Search

Herein, a novel fluorescent ionic covalent organic framework (BTTA–BDNP) based on a linked carbazole unit was constructed for the synchronous monitoring and capture of TcO4−/ReO4−. BTTA–BDNP has a fast fluorescence response time with a low detection limit (66.7 nM) for ReO4− (a non-radioactive substitute for TcO4−). Meanwhile, the high charge density and hydrophobic skeleton of BTTA–BDNP enable it to exhibit rapid and selective trapping of ReO4− in complex environments. [ABSTRACT FROM AUTHOR]

Abstract Industrial experiments were conducted to investigate the differences in the porosity alleviation between the multi-roll and single-roll reduction modes during continuous casting and develop a simulation model of the porosity closure. The experimental results revealed that heavy reduction and a high solid fraction were beneficial to the porosity alleviation in billets. The simulation results showed that the large plastic strain along the thickness direction (PE22) at the center region caused by the heavy reduction contributed to the porosity closure. The PE22 at the center region of the billet between the single-roll and the multi-roll reduction mode was little different for the same reduction amounts and reduction positions. The reduction efficiency was high at the position of the low solid fraction, which contributed to porosity closure. Since most areas of porosities were formed at the center region of the billet at a high solid fraction, the reduction prior to the formation of the porosities had little effect on the porosity alleviation. The single-roll reduction mode had a better effect on the porosity alleviation than the multi-roll reduction mode because the solid fraction was higher for the single-roll reduction mode. The experimental results are mostly in agreement with the simulation results. [ABSTRACT FROM AUTHOR]

[Display omitted] • A 3D cationic covalent organic framework (TFAM-BDNP) was synthesized via Zincke reaction. • TFAM-BDNP exhibits high adsorption capacity and extremely fast exchange kinetic for ReO 4 −. • TFAM-BDNP demonstrates remarkable selectivity for ReO 4 −. • TFAM-BDNP has outstanding removal efficiency of ReO 4 − from simulated Hanford flow sample. Due to the long half-life and high environmental mobility, the selective and efficient capture of TcO 4 − from nuclear effluents is very important, but it is still very challenging. Herein, we design and synthesize a novel three-dimensional (3D) cationic covalent organic framework (TFAM-BDNP) via Zincke reaction for selective capture of TcO 4 −/ReO 4 −. TFAM-BDNP exhibits high adsorption capacity (998 mg g−1) and extremely fast exchange kinetic (60 s) for ReO 4 − (the non-radioactive alternative to TcO 4 −), attributing to the open 3D hydrophobic channels, abundant active sites, and high chemical stability. More importantly, TFAM-BDNP shows good adsorption performance for ReO 4 − in the presence of significant excess competing anions with a wide pH value range of 2 to 12. Under complex simulated Hanford flow sample, TFAM-BDNP has outstanding removal efficiency of ReO 4 −. The adsorption mechanism of ReO 4 − is mainly caused by anion exchange process. This study provides a novel adsorbent for efficient capture of TcO 4 −/ReO 4 − in complex environmental systems and exploits an effective strategy for broadening the types of 3D COFs. [ABSTRACT FROM AUTHOR]

Uranium is a key element in the nuclear industry and also a global environmental contaminant with combined highly toxic and radioactive. Currently, the materials based on post-modification of amidoxime have been developed for uranium detection and adsorption. However, the affinity of amidoxime group for vanadium is stronger than that of uranium, which is the main challenge hindering the practical application of amidoxime-based adsorbents. Herein, we synthesized a fluorescent covalent organic framework (TFPPy-BDOH) through integrating biphenyl diamine and pyrene unit into the π-conjugated framework. TFPPy-BDOH has an excellent selectivity to uranium due to the synergistic effect of nitrogen atom in the imine bond and hydroxyl groups in conjugated framework. It can achieve ultra-fast fluorescence response time (2 s) and ultra-low detection limit (8.8 nM), which may be attributed to its intrinsic regular porous channel structures and excellent hydrophilicity. More excitingly, TFPPy-BDOH can chemically reduce soluble U (VI) to insoluble U (IV), and release the binding site to adsorb additional U (VI), achieving high adsorption capacity of 982.6 ± 49.1 mg g−1. Therefore, TFPPy-BDOH can overcome the challenges faced by current amidoxime-based adsorbents, making it as a potential adsorbent in practical applications. [Display omitted] • A fluorescent COF (TFPPy-BDOH) is synthesized by a one-step method. • TFPPy-BDOH has ultra-fast fluorescence response time for UO 2 2+. • TFPPy-BDOH can selectively chemically reduce soluble U(VI) to insoluble U(IV). • TFPPy-BDOH achieves high sensitivity and selectivity for detecting and capturing UO 2 2+ in harsh environments. [ABSTRACT FROM AUTHOR]

