Synthesis And Adsorption Performance Of LDH Materials With Different Morphologies

While the booming development of textile,dyeing and breeding industries has brought economic benefits to the society,the discharge of a large amount of untreated wastewater also poses a serious threat to the aquatic environment.For example,azo dyes commonly used in printing and dyeing technology are difficult to degrade after being discharged into wastewater,which directly affects the living environment of aquatic organisms.The overuse of antibiotics such as tetracycline,commonly used as growth promoters and antimicrobial agents in animal husbandry,can also adversely affect the healthy development of humans and animals through water recycling.Therefore,it is of great significance to explore efficient,eco-friendly,energy saving and economic wastewater treatment technology to protect water environment and maintain ecological balance.Adsorption method is popular because of its low cost,simple operation,high adsorption efficiency and rich source of adsorbents.Layered double hydroxide（LDH）materials have many advantages such as large specific surface area,excellent ion exchange property,easily regulated morphology and composition structure,so they are often studied as potential efficient adsorbents.Hierarchical porous LDH nano sorbent with hollow structure can be obtained by specific means.Its large specific surface area and appropriate pore structure can provide more active adsorption sites for adsorbate,and facilitate the diffusion of molecules in the pore,thus improving the adsorption capacity and adsorption speed.In this paper,Congo red and tetracycline are used as simulated wastewater pollutants,and LDH materials with hollow structure are constructed as adsorbents to evaluate their adsorption performance for above contaminant.The main research contents are as follows:（1）MgNiCo LDH dodecahedra hollow structure（MNC HS）is fabricated through a simple one-step solvothermal method using ZIF-67 as the sacrificial template.Transmission electron microscope shows that the MNC HS retains the dodecahedral shape of ZIF-67.The as-prepared sample exhibits efficient adsorption for Congo red（CR）in water,which is due to the hierarchical structure and large specific surface area that provides more adsorption sites and electrostatic interaction.The CR adsorption process fits the pseudo-second-order model better by kinetics simulation;while Langmuir model is more accurate than Freundlich model in describing the adsorption isotherms of CR.The maximum adsorption capacity calculated by the Langmuir model can reach 1194.7 mg g^-1,which is much higher than that of MgNiCo LDH（MNC）synthesized by conventional methods.The cycle tests also show that the as-prepared adsorbent has good stability and recycling ability.（2）NiFe LDH hollow microspheres（NFHMS）were synthesized by a facile hydrothermal method using silica spheres as templates.To investigate the removal effect of tetracycline（TC）in aquatic environment by the as-prepared material,some characterization methods like X-ray diffraction（XRD）,Brunauer-Emmett-Teller（BET）,Fourier transform infrared spectroscopy（FT-IR）and X-ray photoelectron spectroscopy（XPS）have been applied.The NFHMS sample(92 m² g^-1)presents lager specific surface area than the other two(8 and 50 m² g^-1 for SiO₂ and NF,respectively),which contributes to its higher adsorption capacity.The adsorption mechanisms of TC on NFHMS include pore filling,as well as H-bonding,ion exchange and electrostatic interaction.The kinetic simulation results of experimental data coincide well with pseudo-second-order and Weber-Morris models.Moreover,Langmuir model is verified to be more suitable than Freundlich model in elucidating molecular surface adsorption,and the maximum adsorption capacity of NFHMS obtained from Langmuir model is 90.9 mg g^-1.The initial pH of the solution will affect the adsorption capacity,and the weak alkaline condition is more favorable.In addition,cyclic experiments show that NFHMS has good stability and reusability.Therefore,NFHMS material is expected to be a very promising adsorbent for treating tetracycline in wastewater.