High adsorption capacities of crystal violet dye by low-cost activated carbon prepared from Moroccan Moringa oleifera wastes: Characterization, adsorption and mechanism study

Moringa oleifera is a versatile tree whose seeds are used as coagulants in water treatment. The seed husks are usually discarded as waste, since they serve no scientific purpose. In this work, we reported the interest of using this waste to produce a low cost activated carbon, using an improved pyrolysis method with thermal shock under atmospheric pressure, followed by chemical activation with (HPO4)-P-3. The prepared activated carbon displays a high specific surface area of 1394 m(2)/g, and a pore volume of 0.714 cm(3)/g. It was applied for the crystal violet cationic dye adsorption. Equilibrium adsorption data were tested using four different isothermal models: Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich by nonlinear regression. The Langmuir model was found to be the best fit with a maximum monolayer adsorption capacity of 469.55 mg.g(-1) at 298 K. The kinetic study revealed that the second-order model is the best suited for a contact time of about 60 min. The thermo-dynamic study revealed a spontaneous, endothermic process, as well as the adsorption is of physical type. The desorption of crystal violet dye in an aqueous solution of acetic acid CH3COOH by MO CA-H3PO4 reached 82.9 %, the re-adsorption study confirmed the reusability of activated carbon up to 5 cycles. A test on real textile wastewater confirmed the effectiveness of low cost activated carbon adsorption on an industrial scale.

Automated summary

Moringa oleifera seed husks, usually discarded as waste, were used to produce low-cost activated carbon with high specific surface area and pore volume. The activated carbon exhibited effective adsorption of dyes with a maximum monolayer adsorption capacity of 469.55mg/g and could be reused up to 5 cycles. It also showed excellent adsorption performance on industrial-scale textile wastewater.