Crystalline versus Amorphous: High-Performance Hafnium Phosphonate Framework for the Separation of Uranium and Transuranium Elements.

Metal phosphonate frameworks (MPFs) consisting of tetravalent metal ions and aryl-phosphonate ligands feature a large affinity for actinides and excellent stabilities in harsh aqueous environments. However, it remains elusive how the crystallinity of MPFs influences their performance in actinide separation. To this end, we prepared a new category of porous, ultrastable MPF with different crystallinities for uranyl and transuranium separation. The results demonstrated that crystalline MPF was generally a better adsorbent for uranyl than the amorphous counterpart and ranked as the top-performing one for uranyl and plutonium in strong acidic solutions. A plausible uranyl sequestration mechanism was unveiled by using powder X-ray diffraction in tandem with vibrational spectroscopy, thermogravimetry, and elemental analysis.

Polymerizable Surfactant Ligand for Stabilization and Film Formation of CsPbBr3 Nanocrystals.

Surfactant ligands are important in the synthesis of inorganic perovskite nanocrystals (NCs), not only for stabilizing NCs but also for surface defect passivation. A new polymerizable surfactant ligand with a multidentate l-cysteine head, a long oleoyl tail, and a polymerizable styrenyl group (NOSVC) is designed for the post-synthesis treatment and stabilization of colloidal CsPbBr3 NCs in this work. 1H nuclear magnetic resonance and X-ray photoelectron spectroscopy analysis show that the l-cysteine head has strong interactions with the NCs. The absolute photoluminescence quantum yields of the colloidal NCs are increased from 45.1% of the pristine NCs stabilized with oleic acid/oleyl amine to 91.8% after NOSVC treatment. NOSVC-stabilized CsPbBr3 colloidal NCs show enhanced stabilities when exposed in polar solvents. The NOSVC-stabilized CsPbBr3 NCs in a solid film state allow for a photopolymerization to be carried out with the assistance of a photoinitiator. The polymerized films of NOSVC-treated NCs exhibit significantly enhanced stability against thermal radiation, ultraviolet irradiation, and humidity. We also fabricated self-healing polymer films incorporating NOSVC-treated CsPbBr3 NCs as a green filter for a white light-emitting diode device. The green light-emitting films are very stable in humid environments, revealing the great application potential of NOSVC-treated CsPbBr3 NCs in flexible display and lighting devices.

Phototropic Aggregation and Light-Guided Long-Distance Collective Transport of Colloidal Particles.

Phoretic swarming and collective transport of colloidal particles in response to environmental stimuli have attracted tremendous interest in a variety of fields. In this work, we investigate the light-actuated motion, aggregation, and light-guided long-distance mass transport of silica microspheres in simple spiropyran solutions under the illumination of UV spot sources. The phototactic motion is confirmed by the dependence of swarming on the illumination intensity and spiropyran concentrations, ON-OFF switching tests, pattern-masked UV sources, etc. The aggregates formed via swarming of silica spheres can chase after a moving UV source, however, relying on a critical speed of the UV source. Only when the UV source speed is below the critical value, the aggregates follow the UV spot at a constant relative speed to the light spot. Analysis on the shape of silica microsphere currents indicates that continuous illumination of the UV spot source and resultant chemical gradients are important for the formation of steady microsphere currents. Light-guided aggregation and long-distance mass transport are interesting for targeted delivery and remote-controlled enrichment of environmental hazards.

Preparation of high internal water-phase double emulsions stabilized by a single anionic surfactant for fabricating interconnecting porous polymer microspheres.

