Understanding iodine adsorption sites on monolithic N/O co-doped carbon fibers with scaffolding structure

Effectively capturing radioactive iodides from nuclear waste poses a significant challenge with low uptake capacity, high costs, and non-recyclability. Monolithic nitrogen/oxygen co-doped carbon fibers with scaffolding structure exhibit high porosity, repeatability, and mechanical strength, making them effective for capturing radioactive iodides from nuclear waste. In this study, monolithic nitrogen/oxygen co-doped carbon fibers with a scaffold structure were investigated as effective iodine capture agents. These fibers demonstrate excellent iodine adsorption capabilities, reaching up to 58.77 mg q−1 in a 100 mg/L and 167.87 mg q−1 in a 500 mg/L iodine-cyclohexane solution. The adsorption isotherm follows the Langmuir model and the pseudo-second-order kinetic model. Experiments and theoretical calculations show that hydroxyl (C-OH) and quaternary nitrogen (NG) groups as active sites have different adsorption mechanisms during iodine adsorption in the different concentration iodine-cyclohexane solution. According to multiple linear regression (MLR) analysis, the C-OH groups primarily facilitate iodine adsorption in a 100 mg/L solution, whereas NG groups play a pivotal role in a 500 mg/L solution. Furthermore, the incorporation of a flexible monolithic carbon fiber featuring a scaffolding structure presents a novel and environmentally friendly approach for practical applications, eliminating the risk of secondary pollution.