Showing papers in "Npg Asia Materials in 2014"

Cerium oxide nanoparticle: a remarkably versatile rare earth nanomaterial for biological applications

Abstract: Cerium oxide nanoparticles have the unique power to act as both oxidation and reduction catalysts, thanks to the ability of cerium to rapidly switch between two oxidation states. Can Xu and Xiaogang Qu from the Chinese Academy of Sciences review how this dual catalytic activity yields enzyme-like behavior that can be harnessed for cancer-detecting assays and new biomedical applications. The nanoparticles mimic enzyme species, such as superoxide dismutases and catalases, that repair the damage caused by free radicals and reduce harmful reactive oxygen levels in the body. With tiny dimensions that allow them to enter cellular spaces inaccessible to traditional medicines - including crossing the blood-brain barrier for Alzheimer's disease treatments - these nanomaterials may offer potent remedies against degenerative diseases. Xu and Qu stress the need for systematic biological testing, however, to resolve possible toxicity concerns.

Cellulose nanocrystal-based materials: from liquid crystal self-assembly and glass formation to multifunctional thin films

Abstract: Cellulose nanocrystals (CNCs), produced by the acid hydrolysis of wood, cotton or other cellulose-rich sources, constitute a renewable nanosized raw material with a broad range of envisaged uses: f ...

Recent progress in developing advanced membranes for emulsified oil/water separation

Abstract: Oil/water separation, especially emulsified oil/water mixture separation, has become a widespread concern because of the severe fouling problem caused by the easy adsorption of oil droplets onto the surfaces of filtration membranes. Many strategies have been employed to eliminate the fouling problem, but it remains a challenge and impedes the development of membrane technology. In this short review, we discuss the recent development of membrane technology for emulsified oil/water separation. As shown in the image, in addition to polymer- and ceramic-dominated traditional membranes, nanomaterial-based membranes have recently demonstrated their superiority and have achieved high performance.

The design and applications of superomniphobic surfaces

Abstract: Surfaces that display contact angles >150° along with low contact angle hysteresis with essentially all high and low surface tension liquids, including water, oils and alcohols, are known as superomniphobic surfaces. Such surfaces have a range of commercial applications, including self-cleaning, non-fouling, stain-free clothing, drag reduction, corrosion prevention and separation of liquids. Such surfaces have thus generated immense academic and industrial interest in recent years. In this review, we discuss the systematic design of superomniphobic surfaces. In particular, we discuss the significance of surface energy, roughness and the critical role of re-entrant texture in obtaining the so-called Cassie–Baxter state with low surface tension liquids. We also discuss how hierarchical scales of texture can yield high contact angles and decrease the contact angle hysteresis of superomniphobic surfaces by reducing the solid–liquid contact area. On the basis of this understanding, we discuss dimensionless design parameters that allow for the systematic design of superomniphobic surfaces. We also review the current literature on superomniphobic surfaces, paying particular attention to surfaces that demonstrate good mechanical, chemical and radiation durability—traits that are essential for any commercial application of superomniphobic surfaces. Finally, we conclude by identifying the unresolved challenges in the fabrication of durable superomniphobic surfaces and highlight the future needs in the field. Surfaces that display contact angles >150° along with a low contact angle hysteresis for both low and high surface tension liquids are known as superomniphobic surfaces. Such surfaces have several applications, including self-cleaning, non-fouling, stain-free clothing, drag reduction, corrosion prevention and separation of liquids. In this review, we discuss the design criteria, recent studies, applications, challenges and potential of superomniphobic surfaces. Surfaces that strongly repel low surface tension liquids (e.g. oils and alcohols) are classified as superoleophobic and those that strongly repel high surface tension liquids (e.g. water) are classified as superhydrophobic. However, if a surface shows both these characteristics, it can be considered superomniphobic. Liquid droplets on superomniphobic surfaces roll off very easily and, as a result, these surfaces are attractive as non-fouling coatings, self-cleaning surfaces and liquid-separation techniques. Anish Tuteja at the University of Michigan, United States, and colleagues review the design principles required to fabricate superomniphobic surfaces. They discuss surface energy, roughness and hierarchical scales of surface texture, and recognize the importance of re-entrant textures (i.e. convex topography) to achieve superomniphobicity. Several examples of superomniphobic surfaces are presented with particular focus on the need to improve chemical and mechanical durability, to realize their full potential in commercial and industrial applications.

