Table 2.
Results from the Debye scattering equation (DSE) analysis of P90 and P25 using synchrotron wide-angle X-ray scattering (WAXTS) data and the bipyramids (BIPY) and/or prismatic BIPYPAR models for anatase nanocrystals (NCs). Averages are all mass based: equatorial width (<Lw>M) and length (<2Lh>M) of bipyramids, their relative dispersions (σw/<Lw>M and σh/<2Lh>M) and correlation angle (φ) between growth directions. The aspect ratio (AR) is computed from the average width and length of the (pristine or recovered) bipyramids. {101} and {001} surface areas (as % of the total area) are calculated by summing the contribution of all NCs in the population of bipyramids, each NC weighted by its number fraction. The diameter (<D>M) and its relative dispersion (σ/<D>M) is provided for rutile; for anatase, it refers to the sphere of equivalent volume to that of bipyramids. The number-based averages values are reported in Table A2.
| Parameter | P90 (BIPY) | P90 (BIPYPAR) | P25 (BIPYPAR) | |||
|---|---|---|---|---|---|---|
| Anatase1 | Rutile | Anatase | Rutile | Anatase | Rutile | |
| <Lw >M, (nm) | 13.75 | - | 13.73 | - | 23.00 | - |
| <2Lh>M (nm) | 13.09 | - | 13.18 | - | 20.71 | - |
| σw/<Lw>M (×100) | 37.75 | - | 37.75 | - | 41.32 | - |
| σh/<2Lh>M (×100) | 50.06 | - | 51.25 | - | 50.98 | - |
| φ (°) | 41.00 | - | 42.54 | - | 42.80 | - |
| AR = <2Lh>M/<Lw> M | 0.95 | - | 0.95 | - | 0.89 | - |
| {001}, {101} surface % | 21.3, 78.8 | - | 20.86, 79.14 | - | 22.73, 77.37 | - |
| SSA (m2/g) | 147.4 | 146.6 | 95.6 | |||
|
<D>M, (nm) σ/<D>M (×100) |
14.22, 36.07 | 18.13, 24.47 | 14.17, 36.08 | 18.19, 22.44 | 23.74, 9.68 | 41.85, 52.62 |
| wt% | 87.00 | 13.00 | 86.83 | 13.17 | 89.59 | 10.41 |
| B (Å2), Ti, O | 0.31, 0.89 | 0.44, 0.80 | 0.30, 0.84 | 0.44, 1.00 | 0.37, 0.99 | |
| S.o.f., Ti 2 | 0.94 | - | 0.95 | - | 0.92 | - |
| GoF | 11.57 | 12.12 | 11.05 | |||
1 A small fraction (amounting to ca. 20%) of the BIPY largest NCs was replaced by the prismatic shape to save computational time. NCs within the bivariate population having AR > 2.5 (0.4 wt% in P25 and 2.0 wt% in P90) were modelled as prisms.2 The slightly below unity values are likely due to the use of atomic form factor of neutral Ti atoms rather than the positively charged ions.