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

Abstract

Two-dimensional TiO 2 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 TiO 2 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. TiF 4 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:H 2 O: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.

New insight on facet-dependent physicochemical properties of anatase TiO2 nanostructures for efficient photocatalysis

“…The lattice spacing of 0.35 nm and 0.235 nm, respectively, confirm the exposure of the {101} and {001} facets28 .The much thinner TF80 shows clear lattice spacing of 0.19 nm which can be assigned to the (020) and (200) planes. TF0 has an irregular morphology, even its lattice fringe can be observed clearly.…”

Solvothermal Temperature Drives Morphological and Compositional Changes through Dehydroxyfluorination in Anatase Nanoparticles

“…Finally, increasing the reaction temperature (from 90 to 160 °C) induces the decrease of the titanium vacancies, that is the extent of the hydroxyfluorination, as revealed by real‐space refinements of pair distribution function (PDF) data . Nevertheless, the reaction temperatures typically used in the literature commonly range from 150 to 200 °C . In order to understand how the temperature affects both the composition and the morphology of anatase nanoparticles, we systematically investigated both aspects in the reaction temperature range of 110–190 °C.…”

Probing the size dependence on the optical modes of anatase nanoplatelets using STEM-EELS

“…26 Assuming this zone axis, in Figure 1b, the probe is equidistant from the {010} edges of the platelet, along the line of pixels marked by open circles. Each EEL spectrum is labeled according to the distance of the probe, x, from a {100} edge, where x = 0.…”

“…26 Platelets oriented in the [100] zone axis are referred to as 'edge-on'. In contrast to the case of a face-on platelet, the effect of thickness in the edge-on configuration plays a double role in the determination of the features of the EEL spectrum.…”

“…26 In the same study, the samples were characterized using X-ray diffraction (XRD), energy-dispersive Xray spectroscopy (EDX) and electron diffraction (ED). The size distribution of the platelets was characterized by means of intensity profiles extracted from bright-field TEM images (see Figure S4 and S5 for histogram plots of length and thickness distribution).…”