Factorial experimental design for the optimization of highly selective adsorption removal of lead and copper ions using metal organic framework MOF-2 (Cd)

This paper reports the ultrasonic synthesis of a cadmium terephthalate metal-organic framework MOF-2 (Cd), Cd-TPA, at room temperature as adsorbent for high efficiency ultrasonic assisted removal of lead and copper from aqueous solution. The MOF-2 (Cd) was characterized using XRD, EDS, FT-IR and SEM techniques. In order to assess the impact of various variables affecting the adsorption of lead (Pb) and copper (Cu), a factorial design analysis was used. The parameters examined contain; sonication time, initial concentration and adsorbent dose. It was seen that the adsorbent dosage effect was most significant and exhibited a positive effect for the removal efficiency of both lead and copper. The removal percentage values of 99.9 and 97.9% were achieved using 1.0 g adsorbent dose for lead and copper, respectively. It was established that the kinetic of adsorption followed pseudo-second order model with coefficient of determination values of 0.9998 and 0.9999 respectively for Pb2+ and Cu2+ ions. The isotherm of adsorption of both lead and copper followed Langmuir isotherm with maximum monolayer adsorption capacity of 434.78 and 769.23 mg/g respectively for copper and lead. The MOF-2 (Cd) reveals chemical stability against common organic solvents for instance DMF, CAN, methanol and aqueous solution with different pHs except at pH 2. The thermal stability of MOF-2 (Cd) was demonstrated by TGA. The high temperature structure of the MOF-2 (Cd) (400 °C) exhibits the thermal stability of the MOF-2 (Cd). Furthermore, the reuse results illustrate that the MOF-2 (Cd) can be used for at least three times for the removal of Pb and Cu ions from aqueous solutions due to its durability and stability.