Adsorption of Reactive Red 4 by immobilized chitosan on glass plates: Towards the design of immobilized TiO2–chitosan synergistic photocatalyst-adsorption bilayer system

Immobilized chitosan adsorbent on glass plates (CS/glass) has been fabricated as a pre-step towards the design of bilayer immobilized TiO2–chitosan synergistic photocatalyst-adsorbent system. The characterizations of the immobilized chitosan were studied by SEM, FTIR, BET, and strength test. Experiments were carried out as a function of adsorbent loading, pH, contact time, initial dye concentration and temperature using Reactive Red 4 anionic dye (RR4) as a model pollutant. The adsorption equilibrium data can be described well by the Langmuir and Freundlich isotherm models. The maximum adsorption capacity calculated from the Langmuir model was found to be 172.41 mg g−1. Experimental kinetic data were analyzed using pseudo-first and pseudo-second order rate models. Pseudo-second order model demonstrated to be the best kinetic model for the system suggesting that the rate-limiting step may be chemisorption. The negative value of free energy and enthalpy obtained indicates that the adsorption process is spontaneous and exothermic.