Bo Li

Preparation and adsorption performance of 5-azacytosine-functionalized hydrothermal carbon for selective solid-phase extraction of uranium

A new solid-phase extraction adsorbent was prepared by employing a two-step grafting from approach to anchor a multidentate N-donor ligand, 5-azacytosine onto hydrothermal carbon (HTC) microspheres for highly selective separation of U(VI) from multi-ion system. Fourier-transform infrared and X-ray photoelectron spectroscopies were used to analyze the chemical structure and properties of resultant HTC-based materials. The adsorption behavior of U(VI) onto the adsorbent was investigated as functions of pH, contact time, ionic strength, temperature, and initial U(VI) concentration using batch adsorption experiments. The U(VI) adsorption was of pH dependent. The adsorption achieved equilibrium within 30 min and followed a pseudo-second-order equation. The adsorption amount of U(VI) increased with raising the temperature from 283.15 to 333.15K. Remarkably, high ionic strength up to 5.0 mol L(-1) NaNO(3) had only slight effect on the adsorption. The maximum U(VI) adsorption capacity reached 408.36 mg g(-1) at 333.15K and pH 4.5. Results from batch experiments in a simulated nuclear industrial effluent, containing 13 co-existing cations including uranyl ion, showed a high adsorption capacity and selectivity of the adsorbent for uranium (0.63 mmol U g(-1), accounting for about 67% of the total adsorption amount).

Simple small molecule carbon source strategy for synthesis of functional hydrothermal carbon: preparation of highly efficient uranium selective solid phase extractant

In this paper, simple small molecules, glyoxal and acrylonitrile, are chosen as starting materials to prepare an amidoxime-functionalized hydrothermal carbon-based solid phase extractant (HTC-AO) via a one-step hydrothermal process following a simple oximation. The resulting HTC-AO exhibits the anticipated properties, i.e., low porosity (0.01 cm3 g−1) and intraparticle diffusion coefficient (kint = 0.042 mmol g−1 min−0.5), high content of amidoxime groups (1.66 mmol g−1) and minimal undesired functional groups (typically carboxylic group: 0.07 mmol g−1; phenolic group: 0.38 mmol g−1; lactonic group: 0.01 mmol g−1). Moreover, the results of irradiation experiments under γ-ray dosages between 1 and 100 kGy indicate that HTC-AO has good radiation stability. The sorption behavior of U(VI) onto HTC-AO is investigated in detail using batch sorption experiments. A saturation U(VI) sorption capacity over that of all the uranium sorbents reported previously is found to be 1021.6 mg g−1 at pH 4.5 in single uranium solution, and a so far unreported highest uranium selectivity of 81.6% with a sorption capacity of 268.9 mg g−1 is observed at pH 2.5 in multi-ion solution. The significant outcomes in this work confirms that the “simple small molecule carbon source” strategy is practical and efficient, and may have the potential for the preparation of other types of functional materials such as highly specific catalysts, drug targeting carriers and others.

A catechol-like phenolic ligand-functionalized hydrothermal carbon: One-pot synthesis, characterization and sorption behavior toward uranium

We proposed a new approach for preparing an efficient uranium-selective solid phase extractant (HTC-btg) by choosing bayberry tannin as the main building block and especially glyoxal as crosslinking agent via a simple, economic, and green one-pot hydrothermal synthesis. The results of characterization and analysis show that after addition of glyoxal into only bayberry tannin-based hydrothermal reaction system, the as-synthesized HTC-btg displayed higher thermal stability, larger specific surface area and more than doubled surface phenolic hydroxyl groups. The sorption behavior of the sorbents toward uranium under various conditions was investigated in detail and the results indicated that the process is fast, endothermic, spontaneous, and pseudo-second-order chemisorption. The U(VI) sorption capacity reached up to 307.3 mg g(-1) under the current experimental conditions. The selective sorption in a specially designed multi-ion solution containing 12 co-existing cations over the range of pH 1.0-4.5 shown that the amount of uranium sorbed accounts for about 53% of the total sorption amount at pH 4.5 and distinctively about 85%, unreported so far to our knowledge, at pH 2.0. Finally, a possible mechanism involving interaction between uranyl ions and phenolic hydroxyl groups on HTC-btg was proposed.

A novel benzimidazole-functionalized 2-D COF material: Synthesis and application as a selective solid-phase extractant for separation of uranium

A novel COF-based material (COF-COOH) containing large amounts of carboxylic groups was prepared for the first time by using a simple and effective one-step synthetic method, in which the cheap and commercially available raw materials, trimesoyl chloride and p-phenylenediamine, were used. The as-synthesized COF-COOH was modified with previously synthesized 2-(2,4-dihydroxyphenyl)-benzimidazole (HBI) by grafting to method, and a new solid-phase extractant (COF-HBI) with highly efficient sorption performance for uranium(VI) was consequently obtained. A series of characterizations demonstrated that COF-COOH and COF-HBI exhibited great thermostabilities and irradiation stabilities. Sorption behavior of the COF-based materials toward U(VI) was compared in simulated nuclear industrial effluent containing UO2(2+) and 11 undesired ions, and the UO2(2+) sorption amount of COF-HBI was 81 mg g(-1), accounting for approximately 58% of the total sorption amount, which was much higher than the sorption selectivity of COF-COOH to UO2(2+) (39%). Batch sorption experiment results indicated that the uranium(VI) sorption on COF-HBI was a pH dependent, rapid (sorption equilibrium was reached in 30 min), endothermic and spontaneous process. In the most favorable conditions, the equilibrium sorption capacity of the adsorbent for uranium could reach 211 mg g(-1).

