Functional Aerogels Composed of Regenerated Cellulose and Tungsten Oxide for UV Detection and Seawater Desalination.

Functional aerogels composed of regenerated cellulose and tungsten oxide were fabricated by implanting tungsten-oxide nanodots into regenerated cellulose fiber. This superfast photochromic property benefitted from the small size and even distribution of tungsten oxide, which was caused by the confinement effect of the regenerated cellulose fiber. The composite was characterized using XRD and TEM to illustrate the successful loading of tungsten oxide. The composite turned from pale white to bright blue under ambient solar irradiation in five seconds. The evidence of solar absorption and electron paramagnetic resonance (EPR) demonstrated the fast photochromic nature of the composite and its mechanism. Furthermore, carbon fiber filled with preferential growth tungsten-oxide nanorods was obtained by annealing the photochromic composite in a N2 atmosphere. This annealed product exhibited good absorption across the whole solar spectrum and revealed an excellent photothermal conversion performance. The water evaporation rate reached 1.75 kg m-2 h-1 under one sun illumination, which is 4.4 times higher than that of pure water. The photothermal conversion efficiency was 85%, which shows its potential application prospects in seawater desalination.

PVDF-Modified TiO2 Nanowires Membrane with Underliquid Dual Superlyophobic Property for Switchable Separation of Oil-Water Emulsions.

Separation membranes with underliquid dual superlyophobicity have recently caused widespread concern due to their switchable separation of oil-water mixtures and emulsions. However, the fabrication of the reported underliquid dual superlyophobic membranes is difficult, and the design of the underliquid dual superlyophobic surface of these membranes is challenging because of their complex surface composition. Theoretically, underliquid dual superlyophobicity is an underliquid Cassie state attainable by the synergy of the underliquid dual lyophobic surface and the construction of a high-roughness surface. Herein, we fabricated an underliquid dual superlyophobic membrane by combining underliquid dual lyophobic polyvinylidene fluoride (PVDF) and TiO2 nanowires. PVDF-modified TiO2 nanowire membranes with underliquid dual superlyophobicity were prepared via a simple adsorption and filtration approach. PVDF was coated onto TiO2 nanowires to form a PVDF layer with a thickness of 6 nm. The PVDF modification provided flexibility to the fragile TiO2 nanowires membrane and changed its wettability from underwater superoleophobicity/underoil superhydrophilicity to underliquid dual superlyophobicity. The PVDF-modified TiO2 nanowires membrane efficiently separated both oil-in-water and water-in-oil emulsions. The binary cooperative effect between the TiO2 nanowires and the coated PVDF layer was responsible for the underliquid dual superlyophobicity.

A Flexible, Self-Floating Composite for Efficient Water Evaporation.

A flexible, self-floating W18O49/carbon foam composite is fabricated by calcining melamine foam with W18O49 as an adsorbate in N2 atmosphere. This self-floating property is simply realized by a carbonization process other than the complicated surface modification process. The simple synthesis procedure helps to increase not only the solar absorption but also the retention of W18O49 in the porous net structure. This composite absorbs almost the whole solar spectrum and generates localized heat at the surface, which is beneficial for water evaporation. Its water evaporation rate is 6.6 times higher than that of pure water. It has a stable cyclic performance over ten cycles under the illumination of simulated sunlight (500 W Xe lamp). Its flexibility makes it easy to reuse and transfer, which is evaluated by the bending deformation test. The W18O49/carbon foam composite is a prospective material in solar energy conversion field, and the preparation procedure is feasible to scale-up.

Hollow Metal-Organic-Framework Micro/Nanostructures and their Derivatives: Emerging Multifunctional Materials.

Hollow metal-organic framework (MOF) micro/nanostructures and their derivatives are attracting a great amount of research interest in recent years because their hierarchical porous structures not only provide abundant, easily accessed metal sites but also endow 3D channels for rapid mass transport. As a result, they demonstrate significant advantages in many applications including catalysis, gas sensors, batteries, supercapacitors, and so on. Nevertheless, studies on hollow MOFs and their derivatives are still at the beginning of this field, and the relationship between their structures and application performances is not yet reviewed comprehensively. Herein, the synthetic strategies and practical applications of hollow micro/nanostructured MOFs and their derivatives are summarized, and their corresponding prospects are also discussed.

Photothermal Conversion of W18O49 with a Tunable Oxidation State.

W18O49 with a tunable oxidation state was prepared by addition of NaNO3 or NaBH4 as a redox agent in the solvothermal system. The addition of redox agents has no influence on the crystallization of W18O49. The obtained W18O49 structures keep their morphology as a bundle of nanowires with a regular hexagonal on the cross-section. W18O49 exhibits strong valence-dependent absorption features in the near-IR region. Reduced W18O49 with more W5+ has a higher concentration of oxygen vacancies, which enhances the localized surface plasmon resonance effect. Reduced W18O49 exhibits a high photothermal conversion efficiency of 59.6 % and has good photothermal stability.

