Degradation of Methyl Parathion using Manganese oxide (MnO2) nanoparticles through photocatalysis

Abstract

Methyl parathion is a type of organophosphate (OP) compound that has been considered a pesticide and warfare agent. This is irreversible enzyme acetylcholinesterase inhibitors causing damage to the nervous system of exposed organisms (respiratory paralysis) and death. [1,2] OP is an ester of phosphoric acid and exists in two forms, ‘Thion and Oxon’. Parathion is a methyl part which is a highly toxic group in nature and broadly used in crops such as mainly cotton, corn, wheat, alfalfa, soybeans, fruits, and vegetables. Domestic work also leads to various hazards. [3,4] Methyl parathion (MP) is known to be O, O‐dimethyl‐O‐4‐p‐nitrophenyl phosphorothioate and it is classified as a class I insecticides. U.S. Environmental Protection Agency has categorized the Methyl parathion as restricted use of pesticides due to its high toxicity level. [5] MP is known as a cotton poison because it is utilized on the large scale in sunflower, and peaches etc. MP is also known as metaphos, is exposed to the environment in the form of agricultural insecticides through spraying using ground spray equipment. [6,7]

MP is harmful to human health and its absorption, inhalation and contact with materials contamination are also responsible for MP exposure. [8,9] It leads to several health issues such as mutagenic effects also influence the DNA sequences. Exposure of MP is also reported for the cardiovascular effects on the organisms in previous studies.[10] MnO₂ is the most stable and significant nanomaterial which attracts several researchers for its application. Due to its less toxicity and cost-effectiveness properties, it is considered an ideal nanomaterial and used as a catalyst. [11] MnO₂ nps is very promising nanomaterial which is explored in various sectors such as sensing, drug delivery system, rechargeable battery and catalysts etc.  [12] Despite having several properties, MnO₂ nps is less explored in terms of photocatalytic degradation. Herein, a photocatalytic degradation of MP is reported using MnO₂ nps through visible and UV light. [13,14] The MnO₂ nps was synthesized using the co-precipitation method and calcined at 350 °C. UV-Visible absorption study was performed to calculate the band gap which was found to be 2.77 eV using Tauc plot. The photocatalytic study was performed without light source, under visible light source, and under UV light source and their corresponding percentage were recorded 40%, 58% and 72%, respectively. The pseudo-first order rate constant (k) was 0.02. [15]

Fig. 1: a) UV-vis absorption spectra of MnO₂nps and inset shows the corresponding bandgap, and b) SEM image of the MnO₂nps.

Fig. 2. UV–Visible absorbance plot of MP in presence of MnO₂nps performed (a) without light source, (b) under visible light source, (c) under UV light source, and (d) shows the change in the intensity of MP with time. The inset shows the kinetic study of degradation studied under UV light source (plot (c)).