Mechanistic Understanding of the Adsorption Behavior of Metal Lead Ions by Attapulgite-Induced Porous Nanocomposite Hydrogels

Hydrogels have many advantages as a kind of heavy-metal adsorbent, such as simple separation, high efficiency, and recyclability, but their applications are limited by their poor mechanical strengths. To this end, versatile natural phyllosilicate minerals are introduced into hydrogels to enhance the mechanical strengths of hydrogels. However, mechanistically understanding the clay-induced effect is still limited. In this work, attapulgite-induced porous network structures were observed, which are interpreted in terms of the nonsacrificial starch-like pore formation mechanism. Furthermore, the influence of the porous structure of the attapulgite nanocomposite hydrogels on the adsorption of Pb2+ from an aqueous solution was comprehensively studied. The adsorption kinetics fits a pseudo-second kinetic model well, and the syllogistic Weber Morris model study reveals that the porous structures of nanocomposite hydrogels improves their ability to internally diffuse. The adsorption isotherm displays over 98.2% of goodness of fit for the Langmuir isothermal model, with a maximum adsorption capacity of 864.5 mg/g for the adsorption of Pb2+. Moreover, the adsorption thermodynamics study indicates that the enthalpy changes of chemical adsorption decrease from 62.31 to 51.01 kJ/mol for hydrogels after the addition of 10% attapulgite. On the basis of the above findings, a reasonable adsorption mechanism including surface adsorption and internal diffusion is proposed.