Synthesis of Catalysts and Photocatalytic Degradation of Methyl Red Using Keggin Tungstoborates Substituted by Transition Elements as Catalysts

Five Keggin Tungstoborates with K_n[BW₁₁O₃₉Z(H₂O)] (BW₁₁Z, Z = Cr(1), Mn(2), Fe(3), Ni(4), Co(5)) were synthesized by one-pot method. The structures and properties of these compounds were characterized by Fourier transform infrared spectroscopy (FT–IR), Ultraviolet spectrum (UV), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS). By changing the type and concentration of catalyst, initial concentration and pH of methyl red (MR) solution, the activity of them as photocatalysts to degrade MR solution was examined. The order of photocatalytic activity of BW₁₁Z was as follows: 1 > 2 > 3 > 4 > 5. Compound 1 has the highest photocatalytic degradation activity for 25 μmol/L MR solution, and the degradation efficiency can reach 97% within 240 min with 20 mg/L. When the initial concentration of MR solution is 10 μmol/L, the degradation efficiency can reach 98% in 20 min by using 1 as catalyst. The degradation efficiency of 25 μmol/L MR solution is the best which can reach 89% in 50 min at pH = 1.5 using 1 as catalyst. In addition, the degradation efficiency of MR with 25 μmol/L is the highest with 98% in 20 min by using 3 as catalyst with 28 mg/L.