Cd 2+ and Zn 2+ Complexes with 2,4,6-Tri(2-pyridyl)-s-Triazine and Terephthalate for Rapid, High-Capacity Adsorption of Congo Red.

Three crystal complexes were designed and synthesised through the solvothermal method, with Cu , Zn , and Cd ions as the metal centres and 2,4,6-tri(2-pyridyl)-s-triazine (TPTZ) and terephthalate (BDC ) as the ligands. Their compositions were determined to be Cd(TPTZ)Cl (Cd-MOF), {[Zn(TPTZ)(BDC)] ⋅ 3H O} (Zn-MOF), and Cu (PCA) (BDC)(H O) (Cu-MOF) (PCA =2-pyridinium amide), respectively. Cd-MOF can adsorb 90 % of Congo red (CR) in 10 s at room temperature and atmospheric pressure, and CR removal was complete at 20 s over a wide pH range. The adsorption capacity for CR reached 1440 mg g in 5 min. Selective adsorption was demonstrated in mixed dyes. The adsorption kinetic data agree well with the pseudo-second-order kinetic model. The Temkin model was successfully used to evaluate the adsorption isotherms of CR on Cd-MOF at room temperature, suggesting that adsorption occurs through a hybrid of monolayer and multilayer mechanisms.