## 3 Results and Discussion  
### Physicochemical Properties of the Obtained Samples  
Figure 1 shows the crystalline structure of the as-prepared samples obtained at different calcination temperatures. Apparently, the samples of S\({}_{750}\), S\({}_{850}\), and S\({}_{950}\) exhibited diffraction peaks that were basically attributed to GaN:ZnO solid solution with a wurtzite structure [21]. However, in the comparison of S\({}_{850}\) and S\({}_{950}\), S\({}_{750}\) showed three peaks at 20 values of 30.30, 35.70, and 43.39\({}^{\circ}\), which corresponded to (220), (311), and (400) diffraction planes for ZnGa\({}_{2}\)O\({}_{4}\) (JCPDS card 860415), indicating its incomplete nitridation. Furthermore, the intensity of the peaks corresponding to the GaN:ZnO solid solution in S\({}_{750}\) were weaker than that of S\({}_{850}\) and S\({}_{950}\), which means the higher nitridation temperature induced a higher crystallinity. The peaks around 37\({}^{\circ}\) of the samples exhibited a higher intensity than that of GaN:ZnO solid solution with the general wurtzite structure, which can be attributed to the stacking disorder of the zinc-blende domain [39; 40]. To determine the energy range of photoexcitation, diffuse reflectance spectra are illustrated in Figure 1b. It shows the UV-visible absorption spectra of GaN:ZnO solid solution subjected to different calcination temperatures. The samples showed obvious absorption in the visible light region while the calcination temperature had a certain influence on the band gap of the samples. S\({}_{850}\) displayed an absorption edge at around 450 nm, corresponding to a bandgap of about 2.76 eV. After increasing the calcination temperature, the absorption edge shifted slightly to longer wavelengths because of the increase of the particle size. For S\({}_{750}\), the blue shift in the absorption edge was mainly attributed to the presence of ZnGa\({}_{2}\)O\({}_{4}\). The N\({}_{2}\) adsorption-desorption isotherms (Figure 1c) show that all three samples (S\({}_{750}\), S\({}_{850}\), and S\({}_{950}\)) displayed type-IV isotherms, which correspond to the mesoporous materials. The BET surface areas of S\({}_{750}\), S\({}_{850}\), and S\({}_{950}\) were estimated as 18.3, 44.8, and 11.7 m\({}^{2}\)/g, respectively. Additionally, the average pore sizes were about 4.0, 4.3, and 5.2 nm for the S\({}_{750}\), S\({}_{850}\), and S\({}_{950}\) nanorods (Figure 1d). The main reason for S\({}_{850}\) having a larger surface area than S\({}_{750}\) is that the higher temperature is well situated to the pore-forming effect of the release of gases from the thermal polycondensation of PAN. As for S\({}_{950}\), the increase of the nitridation temperature led to an enlargement of the nanoparticles that make up the nanorods, resulting in a small surface area. Further, the increased average pore size with the nitridation temperatures can be ascribed to the enlarged particles with an enhanced temperature. In most cases, the higher surface area could provide more active sites in the process of photocatalytic H\({}_{2}\) evolution. These results indicate that the change in the specific surface area caused by different nitriding temperatures plays a significant role in the improved photocatalytic performance. Figure 2a-d show the SEM images of Ga(NO\({}_{3}\))\({}_{3}\)-Zn(NO\({}_{3}\))\({}_{3}\)/PAN, S\({}_{750}\), S\({}_{850}\), and S\({}_{950}\). Ga(NO\({}_{3}\))\({}_{3}\)-Zn(NO\({}_{3}\))\({}_{3}\)/PAN nanofibers with diameters of around 180 nm, which possess continuous uniform and unblenished smooth structures. Figure 2b shows a broken fiber morphology of S\({}_{750}\), which can be attributed to the rapid escape of the gas-phase product during the calcination process.