Formation and Growth of Silver Nanocubes upon Nanosecond Pulsed Laser Irradiation: Effects of Laser Intensity and Irradiation Time

Silver nanoparticles (AgNPs) were fabricated by repetitive irradiation of near ultraviolet (UV) nanosecond laser pulses (355 nm, 5 ns) in an aqueous solution of silver nitrate in the absence of stabilizing agents. A broad absorption peak was observed in the visible region showing the formation of a variety of AgNPs in the solution. Among the variety of products, it was found that silver nanocubes (AgNCs) grew in size with longer laser irradiation time. The size of AgNCs also increased with higher laser intensity. The average size of AgNCs, investigated by a scanning electron microscope (SEM) was in the range of 75 - 200 nm. The number of reduced atoms in AgNCs as a function of laser intensity showed that the AgNCs are apparently produced by a four photon process, implying that the formation of dimer silver atoms is essential for the formation.

Investigation and Mitigation of Carbon Deposition over Copper Catalyst during Electrochemical CO_(2)Reduction

Copper(Cu)is considered to be the most effective catalyst for electrochemical conversion of carbon dioxide(CO_(2))into value-added hydrocarbons,but its stability still faces considerable challenge.Here,we report the poisoning effect of carbon deposition during CO_(2)reduction on the active sites of Cu electrodea critical deactivation factor that is often overlooked.We find that,*C,an intermediate toward methane formation,could desorb on the electrode surface to form carbon species.We reveal a strong correlation between the formation of methane and the carbon deposition,and the reaction conditions favoring methane production result in more carbon deposition.The deposited carbon blocks the active sites and consequently causes rapid deterioration of the catalytic performance.We further demonstrate that the carbon deposition can be mitigated by increasing the roughness of the electrode and increasing the pH of the electrolyte.This work offers a new guidance for designing more stable catalysts for CO_(2)reduction.

Enhanced Fenton,photo-Fenton and peroxidase-like activity and stability over Fe_3O_4/g-C_3N_4 nanocomposites

We prepared the Fe3O4/g‐C3N4nanoparticles(NPs)through a simple electrostatic self‐assembly method with a3:97weight ratio to investigate their Fenton,photo‐Fenton and oxidative functionalities besides photocatalytic functionality.We observed an improvement of the Fenton and photo‐Fenton activities of the Fe3O4/g‐C3N4nanocomposites.This improvement was attributed to efficient charge transfer between Fe3O4and g‐C3N4at the heterojunctions,inhibition of electron‐hole recombination,a high surface area,and stabilization of Fe3O4against leaching by the hydrophobic g‐C3N4.The obtained NPs showed a higher degradation potential for rhodamine B(RhB)dye than those of Fe3O4and g‐C3N4.As compared to photocatalysis,the efficiency of RhB degradation in the Fenton and photo‐Fenton reactions was increased by20%and90%,respectively.Additionally,the horseradish peroxidase(HRP)activity of the prepared nanomaterials was studied with3,3,5,5‐tetramethylbenzidinedihydrochloride(TMB)as a substrate.Dopamine oxidation was also examined.Results indicate that Fe3O4/g‐C3N4nanocomposites offers more efficient degradation of RhB dye in a photo‐Fenton system compared with regular photocatalytic degradation,which requires a long time.Our study also confirmed that Fe3O4/g‐C3N4nanocomposites can be used as a potential material for mimicking HRP owing to its high affinity for TMB.These findings suggest good potential for applications in biosensing and as a catalyst in oxidation reactions.

Porous Y_2O_3 microcubes:synthesis and characterization

In this work, a facile route using a simple solvothermal reaction and sequential heat treatment process to prepare porous Y2O3 microcubes is presented. The as-synthesized products were characterized by X-ray powder diffraction （XRD）, scanning electronic microscope （SEM）, energy dispersive spectrometer （EDS）, thermogravimetric analysis （TG）, and differential thermal analysis （DTA）. The thermal decomposition process of the Y203 precursor was investigated. SEM results demonstrated that the as-prepared porous Y203 microcubes were with an average width of about 20 μm and thickness of about 8μm. It was found that the morphology of the Y2O3 precursor could be readily tuned by varying the molar ratio of S2O2- to y3＋. Y203：Eu3＋ （6.6%） microcubes were also prepared and their photoluminescence properties were investigated.

