A Master of Science thesis in Chemical Engineering by Tamara Georgesaleh Dokmaji entitled, “Removal of Hexavalent Chromium from Wastewater using Modified Multiwall Carbon Nanotubes”, submitted in December 2018. Thesis advisor is Dr. Taleb Ibrahim and thesis co-advisor is Dr. Mustafa Khamis. Soft and hard copy available.
Recently, the interest and research on the removal of heavy metals from wastewater have dramatically increased due to the adverse effects they have on humans, flora and fauna. Chromium, which is a heavy metal, is the tenth most abundant element in the universe and naturally occurs in the form of hexavalent chromium [Cr(VI)] and trivalent chromium [Cr(III)]. In this thesis, an adsorption technique using modified multiwall carbon nanotubes (MWCNTs) is investigated for Cr(VI) removal from wastewater. The surface of the MWCNTs was modified with a cationic surfactant, cetyl trimethylammonium bromide (CTAB). Surface characterization was conducted using Fourier Transform Infrared spectroscopy (FTIR), Thermal Gravimetric Analyzer (TGA), Scanning Electron Microscope (SEM), and Energy Dispersive X-ray Spectroscope (EDS) in which a thorough review of results revealed that MWCNTs modification with CTAB was successful. The optimum conditions for adsorption using MWCNTs-CTAB were determined. The optimum values in terms of adsorbent dosage, contact time, pH, and temperature were found to be 0.05 g, 25 min, 4.5, and 25 oC, respectively. Fitting equilibrium data using various isotherm models revealed that the adsorption of Cr(VI) on MWCNTs-CTAB follows a Langmuir isotherm model with maximum adsorption capacity of 27.78 mg/g and Langmuir adsorption capacity of 3.956 L/mg. In addition, kinetic parameters were also fitted on several models and the data revealed that MWCNTs-CTAB followed a pseudo- second order reaction model with rate constant 9.85*10-4 g/mg.min. A thermodynamic study showed that the proposed adsorption process is spontaneous, endothermic and the mode of adsorption is physisorption with Gibbs free energy of -1.3 kJ/mol at 25 oC. From this batch experimental study, it can be concluded that the removal of Cr(VI) from wastewater using MWCNTs-CTAB was successful and a removal efficiency of 98% was achieved at the selected optimum conditions.