Synergistic and Antagonistic Effects on Removal of Diclofenac and Cadmium Onto Hydrous Manganese Dioxide

The adsorption behavior and mechanism of diclofenac (DCF), cadmium (Cd(II)) and the composite pollutant (Cd(II)-DCF) onto hydrous manganese dioxide (HMO) were systematically investigated and the results showed obviously synergistic and antagonistic effects. The adsorption equilibrium data were well described by Langmuir model. The maximum adsorption capacity for DCF had a 28.9% increase in the presence of Cd(II), while the maximum adsorption capacity of Cd(II) decreased 8.58% with the presence of DCF at 298 K. The uptake rate of DCF was obviously limited by the addition of Cd(II), while low concentration of DCF had a little effect on uptake of Cd(II). The chemisorption dominated the adsorption process of Cd(II) and Cd(II)-DCF, while the predominant mechanism of the uptake of DCF was physisorption. FTIR and XPS results revealed that the cationic bridging of Cd(II) between carboxyl groups on DCF and HMO contributed to the synergistic results, and the competition between Cd(II) and Cd(II)-DCF was account for the antagonistic effect on removal of Cd(II) onto HMO.