Fengcheng Wu

Performance and Mechanism of Uranium Adsorption from Seawater to Poly(dopamine)-Inspired Sorbents

Developing facile and robust technologies for effective enrichment of uranium from seawater is of great significance for resource sustainability and environmental safety. By exploiting mussel-inspired polydopamine (PDA) chemistry, diverse types of PDA-functionalized sorbents including magnetic nanoparticle (MNP), ordered mesoporous carbon (OMC), and glass fiber carpet (GFC) were synthesized. The PDA functional layers with abundant catechol and amine/imine groups provided an excellent platform for binding to uranium. Due to the distinctive structure of PDA, the sorbents exhibited multistage kinetics which was simultaneously controlled by chemisorption and intralayer diffusion. Applying the diverse PDA-modified sorbents for enrichment of low concentration (parts per billion) uranium in laboratory-prepared solutions and unpurified seawater was fully evaluated under different scenarios: that is, by batch adsorption for MNP and OMC and by selective filtration for GFC. Moreover, high-resolution X-ray photoelectron spectroscopic and extended X-ray absorption fine structure studies were performed for probing the underlying coordination mechanism between PDA and U(VI). The catechol hydroxyls of PDA were identified as the main bidentate ligands to coordinate U(VI) at the equatorial plane. This study assessed the potential of versatile PDA chemistry for development of efficient uranium sorbents and provided new insights into the interaction mechanism between PDA and uranium.

Highly efficient removal of 137Cs in seawater by potassium titanium ferrocyanide functionalized magnetic microspheres with multilayer core–shell structure

In this study, a novel kind of core–shell-structured magnetic microsphere functionalized with potassium titanium ferrocyanide (KTiFC) was developed for the highly efficient removal of radioactive cesium from seawater. During the synthesis, a compact silica protective interlayer was deliberately constructed to stabilize the nano-sized magnetite cores, while preventing erosion under harsh environmental conditions. Because of high ion exchange capacity of the KTiFC functional layer, the magnetic microspheres exhibited high removal efficiency (≥97.7%) of radiocesium from 137Cs-spiked solutions (3000–35 000 Bq L−1) and contaminated seawater. Batch experiments revealed that adsorption equilibrium was rapidly achieved within 30 min and the maximum adsorption capacity was up to 43.09 mg g−1. Kinetic models and Langmuir/Freundlich adsorption isotherm equations were used to fit the experiment data for describing the adsorption process. Because of the favorable magnetic property, a facile separation and reclamation of the magnetic microspheres from aqueous solution was achieved under an external magnetic field. Moreover, from a practical viewpoint, the magnetic microspheres were proven to have good re-dispersion properties and long-term stability against strong HNO3 solutions (1.0 mol L−1). These magnetic microspheres are believed to hold great promise for the clean-up of radiocesium contaminated water around nuclear facilities and/or after nuclear accidents.

Novel core–shell structured superparamagnetic microspheres decorated with macrocyclic host molecules for specific recognition and magnetic removal of Pb(II)

In this work, core–shell structured superparamagnetic microspheres with highly specific recognition ability towards Pb(II), based on host–guest interactions, were developed for the first time. The four-component microspheres consist of a superparamagnetic Fe3O4 core, two-layer silica serving as a protection shell and functional spacer, and a macrocyclic host molecule 1,3-alternate calix[4]arene-crown-6 decorated periphery. The magnetic microspheres showed easy dispersibility, high magnetization (45.8 emu g−1) and a sensitive response to an applied magnetic field. Reversible magnetic separation could be accomplished within 15 seconds. The superparamagnetic properties guaranteed convenient redispersion of the magnetic microspheres. Batch experiments revealed that the magnetic microspheres had a remarkable selectivity to Pb(II) in the presence of various interfering metals. Furthermore, the magnetic microspheres showed good stability against acid erosion for 20 days. The characterization of the structure, micro-morphology and magnetic properties of the microspheres are detailed herein. The recognition mechanism concerning the host–guest interaction and the effect of neighboring amino donors is discussed. This work offers a facile and efficient pathway to build host molecule functionalized core–shell magnetic microspheres, which have great potential for molecular recognition and separation applications.

Surface-initiated SET-LRP mediated by mussel-inspired polydopamine chemistry for controlled building of novel core–shell magnetic nanoparticles for highly-efficient uranium enrichment

This study presents an effective and facile strategy by integrating surface-initiated single electron transfer living radical polymerization (SET-LRP) with mussel-inspired polydopamine (PDA) chemistry for controlled building of a novel class of core–shell magnetic nanoparticles (MNPs) for highly-efficient uranium enrichment. The strategy initially involves the deposition of a PDA encapsulation layer by spontaneous self-polymerization on the Fe3O4 core, which serves as a safety shell and provides an enabling platform for anchoring of 2-bromoisobutyryl bromide (BiBB) to form macro-initiators. Dense polyacrylonitrile (PAN) brushes are grown from the BiBB-attached PDA shell via SET-LRP using Cu(0)/Me6TREN as a catalytic/ligand system, followed by conversion to amidoxime (AO) functionalized polymer brushes. The core–shell Fe3O4@PDA@PAO MNPs exhibit favorable superparamagnetic characteristics and a fast response within 6 s under an applied magnetic field. Due to the strong binding ability of AO ligands, Fe3O4@PDA@PAO shows a remarkable adsorption capacity (qe = 162.5 mg g−1) toward uranyl ions under optimal pH conditions. A study on the adsorption kinetics suggests that the adsorption process might conform to the pseudo-second-order model. We conclude that the Fe3O4@PDA@PAO MNPs have the potential for effective enrichment and magnetic separation of uranium, and the integrative synthetic strategy combining the SET-LRP technique and PDA chemistry would bring extensive opportunities for versatile surface modification of nanomaterials for more demanding applications.

