2.5. Catalytic reduction of CrVI
For the reduction of CrVI, K2Cr2O7 was the source of CrVI and HCOOH was the TH287 donor under an acidic solution. Typically, 20 μL of Pd-NWWs aqueous solution (2.0 g L−1) was added into 10 mL of 0.8 mM K2Cr2O7 + 0.45 M HCOOH mixture solution under gentle magnetic stirring. The reaction process was monitored by measuring the UV–Vis’ absorbance of K2Cr2O7 at 350 nm. For comparison, commercial Pd black was used as the catalyst for the catalytic reduction of CrVI.
3. Results and discussion
3.1. Characterization of Pd-NWWs
Fig. 1. (A) SEM image, (B) EDX spectrum, (C) Pd 3d XPS spectrum, and (D) XRD pattern of Pd-NWWs.Figure optionsDownload full-size imageDownload as PowerPoint slide
The morphology and structure of the as-synthesized Pd-NWWs were further characterized by TEM. The TEM images show that the Pd-NWWs consist of Pd nanowires with an average diameter of 3.5 ± 1.0 nm and length of a few tens of nanometers (Fig. 2A and B). The selected area electron diffraction (SAED) pattern of the Pd-NWWs shows the discrete diffraction rings (Fig. 2C), suggesting that the Pd-NWWs are polycrystalline. Further the high resolution TEM (HR-TEM) image shows the d-spacing of 0.221 nm (Fig. 2D), which is close to the (1 1 1) inter-planar distance of fcc Pd (0.226 nm). Mainly, PAH preferentially binds onto the (1 1 1) facets of Pd nanocrystals, resulting in the restricted growth of the ( 11 1) facets . Moreover, it is clearly observed that fringes are discontinuous, predicting the oriented attachment grown mechanism .