A Novel Preparation and Vapour Phase Modification of 2D-open Channel Bio-adsorbent Via ATRP for Uranium Separation
Mudasir Ahmad a, b, Jianquan Ren a, Tao Xiu a, Mehraj-ud-din Naik c, Qiuyu Zhang a, b, Baoliang Zhang a, d, 11Corresponding author, Northwestern Polytechnical University, Youyi Road 127#, Xi’an (710072), China. Email: blzhang@nwpu.edu.cn
a School of Chemistry and Chemical Engineering, Northwestern Polytechnical University, Xian, China, 710072.
b Xian Key laboratory of Functional Organic porous materials, Northwestern Polytechnical University, China, 710129.
c Department of Chemical Engineering, College of Engineering, Jazan University, Jazan 45142, Kingdom of Saudi Arabia.
d Shaanxi Engineering and Research Center for Functional Polymers on Adsorption and Separation, Sunresins New Materials Co. Ltd., Xi’an, 710072, China.
Abstract: An economical and highly uranium extraction from seawater remains a crucial task for energy sources and environmental safety. Aiming for improving mass transfer rate of uranium adsorption from seawater, a new synthetic strategy was adopted for the fabrication of 2D-open channel microporous bio-adsorbent for uranium extraction from seawater. Herein, the in-situ ATRP grafting approach was adopted to graft divinylbenzene, polyacrylonitrile onto the surfaces of microporous frameworks via the vapour phase method. The post-synthetic functionalization was carried out by hydrothermal method, where amidoxime groups are structure-directing agents to trap uranium. Further, amidoxime groups not only enhanced hydrophilicity but also adjusts adsorbents pKa. AO-Fc faces minimum interference of competing ions and achieves a high uranium adsorption capacity of 8.57±0.02 and 409±1 mg/g in seawater and simulated solution. Despite its stable structure, AO-Fc exhibits a long life span and negligible weight loss revealed AO-Fc could be applied as a potential adsorbent for radionuclide.
Keywords: Microporous bioadsorbent; 2D-open channel; vapor-phase modification; ATRP; uranium
Introduction
A rapid increase in energy demands has given rise to energy shortage, nuclear energy with the advantage of low carbon emission play an important role in sustainable energy source1,2. Uranium plays a key role in nuclear energy sources, therefore its extraction is very important for continuous energy supply3-5. However, it is estimated uranium in the terrestrial ores is limited and at the current usage, the terrestrial resources might be ended at the end of the current century6. Comparatively, it is estimated 4.5 billion tons of uranium in seawater, which is a thousand times higher than terrestrial ores7-9. Therefore, a new strategy needs to develop to extract efficient uranium from seawater to fill the energy gap, environmental protection and sustainable development. However, the presence of competing ions, low uranium concentration (3.3 ppb) and high-cost synthetic preparation hinder the development of materials for the extraction of uranium from natural seawater10-14. Various materials such as porous organic polymers (POPs)15,16, covalent organic frameworks (COFs)17-19, porous aromatic frameworks (PAFs)3,20, metal-organic frameworks (MOFs)21,22 and biopolymers23-25have been used for the extraction of uranium from seawater. Among all of them, amidoxime-modified adsorbents are promising with the advantage of high selectivity towards uranium in seawater26-29. However, the development of most of the material is either expensive, difficult to synthesize, poor stability and low uranium adsorption efficiency in seawater. Recently, efforts have been devoted to developing advanced materials via simple and facile methods from inexpensive raw materials with ample uranium adsorption capacity.
Charcoal-based materials are highly interested due to their low cost, porous structure, and environmentally friendly nature1,30-32. Recently, amidoxime modified hollow fibers were used for uranium adsorption33. Zhou et al. reported 1D porous adsorbent from wood waste for adsorption of polycyclic aromatic hydrocarbons34. Liao et al. reported pig manure-based biochar for uranium extraction35. Wang et al. reported 1D amidoxime modified bamboo charcoal for uranium extraction from seawater36. The drawbacks of already available amidoxime modified charcoal-based adsorbents for uranium extraction are as follows; (i) Regarding the analysis and reporting the adsorption results, the experimental adsorption uncertainty is currently missing, (ii) the preparation method is difficult or low functionalization yield and or perform well under inert atmospheres, (iii) use of high cost solvents for the preparation and purification process and (iv) requirement of typical experimental procedure with critical conditions. In this wok we could sort out these problems as well by carrying a simple method by carbonization process in vacuum and subsequent vapor phase modification via ATRP to obtain highly functionalized ultra-porous material. Then after the post-synthetic modification was carried to convert nitrile groups into amidoxime functional groups onto the surface of 2D channels by hydrothermal method. The uncertainty in uranium adsorption experiment was measurement by using classic concepts of error propagation.