Experimental investigation of titanium dioxide as an adsorbent for removal of Congo red from aqueous solution, equilibrium and kinetics modeling

Abstract

The adsorption of Congo red onto titanium dioxide (TiO2) material has been investigated at batch conditions. The effects of contact time (0–60 min), initial pH (3–11), agitation speed (100–500 rpm), temperature (298–343 K), adsorbent dosage (0.5–2 g/L), and Congo red concentration (5–15 mg/L) on the Congo red adsorption by TiO2 have been studied. The kinetic parameters, rate constants, and equilibrium adsorption capacities were calculated and discussed for each kinetic model. The adsorption of Congo red onto TiO2 is well described by the pseudo-second order equation. The adsorption isotherm follows the Langmuir model, providing a better fit of the equilibrium data. The batch adsorption experiments were carried out to optimize the physical parameters on the Congo red removal efficiency. It has been found that 152 mg/g at 25 °C is removed. The thermodynamic parameters indicate the spontaneous and endothermic nature of the adsorption process with activation energy (Ea) of −64.193 kJ/mol. The positive value of the entropy (ΔS°) clearly shows that the randomness is decreased at the solid–solution interface during the Congo red adsorption onto TiO2, indicating that some structural exchange may occur among the active sites of the adsorbent and the ions