Enhanced Fenton-like degradation of pharmaceuticals over framework copper species in copper-doped mesoporous silica microspheres

Abstract

Copper-doped mesoporous silica microspheres (Cu-MSMs) with the coexistence of Cu(I) and Cu(II) were prepared using a hydrothermal process and characterized by several methods. The characterization studies suggested that 0.91wt% of the copper species could exist in the framework of the mesoporous silica microspheres by chemical binding of SiOCu; excess copper species were located in the extraframework sites, leading to more oxygen vacancies on the surface of the catalysts. The framework Cu of Cu-MSMs was found to be highly effective and stable for the degradation of pharmaceutical pollutants, as demonstrated with phenytoin, ibuprofen and diphenhydramine in the presence of H2O2 at neutral pH values. The conversion of the three pharmaceuticals could reach 100% within 75, 120 and 90min, respectively; the leaching of Cu was much lower than the EU directives and USA regulations. By the studies of electron spin resonance, gas chromatography–mass spectrometry, Fourier-transform infrared spectra, in situ Raman spectra and X-ray photoelectron spectroscopy, an interaction process among the framework Cu of Cu-MSMs, pharmaceuticals and H2O2 was proposed: During the Fenton-like reaction, the framework Cu(I) in Cu-MSMs primarily converted H2O2 into OH, and Cu(I) was oxidized to Cu(II) by H2O2. The pharmaceuticals were attacked by OH to form phenolic intermediates, adsorbing on the surface of Cu-MSMs, complexing with the framework Cu(II), forming Cu-ligands. Cu-ligands interacted with H2O2 and enhanced the reduction rate of Cu(II), resulting in the more Cu(I) production; consequently, accelerated the Cu(II)/Cu(I) cycles on the catalyst surface, leading to more OH generation for the pharmaceuticals oxidation.