Effect of pH, ionic strength, and temperature on the adsorption behavior of Acid Blue 113 onto mesoporous carbon

Mesoporous carbon (MC) derived from cassava starch was used to remove Acid Blue 113 azo dye from aqueous solutions. The influence of temperature, pH, ionic strength, and the adsorbent dose was investigated in a set of batch experiments. Experimental data showed that Acid Blue 113 adsorption was higher in the acid pH range than in the alkaline one, that dye adsorption increases when the ionic strength and temperature increase, and that adsorption results presented a good correlation with the Langmuir isotherm model. The adsorption capacity of MC was 295 mg g^-1, at pH = 7.0 and 298 K, respectively. Zeta potential (ζ) showed the compression of the diffuse double layer of adsorbent with an increase in temperature and ionic strength, promoting the decrease of electrostatic repulsion between the negatively charged surface of the carbon particles and the anionic dye. Thermodynamic results demonstrate that the adsorption process was spontaneous and endothermic. Moreover, for the first time, this work has demonstrated that the pH, temperature, and ionic strength of the aqueous medium are also able to change the surface charge of carbon-based adsorbents and surely influence the adsorption capacity. Finally, the regeneration of the adsorbent by the photo-Fenton reaction regenerated the adsorption capacity of the adsorbent without generating secondary pollution to the environment.