Herein we report a one-step method to prepare high internal water-phase double emulsions (W/O/W) via catastrophic phase inversion of water-in-oil high internal phase emulsions (W/O HIPEs) stabilized solely by 12-acryloxy-9-octadecenoic acid (AOA) through increasing the content of water phase. This is the first time for double emulsions to be stabilized solely by a single small molecular surfactant, which are usually costabilized by both hydrophilic and hydrophobic surfactants. After neutralized with ammonia, AOA is confirmed to be capable of stabilizing both W/O emulsions and O/W emulsions, which may account for its unique ability to stabilize double emulsions. The effects of different conditions (including changing the concentrations of AOA and salt (NaCl), pH value, the polarity of oils, the addition interval of water and stirring rate, etc.) on the formation and the stability of double emulsions as well as the inversion point have been investigated by using optical microscopy and conductivity monitoring. Finally, porous polymer microspheres with high interconnection (polyHIPE microspheres) were fabricated by γ-ray initiated polymerization of the as-prepared double emulsions composed of different monomers (styrene, or n-butyl acrylate, or methyl methacrylate), which have been confirmed by scanning electron microscopy. Our method is facile and effective for preparing high interconnecting porous polymer microspheres without tedious post-treatment of the products in common emulsion polymerization due to the use of polymerizable surfactant.

UV light induced plasticization and light activated shape memory of spiropyran doped ethylene-vinyl acetate copolymers.

Light activated shape memory polymers (LASMPs) are relatively new kinds of smart materials and have significant technological applications ranging from biomedical devices to aerospace technology. EVA films doped with spiropyran with contents ranging from 0.1% to 3% show efficient UV activated shape memory behaviors if the fixed shape deformation is limited within 80%. For EVA films containing 3% spiropyran, UV irradiation causes a decrease in EVA modulus of about 44%. FT-IR and solid (13)C NMR in association with UV-vis absorption analysis demonstrate that UV irradiation transforms spiropyran from the SP form to the MC form, meanwhile, it induces an increase in the molecular mobility in the amorphous phase of EVA. Thus, the spiropyran-doped EVA films act as LASMPs via a mechanism of light induced plasticization. Light activated spiropyran acts as a plasticizer to EVA.

Dramatic fluorescence enhancement of bare carbon dots through facile reduction chemistry.

Reduction of bare carbon dots (CDs) in aqueous NaBH(4) solution is a facile and effective approach to enhance their fluorescence without any surface coverage. CDs are treated with dilute aqueous NaBH(4) solutions, enhancing their quantum yields (QYs) successfully from 1.6 % to 16 % which is comparable to semiconductive QDs in aqueous environments. If pristine CDs are treated hydrothermally prior to reduction by NaBH(4), QYs reach 40.5 %. This value is among the highest QYs reported for bare CDs in the literature. The approach to enhance fluorescence through chemical reduction is generally applicable to other kinds of CDs synthesized by various methods. Alteration of the chemical structure of the CDs by NaBH(4)-reduction is analyzed by (13) C NMR, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy, which demonstrate that the carbonyl group content is decreased after NaBH(4)-reduction, whereas the number of sp(3)-type carbon defects is increased. The valence-band maxima (VBM) near the surface related to the surface energy bands of the CDs are estimated by XPS. VBM data show a semiconducting layer on the surface of the CDs, and the VBM of the CDs decrease with increasing NaBH(4)-reduction time. The layered graphite structures in the cores of the CDs are clearly observed by transmission electron microscopy (TEM). CDs could perhaps be regarded as semiconductive surface defect layers formed by chemical erosion over conductive graphite cores. Chemical reduction by NaBH(4) changes the surface-energy bands of the CDs, thus, enhances their fluorescence. The fluorescence properties of aqueous NaBH(4)-reduced CDs are also studied for possible biological applications.

A two-year water-stable 2D MOF with aqueous NIR photothermal conversion ability.

Structural lability in humid air or water severely limits the practical use of MOFs. Developing new MOFs with exceptional water stability is interesting for both industrial applications and academic research. Herein we report a new method to improve the water stability of MOFs by using three-dimensional rigid shielding ligands. A very highly stable two-dimensional MOF (CuCP-MOF) is synthesized in this work, in which [2,2]paracyclophane dicarboxylate ligands are coordinated with Cu(ii) ions to form a paddle wheel structure. CuCP-MOF is a triclinic crystal with unit cell parameters a = 10.065 Å, b = 10.897 Å, c = 10.940 Å, α = 90.676°, ß = 91.729°, and γ = 92.725° determined by single crystal X-ray diffraction and DFT simulation. It can easily form MOF nanosheets due to the large interlayer distance and weak interlayer interactions. It shows good aqueous stability, and remains intact after storage in water for two years, as evidenced by FTIR and XRD analyses. CuCP-MOF shows a strong absorption in the NIR range due to the d-d transition of Cu(ii). The aqueous dispersions of CuCP-MOF exhibit high NIR photothermal conversion efficiency, about 17.5% for a laser with an energy density of 5 W cm-2 (808 nm) and 22.0% for a laser of 2 W cm-2 on average.