Visualization of Adsorption: Luminescent Mesoporous Silica-Carbon Dots Composite for Rapid and Selective Removal of U(VI) and in Situ Monitoring the Adsorption Behavior

The removal and separation of uranium from aqueous solutions are quite important for resource reclamation and environmental protection. Being one of the most effective techniques for metal separation, adsorption of uranium by a variety of adsorbent materials has been a subject of study with high interest in recent years. However, current methods for monitoring the adsorption process require complicated procedures and tedious measurements, which hinders the development of processes for efficient separation of uranium. In this work, we prepared a type of luminescent mesoporous silica-carbon dots composite material that has high efficiency for the adsorption of uranium and allows simultaneous in situ monitoring of the adsorption process. Carbon dots (CDs) were prepared in situ and introduced onto amino-functionalized ordered mesoporous silica (SBA-NH2) by a facile microplasma-assisted method. The prepared CDs/SBA-NH2 nanocomposites preserved the high specific surface area of the mesoporous silica, as well as the fluorescent properties of the CDs. Compared with bare SBA-NH2, the CDs/SBA-NH2 nanocomposites showed much improved adsorption ability and excellent selectivity for uranyl ions. Moreover, the fluorescence intensity of the composites decreased along with the increase of uranium uptake, indicating that the CDs/SBA-NH2 nanocomposites could be used for on-site monitoring of the adsorption behavior. More interestingly, the adsorption selectivity of the composites for metal ions was in good agreement with the selective fluorescence response of the original CDs, which means that the adsorption selectivity of CDs-based composite materials can be predicted by evaluating the fluorescence selectivity of the CDs for metal ions. As the first study of CDs-based nanocomposites for the adsorption of actinide elements, this work opens a new avenue for the in situ monitoring of adsorption behavior of CDs-based nanocomposites while extending their application areas.

New short-channel SBA-15 mesoporous silicas functionalized with polyazamacrocyclic ligands for selective capturing of palladium ions in HNO3 media

In this study, a new kind of short-channel SBA-15 mesoporous silica decorated with polyazamacrocyclic ligands was developed, showing selective binding ability to palladium ions based on host–guest interaction. The established synthesis protocol involved the co-condensation synthesis of an SBA-15 precursor with halogen atoms uniformly incorporated in the mesoporous silica matrix, followed by the anchoring of 1,4,7,10-teraazacyclododecane (Cyclen) ligands via post-grafting. Due to the short straight channels and large pore size facilitating the diffusion of the molecules and ions, the mesoporous silicas were found to possess a high density of the functional Cyclen ligands, as well as high adsorption capacity of Pd(II) in HNO3 solutions. The structure and morphology of the Cyclen functionalized mesoporous silicas were fully characterized. And, the adsorption behavior toward Pd(II) was investigated combined with the theoretical interpretation of the experimental data based on typical kinetic equations, isotherm models and thermodynamic equations. Furthermore, the detailed coordination mechanism between the Cyclen ligands and Pd(II) was examined by high resolution X-ray photoelectron spectroscopy (XPS). A suggested mechanism involving the synergistic effect of four cyclic amines in the Cyclen ligands was proposed to describe the coordination to Pd(II) in HNO3 solutions. Overall, this work provides a facile and effective pathway to build polyazamacrocycle ligand decorated mesoporous silicas with short-channels and large pores, which might be potentially used for molecule recognition and selective enrichment of precious metals.

Macrocyclic ligand decorated ordered mesoporous silica with large-pore and short-channel characteristics for effective separation of lithium isotopes: synthesis, adsorptive behavior study and DFT modeling

Effective separation of lithium isotopes is of strategic value which attracts growing attention worldwide. This study reports a new class of macrocyclic ligand decorated ordered mesoporous silica (OMS) with large-pore and short-channel characteristics, which holds the potential to effectively separate lithium isotopes in aqueous solutions. Initially, a series of benzo-15-crown-5 (B15C5) derivatives containing different electron-donating or -withdrawing substituents were synthesized. Extractive separation of lithium isotopes in a liquid-liquid system was comparatively studied, highlighting the effect of the substituent, solvent, counter anion and temperature. The optimal NH2-B15C5 ligands were then covalently anchored to a short-channel SBA-15 OMS precursor bearing alkyl halides via a post-modification protocol. Adsorptive separation of the lithium isotopes was fully investigated, combined with kinetics and thermodynamics analysis, and simulation by using classic adsorption isotherm models. The NH2-B15C5 ligand functionalized OMSs exhibited selectivity to lithium ions against other alkali metal ions including K(i). Additionally, a more efficient separation of lithium isotopes could be obtained at a lower temperature in systems with softer counter anions and solvents with a lower dielectric constant. The highest value separation factor (α = 1.049 ± 0.002) was obtained in CF3COOLi aqueous solution at 288.15 K. Moreover, theoretical computation based on the density functional theory (DFT) was performed to elucidate the complexation interactions between the macrocyclic ligands and lithium ions. A suggested mechanism involving an isotopic exchange equilibrium was proposed to describe the lithium isotope separation by the functionalized OMSs.