Novel Ti3C2/Bi@BiOI nanosheets with gradient oxygen vacancies for the enhancement of spatial charge separation and photocatalytic performance: The roles of reactive oxygen and iodine species

In this study, we reported a series of novel Ti3C2/Bi@OVs-BiOI photocatalysts using MXene to tailor the surface structure and photocatalytic activity of BiOI nanosheets. Notably, the Ti3C2 with surface terminal Ti sites can induce the formation of gradient oxygen vacancies (OVs) and in-situ generation of metallic Bi on BiOI nanosheets. Compared with pristine BiOI, 10% Ti3C2/Bi@OVs-BiOI photocatalyst exhibited a higher photodegradation efficiency and the corresponding first-order reaction rates of antipyrine (ANT) and bisphenol A (BPA) photodegradation were increased by 2.4 times and 18.6 times, respectively. The high photodegradation efficiency was mainly attributed to the enhanced light absorption ability and accelerating spatial charge carriers separation. Interestingly, there existed a significant decrease of photocatalytic performance in the ANT photodegradation cycle test, which is attributed to the break of "interlayer anion exchange" chemical equilibrium. Further radicals trapping experiments confirmed that reactive oxygen species (ROSs: h(+) and center dot O-2(-)) were the dominant reactive species for ANT and BPA photodegradation. In addition, free iodine analysis and LC-MS/MS results suggested that reactive iodine species (RISs: center dot I and center dot I-2(-)) played the important roles in the photocatalysis process. According to the theoretical calculation of frontier electron densities (FEDs), the contribution and reactivity of RISs were firstly proposed in the BiOI-based photocatalysis process. These new findings not only provide a potential approach to the application of BiOI-based photocatalysis but also clarify the relationship between the stability of BiOI and interlayer anion exchange.