A problem derived to the increasing emergence of microorganisms resistant to antibacterial agents of such phenomenon is related with water quality and the diseases provoked by the presence of bacteria and parasites. The advanced oxidation processes (AOP’s) have attracted attention as processes that imply the formation of hydroxyl radicals (OH) with a high oxidation potential. In the case of microorganisms, this radicals attack the lipid bilayer that conforms the external cell wall, generating reactions of lipid peroxidation that are lethal for microorganisms. The heterogeneous photocatalysis, involves the absorption of light by a catalyst (semiconductor). During the process, oxidation-reduction reactions occur, that can degrade organic compounds and reduce inorganic ions.
Bismuth oxide is a semiconductor that in last years has reached importance as a photocatalyst, in particular when it is tetragonal beta phase which presents a low bandgap (~2.7 eV). The intention of using the bismuth oxide as photocatalyst is because Mexico is the second worldwide bismuth producer and it would be attractive to give this mineral a higher value. The objective of this research is to use bismuth oxide films as antibacterial agent for water treatment. The antibacterial effect was tested by the inhibition of E. coli in presence of Bi2O3 under UV and visible light.
Bi2O3 films were deposited by the spray pyrolysis technique using Bismuth acetate (CCH3CO2)3Bi) as precursor in a solution 0.05 M dissolved in 25%v acetic acid and 75%v deionized water. The films were grown on Corning glass substrates of 1.5 cm x 1.5 cm. The deposition temperature and time were 450°C and 20 min. respectively. The antibacterial effect of Bi2O3 films was determined by counting the E. coli colony-forming units (CFU). 2 mL of E. coli culture with a concentration of 1x107 cell/mL were put in each well with a Bi2O3 sample and irradiated with UV light. A similar sample was irradiated with white light.. After two hours of irradiation the samples were poured into a Petri dish with agar and the bacteria were incubated during 24 hours. Afterwards the CFU were counted. All the experiments were performed by triplicate.
The XRD pattern of the Bi2O3 film shows that the material presents a beta phase, with a tetragonal crystalline structure. After the experimental process it’s possible to observe a decrease in the bacteria proliferation when the culture is in contact with the photocatalytic Bi2O3 film. It was found a lower bacteria proliferation when the semiconductor is irradiated with UV light.
Discussion and conclusion
The results demonstrate that the bismuth oxide present antibacterial activity under both white light and UV light after two hours of exposition. It is necessary to perform more experiments to optimize the deposition conditions as well as the concentration of the bacterial culture in order to enhance the bacteria annihilation by the photocatalyst.