The Preparation Of Mg–Fe Layered Double Hydroxides Composite Materials And Adsorption Characteristics Of Organic Pollutant In Wastewater

The contamination caused by organic pollutants in surface and groungwater poses a great threat to the safety of water ecosystems and human health.In recent years,many studies have been carried out on the removal of organic pollutants because of the increasing concentration in aqueous solutions caused by sewage discharge from industry,household,and agriculture.Adsorption is most promising and widely used because of its low cost,friendly environment,high efficiency and simple operation.However,the greatest drawback to traditional adsorption materials is the fact that these have a low removal performance in actual water treatment and limited recycling ability.In view of this,there is considerable interest in developing novel materials for the adsorptive removal of such pollutants.In this paper,four kinds of Mg-Fe hydrotalcite supported organic/inorganic composite adsorbent were synthesized.The study of the adsorption properites and mechanism of these adsorbents for different pollutants were carried out.The research results are as follows:1)Calcined chitosan-supported layered double hydroxides?CSLDO?were synthesized through a co-precipitation method that restrained the particles aggregation of LDHs and exhibited huge specific surface areas,which can enhance the adsorption capacity.CSLDO were characterized by physical and chemical methods and used for pollution adsorption in an aqueous solution.The results indicated that the nanoparticles were constructed first and then assembled to form a porous and layered structure,and chitosan-supported layered double hydroxides?CSLDHs?calcined at 400°C?CSLDO400?showed the highest specific surface area of 116.98 m²·g^-1 and the largest pore volume of 0.411 cm³·g^-1.CSLDO400 exhibited excellent adsorption performance at a wide pH range from 5 to 9 for MO,while the adsorption of TC was most efficient at a pH of 9.The divalent and trivalent anions have a great effect on removal efficiency,while the effect of monovalent anions adsorption can be neglected.The adsorption kinetics indicated that the adsorption of MO and TC followed a pseudo-second-order model.The adsorption process of MO agreed well with the Langmuir isotherm,while that of TC agreed well with the Freundlich isotherm.From Langmuir isotherm,the maximum adsorption capacity of MO and TC were 1266.42 and 195.31 mg·g^-1 at 295 K,respectively.The adsorption of MO and TC were both spontaneous and endothermic.Furthermore,CSLDO400 showed a high stability after repeating five times of adsorption–desorption cycles.The adsorption mechanism involved ion exchange interaction and original LDH structure reconstruction by rehydration of mixed metal oxides and concomitant intercalation of MO and TC anions into the interplayer region.2)g-C₃N₄@Mg Fe-LDH composites were prepared via a hydrothermal synthesis,using g-C₃N₄ as the plate support.And then,the surface of g-C₃N₄@Mg Fe-LDH was modified with HA.The surface modification of g-C₃N₄@Mg Fe-LDH?g-C₃N₄@Mg Fe-LDH/HA?was characterized by scanning and transmission electron microscopy?SEM and TEM?,X-ray diffraction?XRD?,Fourier transformed infrared?FT-IR?,Brunauer-Emmet-Teller?BET?,thermogravimetry analysis?TGA?and X-ray photoelectron spectroscopy?XPS?.SEM results indicated that g-C₃N₄@Mg Fe-LDH/HA displayed obvious layered structure,and HA was successfully coated on the surface of g-C₃N₄@Mg Fe-LDH.Adsorption experimental results of tetracycline?TC?,2,4-dichlorophenol?2,4-DCP?and glyphosate?GP?are as follows.HA concentration with 100 mg L^-11 resulting in comparatively higher adsorption capacity for TC,2,4-DCP and GP.The action pH value was ranged from 7 to 9 for TC 3 to 9 for2,4-DCP and GP,respectively.Sodium chloride concentration had slightly effect on the adsorption reaction.The adsorption process could be well described by pseudo-second-order model for TC,2,4-DCP and GP.The experimental data of TC and GP could be fitted better with Freundlich model,while that of 2,4-DCP were fitted better with Langmuir model.The adsorptions of TC,2,4-DCP and GP were both spontaneous and endothermic.The adsorption mechanism involved ion exchange interaction,hydrogen bonding interactions and surface complexation between organic pollutants and HA.3)g-C₃N₄ supported porous polyamide?g-C₃N₄@PI?was synthesized by solve-thermal synthesis and co-precipitation process,and then an organic/inorganic composites materials g-C₃N₄@PI@Mg Fe-LDO was prepared with the support of g-C₃N₄@PI.SEM,TEM,XRD,FT-IR,BET,TGA and XPS were used to test the physical and chemical properties of g-C₃N₄@PI@Mg Fe-LDO composites.SEM and BET results indicated that surface morphology and specific surface area of Mg Fe-LDH changed obviously because of g-C₃N₄@PI.Adsorption experimental results of TC,2,4-DCP and GP are as follows.g-C₃N₄@PI@Mg Fe-LDO exhibited excellent adsorption performance at a wide pH range from 7 to 9 for TC and 5 to 9 for 2,4-DCP,while the adsorption of GP was most efficient at a pH of 9.Sodium chloride and HA concentration showed a limit effect on the adsorption process.The adsorption kinetics indicated that the adsorption of TC and GP followed a pseudo-second-order model,while the adsorption of 2,4-DCP followed a pseudo-first-order model.The adsorption process of TC,2,4-DCP and GP both agreed well with the Freundlich isotherm.From Langmuir isotherm,the maximum adsorption capacity of TC,2,4-DCP and GP were154.8,170.36 and 197.63 mg·g^-1 at 295 K,respectively.The adsorption process were both spontaneous and endothermic,g-C₃N₄@PI@Mg Fe-LDO ensures excellent stability and reusability after repeating five times of adsorption–desorption cycles.The adsorption mechanism involved ion exchange interaction,hydrogen bonding interactions and surface complexation between organic pollutants and PI.4)A novel core-shell structured magnetic polyimide@layered double oxides?LDO?composites coating a porous polyimide?PI?-coated Fe₃O₄ magnetic core and layered double hydroxide?LDH?has been successfully synthesized by solve-thermal synthesis and co-precipitation process.The magnetic PI@LDO composites were characterized by SEM,TEM,XRD,FT-IR,BET,TGA,XPS and magnetic properties analysis.The composite materials displayed core-shell structure with flower-like morphology and high specific surface area(154 m² g^-1).The magnetic PI@LDO composites were applied to remove TC,2,4-DCP and GP from aqueous solution.The action pH value was ranged from 5 to 9 for TC and GP and 3 to 7 for 2,4-DCP,respectively.Cl^-showed a weak competitive adsorption effect to TC,2,4-DCP and GP.In addition,the presence of humic acid?HA?could slightly reduce the adsorption capacity of magnetic PI@LDO composites.The adsorption process could be well described by pseudo-second-order model for TC and GP,while pseudo-first-order model for 2,4-DCP.The experimental data of TC and 2,4-DCP could be fitted better with Freundlich model,while that of GP were fitted better with Langmuir model.The adsorptions of TC,2,4-DCP and GP were both spontaneous and endothermic,and an excellent reusability and stability was obtained in regeneration test.The adsorption mechanism involved ion exchange interaction,hydrogen bonding interactions and surface complexation between organic pollutants and PI.