Solar photocatalysis for water disinfection: materials and reactor design

Abstract

As of 2010, access to clean drinking water is a human right according to UN regulations. Nevertheless, the number of people living in areas without safe drinking water is predicted to increase by three billion by the end of this decade. Several recent cases of E. coli and Cryptosporidium contamination in drinking water are also reported in a number of advanced countries. Therefore ensuring the potability of drinking water is urgent, but highly challenging to both the developing and developed world in the future. A combination of solar disinfection and photocatalysis technology offers real possibilities for removing lethal pathogenic microroganisms from drinking water. The time taken for the conventional SODIS process can be greatly reduced by semiconductor (e.g. TiO2, ZnO, nano-heterojunctions) based photocatalysis. This review addresses the fundamental reaction mechanism, advances in materials synthesis and selection and recent developments in the reactor design for solar energy driven photocatalysis using titanium dioxide. The major advantage of using photo-reactors is that they enhance disinfection by increasing photon flux into the photocatalyst. Other major factors affecting such efficiency of solar-based photocatalysis such as the illuminated volume/total volume ratio, catalyst load and flow rate, are discussed in detail. The significance of using immobilised catalysts over the catalyst powder in slurries is also highlighted. It is noted that, despite encouraging early field studies, the commercialisation and mass production of solar photocatalysis systems remains highly challenging. Recommendations for future directions for addressing issues such as mass transfer, requirement of a standard test method, photo-reactors design and visible light absorption by TiO2 coatings are also discussed

Antibacterial properties of F-doped ZnO visible light photocatalyst

“…9). It is known that the holes produced during the visible light irradiation will not have sufficient reduction potential to generate hydroxyl radical by oxidizing water molecules [5,20,41,42]. However, less oxidative species such as superoxide anions and singlet oxygen ( 1 O 2 ) are believed to be responsible for the anti-bacterial action during the visible light induced photocatalysis [5,20].…”

“…For example doping with low concentration of fluorine can significantly improve its photocatalytic activity in visible light, increase the mobility of ROS carriers and hence enhance the antimicrobial activity of ZnO in environments void of UV radiation [18]. Although the antimicrobial property of ZnO has already gained significant attention [19][20][21], its photocatalytic activity in visible light still requires improvement. The aim of this investigation was therefore to synthesize fluorine-doped nanoparticulate ZnO powder via a sol-gel route and to explore the effect of this process on ZnO with respect to its antimicrobial activity against selected pathogens under visible light conditions.…”

Can solar water-treatment really help in the fight against water shortages?

“…In this sense, the main design developments in recent years are low-cost solar reactors for SODIS deployment [12]. These systems favour the collection of global solar UV radiation, using compound parabolic collectors (CPCs).…”

Nanotechnology Solutions for Global Water Challenges

“…It is estimated that SODIS is currently being used by nearly more than 5.5 million people around the world, mainly in the developing regions of Asia, Africa and Latin America. SODIS has been compared with other household water treatment and storage methods and it was found that SODIS was slightly less cost-effective when compared to chlorination; however, the latter requires the distribution of sodium hypochlorite or chlorine tablets, whereas solar energy is widely and freely available (6).…”