Preparation Of Pseudo-boehmite-based Composite Film And Its Pb(Ⅱ) Adsorption Performance

Pb（Ⅱ）is seriously harmful to the human and environment,and the environmental problem caused by Pb（Ⅱ）is become more and more serious with the development of industrial field.Because of its unique physical and chemical properties such as high specific surface,great dispersion and thixotropy gel,boehmite adsorbents have attracted much attention in the study of the adsorption of heavy metal in wastewater.However,after adsorbing heavy metals,the powder boehmite adsorbents have some problems,including complicated separation operation and expensive equipment cost.Moreover,the residual powder adsorbents with heavy metal may result in secondary pollution,limiting their application.In order to solve these problems,the boehmite-based composite films with excellent adsorption performance for Pb（Ⅱ）and easy separation from water were prepared via the sol-gel method,hydrothermal method and precipitation method.The results as follows:（1）A chitosan-boehmite composite film（CS-BCF）was successfully synthesized via using glutaraldehyde as cross-linking agent and mixing boehmite sol and chitosan sol.The physical and chemical properties of CS-BCF,boehmite film（BF）and chitosan film（CSF）were characterized by XRD,FT-IR and SEM.The adsorption experiments were used to evaluate the adsorption performance of the sample for Pb（Ⅱ）,indicating that the Pb（Ⅱ）adsorption affinity of CS-BCF is much better than those of the BF and the CSF.Moreover,their adsorption data of Pb（Ⅱ）are more closely match the pseudo-second-order kinetic model and Langmuir isotherm with the maximum adsorption capacities of 33.00 mg/g,19.57 mg/g and 17.45 mg/g,respectively.In the interference experiment of coexisting cations,it was found that the Pb（II）adsorption performance of the CS-BCF was rarely affected by Na⁺,K⁺,Mg²⁺and Ca²⁺.According to XRD,FT-IR and XPS characterization results,the adsorption mechanism of CS-BCF to Pb（II）included electrostatic attraction,chemical reaction and the formation of Pb₃（CO₃）₂（OH）₂ precipitation on the surface of film.Especially,the acid resistance of the CS-BCF in water is greatly enhanced,it did not dissolve after shaking in an acidic solution of pH=2.0 for 1 h,while the BF and CSF dissolved 24 wt%and 100 wt%,respectively.（2）A MgAl-LDH@boehmite composite film（MgAl-LDH@BCF）was successfully prepared using MgSO₄·7H₂O as the hydrotalcite precursor and in situ growing Mg Al-LDH on the BF substrate via hydrothermal method.According to XRD,FT-IR,SEM and N₂adsorption-desorption characterization results,when the amount of Mg（Ⅱ）increased from 0.1mmol to 3 mmol,the crystallinity and amounts of the MgAl-LDH increased.The specific surface and pore volume of MgAl-LDH@BCF are 23.48 m²/g and 0.0354 cm³/g,higher than the BF（4.12 m²/g and 0.0051 cm³/g）.Moreover,the MgAl-LDH@BCF samples showed better adsorption performance than the BF,and the adsorption data for Pb（Ⅱ）conformed to the pseudo-second-order kinetic mode.Among all samples,the Pb（II）adsorption of MgAl-LDH@BCF prepared with 0.5 mmol Mg（Ⅱ）showed the best adsorption rate,adsorption capacity（99.83 mg/g）and removal rate（99.83%）,rarely affected by the coexisting cations of Na⁺,K⁺,Mg²⁺,Cu²⁺and Ca²⁺.In addition,according to the extensive experiments,replacing MgSO₄·7H₂O with Mg（NO₃）₂·6H₂O,MgCl₂,Ni（NO₃）₂·6H₂O,CoSO₄·7H₂O and Zn（NO₃）₂·6H₂O as the precursor also can successfully grow LDH in situ on the BF surface to prepare the MAl-LDH@BCF（M=Mg,Ni,Co and Zn）.Furthermore,the adsorption mechanism analysis results showed that Pb（Ⅱ）formed the precipitate on the surface of MgAl-LDH@BCF via electrostatic attraction and complexation reaction.（3）The MgAl-LDH@BF-X（X represents S,N and C,respectively）with enhanced affinity toward Pb（II）was synthesized via precipitation method at room temperature,using MgSO₄·7H₂O,Mg（NO₃）₂·6H₂O and MgCl₂ as the hydrotalcite precursors to grow LDH in situ on the BF,respectively.The XRD and SEM characterization results showed that the pH and Mg（II）concentration had an important influence on the LDH formation,wherein the pH=11 and Mg（II）=2 mmol/L were better conditions.In 50mL 50mg/g Pb（II）solution,the adsorption capacities of the MgAl-LDH@BF-N,MgAl-LDH@BF-S and MgAl-LDH@BF-C were 49.80 mg/g,48.49 mg/g and 49.72 mg/g,their removal rates were 99.60%,96.98%and99.44%,respectively.