Experimental and theoretical investigation of allylated chitosan and acrylic acid-based smart polymer hydrogel for the removal of brilliant green from aqueous media.

Smart polymer hydrogels with superior dye adsorption (brilliant green) characteristics were synthesized via free-radical polymerization by grafting acrylic acid segments onto allylated chitosan and inducing crosslinking with a trimethylolpropane triacrylate crosslinker. The synthesized adsorbents were characterized for their chemical structure (FT-IR and H NMR), thermal stability (TG/DTG), and morphological features (SEM). The adsorption capacity for brilliant green (934 mg/g) and water uptake (712 g/g) were determined using spectrophotometric and gravimetric methods, respectively. The interaction between the synthesized adsorbent and brilliant green, including potential dye orientation on the adsorbent and hydrogen bond formation was analyzed using Density Functional Theory. The maximum adsorption of brilliant green (934 mg/g) and water uptake was achieved by optimizing the monomer feed compositions. Adsorption studies revealed that dye uptake followed Fickian diffusion and the Langmuir isotherm model, with pseudo-second-order kinetics. Thermodynamic analysis demonstrated that the adsorption process was spontaneous and exothermic, as evidenced by changes in free energy, enthalpy, and entropy under varying temperatures. Theoretical investigations confirmed the excellent affinity of the synthesized adsorbent toward brilliant green. Furthermore, reusability studies showed that the adsorbent retained its dye-holding capability over 20 adsorption-desorption cycles, highlighting its potential for sustainable and efficient dye removal applications.