A “Two birds one Stone” strategy for preparing chemically modified phenolic xerogels with inner pore surfaces for heavy metal ion adsorption

Abstract

Heavy metal ions (HMIs) pollution in water poses significant threats to the natural environment and human health, making the development of efficient and convenient remediation materials an urgent priority. Hence, we prepared a monolithic phenolic xerogel (PFX) via ambient pressure drying and further proposed a “two birds with one stone” strategy for simultaneous inner-pore surface modification and carbonization, yielding modified phenolic xerogels (SPFXs) as adsorbents for the adsorption of heavy metal ions in water. The SPFXs retained the original 3D interconnecting porous structure, significantly enhanced the wetting properties and compression modulus, and provided abundant accessible active sites for the adsorption of heavy metal ions, such as lead (Pb²⁺), copper (Cu²⁺), cadmium (Cd²⁺), the maximum adsorption amounts reached excellent 500.4, 299.83 and 339.95 mg/g, respectively. The results revealed that the adsorption process of the SPFXs followed the second-order kinetics and Langmuir isotherm model, which was a spontaneous endothermic reaction. It was demonstrated by advanced technical characterization methods that the adsorption mechanism of SPFXs primarily stemmed from ion exchange and chelation. Density functional theory was utilized to calculate the adsorption energies of SPFXs on three heavy metal ions, namely, Pb²⁺, Cu²⁺ and Cd²⁺, and it was demonstrated that the affinity between SPFXs and Pb²⁺ was the largest, and the best adsorption effect was achieved, which was consistent with the experimental results. This economical, simple and scalable “two birds with one stone” strategy provides a strong technical support for the preparation of phenolic-based porous materials, which is expected to become a heavy metal ion adsorbent with strong competitive potential.