“Stereoscopic” 2D super-microporous phosphazene-based covalent organic framework: Design, synthesis and selective sorption towards uranium at high acidic condition

So far, only five primary elements (C, H, O, N and B) and two types of spatial configuration (C2-C4, C6 and Td) are reported to build the monomers for synthesis of covalent organic frameworks (COFs), which have partially limited the route selection for accessing COFs with new topological structure and novel properties. Here, we reported the design and synthesis of a new stereoscopic 2D super-microporous phosphazene-based covalent organic framework (MPCOF) by using hexachorocyclotriphosphazene (a P-containing monomer in a C3-like spatial configuration) and p-phenylenediamine (a linker). The as-synthesized MPCOF shows high crystallinity, relatively high heat and acid stability and distinctive super-microporous structure with narrow pore-size distributions ranging from 1.0-2.1nm. The results of batch sorption experiments with a multi-ion solution containing 12 co-existing cations show that in the pH range of 1-2.5, MPCOF exhibits excellent separation efficiency for uranium with adsorption capacity more than 71mg/g and selectivity up to record-breaking 92%, and furthermore, an unreported sorption capacity (>50mg/g) and selectivity (>60%) were obtained under strong acidic condition (1M HNO3). Studies on sorption mechanism indicate that the uranium separation by MPCOF in acidic solution is realized mainly through both intra-particle diffusion and size-sieving effect.

An adaptive supramolecular organic framework for highly efficient separation of uranium via an in situ induced fit mechanism

On the basis of the unusual coordination structure of UO22+ combined with the adaptive nature of supramolecular organic frameworks (SOFs), here we have designed and prepared a novel SOF-based solid phase extraction adsorbent (MA–TMA) using N-donor-containing melamine (MA) and O-donor-containing trimesic acid (TMA) as bifunctional building blocks mutually linked via hydrogen bonds. The as-prepared MA–TMA, with a rich N-/N- and N-/O-heterocyclic structure throughout its framework, provides an accessible coordination geometry and/or ligand environment for the uranyl ion, which builds the crucial structural basis for the pre-organized adaptive frameworks closely related to the “induced-fit” and selective recognition of uranyl ions. The main results are as follows: (1) the highest selectivity of 92%, so far unreported, and a considerable capacity of 324 mg g−1 for uranium adsorption by MA–TMA are observed in weak acidic multi-cation solution (pH 2.5), accompanied by a distribution coefficient Kd value of 16u2006000 mL g−1, 100-fold or more over other 11 competitive cations; (2) MA–TMA could reach its limiting saturation capacity of 1028 mg g−1 at pH 4.5 in pure-U(VI) solution; (3) noteworthily, the morphology of MA–TMA changed from a ribbon-like structure with a nano-diameter before adsorption into aggregated granules with a size of tens of microns after adsorption, which would be much more favorable for subsequent solid–liquid separation. Furthermore, possible mechanisms for the selective recognition of uranyl ions and the morphological changes of MA–TMA after adsorption are explored based on experimental characterization and chemical rationale.

Three novel triazine-based materials with different O/S/N set of donor atoms: One-step preparation and comparison of their capability in selective separation of uranium

Cyanuric chloride was chosen as a core skeleton which reacted with desired linker molecules, urea, thiourea and thiosemicarbazide, to prepare three novel functional covalent triazine-based frameworks, CCU (O-donor set), CCTU (S-donor set) and CCTS (S, N-donor set) respectively, designed for selective adsorption of U(VI). The products have high nitrogen concentration (>30 wt%), regular structure, relatively high chemical and thermal stability. Adsorption behaviors of the products on U(VI) were examined by batch experiments. CCU and CCTU can extract U(VI) from simulated nuclear industrial effluent containing 12 co-existing cations with relatively high selectivity (54.4% and 54.2%, respectively). Especially, effects of donor atoms O/S on adsorption were investigated, and the outcomes indicate that the difference in coordinating ability between the donor atoms is weakened in large conjugated systems, and the related functional groups with originally very strong coordination abilities may not be the best choice for the application in selective adsorption of uranium and also other metals. The as-proposed approach can easily be expanded into design and preparation of new highly efficient adsorbents for selective separation and recovery of uranium through adjusting the structures, types and amounts of functional groups of adsorbents by choosing suitable linkers.

