Comparison with adsorption of Re (VII) by two different γ-radiation synthesized silica-grafting of vinylimidazole/4-vinylpyridine adsorbents

Ultrafast and selective capture of 99TcO4-/ReO4- from wastewater by hyper-branched quaternary ammonium group-functionalized resin

99Tc primarily exists high mobility in the natural aqueous environment due to its extremely high solubility and non-complexing features, which can easily cause radioactive pollution. We herein report a general strategy for constructing a novel resin (SiPAN-PEI) with multiple positive charges nitrogen, exhibiting ultrafast adsorption kinetics (< 3 min), superior adsorption capacities (463.96 mg g-1), and excellent selectivity in the presence of excess competitive anions, which exceed those of most commercial resins. Moreover, based on impressive structure stability in extreme conditions, SiPAN-PEI can still maintain superior adsorption abilities after suffering irradiation, calcination, and immersion in strong acid. In addition, the separation performance kept excellently after five loading-washing-eluting cycles and the total adsorption ratio can still reach 97 %. Outstandingly, SiPAN-PEI can remove most of ReO4- from simulated nuclear wastewater through a sequential injection automatic separation system and can reduce the concentration of ReO4- to the maximum concentration standard set by the World Health Organization (WHO) in a short time. Leveraging density functional theory calculations and other characteristics clearly elucidated adsorption mechanism of anion-exchange between Cl- and TcO4-/ReO4-. In terms of superior adsorption property, SiPAN-PEI is demonstrated to be a pretty candidate for 99Tc elimination from wastewater.

Toward a mechanistic understanding of Rhenium(VII) adsorption behavior onto aminated polymeric adsorbents: Batch experiments, spectroscopic analyses, and theoretical computations

Rhenium, a rare and critical metal, existing in the industrial wastewater has been aroused extensive interests recently, due to its environmental and resource issues. Chitosan, an easily available, low-cost and eco-friendly biopolymer, was prepared and modified by grafting primary, secondary, tertiary and quaternary amino groups, respectively. Adsorption behaviors and interactions between ReO4- and these four types of aminated adsorbents were investigated through batch experiments, spectroscopic analysis, and theoretical computations. Chitosan modified with secondary amines showed an extremely high uptake of ReO4- with 742.0 mg g-1, which was higher than any reported adsorbents so far. Furthermore, a relatively high adsorption selectivity for Re(VII), as well as the stable and facile regeneration of these aminated adsorbents revealed a promising approach for Re(VII) recovery in full-scale applications. The electrostatic attraction was illustrated to be the main adsorption mechanism by Fourier Transform Infrared Spectroscopy and X-ray Photoelectron Spectroscopy analyses. Significantly, the sub-steps of the adsorption process, encompassing the transformation of binding sites and the subsequent binding between these sites and the adsorbate, have been thoroughly investigated through the density functional theory (DFT) calculation method. This approach was firstly proposed to clearly demonstrate the differences in Re(VII) adsorption behavior onto four types of aminated adsorbents, resulting the importance of not only strong binding energy but also an appropriate binding spatial environmental for effective Re(VII) adsorption.

Radiation synthesis of imidazolium-based polymeric ionic liquid gel for efficient adsorption of Re(VII) and U(VI) from aqueous solution

In this research, an imidazolium-based polymeric ionic liquid (PIL) gel was effectively synthesized in one step via electron beam (EB) radiation technology. The synthesized gel with gel fraction of 78% under 80 kGy was used for the adsorption and separation of Re(VII) and U(VI). The structure of the gel was characterized by FTIR, SEM, BET, and XPS. Furthermore, batch adsorption was experimented to explore its performance of Re(VII) and U(VI) removal. The two adsorption processes all more fitted the Langmuir isotherm model with the maximum adsorption capacities of 892.9 mg/g for Re(VII) and 243.9 mg/g for U(VI). The adsorption reached equilibrium within 1 min for Re(VII), while within 4 min for U(VI), showing its greatly rapid adsorption rate because of its three-dimensional porous network structure. In addition, the separation experiments of Re/U replied that PIL gel could effectively separate Re(VII) from the simulated uranium leaching solution. Regeneration experiments present the good reusability of PIL gel. This work demonstrated the practical application of EB-radiation technology in the synthesis of PIL gel, which is a promising adsorbent for Re(VII) and U(VI) recovery .

