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    Toward Long-Term Accurate and Continuous Monitoring of Nitrate in Wastewater Using Poly(tetrafluoroethylene) (PTFE)-Solid-State Ion-Selective Electrodes (S-ISEs)

    Year: 2020

    Journal: ACS Sens., Volume 5, OCT 23, page 3182–3193

    Authors: Fan, Yingzheng; Huang, Yuankai; Linthicum, Will; Liu, Fangyuan; Beringhs, Andre O'Reilly; Dang, Yanliu; Xu, Zhiheng; Chang, Shing-Yun; Ling, Jing; Huey, Bryan D.; Suib, Steven L.; Anson, W. K.; Gao, Pu-Xian; Lu, Xiuling; Lei, Yu; Shaw, Montgomery T.; Li, Baikun

    Organizations: National Science Foundation (NSF) Environmental Engineering Program GOALI ProjectNational Science Foundation (NSF) [1706343]; NSF Partnerships for Innovation (PFI) Accelerate Innovative Research (AIR) Project [1640701]; Connecticut Biopipeline Program; Infiltrator Water Technologies LLC; UConn Institute of Materials Science; NSF DMR:MRI [1726862]; UConn CARIC Initiative program; National Science FoundationNational Science Foundation (NSF) [1803343]

    Keywords: poly(tetrafluoroethylene); NO3- S-ISEs; wastewater; long-term accuracy and durability; antifouling; reading (mV) drifting; negative charge; surface roughness

    Long-term accurate and continuous monitoring of nitrate (NO3-) concentration in wastewater and groundwater is critical for determining treatment efficiency and tracking contaminant transport. Current nitrate monitoring technologies, including colorimetric, chromatographic, biometric, and electrochemical sensors, are not feasible for continuous monitoring. This study addressed this challenge by modifying NO3- solid-state ion-selective electrodes (S-ISEs) with poly(tetrafluoroethylene) (PTFE, (C2F4)(n)). The PTFE-loaded S-ISE membrane polymer matrix reduces water layer formation between the membrane and electrode/solid contact, while paradoxically, the even more hydrophobic PTFE-loaded S-ISE membrane prevents bacterial attachment despite the opposite approach of hydrophilic modifications in other antifouling sensor designs. Specifically, an optimal ratio of 5% PTFE in the S-ISE polymer matrix was determined by a series of characterization tests in real wastewater. Five percent of PTFE alleviated biofouling to the sensor surface by enhancing the negative charge (-4.5 to -45.8 mV) and lowering surface roughness (R-a: 0.56 +/- 0.02 nm). It simultaneously mitigated water layer formation between the membrane and electrode by increasing hydrophobicity (contact angle: 104 degrees) and membrane adhesion and thus minimized the reading (mV) drift in the baseline sensitivity ("data drifting"). Long-term accuracy and durability of 5% PTFE-loaded NO3- S-ISEs were well demonstrated in real wastewater over 20 days, an improvement over commercial sensor longevity.
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