Bridging Component Strategy in Phosphomolybdate-Based Sensors for Electrochemical Determination of Trace Cr(VI)

Abstract

Rapid and sensitive electrochemical determination of trace carcinogenic Cr(VI) pollutants remains an urgent and important task, which requires the development of active sensing materials. Herein, four cases of reduced phosphomolybdates with formulas of the (H 2 bib) 3 [Zn(H 2 PO 4 )] 2 {Mn[P 4 Mo 6 O 31 H 7were hydrothermally synthesized under the guidance of a bridging component strategy, which function as effective electrochemical sensors to detect trace Cr(VI). The difference of hybrids 1−4 is in the inorganic moiety, in which the reduced phosphomolybdates {M[P 4 Mo V 6 O 31 ] 2 } (M{P 4 Mo 6 } 2 ) exhibited different arrangements bridged by different cationic components ({Zn(H 2 PO 4 )} subunit for 1, [Mn 2 (H 2 O) 2 ] 4+ dimer for 2, and [Mo V 2 (μ 2 -O) 2 (H 2 O) 4 ] 6+for 3). As a result, hybrids 1 and 3 display noticeable Cr(VI) detection activity with low detection limits of 14.3 nM (1.48 ppb) for 1 and 6.61 nM (0.69 ppb) for 3 and high sensitivities of 97.3 and 95.3 μA•mM −1 , respectively, which are much beyond the World Health Organization's detection threshold (0.05 ppm) and superior to those of the contrast samples (inorganic Mn{P 4 Mo 6 } 2 salt and hybrid 4), even the most reported noble-metal catalysts. This work supplies a prospective pathway to build effective electrochemical sensors based on phosphomolybdates for environmental pollutant treatment.

Four Chromic Compounds Constructed from Keggin Polyoxometalates and Viologens with Applications in Ultraviolet, Metal Ion Detection, and Ink-Free Printing

“…Polyoxometalate (POM) is an important branch of the inorganic field, which is a kind of metal oxygen clusters formed by oxygen connection of pretransition metal ions. − Until now, POM has been widely studied as a functional component and applied in many fields such as light, electricity, and magnetism. − Moreover, the surface of POMs is rich in electrons, which can provide electrons easily. Thus, POMs own excellent redox properties, inducing the applications in electrochemistry and catalysis. − Furthermore, the characteristics of rich electrons of POMs can conduce electron transition, which makes POMs act as precursors of chromic materials .…”

Reduced phosphomolybdate as photoassisted electrochemical crystalline sensor for trace Cr(VI) detection

“…Nevertheless, the PAEC sensing method for detecting Cr(VI) in water environments is limited at present. During the PEAC detection process, Cr(VI) is converted into Cr(III) via an electron transfer on the electrode surface, which generates an electroanalytical signal for quantitative determination [19,20]. Meanwhile, the photoactive electrode materials in PAEC sensor are excited by visible light to produce photoinduced electron transfer processes at the electrode or interfaces to accelerate the Cr(VI) sensing process and amplify the electrical recognition signals, thus realizing the rapid and sensitive detection of ultratrace Cr(VI).…”