Inactivation of E. Coli in Water Using Photocatalytic, Nanostructured Films Synthesized by Aerosol Routes (original) (raw)
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Coatings, 2014
In damp environments, indoor building materials are among the main proliferation substrates for microorganisms. Photocatalytic coatings, including nanoparticles of TiO 2 , could be a way to prevent microbial proliferation or, at least, to significantly reduce the amount of microorganisms that grow on indoor building materials. Previous works involving TiO 2 have already shown the inactivation of bacteria by the photocatalysis process. This paper studies the inactivation of Escherichia coli bacteria by photocatalysis involving TiO 2 nanoparticles alone or in transparent coatings (varnishes) and investigates different parameters that significantly influence the antibacterial activity. The antibacterial activity of TiO 2 was evaluated through two types of experiments under UV irradiation: (I) in slurry with physiological water (stirred suspension); and (II) in a drop deposited on a glass plate. The results confirmed the difference in antibacterial activity between simple drop-deposited inoculum and inoculum spread under a plastic film, which increased the probability of contact between TiO 2 and bacteria (forced contact). In addition, the major effect of the nature of the suspension on the photocatalytic disinfection ability was highlighted. Experiments were also carried out at the surface of transparent coatings formulated using nanoparticles of TiO 2 . The results showed significant antibacterial activities after 2 h and 4 h and suggested that improving the formulation would increase efficiency.
The antibacterial photocatalytic activity of TiO 2 supported over two types of substrates, borosilicate glass tubes (TiO 2 /SiO 2-borosilicate glass tubes (BGT)) and low-density polyethylene pellets (TiO 2-LDPE pellets), which were placed in a compound parabolic collectors (CPC) reactor, was evaluated against Enterobacter cloacae and Escherichia coli under sunlight. Three solar photocatalytic systems were assessed, suspended TiO 2 , TiO 2 /SiO 2-BGT and TiO 2-LDPE pellets, at three initial bacterial concentrations, 1 × 10 5 ; 1 × 10 3 ; 1 × 10 1 CFU/mL of E. coli and total bacteria (E. cloacae and E. coli). The solar photo-inactivation of E. coli was achieved after two hours with 7.2 kJ/L of UV-A, while total bacteria required four hours and 16.5 kJ/L of UV-A. Inactivation order of E. coli was determined, as follows, suspended TiO 2 /sunlight (50 mg/L) > TiO 2-LDPE pellets/sunlight (52 mg/L) > TiO 2 /SiO 2-BGT/sunlight (59 mg/L), the best E. coli. inactivation rate was obtained with TiO 2-LDPE pellets/sunlight, within 4.5 kJ/L and 90 min. The highest total bacteria inactivation rate was found for TiO 2 /sunlight (50 mg/L) and TiO 2-LDPE pellets/sunlight (52 mg/L), within 11.2 kJ/L and 180 min. TiO 2 deposited over LDPE pellets was the most effective material, which can be successfully used for water disinfection applications. Bacterial regrowth was assessed 24 h after all photocatalytic treatments, none of those microorganisms showed any recovery above the detection limit (2 CFU/mL).
Journal of Materials Science, 2014
Using a low-temperature, simple, and economic processing technique, TiO 2 nanoparticles (rutile phase) are immobilized in an inorganic matrix and then deposited on glass for bacteria inactivation in water. Using this low thermal budget method (maximum processing temperature of 220°C), thin films of immobilized TiO 2 nanoparticles are obtained so that practical water decontamination after UV radiation is possible by avoiding the additional step of catalyst separation from treated water. In order to validate the photocatalytic activities of these TiO 2 nanoparticles (prepared as thin films), they were tested for bacteria inactivation in water under UV-A radiation (k [ 365 nm), while extensive characterizations by dynamic light scattering, X-ray diffraction, ultra violet-visible absorption spectroscopy, fourier-transform infra red spectroscopy, and profilometry were also carried out. Despite previous reports on the low or lack of photocatalytic activity of rutile-phase TiO 2 , inactivation of Escherichia coli in water was observed when thin films of this material were used when compared with the application of UV radiation alone. Physical characterization of the films suggests that size and concentrationrelated effects may allow the existence of photocatalytic activity for rutile-TiO 2 as long as they are exposed under UV-A radiation, whereas no effect on bacteria inactivation was observed for thin films in the absence of TiO 2 or radiation. In brief, a low thermal budget process applied to thin films based on TiO 2 nanoparticles has shown to be useful for bacteria inactivation, while possible application of these films on widely available substrates like polyethylene terephthalate materials is expected.