Tuning the Aggregation/Disaggregation Behavior of Graphene Quantum Dots by Structure-Switching Aptamer for High-Sensitivity Fluorescent Ochratoxin A Sensor.

The design of graphene quantum dots (GQDs)-aptamer bioconjugates as the new sensing platform is very important for developing high-sensitivity fluorescent biosensors; however, achieving new bioconjugates is still a great challenge. Herein, we report the development of a new high-sensitivity fluorescent aptasensor for the detection of ochratoxin A (OTA) based on tuning aggregation/disaggregation behavior of GQDs by structure-switching aptamers. The fluorescence sensing process for OTA detection involved two key steps: (1) cDNA-aptamer (cDNA, complementary to part of the OTA aptamer) hybridization induced the aggregation of GQD (fluorescence quenching) after cDNA was added into the GQDs-aptamer bioconjugate solution, and (2) the target of OTA triggered disaggregation of GQD aggregates (fluorescence recovery). Such new fluorescent sensing platform can be used to monitor OTA with a linear range of 0 to 1 ng/mL and very low detection limit of 13 pg/mL, which is among the best in all the developed fluorescent nanoparticles-based sensors. Such sensing strategy is also successful in analyzing OTA in practical red wine sample with 94.4-102.7% of recoveries and relative standard deviation in the range of 2.9-5.8%. The present works open a new way for signaling the target-aptamer binding event by tuning aggregation/disaggregation behavior of GQDs-bioconjugates.

Porous TiO2 Assembled from Monodispersed Nanoparticles.

Porous TiO2 were assembled by evaporating or refluxing TiO2 colloid, which was obtained by dispersing the TiO2 nanoparticles with a crystallite size (d XRD) of 3.2 nm into water or ethanol without any additives. Porous transparent bulk TiO2 was obtained by evaporating the TiO2-C2H5OH colloid at room temperature for 2 weeks, while porous TiO2 nanospheres were assembled by refluxing the TiO2-H2O colloid at 80 °C for 36 h. Both of the porous TiO2 architectures were pore-size-adjustable depending on the further treating temperature. Porous TiO2 nanospheres exhibited enhanced photocatalysis activity compared to the nanoparticles.

Synthesis of fluorinated carbazoles via C-H arylation catalyzed by Pd/Cu bimetal system and their antibacterial activities.

An effective intramolecular C-H arylation reaction catalyzed by a bimetallic catalytic system Pd(OAc)2/CuI for the synthesis of fluorine-substituted carbazoles from corresponding N-phenyl-2-haloaniline derivatives under ligand free conditions is demonstrated. The established method is effective for both N-phenyl-2-bromoaniline and N-phenyl-2-chloroaniline, and requires the low loading of Pd(OAc)2 (0.5 mol%). A series of new fluorinated carbazoles were synthesized in excellent yields using the protocol (>83%, 19 examples) and were fully characterized by (1)H, (13)C and (19)F NMR spectral data, HRMS and elemental analysis. All compounds were evaluated for their antibacterial activities against four bacteria (Bacillus subtilis, Staphylococcus aureus, Escherichia coli and methicillin-resistant S. aureus with resistance to gentamicin) by serial dilution technique. All tested compounds showed antibacterial activity against three test strains (S. aureus, B. subtilis and MRSA), and most of these compounds displayed pronounced antimicrobial activities against these three strains with low MIC values ranging from 0.39 to 6.25 µg/mL. Among them, compounds 7 and 14 exhibited potent inhibitory activity better than reference drugs meropenem and streptomycin. Three compounds (2, 4 and 5) showed antibacterial activity against E. coli. with MIC values from 12.5 to 25 µg/mL.

Synthesis and Characterization of N-Doped Porous TiO2 Hollow Spheres and Their Photocatalytic and Optical Properties.

Three kinds of N-doped mesoporous TiO2 hollow spheres with different N-doping contents, surface area, and pore size distributions were prepared based on a sol-gel synthesis and combined with a calcination process. Melamine formaldehyde (MF) microspheres have been used as sacrificial template and cetyltrimethyl ammonium bromide (CTAB) or polyvinylpyrrolidone (PVP) was selected as pore-directing agent. Core-shell intermediate spheres of titania-coated MF with diameters of 1.2-1.6 µm were fabricated by varying the volume concentration of TiO2 precursor from 1 to 3 vol %. By calcining the core-shell composite spheres at 500 °C for 3 h in air, an in situ N-doping process occurred upon the decomposition of the MF template and CTAB or PVP pore-directing surfactant. N-doped mesoporous TiO2 hollow spheres with sizes in the range of 0.4-1.2 µm and shell thickness from 40 to 110 nm were obtained. The composition and N-doping content, thermal stability, morphology, surface area and pore size distribution, wall thickness, photocatalytic activities, and optical properties of the mesoporous TiO2 hollow spheres derived from different conditions were investigated and compared based on Fourier-transformation infrared (FTIR), SEM, TEM, thermogravimetric analysis (TGA), nitrogen adsorption-desorption, and UV-vis spectrophotoscopy techniques. The influences of particle size, N-doping, porous, and hollow characteristics of the TiO2 hollow spheres on their photocatalytic activities and optical properties have been studied and discussed based on the composition analysis, structure characterization, and optical property investigation of these hollow spherical TiO2 matrices.

