Stabilization Of Nanosized Semiconductors And Their Stormwater Disinfection Performance Investigation

Effective utilization of stormwater is helpful to address the water scarcity occurring globally. Conventional stormwater treatment technology such as bio-filtration system is effective to remove most of the contaminants but fecal bacteria such as E.coli. Hence a disinfection system is needed for stormwater utilization. Comparing to conventional disinfection technology such as chlorine, ozonation and electrochemical disinfection, photocatalytic disinfection has shown great advantage as a low-cost and environmental friendly technology for stormwater disinfection.Among various semiconductors applied in photocatalyis, TiO₂ nanoparticle is the most commonly studied catalyst for water purification. However, due to its ultra-small particle size and polydispersity, separation of nanosized TiO₂ particles from treated water is extremely difficult. High speed centrifugation and membrane filtration are able to separate TiO₂ nanoparticles from water, but a high cost is required. Therefore, to develop a feasible photocatalytic stormwater disinfection method, a simple method to immobilize TiO₂ nanoparticles is highly required.Additionally, conventional semiconductor catalysts such as TiO₂ are only active under light irradiation and they will stop functioning once external irradiation ceases, as the life spans of photoinduced charge carriers and resultant reactive oxygen species are generally around a few nanoseconds. It means that the photocatalytic disinfection is not effective toward bacterial after light is ceased and is lack of continuous sterilization ability. Therefore, semiconductors which are able to deactivate bacteria after light irradiation are also needed to develop reliable photocatalytic stormwater disinfection systems.In the present study, we developed highly recoverable TiO₂-GO composites firstly. Its separation in stormwater and disinfection performance toward E.coli were investigated. Then we developed two kinds of two dimensional ?2D? materials, Tungsten oxide nanodots ?TODs? and Titanium oxide nanosheets ?TONs?, which were capable of storing photoinduced electrons. The nanosized 2D materials were immobilized on glass substrates, forming ultrathin TODs and TONs photocatalytic films, which were able to store electrons under UV irradiation and showed post-illumination bactericidal activity toward E.coli after the irradiation was ceased. The results are as follows:?1? TiO₂-GO composites could be easily separated from water through accelerated sedimentation. For the composites of 1.0 g/L in ultrapure water, its turbidity was declined from 5200 NTU to less than 30 NTU after 5 hours of sedimentation. In the stormwater, its turbidity could also be declined to less than 50 NTU after 8 hours of sedimentation. The accelerated sedimentation of the TiO₂-GO composites was attributed to its larger particle size formed by electron static attraction between positively charged TiO₂ nanoparticles and negatively charged GO nanosheets.?2? TiO₂-GO showed good photocatalytic activity and excellent durability toward E.coli disinfection in stormwater under solar light illumination. When the initial concentration of E.coli was 104 CFU/mL, the bacteria could be removed by TiO₂-2%GO after 90 minutes of irradiation, and no apparent change in the separability of TiO₂-2%GO was observed after 10 treatment cycles. Scavenger experiments revealed that the E.coli removal was mainly caused by-OH and H2O₂ formed during the photocatalysis. TEM analysis showed that the cell walls of E.coli were destroyed during the disinfection.?3? Na₂WO₄ and TiO₂ could be transformed to 2D TODs and TONs, respectively. TODs and TONs were capable of storing electrons due to the reduction/oxidation of W6+/W5+ and Ti4+/Ti3+. respectively. The stored electrons could be released slowly after the light was ceased and reacted with O₂ forming H2O₂ and ·O₂ which were effective to kill E.coli.?4? The prepared 2D TODs and TONs were negatively charged and could be immobilized on glass substrates forming highly transparent TODs and TONs photocatalytic films. The films were able to store electrons under UV irradiation and kill E.coli after the irradiation was ceased.?5? Owing to the different band gap structures of TODs and TONs, the latter could enhance the electron storage capacity of the former. After 60 minutes of UV irradiation, the TODs-TONs hybrid film could store more electrons (14.2±0.1×10^-6 C/cm²) than the total amount of electrons stored in TONs (7.8±0.3×10^-6 C/cm²) and TODs (2.7±0.1×10^-6 C/cm²). As a consequence, the hybrid TODs-TONs film showed higher post-illumination bactericidal activity and could remove more E.coli than TODs or TONs film.Highly recoverable TiO₂-GO composites were synthesized in a simple method and showed good performance for E.oli removal. It would be a promising candidate for stormwater disinfection. Ultrathin and highly transparent TODs and TONs films showed post-illumination bactericidal activity toward E.coli. Our research would be helpful to develop a low-cost, efficient and reliable photocatalytic system for stormwater disinfection.