Structural, thermodynamics, and mechanistic insights into a tobacco-waste derived activated carbon/polysaccharide composite sponge for efficient Cr( <scp>vi</scp> ) adsorption and reusability

This study presents the creation of an innovative bioadsorbent a porous carbon-polymer composite, referred to as TACGC, was synthesized utilizing residues from tobacco processing and subsequently assessed for its efficacy as an adsorbent of hexavalent chromium (Cr(vi)) from aqueous solutions. The composite was fabricated by integrating tobacco-derived activated carbon into a matrix composed of guar gum and carboxymethyl cellulose, which was chemically cross-linked with itaconic acid, resulting in a stable and functional sponge-like structure. The structural and surface characteristics were investigated through various analytical techniques, including XRD, FT-IR, XPS, SEM-EDX, and BET analysis. These analyses collectively confirmed the development of a mesoporous network characterized by an abundance of oxygenated functional groups. Batch adsorption experiments indicated that factors such as pH, adsorbent dosage, initial Cr(vi) concentration, contact time, and temperature significantly impacted the removal efficiency. The observed adsorption behavior adhered to the Langmuir isotherm model, achieving a maximum adsorption capacity of 404.87 mg g^-1, while the kinetic data conformed to the pseudo-second-order model, suggesting that the uptake mechanism is predominantly chemisorption-driven. Thermodynamic analysis (Δ<i>H</i>° = 93.45 kJ mol^-1; Δ<i>S</i>° = 325.7 J mol^-1 K^-1) established that the adsorption process is both spontaneous and endothermic. Moreover, TACGC demonstrated sustained efficiency over five cycles of adsorption-desorption, underscoring its structural integrity and reusability. The robustness of the system was further corroborated through statistical optimization employing the Box-Behnken design. These results underscore the significant potential of TACGC as an effective and sustainable solution for Cr(vi) remediation in wastewater treatment contexts.