Hydrothermal synthesis was used to create four different POM-based compounds, namely {[Co(Hptpm)₂(β-Mo₈O₂₆)_0.5(ξ-Mo₈O₂₆)_0.5]}·H₂O (1), [Co(Hptpm)₂(δ-Mo₈O₂₆)]·H₂O (2), [Co(Hptpm)₂(β-Mo₈O₂₆)] (3) and [Zn(Hptpm)₂(β-Mo₈O₂₆)] (4) (ptpm = 4-[3-(3-pyridine-2-yl-[1,2,4]triazol-4-yl)-propyl]-morpholine). 1–4 containing different octamolybdate isomers were characterized. Compounds 1–4 showed good electrochemical performance and can be utilized as bifunctional sensors for NO₂⁻, H₂O₂, Cr(VI) and Fe(III). Taking compound 1 as an example, the detection limits are 0.081 μM for NO₂⁻, 0.072 μM for H₂O₂, 0.054 μM for Cr(VI) and 0.063 μM for Fe(III), respectively. Compounds 1–4 have good capacitance. Moreover, compounds 1–4 also show good adsorption properties for organic cationic dyes. The cationic dyes include methylene blue (MB), crystal violet (CV) and neutral red (NR). In addition, 1–4 have excellent characteristics that can reduce Cr(VI) to Cr(III) by photocatalytic technology. Within 30 min, the reduction rates were 95.85% for 1, 93.99% for 2, 90.29% for 3 and 88.18% for 4.