Study On The Adsorption Performance Of Modified Hydrotalcite For Organic Pollutants In Water

Layered double hydroxides（LDHs）is commonly known as hydrotalcite.It is a two-dimensional inorganic flake material with good anion exchange ability,abundant active sites and environmental friendliness,which has broad application prospects in the fields of adsorption and catalysis.After high temperature calcination,LDHs is transformed into layered metal oxides（LDOs）.Compared with LDHs,LDOs obtained by calcination has been reported to have better adsorption properties.However,layered double hydroxides compounds have limited adsorption capacity for cationic and nonionic organic pollutants.Based on this,in this paper,carbon dots（CDs）were modified on the surface of LDOs to obtain a new type of LDOs composites with strong adsorption properties for both anionic and cationic dyes.In this study,Mg Al-LDH modified by anionic surfactant sodium dodecylbenzene sulfonate（SDBS）was first prepared by hydrothermal synthesis.Then it was calcined at 450^oC under N₂ protection,and the SDBS on the Mg Al-LDH surface were in-situ converted into nano CDs,which were evenly distributed on the surface of Mg Al-LDO.A multifunctional LDO hybrid material modified by CDs was obtained（CDs@Mg Al-LDO）.It can achieve efficient adsorption for both anionic and cationic dyes.The achievements are summarized as following:（1）CDs@Mg Al-LDO has a hexagonal lamellar structure with a transverse size of about 500 nm and uniform thickness of nanosheets.X-ray diffraction analysis revealed that CDs@Mg Al-LDO maintained the“memory effect”of LDOs and could retrieve the original structure when dispersed in water.The CDs are graphitized carbon and are uniformly distributed on the surface of CDs@Mg Al-LDO.Moreover,CDs increases the hydrophobic binding site of LDO and help to improve the affinity for organic contaminants,including both cationic and anionic dyes.（2）The adsorption results of CDs@Mg Al-LDO on malachite green（cationic dye）,congo red and direct blue 5B（anionic dye）showed that:CDs@Mg Al-LDO has excellent adsorption properties for malachite green in the range of p H=5-10.When the p H value increases,the adsorption capacity of CDs@Mg Al-LDO to congo red and direct blue 5B gradually decreases.The adsorption of dyes on CDs@Mg Al-LDO followed a pseudo-second-order kinetic model with correlation coefficients（R²）ranging from 0.9901 to 0.9911 and exhibited Freundlich-type heterogeneous adsorption.It showed superior adsorption performance for three dyes,with the maximum adsorption capacity of 3628.9–5174.1 mg/g by fitting the Langmuir isotherm adsorption model.The adsorption mechanism of CDs@Mg Al-LDO for malachite green includes hydrophobic interaction,surface complexation and hydrogen bonding.The adsorption mechanisms of congo red and direct blue 5B include hydrophobic interaction,surface complexation,hydrogen bonding and electrostatic interaction.