Preparation Of Hydrotalcite Composite Films And Study On Their Pb(?) Adsorption Properties

In recent years,a large amount of industrial waste water containing Pb(?)has been discharged into the environment from electroplating and battery plants,and excessive Pb(?)will seriously threat the sustainable development of the ecosystem and human health.Layered double hydroxides(LDH)have the properties of layer anion exchangeability and memory effect,so they are often used in the field of wastewater treatment.However,conventional LDH powders especially nano-powders are difficult to separate from the water after adsorption,and these powders can be a source of secondary pollution.In this paper,the LDH composite membrane which were easy to separated and have excellent adsorption capacity for Pb(?)was prepared through a mild hydrothermal method.The main contents are as follows:(1)Inspired by mussel adhesion protein,a novel carbon paper@polydopamine@Magnesium aluminum hydrotalcite(CP@PDA@MgAl-LDH)composite membrane with excellent adsorption capacity for Pb(?)were successfully prepared via a simple hydrothermal method.The PDA not only improves the wettability of carbon fiber,but also can be used as stable anchors for the immobilization of metal ions by coordination reaction,and then the MgAl-LDH growth units can grow into the MgAl-LDH nanosheets on the carbon fiber.In addition,PDA also can act as“binder”that contributes to the affinity between the MgAl-LDH nanosheets and carbon fiber.The MgAl-LDH nanosheets of the CP@PDA@MgAl-LDH membrane remains almost unchanged after shaking and ultrasonic treatment.In the adsorption experiments,the appropriate solution p H range is 5.0?6.0,and the maximum adsorption capacity calculated by the Langmuir model is 1223.15mg/g.The CP@PDA@MgAl-LDH membrane shows excellent recycle performance and the removal efficiency for Pb(?)also remains 98.8%after 7 times adsorption-desorption cycles.Furthermore,this method can be applied to other LDH(NiAl-LDH,ZnAl-LDH and CoAl-LDH),indicating that it is an efficient and universal method for fabricating LDH composite membrane.(2)By adding propanol,ethylene glycol,1,3-propanediol,1,4-butanediol and glycerol as co-solvents,hydrotalcite composite membranes were prepared by one-step solvothermal method.SEM results show that with the increase of alcohol hydroxyl and the length of carbon chain,the particle size of the MgAl-LDH nanosheets decreases,and the particle size of the MgAl-LDH nanosheets prepared by adding glycerol is the smallest.According to the Zeta potential results,with the increase of alcohol hydroxyl and carbon chain length,the amount of hydroxyl groups carried by the composite membranes increase.The adsorption performance Pb(?)of composite membrane was studied by static adsorption.The adsorption kinetic results show that with the increase of hydroxy volume and the length of carbon chain,the adsorption capacity for Pb(?)of the composite membrane increase.When adding glycerol as co-solvent,the prepared composite membrane(CP@gle-MgAl-LDH)has the largest adsorption capacity for Pb(?).When adding glycerol as co-solvent,the adsorption data of Pb(?)on CP@gle-MgAl-LDH composite membrane fits the Langmuir model and the pseudo-second-order kinetic model,and the maximum adsorption capacity calculated by the Langmuir model is 1303.43mg/g.Therefore,among these studied alcohols,glycerol as co-solvent is the best choice to prepare composite membrane.In addition,XRD and XPS were tested to study the adsorption mechanism for Pb(?)of CP@gle-MgAl-LDH.The interaction between CP@PDA@MgAl-LDH membrane and Pb(?)can be ascribed to:(1)the formation of Pb₃(CO₃)₂(OH)₂;(2)cation exchange between Mg(?)and Pb(?);(3)the electrostatic attraction between-OH and Pb(?).This is a simple and easy method for fabricating LDH composite membrane.