Application of graphene oxide and its derivatives on the adsorption of a cationic surfactant (interaction mechanism, kinetic, isotherm curves and thermodynamic studies)

Abstract

In this research, the adsorption of a cationic surfactant, Cetyl Trimethyl Ammonium Bromide (CTAB), on graphene oxide-based adsorbents was investigated. The adsorbents consist of graphene oxide (GO), reduced graphene oxide (rGO), functionalized graphene oxid by humic acid (GO-HA), and functionalized reduced graphene oxid by thionine acetate (rGO-Th) that are characterized by the Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectrophotometry (FT-IR), X-ray Diffraction (XRD) and Brunauer-Emmett-Teller (BET) analysis. Examine factors affecting the adsorption of CTAB such as pH, contact time, adsorbent dosage, and agitation speed were investigated. Based on the results, the optimum pH for GO, rGO, GO-HA, and rGO-Th were 7, 8, 6.5, and 10, respectively and the optimum contact time and agitation speed were 30 min and 450 rpm, respectively. Also, kinetic, isothermal, and thermodynamic studies were done and the results indicated that the pseudo-second-order kinetic model fitted on experimental data for all of adsorbents. Under the optimum conditions, the maximum adsorption capacity of GO, rGO, GO-HA, and rGO-Th were 2000, 238, 3333, and 159 mg/g, and the fitted isotherm models were BET, Langmuir, Freundlich, and Langmuir, respectively. The adsorption thermodynamic suggested that CTAB adsorption on GO and GO-HA are exothermic and on rGO and rGO-Th are endothermic processes. The results indicated that physical properties of adsorbents such as surface area do not play a significant role and the electrostatic interaction between CTAB molecules and the functional groups of adsorbents plays a key role in CTAB adsorption on GO-based adsorbents.