用XANES方法研究SO2在超细Fe3O4颗粒表面的非均相反应

Heterogeneous catalytic reaction of SO_2 on the surface of ultrafine Fe_3O_4 particle by XANES

超细颗粒物为大气中痕量气态污染物转化提供了广泛的反应界面,在其表面发生多相界面反应是大气二次颗粒物形成的主要途径。含铁超细颗粒是大气气溶胶的主要成分之一。本研究采用同步辐射X射线近边吸收谱(X-ray Absorption Near Edge Structure,XANES)技术开展了Fe_3O_4超细颗粒表面的多相反应研究,分析了反应时间、紫外照射及臭氧存在条件对二次颗粒物形成的影响。研究发现:SO_2在Fe_3O_4超细颗粒表面能被快速氧化形成硫酸根(SO_4^(2-)),其中紫外光照(Ultra-Violet,UV)和O_3可以促进硫酸根的生成。从反应时间上看,SO_2在Fe_3O_4超细颗粒表面可快速反应生成高价态硫酸根,30 min时,约99%的硫化物转化成硫酸根。通过对S的XANES谱进行一阶导数处理,发现产物中还存在亚硫酸根(SO_3^(2-))的峰,提示SO_2在Fe_3O_4颗粒物表面可先生成亚硫酸根,进而被快速氧化成硫酸根。

[Background] Ultrafine particles （UFPs） may provide various micro-locations of heterogeneous chemical reactions of trace of gaseous substances in atmospheric environment. Iron-containing UFPs are the main components of atmospheric aerosol [Purpose] This study aims to investigate heterogeneous reactions of SO2 on Fe3O4 UFPs.[Methods] S K-edge of products was investigated by synchrotron radiation X-ray absorption near edge structure （XANES）. [Results] The results indicated that SO2 could be rapidly oxidized to form sulfate on the surface of Fe3O4. Formation of sulfate can be promoted under the UV and O3 conditions. [Conclusion] The formation of adsorbed sulfate likely involves the formation ofpre-absorbed sulfite （SO3^2-） and subsequent oxidation.