N-Type SnO2-Based Trace-Level Fe(III) Ion Sensor for Drinking Water Quality Monitoring

Abstract

Iron(III) contamination in potable water systems represents a critical environmental and public health concern due to its widespread prevalence and associated toxicity. This study details the development of a highly efficient, cost-effective conductometric sensor based on nanostructured n-type $\text {SnO}_{{2}}$ for rapid, trace-level quantification of Fe(III) ions in aqueous environments. The fabricated device exhibits exceptional analytical performance, achieving a peak current response ratio ( $\text {I}_{\text {Fe(III)}}/\text {I}_{\text {Bare}}$ ) of approximately 403 at a 10-ppm Fe(III) concentration, alongside an ultralow limit of detection (LOD) of 0.001 ppm experimentally. Furthermore, the sensor demonstrates rapid dynamic kinetics, characterized by response and recovery times of 4.82 and 12.01 s, respectively. It also maintains robust long-term stability over a 31-day period with a marginal performance deviation of $\pm {2}.{23}\%$ . The platform exhibits stringent selectivity for Fe(III) against a background of ubiquitous interfering ions typical of drinking water, combined with outstanding device-to-device reproducibility, attributed to surface adsorption-desorption, yielding a maximum error of only 0.891%. Mechanistically, the enhanced sensing paradigm is attributed to a surface adsorption–desorption process. This phenomenon is governed by exponential defect-induced injection and depletion of charge carriers, which are fundamentally facilitated by abundant oxygen vacancies within the $\text {SnO}_{{2}}$ lattice. In summary, the integration of profound sensitivity, rapid response kinetics, strict reproducibility, and extended operational stability positions this $\text {SnO}_{{2}}$ -based chemiresistive platform as a highly viable architecture for the real-time, continuous monitoring of iron pollutants in aquatic ecosystems and water infrastructure.