磁性CoFe2O4/MgAl-LDH的制备及对水中刚果红的去除

采用水热法制备了CoFe_2O_4,采用化学共沉淀法将镁铝水滑石(Mg Al-LDH)覆盖在CoFe_2O_4上,制成磁性CoFe_2O_4/Mg Al-LDH复合材料,用于去除水中阴离子染料刚果红。考察了溶液p H值、吸附时间、共存阴离子等对吸附过程的影响,研究了CoFe_2O_4/Mg Al-LDH对刚果红吸附动力学、吸附等温线。结果表明,溶液p H值、共存离子对CoFe_2O_4/Mg Al-LDH去除刚果红效果的影响较小。吸附剂对刚果红的吸附过程符合准二级动力学模型,且在吸附时间180 min内基本达到吸附平衡。吸附等温线符合Langmuir等温吸附模型,CoFe_2O_4/Mg Al-LDH对刚果红的理论最大吸附容量为610.8 mg/g。

On the synthesis of magnetic CoFe2O4/MgAl-LDH for its function to remove Congo red from the aqueous solution

The paper is engaged in a study on the synthetic preparation of magnetic CoFe2O4/MgAl-LDH by coating MgAl-LDH on CoFe2O4 through co-precipitation method.For the research purpose,we have conducted a batch of experiments to identify and determine the effects of the solution pH value,the adsorption time,the coexisting ions on Congo rod adsorption from the aqueous solution by CoFe2O4/MgAl-LDH.The results of the aforementioned batch-experiment study have shown that the adsorbed amount of Congo red by CoFe2O4/MgAl-LDH has been found equal to 236.6 mg/g in the solution without pH adjustment (pH =6.2),whereas the value of qe tends to change little in a wide solution pH value range of 2.5-11.0.Besides,it has also been found possible for the solid composite to be quickly separated from the said aqueous solution by an external magnet after an adsorption process of no more than 30 s.Furthermore,the adsorption process has reached the state of equilibrium within 180 min at the adsorbent dosage of 10 mg,Congo red mass concentration of 50 mg/L.And,next,we have discussed the kinetic of the adsorption with the models of the pseudo-first-order and pseudosecond-order.Thus,we have also determined the rate constants of the two models and the amount of Congo red adsorbed at equilibrium condition.It has turned out that the pseudo-second-order model has been found more suitable for modeling the adsorption of Congo red onto CoFe2O4/MgAl-LDH than the pseudo-first-order one,based on a higher correlation coefficient (R2 =0.998 7),indicating that the rate-limiting step should be attributed to the chemical adsorption between the adsorbent and adsorbate (chemisorption).The data from the adsorption isotherm can be modeled by using Langmuir and Freundlich equations,whereas the corresponding data from the above said experiments prove to be fitted fairly well for Langmuir model.Furthermore,we have also found that the maximum adsorption capacity should be equal to 610.8 mg/g,which turns to be much higher than many other adsorbents that have ever been reported in the corresponding literature.However,the presence of common anions,such as Cl-,NO3-,SO42-and PO43-in the solution prove to have little impact on the adsorbed amounts of Congo red onto CoFe2O4/MgAl-LDH.Thus,it can be said that the paper has provided an efficient,fast and convenient approach to the removal of Congo red from the aqueous solutions.