Aminomethylpyridine isomers functionalized cellulose microspheres for TcO4-/ReO4- uptake: Structure-properties relationship and their application in different aquatic systems

Technetium-99 (⁹⁹Tc) is a long-lived radioactive nuclide that poses great threat to environment, hence selective removal of ⁹⁹Tc from aquatic system is always an issue. Aminomethylpyridine (AMP) equipped with pyridine and amino, is a promising receptor for TcO₄^- and its surrogate ReO₄^-, thus it is of interest to explore and understand the structure-properties relationship of ReO₄^- adsorption related to n-AMP structure that differ in amino methyl position. In this work, three n-AMP functionalized cellulose microspheres (n-AMPR, n = 2, 3, 4) were synthesized and employed for TcO₄^-/ReO₄^- uptake. The effect of aminomethyl position on adsorption properties of n-AMPR for ReO₄^- were investigated and compared. Adsorption kinetics and adsorption isotherm showed that adsorption speed and adsorption capacity were in order of 3-AMPR > 2-AMPR > 4-AMPR. DFT calculation verified that the adsorption of ReO₄^- by n-AMPR was attributed to electrostatic interaction and hydrogen bonding interaction, the order of adsorption abilities of n-AMPR was due to that steric effect and hydrogen bond collaborated in stabilizing n-AMPR-ReO₄^- complexes. The column experiments demonstrated that 3-AMPR can be selectively remove ReO₄^- from simulated groundwater. More importantly, ⁹⁹Tc column experiments showed that 3-AMPR had a better ability for actual radioactive TcO₄^-.

Recent progress in environmental applications of functional adsorbent prepared by radiation techniques: A review

Environmental pollution has been accelerated due to fast urbanization and industrialization, and thus hazardous contaminants removal and valuable metal recovery have become urgent. Adsorption has become a promising technology for water treatment because of its advantages of low-cost, good reusability, low energy consumption, high capacity and high selectivity. Particularly, radiation techniques including radiation induced graft copolymerization and radiation crosslinking have been found to be widely utilized to exploit adsorbents for water treatment. In this review, the current status and progress of adsorbents in environmental pollution in the past decade are summarized, including adsorbents (in form of particles, fiber and fabric, membrane, novel nanomaterials) synthesized by radiation induced graft copolymerization and hydrogel-based adsorbents fabricated by radiation crosslinking. Finally, further perspective on the development and challenge of adsorbents by radiation techniques is also suggested.

Radiation synthesis of ionic liquid-functionalized silica-based adsorbents: a preliminary investigation on its application for removal of ReO4- as an analog for TcO4. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2021;28:17752-17762. [PMID: 33400123 DOI: 10.1007/s11356-020-12078-z]

The decontamination of radioactive TcO₄^- from nuclear wastes is becoming increasingly crucial for spent nuclear fuel reprocessing and environmental remediation. In this work, a series of ionic liquid-immobilized silica-based adsorbents (SVIL-Cn, n = 1, 4, 8) were newly synthesized using the radiation-induced grafting of 4-vinylbenzyl chloride onto silanized silica and subsequent functionalization with 1-methylimidazole, 1-butylimidazole, or 1-octylimidazole. The synthesis conditions such as the solvent, absorbed dose, and monomer concentration were investigated in detail, and the resulting adsorbents were characterized by elemental analysis, FT-IR, SEM, and TGA. In batch experiments, the adsorbents exhibited a high ReO₄^- (a nonradioactive surrogate of TcO₄^-) removal efficiency over a wide pH range (3 ~ 8), and SVIL-C1 showed a maximum adsorption capacity of 70.62 mg g^-1 towards ReO₄^-. In addition, their adsorption performance barely changed after 800 kGy radiation. The column experiments for treating simulated radioactive wastewater showed that the SVIL-Cn adsorbents could selectively separate TcO₄^-/ReO₄^- from a variety of fission products, and they could be recycled four times with negligible capacity loss. Lastly, XPS and FT-IR analysis confirmed that the adsorption proceeded via an ion-exchange mechanism. The results showed that these adsorbents are suitable for the efficient removal of TcO₄^-/ReO₄^- from radioactive wastewater with complex compositions.

