Study On Removal Performance And Mechanism Of Phosphate And As(Ⅴ) In Water Using Several MOFs Adsorbents

UiO-66-NH2 and MIL-101-NH2(Fe)have been widely used for the removal of phosphate and As(V)from water,but UiO-66-NH2 has poor selectivity and low removal efficiency,while MIL-101-NH2(Fe)is less stable,and the selectivity and removal efficiency also cannot meet practical needs.In order to increase the adsorption performance of such MOF materials and enhance their practicality.In this paper,Nd-UiO-66-NH2 and Nd-MIL-101-NH2(Fe)adsorbents were prepared by doping the rare earth element neodymium(Nd)into UiO-66-NH2 and MIL-101-NH2(Fe).The Nd-doped NdUiO-66-NH2,Nd-MIL-101-NH2(Fe)and the quaternary ammonium modified MIL-101-N+(Et)3(Fe)MOF adsorbents were used to remove phosphate and As(V)from water bodies.The specific research contents are as follows:1.Neodymium element-doped Nd-UiO-66-NH2 Zr-MOF adsorbents were prepared for the removal of phosphate from water bodies.The main adsorption parameters,such as p H,reaction time,temperature and reusability were investigated.The results showed that when the mole ratio of Nd/Zr was 0.50/1.00,the adsorption effect was the best,with the maximum adsorption capacity being 97.50 mg P/g and the equilibration time was 120 min.The 0.5Nd-UiO-66-NH2 adsorbent had high stability and good reusability for phosphate removal in solution with p H = 3-9.The main adsorption mechanism of phosphate by 0.5Nd-UiO-66-NH2 was confirmed by spectroscopic analysis(FTIR and XPS)and theoretical calculations(DFT and LOBA)as ligand exchange and unconventional hydrogen bonding.2.MIL-101-N+(Et)3(Fe)adsorbent was prepared for the removal of phosphate from water bodies.The effects of p H,initial concentration,reaction time and temperature on the adsorption efficiency were investigated.The results showed that the removal effect of phosphate is the best in neutral solution.The adsorption isotherm conformed to the Langmuir model,and the maximum adsorption capacity was 93.70 mg P/g.Compared with that of MIL-101-NH2(Fe)(65.92 mg P/ g),the adsorption capacity of MIL-101-N+(Et)3(Fe)was significantly improved.The adsorption process conformed to the pseudo-second-order kinetic model and reached equilibrium within 150 min.Thermodynamic experiments showed that the adsorption process was an endothermic reaction.MIL-101-N+(Et)3(Fe)showed good selectivity for phosphate removal.The main adsorption mechanisms of MIL-101-N+(Et)3(Fe)for phosphate were confirmed by spectroscopic analysis(FTIR and XPS)and Zeta potential test as ligand exchange,ion exchange and electrostatic attraction.3.Neodymium-doped Nd-MIL-101-NH2(Fe)adsorbents were prepared for the removal of phosphate and As(V)from water bodies,respectively.The adsorption results showed that the Nd/Fe molar ratio of 1.50/1.00 had the best adsorption performance for both phosphate and As(Ⅴ),and the maximum adsorption capacities were 105.00 mg P/g and 260.24 mg/g,respectively.The adsorption kinetics of the adsorbent for phosphate and As(Ⅴ)fit the pseudo-second-order kinetic model.1.5Nd-MIL-101-NH2(Fe)has high selectivity for the removal of phosphate and As(V).Spectral analysis(FTIR and XPS)and Zeta potential test confirmed that the main adsorption mechanisms of phosphate and As(V)by 1.5Nd-MIL-101-NH2(Fe)were ligand exchange and electrostatic attraction.