Nano-diamond particles functionalized with single/double-arm amide–thiourea ligands for adsorption of metal ions

Separation efficiency of solid-phase extractant is greatly subjected to the spatial configurations of functional ligands attached to the matrix, which has not been studied efficiently till now. In order to further understand the relationship between spatial configurations of the attached functional ligand and the adsorption ability of the extractant, two novel molecules (single-armed ligand, SA and double-armed ligand, DA) with identical coordination unit (amide-thiourea) but different spatial configurations (single/double arms) were designed and synthesized. The corresponding extractants, ND-SA and ND-DA were obtained by modification of nanodiamond (ND) with SA and DA and both the extractants displayed good chemical and thermal stabilities. The batch adsorption experiments showed that ND-SA and ND-DA possess large adsorption capacities (∼200 mg g(-1)), very fast adsorption kinetics (reaching equilibrium within 2 min) and excellent selectivities (up to 82% and 72%, respectively) for uranium. The study of the possible mechanism indicated that ND-DA tends to utilize its tweezer-like double arms to clamp metal ions and the stronger chelate interaction could to some extent weaken the coordination selectivity of attached DA ligand. In contrast, single-armed adsorbent ND-SA unexpectedly exhibited better adsorption selectivity for uranium than ND-DA owing to its more flexible spatial configuration and moderate complexing ability.

Effective charge-discriminated group separation of metal ions under highly acidic conditions using nanodiamond-pillared graphene oxide membrane

It has been a major challenge for separation science to separate selectively valuable metal ions from multi-cation aqueous solutions, especially in highly acidic media. In this study, a novel nanodiamond-pillared graphene oxide (NPG) membrane was, for the first time, prepared via intercalation of nanodiamond (ND) into graphene oxide (GO) by using a simple vacuum-assisted self-assembly method. Comprehensive characterization and comparison of GO and its derivative membranes show that after intercalation of ND into GO, the interlayer space and intrastratal nanochannels (similar to “the number of theoretical plates” in chromatography) are markedly increased; the channel-size distribution is profitably narrowed, and the thermal stability and hydrophilicity are enhanced; distinctively, the surface microroughness is significantly improved. The results of ion-sieving experiments demonstrate that the NPG nanofiltration membrane possesses a precise charge-discriminated group separation ability in a strong acidic solution containing 10 coexisting cations. Compared with the unmodified GO membrane, the average filtration rates of the NPG membrane were improved by 76.8% (for monovalent ions), 63.5% (for divalent ions), 118.0% (for trivalent lanthanide ions), 71.0% (for UO22+) and 105.1% (for Th4+) respectively, under the same conditions, meanwhile, the permeation rate of the multivalent cations with same charges shows much better consistency. It’s worth mentioning that UO22+ has the largest hydrated diameter among the cations used in this work, but the filtration rate of UO22+ is actually similar to that of the trivalent lanthanide cations, which may be attributed to the effective charge near +3 of UO22+, as reported in the literature. Finally, the reusability of the as-prepared nanofiltration membrane was investigated in 4 M nitric acid solution. After 5 runs of recycling tests, the group separation ability of the NPG membrane was basically maintained, and the filtration rate was reduced by up to 15.2% (for K+). These findings suggest that the as-prepared carbonaceous nanofiltration membrane could be among the most attractive membrane materials for the separation of valuable metal ions and have great potential applications in not only the nuclear power industry, but also the metallurgical, chemical manufacturing, electroplating and metal finishing industries.

Conversion of supramolecular organic framework to uranyl-organic coordination complex: a new “matrix-free” strategy for highly efficient capture of uranium

Herein, an innovative “matrix-free” strategy has been proposed for highly efficient uranium capture via uranyl-induced disassembly and reassembly of the two functional building blocks of the as-prepared hydrogen-bonded supramolecular organic framework (HSOF), which is composed of N-donor-containing melamine and O-donor-containing trimesic acid self-assembled through hydrogen bonding. The batch experimental results demonstrated that HSOF possesses excellent extraction capacity (qm = 444 mg g−1), >99% removal efficiency in the range of tested U(VI) concentration (20–130 ppm) with a considerably large KUd value of 1.3 × 107 mL g−1 at 130 ppm, and very fast extraction rate (<10 min) for UO22+. Especially, the uranium selectivity (SU = qe-U/qe-tol) of HSOF stays above 80% over the pH range tested in a uranium-containing solution with 11 competing cations, and distinctively, reaches the so far unreported 99% with a great capacity of 309 mg g−1 at pH 2.5. It is worth noting that a clear morphology transformation of HSOF nanowires to nanosheets of the uranyl-organic coordination complex (UOCC) after extraction has been observed only in the presence of uranyl ions. Moreover, according to experimental characterization and DFT studies, a possible mechanism for the efficient capture of uranium is proposed: the stronger coordination interaction among uranyl, TMA and MA could replace the weaker hydrogen-bond interaction originally linking the two building blocks in HSOF in the extraction process.