Multifunctional conjugates to prepare nucleolar-targeting CdS quantum dots.

We used a click reaction to synthesize a bidentate 1,2,3-triazole-based ligand, TA, for use in the preparation of aqueous CdS quantum dots (QDs). TA-conjugated CdS QDs exhibited two fluorescence emission peaks, one at 540 nm arising from CdS nanocrystals and the other at approximately 670 nm arising from TA-CdS QD complexes formed via surface coordination. Coordination between TA and CdS was verified by using X-ray photoelectron (N 1s) spectra as well as Raman and NMR spectra of TA-capped QDs. Electrochemical analysis revealed that the 1,2,3-triazole moities in TA form complexes with the Cd(II) ions. The aqueous QDs protected by TA were very stable at different ionic strengths and over a broad pH range, according to fluorescence analysis. The ethidium bromide exclusion assay demonstrated that the bidentate TA ligand interacts strongly with DNA. Fluorescent micrographs and TEM images of cancer cells stained with TA-capped QDs clearly showed that the TA ligand targeted CdS QDs to the nucleoli of cells. In contrast, thioglycolic acid-capped CdS QDs just stained the cell membranes and could not pass the cell membranes to reach the cell nucleus.

Temperature dependent luminescence of azobenzene capped CdS quantum dots.

Cadmium sulfide (CdS) quantum dots (QDs) are prepared at room temperature by "form-fill-seal" method, while the azobenzene is used as surfactant to control the particle size and to prevent agglomeration. The typical size of CdS nanoparticles is estimated as 2 nm by X-ray diffraction. The absorption spectra of CdS QDs are measured at room temperature and a new absorption peak associated with the surface excited state is found. The luminescence property of the CdS QDs is studied at room temperature and low temperature. Two photoluminescence peaks exist in the temperature range of 8-300 K. One peak at 460 nm is attributed to CdS QDs, while the other one at 667 nm comes from the transition of surface excited state and its intensity decreases with temperature increasing.

High-efficiency preparation of macrocyclic diblock copolymers via selective click reaction in micellar media.

We report a novel strategy for the high-efficiency preparation of macrocyclic diblock copolymers at relatively high concentrations via the combination of supramolecular self-assembly and "selective" click reactions, relying on the fine control of spatial accessibility between terminal reactive groups. The linear precursor, alpha-alkynyl-omega-azido heterodifunctional poly(2-(2-methoxyethoxy)ethyl methacrylate)-b-poly(oligo(ethylene glycol) methyl ether methacrylate), linear-PMEO(2)MA-b-POEGMA-N(3), self-assembles into micelles with PMEO(2)MA cores and POEGMA coronas at elevated temperatures. The spatial separation between reactive alkynyl and azide groups precludes click reactions within micelle entities. On the other hand, due to the unimer-micelle exchange equilibrium and the fact that unimer concentration is typically low (critical micellization concentration, CMC), click reactions occur exclusively for unimers. This eventually led to complete intramolecular cyclization of all linear precursors.

Polymer-functionalized multiwalled carbon nanotubes as lithium intercalation hosts.

Multiwalled carbon nanotubes (MWNTs) functionalized with a hyperbranched aliphatic polyester and two different poly(ethylene glycol)s were synthesized by the reactions of carbonyl chloride groups on the surface of MWNTs and hydroxyl groups of polymers. Electrochemical intercalation of lithium in the three materials was investigated with galvanostatic charge-discharge experiments. The hyperbranched polymer-functionalized MWNT as an electrode material for lithium batteries showed a significant improvement over linear polymer-functionalized MWNTs in lithium insertion/deinsertion capacity and cycle stability. The MWNT functionalized with linear poly(ethylene glycol) showed a high initial capacity of lithium insertion/deinsertion but had the highest capacity fade rate among the materials. Because the polymers were chemically localized in the electrode-electrolyte interface, the comparison between hyperbranched and linear polymer-modified MWNTs manifested the important influence of the electrode-electrolyte interface on the electrochemical properties of lithium batteries.

