Surface activation of calcium tungstate by europium doping for improving photocatalytic performance: Towards lanthanide site photocatalysis

Lanthanides doping can improve the performance of photocatalysts due to the enhanced optical absorption or charge separation. Here, we demonstrate the important role of lanthanide in photocatalysis in terms of surface reactivity. The Eu3+ on the surface of CaWO4, especially for the 1st-layer lattice, substantially raised the surface energy by heightening the d-band center, so that the adsorption ability at the surface was improved. Calcination at a proper temperature promoted the mobility of more excited charge carrier to the Eu3+ sites on the catalyst surface. The synergistic effect of the enhanced adsorption ability and carrier mobility improved the photocatalytic performance as in the case of CaWO4 calcined at 600 °C, where Rhodamine B, Ciprofloxacin and nitroblue tetrazolium were degraded at the highest rate among all the CaWO4 samples. Our study provides important insights into lanthanide site photocatalysis (i.e. migration of Eu3+ into the inner part of the crystal contributed to photoluminescence rather than catalysis).