A comprehensive experimental study on heavy metal ion sensing performance of ZnPc and its electrospun nanofibers

The interactions of various heavy metal ions (HMIs) including Cu²⁺, Fe²⁺, Zn²⁺, and Cr³⁺ with zinc phthalocyanine (ZnPc) thin film and electrospun nanofibers (nZnPc) in aqueous solutions were comparatively investigated by using quartz crystal microbalance (QCM) technique, giving the order of maximum sensitivity S_Fe²⁺ > S_Cu²⁺ > S_Zn²⁺ > S_Cr³⁺ for ZnPc, while for the nZnPc-based sensor was S_Zn²⁺ > S_Cr³⁺ > S_Fe²⁺ > S_Cu²⁺. Formation of the ZnPc nanofibers was investigated by scanning electron microscopy (SEM) images, and these analyses showed that PVA/ZnPc composite nanofibers were successfully produced. QCM results have shown that ZnPc and nZnPc-based sensors are very promising materials for the sensing of the HMIs in water with a response time of 2 s. Limit of detection (LoD) calculations also showed that ZnPc and nZnPc have great potential for the detection of Cu²⁺ ions, with the LoD values of 0.14 and 0.19 ppm, respectively. HMI adsorption data were analyzed using Langmuir, Freundlich, and Temkin models, and it was found that the Freundlich model was the most suitable isotherm to represent HMI adsorption onto ZnPc and nZnPc, except for the adsorption of Fe²⁺ ions on the nZnPc surface.