Preparation And Properties Of Thin Layer LDHs By Atomic Economic Method

As a two-dimensional layered compound,layered double hydroxides(LDHs)are widely used in adsorption,catalysis,smoke suppression and many other fields.The traditional synthesis of LDHs usually adopts coprecipitate method,which will produce a large number of by-products and need to consume a lot of water for washing,serious waste of water resources and materials,which is not in line with the green chemistry concept advocated by the development of modern chemical industry.Based on atomic economic reaction,the laboratory realized the preparation of Mg Al-CO3 LDHs and the atomic utilization rate of 100%by optimizing the reaction route design,reducing the waste of water and materials in the washing process.However,there are many problems in the preparation of LDHs by this method,such as single composition,micron size and small specific surface area,which seriously limit the performance and application range of LDHs in adsorption and smoke suppression.In this paper,in view of the above problems,based on the atomic economic reaction strategy,by optimizing the design of raw material route,nickel hydroxide and pseudo-boehite as raw materials,by regulating the reaction solvent system,reaction time and temperature and other synthetic conditions,to achieve the controllable preparation of Ni Al LDHs and C-axis size regulation.In addition,the C-axis size of Mg Al LDHs can be controlled by strengthening the reaction system and condition control.Ni Al and Mg Al LDHs with different C-axis sizes were prepared to study the adsorption properties of methyl orange dye and smoke suppression properties of EVA.The main research results of this paper are as follows:1)Size regulation and adsorption properties of Ni Al LDHs prepared by atomic economic reactionWith nickel hydroxide,pseudo-boehmite and hexahydrate aluminum chloride as raw materials,water/formamide as the reaction solvent,by adjusting the reaction process temperature,time and formamide content,to achieve the controlled preparation of Ni Al LDHs and the adjustment of the size of the C-axis.The study found that with the increase of reaction temperature,reaction time,Ni Al LDHs crystal regularity increased,at140 ℃,8 h preparation of a single phase of Ni Al LDHs.When the content of formamide in the solvent increased from 0 wt% to 15 wt%,the C-axis size of Ni Al LDHs main lamellar decreased from 7.51 nm to 2.15 nm.This is because formate is generated by formamide hydrolysis and enters into LDHs interlayer assembly.The interlayer spacing is increased,so that LDHs can separate laminates under formamide swelling and reduce the thickness of laminates.At the same time,the specific surface area of thin layer LDHs increased from 9.12 m2/g to 76.85 m2/g,thus exposing more surface adsorption active sites.Under the synergistic action of surface adsorption and interlayer ion exchange,the maximum adsorption capacity of methyl orange dye was increased from 887.0 mg/g to 992.3 mg/g,and the adsorption performance was improved.The adsorption kinetics results showed that the adsorption process was chemical adsorption,which was more consistent with Langmuir isotherm equation,and the maximum theoretical adsorption capacity of methyl orange could reach 1642.7 mg/g.2)Size regulation and smoke suppression of Mg Al LDHs prepared by atomic economic reactionUsing magnesium hydroxide,pseudo-bauxite and magnesium chloride hexahydrate as raw materials,glycol and polyethylene glycol200 as mixed solvents,the size of C-axis of two-dimensional layered structure of Mg Al LDHs was controlled by adjusting the reaction temperature,time and mixing solvent ratio.It was found that with the increase of temperature and reaction time,the regularity of LDHs crystals showed an increasing trend.Mg Al LDHs with single crystalline phase was prepared at 140 ℃ for 6 h,The overall particle size of Mg Al LDHs ranged from 50-150 nm.When the ratio of ethylene glycol and polyethylene glycol 200 was 1:2,the size of the prepared Mg Al LDHs was 5.39 nm in the C-axis direction,which was significantly decreased compared with that of the water solvent prepared Mg Al LDHs(13.05 nm).The dispersion and smoke suppression properties of Mg Al LDHs prepared with different C-axis sizes were studied in EVA.The results showed that,with the decrease of the size of C-axis,the dispersion in EVA and smoke suppression properties of EVA were improved.The maximum smoke density of thin layer Mg Al LDHs/EVA composite can be reduced to 65.7,with a decrease of 77.2%.The smoke suppression performance of thin layer Mg Al LDHs/EVA composite is 11% higher than that of larger C-axis Mg Al LDHs.