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Fig. 1 (a) Schematic diagram of the band structure of the photocatalytic materials of Bi/TiO2 (rutile) and nano-Bi/TiO2 (rutile) composite photocatalysts. (c) Photo-catalytic reduction of bromate by nano-Bi/TiO2 (rutile) composite photocatalytic materials.
Since the 1970s, photocatalytic technology has received wide attention due to its great potential in solving the energy crisis and environmental pollution that human beings face. In the photocatalytic reaction, the photocatalytic material (such as TiO2) absorbs light and is excited to generate photoelectrons and holes. After the photogenerated electrons and holes migrate to the surface of the material, either an oxidation reaction or a reduction reaction may occur. The photocatalytic reduction reaction dominated by photoelectron can effectively remove many kinds of carcinogenic oxygen anions in water. However, the existing photocatalytic reduction materials have low reaction efficiency, which limits their practical application. In order to enhance the efficiency of the photocatalytic reduction reaction, it is usually required to add a hole sacrificial agent in the reaction system to consume the photogenerated holes, thereby avoiding the influence of the photogenerated holes on the reduction reaction. However, this method increases the cost of treatment, easily causes secondary pollution of the water body, and is not suitable for drinking water treatment.
The noble metal/transition metal has a high work function and combines with a photocatalytic material to form a heterojunction, capable of trapping photo-generated electrons, enhancing the separation of photo-generated electrons and holes, and thereby enhancing the photocatalytic reaction efficiency, and is obtained in the design of high-efficiency photocatalytic materials. Widely used. However, this photocatalytic material design cannot effectively consume photoexcited holes with strong oxidizing properties, and the effective photocatalytic reduction reaction still depends on the addition of a hole sacrificial agent in the reaction system. In the design of photocatalytic reduction materials, if the separation of photogenerated electrons and holes can be enhanced by hole trapping and consumption, it is possible to increase the efficiency of the photocatalytic reduction reaction while avoiding the addition of a hole sacrificial agent in the reaction system. Existing photocatalytic reduction of water purification material problems.
Under the guidance of this idea, Li Qi, a researcher of the Environmental Functional Materials Research Department of the Shenyang (China) Institute of Materials Science, Chinese Academy of Sciences, and his research team have developed an efficient photocatalytic reduction water purification material without the need to add sacrificial sacrificial agents. The efficient removal of bromine, a carcinogenic anion common in drinking water under visible light, is achieved. After theoretical analysis and material screening, they chose the combination of semi-metallic Bi and rutile TiO2 to form a heterojunction. Bi, a semi-metal, has special physical properties. Compared with noble metals or transition metals, the work function of Bi is relatively low, about 4.22eV, which is close to that of rutile TiO2. The photogenerated electrons generated by TiO2 can still be captured by the bulk Bi when the bulk Bi and rutile TiO2 combine to form a heterojunction. . As its size is reduced to the nanometer scale, the semi-metal Bi transitions from a metal to a semiconductor, with the concomitant conversion of the nano-Bi to semiconductor characteristics in which the conduction band position rises and the valence band position decreases. At this point, the conduction band of the semiconductor nano Bi is higher than the conduction band of the rutile TiO2, and the photoreactive electrons generated under light irradiation cannot be transferred to the nano Bi but remain on the rutile TiO2; and the photo holes can be transferred to Nano Bi is consumed by oxidation of Bi to Bi3+. Therefore, this material system not only enhances the photocatalytic reduction efficiency by increasing the lifetime of photoelectrons, but also avoids the addition of a hole sacrificial agent in the reaction system, which is very suitable for the application of photocatalytic reduction technology in drinking water treatment. This study provides a new idea for the design of high-efficiency photocatalytic reduction materials, which is expected to be widely used. Related research results are published in Applied Catalysis B: Environmental.
This research work has been supported by the National Natural Science Foundation of China, Shenyang Fundamental Frontier Innovation Project of the National Laboratory for Materials Science, and the “123 Project†project of Liaoning Green Action-Liaoning Environmental Research Education.
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