Homogeneous synthesis of Schiff base modified PAMAM dendrimers/silica for efficient adsorption of Hg(II)

Water pollution caused by Hg(II) is a serious environmental issue and poses great risk to human health. Adsorption is a promising method for decontaminating aqueous Hg(II). Therefore, a family of Schiff base modified polyamidoamine (PAMAM) dendrimer/silica (G0-T1/x-S, G1-T1/x-S and G2-T1/x-S (x = 2, 4, 6)) were synthesized by homogeneous method for removing Hg(II) from water solution. The adsorption property of the adsorbents for Hg(II) was comprehensively evaluated. The adsorption capacity for Hg(II) was found to depend on the dendrimer generation. The effects of solution pH, time, temperature, and interfering metal ions on the adsorption property for Hg(II) were determined by selecting G0-T1/2-S, G1-T1/2-S and G2-T1/2-S as models. The optimal pH for the adsorption of Hg(II) is 6. Adsorption kinetic shows that the adsorption is fast at initial, and the equilibrium can be reached at 400 min. Adsorption isotherm demonstrates the increase of temperature and concentration can promote the adsorption for Hg(II). The kinetic and isotherm process can be fitted by pseudo-second-order kinetic model and Langmuir model, respectively. The adsorbents display good adsorption selectivity for Hg(II) and the functional groups of CONH, C-N, C = N and OH dominate the adsorption. The adsorbents exhibit good removal efficiency for Hg(II) from simulated industrial wastewater with the coexistence of multiple pollutants. Moreover, the adsorbents show excellent reusability as the regeneration rate of G2-T1/2-S can still maintain 92.45 % after the tenth adsorption–desorption cycles. The research work provides a feasible method for the preparation of efficient adsorbents to remove aqueous Hg(II) with practical values.