Synthesis And Application Of Two-dimensional Materials Based On Layered Double Hydroxides

Two-dimensional（2D）materials,as a hot spot in recent years,have very important applications both in energy development and environmental protection.Layered doubled hydroxide（LDH）is a quite significant branch among various 2D materials.Its unique structures and physicochemical properties endow it with many special functions,including good ion exchange capability,good adsorption and catalytic performance,excellent heat resistance and alkali resistance.In our paper,based on MAl（M=Mg,Co）LDH,we have controlled the species of counter anion,synthesized the amino acid/LDH composite and ultrathin 2D LDH nanosheets through the exfoliation of bulk LDH.In addition,some 2D materials based on CoAl LDH were studied and researched,which can be used for the efficient adsorption of organic dyes in aqueous solution.The specific contents are as follows:1)MgAl LDH nanosheets with high dispersibility and good uniformity were prepared by using arginine as the alkali source with co-precipitation and hydrothermal method.The effects of the addition of different arginine amount and hydrothermal temperature on the morphology of the materials were studied.Different kinds of anions and acidic amino acids were inserted into the LDH,which improved the thermal stability of amino acids.The amino acids/LDH composite was successfully prepared.Based on the unique layered structures of LDH and the swelling effect between the MgAl-NO₃^-LDH and formamide solvent,the resulting unilamellar nanosheets were below 1 nm.2)LDH@PDA composite was prepared by coating CoAl LDH with PDA through self-polymerization of dopamine.The carbonization of LDH@PDA led to the formation of hexagonal nanoplates containing magnetic Co nanoparitcles.The Co nanoparitcles distributed evenly on the nanoplates with the size of around 21 nm.The nanoplates maintain the hexagonal shape originated from LDH and possess relatively specific surface area.The obtained hexagonal magnetic mesoporous nanoplates showed a much larger adsorption capacity towards removal of RB from water than those observed in other adsorbents.The maximum adsorption capacity approached 172.41 mg/g.The adsorption rate reached 17.21 mg/g·min and the removal efficiency of dyes reached 99.8%.Moreover,after five desorption cycles,the removal efficiency of rhodamine B was still more than 92%.3)Using LDH as a hard template,the uniform adhesion of PDA on the LDH surface was achieved under basic conditions at room temperature.After subsequent calcination and acid treatment process,a hollow carbon box was successfully synthesized.The existence of hollow structure is proved by a series of characterization methods.Because of the special structure,it has a wide application prospect in many fields and expected to use as hard templates for preparation of various non-layered two-dimensional nanosheets.4)The LDH@SiO₂ composite was synthetized by the electrostatic interaction and hydrogen bonding between the LDH surface and the SiO₂ nanospheres.On the basis of this,LDH@SiO₂@PDA composite materials were synthesized through a uniform coating of PDA.This work provides a good foundation for the preparation of2D carbon nanosheets with mesoporous by removing the LDH and SiO₂.