A fast and highly selective Congo red adsorption material based on a cadmium-phosphonate network.

In this work, a cadmium-phosphonate network was prepared based on a tetrahedral shaped tetraphosphonic acid linker. The resulting three-dimensional compound Cd(HL)(phen)(HO) (1) exhibited a rapid and efficient adsorption of Congo red (CR) dye, the adsorption capacity of which reached 684 mg g. Furthermore, this adsorbent showed excellent structural stability and adsorptive recyclability after three times of adsorption and desorption. The absorption kinetics fitted well with the pseudo-second-order kinetic model, revealing that the adsorption of the cadmium-phosphonate compound undergoes a chemical process, where hydrogen bonding between the amide groups (from CR) and the uncoordinated phosphonate oxygen atoms of the compound plays a pivotal role.