Synthesis, crystal structure and photocatalytic studies of new oxyfluoride Cu5AsO5F5

Abstract

A new photocatalyst Cu5AsO5F5, a metal oxyfluoride comprising a p-block cation, has been synthesized via the hydrothermal method. Single-crystal X-ray diffraction studies reveal that the compound crystallizes in the orthorhombic space group Pnma (no. 62) with lattice parameters a = 14.9966(18) Å, b = 6.0553(12) Å, c = 8.5066(14) Å and Z = 4. The basic geometry comprises of three tetra-coordinated units of [Cu(III)OF3], [Cu(I)O2F2] and [As(V)O4], and two penta-coordinated units of [Cu(II)O2F3]. Cu5AsO5F5 proves to be good photocatalyst, showing ∼90% methylene blue (MB) dye degradation under sunlight, though the efficacy increases by two-fold in presence of H2O2. Morphological studies reveal rectangular shaped particles with greater surface area, which may have enhanced dye degradation. Density functional theory (DFT) studies is also commensurate with the experimental findings. TG-DTA shows a weak endothermic response at 390 ⁰C and a strong exothermic response at 450 ⁰C, which corresponds to the mass loss of F2 and Cu2O respectively.