Schiff Base-Functionalized Melamine Sponge with Hierarchical Porous Architecture for High-Efficiency Removal of Organic Dyes in Wastewater

Abstract

Melamine sponges have demonstrated significant application potential in the field of adsorption materials due to their unique three-dimensional porous network structure, excellent chemical/mechanical stability, and abundant amino active sites on the surface. However, the development of modified melamine sponges with efficient Congo red dye removal capabilities remains a substantial challenge. In this study, a stable linear polymer network structure was constructed on the surface of melamine sponges via an in situ polymerization strategy based on the Schiff base reaction mechanism. Characterization analyses reveal that the modified sponge not only retained the original porous skeleton structure but also significantly enhanced the density of surface active sites. Experimental data demonstrate that the modified sponge exhibited excellent adsorption performance for Congo red dye, with the adsorption process conforming to the pseudo-second-order kinetic model and achieving a practical maximum adsorption capacity of 380.4 mg/g. Notably, the material also displayed favorable cyclic stability. This study provides an efficient adsorbent for Congo red dye-contaminated wastewater treatment through the development of a novel surface-functionalized sponge material while also offering new solutions for advancing the practical applications of melamine-based porous materials and environmental remediation technologies.

Keywords: Congo red dye; absorption; composite foam; melamine foam.

Figure 1

Synthesis process of BD-MS and its adsorption capacity for CR.

Figure 2

(a) Optical images of MS and BD-MS under natural light; (b) SEM image of MS; (c,d) SEM images of BD-MS.

Figure 3

(a) FTIR spectra of MS, BD-MS, and BD-MS@CR; (b) XRD patterns of MS and BD-MS; (c) XPS spectra of BD-MS and BD-MS@CR; (d) N₂ adsorption–desorption isotherm of BD-MS.

Figure 4

Adsorption isotherm models for BD-MS toward Congo red: (a) Langmuir model; (b) Freundlich model; (c) Temkin model; (d) Sips model.

Figure 5

Kinetic models for the adsorption of Congo red onto BD-MS: (a) pseudo-first-order; (b) pseudo-second-order; (c) Elovich; (d) intra-particle diffusion model.

Figure 6

Adsorption mechanism of Congo red by BD-MS.

Figure 7

Adsorption performance of BD-MS for Congo red: (a) time-dependent removal efficiency; (b) pH-dependent removal efficiency; (c) removal efficiency under regeneration cycles; (d) comparative maximum adsorption capacity with other adsorbents.