Preparation Of Nano-alumina Membranes And Their Adsorption Performance Towards Cr(Ⅵ)

Due to its carcinogenicity to human and high toxicity to living organisms,Cr（Ⅵ）pollutant has become a serious environmental issue.In recent years,Al-based powder adsorbents,including aluminum oxide,aluminum hydroxide and aluminum oxyhydroxide for removing Cr（Ⅵ）from wastewater have been widely studied because of their unique physicochemical properties which are suitable for heavy metal ions removal.However,there exist some defects,including the agglomeration of fine particles,complicated separation process and expensive recovery equipment cost in actual application occasion for the powder adsorbent.Moreover,residual sludge with heavy metal ions species may result in the secondary pollution.In order to extend the application of nano-alumina in the adsorption of heavy metal ions,nano-alumina membrane materials with excellent adsorption performance towards Cr（Ⅵ）was successfully prepared by mild sol-gel method.The mainly research results as follows:（1）A boehmite/PVA composite membrane（BPCM）was successfully synthesized using Al（NO₃）₃·9H₂O as the aluminium precursor and HAc as the peptizing agent.The physicochemical properties of the BPCM,the boehmite powder（BP）without PVA and a commercial boehmite powder（CBP）were comparatively characterized by XRD,TGA-DSC,FT-IR and XPS.Batch adsorption experiments indicated that the adsorption performance of the BPCM is much better than those of the BP and the CBP.Its adsorption process was well described by the pseudo-second-order kinetic model,and its adsorption equilibrium data fit the Langmuir isotherm well with the maximum adsorption capacity of 36.45 mg/g.Its coexisting anions interference experiment revealed that SO₄^2-and HPO₄^2-have greater effect than those of the Cl^-,F^-,C₂O₄^2-and HCO₃^-on the Cr（Ⅵ）adsorption process.Moreover,FT-IR and XPS spectroscopy confirmed the existence of inter-sphere complex and the reduced Cr（III）species on the surface of the BPCM.A three step action mechanism including adsorption of Cr（Ⅵ）anions,complexation between Cr（Ⅵ）anions and the functional groups on the surface of BPCM,and the reduction of Cr（Ⅵ）anions to Cr（III）was further put forward to describe the adsorption process.（2）Amino-modified mesoporous alumina membranes with enhanced affinity towards Cr（Ⅵ）were successfully prepared by impregnation and grafting process.The physicochemical properties of membranes were characterized by XRD,SEM,Elements Analyzer,FT-IR and Zeta potential.The results indicated that amino silane was successfully graftied on the surface of the alumina membranes by Al-O-Si covalent bonds form,the membranes were completed and without defect.The specific surface area,pore size,pore volume,surface acid-base and N-element content properties of the membranes were affected by the amino modifier types and added amount.（3）Adsorption behavior of Cr（Ⅵ）on amino-modified mesoporous alumina membranes were described by kinetic and isotherm model.0.5 g N-[3-（Trimethoxysilyl）-propyl]ethylenediamine adding amount of alumina membrane（F-Al2O3-TS-0.5）showed excellent adsorption performance for Cr（Ⅵ）.The equilibrium adsorption capacity of F-Al2O3-TS-0.5 toward Cr（Ⅵ）from the langmuir isotherm model can be reached 64.6 mg/g at an optimal pH=3.It is much higher than other alumina adsorption materials of Cr（Ⅵ）.The sample of F-Al2O3-TS-0.5 can maintain stable cycle adsorption performance by using 200 ml 0.005 mol/L NaOH solution regeneration.Besides,this sorbent can be used to selective separate Cr（Ⅵ）from multicomponent mixted solution include Ni（II）,Cu（II）,Zn（II）and Cd（II）.This unique membranes with an easily separated characteristic after adsorption has high potential for removal of Cr（Ⅵ）from aqueous solution,and other fields of environmental remediation.