Fabrication of lanthanum and nitrogen – co-doped SrTiO3 – TiO2 heterostructured macroporous monolithic materials for photocatalytic degradation of organic dyes under visible light

Abstract

Herein, we demonstrate a facile way of fabricating visible-light-active lanthanum and nitrogen – co-doped SrTiO3 – TiO2 heterostructured macroporous monolithic materials with bicontinuous morphology by impregnating strontium and lanthanum ions into a preformed porous TiO2 gel in aqeuous solution containing urea followed by heat treatment in NH3 atmosphere. The SrTiO3 macroporous monolithic materials were formed by a solid-state reaction between the TiO2 gel phase and precipitated SrCO3, while Sr2+ was partially substituted with La3+ ions. The SrCO3 was precipitated within the TiO2 wet gel by the reaction between impregnated Sr2+ and CO2, which was produced by hydrolysis and decarbonation of a chelating agent in the TiO2 wet gels and by hydrolysis of urea at 60 °C. X-ray powder diffraction studies showed that the incorporation of strontium, lanthanum, and nitrogen could effectively retard the phase transformation of TiO2 from anatase to rutile and growth of crystallites. XPS analysis confirmed that lanthanum atoms were incorporated into the SrTiO3 lattice by substituting strontium atoms, and nitrogen was incorporated in the TiO2 lattice (i) substitutionally forming Ti – N-bonds and (ii) interstitially. The resultant lanthanum and nitrogen – co-doped SrTiO3 - TiO2 heterostructured monolithic materials retained a narrow macropore size distribution at the diameter ∼1.7 μm.