Fully Reduced Cu I {P 4 Mo 6 } 2 Supramolecular Architectures for Ultraselective Photoelectrochemical Detection of Cr(VI)

The sensitive and selective detection of toxic Cr(VI) depends on the development of high-performance photoelectrochemical sensing materials. Herein, two supramolecular architectures of CuI{P4Mo6}2-based phosphomolybdates, with formula of (H2bib)3Pb{CuI[P4Mo6O31]2H15}·10H2O (1), [CuI(bib)]4[Na2(H2O)7]{CuI[P4Mo6O31]2H17}·26H2O (2) (bib = 4,4′-bis(imidazolyl)bipheny), were synthesized as photoelectrochemical sensors for determining Cr(VI) ion. Compound 1 consisted of one-dimensional Pb2+-bridged fully reduced CuI{P4Mo6}2 clusters and protonated [H2bib]2+ cations. Compound 2 was composed of Na+-capped CuI{P4Mo6}2 clusters and [CuI(bib)]+ chains. Both compounds 1 and 2 displayed excellent electrochemical redox properties, broad spectral absorption capabilities, and rapid photoelectrochemical response. Using as photoelectrochemical sensors, compound 1 showed a high sensitivity of 255.41 μA·μM–1 and an extremely low detection limit of 0.54 nM (0.056 ppb) toward Cr(VI) detection, and compound 2 presented a sensitivity of 62.53 μA·μM–1 and detection limit of 3.64 nM (0.38 ppb). Structure–function relationship analysis showed that the one-dimensional framework of CuI{P4Mo6}2 clusters effectively promotes the separation and transport of photogenerated charge carriers. Compound 1 also exhibited high anti-interference capability and stability in the photoelectrochemical detection process. This work provides some insights for designing advanced polyoxometalate-based sensor materials for highly efficient monitoring of environmental pollutants.