Abstract: The adsorption of Na atoms on the Si(111)-7×7 surface is studied using first-principles calculations. Compared to the Triangle-Trimer model reported previously, we propose a more stable and robust Na6Si3 Hexagon-Trimer model which has six Na atoms with hexagon shape and three Si edge adatoms moving inward to form a trimer. The total energy of Hexagon-Trimer model is 0.252eV lower than that of Triangle-Trimer model and 0.552eV lower than that of Hexagon model. The simulated STM images of Hexagon-Trimer model are in good agreement with experimental STM observations. The most probable formation process of Hexagon-Trimer model is analyzed. The reaction is catalyzed by a Na atom and the energy barrier is reduced from 0.89 to 0.44eV. These results have provided a complete picture for the formation mechanism of Na6Si3 surface magic clusters on the Si(111)-7×7 surface. [Copyright &y& Elsevier]

We report the first example of vinylene-linked covalent organic framework (Tp-TMT) with enhanced uranium adsorption through combined selective ligand binding, chemical reduction and photocatalytic reduction. The dense hydroxyl functional groups on the Tp-TMT framework had good selectivity and excellent chemical reduction performance for U(VI). Meanwhile, the synergistic effect of hydroxyl groups and triazine unit significantly enhanced the photocatalytic reduction activity. Thus Tp-TMT exhibited incredible adsorption kinetics and capacity for uranium. [Display omitted] • COFs effectively capture uranium through three coordinated mechanisms. • Tp-TMT has excellent visible light conversion efficiency and low band gap. • Tp-TMT enhances uranium adsorption through selective ligand binding and reduction. • Tp-TMT exhibits incredible adsorption kinetics and capacity for uranium. So far, it remains a challenge to synthesize uranium adsorbents with robust stability, high adsorption capacity, excellent photocatalytic activity and easy regeneration. Herein, we report the first example of vinylene-linked covalent organic framework (Tp-TMT) with enhanced uranium adsorption through combined selective ligand binding, chemical reduction and photocatalytic reduction. The unique structure and excellent photocatalytic activity of Tp-TMT make it very suitable for photo-enhanced uranium adsorption through three synergistic mechanisms, thus exhibiting an outstanding uranium adsorption capacity (2362.4 mg g−1). In the dark, a large number of hydroxyl groups in the Tp-TMT framework serve as selective binding sites for uranium, and reduce part of U(VI) to U(IV), thereby greatly improving the adsorption capacity. Meanwhile, the synergistic effect of the triazine units and hydroxyl groups in the highly conjugated framework greatly decreases the optical band gap of Tp-TMT, and an additional U(VI) photocatalytic reduction process can occur under light irradiation, further increasing the adsorption kinetics and capacity. This work explored the structural and functional design of covalent organic frameworks for the adsorption and reduction of uranium in nuclear industry wastewater. [ABSTRACT FROM AUTHOR]

