Hou Wen-Che, He Chen-Jing, Wang Yi-Sheng, Wang David K, Zepp Richard G
Department of Environmental Engineering, National Cheng Kung University , Tainan City, Taiwan 70101.
FIMLab-Films and Inorganic Membrane Laboratory, School of Chemical Engineering, The University of Queensland , Brisbane, Qld 4072, Australia.
Environ Sci Technol. 2016 Apr 5;50(7):3494-502. doi: 10.1021/acs.est.5b04727. Epub 2016 Mar 16.
Single-walled carbon nanotubes (SWCNTs) with proper functionalization are desirable for applications that require dispersion in aqueous and biological environments, and functionalized SWCNTs also serve as building blocks for conjugation with specific molecules in these applications. In this study, we examined the phototransformation of carboxylated SWCNTs and associated amorphous carbon impurities in the presence or absence of H2O2 under simulated sunlight conditions. We found that while carboxylated SWCNTs were rather unreactive with respect to direct solar photolysis, they photoreacted in the presence of H2O2, forming CO2 and strongly aggregated SWCNT products that precipitated. Photoreaction caused SWCNTs to lose oxygen-containing functionalities, and interestingly, the resulting photoproducts had spectral characteristics similar to those of parent carboxylated SWCNTs whose amorphous carbon was removed by base washing. These results indicated that photoreaction of the amorphous carbon was likely involved. The removal of amorphous carbon after indirect photoreaction was confirmed with thermogravimetric analysis (TGA). Further studies using carboxylated SWCNTs with and without base washing indicate that amorphous carbon reduced the extent of aggregation caused by photoreaction. The second-order rate constant for carboxylated SWCNTs reacting with (•)OH was estimated to be in the range of 1.7-3.8 × 10(9) MC(-1) s(-1). The modeled phototransformation half-lives fall in the range of 2.8-280 days in typical sunlit freshwaters. Our study indicates that photosensitized reactions involving (•)OH may be a transformation and removal pathway of functionalized SWCNTs in the aquatic environment, and that the residual amorphous carbon associated with SWCNTs plays a role in SWCNT stabilization.
具有适当功能化的单壁碳纳米管（SWCNTs）适用于需要在水性和生物环境中分散的应用，并且功能化的SWCNTs在这些应用中还可作为与特定分子共轭的构建单元。在本研究中，我们研究了在模拟阳光条件下，有无过氧化氢存在时羧基化SWCNTs及其相关无定形碳杂质的光转化情况。我们发现，虽然羧基化SWCNTs对直接太阳光解反应性较低，但它们在过氧化氢存在下会发生光反应，形成二氧化碳和强烈聚集的SWCNT产物并沉淀。光反应导致SWCNTs失去含氧官能团，有趣的是，所得光产物的光谱特征与通过碱洗去除无定形碳后的母体羧基化SWCNTs相似。这些结果表明可能涉及无定形碳的光反应。通过热重分析（TGA）证实了间接光反应后无定形碳的去除。使用经过和未经过碱洗的羧基化SWCNTs的进一步研究表明，无定形碳降低了光反应引起的聚集程度。羧基化SWCNTs与（•）OH反应的二级速率常数估计在1.7 - 3.8×10⁹ M⁻¹ s⁻¹范围内。在典型的阳光照射的淡水中，模拟的光转化半衰期在2.8 - 280天范围内。我们的研究表明，涉及（•）OH的光敏反应可能是功能化SWCNTs在水环境中的一种转化和去除途径，并且与SWCNTs相关的残留无定形碳在SWCNT的稳定中起作用。
