Decolorization of bismarck brown R and crystal violet in liquid phase using modified pea peels: non-linear isotherm and kinetics modeling

Abstract

The batch adsorption studies to assess the adsorption efficiency of citric acid modified pea peels (CAPP) for uptake of bismarck brown R (BB) and crystal violet (CV) from liquid phase were performed. The dyes uptake was found to increase with increase in agitation time, adsorbent dosage, temperature, solution pH and with decreasing initial dyes concentrations. The non-linear isotherm modeling revealed that Freundlich and Sips isotherm model correlated the data well indicating multilayer adsorption onto heterogeneous CAPP surface. Langmuir adsorption capacity, Qm for BB and CV was 5.37 and 17.61 mg/g, respectively. The separation factor, RL < 1 and Freundlich constant, n > 1 indicated favorable adsorption. The kinetic studies showed that the pseudo-second order rate equation correctly explained the adsorption process, supporting the adsorption of one dye molecule onto two adsorption sites, with intra-particle and liquid-film diffusion as the rate controlling steps. The negative values of ΔG° (−20 to 0 kJ/mol) suggested the spontaneous and physical adsorption. The positive ΔH° and ΔS° values suggested endothermic adsorption and increased entropy at solid-solution interface. The CAPP proved to be an inexpensive and efficient adsorbent for BB and CV removal from wastewater.