Fabrication of hyperbranched polyamidoamine immobilized mesocellular siliceous foam for rapid decontamination of lead(II) from aqueous solution

Abstract

Developing of adsorbents with merits of higher adsorption capacity and quicker adsorption equilibrium through facile method merits more attention. Generally, large specific surface area porous adsorbent coupled with multi functional groups is a wise option. In the current work, a feasible protocol of preparing efficient adsorbent toward Pb2+ was established via integrating amino abundant hyperbranched polyamidoamine and bimodal pore structured mesocellular siliceous foam. The polyamidoamine was synthesized through a vacuum thermo polymerization method by gradually elevating temperature. The uniform spherical mesocellular siliceous foam substrate was prepared via inorganic salt-assisted soft-template method, and the pore structure and particle morphology were adjusted through post hydrothermal treatment. The obtained hyperbranched polyamidoamine immobilized mesocellular siliceous foam was characterized using FT-IR, SAXS, BET, SEM, TEM, TGA and zeta potential measurement techniques. Large specific surface area, unique bimodal pore structure with interconnected spherical and window pore and ultra large pore diameter rendered the adsorbent high adsorption capacity and efficient elimination. Batch experiment results elucidated that various operating parameters including pH, contact time, initial Pb2+ concentration, temperature and ionic strength deemed to be at play in adsorption behavior. The measured experimental maximum adsorption capacity at 298.15 K was 142.87 mg·g−1. The equilibrium data fitted well by pseudo second order kinetic model unveiled that the rate determining step might be chemical adsorption. The adsorption behavior was found to more suitable described with Langmuir isotherm model, implying the formation of adsorbate monolayer, and thus a maximum adsorption capacity of 315.46 mg·g−1 at 298.15 K was estimated. An underlying spontaneous entropy increased endothermic nature of adsorption of Pb2+ by the as-prepared adsorbent was conceived through adsorption thermodynamics study. Furthermore, a possible adsorption mechanism of comprehensive interaction of chemical chelation and ion exchange was proposed. This study supports the prospect that hyperbranched polyamidoamine immobilized mesocellular siliceous foam can serve as a candidate for efficiently removing Pb2+ from aqueous solution.