# Photocatalytic Cementitious Material for Eco-Efficient Construction--A Systematic Literature Review
## 3 Photocatalytic Cemertitious Materials
### Self-Sterilizing Cement-Based Coated Surfaces  
The researchers have shown that photocatalysis reaction induced by light-activated TiO\({}_{2}\) is significantly effective in destructing the pathogenic microorganisms [62; 63; 64; 65; 23]. _Escherichia coli_, _Lactobacillus acidophilus_, _Salmonella enteritis_, and _Clostridium perfingers_ are ranges of test bacteria that have been investigated [52]. The basic photocatalytic disinfection mechanism is mainly caused by an initial attack on the bacteria cell wall. [PERSON], [PERSON] [62] revealed dual effects of superoxide anions (O\({}_{2}\)\({}^{-}\)) on lipid peroxidation that could enhance membrane fluidity and disrupt cell integrity. After eliminating the cell wall protection, the oxidative damage takes place on the plasma membrane of the bacteria, resulting in subsequent rapid death of cell. It was also found that the cell exposed to TiO\({}_{2}\)-UV treatment exhibits rapid cell inactivation at the signaling stages, which affects a restricted set of respiratory components [23].  
Furthermore, the cells exposed to TiO\({}_{2}\)-UV treatment exhibit rapid cell inactivation at the signaling stages, which affects a restricted set of respiratory components [23]. It was possible that superoxide anions (O\({}_{2}\)\({}^{-}\)) might inhibit the bacterial respiration process. For example, _Shewanella oneidensis_ used the cytochromes MtrA, MtrB, MtrC, and OmcA for electron transfer [66; 67; 68]. By the cytochromes, the bacteria were able to transfer the electron from an intracellular region to an extracellular space and have the redox reaction in the outer membrane or extracellular space, known as one of the important steps in bacteria [69]. However, the superoxide anions (O\({}_{2}\)\({}^{-}\)) were highly active, which might further affect the cytochromes stability and/or inhibit the normal redox process in bacterial respiration.  
Bacteria were ubiquitous and they formed the biofilms after attaching on the cementitious materials [70]. Previous studies have reported that the bacteria in the biofilm stage were more tolerant in the harsh environment (e.g., temperature fluctuation, antimicrobial agents) compared to the bacteria in the free-swimming stage. The bacteria and the biofilms  
Figure 8: Mechanism of photoinduced hydrophilicity.  
might further affect the human body and cause serious infection [71; 72]. As a result, the antibacterial and antib biofilm techniques were strongly needed in the cementitious materials. One of the emerging techniques was immobilization of TiO\({}_{2}\) in cementitious materials.  
Immodilization of TiO\({}_{2}\) into cementitious materials has led to the development of versatile self-sterilizing cement-based surfaces that are useful for a wide variety of applications. Self-sterilizing surfaces are particularly useful for construction of microbiologically sensitive places, such as healthcare facilities and manufacturing facilities, that produce microbiologically sensitive products. A previous study demonstrated that the photocatalytic cementitious materials could deactivate the _Escherichia coli_ under UV irradiation within relatively short time [17; 18; 54; 73; 74]. The biocidal capabilities of photocatalytic cement-based surfaces can induce microbial death and maintain the sterile surface. However, compared with air-purification and self-cleaning applications, little research has been carried out to investigate the antimicrobial effect of photocatalytic cementitious materials.