Mechanochemical synthesis of ionic solids based on phosphotungstic acid and triethylamine for photocatalytic dye degradation

Ionic solid catalysts (TTA) based on phosphotungstic acid (PTA) and triethylamine (TEA) were prepared by mechanochemical/thermal treatment of mixtures possessing different mole fractions of constituents under solventless conditions. In contrast to PTA, ionic solids had high thermal stability and they were insoluble in water. Hence, they could be used in heterogeneous catalysis and recycled. The crystallite sizes of selected ionic solids were ∼24 and 30 nm as obtained by Scherrer and Williamson-Hall plots in x-ray diffraction analysis (XRD). Scanning electron microscopy, vibrational spectroscopy, and XRD showed that the Keggin structure of PTA was retained in ionic solids. The catalyst was studied for its effectiveness in sunlight aided degradation of Erichrome black T (EBT) dye. Most ionic solids with X PTA exceeding 0.5 showed superior photocatalytic activity compared to PTA. The degradation reached 87% with 6.0 mg of TTA5 (having PTA/TEA = 5/5) in solution containing 10 mM of EBT.