Construction of Plasmonic Core-Satellite Nanostructures on Substrates Based on DNA-Directed Self-Assembly as a Sensitive and Reproducible Biosensor.

We report the successful construction of plasmonic core-satellite nanostructured assemblies on two-dimensional substrates, based on a strategy of combining DNA-functionalized plasmonic nanoparticles (NPs) with the specific recognition ability toward target to enable satellite NPs to self-assemble around the core immobilized on substrates. A strongly coupled plasmonic resonance band was observed because of the close proximity between core and satellite NPs, which presented significant red-shift and enhanced extinction with respect to the local surface plasmon resonance (LSPR) band of individual core NPs on the substrate. The functionality of this core-satellite nanostructured assembly as a biosensor was further explored, and the changes in extinction intensity and the peak shift of the plasmonic coupling resonance band arising from the probe-target DNA binding event all proved to be useful criteria for target DNA detection. Moreover, high selectivity down to single-base mismatched DNA was achieved using this strongly coupled plasmonic core-satellite nanostructured assembly on a substrate. Such substrate-based detection was advantageous, and its reusability and high cycle stability were demonstrated after five cycles of disassembly and reassembly. Our work demonstrates the biosensing capacity of this DNA-functionalized plasmonic nanoassembly model system on two-dimensional substrate, which is also applicable to the detection of numerous DNA-recognized biomolecules. Likewise, the presented construction method can be extended to fabricate other compositional core-satellite nanoassemblies.

Assembly of Maghemite Nanoparticles Into Particulate Nanosheets and Their Application in Wastewater Treatment.

The maghemite particulate nanosheets (MPNs) are prepared in solvothermal system by connecting the nanoparticles in two-dimension. The interconnected MPNs sustain a mesopores structure with a high accessible surface area of 164 m2/g, and have a high performance for Cr6+ adsorption. The Cr6+ removal process fit with Langmuir adsorption model with an adsorption capacity of 20.41 mg/g. The purified solution could reach a residual concentration of 0.002 mg/L for MPNs, which is much less than the concentration in the solution of 0.249 mg/L when the nanoparticles are used. The synthesized MPNs with a saturation magnetization of 70.51 emu/g at room temperature can be easily collected and separated by an external magnet in liquid. Exchange coupling and shape anisotropy are the main reason for the higher Ms of MPNs. The unique structure with large surface area and high saturation magnetization make the MPNs favourable for the application of magnetic separation.

Observation of Body-Centered Cubic Gold Nanocluster.

The structure of nanoparticles plays a critical role in dictating their material properties. Gold is well known to adopt face-centered cubic (fcc) structure. Herein we report the first observation of a body-centered cubic (bcc) gold nanocluster composed of 38 gold atoms protected by 20 adamantanethiolate ligands and two sulfido atoms ([Au38S2(SR)20], where R=C10H15) as revealed by single-crystal X-ray crystallography. This bcc structure is in striking contrast with the fcc structure of bulk gold and conventional Au nanoparticles, as well as the bi-icosahedral structure of [Au38(SCH2CH2Ph)24]. The bcc nanocluster has a distinct HOMO-LUMO gap of ca. 1.5 eV, much larger than the gap (0.9 eV) of the bi-icosahedral [Au38(SCH2CH2Ph)24]. The unique structure of the bcc gold nanocluster may be promising in catalytic applications.

Magnetic photocatalysts with a p-n junction: Fe3O4 nanoparticle and FeWO4 nanowire heterostructures.

Magnetic n-type semiconductor Fe3O4 nanoparticle and p-type semiconductor FeWO4 nanowire heterostructures were successfully synthesized without any surfactants or templates via a facile one-step hydrothermal process at 160 °C. The heterojunction structure and morphology were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). Magnetic measurements indicated the coexistence of ferrimagnetic behavior of Fe3O4 and weak antiferromagnetic behavior of FeWO4. The degradation of methylene blue (MB) under UV-Visible light irradiation was studied as a model experiment to evaluate the catalytic activity of the Fe3O4/FeWO4 heterostructure p-n junctions. The decomposition efficiency was 97.1% after one hour UV-Visible irradiation. This magnetic photocatalyst can be easily recovered from the solution using a permanent magnet and redispersed by removing the magnet.

