Comparative Adsorption Of Polycylic Aromatic Compounds On Organo-vermiculites Modified By Imidazolium-and Pyridinium-based Gemini Surfactants

Organo-vermiculite is a low-cost and effective adsorbent,which has important application value in the field of removing pollutants from water.Gemini surfactant can be used as modifier of vermiculite due to its superior physical and chemical properties.In this work,gemini surfactant（DDBI）containing imidazoline functional group and gemini surfactant（DDBP）containing pyridine functional group were synthesized,and two organo-vermiculite（DDBI-Vt and DDBP-Vt）were prepared by modifying vermiculite with DDBI and DDBP,respectively.Their structure and wettability were characterized by a series of characterization methods.Taking 2-naphthol（NP）and naproxen（NPX）as target pollutants,the influence of key factors（e.g.modifier dosage,contact time,pH,concentration of adsorbate,temperature,and ionic strength）on adsorption performance was investigated,and the adsorption mechanism was deeply explored.The research results were as follows:A series of characterization results showed that the saturated dosage of organo-vermiculite was 0.6 CEC,and the modifier was arranged by paraffin-bilayer in the interlamellar space.Compared with DDBP-Vt,DDBI-Vt had a larger interlayer spacing but slightly lower hydrophobicity.The maximum adsorption capacities of DDBI-Vt and DDBP-Vt for NP were 206.82 and 200.33 mg g^-1,respectively,and the maximum adsorption capacities of DDBI-Vt and DDBP-Vt for NPX were 74.48 and52.99 mg g^-1,respectively.For the same adsorbent,the adsorption capacity of NP was significantly higher than that of NPX,which was due to theπ-πinteraction between adsorbent and NP was larger than that between adsorbent and NPX.Adsorption kinetics and isotherms results certified that all adsorption processes followed pseudo-second-order kinetics model.The adsorption processes of NP and NPX onto DDBI-Vt fit well with Redlich Peterson model,and adsorption processes of DDBP-Vt accorded well with Freundlich model.Thermodynamic results indicated that all adsorption processes were exothermic and randomness-decreased physical processes.The research mechanism showed that hydrophobic interaction,π-πinteraction and electrostatic attraction were involved in the adsorption process,andπ-πinteraction played the dominant role in the adsorption process.This study showed the advantage of imidazoline-modified organo-vermiculite in the removal of electron-rich pollutants,and provided a new idea for the design and synthesis of new adsorbents.