Abstract
Copper (Cu(2+)), cadmium (Cd(2+)) and lead ions (Pb(2+)) are toxic to human beings and other organisms. In this study, a silica gel material modified with nitrilotriacetic acid (NTA-silica gel) was sensibly designed and prepared via a simple amidation procedure for the removal of Cu(2+), Cd(2+) and Pb(2+) from water. The NTA-silica gels showed rapid removal performances for the three metal ions (Pb(2+) (<2 min), Cu(2+) and Cd(2+) (<20 min)) with relatively high adsorption capacities (63.5, 53.14 and 76.22 mg g(-1) for Cu(2+), Cd(2+) and Pb(2+), respectively). At the same concentration of 20 mg L(-1), the removal efficiencies of the three metals by the adsorbent ranged from 96% to 99%. The Freundlich and Langmuir models were utilized to fit the adsorption isotherms. The adsorption kinetics for the three metal ions was pseudo-second-order kinetics. The removal performance of the NTA-silica gels increased in a wide pH range (2-9) and maintained in the presence of competitive metal ions (Na(+), Mg(2+), Ca(2+) and Al(3+)) with different concentrations. In addition, the NTA-silica gels were easily regenerated (washed with 1% HNO(3)) and reused for 5 cycles with high adsorption capacity. This study indicates that the NTA-silica gel is a reusable adsorbent for the rapid, convenient, and efficient removal of Cu(2+), Cd(2+), and Pb(2+) from contaminated aquatic environments.