Novel polyamidoamine dendrimer-functionalized palygorskite adsorbents with high adsorption capacity for Pb²⁺ and reactive dyes

Novel polyamidoamine (PAMAM) dendrimer-functionalized palygorskite (Pal) adsorbents, up to generation 4.0, with high adsorption capacity, were designed and efficiently synthesized by grafting PAMAM onto 3-aminopropyltriethoxysilane-modified palygorskite (NH₂-Pal) surfaces. This was carried out using a divergent method including the Michael addition of methyl acrylate (MA) and amidation of the resultant ester moieties with ethylenediamine (EDA). The optimal conditions for Michael addition were achieved using 88.8mmol MA (relative to 4.0g NH₂-Pal) at 323K for 24h. The optimal conditions for amidation of the resultant esters were achieved using 179.3mmol EDA (relative to 2.1g Pal-PAMAM G0.5) at 323K for 48h. All of the amino-terminated Pal-PAMAM G(n) (n=0, 1, 2, 3 and 4) adsorbents exhibited very high density amino-terminated groups and adsorption capacities for both Pb²⁺ and Reactive Red 3BS, which increased with increasing generation number. The maximum adsorption capacity for Pb²⁺ at 293K was 68.5±3.3, 151.1±5.7, 196.5±6.1, 389.1±9.6 and 694.4±12.9mg/g for Pal-PAMAM G(n) (n=0, 1, 2, 3 and 4), respectively. The maximum adsorption capacity for Reactive Red 3BS at 293K was 34.2±2.7, 69.9±4.3, 122.0±6.4, 242.7±7.1 and 322.6±6.9mg/g for Pal-PAMAM G(n) (n=0, 1, 2, 3 and 4), respectively.