Novel chitosan-based derivative material loaded with the diethylenetriamine pentamethylene phosphonic acid for efficient adsorption of uranyl ions from weakly acidic wastewater

An ideal adsorption material capable of efficiently and selectively capture uranyl ions from radioactive wastewater remains a serious challenge. In this work, diethylenetriamine pentamethylene phosphonic acid (DTPMP), one of the common metal ion extractants with five negatively charged phosphate groups, was innovatively used to modify chitosan chains for better uranyl adsorption capacity. Two chitosan derivatives were designed, DTPMP protonated chitosan crosslinked with potassium tripolyphosphate (DTPP) and DTPMP reinforced potassium tripolyphosphate crosslinked chitosan (DCTPP), in which DCTPP possessed an excellent maximum adsorption capacity of up to 1316.82 mg/g for uranyl ions at 298 K. Compared to the 60 min taken-for 90 % by DTPP, the time taken to reach same percentage by DCTPP was only about 5 min, indicating its superior uranyl removal efficiency. Outstanding affinity and capture performance could be attributable to the remarkable mesoporous surfaces and abundant P-containing active sites. Influence of initial solution pH on the removal efficiency for uranyl was significantly attenuated due to the C-P bond. The fitting results of kinetic and isotherm models revealed that the uranyl adsorption mechanisms by as-prepared composites were physicochemical processes, mainly including surface complexation/chelation, chemisorption, and intra-particle diffusion. Theory calculations predicted potential binding modes and electrons transfer between the organophosphonic acid molecule and uranyl unit, validating the strong interaction and reduction of phosphorus-oxygen groups on uranyl ions. Furthermore, DCTPP showed great potentials to separate uranyl from simulated uranium-contaminated wastewater. Design and development of novel chitosan derivatives will provide theoretical support and technical reference for an effective treatment of weakly acidic radioactive wastewater.