Strong and tough chitin hydrogel constructed by dehydration and rehydration strategy

As a renewable,biocompatible,biodegradable soft material,chitin hydrogels have better advantages in stability,antibacterial activity,antifouling,cost,immunogenicity,and so on than most polymer hydrogels.However,compared with other widely used polymer hydrogels with high strength and toughness,the practical applications of chitin-based hydrogels have been limited by their weak mechanical properties,such as cartilage repair and meniscus replacement.Here,we present the design and fabrication of chitin hydrogels with excellent mechanical strength and toughness by a dehydration and rehydration strategy.By sequential dehydration and rehydration processes,the crystalline domains in the chitin hydrogels can be properly controlled.With optimized crystallinity,the elastic modulus of the chitin hydrogels exceeds all previously reported values,and the fracture toughness is even comparable to some synthetic polymer hydrogels,while maintaining a high-water-content of about 80 wt.%.At the same water content,the mechanical properties of the chitin hydrogels are positively correlated with the hydrogel crystallinity,which proves that the change of mechanical properties of hydrogels is not simply dependent on weight concentration.The hydrogels can be further strengthened by incorporating other biopolymers that are intrinsically weak,which makes the hydrogels promising for applications in fields such as cartilage repair and meniscus replacement.Moreover,the hydrogels enable loading and release of water-soluble and poorly water-soluble drugs.This highly extendable strengthening and toughening strategy of chitin and chitin-based biopolymer hydrogels paves the way for their widely applications.

Binary synergistic enhancement of dielectric and microwave absorption properties： A composite of arm symmetrical PbS dendrites and polyvinylidene fluoride

Arm symmetrical PbS dendrite （ASD-PbS） nanostructures can be prepared on a large scale by a solvothermal process. The ASD-PbSs exhibit a three-dimensional symmetrical structure, and each dendrite grows multiple branches on the main trunk. Such unique ASD-PbSs can be combined with polyvinylidene fluoride （PVDF） to prepare a composite material with enhanced dielectric and microwave-absorption properties. A detailed investigation of the dependence of the dielectric properties on the frequency and temperature shows that the ASD-PbS/PVDF composite has an ultrahigh dielectric constant and a low percolation threshold. The dielectric permittivity is as high as 1,548 when the concentration of the ASD-PbS filler reaches 13.79 vol.% at 102 Hz, which is 150 times larger than that of pure PVDF, while the composite is as flexible as pure PVDF. Furthermore, the maximum reflection loss can reach -36.69 dB at 16.16 GHz with a filler content of only 2 wt.%, which indicates excellent microwave absorption. The loss mechanism is also elucidated. The present work demonstrates that the addition of metal sulfide microcrystals to polymer matrix composites provides a useful method for improving the dielectric and microwave-absorption properties.

Nanoheterostructured photocatalysts for improving photocatalytic hydrogen production

Rapid industrialization has accordingly increased the demand for energy.This has resulted in the increasingly severe energy and environmental crises.Hydrogen production,based on the photocatalytic water splitting driven by sunlight,is able to directly convert solar energy into a usable or storable energy resource,which is considered to be an ideal alternative energy source to assist in solving the energy crisis and environmental pollution.Unfortunately,the hydrogen production efficiency of single phase photocatalysts is too low to meet the practical requirements.The construction of heterostructured photocatalyst systems,which are comprised of multiple components or multiple phases,is an efficient method to facilitate the separation of electron‐hole pairs to minimize the energy‐waste,provide more electrons,enhance their redox ability,and hence improve the photocatalytic activity.We summarize the recent progress in the rational design and fabrication of nanoheterostructured photocatalysts.The heterojunction photocatalytic hydrogen generation systems can be divided into type‐I,type‐II,pn‐junction and Z‐scheme junction,according to the differences in the transfer of the photogenerated electrons and holes.Finally,a summary and some of the challenges and prospects for the future development of heterojunction photocatalytic systems are discussed.

Microwave-assisted synthesis of photoluminescent glutathione-capped Au/Ag nanoclusters： A unique sensor-on-a-nanoparticle for metal ions, anions, and small molecules

Even though great advances have been achieved in the synthesis of luminescent metal nanoclusters, it is still challenging to develop metal nanoclusters with high quantum efficiency as well as multiple sensing functionalities. Here, we demonstrate the rapid preparation of glutathione-capped Au/Ag nanoclusters （GS-Au/Ag NCs） using microwave irradiation and their unique sensing capacities. Compared to bare GS-Au NCs, the doped Au/Ag NCs possess an enhanced quantum yield （7.8% compared to 2.2% for GS-Au NCs）. Several characterization techniques were used to elucidate the atomic composition, particulate character, and electronic structure of the fabricated NCs. According to the X-ray photoelectron spectroscopy （XPS） and X-ray absorption near-edge structure （XANES） spectra, a significant amount of Au exists in the oxidized state as Au（I）, and the Ag atoms are positively charged. In contrast to those nanoclusters that detect only one analyte, the GS-Au/Ag NCs can be used as a versatile sensor for metal ions, anions, and small molecules. In this manner, the NCs can be regarded as a unique sensor-on-a-nanoparticle.

