Study On The Adsorption Of Asymmetric Gemini Surfactant Modified Vermiculite And SiO₂ Nanosheets

Asymmetric gemini surfactants are a special class of gemini surfactants with two different alkyl chains or hydrophilic groups.Compared with symmetric gemini surfactants,they have many advantages such as lower cmc and stronger solvophobic effect.In this work,asymmetric and symmetric gemini surfactants with the same carbon number（22-6-6 and 14-6-14）,asymmetric gemini surfactants（22-s-6,s=2,3 and 6）with different spacers and these surfactants modified vermiculite（Vt）or Si O₂nanosheets（Si NSs）were prepared and characterized.p-chlorophenol（PCP）,phenol（P）and p-methylphenol（PMP）were selected as representative contaminants to study the structure,surface and adsorption properties of 22-6-6-Vt and 14-6-14-Vt towards phenols.Cationic crystal violet（CV）and anionic methyl orange（MO）were selected as the target pollutants to study the adsorption performance of Vt,Si NSs,22-s-6-Vt and22-s-6-Si NSs for dyes with different charge properties.The influence of time,temperature,p H and other factors on the adsorption performance was explored in detail.The kinetics,thermodynamics and isotherms in the adsorption process were also thoroughly investigated.The results were as follows:The arrangement of 14-6-14 in the vermiculite layers is loose paraffin bilayer,and that of 22-2-6 is tighter paraffin-type double layer,while 22-3-6 and 22-6-6 are arranged in the coexistence of paraffin-type monolayer and bilayer.The results of adsorption experiments for14-6-14-Vt and 22-6-6-Vt towards PCP,P and PMP showed that the adsorption capacities of P,PCP and PMP on 14-6-14-Vt are stronger than that on 22-6-6-Vt,and the adsorption capacities of PCP,P and PMP onto two OVts followe the order of PCP>PMP>P.In addition,kinetic,isotherm and thermodynamic results indicated that the adsorption of the three phenols on the two OVts is more in line with the pseudo-second-order kinetics and Langmuir models,and the adsorption process is spontaneous and exothermic physical adsorption.Mechanism research revealed that hydrophobic,electrostatic interactions,hydrogen bonding and special interactions（cation-πandπ-π）promote the adsorption of the three phenols.Regeneration experiments manifested that these two OVts can be regenerated with ethanol at least three times.The experimental results of Vt,Si NSs,22-s-6-Vt and 22-s-6-Si NSs adsorbing CV and MO showed that the adsorption capacity of CV on Si NSs is significantly stronger than that of Vt,OVts and OSi NSs,nevertheless,the adsorption capacity of 22-3-6-Vt for MO is superior to that of Vt,22-2-6-Vt,22-6-6-Vt,Si NSs and OSi NSs.The maximum adsorption capacities of CV and MO are 752.6 and 153.3 mg g^-1 at 25℃,respectively.The kinetic and thermodynamic results demonstrated that the adsorption of CV and MO is more in line with pseudo-second-order kinetics,and the adsorption process is spontaneous and exothermic physical adsorption.The results of adsorption-desorption experiments indicated that the spent 22-3-6-Vt and Si NSs can be regenerated by water and a mixture of 0.1 mol L^-1 HCl solution and ethanol at least three times,respectively.