Experimental Investigations on Adsorption of Reactive Toxic Dyes Using Hedyotis umbellate Activated Carbon

Hedyotis umbellate activated carbon (HUAC) was prepared by chemical and thermal activation. The adsorption behavior of Hedyotis umbellate activated carbon in aqueous basic green 4 (BG4) and acid fuchsin (AF) was investigated and characterized by UV-vis, FTIR, and FESEM. The possible mechanism of the adsorption of BG4 and AF dyes on the HUAC surface was framed. The influence of various adsorption control parameters like the initial dye concentration, pH, adsorbent dose, contact time, and temperature was studied. The data confirmed excellent BG4 removal of 97.94% at pH 10 and AF removal of 76.7% at pH 4. The experimental data were fitted using Langmuir, Freundlich, and Temkin isotherms to examine the adsorption mechanism. The adsorption data revealed monolayer adsorption of BG4 with the maximum capacity of 102.38 mg/g and multilayer adsorption of AF with the capacity of 139.33 mg/g. The kinetic data for different initial dye concentrations were computed using pseudofirst order, pseudosecond order, and intraparticle diffusion models. Thermodynamic parameters like Gibbs free energy change ΔG0, enthalpy change ΔH0, and entropy change ΔS0 were evaluated. From the values obtained, the negative values of ΔG0 and ΔH0 indicate that the adsorption of BG4 and AF by HUAC is spontaneous and exothermic.