Highly enhanced visible-light photocatalytic hydrogen evolution on g-C_3N_4 decorated with vopc through π-π interaction

Photocatalytic H2 evolution reactions on pristine graphitic carbon nitrides(g-C3N4),as a promising approach for converting solar energy to fuel,are attractive for tackling global energy concerns but still suffer from low efficiencies.In this article,we report a tractable approach to modifying g-C3N4 with vanadyl phthalocyanine(VOPc/CN)for efficient visible-light-driven hydrogen production.A non-covalent VOPc/CN hybrid photocatalyst formed viaπ-πstacking interactions between the two components,as confirmed by analysis of UV-vis absorption spectra.The VOPc/CN hybrid photocatalyst shows excellent visible-light-driven photocatalytic performance and good stability.Under optimal conditions,the corresponding H2 evolution rate is nearly 6 times higher than that of pure g-C3N4.The role of VOPc in promoting hydrogen evolution activity was to extend the visible light absorption range and prevent the recombination of photoexcited electron-hole pairs effectively.It is expected that this facile modification method could be a new inspiration for the rational design and exploration of g-C3N4-based hybrid systems with strong light absorption and high-efficiency carrier separation.

Understanding the stability and reactivity of ultrathin tellurium nanowires in solution： An emerging platform for chemical transformation and material design

The stability and reactivity of nanomaterials are of crucial importance for their application, but the long-term effects of stability and reactivity of nanomaterials under practical conditions are still not well understood. In this study, we first established a comprehensive strategy to investigate the stability of a highly reactive nanomaterial from the viewpoint of reaction kinetics with ultrathin tellurium nanowires （TeNWs） as a model material in aqueous solution through an accelerated oxidation process. This allowed us to propose a new approach for the design and synthesis of other unique one-dimensional nanostructures by a chemical transformation process using the intermediate nanostructures ＂captured＂ during the dynamic oxidation process under different conditions. In essence, the oxidation of ultrathin TeNWs is a gas-solid reaction which involves liquid, gas and solid phases. It has been demonstrated that the oxidation process of ultrathin TeNWs in aqueous solution can be divided into three stages, namely oxygen limiting, ultrathin TeNWs limiting and mass transfer resistance limiting stages. The apparent oxidation kinetics for ultrathin TeNWs is approximately in accord with a first order reaction kinetics model and has an apparent activation energy as low as TeNWs are thermodynamically unstable 13.53 kJ.mol^-1, indicating that ultrathin However, the unstable nature of ultrathin TeNWs is actually an advantage since it can act as an excellent platform to help us synthesize and design one-dimensional functional nanomaterials--with special structures and distinctive properties--which are difficult to obtain by a direct synthesis method.

A Robust Wood-inspired Catalytic System for Highly Efficient Reduction of 4-Nitrophenol

Porous solid scaffolds play key roles in preventing nanocatalysts from agglomeration,greatly maintaining the catalytic efficiency and stability of nanocatalysts.However,facile preparation of robust scaffolds with high mass transfer efficiency for loading nanocatalysts remains a major challenge.Here,we fabricate a wood-inspired shape-memory chitosan scaffold for loading Au nanoparticles to reduce 4-nitrophenol via a simple“freeze-casting and dip-adsorption”approach.The obtained catalytic scaffold highly resembles the unidirectional microchannel structure of natural wood,resulting in robust mechanical properties and outstanding water absorption capacity.Additionally,Au nanoparticles can be firmly and uniformly anchored on the inner surface of these microchannels via electrostatic interaction,forming numerous microreactors.This catalytic system exhibits a high 4-nitrophenol conversion rate of 99%in 5 s and impressive catalytic stability even after continuously treating with more than 3 L of highly concentrated 4-nitrophenol solution(1 mmol/L).Therefore,the wood-like catalytic system presented here demonstrates the potential to be applied in the field of water treatment and environmental protection.

Dyeing bacterial cellulose pellicles for energetic heteroatom doped carbon nanofiber aerogels

The energy crisis and environmental pollution are serious challenges that humanity will face for the long-term. Despite tremendous efforts, the development of environmentally friendly methods to fabricate new energy materials is still challenging. Here we report, for the first time, a new strategy to fabricate various doped carbon nanofiber （CNF） aerogels by pyrolysis of bacterial cellulose （BC） pellicles which had adsorbed or were dyed with different toxic organic dyes. The proposed strategy makes it possible to remove the toxic dyes from waste-water and then synthesize doped CNF aerogels using the dyed BC pellicles as precursors. Compared with other reported processes for preparing heteroatom doped carbon （HDC） nanomaterials, the present synthetic method has some significant advantages, such as being green, general, low-cost and easily scalable. Moreover, the as-prepared doped CNF aerogels exhibit great potential as electrocatalysts for the oxygen reduction reaction （ORR） and as electrode materials for supercapacitors.

