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Green synthesis of ZnO@ZnS core–shell nanoparticles for detection of lead and iron ions in aqueous solutions by colorimetric paper sensors

Safiye Ahmadi Bakhtiari, Hassan Abdoos, and Fathallah Karimzadeh

Department of Nanotechnology, Faculty of New Sciences and Technologies, Semnan University, Semnan, Iran



Received: 2 July 2021  Accepted: 23 August 2021


Given the effects of metal ions on environment and human’s health, it is very important to identify them in aqueous solutions. Core–shell structures can be used to identify metal ions through preparation of paper sensors. In the present research, ZnO@ZnS nanoparticles with core–shell structure were prepared through two-step low temperature green synthesis process using aloe vera and lettuce extracts. The synthesized nanoparticles were characterized by Fourier transform infrared, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy analyses. The results of FTIR and XRD analyses confirmed successful formation of ZnO@ZnS core–shell structures. Micrographs of the synthesized particles also showed flaky shapes with sharp edges and random orientations. Size range of core–shell nanoparticles varied between 20 and 70 nm. Then, the solution containing green synthesized ZnO@ZnS nanoparticles was distributed onto the papers and after drying at room temperature was used as paper sensors to identify Pb2+ and Fe2+ ions. The color intensity of the sensors changed due to contact with solutions containing different concentrations of Pb2+ and Fe2+ ions (75–1500 μM). In addition, increasing concentration of ions increased color intensity of sensors and the relationship between color intensity and ion concentration was expressed by related equations. Therefore, it was possible to determine the concentration of lead and iron ions according to the color intensity. Comparison between the performance of the sensors exposed to the solutions prepared from deionized water and ZayandehRud River water showed an acceptable error of up to 5%. The results of XRD analysis on paper sensors after contacting with Pb2+ and Fe2+ ions confirmed the formation of PbS and FeS.

Keywords: Green synthesis; Core–shell nanoparticles; ZnO@ZnS; Colorimetric paper sensor; Metal ions

Full paper is available at

DOI: 10.1007/s11696-021-01840-3


Chemical Papers 76 (1) 99–109 (2022)

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