Cellulose based pH-sensitive hydrogel for highly efficient dye removal in water treatment: kinetic, thermodynamic, theoretical and computational studies

In this paper, a new green pH-sensitive EDTA crosslinked HEC (cellulose-based hydrogel (swelling rate ~ 1005%)) adsorbent was successfully elaborated. The synthesis of HEC-EDTA at the high advanced crosslinking degree (up to 92%), was carried out using DAEDT and DMAP as acyl transfer agent, where the lamellar morphology (2D-microstructure) was highly suggested based on the average functionality of the reaction system. The crosslinking degree was confirmed using structural analyzes (FTIR and 13C CP/MAS-NMR) and elemental profile analysis. The new EDTA crosslinked HEC demonstrated a high uptake capacity (~ 2000 mg g−1) to aquatic micropollutants, especially methylene blue as cationic dyes model. The kinetic study showed that the adsorption process was well described by the pseudo-second-order kinetic, while the thermodynamic parameters exhibited a negative effect of temperature indicating a physical adsorption process. In addition, the adsorption capacity was studied varying to the experimental conditions (pH, contact time, concentration, etc.), and the Freundlich model revealed a strong correlation to the experimental data indicating an energetic heterogeneity of the surface active sites. Furthermore, using COMPASS II, the molecular dynamics (MD) simulations were conducted to optimize the chemical system, where the results showed the predominance of non-covalent molecular adsorbent-adsorbate interactions, which governs cluster design and configurations.