One-dimensional (1D) europium coordination polymer wires:Synthesis,characterization and photoluminescence properties

1D europium coordination polymer wires were successfully prepared by reacting europium chloride with tributyl phosphate(TBP) at 160 oC for 12 h. The products were characterized by XRD,IR,TG,DTA,SEM,and EDS. SEM results showed that the wires were with diameters ranging from several hundreds of nanometers to ～5 μm and lengths going up to several hundreds of micrometers. Influencing factors such as the dosage of reactants and reaction time on the preparation were systematically investigated. Strong emission centering at 590 nm was realized in the coordination polymer wires on excitation at 395 nm.

A selective sensor for cyanide ion(CN^-) based on the inner filter effect of metal nanoparticles with photoluminescent carbon dots as the fluorophore

Herein, we report a plasmonic metal nanoparti- cle-involved sensor for cyanide ion based on the inner filter effect by using photoluminescent carbon dots as the signal reporter. With commercial bee pollen as the carbon resource, we synthesized photoluminescent nitrogen-doped carbon dots by a one-pot hydrothermal process, and their fluores- cence quantum yield reached as high as 10.2 % ± 0.5 %. Fluorescence measurements indicated that the fluorescence of the carbon dots was insusceptible to the presence of many environmentally ordinary ions. Thanks to this “inert” property, we then developed a turn-on fluorescent sensor for cyanide ion in an inner filter effect manner by using carbon dots as the fluorophore and gold or silver nanoparticle as the light absorber. This detection technique is expected to be used for other metal nanoparticles-carbon dots ensemble fluorescent assays.

Joule-heated carbonized melamine sponge for high-speed absorption of viscous oil spills

Introducing heating function to oil sorbents opens up a new pathway to the fast cleanup of viscous crude oil spills in situ.The oil sorption speed increases with the rise of the temperature,thus oil sorbents with high heating temperature are desirable.Besides,the oil sorbents also need to be produced environment-friendly.Here we present carbonized melamine-formaldehyde sponges(CMSs)that exhibited superior heating performance and the CMSs could be massively fabricated through a non-polluting pyrolysis process.The conductive CMSs could be heated over 300℃with a low applied voltage of 6.9 V and keep above 250℃for 30 min in the air without obvious damage.Such high heating performance enabled heating up the oil spills with a high rate of 2.65℃·s^(-1) and 14%improvement of oil sorption coefficient compared with the state-of-the-art value.We demonstrated that one joule-heated CMS could continuously and selectively collect viscous oil spills(9,010 mPa·s)690 times its own weight in one hour.The CMSs will be a highly competitive sorbent material for the fast remediation of future crude oil spills.

In situ assembly of magnetic nanocrystals/graphene oxide nanosheets on tumor cells enables efficient cancer therapy

Owing to the stimulus-responsive and dynamic properties,magnetism-driven assembly of building blocks to form ordered structures is always a marvelous topic.While abundant magnetic assemblies have been developed in ideal physical and chemical conditions,it remains a challenge to realize magnetic assembly in complicated biological systems.Herein,we report a kind of biomacromolecule-modified magnetic nanosheets,which are mainly composed of superparamagnetic graphene oxide(Y-Fe2O3@GO),the tumor-targeting protein transferrin(TF),and the mitochondrion-targeting peptide(MitP).Such large-size nanosheets(0.5-1μm),noted as L-Fe2O3@GO-MitP-TF,can successfully in s itu assemble on the surface of tumor cells in a size-dependent and tumor cell-specific way,leading to severe inhibition of nutrient uptake for the tumor cells.More significantly,the nanostructures could efficiently confine the tumor cells,preventing both invasion and metastasis of tumor cells both in vitro and in vivo.Moreover,the 2D assemblies could remarkably disrupt the mitochondria and induce apoptosis,remarkably eradicating tumors under near-infrared(NIR)irradiation.This study sheds light on the development of new nano-systems for efficient cancer therapy and other biomedical applications.

