Sol-gel engineered xanthan gum/carboxymethyl cellulose/silica hybrid adsorbent for efficient removal of cationic and...

Synthetic dyes released from industrial activities continue to pose a serious threat to aquatic systems, and their treatment requires adsorbents that are efficient, inexpensive, and environmentally benign. In this work, an organic-inorganic hybrid based on xanthan gum, carboxymethyl cellulose, and silica (XG/CMC/silica) was produced by a sol-gel approach using 3-aminopropyltriethoxysilane (APTES) as the silica-forming and amine-bearing precursor. The hybrid was examined by FTIR, XRD, SEM-EDX, and TGA. FTIR spectra verified the coexistence of polysaccharide bands and Si-O-Si vibrations, whereas XRD showed that the silica phase lowered the ordered domains of the XG/CMC blend and generated a largely amorphous hybrid network. SEM-EDX images revealed an open, rough, and porous architecture in which silicon was distributed throughout the matrix. TGA further showed enhanced thermal resistance, with a residual mass of about 49% at 600 °C for the silica-containing material. The adsorbent was tested for the uptake of methyl orange (MO) and methylene blue (MB) as representative anionic and cationic dyes. Dye removal depended strongly on pH; MB uptake was highest at pH 6, while MO removal was favored at pH 3, reflecting the contribution of deprotonated carboxylate/silanol sites and protonated amine groups, respectively. The kinetic profiles agreed better with the pseudo-first-order equation. The Langmuir provided the best representation of the data of equilibrium, giving maximum capacities of 116 and 107 mg g^-1 for MB and MO. Thermodynamic analysis confirmed that the adsorption process was spontaneous, with ΔG values ranging from -1.5 to -2.1 kJ mol^-1 for MB and -0.7 to -1.3 kJ mol^-1 for MO, and endothermic, with ΔH values of 7.13 kJ mol^-1 (MB) and 7.86 kJ mol^-1 (MO). Furthermore, the hybrid retained useful adsorption capacity after five adsorption-desorption cycles, demonstrating good reusability. The XG/CMC/silica hybrid represents a promising, reusable, bio-based adsorbent for the efficient removal of both cationic and anionic dyes from aqueous media.