Improving geopolymers with multi-walled carbon nanotubes for simultaneous adsorption of lead and anthracene from rainwater

The aim of this study was to prepare and assess the effectiveness of a geopolymer doped with multi-walled carbon nanotubes functionalized with carboxyl groups (GEO+MWCNT) for removing lead (Pb(II)) and anthracene (ANT) from rainwater. Characterization of the GEO+MWCNT demonstrated an increased specific surface area and microporosity compared to the pristine geopolymer (GEO). Adsorption experiments revealed that GEO+MWCNT achieved higher removal efficiencies for Pb(II) and ANT compared to GEO alone. The maximum removal rates of lead and anthracene by GEO+MWCNT were 100% and 87.5%, respectively, compared to 71.5% and 76.2% for GEO. For GEO+MWCNT, lead removal was 78.2% in anthracene-containing solutions and 86.7% in anthracene-free rainwater. The optimal removal of Pb(II) occurred at pH 8. The adsorption kinetics followed a pseudo-second-order model, indicating a complex mechanism involving physical adsorption, chemisorption, and electrostatic attraction. These findings suggest that geopolymers, particularly when combined with MWCNT-COOH, have significant application potential for rainwater purification processes.