Formation of three-dimensionally ordered macroporous TiO2@nanosheet SnS2 heterojunctions for exceptional visible-light driven photocatalytic activity

In this paper, a simple colloidal crystal-templating method assisted by a hydrothermal process has been proposed to prepare novel three-dimensionally ordered macroporous (3DOM) TiO2@nanosheet SnS2 heterojunction photocatalysts. The photoactivities of all the obtained samples were measured by the photodecomposition of rhodamine B (RhB), the photoreduction of Cr(VI) and photocatalytic hydrogen generation from water splitting. In comparison with pure SnS2 nanosheets and 3DOM TiO2, the 3DOM TiO2@ SnS2 sample with a Sn/Ti molar ratio of 7.5 : 100 showed the highest photocatalytic activity for wastewater purification (kapp for RhB solution = 0.035 min(-1) and for Cr6+ solution = 0.0845 min(-1)) and hydrogen generation under visible light irradiation. By means of ultraviolet-visible diffuse reflectance spectra (UV-vis DRS), photoluminescence (PL) spectra, transient photocurrent spectra, electron paramagnetic resonance (EPR) measurements and photocatalytic experiments, a suggested mechanism for the charge generation and transfer in the 3DOM TiO2@ nanosheet SnS2 heterojunction was proposed. The improved charge separation and enhanced photocatalytic activity for the as-prepared TiO2@ SnS2 composition can be attributed to the well-defined 3DOM heterojunction structure and the spatial transfer of the visible-light excited high energy electrons of SnS2 to TiO2. This work will provide a novel route to prepare highly active heterojunction photocatalysts and a new insight into the study of electron migration paths in TiO2@ SnS2 composites.