A Novel Preparation and Vapour Phase Modification of 2D-open Channel Bio-adsorbent for Uranium Separation
Mudasir Ahmad a, b, Jianquan Ren a, Tao Xiua, 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 the mass transfer rate of uranium from seawater, a new synthetic strategy was adopted to synthesize 2D-open channel microporous bio-adsorbent for uranium extraction from seawater. Herein, a vapor phase modification approach was adopted to graft divinylbenzene(DVB), and polyacrylonitrile(AN) onto the surfaces of microporous frameworks via a free radical polymerization method. The post-synthetic functionalization was carried out by hydrothermal process, 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 radionuclides.
Keywords: Microporous bioadsorbent; 2D-open channel; vapor-phase modification; uranium
Introduction
A rapid increase in energy demands has given rise to energy shortage, nuclear energy with the advantage of low carbon emission plays 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 that 4.5 billion tons of uranium in seawater 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. Although fewer amidoxime modified adsorbents show higher uranium adsorption capacity in natural seawater. However, most of them suffer some drawbacks such as high cost, difficult synthetic procedures, and systematic examination is necessary to find the uranium adsorption mechanism. The efficient adsorption of uranium from seawater in a sustainable way remains a major task due to the lack of functional adsorbent.
In this work, we have implemented two ways to prepare amidoxime polymer chain grafted charcoal adsorbent material by free radical polymerization for uranium adsorption from seawater. (i) polymerization of AN in presence of azobisisobutyronitrile (AIBN) and (ii) the enhancement of polymerization using DVB as a crosslinking agent. Accordingly, a porous polymer chain grafted adsorbent was synthesized chemically for efficient uranium adsorption. Various batch adsorption experiments, theoretical models, and analytical techniques were used to investigate the adsorption characteristics and adsorption mechanism including adsorption capacity, kinetics, and selectivity, the interaction between uranium and chelating sites, interference due to competing ions, and investigation of uranium recovery and adsorbent stability. The uncertainty in uranium adsorption results due to error propagation is also reported in this study.