Shifting up the optimum figure of merit of p -type bismuth telluride-based thermoelectric materials for power generation by suppressing intrinsic conduction

Abstract: The abundance of low-temperature waste heat produced by industry and automobile exhaust necessitates the development of power generation with thermoelectric (TE) materials. Commercially available bismuth telluride-based alloys are generally used near room temperature. Materials that are composed of p-type bismuth telluride, which are suitable for low-temperature power generation (near 380 K), were successfully obtained through Sb-alloying, which suppresses detrimental intrinsic conduction at elevated temperatures by increasing hole concentrations and material band gaps. Furthermore, hot deformation (HD)-induced multi-scale microstructures were successfully realized in the high-performance p-type TE materials. Enhanced textures and donor-like effects all contributed to improved electrical transport properties. Multiple phonon scattering centers, including local nanostructures induced by dynamic recrystallization and high-density lattice defects, significantly reduced the lattice thermal conductivity. These combined effects resulted in observable improvement of ZT over the entire temperature range, with all TE parameters measured along the in-plane direction. The maximum ZT of 1.3 for the hot-deformed Bi0.3Sb1.7Te3 alloy was reached at 380 K, whereas the average ZTav of 1.18 was found in the range of 300–480 K, indicating potential for application in low-temperature TE power generation. Thermoelectric materials, which convert temperature differences and electric voltage into each other, serve in refrigeration or power generation applications. Currently, bismuth telluride (Bi2Te3) and its alloys are the most widely used thermoelectric materials. Tie-Jun Zhu, Xin-Bing Zhao and co-workers from Zhejiang University, China, have now investigated the effect of antimony (Sb) alloying on bismuth tellurides through a series of polycrystalline solid solutions of Bi2-xSbxTe3—where x varies between 1.4 and 1.8—prepared by hot deformation. Systematic tuning of the alloy composition showed that higher antimony content raised the material's optimal conversion temperature by repressing undesirable conduction. This effect arises from an increase in both the hole concentration and the band gap in the material. For a composition where x is 1.7, the alloy showed optimal performances at 380 kelvin—a suitable temperature for low-temperature power generation from the waste heat generated by industry or vehicles. The p-type bismuth telluride-based polycrystalline materials suiting for low-temperature power generations (near 380 K) have been obtained through Sb-alloying and HD, which suppresses the detrimental effect of intrinsic conduction at elevated temperature via increasing the hole concentration and band gap. The hot-deformed Bi0.3Sb1.7Te3 alloy, not usual composition Bi0.5Sb1.5Te3, shows a maximum ZT of 1.3 at 380 K, indicating a bright application potential in low-temperature power generations.

Scalable self-growth of Ni@NiO core-shell electrode with ultrahigh capacitance and super-long cyclic stability for supercapacitors