Anisotropic nanowire growth via a self-confined amorphous template process： A reconsideration on the role of amorphous calcium carbonate

Calcium carbonate crystals with various morphologies have been found in a variety of biospecimens and artificially synthesized structures. Usually, the diversity in morphology can be attributed to different types of interactions between the specific crystal faces and the environment or the templates used for the growth of CaCO3 crystals. On the other hand, isotropic amorphous calcium carbonate （ACC） has been recognized as the precursor of other crystalline calcium carbonate forms for both in vivo and in vitro systems. However, here we propose a self-confined amorphous template process leading to the anisotropic growth of single-crystalline calcite nanowires. Initiated by the assembly of precipitated nanoparticles, the calcite nanowires grew via the continuous precipitation of partly crystallized ACC nanodroplets onto their tips. Then, the crystalline domains in the tip, which were generated from the partly crystallized nanodroplets, coalesced in the interior of the nanowire to form a single-crystalline core. The ACC domains were left outside and spontaneously formed a protective shell to retard the precipitation of CaCO3 onto the side surface of the nanowire and thus guided the highly anisotropic growth of nanowires as a template.

Strong and tough graphene papers constructed with pyrene-containing small molecules via π-π/Hbonding synergistic interactions

Lightweight yet strong paper with high toughness is desirable especially for impact protection. Herein we demonstrated electrically conductive and mechanically robust paper(AP/PB-GP) made of reduced graphene oxide via interfacial crosslinking with 1-aminopyrene(AP) and 1-pyrenebutyrat(PB) small molecules. The AP/PB-GP with thickness of over ten micrometer delivers a record-high toughness(~69.67 ± 15.3 MJ m^(-3) in average), simultaneously with superior strength(close to 1 GPa), allowing an impressive specific penetration energy absorption(~0.17 MJ kg^(-1)) at high impact velocities when used for ballistic impact protection. Detailed interfacial and structural analysis reveals that the reinforcement is synergistically determined by π-π interaction and H-bonding linkage between adjacent graphene lamellae. Especially, the defective pores within the graphene platelets benefit the favorable adsorption of the pyrene-containing molecules, which imperatively maximizes the interfacial binding, facilitating deflecting crack and plastic deformation under loading. Density functional theory simulation suggests that the coupling between the polar functional groups, e.g., –COOH, at the edges of graphene platelets and –NH_(2) and –COOH of AP/PB are critical to the formation of hydrogen bonding network.

Hydrazine-Cadmium Tellurite Hybrid Microcrystals: An Efficient Precursor to Porous Cadmium Telluride and Tellurium Architectures Through Its Thermal Decomposition

Well-defined platelet-like hydrazine-cadmium tellurite hybrid microcrystals have been synthesized by a solvothermal reaction of cadmium chloride,sodium tellurite,and hydrazine hydrate in a mixed solvent containing n-propylamine and deionized water.The formula of the hybrid platelet-like microcrystals has been proposed based on a combination of powder X-ray diffraction pattern(PXRD),elemental analysis,thermogravimetic analysis(TGA),and X-ray photoelectron spectroscopy(XPS).Controlled thermal decomposition of this hybrid precursor can lead to the formation of porous platelet-like microarchitectures.Pure porous cadmium telluride architectures were obtained by using hydrochloric acid to dissolve CdTeO3 remaining in the sample after thermal decomposition at 450°C.In addition,unique nanoporous tellurium architectures were obtained by using hydrochloric acid to dissolve the amorphous Cd(N2H4)TeO3 formed after thermal decomposition at 300°C,followed by an in situ topotactic reaction between the residual three-dimensional(3-D)skeleton of cadmium telluride nanocrystallites and−23TeO.Brunauer-Emmett-Teller(BET)analysis and a study of the optical properties of these porous cadmium telluride and tellurium materials have also been carried out.

Hierarchical Silver Indium Tungsten Oxide Mesocrystals with Morphology-, Pressure-, and Temperature-Dependent Luminescence Properties

Highly hierarchical structures of silver indium tungsten oxide(AgIn(WO_(4))_(2))mesocrystals can be rationally fabricated via the microwave-assisted synthesis method by tuning the initial concentrations of the precursors.Photoluminescence spectra of hierarchical AgIn(WO_(4))_(2) mesocrystals were measured to investigate the correlation between the morphology,pressure,and temperature and their luminescence properties.The materials showed interesting white emission when excited by visible light of wavelength 460 nm.AgIn(WO_(4))_(2) materials having different morphologies displayed notable differences in photogenerated emission performance.The emission was strongly correlated with the surface nanostructures of outgrowths,with larger amounts of outgrowths leading to stronger emission intensities.The pressure-and temperature-dependent photoluminescence properties of these materials have also been investigated under hydrostatic pressures up to 16 GPa at room temperature and in the temperature range from 10 to 300 K.