| Eutrophication caused by excessive phosphate discharge has become a serious environmental problem.Among various phosphate removal technologies,the adsorption is an attractive method due to the relatively high efficiency,easy operation and low cost-effectiveness especially under a low phosphate concentration.The adsorbent has strong adsorption capacity for pollutants and fast adsorption rate,which is a critical issue in the field of water treatment and purification.Therefore,it is necessary to develop an adsorbent that can be easily separated to remove phosphate efficiently and stably from water.Spinel ferrite has excellent properties,but its adsorption capacity is always limited.However,lanthanum has a strong phosphate binding ability,which can greatly improve the phosphate adsorption performance of the adsorbent.In this study,La（OH）3-modified magnetic cobalt ferrite（CoFe2O4）nanocomposites（Lax-CF）were synthesized by coprecipitation assisted hydrothermal method.The appropriate characterization methods were used to analyze the morphology and structure of the adsorbent.The influence of various influencing factors on the adsorption properties of the material was investigated and the mechanism of adsorption was further studied.The specific research contents are as follows:（1）For the first time,La（OH）3 modified magnetic CoFe2O4 nanocomposite was synthesized and characterized,and the optimal ratio of La（OH）3 and CoFe2O4 was determined for further exploration experiments.（2）The phosphate adsorption performance of the adsorbent was evaluated by studying the influence factors such as adsorption time,adsorption isotherms,p H and ionic strength,and coexisting anions.The stability and reusability of the adsorbent were evaluated by the adsorption desorption cycle,and its applicability in the actual water sample was also verified to be effective.（3）The experimental data were fitted using adsorption kinetics and adsorption isotherm models.The mechanism of dephosphorization was explained in detail by comparing the changes of physical and chemical properties and structural characteristics of the adsorbent before and after adsorption.The La2-CF with the mass ratio of La（OH）3 to CoFe2O4 of 2:1 exhibited the largest adsorption capacity of 104.01 mg P/g and possessed superparamagnetism for rapid separation from solution.Through data fitting,the adsorption kinetics and adsorption isotherms are in accordance with pseudo second-order model and Langmuir model,respectively.All of these indicate that the adsorption process is chemical adsorption.It was worth noting that La2-CF exhibited high stability and optimal adsorption selectivity to phosphate when the competitive anions were added with the p H in the range of 3.0-9.0.Besides,the adsorption efficiency decreased slightly and remained above 80%after 6 cycles,suggesting excellent reusability of this adsorbent.Moreover,the excellent adsorption performance of La2-CF can be attributed to the following mechanism:ⅰ)protonated and positively charged adsorbent adsorbed the phosphate by electrostatic attraction;ⅱ)the ligand exchange between the hydroxyl group and the phosphate resulted in the formation of an inner sphere complex,thereby enhancing the adsorption capacity for phosphate.This work provides an important reference for the study of phosphate adsorption materials with high selectivity and stability.The application in the field of environmental remediation and sewage treatment is still worthy of more in-depth discussion and research. |
