Effect of dye molecular characteristics on its adsorption in a biopolymeric chitosan sponge: Analysis from the...

This work investigated the effect of structural characteristics of five food dyes on adsorption onto chitosan-based biopolymeric sponges, using statistical physics models, experimental results, and FT-IR analyses to propose a detailed adsorption mechanism. Statistical physics models showed high predictive capacity. The multilayer model was the most effective for predicting the adsorption isotherms of the Indigo carmine, Allura red, and Amaranth. The double-layer model with two adsorption energies was more suitable for the Tartrazine and Sunset yellow. Adsorption energy calculations indicated that the dye removal process occurred through physical interactions. FT-IR analyses revealed that the functional groups of adsorbent (OH and NH₂) are actively involved in adsorption, forming hydrogen bonds and electrostatic interactions with the dyes. The proposed mechanism suggests that the effectiveness is influenced by the ability of the dyes to form multiple interactions with the adsorbent, highlighting the importance of hydrogen bonds. The results showed that the Indigo carmine, Allura red, and Amaranth have a greater affinity for the adsorbent, reflected in higher adsorption capacity and higher adsorption energy values. This behavior occurred because these dyes have more functional groups in their structures, capable of forming more bonds, thus increasing the efficiency of the process.