Enhanced photocatalytic activity of methylene blue dye by DIFS synthesized pure and Mn doped MgO nanostructures

Abstract

A simple Direct Injection Flame Synthesis (DIFS) method is employed to prepare magnesium oxide (MgO) and manganese doped magnesium oxide (Mn:MgO) nanoparticles, and their photocatalytic ability against methylene blue (MB) dye was investigated. The prepared samples are characterized through XRD, Raman spectroscopy, UV-Visible spectroscopy, FESEM, photoluminescence (PL), and EDX analysis. XRD studies reveal that MgO and Mn:MgO nanoparticles contain pure cubical phases and their average crystallite size reduces when Mn is doped with MgO. The characteristics vibrations mode of the synthesized nanoparticles are analyzed from the Raman spectroscopic studies. As per the EDX data, the prepared samples are free from impurities. Pure MgO nanoparticles have irregular, nanocubical and nanoclustered formations, whereas Mn:MgO nanoparticles have crystalline, nanocubical, and nanoflakes structures, according to FESEM analysis. Doping Mn slightly increases the bandgap of the Mn:MgO nanoparticles. UV–visible spectroscopy analysis confirmed a red shift in the wavelength dependent absorbance curve. PL analysis confirms the vacancy and oxygen related defects that are generated due to the doping of Mn with MgO, which enhances the degradation of MB dye. The efficiency of MB degradation by MgO is determined to be 86% and Mn:MgO is about 99%. The analysis of the photocatalytic degradation process revealed that OH- and holes (h+) were crucial for the increased photocatalytic activity of Mn:MgO nanoparticles for MB degradation. The effect of catalyst's initial concentration and the catalysts reusability test were evaluated for five times without significantly losing activity each time. As a result, Mn:MgO is a useful and active catalyst that can be activated effectively using UVA-LEDs to break down and mineralize the wastewater's organics.