1. A method of synthesizing TiO2/Co3O4 core-shell photocatalysts, comprising:preparing SiO2 hollow nanospheres via sol-gel synthesis in the presence of a non-ionic surfactant and a cationic surfactant;
adding titanium sec-butoxide to a solution containing the SiO2 hollow nanospheres to provide a first combined sample;
calcinating the first combined sample to provide hollow mesoporous TiO2 nanospheres;
adding cobalt nitrate to a solution comprising the hollow mesoporous TiO2 nanospheres to provide a second combined sample; and
calcinating the second combined sample to provide TiO2/Co3O4 core-shell photocatalysts.