Removal of Congo red and Naphthol blue black dyes from aqueous solution by adsorption on activated carbon. Characterization, kinetic and equilibrium in nonlinear models studies

The objective of our study is to test the performance of the commercial powdered activated carbon (PAC) in the elimination by adsorption of two di-azo dyes, Congo red (CR) and Naphthol blue black (NBB), were used directly without any treatment. The PAC was characterized using X-ray diffraction, Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller, and the pH point of zero charges (pH(PZC)). The adsorption studies were conducted on a batch process and under the effect of various operational parameters such as contact time, pH, and initial concentration of the tested dyes. The adsorption mechanism with nonlinear equations, such as pseudo-first-order, pseudo-second-order, intraparticle diffusion, Elovich kinetics, Langmuir, Freundlich, and Dubinin- Radushkevich isotherm was also studied. The adsorption process occurred rapidly for NBB than CR. However, the maximum adsorption capacity was obtained with CR (53.17 mg/g). The findings showed that CR and NBB's adsorption processes favor the pattern of pseudo-first-order. The maximum removal of two dyes was achieved under acidic condition. The adsorption efficiency also decreased with the initial increase in the contents of the CR and NBB. The Langmuir isotherm offered the best fit to experimental data suggesting homogeneous dispersion of adsorption sites.