Fast response and highly selective sensing of amine vapors using a luminescent coordination polymer.

Detecting volatile amines is a significant topic in the quality control of food and medical diagnosis. We report the first Eu-coordination polymer (CP) as a sensory material for the detection of a class of amine vapors with high selectivity and rapid response.

Synthesis of ultrasmall platinum nanoparticles and structural relaxation.

We report the synthesis of ligand-protected, ultrasmall Pt nanoparticles of ∼1 nm size via a one-phase wet chemical method. Using matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS), we determined the mass of the nanoparticles to be ∼8 kDa. Characterization of the Pt nanoparticles was further carried out by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), optical absorption spectroscopy, and X-ray photoelectron spectroscopy (XPS). Interestingly, we observed a large structural relaxation in the 8kDa nanoparticles (i.e. lattice parameter elongation by +10%) compared to bulk platinum. XPS analysis revealed a positive shift of Pt 4f core level energy by approximately +1 eV compared with bulk Pt, indicating charge transfer from Pt to S atom of the thiolate ligand on the particle. Compared to bulk Pt, the 5d band of Pt nanoparticles is narrower and shifts to higher binding energy. Overall, the ∼1 nm ultrasmall Pt nanoparticles exhibit quite distinct differences in electronic and structural properties compared to their larger counterparts and bulk Pt.

A top-down route for preparation of ultrathin zinc oxide nanowires.

Zinc oxide nanowires have been successfully obtained through the splitting of layered basic zinc acetates. The layered basic zinc acetates nanobelts served as intermediates are prepared by adding water into zinc oxide ethanol colloids. Zinc oxide nanowires have uniform diameters of about 3-5 nm and lengths of several hundred nanometers. The formation mechanism of zinc oxide nanowires is proposed. The mechanism is that zinc oxide nanowires are generated by the splitting of the layered compound. From this mechanism, we find that the structure characteristic of layered basic zinc acetates is essential for the formation of ZnO nanowires. We also discuss the relationship between the morphology of products obtained after incubating and incubating time. The products are characterized by X-ray powder diffraction, transmission electron microscopy, scanning transmission electron microscopy and infrared spectrum.

A facile synthetic approach for copper iron sulfide nanocrystals with enhanced thermoelectric performance.

Chalcopyrite CuFeS(2) nanocrystals with a diameter of 6.4 nm were synthesized using a facile solution-phase method. Due to quantum confinement, the CuFeS(2) nanocrystals exhibit a maximum ZT value of 0.264 at 500 K, which is 77 times the value of bulk chalcopyrite.

Synthesis and characterization of novel chiral NHC-palladium complexes and their application in copper-free Sonogashira reactions.

A new series of chiral N-heterocyclic carbene (NHC) palladium complexes were synthesized from a relatively inexpensive amino acid, l-phenylalanine. All these compounds were fully characterized by (1)H-NMR, (13)C-NMR and elemental analysis. The X-ray molecular structures of two of the complexes were reported. The catalytic activity of the four palladium complexes was successfully tested in the Sonogashira reaction under copper free conditions in air. The palladium complex 3a provided good activity in the Sonogashira coupling reaction.

Preparation of well-dispersed Mg-doped LaCoO3 nanocrystals with controllable particle size and high visible-light photocatalytic activity.

Mg-doped LaCoO3 nanocrystals are prepared by a modified sol-gel method. Excess MgO is used to inhibit the crystal growth and agglomeration during the calcination process. A series of Mg-doped LaCoO3 nanocrystals with average crystallite size varying from 13.4 to 31.6 nm can be obtained by changing the molar ratio of Mg:La from 4:1 to 1:10 in the reaction mixture. The largest BET surface area observed is 64.5 m2/g if the molar ratio of Mg:La is 4:1. The product can be well dispersed in water and a very stable colloid formed without any stabilizer. The photocatalytic performance of Mg-doped LaCoO3 nanocrystals is evaluated by the degradation of Reactive Brilliant Red X-3B solution. The well-dispersed Mg-doped LaCoO3 nanocrystals exhibit high visible-light photocatalytic activity.

Influence of polyols on the formation of iron oxide nanoparticles in solvothermal system.

We reported a simple solvothermal route in phase-controllable synthesis of iron oxide nanoparticles by using polyols as solvent. Magnetite and hematite are selectively synthesized while Fe(NO3)3.9H2O is used as single iron source and without any additives. While ethylene glycol, 1,2propanediol, 1,3-butanediol, or glycerol is used as solvents, magnetite nanoparticles are obtained, and the average particle sizes vary from 10 to 40 nm. While 1,4-butanediol or 1,5-pentanediol is used as solvents, hematite nanoparticles are obtained. Our results suggest that the polyols with neighboring hydroxyl groups is favorable for the formation of magnetite nanoparticles.