-methylimidazolium chloride (Bent_C₁₂mimCl) with d-value of 17.7 Å. This study shows that ionic liquids enhance bentonite capacity for Congo red sorption with different trends based on the ionic liquid structure. Bentonite-ionic liquid composites are eco-friendly and effective sorbents and due to a substantial increase in their capacity for the removal of textile dyes, they are expected to diminish the environmental impact of industrially used dyes.