Synthesis and characterisation of magnetic activated carbon/diopside nanocomposite for removal of reactive dyes from aqueous solutions: experimental design and optimisation

In this work, a series of magnetic activated carbon/nanodiopside (Fe₃O₄/AC/Diop) nanocomposites were synthesised and used for the removal of reactive green KE-4BD dye from the aqueous solution. After preparation of nanodiopside by sol-gel method and activated carbon from coconut husk, first, Fe₃O₄/AC composite was prepared by in situ synthesis of Fe₃O₄ nanoparticles between activated carbon pores, and then, different percentages of Fe₃O₄/AC/Diop nanocomposites were prepared by simple mixing of Fe₃O₄/AC composite and Diop in ethanol. Formation of Fe₃O₄/AC and Fe₃O₄/AC/Diop composites was characterised by FTIR, field emission scanning electron microscopy, BET, XRD and vibrating sample magnetometer analyses. Thermogravimetric analysis was used to show the adsorption capacity of the adsorbent more accurately. Effects of amount of adsorbent, initial pH, contact time and dye concentration on reactive green dye removal were also studied using central composite design. Optimal conditions for maximum reactive green KE-4BD dye adsorption (98.35%) process were as follows: pH= 4.90, adsorbent amount: 0.015 g, dye concentration: 37.17 mg/L and contact time: 10.12 min, respectively. In addition, the adsorption kinetics, thermodynamics and isotherms were examined. Adsorption isotherms (q_max: 344.827 mg/g), kinetics and thermodynamics were demonstrated that the sorption processes were better described by the pseudo-second-order equation and the Langmuir equation.