Adsorption of PO43-,Cd(II), Pb(II), Cu(II), As(III), and As(V) using the La-based and modified La-based metal-organic framework materials

Metal-organic framework (MOF) materials are novel adsorption materials for water treatment. In this study, LaMOF ({[La2(H2DHTPA)3(H2O)7]& sdot;4H2O}n, 2 (H 2 DHTPA) 3 (H 2 O) 7 ]& sdot;4H 2 O} n , H4DHTPA 4 DHTPA denotes 2,5-dihydroxyterephthalic acid) was synthesized by a hydrothermal method. The material had a strong water stability, but its adsorption performance was weak and its processability was poor. K-La-MOF, with good processability, was obtained using a potassium permanganate oxidation modification method to modify the La-MOF. The results showed that the maximum adsorption capacity (qmax) q max ) of the La-MOF for PO 4 3- was 72.19 mg/g, and the adsorption was monolayer chemical adsorption. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) showed that P was adsorbed on the surface of the La-MOF material in the form of HPO42-. 4 2- . The adsorption properties of the K-La-MOF were also investigated. The results showed that the maximum adsorption capacities of the K-La-MOF for PO 4 3- , Cd(II), Pb(II), Cu(II), As(III), and As(V) were 87.56, 37.08, 992.99, 190.51, 42.20, and 131.66 mg/g, respectively. The adsorption of PO 4 3- , Cd (II), Cu(II), and As(III) by the K-La-MOF was determined to be monolayer chemisorption by fitting adsorption isotherm and kinetics models. The adsorption process of Pb(II) by the K-La-MOF involved both single-molecular- layer and lateral-multi-molecular-layer chemisorption. In contrast, the adsorption of As(V) by the K-La-MOF occurred through both monolayer chemical adsorption and pore physical adsorption. XRD and XPS analyses showed that P, Cd(II), Pb(II), Cu(II), As(III), and As(V) were adsorbed on the K-La-MOF in the forms of PO 4 3- , CdO, PbO and Pb(OH)2, 2 , CuO, K3AsO4, 3 AsO 4 , and K4As2O7, 4 As 2 O 7 , respectively.