Abstract <p>This paper considers the photocatalytic activity of silicon nitride–based composites in the degradation of the pharmaceutical pollutant ketoprofen (KTF). The composites were obtained by nitriding ferrosilicon with various Eu₂O₃ additives (0–7 wt %) in a combustion mode with a preliminary stage of mechanical activation. The samples were studied using X-ray diffraction analysis, scanning electron microscopy, low-temperature nitrogen adsorption–desorption, X-ray photoelectron spectroscopy, and diffuse reflectance electron spectroscopy. The photocatalytic activity of the samples was evaluated during the oxidative destruction of KTF under UV irradiation, in particular, with the addition of hydrogen peroxide to carry out the Fenton reaction. It was found that the rate constant of the heterogeneous photocatalytic reaction reached a maximum value (<i>k</i> = 0.041 min^–1) for the composite synthesized with the addition of 7 wt % Eu₂O₃. Under conditions of combined heterogeneous photocatalysis and the Fenton process, the modified samples obtained with 3–7 wt % Eu₂O₃ additives showed the highest efficiency; the degree of KTF degradation reached 52–55% in 10 min.</p>