CoFe2O4/TiO2-Nb2O5 magnetic catalysts synthesized by chemical and physical mixture applied in the reduction of Cr(VI).

Among heavy metals, chromium stands out, given the high toxicity and carcinogenicity of Cr(VI). The use of magnetic photocatalysts has opened up new possibilities for their large-scale application, given the ease of catalyst separation. The present work was dedicated to the synthesis and characterization of CoFe2O4/TiO2-Nb2O5 magnetic catalysts and their application in the photocatalytic reduction of chromium. Cobalt ferrite and TiO2-Nb2O5 were combined through chemical (sol-gel synthesis) or physical (mortar and pestle) mixing. In preliminary tests to assess the catalytic activity, approximately 60% of salicylic acid degradation was achieved using CoFe2O4/TiO2-Nb2O5. For the tests with chromium, both a synthetic solution and a real effluent were considered, under different reaction conditions. Sodium formate used as a hole scavenger made it possible to achieve chromium removal percentages above 90% in 60 min. Cobalt ferrite stood out for its Cr(VI) removal capacity, but only pure TiO2-Nb2O5 showed considerable total chromium removal capacity. As for the CoFe2O4/TiO2-Nb2O5 combination, only the catalyst obtained by physical mixing was able to remove both Cr(VI) and total chromium. CoFe2O4/TiO2-Nb2O5 catalyst also exhibited considerable magnetic properties. In effluent tests, this catalyst achieved 33.9% removal of total chromium in 60 min of irradiation.