Two new enhanced adsorbents Urea-CS and Thiourea-Cs for Pb2+removal were prepared by hydrothermal synthesis of N-doped hollow carbon spheres(CS).Urea and Thiourea were grafted onto hollow carbon spheres with hydroxy-rich surface through activation reaction,respectively.Under the adsorption experimental conditions of adsorbent mass 40 mg,initial Pb2+concentration 800 mg/L,solution pH 6 and temperature 25℃,the maximum adsorption amounts of Thiourea-CS and Urea-CS were 212.35 mg/g and 166.54 mg/g.The removal rates were 42.30% and 33.30%,respectively,which were consistent with Langmuir adsorption model.Thermodynamic studies show that adsorption is a spontaneous,endothermic and entropy increasing process.The quasi-secondary adsorption kinetics model is consistent with the experimental data of Urea-CS and Thiourea-CS.After five sorbation-desorption cycles of 200 mg/L Pb2+solution,Urea-CS and Thiourea-CS still had good stability and repeatability,with removal rates of 95.24% and 98.40%,respectively.The XPS results show that the complexation between nitrogen/oxygen and Pb2+plays an important role in the adsorption mechanism.The method has good repeatability and selectivity for the removal of Pb2+.
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