Efficient and Ultrafast Adsorption of Rhenium by Functionalized Hierarchically Mesoporous Silica: A Combined Strategy of Topological Construction and Chemical Modification

Radioactive Tc-99 released by nuclear accidents threatens the environment and human health due to its long half-life and strong transportability. A combined strategy synergizing topological construction and chemical modification was proposed for the synthesis of high-performance adsorbents for Re as an analogue to Tc. On the one hand, hierarchically mesoporous SiO₂ with a fibrous structure (F-SiO₂), a peculiar topology integrating wrinkled open mesopores around 12 nm and on-wall mesopores around 3 nm, was adopted as the substrate of adsorbents. The larger mesopores can act as the superhighway for mass transfer, while the abundant smaller mesopores provide numerous adsorption sites. On the other hand, a series of dicationic pyridine (DCP) derivative groups (-Py⁺C_nH_2nN⁺Me₃) were designed to functionalize F-SiO₂ for improving the adsorption performance toward ReO₄^- anions, the dominating form of Re in aqueous solution. Density functional theory (DFT) calculation combined with batch adsorption experiments revealed that the ReO₄^- adsorption on -Py⁺C₅H₁₀N⁺Me₃ was the most favorable when the length of the spacer between the two positively charged N atoms ranged from 2 to 7 carbons (n = 2-7). However, -Py⁺C₅H₁₀N⁺Me₃ exhibited a much slower adsorption rate than -Py⁺C₂H₄N⁺Me₃. The stronger interaction between ReO₄^- and -Py⁺C₅H₁₀N⁺Me₃ suppresses the adsorbate diffusion. The two positive charges of -Py⁺C₅H₁₀N⁺Me₃ may be perpendicularly distributed, sterically hindering ReO₄^- transport in smaller mesopores. The longer and flexible carbon chains may be aggregated to form the hydrophobic region, repulsing the hydrated ReO₄^- anions. Therefore, the efficient and ultrafast Re adsorption was achieved by synergizing the unique topology of F-SiO₂ and functionalization by -Py⁺C₂H₄N⁺Me₃ with a shorter spacer and weaker affinity ReO₄^-. The detailed investigation demonstrated that -Py⁺C₂H₄N⁺Me₃ possessed exothermic adsorption nature, adequate radiation-resistance, and excellent reusability. Meanwhile, -Py⁺C₅H₁₀N⁺Me₃ exhibited stronger salinity tolerance and higher selectivity. The DCP groups are promising in decontamination of radioactive Tc, as they can meet specific requirements by manipulating the length of spacers.

Quaternary phosphonium modified cellulose microsphere adsorbent for 99Tc decontamination with ultra-high selectivity

Decontamination of radioactive TcO₄^- from nuclear wastes is increasingly crucial for spent nuclear fuel reprocessing and environmental remediation. In the presence of a large excess of competitive anions, the selective separation of TcO₄^- is a major challenge for adsorbents. Herein, by using pre-radiation induced grafting polymerization, we have modified economical and environmentally friendly cellulose microspheres to obtain quaternary phosphonium decorated TcO₄^- adsorbents with an ultra-high selectivity, designated CMS-g-VBPPh₃NO₃. The prepared materials show adsorption capacities of 251 mg g^-1 (for the surrogate Re). The selective factor against NO₃^- in 0.5 mol kg^-1 HNO₃ is as high as 168, showing excellent anion-exchange selectivity towards TcO₄^-. Moreover, CMS-g-VBPPh₃NO₃ was packed in column for treating simulated acidic waste solutions containing Cs, Sr, Eu, Zr, Ru, U and Re, and it showed excellent Re separation performance. Tracer amount of ^99mTc experiments showed that comparing to ReO₄^-, CMS-g-VBPPh₃NO₃ has a better adsorption selectivity for TcO₄^-.

