| Photocatalytic technology is considered to be one of the most important sciences and technologies in the21st century as it can effectively utilize solar energy, showing good application prospect in solving energy shortage and environmental pollution. However, now extensive studies focus on TiO2with disadvantages of wide band gaps and only responding to ultraviolet light below380nm, which severely restricts the use of sunlight, and it still has some problems such as poor utilization ratio of sunlight and low response range of visible light after some modification treatments. Therefore, synthesizing a new and efficient visible light photocatalyst is the focus and hotspot in current research of the photocatalytic materials. Among various kinds of photocatalysts in visible region, the niobate attracts widespread attention due to its controlled composition and structure, superior physico-chemical property and high photocatalytic activity. But now, this material has disadvantages of high production cost, complex preparation process and being difficult to recycle. Aiming at these problems, with inorganic source instead of organic niobium source, niobate visible-light photocatalyst supported on diatomite ball was prepared by an improved sol-gel method in order to simplify preparation technology and reduce preparation cost. Besides, with diatomite balls of high specific surface area, strong adsorption performance as carriers, the supported photocatalysts are easy to recycle and can be reused directly, showing a longer service life.With cheaper inorganic niobium source (Nb2O5) instead of expensive organic niobium source (Nb(OC2H5)5), potassium niobate powders were prepared by an improved sol-gel method. XRD, SEM, EDS, UV-Visible absorption spectroscopy and laser particle size analysis methods were adopted to characterize this material and the best preparation conditions were determined. The optimal preparation conditions are:the mass ratio of Nb2O5and KOH being1and7, the holding temperature being450℃, the holding time being2h, the calcination temperature being600℃and the calcination time being5h. Under this preparation condition, the prepared potassium niobate is perovskite type KNbO3with high purity and strong visible-light responsiveness. Besides, the powder is approximate rectangle with small particle size, and the average particle size is5.568μm. Crude diatomite was made into balls after pretreatment, and with diatomite balls as carriers, the niobate visible-light photocatalysts supported on diatomite balls were prepared by a sol-gel impregnation method. Degradation effect of Rhodamine B solution as an index, combined with XRD, SEM, EDS and other analytical methods, the best preparation conditions were determined. The optimal preparation conditions are:the dipping time being3h, the calcination temperature being600℃and the calcination time being5h. Under this preparation condition, the loaded amount of KNbO3is0.166g/g diatomite balls, and the white perovskite type KNbO3particles uniformly distribute around the surface of diatomite balls. Photocatalytic degradation effect is affected by the air flux, the initial concentration of solution, the amount of photocatalyst, solution pH value, light intensity, and light sources. The optimum pH value is6, indicating the prepared photocatalysts suitable to treat organic pollutants in weakly acidic condition. After illuminating3h, the degradation rates reach89.0%and86.4%by using high-pressure sodium lamp and metal halide lamp within visible range respectively, better than that the optimal conditions of Ce-TiO2photocatalysts supported on diatomite balls of84.7%. The prepared photocatalysts can be continuously reused many times, and it can be restored to its original level of activity by calcinating2h at600℃after activity decrease, showing high photocatalytic activity and favorable stability.The results of the as-synthesized supported photocatalyst sterilize strains experiments show that photocatalytic antibacterial activity is affected by the initial bacterial concentration, the amount of photocatalyst, light sources, illumination time and different strains. With sunlight as light source, the sterilization rate of E. coli, S. aureus, K. pneumoniae all reach100%after illuminating2h, meaning these strains are killed completely.The results of the as-synthesized supported photocatalyst degrade formaldehyde experiments show that the formaldehyde degradation is affected by the initial concentration of formaldehyde, the amount of photocatalyst, temperature, light sources, illumination time and gas state. Under the best photocatalytic reaction condition, the degradation rate of87.9%is attained when ordinary fluorescent lamp illuminates3.5h. The photocatalytic performance remains basically stable after reusing many times and the poisoning deactivation phenomenon basically does not occur after a simple ventilation treatment, meaning it is a kind of ideal photocatalyst with long service life.The prepared photocatalyst not only makes full use of the targeted enrichment action of diatomite of high porosity, accelerating the photocatalytic reaction rate, but also is easy to recycle and has a very good response capability to visible light. It can utilize solar energy directly, and avoid using artificial light of high cost and large energy consumption, reducing the operation cost and showing great application prospects in wastewater treatment, antibacterial sterilization, air purification and other areas. |
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