Phototreatment of Water by Organic Photosensitizers and Comparison with Inorganic Semiconductors

Table 3

Comparison of features of photosensitizers and photocatalyst.

Feature	Photocatalyst	Organic photosensitizers
Light	UV (only 5% of solar spectrum can be used) [15, 68]	Visible light [52, 54]
ROS	Hydroxyl radicals (•OH) and super oxide anion () [1]	Singlet oxygen (^1O2) and also superoxide anion () [23]
Availability	Easily available and extensively used for photocatalytic disinfection and decontamination	Wide range of photosensitizers are available but require to be synthesized hence increasing the cost [17]
Stability	Long-term stability	Some photosensitizers like MB, RB, and Ruthenium complexes are susceptible to photo bleaching. In some cases, photodegradation can convert the photosensitizers into harmless compounds and hence avoid the separation step [46]
Immobilized systems	Immobilized TiO2 systems work less efficiently than in suspension [1]	Quantum yield of immobilized photosensitizer is less than free photosensitizer [8]
Scope of photocatalysis	Efficiently capable of decomposing organic and inorganic pollutants and disinfecting Gram-positive and Gram-negative bacteria [14, 69]	Destruction of Gram-negative bacteria requires positively charged photosensitizer whereas Gram-positive bacteria are readily photodisinfected by anionic and neutral photosensitizers [57]. Very few reports of decomposition of pollutants are published [68, 70–73]