Radiation synthesis of imidazolium-based ionic liquid modified silica adsorbents for ReO4− adsorption

A series of ionic liquid functionalized silica-based adsorbents were synthesized and used to remove ReO₄⁻ from simulated radioactive wastewater.

Synthesis of ZnO nanoparticle-anchored biochar composites for the selective removal of perrhenate, a surrogate for pertechnetate, from radioactive effluents

Pertechnetate (TcO₄-) is a component of low-activity waste (LAW) fractions of legacy nuclear waste, and the adsorption removal of TcO₄- from LAW effluents would greatly benefit the site remediation process. However, available adsorbent materials lack the desired combination of low cost, radiolytic stability, and high selectivity. In this study, a ZnO nanoparticle-anchored biochar composite (ZBC) was fabricated and applied to potentially separate TcO₄- from radioactive effluents. The as-synthesized material exhibited γ radiation resistance and superhydrophobicity, with a strong sorption capacity of 25,916 mg/kg for perrhenate (ReO₄-), which was used in this study as a surrogate for radioactive pertechnetate (TcO₄-). Additionally, the selectivity for ReO₄- exceeded that for the competing ions I-, NO₂-, NO₃-, SO₄^2-, PO₄^3-, Cu²⁺, Fe³⁺, Al³⁺, and UO₂²⁺. These unique features show that ZBC is capable of selectively removing ReO₄- from Hanford LAW melter off-gas scrubber simulant effluent. This selectivity stems from the synergistic effects of both the superhydrophobic surface of the sorbent and the inherent nature of sorbates. Furthermore, density functional theory (DFT) calculations indicated that ReO₄- can form stable complexes on both the (100) and (002) planes of ZnO, of which, the (002) complexes have greater stability. Electron transfer from ReO₄- on (002) was greater than that on (100). These phenomena may be because (002) has a lower surface energy than (100). Partial density of state (PDOS) analysis further confirms that ReO₄- is chemisorbed on ZBC, which agrees with the findings of the Elovich kinetic model. This work provides a feasible pathway for scale-up to produce high-efficiency and cost-effective biosorbents for the removal of radionuclides.

Polymeric ionic liquid gels composed of hydrophilic and hydrophobic units for high adsorption selectivity of perrhenate

The removal of TcO₄⁻ from aqueous solutions has attracted more and more attention recently, and ReO₄⁻ has been widely used as its natural analog. In this work, polymeric ionic liquid gel adsorbents, PC₂-C₁₂vimBr, with high adsorption capacity and selectivity towards ReO₄⁻ were synthesized by radiation-induced polymerization and crosslinking. PC₂-C₁₂vimBr was composed of two monomers: a hydrophobic unit, 1-vinyl-3-dodecylimidazolium bromide for high selectivity, and a hydrophilic unit, 1-vinyl-3-ethylimidazolium bromide for improved kinetics. A gel fraction up to 90% could be achieved under 40 kGy with varied monomer ratios. The adsorption of PC₂-C₁₂vimBr gels for ReO₄⁻ was evaluated by batch adsorption. The PC₂-C₁₂vimBr gel containing 20 mol% hydrophilic unit (named PC₂-C₁₂vimBr-A) could significantly improve the adsorption kinetics, which had an equilibrium time of ca. 24 h. The adsorption capacity obtained from the Langmuir model was 559 mg g⁻¹ (Re/gel). The selective factor against NO₃⁻ was 33.4 ± 1.9, which was more than 10 times higher than that of PC₂vimBr, and it could maintain ReO₄⁻ uptake as high as 100 mg g⁻¹ in 0.5 mol kg⁻¹ HNO₃. The ΔH^Θ and ΔS^Θ of the NO₃⁻/ReO₄⁻ ion-exchange reaction of PC₂-C₁₂vimNO₃-A were −16.9 kJ mol⁻¹ and 29 J mol⁻¹ K⁻¹, respectively, indicating physical adsorption. The adsorption mechanism of ReO₄⁻ onto PC₂-C₁₂vimBr-A gel was ion-exchange, and it could be recovered using 5.4 mol kg⁻¹ HNO₃.

Polymeric ionic liquid gels composed of hydrophilic and hydrophobic units with high adsorption selectivity towards perrhenate were synthesized.