Direct Synthesis of Sulfur-Decorating PAMAM Dendrimer/Mesoporous Silica for Enhanced Hg(II) and Cd(II) Adsorption

Abstract

Water security caused by heavy metals poses a deleterious hazard to public health and the ecological system. The construction of adsorbents by polyamidoamine (PAMAM) dendrimers for efficient removal of metal ions has attracted considerable interest. However, the general method for the fabrication of these adsorbents was achieved by the surface chemical modification of the substrates with PAMAM dendrimer, which usually causes the defects of low density and uneven distribution of the dendrimer, the blocking of pores, and reducing the adsorption performance. Hence, the development of a new method for preparation of PAMAM dendrimer-based adsorbent to realize the efficient and enhanced adsorption of metal ions is still a challenge. Herein, methylisothiocyanate decorated PAMAM dendrimer/mesoporous silica composites (G0-S-1/x, G1.0-S-1/x, G2.0-S-1/x, x = 2, 4, 6, 8, 10) were synthesized by the direct sol-gel reaction of alkoxysilyl-containing functional PAMAM dendrimer. The adsorbents display enhanced adsorption property for Hg(II) and Cd(II) as compared with the same adsorbents which were prepared by traditional chemical modification method. Take G2.0-S-1/2 as an example, the maximum adsorption capacities are 2.41 and 0.87 mmol·g-1 for Hg(II) and Cd(II), respectively . Moreover, the adsorbents show excellent selective adsorption and regeneration property. G2.0-S-1/2 displays distinct selectivity for Hg(II) with the presence of Co(II), Pb(II), Cd(II), and Cu(II). The regeneration percentage still maintains 95.2% after five adsorption-desorption cycles. The adsorption mechanism is also certified by the experimental method and theoretical calculation.