Abstract: Three-dimensional (3D) electrodes have been demonstrated to be promising candidates for high-performance supercapacitors because of their unique architectures and outstanding electrochemical properties. However, the fabrication process for current 3D electrodes is not scalable. Herein, a novel and cost-effective activation process has been developed to macroscopically produce 3D porous Ni@NiO core-shell electrodes with enhanced electrochemical properties. The porous Ni@NiO core-shell electrode obtained by activated commercial Ni foam (NF) in a 3 M HCl solution yields an ultrahigh areal capacitance of 2.0 F cm−2 at a high current density of 8 mA cm−2, which is substantially higher than that of most reported 3D NF-based electrodes. Moreover, the activated NF (ANF) electrode exhibited super-long cycling stability. Owing to the increased accessible surface area and continual formation of electrochemically active NiO during cycling, the areal capacitance of the ANF electrode did not exhibit any decay and instead increased from 0.47 to 1.27 F cm−2 after 100 000 cycles at 100 mV s−1. This is the best cycling stability achieved by a 3D NF-based electrode. Additionally, a high-performance asymmetrical supercapacitor (ASC) device based on the as-prepared ANF cathode and a reduced graphene oxide (RGO) anode was also prepared. The ANF//RGO-ASC device was able to deliver a maximum energy density of 1.06 mWh cm−3 and a maximum power density of 0.42 W cm−3. Researchers from China have discovered a cost-effective way to produce supercapacitors on large scales using nickel foam. This three-dimensional porous metal is an ideal electrode for high-capacity energy storage because of its lightweight, corrosion-resistant structure. To achieve supercapacitance, however, researchers must insert active substances, such as graphene, deep into the nickel pores. Xihong Lu and colleagues from Sun Yat-Sen University solved this problem by immersing commercial-grade nickel foam into hot hydrochloric acid for several minutes. The one-step reaction pitted the formerly smooth nickel foam surface and created a thin outer ‘shell’ of nickel oxide that surrounded an inner nickel ‘core’. Electrochemical experiments revealed that the favorable core–shell structure, combined with a more accessible surface area achieved from the acid etching, yielded an energy-dense supercapacitor electrode that was effective for more than 100,000 charge–recharge cycles. A novel and cost-effective activation process has been developed to macroscopically produce three-dimensional (3D) porous Ni@NiO core-shell electrode by activated Ni foam (ANF) in HCl aqueous solution. The ANF electrode yielded a remarkable areal capacitance of 2.0 F cm−2 at a high current density of 8 mA cm−2 and exhibited ultrahigh long-term cycling stability without any decay of capacitance after 100 000 cycles.

Quantum spin Hall insulators and quantum valley Hall insulators of BiX/SbX (X=H, F, Cl and Br) monolayers with a record bulk band gap

Abstract: A large bulk band gap is critical for the application of quantum spin Hall (QSH) insulators or two-dimensional (2D) topological insulators (TIs) in spintronic devices operating at room temperature (RT). On the basis of first-principles calculations, we predicted a group of 2D TI BiX/SbX (X=H, F, Cl and Br) monolayers with extraordinarily large bulk gaps from 0.32 eV to a record value of 1.08 eV. These giant-gaps are entirely due to the result of the strong spin-orbit interaction related to the px and py orbitals of the Bi/Sb atoms around the two valleys K and K′ of the honeycomb lattice, which is significantly different from that consisting of the pz orbital as in graphene/silicene. The topological characteristic of BiX/SbX monolayers is confirmed by the calculated nontrivial Z2 index and an explicit construction of the low-energy effective Hamiltonian in these systems. We demonstrate that the honeycomb structures of BiX monolayers remain stable even at 600 K. Owing to these features, the giant-gap TIs BiX/SbX monolayers are an ideal platform to realize many exotic phenomena and fabricate new quantum devices operating at RT. Furthermore, biased BiX/SbX monolayers become a quantum valley Hall insulator, exhibiting valley-selective circular dichroism. Chinese researchers have identified new materials with record ‘bulk bandgaps’ ideal for generating stable, quantum-based devices. Jinbo Yang from Peking University and co-workers performed first-principles calculations to investigate two-dimensional topological insulators — recently discovered crystals with an insulating core and surface ‘quantum spin Hall states’, which can move electrons without energy loss. The quantum features of topological insulators normally emerge only at temperatures close to absolute zero, but the team's computations revealed that ultrathin bismuth- and antimony-based films arranged in graphene-like, honeycomb frameworks can produce quantum effects much closer to room temperature thanks to giant energy gaps (0.32–1.08 eV) between the materials' conduction and valence bands. These gaps, which result from strong electron spin–orbit interactions, stabilize the surface states against interference from thermally activated carriers and make these materials intriguing targets for future experiments. A group of 2D topological insulators BiX/SbX (X=H, F, Cl and Br) monolayers with extraordinarily large bulk gaps from 0.32 to a record value of 1.08 eV were predicated. These giant-gaps result from the strong spin-orbit interaction related to px and py orbitals of Bi/Sb atoms around the two valleys K and K′. The honeycomb structures of BiX monolayers remain stable even at a temperature of 600 K. The electric field-biased BiX/SbX monolayers become quantum valley Hall insulators, showing valley-selective circular dichroism. These features make the BiX/SbX monolayers an ideal platform to realize many exotic phenomena and fabricate new quantum devices.

