Adsorption isotherm and kinetics of paraquat removal using activated carbon/iron oxide composite material

A composite material between activated carbon (AC) and iron oxide in nanoscale was used to remove paraquat from contaminated water. The surface area of AC/iron oxide nanoparticles was in the range of 754.39 to 775.81 m2/g for the ratio 1:1 to 10:1 AC:iron oxide nanoparticles. The maximum adsorption capacity was found at pH 11. Adsorption of paraquat increases with increase in temperature indicating an endothermic process. Sorption behaviour of paraquat onto AC/iron oxide nanoparticles was evaluated using the Langmuir and Freundlich isotherm. The adsorption behaviour of paraquat was well described by Freundlich isotherm indicated that AC/iron oxide nanoparticles posed heterogeneous surface with heterolayer paraquat coverage on the surface of composite material. First and second order kinetic models were tested. The paraquat adsorption rate fits a pseudo-second-order kinetic model where the rate-limiting step is assumed to be chemical sorption between the adsorbate and adsorbent. The AC/iron oxide nanoparticles can readily be separated from the solution using a permanent magnet.