Insight into the Adsorption and Photocatalytic Behaviors of an Organo-bentonite/Co3O4 Green Nanocomposite for Malachite Green Synthetic Dye and Cr(VI) Metal Ions: Application and Mechanisms.

Abstract

A green composite of organically modified bentonite supported by Co3O4 nanoparticles (OB/Co) was successfully fabricated and investigated as a potential eco-friendly, low-cost adsorbent and photocatalyst for promising removal of both malachite green dye (MG.D) and Cr(VI) ions. The composite showed high adsorption properties and achieved experimental qmax values of 223 and 139 mg/g for MG.D and Cr(VI) after equilibration times of 360 min and 480 min for the inspected contaminants, respectively. The kinetic and equilibrium inspection reflected the best description of their adsorption behaviors by the pseudo-first-order kinetic model and the Langmuir isotherm model, respectively. This revealed favorable and homogeneous uptake of both MG.D and Cr(VI) in a monolayer form with theoretical Langmuir qmax values of 343.6 and 194.5 mg/g, respectively. The theoretical adsorption energies of MG.D (0.6 kJ/mol) and Cr(VI) (0.5 kJ/mol) from the Dubinin–Radushkevich (D–R) model revealed physisorption properties that might be resulted from some types of Coulombic attractive forces, achieving theoretical qmax values of 226.5 and 144.6 mg/g, respectively. The suggested adsorption mechanism was confirmed by the main mathematical parameters of thermodynamic studies that revealed physical, spontaneous, and exothermic uptake processes. Also, the composite showed high photocatalytic performance under visible light, which resulted in a 100% removal percentage of 100 mg/L of MG.D and Cr(VI) after about 180 and 240 min, respectively, from the adsorption equilibrium time.