Detection of Zn in water using novel functionalised planar microwave sensors

Highlights: • Feasibility of using f-EM-sensors with β-Bi₂O₃ based film for Zn monitoring in water. • S₁₁ spectra show good linear correlations (R² = 0.93–0.99) for diverse Zn concentrations. • Sensor response to low-concentration of Zn depends on the thickness of coatings. • Cost-effective monitoring of Zn concentration to meet freshwater EQS requirements. -- Abstract: Metal pollution in aquatic environments has attracted global attention. Current methods are not able to monitor water quality in-situ at low-cost. This paper reports on a novel approach for detecting changes in the concentration of zinc in water using electrical and a microwave sensor method, adopting two planar sensors: one was functionalised with a screen-printed β-Bi₂O₃ based coating, while the other was uncoated. Results show that both electrical and the microwave sensor responses were dependent on the presence and concentration of Zn in water with R² = 0.93–0.99. The functionalised sensor with a 60 μm thick β-Bi₂O₃ based film offers improved performance compared with both uncoated and functionalised sensors with 40 µm thick coating for detecting the changes of Zn concentrations in water for low levels (100 and 500 µg/L). This novel sensing system could be a cost-effective alternative to the current offline methods.