Amorphous iron phosphate: potential host for various charge carrier ions

Abstract: Unlike crystalline electrodes wherein ion insertion is crucially dependent on the presence of energetically equivalent sites, nanostructured amorphous iron(III) phosphate hosts prepared by room temperature strategies and possessing porous properties facilitate the insertion of alkali ions with different sizes and also higher charge carriers including divalent cations (Mg2+−0.72A, Zn2+-0.74 A) or trivalent cations (Al3+−0.53 A). This versatile cathode stores electrical energy by a reversible amorphous to crystalline reconstitutive reaction that occurs during electrochemical reaction with monovalent sodium, potassium and lithium. The study presents opportunities to develop amorphous electrodes with similar phase behavior for energy storage applications.

Uniformly connected conductive networks on cellulose nanofiber paper for transparent paper electronics

Abstract: Paper has been used throughout history for numerous purposes and continues to be extremely useful. The cellulose-based material has even been investigated as a support for flexible electronics. Traditional paper, however, does not provide the transparency that is increasingly sought after in this field. Now, Hirotaka Koga, Masaya Nogi and co-workers from Osaka University, Japan, have coated a type of transparent paper that they previously developed with conductive materials. Their paper is based on cellulose nanofibers rather than the microfibers from which traditional paper is composed. The team used silver nanowires or carbon nanotubes as the conductive material—both show promise in transparent flexible electronics that employ plastic substrates. By depositing the silver or carbon on the ‘cellulose nanopaper’ through a simple filtration process, the researchers obtained uniform networks, thus avoiding the uneven distribution that typically occurs with plastic-based substrates. The resulting flexible materials showed good conductivity and optical transparency.

Graphene fiber: a new material platform for unique applications

Abstract: Graphene fiber (GF) is of practical importance because it integrates the remarkable properties of individual graphene sheets into useful, macroscopic ensembles that possess the common characteristics of fibers, such as mechanical flexibility for textiles, while maintaining the unique advantages over conventional carbon fibers, such as low cost, light weight, shapeability and ease of functionalization in an in situ or post-synthetic manner for various applications. In this review, we judiciously summarize the significant advances in GFs achieved by our group and others in recent years, including the tunable and controllable preparation of GFs with functionality and their remarkable applications for unconventional devices, such as flexible fiber-type actuators, robots, motors, photovoltaic cells and supercapacitors. In this review, the significant advances of the new type of graphene fibers (GFs) achieved during the recent few years have been systematically summarized, including the tunable and controllable preparation of GFs with functionalizations and their remarkable applications for unconventional devices such as flexible fiber-type of actuators, robots, motors, photovoltaic cells and supercapacitors. Graphene has set records for both its mechanical strength and electrical conductivity. Exploiting these properties for use in practical devices, however, requires techniques that transform this atom-thin substance into large-scale objects. Liangti Qu and colleagues from the Beijing Institute of Technology in China review an innovative approach to achieving this goal that uses ‘graphene fibers’ — long, thin and robust materials that can be synthesized by extruding liquid-crystal-like graphene oxide suspensions into filaments or through spontaneous reactions inside dimensionally confined glass pipelines. These stretchable fibers can be woven inside textiles for wearable electronics applications, combined with photovoltaic elements to make solar wires or used as shape-shifting actuators for robotic devices. The researchers caution, however, that more effort is needed to reduce defects inside graphene fibers that currently hinder their performance.

