Zeolitic Imidazolate Framework-8 Integrated Ion-Selective Electrodes with Ion-Transport Data Processing for Stable Wastewater Monitoring

Ion-selective electrode (ISE) sensors can stream high-temporal-resolution nitrogen data that drive wastewater plant control loops (e.g., aeration and chemical dosing), but their long-term accuracy is limited by aqueous-layer formation, membrane-component leaching, and biofouling. Here, we developed a zeolitic imidazolate framework-8 (ZIF-8)-enabled polyvinyl chloride (PVC)-lean NH 4 + ISE and paired it with an ion-transport denoising data-processing algorithm (IT-DDPA) for continuous NH 4 + monitoring. Specifically, ZIF-8 was used as a pore-defined membrane-phase host to retain the NH 4 + ionophore (nonactin) and lipophilic additives, thereby reducing water uptake at the membrane/electrode interface and improving fouling resistance in wastewater. The ZIF-8 ISE sensors exhibited a near-Nernstian slope (54.15 mV dec –1 ), a fast response time (∼12 s), and a low detection limit (10 –6.79 M). Furthermore, IT-DDPA corrected open-circuit-potential (OCP) drift associated with time-varying ion transport near the membrane surface. During the 30-day continuous wastewater test (NH 4 + concentration: 5–30 mg L –1 ), the ZIF-8 ISE sensors retained ∼75% of the initial slope and achieved a mean error of 3.42%. IT-DDPA reduced the NH 4 + concentration discrepancy from 2.39 to 0.38 mg L –1 and bolstered R 2 from 92.4% to 99.6% in wastewater. This ZIF-8-enabled PVC-lean ISE and IT-DDPA-guided strategy deliver reliable NH 4 + sensing for long-term, continuous monitoring in wastewater.