Study On Preparation Of Multi-porous Hydrotalcite By Soft Template Method And Its Adsorption Enhancement Effect

In this paper,the quaternary ammonium salt cationic surfactants cetyl trimethyl ammonium bromide(CTAB)and cetyl trimethyl ammonium chloride(CTAC)are used as templates,and the specific chemical reagent salicylic acid(SA)was added to form the worm-like linear aggregate,which is used as the directing agent to induce the precipitation process of the metal salt and the alkaline solution to realize the in-situ synthesis of the hydrotalcite on the three-dimensional network linear aggregate,thereby obtaining the new hydrotalcite material with multi-level pore structure.During the preparation process of multi-porous hydrotalcite materials,the effects of preparation conditions(such as the concentration of metal salt solution,the molar ratio of Mg to Al,surfactant concentration,aging time,aging temperature,etc.)on the surface morphology,specific surface area and phase structure of the materialwere investigated in detail.And the adsorption performance of the new material on the strongly stable and refractory organic macromolecular pollutants in the oilfield sewage are examined through the adsorption experiment of sulfonated lignite.The main conclusions are as follows:When the surfactant(CTAB-SA)concentration is 2.8%and theconcentration of metal salt solution is 0.9 mol/L(the molar ratio of Mg to Al is 2),the Mg Al-LDHwith multi-porousstructure(2.8%CB-0.9MLDH-160?)can be prepared by hydrothermal synthesis(160?,6 h).The SEM image shows that the material has a rosette-like morphology;XRD analysis shows that it has a series of characteristic phases of hydrotalcite;The specific surface area of the ordinary hydrotalcite(0.9MLDH-160?)and the multi-porous hydrotalcite prepared under the same conditions are 51.9103 and 126.3137 m~2/g,respectively,and the pore volume is 0.2039 and 0.3040 cm~3/g,so theprepared multi-porous hydrotalcite has a better pore structure than ordinary hydrotalcite.Adsorption experiments show that the adsorption process of sulfonated lignite conforms to the pseudo-second-order kinetic equation and Freundlich model with spontaneous exothermic nature.When the initial p H of the solution is neutral at25?,the maximum adsorption capacity of multi-porous hydrotalcite for sulfonated lignite is as high as 1014.20 mg/g.After three adsorption regenerations,the adsorption capacity for sulfonated lignite only decreased by 32.1 mg/g.The main adsorption mechanism is electrostatic adsorption and surface adsorption between multi-porous hydrotalcite and sulfonated lignite.When the concentration of surfactant(CTAC-SA)is 2%and the molar ratio of Mg to Al is 2(the concentration of metal salt solution is 0.9 mol/L),the Mg Al-LDH with multi-porous structure(2%CB-Mg2Al-LDH)can be prepared by hydrothermal synthesis(160?,6 h).XRD analysis shows that the new material has a series of characteristic phases of hydrotalcite;SEM shows that the Mg Al-LDH with multi-porous structure has a regular morphology,and the nanosheets grow staggered along the micelle interface;and the specific surface area and pore volume of the the multi-porous hydrotalcite is 146.0759 m~2/g and 0.2557 cm~3/g higher than ordinary hydrotalcite(Mg2Al-LDH)respectively,thus providing more active adsorption sites.Adsorption experiments show that the adsorption process of sulfonated lignite by multi-porous hydrotalcite conforms to the pseudo-second-order kinetic equation and Freundlich model,and is a spontaneous exothermic process.When the initial p H of the solution is neutral at 25?,the maximum adsorption capacity of multi-porous hydrotalcite for sulfonated lignite can reach854.70 mg/g.After three adsorption regenerations,the adsorption capacity for sulfonated lignite decreased by 47.7 mg/g.Adsorption mechanisms include electrostatic attraction,ion exchange and so on.When the concentration of surfactant(CTAB-SA)is 2.8%and the molar ratio of Mg to Al is 3(the concentration of metal salt solution is 1.2 mol/L),the Mg Al-LDH with multi-porous structure(2.8%CB-Mg3Al-LDH-24h)can be prepared by co-precipitation method(65?,24h).XRD analysis shows that the material has a series of characteristic phases of hydrotalcite;SEM image shows that its particle size is uniform particle and has high dispersibility;The specific surface area of the ordinary hydrotalcite(Mg3Al-LDH)and the multi-porous hydrotalcite prepared under the same conditions are 39.4882 and 214.1746 m~2/g,respectively,and the pore volume is 0.2149 and 0.7349 cm~3/g,so the multi-porous hydrotalcite has a better pore structure than ordinary hydrotalcite.Adsorption experiments show that the adsorption process of sulfonated lignite by multi-porous hydrotalcite conforms to the pesudo-second-order kinetic equation and Langmuir model,and is a spontaneous exothermic process.When the initial p H of the solution is neutral at 25?,the maximum adsorption capacity of sulfonated lignite by multi-porous hydrotalcite can reach 507.61 mg/g.After three adsorption regenerations,adsorption capacity for sulfonated lignite still reached 293.0 mg/g.Adsorption mechanisms include electrostatic attraction,ion exchange and so on.