Adsorption characteristics of phosphoric acid induced activation of bio-carbon: Equilibrium, kinetics, thermodynamics and batch adsorber design

Abstract

Abstract Activated carbon from Sterculia foetida was prepared using phosphoric acid as activating agent for efficient removal of methylene blue (MB). The effect of different operational parameters like pH (2–12), loading (1–4 g/l), initial dye concentration (50–500 ppm), temperature (298–328 K), and contact time (0–24 h) were investigated for the adsorption of MB. Langmuir, Freundlich, Temkin and Dubinin–Radushkevich models were used to analyse the equilibrium data. The Langmuir model fitted well with maximum monolayer adsorption capacity of 181.81 mg/g. Adsorption kinetics followed pseudo-second order kinetic model. The adsorption process was found to be governed both by intra-particle and film diffusion. Thermodynamic parameters like entropy, enthalpy, and Gibb’s free energy were also evaluated. It was found that the adsorption was spontaneous, endothermic and physisorption in nature. The liquid phase volumetric mass transfer coefficient was found to decrease from 1.03 min−1 to 0.088 min−1 with increase in initial concentration from 50 ppm to 300 ppm. A single-stage batch adsorber design for dye adsorption has been proposed based on the Langmuir isotherm model equation. The reusability study demonstrated that the prepared adsorbent could effectively be used up to 5 cycles without regeneration. The study showed that the activated carbon prepared from Sterculia foetida can be effectively used as an adsorbent for methylene blue removal from aqueous solutions.