Singlet Oxygen Photosensitizing Materials for Point‐of‐Use Water Disinfection with Solar Reactors

Abstract

Singlet molecular oxygen (1O2) is a potent electrophile and a strong oxidizing agent and can be easily generated by photosensitization via illumination of appropriate dyes with visible light. This short‐lived reactive oxygen species is able to photooxidize many electron‐rich organic compounds and, therefore, 1O2 can damage many cellular components, such as membrane lipids, proteins and DNA, causing the photoinactivation of microorganisms in water. This Review summarises the most relevant work to date on solar water disinfection by photocatalytic 1O2 production, using photosensitizing materials suitable for their use in solar reactors for water treatment. The prototypes were equipped with compound parabolic collectors of sunlight and designed for point‐of‐use water treatment. The choice of the type of dye (RuII complexes or fullerenes) and polymeric support for the preparation of the 1O2 photosensitizing material, as well as the most important photophysical and operational parameters to be optimized to achieve efficient water disinfection with solar reactors, will be discussed.

Water Disinfection by Immobilized Photosensitizers

“…Further development of the method may include using sunlight as the illumination source, as proposed previously by García-Fresnadillo [7,26,27]. Since bacterial eradication by immobilized PSs occurs effectively even at a very moderate light fluence rate (1.25 mW/cm 2 ), exposure to much more intense sunlight is expected to significantly increase the efficiency of water disinfection.…”

“…The Type II reaction is accompanied by energy transfer to molecular oxygen dissolved in an aqueous phase [5]. The photosensitizers typically interact with triplet oxygen species to produce reactive oxygen species (ROS), such as singlet oxygen, superoxide anion, hydroperoxyl radical, hydrogen peroxide, and hydroxyl radical [6,7]. In nature, singlet oxygen is generated in neutrophils and macrophages for killing microorganisms.…”

Nanomolecular singlet oxygen photosensitizers based on hemiquinonoid-resorcinarenes, the fuchsonarenes

“…6 However, the destructive potential that makes SO hazardous can also be harnessed in benecial applications. These applications are largely destructive involving photoinduced deactivation of undesirable biological entities 7,8 (i.e., viruses, bacteria) and photodecomposition of environmental pollutants. 9,10 However, SO has also been used in a constructive sense, it being a highly effective reagent in chemical syntheses.…”

Cu(i) diimine complexes as immobilised antibacterial photosensitisers operating in water under visible light

“…Currently-used photosensitisers include organic compounds 9,10 (which usually possess nanosecond excited-state lifetimes), porphyrins, and complexes of the 2nd and 3rd row transition metals (including Ir, Ru, Pt, Pd and Os) [12][13][14][15][16][17][18][19][20][21][22][23] which are either rare, expensive, or both. More accessible alternatives are therefore beginning to be developed as photosensitisers.…”