Photocatalytic inactivation of microorganisms using nanotubular TiO2
Applied Catalysis B: Environmental, 2011
Photocatalysis is a well known process for deactivation contaminations in aqueous solutions. However, enhancing the photocatalytic process efficiency remains a challenge and a subject of extensive research. In this paper, nanotubular TiO 2 oxide layer with high surface area was grown and was used as a photocatalyst, inactivating Escherichia coli bacteria and other microorganisms, as well. The photocatalytic process was studied and optimized, subsequent to filtration of the nutrient broth, using saline solution. The double layer capacitance in the interface between the oxide and the solution was measured with the use of electrochemical impedance spectroscopy method and the isoelectric point was found to be at a pH value of 6.8. This result was correlated to the photocatalytic bacteria's inactivation rate in different pH solution. One of the advantages of using immobilized TiO 2 over a powdery photocatalyst is its ability to be recycled and reused. This was well studied with photocatalytic inactivation cycles of the E. coli bacteria along with MeO degradation. It was found that while no concern of reusing the TiO 2 during MeO degradation do exist, the need for a regeneration treatment after several cycles of inactivation E. coli bacteria emerges. Finally, E. coli bacteria were deactivated under a direct sunlight irradiation. This process is proven to be an efficient method for a future commercial photocatalytic cell fabrication.
Environmental Pollution, 2019
The photocatalytic inactivation of Escherichia coli (E. coli) under light-emitting diode (LED) light irradiation was performed with P/Ag/Ag 2 O/Ag 3 PO 4 /TiO 2 photocatalyst to investigate the photocatalytic bactericidal activity. Our work showed that this composite photocatalyst possessed remarkable bacterial disinfection ability and could completely inactivate 10 8 cfu/mL of E. coli within just 40 min under the optimum catalyst loading of 0.5 g/L. The effects of different environmental factors, including light wavelength, light intensity, temperature, solution pH and inorganic ions, on the inactivation efficiency were evaluated. The results showed that bacteria inactivation by P/Ag/Ag 2 O/Ag 3 PO 4 /TiO 2 was more favorable with blue colored LED irradiation, light intensity at 750 W/m 2 , temperature in the range of 30 e37 C and pH values at natural or slightly alkaline condition. The existence of different inorganic ions under normal environmental level had no significant impact on the bactericidal performance. In addition, during the inactivation process, the morphology changes of E. coli cells were directly observed by scanning electron microscope (SEM) and further proved by the measurement of K þ leakage from the inactivated E. coli. The results demonstrated that the photocatalytic inactivation caused drastic damage on bacterial cells membrane. Furthermore, the mechanisms of photocatalytic bacterial inactivation were also systemically studied and the results confirmed that the excellent disinfection activity of P/Ag/Ag 2 O/ Ag 3 PO 4 /TiO 2 resulted from the major reactive species: h þ and $O 2 À from photocatalytic process instead of the leakage of Ag þ (0.085 ± 0.005 mg/L) from photocatalyst. These results indicate that P/Ag/Ag 2 O/ Ag 3 PO 4 /TiO 2 photocatalyst has promising potential for real water sterilization application.
