A novel titanium dioxide/chitosan composite aerogel for efficient removal of Congo red: Experimental and DFT studies

Congo red (CR), a typical anionic azo dye, poses a serious threat to the environment because it does not easily degrade. In this study, chitosan (CS) and tetrabutyl titanate were employed as raw materials to prepare TiO₂/CS composite aerogels using the sol-gel method and freeze-drying technology. The structure was characterized via XRD, FTIR, BET and SEM. Under optimized conditions, the TiO₂/CS-2.5 sample exhibited optimal performance: the adsorption process conformed to the pseudo-second-order kinetic model, and the maximum adsorption capacity reached 247.52 mg/g. The photocatalytic degradation rate was 91 %, which conforms to the quasi-first-order kinetic model. After three adsorption-desorption cycles, the CR removal rate remained at 83 %. The theoretical calculation and analysis attributed the efficient CR removal to the synergistic effect of adsorption-photocatalysis. At the adsorption stage, electrostatic attraction and hydrogen bonding facilitate CR enrichment, and thermodynamic calculations confirm that the process proceeds spontaneously. At the photocatalytic stage, photogenerated holes preferentially attack azo bonds, and hydroxyl radicals (•OH) target and degrade carbon sites, ultimately leading to CR degradation. This composite aerogel provides an efficient material for the treatment of azo dye pollution in water.