Efficient and selective recovery of Gd(III) via polyethyleneimine modification of lanthanum-based metal–organic frameworks

With the development of the economy and the increasing demand for environmental protection, the efficient and selective recovery of Gd(III) from actual wastewater is of critical importance. In this work, lanthanum-based metal–organic framework (LaBDC) materials were prepared by a hydrothermal method, and then polyethyleneimine (PEI) and LaBDC were combined by an impregnation method to form a novel LaBDC@ x PEI composite. The prepared materials were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), Brunauer–Emmett–Teller (BET), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). Experiments show that LaBDC@50%PEI has the highest adsorption capacity (181.77 mg/g) among lanthanum-based MOFs with different PEI loadings at pH = 5.5, which is about 5.1 times that of bare LaBDC. The adsorption isotherm analysis shows that LaBDC@50%PEI follows the Langmuir model. In addition, the adsorption kinetics of LaBDC@50%PEI follows a pseudo-second-order kinetic model, indicating that the adsorption process is chemical adsorption. It is worth noting that LaBDC@50%PEI maintains good adsorption performance and stability after three recycling tests, and exhibits excellent selectivity in cation interference experiments. Overall, the LaBDC@50%PEI composites possess good stability and hold great promises in rapid recovery of Gd(III) from practical aqueous environments.