Enhanced removal of bisphenol A from aqueous solution by organomontmorillonites modified with novel Gemini pyridinium surfactants containing long alkyl chain

To utilize the it-it interaction and the hydrophobic affinity of modifiers with long alkyl chain in the interlayer of montmorillonites for effective removal of bisphenol A (BPA) from aqueous solution, organo-montmorillonites modified with novel Gemini pyridinium surfactants containing both the aromatic ring and long alkyl chain, 1,1'-didodecy1-4,4'-trimethylene bispyridiniurn bromide (BPy-12-3-12) and 1,1'-dihexadecy1-4,4'-trimethylene bispyridinium bromide (BPy-16-3-16) were designed and prepared in this study. The raw montmorillonite and organo-montmorillonites (BPy-12-3-12-Mt and BPy-16-3-16-Mt) were specified with X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), thermogravimetric analysis (TGA). The main effect factors which played a significant role in removal of BPA from aqueous solution, such as the amount of modifier, alkyl chain length, contact time and solution pH were investigated in detail. The experimental results indicated that the maximum adsorption capacities of BPA obtained from Langmuir isotherms were 222.2 mg/g for BPy-12-3-12-Mt and 208.3 mg/g for BPy-16-3-16-Mt at pH 6, suggesting that organoclays with shorter alkyl chain presented higher affinity for BPA. This may be due to the combined contribution of pi-pi interaction and hydrophobic interaction, especially pi-pi interaction played a dominated role in BPA adsorption. Additionally, the experimental data were best fitted with the Langmuir isotherm model. The obtained kinetics data for BPA adsorption onto the organoclays were described well by the pseudo-second-order model. Thermodynamic parameters demonstrated that the adsorption process of BPA was spontaneous and exothermic in nature. (C) 2015 Elsevier B.V. All rights reserved.