According to previous literature, Pt, Se, and Pt–Se NPs were synthesized through a facile and optimized one-step reduction procedure [
46]. The size of the Pt, Se, and Pt–Se NPs was confirmed by transmission electron microscopy (TEM) and dynamic light scattering (DLS) (Fig.
2A and Fig.
S1). The results revealed that the average size of Pt NPs was 5 ± 1 nm, with poor dispersion. Se NPs exhibits spherical shape, with good dispersion and particle size of 10 nm. The size of Pt–Se hybrid structure increased to 20 ± 3 nm, a bit higher than Pt and Se. The distribution of each element on the Pt–Se hybrid NPs was confirmed by energy dispersive spectroscopy (EDS) and High-Angle Annular Dark Field Scanning Transmission Electron Microscope (HAADF). Pt–Se NPs were approximately spherical, similar to the TEM results. In addition, the Pt–Se NPs were observed to have a distribution of C, N, O, Pt, and Se elements. The weight percentage (wt%) of Pt was determined to be 7.64%, while the wt% of Se was 3.64% (Fig.
2B, Fig.
S2, and Table
S1). As shown in Fig.
2C, a strong ultraviolet (UV) absorption peak was observed for H
2PtCl
6 at 265 nm, caused by the [PtCl
6]
2− ion ligand-metal charge transfer transition. The absorption spectra of the mixed solution of H
2PtCl
6 and Na
2SeO
3 were almost the same as those of the aqueous solution of H
2PtCl
6, indicating that H
2PtCl
6 did not interact with Na
2SeO
3 before the reaction took place. However, UV-vis spectra of Pt NPs showed that the peak value at 265 nm disappeared, indicating complete reduction of [PtCl
6]
2− ions. Se NPs did not show obvious peaks. Compared with Pt NPs, the UV absorption peak of Pt–Se NPs at 265 nm also vanished, with a new absorption peak at 300 nm, which was caused by the vibration of the Se NPs. In Fig.
2D, the XRD patterns of Pt, Se, and Pt–Se NPs were observed. The diffraction peaks exhibited by Pt NPs matched the (111), (200), and (220) lattice planes, in agreement with previous measurements reported in JCPDS 80-1268 [
50]. There was a small right shift in the (111), (200), and (220) lattice planes of the Pt–Se nanozymes spectrum, which may be caused by the introduction of Se. Similar to pure Pt NPs, Pt–Se nanozymes containing doped Se may possess crystal structures. There is no typical diffraction peak of crystal Se in the XRD pattern of Pt–Se, indicating that the Se element in Pt–Se may exist in the amorphous form [
51]. To confirm the composition of Pt–Se nanozymes, XPS spectra were collected from the Pt 4f region and Se 3d region. The characteristic binding energies of Pt 4f
7/2 were measured to be 71.5 eV, while the binding energy for Pt 4f
5/2 was found to be 75.0 eV (Fig.
2E), indicating the reduction of Pt (0). An XPS spectrum of the Pt 4f region of Pt–Se nanozymes indicates Pt 4f
7/2 peaks at about 72.1 eV and Pt 4f
5/2 peaks at about 75.4 eV, indicating that it contains element Pt (0). In Pt–Se NPs, the 3d orbit binding energy of Se in the 3d region measured by XPS was found to be about 55.6 eV. Thus, the Pt–Se nanozymes contain Pt in its reduced state (Pt^0) and Se in its reduced state (Se^0). All the above results indicate structural composition of Pt–Se, demonstrating the successful synthesis.