The Adsorption Characteristics Of Organic-vermiculite Modified By Functional Gemini Surfactant

Vermiculite as a crucial clay where one alumina octahedral layer is sandwiched between two tetrahedral silica layers,is a 2:1 layered silicate.The vermivulite has extensively been used as adsorbents for water purification due to its high cation exchange（CEC）,swelling properties,and high surface areas.Naturally vermiculite has unexpected adsorption performance,by the modification of the quaternary ammonium cation（QACs）,the adsorption amount of the organoclays were enhanced.Organo-vermiculites（organo-Vts）with different preheating temperatures and gemini pydidinium surfactants(1,1’-didodecyl-4,4’-trimethylene bispyridinium bromide（BPy-12-3-12）and 1,1’-didodecyl-4,4’bispyridinium bromide（BPy-12-0-12）were prepared for the first time.Furthermore,Organo-vermiculites（organo-Vts）were also prepared by intercalation of four designed gemini surfactants（BDIN,BDHP,BDPD,BDPB）with different functional groups（imino,hydroxy,phenyl,pyridyl）into vermiculite（Vt）.The resultant adsorbents were characterized by FT-IR,XRD,SEM,TEM,TG and Zeta potential.Sulfamethoxazole（SMX）and rhodamine B（RhB）were chosen as the target contaminant to study the effects of type,location of surfactant functional group,and preheating temperature on the adsorption process.Batch experiments were conducted to research adsorption of sulfamethoxazole（SMX）on organo-Vts.Vermiculite with BPy-12-3-12 showed higher removal efficiency（95%）than that of BPy-12-0-12-Vt（43%）,and preheating at 100°C further facilitated the efficiency up to 98%.Adsorption process was observed to be pH dependent and fast（95%were removed in 10 min）,which followed a pseudo-second-order model as well as Freundlich isotherm.In addition,there is an interesting phenomenon that endothermic process occurred on BPy-12-3-12-Vt and BPy-12-3-12-Vt100,but exothermic one on other organo-Vts.In view of the practical significance,low concentration SMX in real-life waters were removed by organo-Vt,and the result showed an excellent and fast adsorption performance of this kind of adsorbent,even in low dosage of BPy-12-3-12（0.4 CEC）.The adsorption of RhB onto organoclays was in the order:BDIN-Vt>BDHP-Vt>BDPD-Vt>BDPB-Vt,especially BDIN with the q_maxax of 528 mg/g,which was much larger than known existing adsorbents so far.Differentiations of the adsorption capacity verify that（i）the combination of hydrogen bond and XH-πinteraction beyondπ-πinteractions,（ii）π-πinteractions between aromatic rings are stronger than that between heteroaromatic ring and aromatic ring,（iii）the gemini surfactant with polar spacers in the main chain is more favorable for adsorption than that in the pendant group.Additionally,the adsorption kinetics was in good agreement with the pseudo-second-order model.Equilibrium data of BDIN-Vt and BDHP-Vt were corrected well by Langmuir isotherm model,while BDPD-Vt was agreed well with Freundlich model.Thermodynamic parameters demonstrated that the adsorption of RhB on BDIN-Vt were non-spontaneous and exothermic process,which contrary to the others.This work provides new insight into the design of organo-clay as excellent adsorbents for the removal of organic contaminants.