Detection and Monitoring of Manganese in Drinking Water and Groundwater Through Photo-Oxidation Sensory Reaction With Ultrasmall Carbon Nanodots

Abstract

The paper focuses on the development of ultra-small carbon nanodots as sensitive sensors for detection and monitoring of manganese in drinking water and groundwater. The environmental contamination with manganese is often a result from industrial activities such as mining and agriculture. The soluble Mn ions are toxic for many organisms and might even cause serious human diseases. The strategy for sensory detection used by us is based on a photo-oxidation reaction, in which the carbon nanodots are dissolved in acidic solution and illuminated with UV irradiation ( = 365 nm). At these conditions the nanoparticles acted as photosensitizer and produced singlet oxygen, which can be monitored by 3,3’,5,5’-tetramethylbenzidine as an organic indicator. However, to proceed this reaction, it is necessary to introduce the redox pair Mn(II)/Mn(III) in the reaction mixture, which plays the role of a catalytic mediator for the electron transfer. Thus, the oxidation of 3,3’,5,5’-tetramethylbenzidine appears, which results in blue colour of the solution with absorbance maximum at 645 nm. The rate of this sensory reaction was significantly enhanced in the presence of EDTA, which was used as a ligand to obtain a stable complex of Mn(III)/EDTA. The formed complex itself oxidised the organic indicator and caused the colorimetric reaction. Among the other metal ions tested, only manganese could be detected by the presented sensory approach.