Preparation And Performances Of Biomaterials-supported Broad-spectrum Nano-photocatalysts

As bacteria widely existed in aquaculture, aquatic pathogens can cause serious diseasein aquatic organisms and it results in severe economic loss to aquaculture. Nowadays, a lotof traditional fungicides and antibiotics are commonly used for control of these aquaticpathogens. However, it is helpless for the sterilization and sometimes even causes drugtolerance in pathogens and drug residues in aquatic organisms. Therefore, to overcome thesedefects, many kinds of photocatalysts were used for the sterilization. As one of the highestused photocatalysts, nano-TiO₂can not only kill bacteria, but also decompose and eliminatemicrobial toxic residues. However, TiO₂can only be excited by UV-light and needhigh-power high-pressure mercury lamp when used. In contrast to nano-TiO₂, nano-Cu₂O isa kind of broad-spectrum photocatalysts that can be excited by UV-light and visible light.Though nano-Cu₂O have been successfully used for the sterilization of Escherichia coli andStaphyloccocus aureus, less researches have been reported in the sterilization of aquaticpathogens. In this paper, an efficient fungicide, namely biomaterials-supportedbroad-spectrum nano-photocatalysts, are prepared and used for the sterilization analysis ofaquatic pathogens.The oyster shells as natural biomaterials are activated at high temperatures, and areused as carriers to support nano-Cu₂O through CuCl2hydrolysis process. Then, theseas-prepared photocatalysts are selected by photocatalytic sterilization experiments and X-raydiffraction (XRD) characterization. At last, this kind of biomaterials-supportedbroad-spectrum nano-photocatalysts are successfully developed. It is found that CaCO₃completely decomposed into activated CaO when oyster shells calcined at the temperaturehigher than850℃. Furthermore, the broad-spectrum nano-photocatalysts produced at 900℃have the highest photocatalytic activity. The characterizations of thisnano-photocatalysts are based on X-ray diffraction (XRD), scanning electron microscopy(SEM), its energy dispersive spectrometer (EDS), and UV-Vis diffuse reflectancespectrometer (UV-Vis). The results show that the main components of thenano-photocatalysts are CaO and Cu₂O, as well as some newly materials CaCu₂O2. TheCu₂O particles, with a theoretical average particle size of37.3nm, were well loaded on andclosely integrated with carriers. As expected, the oyster shell carriers not only successfullysupport nano-Cu₂O, but also not affect its photosensitive effect. The broad-spectrumnano-photocatalysts can perform well absorption of both UV-and visible light, and haveabsorption bands (2.01eV) in the region similar to pure Cu₂O powders.In this paper, four common aquatic pathogens, Aeromonas hydrophila, Bibrioparahemolyticus, Vibrio anguillarum and Vibrio alginolyticus were used to investigate theinvitro antibacterial activity of broad-spectrum nano-photocatalysts through oxford plate anddouble dilution method. Lastly, the inhibition zone diameter, the minimum inhibitoryconcentration (MIC) and minimum bactericidal concentration (MBC) were determined andthe killing curve was achieved. It is surprising to found that the nano-photocatalysts showexcellent bacteriostatic and bactericidal activity and the MIC and MBC of Vibrioanguillarum were12.5mg/L and25mg/L respectively.The photocatalytic bactericidal tests show that the nano-photocatalysts have a goodbactericidal effect on four aquatic pathogens. Under UV-light or sunlight with the use ofappropriate concentration (100-200mg/L) and sufficient duration of action (2h), thesterilization rate of photocatalysts can reach100%. The sterilization of nano-photocatalystsis controlled by the light source, material concentration and reaction time. It is benefit toimprove the bactericidal effect by extending the duration of reaction, increasing the intensityof the light source and improving the concentration of materials. In addition, the GreyRelational Analysis were used to analyze the relational degree of four factors on which thesterilization of the nano-photocatalysts is affected, including intensity of the light source(X1), concentration of materials (X2), reaction time (X3) and activity oxygen concentration(X4). The gray relational degree as follows: RX3> RX1> RX2> RX4. The main factor isphotocatalysis time. Therefore, extending the irradiation time can significantly enhance the sterilization rate of the nano-photocatalysts.The mechanism study of photocatalytic sterilization shows that Fe(phen)₃²⁺spectrophotometry can be used to test the activity of free radicals generated in thephotocatalytic reaction system. Killing microbial cells with nano-photocatalysts under theillumination is the oxidation process of free radical. The active radicals with high reactivityand strong oxidizing ability can react with the cell membrane or DNA, proteins of pathogensand finish other biochemical reactions; thereby these lead to cell lysis or death.