The photochemistry of carbon nanotubes and its impact on the photo-degradation of dye pollutants in aqueous solutions

• The photochemistry of CNTs in aqueous suspensions was investigated.
• CNTs could be photo-ionized and trap hydrated electrons.
• CNTs could both generate and scavenge reactive oxygen species.
• Inner filter effect dominates in the impact of CNTs on dye photo-degradation.

It is reported that carbon nanotubes (CNTs) could either generate reactive oxygen species (ROS) under light irradiation or serve as high-efficient scavenger for ROS. However, it is unclear which role predominates as CNTs enter into aquatic environment. To answer this question, a systematic study of the photochemistry of a pristine and a surface-functionalized CNTs in aqueous suspensions was investigated with both time-resolved and steady state analytical approaches. The transient absorption spectra demonstrate that CNTs could be photo-ionized and trap hydrated electrons upon high energy irradiation. In steady state UV irradiation, CNTs could promote the generation of ROS, such as 1O2 and OH. However, in the presence of H2O2, the OH scavenging effect predominated in the aqueous suspensions of CNTs. The presence of CNTs suppressed the photo-degradation of dye pollutants, as an integrated result of inner filter effect, adsorption effect, and ROS generation and scavenging effect. The results provide useful information for the understanding of the environmental implications of CNTs.

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