Uranium is a key resource for the development of the nuclear industry, and extracting uranium from the natural seawater is one of the most promising ways to address the shortage of uranium resources. Herein, a semiconducting covalent organic framework (named NDA‐TN‐AO) with excellent photocatalytic and photoelectric activities was synthesized. The excellent photocatalytic effect endowed NDA‐TN‐AO with a high anti‐biofouling activity by generating biotoxic reactive oxygen species and promoting photoelectrons to reduce the adsorbed UVI to insoluble UIV, thereby increasing the uranium extraction capacity. Owing to the photoinduced effect, the adsorption capacity of NDA‐TN‐AO to uranium in seawater reaches 6.07 mg g−1, which is 1.33 times of that in dark. The NDA‐TN‐AO with enhanced adsorption capacity is a promising material for extracting uranium from the natural seawater. [ABSTRACT FROM AUTHOR]

Uranium is a key resource for the development of the nuclear industry, and extracting uranium from the natural seawater is one of the most promising ways to address the shortage of uranium resources. Herein, a semiconducting covalent organic framework (named NDA‐TN‐AO) with excellent photocatalytic and photoelectric activities was synthesized. The excellent photocatalytic effect endowed NDA‐TN‐AO with a high anti‐biofouling activity by generating biotoxic reactive oxygen species and promoting photoelectrons to reduce the adsorbed UVI to insoluble UIV, thereby increasing the uranium extraction capacity. Owing to the photoinduced effect, the adsorption capacity of NDA‐TN‐AO to uranium in seawater reaches 6.07 mg g−1, which is 1.33 times of that in dark. The NDA‐TN‐AO with enhanced adsorption capacity is a promising material for extracting uranium from the natural seawater. [ABSTRACT FROM AUTHOR]

Highlights: [•] Nano-TiO2 was an excellent adsorbent for virus removal in drinking water. [•] The adsorption followed Freundlich isotherm and pseudo second-order rate equation. [•] The PAN (0.05μm) membrane had higher removal efficiency than PVDF (0.20μm). [•] The coupling system (nano-TiO2-membrane) increased the removal efficiency of virus. [•] Coupling system can achieve the effective separation and recycle of nano-particles. [ABSTRACT FROM AUTHOR]

It was found that the interface effects in viscous capillary flow influenced the process of viscosity measurement greatly, and the abnormal viscosity behaviors of polyelectrolytes as well as neutral polymers in dilute solution region were ascribed to interface effect. According to this theory, we have reviewed the previous viscosity data of derivatives of poly-2-vinylpyridine reported by Maclay and Fuoss first. Then, the abnormal viscosity behaviors of a series of sodium polystyrene sulfonate samples with various molecular weights in dilute aqueous solutions were studied further. The solute adsorption behaviors and structural information of polymers have been discussed carefully. [ABSTRACT FROM AUTHOR]

• Highly stable sp2 carbon-conjugated covalent organic framework (COF-PDAN-AO) was synthesized and characterization. • Acid and radiation resistant COF-PDAN-AO exhibits efficient adsorption of UO 2 2+ from radioactive wastewater. • COF-PDAN-AO possesses short adsorption equilibrium time and selectivity for uranium. • The emission of COF-PDAN-AO was selectively quenched upon adding UO 2 2+. Uranium is an important element in the nuclear industry while the discharge of radioactive wastewater can cause serious damages to the environment. In this work, an ultra-stable sp2 carbon-conjugated covalent organic framework (COF-PDAN-AO) is synthesized with amidoxime-substituted monomers for detection and efficient adsorption of uranium from radioactive wastewater. Abundant amidoxime groups laced on the open 1D channels of COF-PDAN-AO exhibit exceptional accessibility and the regular pores facilitate the mass transfer. Based on these features, COF-PDAN-AO achieves ultra-low detection limit of 6.5 nM, high uranium adsorption capacity (410 mg/g) and selective interaction with uranium. In addition, various spectroscopies verify COF-PDAN-AO possesses excellent radioresistance in acidic solution. Regeneration studies have shown that COF-PDAN-AO maintained good structural stability after seven cycles. These results indicate that our sp2 carbon conjugated COF can be potentially used for practical detection and adsorption of uranium from radioactive wastewater. This strategy can be extended to detection and extraction of other contaminants by designing the target ligand. [ABSTRACT FROM AUTHOR]