Comparison of the photocatalytic, adsorption and electrochemical methods for the removal of cationic dyes from aqueous solutions

TiO2 nano particles (NPs) were synthesized by precipitation using high purity of TiCl4 and the surface was modified by hydrothermal treatment. The NPs were characterized using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDX), Transmission electron microscopy (TEM), Thermo-Gravimetric Analysis (TGA), X-ray Photoelectron Spectroscopy (XPS) and Brunauer-Emmet-Teller (BET) surface area techniques. The synthesized NPs were utilized for removal of methylene blue (MB) dye from wastewater. The effect of various experimental parameters such as pH, adsorbent dosage, concentration of dye, photocatalyst concentration on the degradation efficiency of the effluent has been studied. The equilibrium studies for adsorption were done using Langmuir and Freundlich isotherms and better agreement was attained with the Langmuir model. The maximum adsorption capacity (q(o)) was calculated as 88.1057 mg/g using Langmuir equation. The kinetic parameters displayed that MB adsorption onto the NPs followed pseudo-second-order kinetics model. In this paper, removal efficiencies of three different techniques photocatalysis, adsorption and electrolysis treatments were compared for methylene blue abatement using surface modified Nps. The results indicated that, photocatalytic and adsorption methods showed similar to 1 and 60.70 percent of removal of dye at chosen higher initial dye concentrations of 25 mg/L and 50 mg/L respectively, whereas electrolysis methods showed 94.95 percent removal of dye even at higher initial concentration of dye (50 mg/L). Electrolysis method seems to be more superior, possibly because of continuous flow of electric current through conductive electrode surface which generates the negative charges and these charges are capable of degrading the dye into constituent products more effectively than the other two methods. Mechanisms for removal/degradation dye from wastewater using NPs for all the above three methods has been predicted. (C) 2020 Elsevier B.V. All rights reserved.