Cadmium(II) and lead(II) adsorption onto hetero-atom functional mesoporous silica and activated carbon

Adsorption of cadmium(II) and lead(II) on amino-, mercapto-functionalized mesoporous silica (HMS) and carboxylic-functionalized activated carbon (AC) were examined. The resultant isotherms fitted the Langmuir model and amino-functionalized HMS exhibited the highest adsorption capacity for both cadmium(II) and lead(II). Adsorption affinities for cadmium(II) were always greater than those for lead(II) in all three adsorbent types, while the difference between the two values was the largest for mercapto-functionalized HMS indicating a selective adsorption of cadmium(II). Influence of equilibrium solution pH on adsorption of cadmium(II), lead(II) and their binary mixtures was also studied. Carboxylic-functionalized AC adsorbed cadmium(II) and lead(II) in a wide pH range than conditions for the mercapto-functionalized HMS. It was concluded that each functional group had its own characteristics and advantages for adsorption of heavy metal ions; amino-groups showed high adsorption capacity, while mercapto-groups had good selectivity toward cadmium(II) adsorption and a wide solution pH in adsorption by carboxylic-groups were established in this study.