Preparation and Properties of Collagen Fiber-based Iodine Adsorbents Modified by Polyethyleneimine

Objective The radioactive iodine pollution (such as ¹²⁹I, ¹³¹I) associated with nuclear energy development poses a serious threat to the ecological environment and public health. How to achieve efficient and stable capture and immobilization of radioactive iodine to prevent its release into the environment is one of the core issues that urgently need to be addressed in the field of nuclear industry waste management and environmental safety. At present, the research on the removal of radioactive iodine vapor and iodine ions in aqueous solutions mainly focuses on the development of solid adsorption materials such as activated carbon, zeolite materials, metal-organic frameworks, and covalent organic frameworks materials. However, these materials have many drawbacks such as limited adsorption capacity, high cost, and difficulties in large-scale production. Therefore, the pursuit of adsorption materials that possess efficient adsorption performance, excellent stability, environmental friendliness, and low cost has become one of the important research directions in the field of radioactive iodine capture. Based on this, this research aims to develop an efficient, stable and environmentally friendly iodine adsorption material using the collagen fibers from animals with abundant resources as the raw material.

Methods In this research, the activated collagen fibers (ACF) were first obtained through alkaline (NaOH) activation treatment of collagen fibers, in which more active sites of collagen fibers were exposed. Using glutaraldehyde as the crosslinking agent, polyethyleneimine (PEI) at different dosages, which is rich in primary and secondary amine groups, was then covalently grafted onto the collagen fiber framework through the Schiff base reaction, aiming to significantly increase the nitrogen content on the material surface and thereby provide abundant iodine adsorption functional groups. The obtained PEI-modified activated collagen fibers (ACFP) adsorption materials were characterized by means of SEM, EDS, XPS, XRD, FTIR, TG and DSC to investigate their morphology, structure and thermal stability. The adsorption capacity of ACFP for iodine vapor was determined by weighing method, while its adsorption performance for I₃⁻ in aqueous solution was studied by UV-vis method, and the effects of initial I₃⁻ concentration, temperature and pH were investigated. The adsorption process was analyzed by using kinetic models.

Results The characterization results showed that PEI was successfully grafted onto the collagen fiber framework through the Schiff base reaction. When the PEI dosage was 0.02 mol, the effective amine group density on the material surface reached the optimal value. Although the nitrogen content decreased, the accessibility of active sites was the best at this dosage. The melting temperature of ACFP was approximately 62.5 ℃, and its thermal stability was good. The adsorption capacity of iodine vapor by ACFP was up to 2464.3 mg/g, which was 1774.5 mg/g higher than that of ACF. After adsorption, the iodine element content on the surface reached 53.0 wt%. In the solution system, the removal rate of I₃⁻ by ACFP was over 90%, and the maximum adsorption capacity was approximately 200 mg/g. The adsorption process conformed to the pseudo-second-order kinetic model and was significantly affected by temperature. Increasing the temperature could significantly shorten the adsorption equilibrium time. The pH had a relatively small influence on the adsorption process.

Conclusions Using collagen fibers as raw material, we successfully prepared an iodine adsorption material ACFP by alkaline activation and PEI grafting modification. After alkaline activation, the resulting ACF exposed a large number of functionalized modification sites, and the subsequent PEI grafting modification resulted in ACFP having a high density of effective amino functional groups and adsorption active sites, which enhanced the capture ability of ACFP for iodine in both gas and liquid phases. The adsorption capacity of ACFP for iodine vapor is attributed to the electron transfer between the N and O elements in the material and iodine monomer. ACFP demonstrates a promising application prospect in the field of radioactive iodine pollution control.