Supplementary Figure S1. Statistical measurements on particle size and aspect ratio of

Transcription

1 Supplementary Figure S1. Statistical measurements on particle size and aspect ratio of as-prepared Cd 0.5 Zn 0.5 S nanocrystals. a,b,c, Histograms of the particle size distribution of the three-type of twin containing Cd 0.5 Zn 0.5 S nanocrystals. d, The corresponding histograms of average aspect ratios.

2 Supplementary Figure S2. Overview HRTEM images of Cd 0.5 Zn 0.5 S-EN10 nanorod. a, A single nanorod. b, Atomic scale image of one twin plane in the nanorod. A WZ segment was generated in the ZB structure. Note red lines in (a) and (b) indicate that the surface of the nanorod is surrounded by zigzag nanostructures arising from the twin planes.

3 Supplementary Figure S3. Atomic models of twinning Cd 0.5 Zn 0.5 S nanocrystals. a, The zinc-blende (ZB) nanostructure with one-layer {111} twin plane (red color) observed from [-110] direction. b, The corresponding translucent sphere models with the same viewing direction as (a). c and d are the corresponding translucent sphere models viewed from [111] and high-index [-hhk] directions, respectively.

4 Supplementary Figure S4. STEM and EDS analyses of Cd 0.5 Zn 0.5 S twinning nanorod. a, STEM image of a single Cd 0.5 Zn 0.5 S twinning nanorod. b, c, d, and e, The corresponding elemental mapping images, and EDS spectrum. f, Spectra of longitude and latitude line scans indicated by red lines in (b). Inset in (a) was a HRSTEM image taken from the nanorod. The densely distributed twin boundaries can be directly observed as indicated by the red zig-zag line

5 Supplementary Figure S5. Crystal structure and optical properties of Cd 1-x Zn x S-EN10 determined by XRD patterns and UV-vis spectra. a, XRD patterns shows a gradual high-angle transformation from WZ CdS to ZB ZnS. b, UV-vis spectra presents a successive blue shift of the on-set absorption edge from CdS to ZnS. Both (a) and (b) demonstrate the formation of Cd 1-x Zn x S-EN10 solid solutions.

6 Supplementary Figure S6. Kinetic study of the photocatalytic reaction over Cd 0.5 Zn 0.5 S-EN10 photocatalyst. Assuming first order kinetics, the kinetic rate constants were determined to be h -1, h -1, h -1, and h -1 for the four-round tests, indicating the stable photocatalytic behavior. The coefficients of determination (R 2 ) for these linear fittings are 0.997, 0.995, 0.997, and 0.998, respectively. Here, C t,na2s represents to the concentration of Na 2 S at the reaction time t.

7 Supplementary Figure S7. Characterizations of Cd 0.5 Zn 0.5 S nanocrystals with different shapes prepared by the process as described in the Method section. a-d, TEM images of (a) twin-free ZB Cd 0.5 Zn 0.5 S-EN0 spherical nanocrystals, (b) twinned ZB Cd 0.5 Zn 0.5 S-EN5 nanorods with an average aspect ratio of 1.9, (c) twinned ZB Cd 0.5 Zn 0.5 S-NaOH spherical nanocrystals, and (d) Cd 0.5 Zn 0.5 S-EN20 non-uniformed nanocrystals consisted with nanorods and spherical polyhedrons. e and f, XRD patterns and UV-vis spectra of these as-prepared Cd 0.5 Zn 0.5 S

8 nanocrystals. The four insets are the corresponding HRTEM images for the white-circled regions of the TEM images. Scale bar in (a) is 50 nm and can be applied to (b), (c), and (d), while that in the inset of (a) is 2 nm, and is the same for the other three insets. C and H in (e) represent for cubic phase and hexagonal phase, respectively. The gradually increased proportion of WZ hexagonal phase from non-twinning crystals to twinning nanorods as indicated by the XRD patterns can be attributed to the increased percentage of twin-induced WZ segments in longer nanorods. In particularly, except for the Cd 0.5 Zn 0.5 S-EN20 rods, which dominated by a WZ structure, most of Cd 0.5 Zn 0.5 S samples crystallized into the form of ZB with similar crystallinity. There also existed certain differences in the four ZB samples. For instance, Cd 0.5 Zn 0.5 S-EN10 and Cd 0.5 Zn 0.5 S-EN5 have higher contents of WZ, and then Cd 0.5 Zn 0.5 S-NaOH. Pure ZB only occurred in Cd 0.5 Zn 0.5 S-EN0 nanocrystals. Different from the above four samples, crystal structure of Cd 0.5 Zn 0.5 S-EN20 is mainly in the form of hexagonal phase, in well agreement with the TEM observation. It is also interesting to find the different absorption property in Cd 0.5 Zn 0.5 S-EN20 nanocrystals (see Supplementary Fig. S7f). The absorption edge shifts to longer wavelength at ca. 540 nm. We then measured the exact composition of these samples using X-ray fluorescence (XRF) spectrometer as shown in Supplementary Table S1. Obviously, only Cd 0.5 Zn 0.5 S-EN20 presented a Cd/Zn ratio of ca. 7/3. As EN has a stronger coordination effect with Zn than that with Cd, this may explain the loss of Zn (stability constants, logk 3, of Cd(EN) 2+ n and Zn(EN) 2+ n are and 14.11, respectively 59 ); and thus the variations in XRD pattern and UV-vis spectra.

9 Supplementary Figure S8. Emission decay at room temperature for the four as-prepared Cd 0.5 Zn 0.5 S photocatalysts (monitored at 495 nm). The excitation wavelength is 305 nm. Solid lines represent the kinetic fit using exponential decay analysis. Inset is the emission spectra of Cd 0.5 Zn 0.5 S-EN0 (exited at 305 nm), indicating the emission of Cd 0.5 Zn 0.5 S photocatalyts at 495 nm.

10 Supplementary Figure S9. Crystal structure, optical, and morphologic properties of Cd 0.5 Zn 0.5 S twinning rods after serving as catalysts for a 20-h H 2 evolution. a, XRD pattern. b, TEM image. Inset in (a) is the UV-vis spectrum. These unchanged properties not only confirm catalytic feature of the nanorods, but also provide another proof on the stability of the catalyst.

11 Supplementary Table S1. XRF results of the various Cd 0.5 Zn 0.5 S samples. Samples Cd 0.5 Zn 0.5 S-EN0 Cd 0.5 Zn 0.5 S-EN5 Cd 0.5 Zn 0.5 S-EN10 Cd 0.5 Zn 0.5 S-En20 Cd 0.5 Zn 0.5 S-OH Cd/Zn 0.51/ / / / /0.49

12 Supplementary Reference 59. Dean, J. A. Lang's Handbook of Chemistry (Mcgraw-Hill, New York,1985).