Two new inorganic–organic hybrids based on Keggin polyoxometalate and methylene blue and application in chemically bulk-modified electrode

Two new inorganic–organic hybrids based on Keggin polyoxometalate and methylene blue (MB), [C16H18N3S]4[PMo12O40]·2DMF·H2O (1) and [C16H18N3S]4[GeMo12O40]·2DMF·H2O (2), were synthesized and characterized. X-ray diffraction analysis shows that the organic layers composed of the parallel MB cations and the inorganic layers of discrete Keggin polyoxoanions are alternatively arranged, and UV–vis diffuse reflectance spectra in the solid state indicate the presence of new bands attributed to charge-transfer transitions between the organic dye donors and polyoxometalate acceptors. The two charge-transfer salts 1–2 were used as a solid bulk modifier to fabricate a three-dimensional bulk-modified carbon paste electrode (1-CPE and 2-CPE). The results show that both 1-CPE and 2-CPE present stability and have good electrocatalytic activities toward the reduction of chlorate, bromate and nitrite.