Highly Porous SnO2/TiO2 Heterojunction Thin-Film Photocatalyst Using Gas-Flow Thermal Evaporation and Atomic Layer Deposition

Abstract

Highly porous heterojunction films of SnO2/TiO2 were prepared using gas-flow thermal evaporation followed by atomic layer deposition (ALD). Highly porous SnO2 was fabricated by introducing an inert gas, Ar, during thermal evaporation. To build heterogeneous structures, the TiO2 layers were conformally deposited on porous SnO2 with a range of 10 to 100 cycles by means of ALD. The photocatalytic properties for different TiO2 thicknesses on the porous SnO2 were compared using the degradation of methylene blue (MB) under UV irradiation. The comparisons showed that the SnO2/TiO2-50 heterostructures had the highest photocatalytic efficiency. It removed 99% of the MB concentration, and the decomposition rate constant (K) was 0.013 min(-1), which was approximately ten times that of the porous SnO2. On the other hand, SnO2/TiO2-100 exhibited a lower photocatalytic efficiency despite having a TiO2 layer thicker than SnO2/TiO2-50. After 100 cycles of TiO2 ALD deposition, the structure was transferred from the heterojunction to the core-sell structure covered with TiO2 on the porous SnO2, which was confirmed by TEM analysis. Since the electrons photogenerated by light irradiation were separated into SnO2 and produced reactive oxygen, O-2(-), the heterojunction structure, in which SnO2 was exposed to the surface, contributed to the high performance of the photocatalyst.