Enhanced catalytic performance of Co3O4/Eu2O3 with sulfur-modification in activating peroxymonosulfate for removal of methylene blue

Co3O4 is a promising heterogeneous catalyst for activating peroxymonosulfate (PMS) to degrade refractory organic wastewater. However, a further improvement in its catalytic performance towards PMS is highly needed for practical applications. For this goal, we prepared sulfur-modified Co3O4/Eu2O3 nanocomposite as the PMS activator using a facile oxalate-pyrolysis approach with thiosulfate as the sulfur source in this study. Methylene blue (MB), a typical cation dye used in diverse applications, was chosen as the degradation model to evaluate the performance of the catalysts. Under the conditions of catalyst dosage of 0.04 g L−1, PMS concentration of 0.6 mmol L−1 and reaction temperature of 25 °C, an MB degradation ratio up to 99.49% was achieved in the sulfur-modified Co3O4/Eu2O3-PMS reaction system within 30 min. Impressively, the reaction rate constant for MB degradation in this system was 0.1704 min−1, which was vastly higher than that in the systems of Co3O4/Eu2O3-PMS and single PMS. In addition, it was confirmed that sulfur was bonded on the surface of Co3O4/Eu2O3 in the form of SO42−. The increased specific surface area and enhanced polarization effect towards PMS caused by the modification of sulfate were regarded as the main reasons for the boosted catalytic performance of Co3O4/Eu2O3. Moreover, it was proven that MB degradation in the sulfur-modified Co3O4/Eu2O3-PMS system was the result of co-action of ˙SO4−, ˙OH, ˙O2− and 1O2 according to the electron paramagnetic resonance (EPR) tests. This work offers a new concept for the design and preparation of non-metal functionalized heterogeneous cobalt-based catalysts for effective PMS activation and rapid removal of recalcitrant pollutants.