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.