Modification of silica nanosheets by gemini surfactants with different spacers and its superb adsorption for rhodamine B

Abstract

To systematically investigate the effect of the non-polar spacer length of gemini surfactants on the adsorption characteristic of organo silica nanosheets (organo-SiNSs), a series of gemini surfactants with different non-polar spacer chain lengths (G16-2-16, G16-3-16, G16-4-16 and G16-6-16) were designed and introduced into silica nanosheets (SiNSs) for the removal of rhodamine B (RhB). Differences in the structure and surface properties of organo-SiNSs were characterized by FT-IR, XRD, TG, BET and zeta potential. Effects of concentration of modifiers and RhB, contact time, pH and temperature have been studied. The adsorption mechanism of different molecular speciation of RhB has been investigated in detail. Gemini surfactants with shorter spacer chain promote the modification process and easily intercalate into interlayer space. Suitable packing density of surfactants on the surface of organo-SiNSs is beneficial to RhB adsorption, and the adsorption capacities of organo-SiNSs decrease in the order G16-3-16-SiNSs (223.36 mg g−1) > G16-4-16-SiNSs (216.18 mg g−1) > G16-6-16-SiNSs (204.88 mg g−1) > G16-2-16-SiNSs (198.09 mg g−1). Hydrophobic interaction between surfactants and RhB plays a dominated role in RhB adsorption; molecular speciation of RhB, electrostatic interaction and competitive adsorption also affect the adsorption. Organo-SiNSs exhibited high adsorption capacity and rapid adsorption equilibrium toward RhB at a low modifier dosage (0.42 mmol for 1 g raw SiNSs). It has been demonstrated that organo-SiNSs can be regenerated at least for 5 cycles. Moreover, the adsorption isotherm data was proved in good agreement with the Redlich Peterson model and the kinetics data was fitted well with pseudo-second-order kinetic model.