Preparation And Modification Of Mesoporous Mesoporous Fe-Mn Binary Oxide For Pb²⁺ Adsorption And Its Mechanisms

Recently,the development of lead smelting,lead regeneration and storage batteries industry lead to the producing of a large amount of lead-containing industrial wastewater.As they cannot be completely removed,lead can enter the aquatic environments and be transmitted through the food chain,which is finally accumulated.The presence of in ambient environment can potentially impart detrimental effects on aquatic ecosystems and human health.Therefore,it is of great practical significance to develop an economic,efficient,and environmentally friendly treatment technologies for the removal of lead contamination.Adsorption method has become the main method for the treatment of lead contamination due to its low cost,simple operation,high treatment efficency.Studies have shown that iron oxides and manganese oxides possess a number of advantages,such as abundance,low environmental toxicity,low cost,high treatment efficency etc..The mesoporous Fe-Mn binary oxide?MFMBO?have been widely used in heavy metal adsorption because of the presence of mesopores.However,pure MFMBO easily agglomerates in water,which greatly reduces its adsorption performance.Therefore,it is particularly important to increase its dispersibility of MFMBO in water via surface modification.In this paper,MFMBO and tannic acid?TA?modified MFMBO(MFMBO@TA-Fe³⁺)were synthesized,and used for the adsorption of Pb²⁺.A series of characterization techniques such as XRD,SEM,TEM,BET,FTIR,XPS,and Zeta potential analysis were used to study the physical and chemical information of the adsorbent.Further,the adsorption mechanisms were investigated.The results can be concluded as follow:?1?MFMBO were synthesized through the controlled thermal decomposition of oxalate precursor.MFMBO showed a worm-like mesoporous structure composed of amorphous manganese oxide and weakly crystalline?-Fe₂O₃ complex with a specific surface area of288.12 m²·g^-1.The maximum adsorption of Pb²⁺by MFMBO was 250 mg·g^-1 at 45°C,initial concentration of 200 mg·L^-1 and pH of 5.The adsorption of Pb²⁺by MFMBO was well coincide with the pseudo-second-order kinetics model and Langmuir model could better describe the adsorption isotherms.Thermodynamic parameters demonstrated that the Pb²⁺adsorption process was nonspontaneous and endothermic.The adsorption mechanism can mainly ascribed to the replacement of Pb²⁺for the H⁺in hydroxyl groups on the surface of MFMBO to form the inner surface complexes.?2?MFMBO@TA-Fe³⁺was prepared by surface modification with TA on the basis of synthetic MFMBO.A series of characterization results indicate that the TA is loaded on the surface of the MFMBO in the form of a package.The maximum adsorption of Pb²⁺by MFMBO@TA-Fe³⁺was 495.12 mg·g^-1 at 45°C,initial concentration of 300 mg·L^-1 and pH of5.The adsorption of Pb²⁺by MFMBO@TA-Fe³⁺was well coincide with the pseudo-second-order kinetics model and Langmuir model could better describe the adsorption isotherms.Thermodynamic parameters demonstrated that the Pb²⁺adsorption process was nonspontaneous and exothermic.The adsorption mechanism can mainly ascribed to the replacement of Pb²⁺for the H⁺in hydroxyl groups on the surface of MFMBO@TA-Fe³⁺to form the inner surface complexes.