Preparation Of Montmorillonite Modified By Polyhydroxy Gemini Surfactant And Its Dye Adsorption

Presently the shortage of resources and environmental pollution have put forward more urgent requirements for the development of water treatment technology.Adsorption technology provides great possibilities for its industrial application due to its low operating cost and universal applicability.Dye is one of the sources of water pollution.As a natural mineral clay,montmorillonite has attracted much attention in the field of dye wastewater treatment with the advantages of low cost,abundant reserves,easy modification and so on.Cationic surfactants are the most commonly used type of montmorillonite organic modifiers.Compared with traditional single-headed surfactants,quaternary ammonium Gemini surfactants with two ammonium head groups have some superior properties such as higher surface activity.What's more,some research reports indicated that Gemini surfactant-modified montmorillonite exhibited better performance than single-head surfactant-modified montmorillonite in removing organic pollutants in dye wastewater.Therefore,it is necessary to do more research on the modification of montmorillonite by new Gemini surfactant.In this paper,with the method molecular design and process optimization,a polyhydroxyl Gemini surfactant called dioctadecyl tetrahydroxyethyl dibromopropane diammonium?DTDD?was synthesized via one-step quaternization reaction under the condition of microwave and high pressure using octadecyl diethanolamine and 1,3-dibromopropane as the main raw materials.The optimum synthesis conditions for the microwave high-pressure method to promote the quaternization reaction were determined as follows:the solvent was n-butanol,the molar ratio of reactants was n?alcoholamine?:n?bromopropane?=2.0:1,the amount of solvent was m?solvent?:m?raw material?=1:1.2,reaction temperature was 140?,reaction time was 8h,and microwave power was set to 900 W.The experiment was repeated three times under the optimal process and the average yield was 92.38%.Compared with the traditional heating method,the microwave method required a shorter reaction time and a larger yield.The structure of the experimental samples were characterized by Fourier Transform infrared spectroscopy?FTIR?,nuclear magnetic resonance hydrogen spectroscopy?¹H NMR?,and thermogravimetric analysis?TGA?,which were consistent with the expected results.The purity of the product determined by high-performance liquid chromatography?HPLC?was confirmed to reach 96.02%.The basic properties of product DTDD such as critical micelle concentration?CMC?,Krafft point,solubilization,emulsification,and foaming performance were studyed.The results showed that the comprehensive performance of DTDD was better than that of the surfactant octadecylmethyldihydroxyethyl ammonium bromide?OMDAB?.Two types of organoclays including DMt and OMt which were prepared with experimental homemade DTDD and OMDAB were fabricated by microwave synthesis for the first time.Infrared spectrum,X-ray diffraction characterization,N₂ adsorption/desorption isotherm,thermogravimetric analysis,and SEM and EDS characterization techniques were used to explore the effects of cation exchange capacity?CEC?and surfactant structure on the structure,morphology and surface properties of montmorillonites.The results showed that both two surfactants were successfully embedded into the interlayer of sodium montmorillonte,expending the spacing of its layers distance.DMt had become saturated with the surfactant at1.0 CEC,and the d₀₀₁ value of the DMt samples increased significantly from 1.24±0.1 nm to4.09±0.1 nm.When the CEC of the montmorillonte samples was increased from 0 to 1.5,the montmorillonite changed from a regular agglomerated compact globular entity with a flat surface structure to a loose sheet-like aggregate state.In the adsorption study of DMt on MO,the effects of DTDD dosage and adsorption time,temperature,dosage of adsorbent,pH and initial concentration of methyl orange on the adsorption performance were investigated.DMt-1.0 had the best adsorption effect in 120 min,and the temperature had little effect on the adsorption performance of DMt-1.0.Considering the adsorption capacity,the dye removal rate,and numerous other factors,the optimal conditions for MO adsorption by DMt were found to be as follows:1.0CEC of the DMt,contact time of 120 min,the pH value of 5,temperature of 25?,DMt-1.0 dosage of 40 mg,MO initial concentration of 80 mg L^-1.Compared with the pristine Na-Mt,OMt,and C₄₃H₉₂N₂Cl₂-modified montmorillonite?18-3-18-Mt?,DMt-1.0 containing hydroxyls in the alkyl chain of Gemini surfactant molecule had the best adsorption capacity for MO removal from aqueous media.The adsorption mechanisms of DMt and OMt to MO and RY were proposed based on adsorption kinetic models and adsorption isotherms.The estimated maximum adsorption capacities of DMt-1.0 on MO and RY predicted by the Langmuir isotherm model was 261.78and 300.30 mg g^-1,respectively,which were significantly higher than OMt.