## 5 Multifunctional mPCMs
### Multifunctional mPCMs  
#### 5.1.1 Photocatalytic and Antibacterial Activity  
The design of mPCMs exhibiting various functions and latent heat storage using an inorganic shell has gained growing interest. Due to the functional properties of inorganic materials, it was possible to give other functionalities to mPCMs. Several photocatalytic materials, such as metal oxides (TiO\({}_{2}\), ZnO, SnO\({}_{2}\), Fe\({}_{2}\)O\({}_{3}\), WO\({}_{3}\), In\({}_{2}\)O\({}_{3}\)), sulfides (ZnS), precious metal semiconductors (AgI, Bi\({}_{2}\)O\({}_{3}\), Bi\({}_{2}\)WO\({}_{6}\)), and nonmetallic semiconductors, were employed in the encapsulation of PCMs.  
Double layers shells were designed by combining functional materials and silica for antibacterial and solar photocatalytic properties. [PERSON] et al. encapsulated \(n\)-eicosane with silica/Cadmium sulfide (CdS) as a double-layered shell through the sol-gel method, followed by in situ precipitation [178]. They indicated that the thermal conductivity of \(n\)-eicosane was significantly improved from 0.15 to 1.02 W\(\cdot\)m\({}^{-1}\cdot\)K\({}^{-1}\) due to the shell materials. In addition, they noted that the CdS is a promising semiconductor material activated by visible light. They denoted that \(n\)-eicosane/silica-CdS microcapsules presented an excellent photocatalytic activity to decompose pollutants, which is confirmed by the photo-degradation of about 90 wt% of methylene blue (MB) after 4 h of sunlight illumination. Microcapsules composed of the \(n\)-eicosane and SiO\({}_{2}\)/Ag double-layered shell were de-signed by [PERSON] et al. via interfacial polycondensation process followed by silver reduction [179]. They indicated that the antibacterial test showed that the microcapsules have suitable reactivity against _Bacillus subtilis_ and _Staphylococcus aureus_.  
[PERSON] et al. prepared \(n\)-octadecane/titania microcapsules through the aerosol process with a hydrothermal post-treatment [180]. They demonstrated that the obtained mPCMs have an enthalpy of 92-97 J\(\cdot\)g\({}^{-1}\) with photocatalytic, antibacterial activities, and reacting with mercaptans. [PERSON] et al. developed \(n\)-eicosane/TiO\({}_{2}\) (crystalline form) [168]. Due to the crystalline TiO\({}_{2}\) shell materials, the mPCMs presented a better photocatalytic effect, which could also be an antimicrobial for some Gram-negative bacteria. They indicated that the developed microcapsules have great potential for food preservation and sterilization, medical protective clothing, solar energy storage, etc. Several studies have suggested doping TiO\({}_{2}\) with nitrogen, carbon material, or by combining it with another metal oxide to improve its photocatalytic activity in visible light.  
[PERSON] et al. used ZnO-doped TiO\({}_{2}\) to develop dual-responsive mPCMs with solar photocatalytic activity and enhanced solar energy storage [181]. On the other hand, antibacterial activity was obtained due to the presence of ZnO. Therefore, the developed dual-responsive mPCMs presented significant properties for heat energy storage, medical and photocatalytic applications.  
ZnO was used as a shell material to develop \(n\)-eicosane microcapsules for thermal energy storage, antibiosis photocatalytic, and antibacterial activities [182]. The bifunctional microcapsules were synthesized via in situ precipitation method in an O/W emulsion system. The mPCMs exhibited excellent phase change performances with a latent heat of about 140 J\(\cdot\)g\({}^{-1}\) and high encapsulation efficiency. Furthermore, they depicted that the microcap  
Figure 14: Different shape of multifunctional mPCMs [177].  
sules revealed a high photocatalytic activity. The antibacterial experiments showed that the developed materials have a high antibacterial response against _Staphylococcus aureus_.