## 1 Introduction  
In the last few decades, with the rapid development of social economies and the continuous expansion of industrial production, environmental pollution has become one of the most important issues in society. In particular, the polluted water from organic dyes, such as Rhodamine B (RhB), has become a serious threat to the environment and human health [1; 2; 3; 4; 5]. Semiconductor photocatalysts can degrade organic pollutants in wastewater under solar light irradiation, saving energy and protecting the environment, and thus attracting tremendous attention [6; 7; 8]. However, traditional semiconductor photocatalysts can only respond to ultraviolet irradiation that occupies about 5% of solar light, which severely limits their practical applications in the utilization of solar light [9; 10; 11; 12; 13]. Therefore, it is urgent to develop photocatalysts that can be excited under visible light irradiation [14].  
In recent years, silver-based photocatalysts have attracted widespread attention. Among them, Ag\({}_{3}\)PO\({}_{4}\) has been extensively studied due to its narrow band gap (about 2.40 eV) and excellent photocatalytic activity under visible light [15; 16; 17]. However, the speedy recombination of photoexcited electron-hole pairs and poor light stability severely weakens its photocatalytic performance [18; 19; 20; 21; 22]. Subsequently, combining Ag\({}_{3}\)PO\({}_{4}\) with other semiconductors to form heterojunction has proved to be a promising strategy [23; 24; 25; 26; 27].  
As a direct wide-bandgap semiconductor, SnO\({}_{2}\) has been widely applied to catalysts, gas sensing and batteries [28; 29; 30; 31; 32]. Due to its good conductivity and stability, SnO\({}_{2}\) is often combined with other semiconductors to form heterojunction, which promotes the separation of photogenerated electron-hole pairs [33; 34; 35]. For example, Ag\({}_{3}\)PO\({}_{4}\)/SnO\({}_{2}\)[36; 37], Ag\({}_{3}\)PO\({}_{4}\)/SnO\({}_{2}\)/porcine bone [38], AgCl/SnO\({}_{2}\)[39] and Ag/AgCl/SnO\({}_{2}\)[40], show enhanced photocatalytic activity over a single photocatalyst.  
In addition, in order to overcome the difficulty in recycling the powder photocatalyst, carbon cloth is usually used for photocatalyst support [5; 41; 42]. [PERSON] et al. designed and prepared TiO\({}_{2}\)/Bi\({}_{2}\)WO\({}_{6}\) nanostructured heterojunctions on carbon fibers, as an effective and weaveable visible-light photocatalyst [5]. [PERSON] et al. reported on the design and preparation of C\({}_{3}\)N\({}_{4}\) nanosheets on carbon-fiber cloth as a filter-membrane-shaped photocatalyst [41]. [PERSON] et al. successfully prepared the heterostructures of CuS/ZnO/CFs, which showed improved photocatalytic activity in the degradation of methylene blue (MB), under visible light irradiation [42]. This is mainly because carbon cloth has a large specific surface area, excellent conductivity and good stability [43; 44]. This not only facilitates the recovery of the photocatalyst, but also helps to increase the contact area of the photocatalyst with the organic dye solution and sunlight, in turn quickly transferring the photogenerated electrons to enhance the separation efficiency of photogenerated electron-hole pairs [45].  
Herein, we synthesized Ag\({}_{3}\)PO\({}_{4}\)/SnO\({}_{2}\) heterojunction on carbon cloth using a two-step method. The results showed that the Ag\({}_{3}\)PO\({}_{4}\)/SnO\({}_{2}\)/CC heterojunction exhibited a remarkable photocatalytic performance for the degradation of RhB under the visible light irradiation. Furthermore, the structure and possible mechanism of the enhanced photocatalytic activity of the Ag\({}_{3}\)PO\({}_{4}\)/SnO\({}_{2}\)/CC heterojunction are discussed in detail.