Preparation Of Ce-MOF/GO Composite And Its Adsorption For Pollutants From Aqueous Solution

The presence of heavy metals and PO₄^3-in wastewater endangers human life as well as the aquatic ecosystem.Among the technologies used to treat wastewater,adsorption is regarded an effective technology for treating wastewater due to its simplicity,low cost,eco-friendliness,and other advantageous features properties inherent to this technique.Recently,Metal-Organic Frameworks（MOFs）have been widely used in wastewater treatment processes due to their high porosity,large specific surface area,pore modification,and etc.Even though they suffer from low stability.On this basis,carbon materials,notably Graphene Oxide（GO）,have been combined with MOFs to improve their physical and chemical properties,mainly because GO has a variety of oxygen-containing functional groups with large surface area,which makes the structure of GO more complicated.This combination was made as a means to mitigate the limitation of MOFs and derive an ideal adsorbent with excellent physiochemical characteristics.In this paper,cerium（Ⅳ）was selected as a metal ion and GO as a carbon material,since cerium（Ⅳ）has high binding affinity towards PO₄^3-,fast adsorption performance,as well as other desirable properties.This thus led to the fabrication of a new adsorbent Ce-MOF/GO composite with a high removal rate towards PO₄^3-and hexavalent chromium（Cr（Ⅵ））from an aqueous solution.The preparation process was optimized,and the removal efficiency of Ce-MOF/GO composite on PO₄^3-and Cr（Ⅵ）in simulated wastewater was studied.The adsorbent was characterized by XRD,SEM,N₂ adsorption-desorption isotherm analysis,FT-IR,and zeta potential analysis.In addition,the adsorption mechanism of the composite material toward PO₄^3-and Cr（Ⅵ）removal was also studied.The main research contents are as follows:（1）Through the analysis of the characteristics,it was observed that the Ce-MOF/GO composite was successfully synthesized with uniform and octahedral morphology and that the addition of optimum GO led to the distortion of the maternal Ce-MOF crystal framework.However,the specific surface area of the composite material remarkably decreased due to particles size increases and partial encapsulation of Ce-MOF particles with GO.Furthermore,loading Ce-MOF on GO changed the surface of the composite and improved the mechanical and chemical properties.Similarly,Ce（Ⅳ）reacted with functional groups of GO,resulting in the formation of an octahedral morphology of the large particles with mesoporous structures,abundant active sites and good pore volume.Meanwhile,adding optimum amount of GO content into maternal Ce-MOF enhanced the adsorption capacity of the composite material,and successfully solved the problem of unsatisfactory removal efficiency in an aqueous solution.（2）The results revealed that the addition of 2%GO in the Ce-MOF/GO composite enhanced the adsorption capacity of the Ce-MOF/GO composite for PO₄^3-and Cr（Ⅵ）removal.Precisely,the equilibrium contact time for adsorption of PO₄^3-via black sample,Ce-MOF,and Ce-MOF/GO was 180 min,and the adsorption of PO₄^3-was higher under low acidic conditions.It was noticed that high temperature was not favorable to the adsorption process,and the highest adsorption capacity of the prepared adsorbent based on the Langmuir adsorption isotherm was found to be 308.64 mg.g^-1 for PO₄^3-removal from an aqueous solution.According to the experimental data,the adsorption kinetic model was consistent with the pseudo-second-order model and the adsorption isotherm was based on the Langmuir model,indicating that the adsorption reaction is a monolayer.Likewise,the adsorption thermodynamic model for Ce-MOF/GO composite material was exothermic.Ultimately,the composite material showed good recycling and its adsorption mechanism was mainly via electrostatic and hydrogen bonding for PO₄^3-removal.（3）The Ce-MOF/GO composite was applied for the removal of Ce（Ⅵ）and its adsorption reached equilibrium within 120 min.The lower alkaline condition and the higher temperature（>25°C）were then found to be favorable for the adsorption reaction.Furthermore,the maximum adsorption capacity of the Ce-MOF/GO-2%composite for the Cr（Ⅵ）removal reached 79.23mg.g^-1,and the kinetic and isotherm adsorption models were more consistent with the pseudo-second-order model and Langmuir isotherm,respectively.In the end,hydrogen bonding and coordination bonding was the primary mechanism for Cr-（Ⅵ）removal by the Ce-MOF/GO-2%composite material.