The Adsorption Of Dyes And P-Nitrophenol Onto Organic-Vermiculite Modified By Novel Gemini Surfactant

Vermiculite（VT）as a typical and inexpensive phyllosilicate with higher charge density has been considered as a type of promising adsorbing material.This clay modified by organic cation converting silicate surface from the normally hydrophilic to lipophilic displays greater adsorption ability than before modification.Butyl group and unsaturated groups（2-butenyl,2-butynyl and dimethylphenyl）have been introduced as spacers of Gemini surfactants for modifying vermiculite（VT）to exploit easily industrialized adsorbents and to explore systematically the effects of spacers on the adsorption of p-nitrophenol（PNP）.Four organo-vermiculites（OVTs including12-A-12-VT,12-P-12-VT（dimethylphenyl）,12-E-12-VT（2-butenyl）,12-Y-12-VT（2-butynyl））have been prepared successfully and 12-A-12-VT and12-P-12-VT have been mixed to remove mixed dyes.OVTs structure properties were characterized by FT-IR,XRD,TG,SEM,BET,elemental analysis and Zeta potential and their adsorption behaviors were investigated by adsorption experiments。Additionally,the test method for the concentration of mixed organic dyes was ascertained,and the standard curves of the binary system dyes were obtained.The characterization results show that the four have low saturated adding amount of surfactant（0.4 CEC）,and 12-A-12 with flexible alkyl group shows higher loading amount（18.8 wt%）on VT than the three surfactants with rigid unsaturated spacer（16.7wt%,15.7 wt%and 15.4 wt%）.The mixed OVT possesses the properties of both12-A-12-VT and 12-P-12-VT.The batch experiment results of OVTs to PNP demonstrate that the four are ranked by adsorption capacity as follow:12-A-12-VT>12-P-12-VT>12-E-12-VT12-Y-12-VT,their maximum adsorption all occur at p H=6 within 20 min and12-A-12-VT possess stronger removal capacity(q_max=106.5 mg/g)than other clay-based adsorbents.Furthermore,Kinetic studies are found pseudo-second-order（R²>0.999）and equilibrium data are fitted well by Freundlich isotherm model（R²>0.98）.The calculated thermodynamic parameters exhibit that the adsorption processes of PNP on OVTs are physical and exothermic.The adsorption experiments of organic vermiculite on dyes show that 12-P-12-VT with larger interlayer spacing has better adsorption capacity to dye（Congo red）with larger molecular dimension,while 12-A-12-VT with higher loadings has a larger adsorption amount to dye（Rhodamine B）with small molecular dimension.The dyes adsorption results show that binary-system Congo red adsorption reaches equilibrium within 1 min,and the removal efficiency of it is 100%（in single system,30min equilibrium,efficiency 67.5%）,and pseudo-second kinetic model of dyes on OVTs perform good.the maximum adsorption amount of single Congo red on OVT is hardly affected by the concentration,while the adsorption amount of mixed Congo red continues to increase greatly with its concentration increasing without sign of saturation,which is caused by the interaction between dye molecules.The adsorption of Rhodamine B on 12-A-12-VT accords with the Redlich-Peterson model,the adsorption behavior of Congo red by 12-P-12-VT fits the Langmuir model,and the adsorption of dual-system rhodamine on mixed OVT is in accordance with the Freundlich model;All the adsorption process of dyes on organic vermiculites are spontaneous and physical.