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.

Zeta Potential and Colloidal Stability Predictions for Inorganic Nanoparticle Dispersions: Effects of Experimental Conditions and Electrokinetic Models on the Interpretation of Results.

In this work, a set of experimental electrophoretic mobility (µe) data was used to show how inappropriate selection of the electrokinetic model used to calculate the zeta potential (ζ-potential) can compromise the interpretation of the results for nanoparticles (NPs). The main consequences of using ζ-potential values as criteria to indicate the colloidal stability of NP dispersions are discussed based on DLVO interaction energy predictions. For this, magnetite (Fe3O4) NPs were synthesized and characterized as a model system for performing electrokinetic experiments. The results showed that the Fe3O4 NPs formed mass fractal aggregates in solution, so the ζ-potential could not be determined under ideal conditions when µe depends on the NP radius. In addition, the Dukhin number (Du) estimated from potentiometric titration results indicated that stagnant layer conduction (SLC) could not be neglected for this system. The electrokinetic models that do not consider SLC grossly underestimated the ζ-potential values for the Fe3O4 NPs. The DLVO interaction energy predictions for the colloidal stability of the Fe3O4 NP dispersions also depended on the electrokinetic model used to calculate the ζ-potential. The results obtained for the Fe3O4 NP dispersions also suggested that, contrary to many reports in the literature, high ζ-potential values do not necessarily reflect high colloidal stability for charge-stabilized NP dispersions.