Organo-vermiculites with biphenyl and dipyridyl gemini surfactants for adsorption of bisphenol A: Structure, mechanism and regeneration.

Two novel biphenyl and dipyridyl gemini surfactants, bis-N, N, N,-hexadecyldimethyl-p-biphenylenediammonium dichloride (BHBP) and 1,1'-dihexadecyl-4,4'-bispyridinium bromide (DHBP) were designed and used to functionalize the high layer charged vermiculite (Vt) for the first time. Key organo-Vt characteristics, such as the modifier loading, arrangement and the stacking unit of platelets were specified by FT-IR, XRD, TG, SEM and Elemental Analysis. The saturated surfactant dosage in the modification process, in reverse relationship with the availability of the modifier, was defined as low as 0.4 CEC of Vt. The adsorption performance of organo-Vts were tested by bisphenol A (BPA), which showed great potential as organic adsorbents (143.5 mg g and 139.7 mg g for BHBP-Vt and DHBP-Vt, respectively). Insights into the adsorption mechanism were discussed through kinetics, isotherms and thermodynamics, as well as characterization of the spent samples. BPA onto orgno-Vts matched well with pseudo-second-order, Freundlich models and an exothermic process in nature. Interestingly, π-π interactions between aromatic rings were stronger than that between heteroaromatic ring and aromatic ring, and π-π stacking between the BPA adsorbed and dissociated in solution turned out to promote the adsorption process. The organo-Vts were sustainable and could reuse by ethanol at least for three cycles. Organo-Vts could not only guide focuses on the high layer charged precursors, but open up a new area for the fabrication of novel materials to serve as tunable and cost-effective adsorbents.