Photodegradation of Methylene Blue and Methyl Orange using Metal Oxide Photocatalysts

Authors

  • Ray Georgeny
  • Rohul Adnan

Keywords:

photocatalysts, methylene blue, methyl orange, metal oxides

Abstract

Dyes are important in textile, food and cosmetic industry. Unfortunately, some dyes are highly toxic even in the presence of a tiny amount. Photocatalyst is a catalyst that drives chemical reactions under light irradiation and produces a strong oxidizing agent to treat the dye. There are several factors that affect the rate of degradation of dye such as the pH, type and amount of photocatalyst and concentration of dye. Out of all metal oxides used in this study, nickel ferrite (NiFe2O4) and zinc ferrite (ZnFe2O4) are catalytically inert while zinc oxide (ZnO) and titanium dioxide (TiO2) are photocatalytically active and thus used in the subsequent studies. Photodegradation of methylene blue (MB) and methyl orange (MO) using ZnO and TiO2 was taken at 90 minutes to show the effect of pH. At pH 5, TiO2 and ZnO showed 67% and 97%, and at pH 9, both photocatalyst have 97% photodegradation rate of MB, respectively. For photodegradation of MO, at pH 5 both photocatalysts have similar photodegradation rate. At pH 9, TiO2 and ZnO has a 78% and 95% photodegradation rate of MO. The rate of was found to increase proportionally with the amount of photocatalyst used but at high concentration, the degradation rate was saturated. The optimized condition for photodegradation of MB is at pH 9 and MO at pH 5 using 30 mg photocatalysts (ZnO or TiO2) owing to the cationic and anionic character of the dyes. The crystal structure of TiO2 and ZnO are tetragonal anatase and hexagonal wurtzite, respectively, as verified by XRD. FESEM images revealed that ZnO consists of nanoparticles and nanoplatelets with average size of 45.5 ± 14.1 nm and TiO2 shows average size of 42.5 ± 10.5 nm. The band gap of TiO2 and ZnO are 3.46 and 3.26 eV, respectively, as calculated from the UV-visible diffuse reflectance spectroscopy (UV-vis DRS). The X-ray photoelectron spectra for TiO2 confirm the presence of Ti4+ and O2- states.

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Published

2020-11-15

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Section

Research Article