Electrocatalytic, photocatalytic, fluorescence sensing and CO2RR properties of a series of homopolymolybdate hybrid coordination polymers

Abstract

By using three different organic ligands, four homopolymolybdate-based coordination polymers were successfully synthesized, namely [Cu(MET)₂][H₂(γ-Mo₈O₂₆)] (1), [Zn(MET)₂(H₂O)₂][H₂(γ-Mo₈O₂₆)] (2), [Cu₂(pca)₂(H₂O)₄(β-Mo₈O₂₆)_0.5]·H₂O (3) and [Cu(bpy)(Mo₂O₇)] (4) (MET = 4-(3-imidazol-1-yl-ethyl)-4H-[1,3,4]triazole, pca = 2-pyrazinecarboxylic acid, bpy = 2,2′-bipyridyl). The asymmetric ligand MET induces the 1D chain structures of 1 and 2. Both the N and O donors in pca coordinate with the metal ions to induce the formation of a 3D framework of 3. Coordination polymer 4 shows an infinite Mo–O chain covered with [Cu(bpy)]²⁺ subunits. The carbon paste electrodes (CPEs) of 1 and 4 possess excellent multifunctional electrocatalytic activities for the reduction of KNO₂, H₂O₂, and KBrO₃ and the oxidation of ascorbic acid (AA). Coordination polymers 1–4 show photocatalytic activities for the degradation of methylene blue (MB) under ultraviolet irradiation. The best photocatalytic effect of 4 can reach 64.2%. The CO₂ electrocatalytic reduction (CO₂RR) performances of the coordination polymers were also studied. Furthermore, coordination polymers 1 and 2 show fluorescence sensing properties for Hg²⁺. 1-CPE and 4-CPE can act as nitrite and H₂O₂ amperometric sensors. For example, the response time of 1-CPE for nitrite was 4.12 s and the detection limit was 8.45 × 10⁻⁶ M. In fluorescence sensing experiments, the fluorescence intensities decrease by more than 72.9% when the Hg²⁺ concentration is 100 μM.