Effect of bridging units on the detection performance of Cd{P <sub>4</sub>Mo <sub>6</sub>} <sub>2</sub>-based electrochemical sensors for trace chromium(VI) and tetracycline
Xinying Ma, Hao‐Xue Bi, Xiujuan Zhang, Jing Du, Yuan‐Yuan Ma, Zhangang Han
Abstract
Exploring functionally electrochemical sensors for simultaneously detecting inorganic heavy metal ion and organic antibiotic contaminants in aquatic environments is of great significance. Herein, three reduced phosphomolybdates with distinct bridging units were hydrothermally synthesized for electrochemical sensing applications to detect trace levels of Cr(VI) and tetracycline (TC), with formulas of (H<sub>2</sub>bib)<sub>2</sub>[Cd(H<sub>2</sub>O)]<sub>2</sub>[Na(H<sub>2</sub>O)][Cd(P<sub>4</sub>Mo<sub>6</sub>O<sub>31</sub>H<sub>6.5</sub>)<sub>2</sub>]·13H<sub>2</sub>O (<strong>1</strong>), (H<sub>2</sub>bib)<sub>2</sub>[Cd(bib)(H<sub>2</sub>O)]<sub>2</sub>[Cd(P<sub>4</sub>Mo<sub>6</sub>O<sub>31</sub>H<sub>7</sub>)<sub>2</sub>]·17H<sub>2</sub>O (<strong>2</strong>), and (H<sub>2</sub>bib)<sub>2</sub>[Cd(H<sub>2</sub>O)][Cd(P<sub>4</sub>Mo<sub>6</sub>O<sub>31</sub>H<sub>8</sub>)<sub>2</sub>]·13H<sub>2</sub>O (<strong>3</strong>) (bib = 4,4'-bis(imidazolyl)biphenyl). In hybrids <strong>1-3</strong>, the reduced phosphomolybdate clusters [Cd(P<sub>4</sub>Mo<sub>6</sub>O<sub>31</sub>)<sub>2</sub>]<sup>22-</sup> (<em>abbr</em>. Cd{P<sub>4</sub>Mo<sub>6</sub>}<sub>2</sub>) featured chain-like configurations bridged by diverse cationic linkers ({[Cd(H<sub>2</sub>O)]<sub>2</sub>[Na(H<sub>2</sub>O)]}<sup>5+</sup> unit for <strong>1</strong>, [Cd(bib)(H<sub>2</sub>O)]<sup>2+</sup> fragment for <strong>2</strong>, and [Cd(H<sub>2</sub>O)]<sup>2+</sup> for <strong>3</strong>). Owing to the excellent electrochemical redox properties, hybrids <strong>1-3</strong> exhibit remarkable dual-mode electrochemical responses toward Cr(VI) reduction and TC oxidation. The detection limits for Cr(VI) are 18.41 nM for <strong>1</strong>, 30.86 nM for <strong>2</strong>, and 38.90 nM for <strong>3</strong>, with sensitivities of 122.49, 113.95, and 103.19 μA·mM<sup>-1</sup>, respectively. For TC detection, the detection limits (LOD) are 6.19 nM for <strong>1</strong>, 9.90 nM for <strong>2</strong>, and 23.52 nM for <strong>3</strong>, with sensitivities of 120.84, 105.44, and 95.95 μA·mM<sup>-1</sup>, respectively. The LODs toward Cr(VI) and TC all reach to the “nM” level. This work offers a potential approach for constructing multi-functional electrochemical sensors for the detection of environmental pollutants.