Hydrogels for cardiac tissue engineering

Abstract: Cardiac failure is a critical condition that results in life-threatening consequences. Due to a limited number of organ donors, tissue engineering has emerged to generate functional tissue constructs and provide an alternative mean to repair and regenerate damaged heart tissues. In this paper, we review the emerging directions associated with cardiac tissue engineering approaches. In particular, we discuss the use of hydrogels in repair and regeneration of damaged hearts. Because of their tissue-like biological, chemical and mechanical properties, hydrogels represent a potentially powerful material for directing cells into functional cardiac tissues. Herein, we will summarize both traditional and next-generation hydrogels with conductive, elastomeric and oxygen-releasing capabilities that can promote vascularization and stem cell differentiation to form properly functioning cardiac tissues. Hydrogel-based scaffolds are promising biomaterials to deliver cells and small biomolecules to regenerate the cardiac muscle. It is anticipated that cell-loaded hydrogels will potentially be able to mend the broken heart. Cardiac tissue damaged after a heart attack is particularly difficult to regenerate. Consequently, researchers are exploring innovative ways to regrow cells in this stressful and oxygen-rich microenvironment. Ali Khademhosseini and colleagues from Harvard Medical School in the United States review recent efforts to create biocompatible scaffolds for cardiac tissue engineering using hydrogels - squishy, three-dimensional polymer networks that expand in water, much like natural tissue. While cardiac cells grown on traditional hydrogel supports such as poly(ethylene glycol) and fibrils have considerably higher viability than those directly injected into cardiac muscle, novel hydrogels that better mimic native heart functions are still needed. The researchers highlight enhanced biomaterials incorporating elastomeric, conductive and oxygen-releasing capabilities. Furthermore, they anticipate that combining renewable stem cells with micropatterning techniques could enable the development of prevascularized, ‘off-the-shelf’ hydrogels that are ready to be implanted into patients.

Annealing-free fabrication of highly oxidation-resistive copper nanowire composite conductors for photovoltaics

Abstract: Copper nanowire (CuNW)-network film is a promising alternative to the conventional indium tin oxide (ITO) as a transparent conductor. However, thermal instability and the ease of oxidation hinder the practical applications of CuNW films. We present oxidation-resistive CuNW-based composite electrodes that are highly transparent, conductive and flexible. Lactic acid treatment effectively removes both the organic capping molecule and the surface oxide/hydroxide from the CuNWs, allowing direct contact between the nanowires. This chemical approach enables the fabrication of transparent electrodes with excellent properties (19.8 Ω sq−1 and 88.7% at 550 nm) at room temperature without any atmospheric control. Furthermore, the embedded structure of CuNWs with Al-doped ZnO (AZO) dramatically improves the thermal stability and oxidation resistance of CuNWs. These AZO/CuNW/AZO composite electrodes exhibit high transparency (83.9% at 550 nm) and low sheet resistance (35.9 Ω sq−1), maintaining these properties even with a bending number of 1280 under a bending radius of 2.5 mm. When implemented in a Cu(In1−x,Gax)(S,Se)2 thin-film solar cell, this composite electrode demonstrated substantial potential as a low-cost (Ag-, In-free), high performance transparent electrode, comparable to a conventional sputtered ITO-based solar cell. A highly thermal and oxidation-resistive AZO/Cu nanowire/AZO composite electrode for thin-film solar cells was fabricated at room temperature without any atmospheric control. Our novel transparent composite electrode showed good thermal oxidation stability as well as high conductivity (∼35.9 Ω/sq), transparency (83.9% at 550 nm) and flexibility. Metal nanowire-based materials are promising alternatives to the conventional transparent electrodes found in solar cells and touchscreen displays because they are naturally flexible and stretchable — attributes that can dramatically improve device lifetimes. Current efforts, however, have been hampered by the need for expensive silver nanowires; lower-cost materials, such as copper nanowires, possess an insulating surface oxide film that deteriorates device conductivity. Jooho Moon and co-workers from Yonsei University, South Korea, have now uncovered a surprising way to remove oxides and organic capping molecules from copper nanowires using lactic acid, a biomolecule commonly found in milk. Room temperature lactic acid treatments, followed by washes with organic solvents, yielded transparent copper nanowire networks that feature direct, metal-to-metal contact. Photovoltaic testing revealed these bendable electrodes had excellent conductivity for high-performance solar applications.

