Crystal facet effect of tin dioxide nanocrystals on photocatalytic degradation and photo-assisted gas sensing properties

Crystal facet effects have been widely studied in the field of photocatalysis and gas sensing in recent years. However, little attention has been paid to the crystal facet effect of tin dioxide (SnO2) on photocatalysis. In the present study, SnO2 nanocrystals with different exposed crystal facets were fabricated. The crystal facet effect of SnO2 on photocatalytic degradation of several typical water pollutants was studied for the first time. The results showed that elongated octahedral SnO2 nanocrystals with coexisting {221} and {110} facets displayed a superior photocatalytic degradation performance compared with octahedral SnO2 with dominant {221} facets and lance-shaped SnO2 with dominant {110} facets, suggesting a strong synergistic effect between the two crystal facets. In addition, this work further realized the detection of ammonia at room temperature through the crystal facet effect combined with photo-assistance. The relevant photocatalytic mechanism and gas sensing mechanism were analyzed in detail based on a series of experimental characterization techniques (including XPS, UV/vis absorption spectroscopy and transient photo-current responses) and theoretical calculations. It was found that the heterojunction formed between the crystal facets could promote the separation of photo-generated charges, which was key to improving the photocatalytic performance. Meanwhile, the efficient adsorption of ammonia on high-energy {221} facets was key to improving the gas sensing performance. The results greatly enrich the research on performance control of functional nanomaterials through crystal facet engineering, which has important practical significance in the field of environmental monitoring and governance.