Amperometric sensing and photocatalytic properties under sunlight irradiation of a series of Keggin–AgI compounds through tuning single and mixed ligands

Abstract

By using a single conjugate ring-rich ligand L^a or L^b and mixed ligands L^a/L^b, eight Keggin–Ag^I-based compounds, namely [Ag₄L^a₅(SiW₁₂O₄₀)]·28H₂O (1), [Ag₃L^a₄(PW₁₂O₄₀)] (2), [Ag₃L^a₂(H₂O)(PW₁₂O₄₀)] (3), [Ag₄L^b₄(SiW₁₂O₄₀)] (4), [Ag₃KL^b₄(SiW₁₂O₄₀)]·H₂O (5), [Ag₆L^b₆(PMo₁₂O₄₀)₂] (6), [Ag₄L^aL^b₃(C₁₄H₁₀O₂)(SiW₁₂O₄₀)]·8H₂O (7) and [Ag₄L^a₂L^b₄(GeMo₁₂O₄₀)] (8) (L^a = 2,3-diphenylpyrazine, L^b = 2,3-diphenylquinoxaline, C₁₄H₁₀O₂ = 1,2-diphenyl-ethane-1,2-dione), were successfully synthesized by controlling the reaction parameters and well established by single-crystal X-ray diffraction, elemental analyses, and IR spectra. Compounds 1–3 are based on the L^a ligand, while 4–6 are based on L^b. The mixed L^a/L^b ligands induce the formation of 7 and 8. In compound 1, the linear [Ag₄L^a₄]⁴⁺ subunits link SiW₁₂ anions to form a chain. Two adjacent chains connect each other through POM anion bonds and a screw-like double track is built. Compound 2 is composed of 1D leaf-like Ag^I-L^a chains, which are further linked by anions to build a 2D grid-like layer. Compound 3 was obtained under the same conditions as 2 except at a different temperature. In 3, the inorganic double chains are connected by linear metal–organic clusters [Ag₃L^a₂]³⁺ and a 2D layer is formed. Compounds 4 and 5 were also obtained at different temperatures. In 4, the adjacent grid-like layers share the same Ag ions to construct a 3D framework. Compound 5 is composed of 1D cycle-connecting-cycle chains, which are further linked by anions and Ag ions to build a 3D structure. Compound 6 is a 3D framework, with dissociative anions accommodated in it. Compounds 7 and 8 are composed of mixed organic ligands L^a and L^b. Compound 7 has two kinds of chains, which are linked by anions to form a “ladder”. Compound 8 contains discrete anions and [Ag₂L^aL^b₂]²⁺ units. The title compound modified CPEs can act as amperometric sensors for detecting hydrogen peroxide, potassium bromate and potassium nitrite. Compounds 1–8 have excellent photocatalytic capacity for degradation of organic dyes MB and RhB under the sunlight irradiation.