Periodic mesoporous organosilicas for advanced applications

Abstract: In recent years, incorporating organic functionalities into inorganic materials has emerged as an efficient strategy for constructing a variety of functional materials. Periodic mesoporous organosilicas (PMOs) were one of the first such classes of composites to be developed. Grafting organic moieties within the channel walls of porous silicas — to act as bridges between neighboring silicon atoms — enables the tuning of their bulk properties, such as mechanical strength, or their surface characteristics — hydrophilicity, hydrophobicity or guest-binding abilities, for example. Chang-Sik Ha and colleagues from Pusan National University, South Korea, review how the wide range of morphologies and functionalities that have been prepared to date make PMOs desirable for numerous and varied practical applications. These hybrid materials have proven attractive for applications ranging from catalysis and drug delivery to the sorption of guest molecules and optoelectronics.

Strong enhancement of phonon scattering through nanoscale grains in lead sulfide thermoelectrics

Abstract: We present nanocrystalline PbS, which was prepared using a solvothermal method followed by spark plasma sintering, as a promising thermoelectric material The effects of grains with different length scales on phonon scattering of PbS samples, and therefore on the thermal conductivity of these samples, were studied using transmission electron microscopy and theoretical calculations We found that a high density of nanoscale grain boundaries dramatically lowered the thermal conductivity by effectively scattering long-wavelength phonons The thermal conductivity at room temperature was reduced from 25 W m−1 K−1 for ingot-PbS (grain size >200 μm) to 23 W m−1 K−1 for micro-PbS (grain size >04 μm); remarkably, thermal conductivity was reduced to 085 W m−1 K−1 for nano-PbS (grain size ∼30 nm) Considering the full phonon spectrum of the material, a theoretical model based on a combination of first-principles calculations and semiempirical phonon scattering rates was proposed to explain this effective enhancement The results show that the high density of nanoscale grains could cause effective phonon scattering of almost 61% These findings shed light on developing high-performance thermoelectrics via nanograins at the intermediate temperature range Thermoelectric materials that transform waste heat generated by equipment or buildings into electricity are emerging as an important green energy technology Currently, researchers are trying to improve thermoelectric substances by embedding within them nanoscale precipitates that allow these materials to capture more heat An international team led by Jiaqing He from the South University of Science and Technology of China has now discovered a way to improve this process by systematically introducing nanoscale crystal structure defects, or ‘nanograins’, into lead sulfide (PbS) particles Their approach tripled the thermoelectric performance of this low-cost mineral from its bulk state without introducing charge-disrupting centers commonly associated with nanoscale precipitates Detailed analysis revealed that the densely packed nanograins trap heat by scattering solid-state vibrations, or phonons, while simultaneously suppressing ‘bipolar’ interactions between charge carriers that can diminish thermoelectric power We report here on the effects of grains of PbS with different length scales on thermal conductivity reduction and bipolar effect ‘suppression’ through macro-properties/microstructure analysis We found that nanograins can achieve the above goals simultaneously Combining experimental results and theoretical calculations, we found that the effect of nanograins on the reduction in lattice thermal conductivity can surpass that of nanoprecipitates Improved properties corresponding to the lowest lattice thermal conductivity in a PbQ (Q=Te, Se, S) system (05 W m K−1 at 923 K) and the highest ZT value in PbQ nanocrystalline materials were achieved by the nanograin method

A highly stretchable, helical copper nanowire conductor exhibiting a stretchability of 700%

Abstract: Jooho Moon, Sunho Jeong and colleagues in South Korea have fabricated conducting meshes and extremely stretchable helices from copper nanowires. Metallic nanowires that are randomly entangled with each other in flexible meshes are of interest as electrical conductors for stretchable electronics. The researchers from Yonsei University and the Korea Research Institute of Chemical Technology fabricated nanowires made of copper with a simple and scalable process based on room-temperature chemical synthesis. When the nanowires were deposited on a flexible polymer substrate, the resulting meshes could stretch to up to twice their original size. When shaped as a helix, the nanowires showed an even greater stretchability of up to 700%. Being more cost-efficient than the silver nanowires used previously for similar applications, these copper nanowires hold a great promise for stretchable electronic circuits or in wearable electronics.

