# Recent Advances and Applications of Semiconductor Photocatalytic Technology
## 6 Application
### Wastewater Treatment  
Since the beginning of the 21 st century, the problem of water pollution has become increasingly severe, and it has become a major issue affecting human health that restricts the harmonious  
Figure 10: (**A**) Photocatalytic hydrogen production of all samples under full range illumination (\(\lambda\geq 250\) nm) in sodium sulfite aqueous solution (0.05 M). (**B**) Average photocatalytic hydrogen production rate under full range (\(\lambda\geq 250\) nm) and visible light illumination (\(\lambda\geq 420\) nm) [339]. Figure 9: (**A**) Comparison of the photocatalytic H\({}_{2}\) production activity of g-C\({}_{3}\)N\({}_{4}\), 0.5% PtNi\({}_{x}\)/g-C\({}_{3}\)N\({}_{4}\), 2.5% PtNi\({}_{x}\)/g-C\({}_{3}\)N\({}_{4}\), 5.0% PtNi\({}_{x}\)/g-C\({}_{3}\)N\({}_{4}\), and 10.0% PtNi\({}_{x}\)/g-C\({}_{3}\)N\({}_{4}\) samples using triethanolamine as the scavenger under a 500 W Xe lamp irradiation. (**B**) Photoluminescence (PL) spectra of 2.5% PtNi\({}_{x}\)-g-C\({}_{3}\)N\({}_{4}\) and g-C\({}_{3}\)N\({}_{4}\)[336]. development of society. One of the main symptoms of water pollution is industrial wastewater. Industrial wastewater often includes oil substances, reaction aids, paper stocks, acids and alkaline substances, fiber impurities, dyes, and inorganic salt substances. Industrial wastewater is generally difficult to degrade. Today, methods for decomposing industrial wastewater are mainly biological methods, chemical methods, and physical methods. However, the above three methods do not clean the waste water completely--they all have some drawbacks. In 1977, [PERSON] et al. applied photocatalytic technology to the degradation of pollutants in water systems [340], laying the foundation for the use of photocatalytic oxidation technology in pollutant treatment. In the photocatalytic degradation of water pollution, active substances such as H\({}^{+}\), H\({}_{2}\)O\({}_{2}\), and -OH generated by photocatalysts have a strong oxidizing activity and can deeply oxidize most of the organic pollutants in water into harmless small molecules. Therefore, a photocatalyst can be used for the purification of wastewater containing organic pollutants. Photocatalysis technology as a new high-efficiency and energy-saving modern sewage treatment technology has many advantages in wastewater treatment [341; 342; 343; 344; 345; 346; 347; 348; 349; 350; 351; 352]. Compared to the traditional wastewater treatment method, photocatalytic technology can fundamentally remove pollutants, and, regardless of the pollutants' liquid or gaseous state, photocatalytic technology can have a good degradation effect. In 2001, [PERSON] et al. [351] used methylene blue to simulate environmental wastewater. Their experimental results showed that titanium dioxide based photocatalysts can successfully degrade methylene blue. [PERSON] et al. [352] used UV light to irradiate a titanium dioxide photocatalyst to achieve the degradation of five different dyes (alizarin S, crocein orange G, methyl red, Congo red, and methylene blue). Experimental results showed that the five dyes not only decolorized successfully but also completely decomposed. [PERSON] et al. [174] prepared flexible composite Fe\({}_{2}\)O\({}_{3}\)/TiO\({}_{2}\) nanofibers by combining a traditional electrospinning method and calcination process, which they successfully applied to photocatalytic wastewater treatment and photocurrent detection. In the photocatalytic degradation of rhodamine B experiment, Fe\({}_{2}\)O\({}_{3}\)/TiO\({}_{2}\) nanofibers have higher photocatalytic activity than pure TiO\({}_{2}\) under UV and visible light. The most important thing is that the Fe\({}_{2}\)O\({}_{3}\)/TiO\({}_{2}\) photocatalyst can be recovered by magnetic materials, thereby avoiding secondary pollution to the environment after photocatalytic treatment. [PERSON] et al. [167] synthesized flexible time-like branched TiO\({}_{2}\)/PVDF composites via the electrospinning method and the hydrothermal method.