Determining the Morphology and Photocatalytic Activity of Two-Dimensional Anatase Nanoplatelets Using Reagent Stoichiometry

Two-dimensional TiO2 anatase nanoplatelets can be synthesized via solvothermal reaction of titanium(IV) isopropoxide in the presence of structure-directing hydrogen fluoride. High resolution electron transmission microscopy (HRTEM), selected area electron diffraction (SAED), and Xray powder diffraction (XRD) show that the resulting nanoplatelets are heavily truncated, octahedral TiO2 anatase nanocrystals with a large fraction of high-energy (001) crystal facets. Systematic studies provide insight into the underlying reaction pathways and the competing, morphology-determining roles of hydrogen fluoride and water during nanocrystal formation. TiF4 can be used as an additional or alternative fluoride source in hydrolytic systems, allowing the study of markedly higher fluoride concentrations than previously reported, and/or avoiding the use of HF as a starting material. The findings can be plotted on a HF:H2O:Ti ternary diagram to provide guidelines for the control of average dimensions, aspect ratio, degree of truncation and, thereby, fraction of (001) crystal facets. Depending on the composition of the reaction system, oriented attachment of the anatase nanoplatelets along either (001) or (101) facets can be observed. The photocatalytic activity of nananocrystals with different aspect ratios, determined in dye degradation experiments, demonstrates higher activity of the (001) than (101) anatase facets.