Stabilization of catanionic vesicles via polymerization.

Polymerizable cationic surfactant methacryloyloxyoctyl trimethylammonium bromide (MOTB) and anionic surfactant sodium 4-(omega-methacryloyloxyoctyl)oxy benzene sulfonate (MOBS) were synthesized. Stable catanionic vesicles can spontaneously form upon mixing the two oppositely charged surfactants in aqueous solution, which was further permanently fixed by polymerization. Surface tensiometry, nuclear magnetic resonance (NMR), static and dynamic laser light scattering (LLS), and cryogenic transmission electron microscopy (cryo-TEM) were used in combination to characterize the catanionic vesicles before and after polymerization. The kinetics of formation and breakdown of unpolymerized catanionic vesicles were studied in detail employing stopped-flow light scattering. In contrast to unpolymerized vesicles, the polymerized ones exhibit permanent stability under external perturbations such as dilution or adding excess MOTB. A tentative explanation is proposed about why free radical polymerization can successfully fix the catanionic vesicles, the structure of which is well-known to be in dynamic equilibrium exchange with unimers.

One-pot radical polymerization of one inimer to form one-dimensional polymeric nanomaterials.

A one-pot polymerization strategy is put forward for producing 1D polymeric nanomaterials directly from a single inimer. An inimer bearing an NMP initiating site is polymerized in the presence of a RAFT CTA to form a pearl-necklace structure constituted of hyperbranched polymer "pearls". The obtained 1D nanorods show high regularity evidenced by the long-range order in small angle XRD patterns and the formation of liquid crystalline phases.

pH-responsive supramolecular self-assembly of well-defined zwitterionic ABC miktoarm star terpolymers.

We report the first example of the synthesis and pH-responsive supramolecular self-assembly of double hydrophilic ABC miktoarm star terpolymers. Well-defined ABC miktoarm star terpolymers consisting of poly(ethylene glycol), poly(tert-butyl methacrylate), and poly(2-(diethylamino)ethyl methacrylate) arms [PEG(-b-PtBMA)-b-PDEA] were synthesized via the combination of consecutive click reactions and atom transfer radical polymerization (ATRP), starting from a trifunctional core molecule, 1-azido-3-chloro-2-propanol (ACP). The click reaction of monoalkynyl-terminated PEG with an excess of ACP afforded difunctional PEG bearing a chlorine and a secondary hydroxyl moiety at the chain end, PEG113(-Cl)-OH (1). After azidation with NaN3, PEG-based macroinitiator PEG113(-N3)-Br (3) was prepared by the esterification of PEG113(-N3)-OH (2) with 2-bromoisobutyryl bromide and then employed in the ATRP of tert-butyl methacrylate (tBMA). The obtained PEG(-N3)-b-PtBMA copolymers (4) possessed an azido moiety at the diblock junction point. The preparation of PEG(-b-PtBMA)-b-PDEA miktoarm star terpolymers was then achieved via the click reaction of 4 with an excess of monoalkynyl-terminated PDEA. The obtained miktoarm star terpolymers were successfully converted into PEG(-b-PMAA)-b-PDEA, where PMAA is poly(methacrylic acid). In aqueous solution, PEG(-b-PMAA)-b-PDEA zwitterionic ABC miktoarm star terpolymers can self-assemble into three types of micellar aggregates by simply adjusting solution pH at room temperature. Above pH 8, PDEA-core micelles stabilized by PEG/ionized PMAA hybrid coronas were formed due to the insolubility of PDEA block. In the range of pH 5-7, micelles possessing polyion complex cores formed as a result of charge compensation between partially ionized PMAA and partially protonated PDEA sequences. At pH<4, hydrogen bonding interactions between fully protonated PMAA and PEG led to the formation of another type of micellar aggregates possessing hydrogen-bonded complex cores stabilized by protonated PDEA coronas. The fully reversible pH-responsive formation of three types of aggregates were characterized by 1H NMR, dynamic and static laser light scattering (LLS), and transmission electron microscopy (TEM).