Photochemical construction of free-standing Sn-filled SnO2 nanotube array on a solution surface for flexible use in photocatalysis

For the first time, a free-standing Sn-filled SnO2 nanotube array has been fabricated at the air-water interface by a one-step photochemical route at room temperature. SnSO4, sodium lauryl sulfate (SLS), and diluted H2SO4 aqueous solution were used as precursors. Under ultraviolet irradiation, a dense SnO2 film first formed and covered the entire surface of the solution, resulting in an anoxic environment in the solution. The film can directly act as a kind of substrate, without the need for an additional solid substrate. The subsequent photochemical reactions would induce production of Sn tetragonal prisms on the film under the assistance of SLS in anoxic conditions. Simultaneously, the Sn4+, also derived from the photochemical reactions, hydrolyzes into SnO2 surrounding the tin prism to form the tube wall with a rectangular cross-section. Such nanotube arrays can be used as an effective photocatalyst for degrading methyl orange. Because of its free-standing ability, the nanotube array can be floated on solution surfaces, transferred on any desired substrate, or dispersed in solutions according to practical applications. This route is green, simple, and reproducible, generates high yields and can be extended to prepare other free-standing doped semiconductor micro/nano-structured arrays.