Inactivation of Escherichia coli in water by TiO2-assisted disinfection using solar light
Journal of the Brazilian Chemical Society, 2007
Estudou-se a desinfecção de águas de abastecimento por fotocatálise heterogênea usando um reator de fluxo em um sistema composto por uma placa de vidro com TiO 2 P 25 (Degussa) imobilizado e luz solar como fonte de radiação. Foram utilizados dois modos de operação do reator: passagem única e recirculação. Os experimentos foram conduzidos utilizando inicialmente uma água preparada em laboratório e posteriormente água coletada em poços e lagos de uma região próxima à Campinas, SP. Estudou-se a influência de fatores, tais como, o modo de operação do reator, a cor e turbidez da água, os quais influenciam significativamente na eficiência fotocatalítica de descontaminação e, portanto, na viabilidade da aplicação do processo. Em dias ensolarados, alcançou-se uma redução na carga bacteriológica de cerca de 100% do valor inicial de Escherichia coli (2 × 10 3 NMP per 100 mL) para soluções de água sintética, e, 80% do valor inicial de Escherichia coli (16.6 to 22.2 × 10 3 MPN per 100 mL) para água in natura, através da fotocatálise heterogênea usando TiO 2. TiO 2-assisted heterogeneous photocatalysis and photolysis were evaluated for the disinfection of water samples using a glass reactor with immobilized TiO 2 (catalyst), solar light and E. coli as an indicator microorganism of the efficiency of disinfection. Parameters such as color and turbidity of the water, level of coliform bacteria (by the Colilert ® method), inclination angle of the solar reactor, solar light intensity, flow rate and retention time were controlled during the experiments. Two different operational modes were used for the solar reactor: single pass mode and recirculation mode. First, synthetic water was used in the disinfection tests as a model system; second, tests were conducted using natural samples specifically groundwater collected from a lake and a well. In bacterial suspensions in synthetic water in the absence of color and turbidity, heterogeneous photocatalysis was responsible for the reduction of approximately 100% of the initial concentration of E. coli. Only a 56.5% reduction was obtained by photolysis during the same solution recirculation time, which indicated a better efficiency using the catalyst. From the natural samples, total inactivation was not achieved in the studied cases. However, photocatalysis using TiO 2 /solar light was shown to be quantitatively efficient in the destruction of the total coliforms in water, reaching values up to around 80% inactivation in natural waters with initial levels of total coliforms ranging from 16.6 to 22.2×10 3 MPN per 100 mL.
Photocatalytic disinfection of E . coli using N-doped TiO 2 composite
2014
Heterogeneous photocatalysis is among an alternative technique for the inactivation of pathogenic microorganisms. Several researchers have achieved the successful killing of bacteria, viruses, fungi or protozoa by semiconductor photocatalysis. This study significantally provides a better understanding of the bactericidal properties of N-TiO2 by identifying specific bacterial targets and cell strcuture during disinfection in pure water. The photocatalytic inactivation of bacteria was investigated using E. coli, a well-known bacterial indicator. Firstly, the effects of the contact of N-doped TiO2 with bacterial cells in the dark on both the bacterial cultivability and the envelope integrity was carried out. Then, assessment of the deleterious effects of N-doped TiO2 on the bacteria’s permeability and cultivability was done under visible radiations exposure. In order to identify the cell structure during the inactivation of the bacteria, monitoring of atomic force microscopy was also c...
Chinese Journal of Catalysis, 2014
TiO2-mediated photocatalysis is widely used in a variety of applications and products in the environmental and energy fields, including photoelectrochemical conversion, self-cleaning surfaces, and especially water purification systems. The dimensionality of the structure of a TiO2 material can affect its properties, functions, and more specifically, its photocatalytic performance. In this work, the photocatalytic inactivation of Gram-negative Escherichia coli using three photocatalysts, differing in their structure and other characteristics, was studied in a batch reactor under UVA light. The aim was to establish the disinfection efficiency of solid TiO2 compared with that of suspended catalysts, widely considered as reference cases for photocatalytic water disinfection. The bacterial inactivation profiles obtained showed that: (1) the photoinactivation was exclusively related to the quantity of photons retained per unit of treated volume, irrespective of the characteristics of the photocatalyst and the emitted light flux densities; (2) across the whole UV light range studied, each of the photocatalytic solids was able to achieve more than 2 log bacterial inactivation with less than 2 h UV irradiation; (3) none of the used catalysts achieved a total bacterial disinfection during the treatment time. For each of the catalysts the quantum yield has been assessed in terms of disinfection efficiency, the 2D material showed almost the same performance as those of suspended catalysts. This catalyst is promising for supported photocatalysis applications.
A Review on TiO 2 Photocatalytic Disinfection of Water with Pathogenic Micro-organisms
During disinfection, the formation of byproducts such as trihalomethanes and other chlorinated byproducts are a major concern. The best alternative to avoid the byproducts formation is photocatalysis. In the past two decades, the studies on photocatalysis have been done using a semiconductor for the treatment of air and water. Among the various semiconductors, TiO 2 is used in various industries as it gives the highest efficiency with the highest stability at a lower cost. This is a powerful process used for disinfecting environment contaminated with pathogenic microorganisms. In this study, a review of previous developments made in the TiO 2 photocatalysis for the disinfection of water contaminated with pathogenic microorganisms is carried out. This paper concludes that TiO 2 photocatalysis can be used in different ways either in suspension or in the form of thin films to disinfect water contaminated with pathogenic microorganisms presenting a potential hazard to animals and human ...