Efficient Removal Of Anionic Pollutants By A Novel 3D Magnetic Hydrotalcite Functional Composite And Its Mechanism Study

With the rapid development of textile,food processing,printing and dyeing,medicine and other industries,the discharge of industrial wastewater has also increased rapidly.These anionic pollutants in wastewater have the traits of strong toxicity,stable chemical properties and poor degradability,which accumulate in the water environment and seriously endanger human health.Therefore,the treatment of anionic pollutants in water has drawn much attention from the society.The adsorption method is widely used in water pollution treatment because of its simple operation,low price and high efficiency.However,traditional adsorbents have poor adsorption performance,low recycling rate,and poor selectivity,which limit their applications.Therefore,the aim of this article is to study a new type of hierarchical structure LDHs material,which is simple and easy to obtain,low cost,superior adsorption performance,and easy to recycle,and used for the removal of anionic pollutants in water.The specific work of this article is as follows:1.The magnetic hierarchical structure NiFe₂O₄/NiFe-LDHs material was prepared by hydrothermal method,and using urea as alkali source,Ni SO₄·7H₂O and Fe（NO₃）₃·9H₂O as raw materials,deionized water as solvent.The isoelectric point of the material was determined by Zeta potential method.And the morphology,composition,internal structure and peculiarity of the adsorbent were characterized by XRD,SEM,EDS,FT-IR,VSM and BET.The adsorption properties of CR and Cr₂O₇2-by magnetic multistage NiFe₂O₄/NiFe-LDHs materials were studied by static adsorption method.Meanwhile,the effects of p H value,initial concentration of CR and Cr₂O₇^2-,adsorption time,adsorption temperature and other factors on the adsorption properties of the materials were investigated.The adsorption kinetics,thermodynamics and thermodynamic behavior of the material in the process of adsosorbing CR and Cr₂O₇^2- were studied,and the possible adsorption mechanism was discussed.The effects of three actual water bodies of the Yangtze River（Nanjing section）,river water and Yueya Lake water on the adsorption performance of the material were studied.The adsorption experimental results of the material on CR showed that: The p H value has a little of influence on the adsorption performance,and the optimum p H value was selected as p H=6.The saturated adsorption capacity of the material was 266 mg·g^-1 at 298 K.The adsorption process of the material to CR conforms to the Langmuir isothermal adsorption model,indicating that the adsorption process is a monolayer adsorption.The adsorption equilibrium was reached within 8h,in line with pseudo-second-order model kinetics.The removal rate of the material for CR is as high as 98%,and it has good adsorption property in practical application.NiFe₂O₄/NiFe-LDHs material has good magnetic properties,and can separate solid-liquid quickly under the action of an external magnetic field,which is conducive to the recycling of materials.The material is reused five times,and the removal rate of CR is still above 91%.The adsorption experimental results of the material on Cr₂O₇^2- showed that: The acidity of solution has a great influence on the existing form of Cr₂O₇^2- in water,and then on the adsorption property of the material,and the optimum p H value was selected as p H=5.The saturated adsorption capacity of the material was 31 mg·g^-1 at 298 K.The adsorption process of the material to Cr₂O₇^2- conforms to the Langmuir isothermal adsorption model,indicating that the adsorption process is a monolayer adsorption.The adsorption equilibrium was reached within 20 min,in line with pseudo-first-order model kinetics.The material removal rate of Cr₂O₇^2- was over 88%,and it has good adsorption property in practical application.NiFe₂O₄/NiFe-LDHs material has good magnetic properties,and can separate solid-liquid quickly under the action of an external magnetic field,which is conducive to the recycling of materials.The material is reused four times,and the removal rate of Cr₂O₇^2- is still above 65%.In the experimental study on the adsorption of CR-Cr₂O₇^2- binary system,it was found that there was competitive adsorption in the adsorption process of CR and Cr₂O₇^2-.2.We have constructed novel three-dimensional flower-like magnetic CoFe₂O₄/CoFe-LDHs microspheres via a facile urea hydrothermal method for the efficient removal of CR and Orange II with a maximum adsorption capacity of 156mg·g^-1 and 1940 mg·g^-1 respectively.The results of structure-activity studies show that three-dimensional regular magnetic CoFe₂O₄/CoFe-LDHs microsphere can own more superior adsorption performance than irregular amorphous CoFe-LDHs.Besides,the strong magnetic performance of CoFe₂O₄/CoFe-LDHs can be attributed to using ferromagnetic Co²⁺ and Fe³⁺ as lamellar ions,contributing to fast separation between adsorbents and solution.The formation mechanism studies indicate that various morphologies of Fe OOH nanoparticles evolved from ferric hydroxide precipitation can act as a substrate and then guide the self-assembling growth of CoFe₂O₄/CoFe-LDHs microsphere.It is worth noting that the skillful selecting Fe³⁺ as lamellar ions can not only act as the nucleation precursor of three-dimensional CoFe₂O₄/CoFe-LDHs microsphere but also serve as magnetic source.Besides,the morphology of CoFe₂O₄/CoFe-LDHs can be adjusted by reaction time and the existence of SO₄^2- in reaction system.Using the static adsorption method and using UV spectrophotometry as the detection method,the removal of CR and Orange II by CoFe₂O₄/CoFe-LDHs was studied.Meanwhile,the effects of p H value,initial concentration of CR and Orange II,adsorption temperature,adsorption time and other factors on the adsorption performance of the material were investigated.The adsorption kinetics,thermodynamics and thermodynamic behavior of the material in the process of adsosorbing CR and Orange II were studied.Desorption and regeneration studies show that CoFe₂O₄/CoFe-LDHs can be reused five times,and the removal rate of CR is still above 75%.To broaden the application range of CoFe₂O₄/CoFe-LDHs,the adsorption mechanism of Orange II by CoFe₂O₄/CoFe-LDHs are examined through various means such as FT-IR,Zeta potential,BET and XPS.The results demonstrate that the adsorption mechanism possibly consists of interlayer anion exchange,hydrogen bonding and coordination,suggesting CoFe₂O₄/CoFe-LDHs can be effectively applied in the remediation of anionic pollutants.At last,CoFe₂O₄/CoFe-LDHs are used to remove CR and Orange II from different real water samples with satisfied results.