A series of four-substituted polyoxometalate-thiacalix[4]arene-based materials for the efficient photocatalytic reduction of Cr(vi)

Abstract

Efficient removal of Cr(VI) from water represents one of the hotspots in global environmental protection. Herein, three isostructural polyoxometalate-thiacalix[4]arene-based coordination materials, namely [Mn₂L₂(H₂O)₂][H₃Mn₄PW₁₀O₄₀]·2C₂H₅OH·4H₂O (1), [Cd₂L₂(H₂O)₂][H₃Cd₄PW₁₀O₄₀]·C₂H₅OH·3H₂O (2) and [Ni₂L₂(H₂O)₂][H₃Ni₄PW₁₀O₄₀]·2C₂H₅OH·5H₂O (3), were prepared under solvothermal conditions (L = tetra-(2-mercaptopyridine 1-oxide)-thiacalix[4]arene). Single-crystal X-ray diffraction analysis showed that they featured rarely reported four-substituted M₄PW₁₀ (M = Mn(II), Cd(II), or Ni(II)). These coordination compounds were employed as efficient photocatalysts for Cr(VI) reduction without the addition of sacrificial agents. The experimental results indicated that 1 possessed the highest photocatalytic activity. The influence of the energy band structure of the photocatalyst on Cr(VI) reduction was also explored. Furthermore, the Bi₂WO₆/1 composite material was successfully prepared. The optimized Bi₂WO₆/1 photocatalyst (80Bi₂WO₆/1) exhibited a remarkably efficient photocatalytic activity, reducing 91% of Cr(VI) within 20 min. This research provides a perspective for the design and application of the polyoxometalate-thiacalix[4]arene-based photocatalysts in the treatment of environmental pollutants.