贵金属Au-Ag合金修饰ZnO用于光催化高效降解乙烯

ZnO nanorod decorated by Au-Ag alloy with greatly increased activity for photocatalytic ethylene oxidation

乙烯是一种植物激素,可以促进水果和蔬菜在生长过程中成熟,然而在水果和蔬菜成熟之后,源源不断产生的乙烯会加速它们的衰老和腐烂,不利于水果和蔬菜的贮存和保鲜.考虑到现实因素,直接在储存环境中去除乙烯很有必要,而光催化技术操作简单易行,在降解乙烯方面具有应用前景.我们发现Zn O具有降解乙烯的作用,但纯ZnO由于光吸收范围窄及载流子分离效率低,使得其降解乙烯的效果不佳.而金、银纳米颗粒由于其表面的等离子体共振效应,可以增强半导体的光吸收,同时贵金属颗粒还可以充当捕获电子的活性位点,加快电子和空穴分离,提高光催化效率.因此,将金或银作为ZnO的助催化剂可能是提高ZnO催化性能的有效途径.一些研究还发现,使用双金属合金作为助催化剂可以达到比单一金属更优越的效果.因此在本论文中,我们采用简单的光沉积工艺和低温煅烧方法合成了Au, Ag和Au-Ag合金负载的ZnO,研究了它们对ZnO光催化效率的促进作用.活性测试表明,在ZnO负载了单独的Au或Ag颗粒后,乙烯降解效率分别是纯ZnO的17.5和26.8倍,光催化活性大幅增加.而当ZnO成功负载Au-Ag合金后,光催化活性进一步提高到纯ZnO的94.8倍.紫外-可见光谱结果表明,由于表面等离子体共振(SPR)效应, Au-Ag合金改性后的ZnO显示出很强的可见光吸收.同时,较高的光电流密度表明AuAg/ZnO具有有效的载流子分离能力.因此,等离子体Au-Ag双金属合金纳米粒子的协同作用和有效的载流子分离能力共同带来了乙烯氧化的优异光催化活性.催化剂稳定性测试表明, Ag/ZnO的光催化稳定性非常差,在10次循环后活性下降很多,而Au/ZnO和AuAg/ZnO在10次循环后光催化稳定性非常好.结合XPS分析可知, Ag单质颗粒可以容易地光氧化成为Ag2O,造成活性降低,而Au-Ag由于形成了合金结构,不易被氧化,因而变得异常稳定.最终我们得到了高活性、高稳定性的AuAg/ZnO光催化剂.这项工作提出了在实际生产中使用金属合金作为助催化剂去除乙烯的新思路,具有良好的应用前景.

In recent years, the preservation of fruits and vegetables in cold storage has become an issue of increasing concern, ethylene plays a leading role among them. We found ZnO has the effect of degrading gaseous ethylene, however its effect is not particularly satisfactory. Therefore, we used simple photo-deposition procedure and low-temperature calcination method to synthesize Au, Ag, and Au Ag alloy supported ZnO to improve the photocatalytic efficiency. Satisfactorily, after ZnO loaded with sole Au or Ag particles, the efficiency of ethylene degradation was 17.5 and 26.8 times than that of pure ZnO, showing a large increase in photocatalytic activity. However, the photocatalytic stability of Ag/ZnO was very poor, because Ag can be easily photooxidized to Ag2O. Surprisingly, when ZnO was successfully loaded with the Au Ag alloy, not only the photocatalytic activity was further improved to 94.8 times than that of pure ZnO, but also the photocatalytic stability was very good after 10 times of cycles. Characterization results explained that the Au-Ag alloy NPs modified ZnO showed great visible-light absorption because of the surface plasmon resonance(SPR) effect. Meanwhile, the higher photocurrent density showed the effective carrier separation ability in Au Ag/ZnO. Therefore, the cooperative action of plasmonic Au Ag bimetallic alloy NPs and efficient carrier separation capability result in the outstanding photoactivity of ethylene oxidation. At the same time, the formation of the alloy produced a new crystal structure different from Au and Ag, which overcomes the problem of poor stability of Ag/ZnO, and finally obtains Au Ag/ZnO photocatalyst with high activity and high stability. This work proposes a new concept of using metal alloys to remove ethylene in actual production.