Batch adsorptive removal of metanil yellow from simulated dye wastewater using nitric acid modified-H3PO4-activated carbon (NAMPAAC) from Gmelina arborea bark: equilibrium and isotherm studies

The aim of this work was to investigate the capacity of nitric acid modified-H 3 PO 4 -activated carbon produced from Gmelina arborea bark in the removal of metanil yellow from aqueous solution. The effects of initial dye concentration, C 0 , contact time, adsorbent dosage, and initial solution pH on the adsorption capacity q e were studied. Experimental data were analyzed with the Langmuir, Freundlich, Flory–Huggins and Temkin isotherm models. Results show low equilibrium adsorption capacities which decreased with increase in C o . The optimum experimental q e obtained was 2.35 mg/g by C o 25 mg/L. The optimum contact time of 300 min was obtained. Correlation coefficient R 2 , values (0.861–0.9781) obtained, show that the four applied isotherm models analyzed experimental data well. The optimum pH and adsorbent dosage were 2 and 0.01 g/25 mL solution, respectively. The ΔG ads value of –11.248 kJ/mol based on the Flory–Huggins isotherm, and the separation factor, R L values 0.489, 0.332, and 0.199 for C o 25, 50, and 100 mg/L, respectively, show the adsorption to be spontaneous and favourable. The H 3 PO 4 -activated carbon was modified with nitric acid, to determine the effect of the modification on the surface area and adsorption capacity. Compared with a similar work with unmodified H 3 PO 4 -activated carbon (yet unpublished), there was a decrease in surface area, and q e by 109.59 m 2 /g and 12.363 mg/g, respectively. These results show that the modification of the activated carbon with nitric acid had a negative effect.