Photocatalytic Degradation of Methylene Blue Dye with Green Zinc Oxide Doped with Nitrogen

Abstract

The non-biodegradability of organic pollutants and their adverse effects on plant and living organisms makes their removal from the environment vital for the preservation of the ecosystem. In this study, Photocatalysis (one of the advanced oxidation processes) was employed for the removal of methylene blue dye (MBD). Phyto-enhanced synthesized Zinc oxide (G.S ZnO) were precipitated from an aqueous solution of zinc nitrate hexahydrate and Papaya leaf extracts. The precipitates were dried at 100 oC for 24 hours, and doped hydrothermally with nitrogen from Urea at different doping ratios (10%, 5% and 2%). Preliminary degradation of MBD with the different compositions of Photocatalyst revealed that 5% G.S N-ZnO had superior photocatalytic capabilities than pure ZnO, 10% G.S N-ZnO, 2% G.S N-ZnO. The effects of solution pH, 5% G.S N-ZnO dosage and initial solution concentration on MBD degradation were studied. An optimum percentage degradation of 83% and 97.5% were observed for pure ZnO and G.S. N-ZnO photocatalyst at a solution pH of 9.0, MB solution concentration of 10 mg/L and photocatalyst of dosage of 100 mg. Scanning Electron Microscope (SEM), X-ray Diffraction (XRD), Brunauer-Emmett-Teller (BET) and Fourier Transform Infrared Spectroscopy (FTIR) were used to study morphology, structural properties, surface area and pore volume, and functional groups of Pure ZnO and 5% G.S N-ZnO. FTIR spectra of the 5% G.S N-ZnO was in the range of 4000-500cm-1, and the ZnO group of G.S N-ZnO was at a low wavenumber. The BET result revealed the surface area of 5% G.S N-ZnO to be 113.3cm2/g which was five times that of pure ZnO. The BET result showed an increase in pore volume and diameter (2.118nm and 0.055cm3/g) of 5% G.S N-ZnO against that of pure ZnO (1.452 nm and 0.010 cm3/g). The shift of the XRD pattern between pure ZnO and 5% G.S N-ZnO affirms the presence of dopants in the crystalline structure of ZnO. The average crystallite sizes of pure ZnO and 5% G.S N-ZnO were 34.7nm and 24.8nm, respectively. The findings from this research revealed that the simultaneous use of green synthesis and doping could further improve the degradation of methylene blue dye compounds in industrial effluents and ultimately increase the efficiency of wastewater treatment processes/systems.