Synthesis, magnetic and dye adsorption properties of three metal-organic frameworks based on purine carboxylic acid

Three metal-organic frameworks (MOFs), namely [La(L)Cl(H2O)2]n(1), {[Nd(L)Cl(H2O)3]center dot 2H2O}n (2) and {[Pr2(L)2Cl2(H2O)6]center dot H2O}n (3), were successfully structured based on ligand 5-((6H-purin-6-yl)amino)isophthalic acid (H2L). X-ray single-crystal diffraction analysis showed that MOFs 1-3 possessed the similar twodimensional (2D) planar structure. Adsorption experiments showed that MOFs 1-3 exhibited good adsorption effect on Congo red (CR), and their maximum adsorption capacities were 1428, 433 and 319 mg & sdot;g- 1, respectively. The adsorption kinetics and isotherms showed that the adsorption process conformed to the quasi-secondorder kinetic model and the Langmuir model, respectively. The adsorption process belonged to chemical adsorption and monolayer adsorption. The adsorption mechanism mainly involves hydrogen bonding, it-it stacking interaction and electrostatic interaction. In addition, the magnetic test results showed that MOFs 2 and 3 have typically antiferromagnetic behavior.