Efficient nuclear waste treatment and environmental management are important hurdles that need to be overcome if nuclear energy is to become more widely used. Recently, two dimensional (2D) transition metal carbide and carbonitride materials (MXene) have garnered great attention in energy and environmental fields. Benefiting from abundant active sites and unique layered structures, MXenes are potential candidates for radionuclide capture. More importantly, this kind of inorganic materials exhibits high radiation resistance and good thermal conductivity, thus can be used for radionuclide separation even under very harsh condition. The Laboratory of Nuclear Energy Chemistry from Institute of High Energy Physics has reported the first case of highly efficient removal of radionuclide by MXene through the capture of uranium on 2D vanadium carbide (V₂CT_x) as a demonstration. Their research has been published on June 7^th, 2016 in ACS Applied Materials & Interfaces.

The team firstly synthesized high quality V₂CT_x by HF etching of V₂AlC. The V₂CT_x material is found to be highly efficient uranium sorbent, evidenced by a high uptake capacity of 174 mg g^-1, fast sorption kinetics (4h), and desirable selectivity. Fitting of the sorption isotherm indicated that the sorption followed a heterogeneous adsorption model most probably due to the presence of heterogeneous adsorption sites such as –OH and -F.

The study of interaction mechanism between uranium and V₂CT_x, and the estimation of equivalent valence of V in V₂CTx and V₂AlC samples using synchrotron radiation techniques at BSRF.

To further understand the adsorption mechanism，the local coordination environment of U(VI) sorbed onto V₂CT_x was carefully examined by EXAFS measurement. The analyzed results suggested that the uranyl ions prefer to coordinate with hydroxyl groups bonded to the V-sites of the nanosheets via forming bidentate inner-sphere complexes. Density functional theory (DFT) has also been employed to calculate the most energetically favorable adsorption configuration and coordination information of V₂CT_x-U complex. They found that the DFT calculations agreed quite well with those obtained from EXAFS results. In addition, the equivalent valence of V in V₂CT_x and V₂AlC samples has been estimated through analyzing the corresponding XANES spectra of V K edge.

Currently the number of known MXenes is > 15. Extending the radionuclide separation study from V₂CT_x to other MXenes will allow many alternatives and varieties due to their different layer structures, bond strengths and physicochemical properties. This research lays new avenue for promoting the applications of MXenes for nuclear waste treatment and radionuclide removal from the environment in the future.

Article: Lin Wang, Liyong Yuan, Ke Chen, Yujuan Zhang, Qihuang Deng, Shiyu Du, Qing Huang,^* Lirong Zheng, Jing Zhang, Zhifang Chai, Michel W. Barsoum,⁴Xiangke Wang, and Weiqun Shi^* Loading Actinides in Multi-layered Structures for Nuclear Waste Treatment: the First Case Study of Uranium Capture with Vanadium Carbide MXene. ACS Appl. Mater. Interfaces 8(2016), 16396？16403.