Influence of carbon-oxygen surface groups on adsorptive removal of malachite green dye from water

Abstract

Equilibrium adsorption of malachite green (a cationic dye) has been studied using four different granulated activated carbons. The porous characteristics of the activated carbons are determined using NOVA win software supplied with Quantachrome Nova 2200 surface area and pore size analyser. The chemical structure of the carbon surface has been studied using FTIR, high temperature evacuations and base neutralization. Different activated carbons adsorb different amounts of the dye, depending on the surface area and the nature of the carbon surface. The adsorption increases on oxidation of the carbon surface due to the formation of carbon-oxygen surface groups and decreases gradually when these surface groups are eliminated on degassing at gradually increasing temperatures. The adsorption data follows linear Langmuir and Freundlich isotherm equations. The adsorption is very small at low <i style="mso-bidi-font-style:normal">p</i>H values of the solution but attains a maximum value at <i style="mso-bidi-font-style:normal">p</i>H around 6. The adsorption involves electrostatic interactions between the negatively charged surface sites and the dye cations. The adsorption kinetics follows second order rate law. The values of activation energies and desorption with solvents indicate that adsorption involves chemisorption or activated adsorption.<b style="mso-bidi-font-weight:normal"><span style="mso-bidi-font-style:italic"></span></b>