## 3 Results and Discussion
### Photocatalytic Performance
The SEM image of Ag\({}_{3}\)PO\({}_{4}\)/SnO\({}_{2}\)/CC after photocatalysis is shown in the Supplementary Materials Figure S2, and the structure and morphology of Ag\({}_{3}\)PO\({}_{4}\)/SnO\({}_{2}\)/CC is still well-preserved. To further study the dominant reactive species in photodegradation, radical trapping experiments of Ag\({}_{3}\)PO\({}_{4}\)/SnO\({}_{2}\)/CC were carried out. In this experiment, benzoquinone (BQ, 1.0 mmol/L), ammonium oxalate (AO, 1.0 mmol/L), and isopropyl alcohol (IPA, 0.5 mL) were used as scavengers for -O\({}_{2}\)-, h\({}^{+}\) and -OH, respectively [41]. The experimental results are displayed in Figure 9b, where 83.7%, 65.5% and 41.1% of RhB was degraded when the BQ, IPA and AO were added, respectively. This indicates that the photocatalytic reaction mainly depends on the h\({}^{+}\), while -O\({}_{2}\)- and -OH only have a slight effect. Therefore, the highly enhanced photodegradation achieved on Ag\({}_{3}\)PO\({}_{4}\)/SnO\({}_{2}\)/CC can be assigned to its heterostructure. Based on the experimental results above, a possible mechanism for highly efficient electron-hole separation is proposed, to explain the improved visible light photocatalytic properties of the Ag\({}_{3}\)PO\({}_{4}\)/SnO\({}_{2}\)/CC sample, as illustrated in Figure 10. The band structure of Ag\({}_{3}\)PO\({}_{4}\) and SnO\({}_{2}\) in the figure is drawn based on the data previously reported in other papers [36; 38; 51; 53; 54]. For the Ag\({}_{3}\)PO\({}_{4}\)/SnO\({}_{2}\)/CC heterojunction, the conduction band (CB) and valence band (VB) edge potentials of Ag\({}_{3}\)PO\({}_{4}\) are more negative than that of SnO\({}_{2}\)[36]. It is well-known that SnO\({}_{2}\) has no absorption response to visible light [55]. However, Ag\({}_{3}\)PO\({}_{4}\) can generate excited-state electrons and holes under visible light irradiation [56]. When the sample is under the visible light irradiation, the excited-state electrons in the CB of Ag\({}_{3}\)PO\({}_{4}\) can easily be transferred to the surface of SnO\({}_{2}\). Subsequently, electrons would migrate quickly to the surface of the carbon cloth, because of the one-dimensional structured SnO\({}_{2}\) nanorods and excellent conductivity of the carbon cloth [42]. This further improves the separation efficiency of photogenerated electron-hole pairs. Eventually, the electrons in the carbon cloth reduce O\({}_{2}\) to produce -O\({}_{2}\)- for degrading RhB molecules, and the holes remaining at the VB of Ag\({}_{3}\)PO\({}_{4}\) directly decompose the RhB into CO\({}_{2}\), H\({}_{2}\)O, and other inorganic molecules [47]. Figure 8: **(a)** Time-course variation of C/C\({}_{0}\) of MB over various catalysts, **(b)** The plots of In(C\({}_{0}\)/C) versus time of various catalysts. Figure 9: Stability study on the photocatalytic degradation of RhB over Ag\({}_{3}\)PO\({}_{4}\)/SnO\({}_{2}\)/CC heterojunction **(a)**. Photocatalytic activities of the Ag\({}_{3}\)PO\({}_{4}\)/SnO\({}_{2}\)/CC heterojunction for the degradation of RhB in the presence of different scavengers **(b)**. In order to reveal the separation and recombination of photogenerated electron-hole pairs of catalysts, Supplementary Materials Figure S3 shows the PL spectra of Ag\({}_{3}\)PO\({}_{4}\)/CC and Ag\({}_{3}\)PO\({}_{4}\)/SnO\({}_{2}\)/CC heterojunction. Generally, the lower PL intensity means that there is lower recombination of the photoinduced electron-hole pairs [57]. As shown in Supplementary Materials Figure S3, the PL intensity of Ag\({}_{3}\)PO\({}_{4}\)/SnO\({}_{2}\)/CC heterojunction is weaker, when compared with that of Ag\({}_{3}\)PO\({}_{4}\)/CC, which can be attributed to the formation of the heterojunction between Ag\({}_{3}\)PO\({}_{4}\) and SnO\({}_{2}\) on carbon cloth. Furthermore, it can be seen from Supplementary Materials Table S1 [58; 59; 37] that the photocatalytic performance of the Ag\({}_{3}\)PO\({}_{4}\)/SnO\({}_{2}\)/CC heterojunction is much better than most of the results previously reported.