A highly reversible, low-strain Mg-ion insertion anode material for rechargeable Mg-ion batteries

Abstract: Rechargeable magnesium (Mg) batteries have been attracting increasing attention recently because of the abundance of the raw material, their relatively low price and their good safety characteristics. However, rechargeable Mg batteries are still in their infancy. Therefore, alternate Mg-ion insertion anode materials are highly desirable to ultimately mass-produce rechargeable Mg batteries. In this study, we introduce the spinel Li4Ti5O12 as an Mg-ion insertion-type anode material with a high reversible capacity of 175 mA h g−1. This material possesses a low-strain characteristic, resulting in an excellent long-term cycle life. The proposed Mg-storage mechanism, including phase separation and transition reaction, is evaluated using advanced atomic scale scanning transmission electron microscopy techniques. This unusual Mg storage mechanism has rarely been reported for ion insertion-type electrode materials for rechargeable batteries. Our findings offer more options for the development of Mg-ion insertion materials for long-life rechargeable Mg batteries. Yu-Guo Guo at the Institute of Chemistry, Chinese Academy of Sciences and colleagues from China and the USA have developed a new battery material based on magnesium ions. Rechargeable lithium-ion batteries are ubiquitous in modern electronic devices. To increase the storage capacity of rechargeable batteries even further, however, the number of electrical charges per ion must be increased. This can be achieved by replacing lithium ions, which have one free electron, with a magnesium ion, which has two. The researchers discovered that Li4Ti5O12 is particularly suitable as a battery electrode for magnesium ions as it easily allows their storage between the crystal layers of the material. They also verified that these ions can be easily moved in and out of the crystal during charging and use of the battery, enhancing the prospects for practical magnesium-ion batteries. Spinel Li4Ti5O12 nanoparticle has been demonstrated as an Mg-ion insertion anode material with ‘zero-strain’ characteristics (only ∼0.8% volume change) during Mg-ion insertion/extraction cycles, and a remarkable capacity retention capability of >95% after 500 cycles.

One drop at a time: toward droplet microfluidics as a versatile tool for single-cell analysis

Abstract: Applying droplet microfluidics to cells trapped within water-in-oil droplets offers a powerful way to study single cells in action. Wilhelm Huck and colleagues at Radboud University in the Netherlands have reviewed the application of this technique and research toward the study of individual cells. Unlike most cell analysis methods, it allows specific chemicals to be associated with the individual cell they come from or interact with. Researchers are currently addressing many technical challenges, including performing washing steps inside droplets and developing better ways to monitor and manipulate the cells at high-throughput rates. Current work is focused on reducing the complexity and enhancing the sensitivity of the technique. The authors also review applications that could soon become routine, including drug and antibody studies, tracking single-cell gene expression, studies of cell evolution and analysis of cellular interactions when droplets fuse.

Bio-inspired porous antenna-like nanocube/nanowire heterostructure as ultra-sensitive cellular interfaces

Abstract: In this study, an unconventional antenna-like heterostructure comprised of arrays of nanoporous Prussian blue (PB) nanocube heads/TiO2 nanowire (NW) arms (PB-TiO2) is developed for efficient three-dimensional interfacial sensing of small molecules and cellular activities. Inspired by insect tentacles, which are comprised of both target recognition and signal transduction units, one-dimensional TiO2 NW arrays are grown, followed by selective growth of nanoporous PB nanocubes on the tips of the NW arrays. Due to their high selectivity and bioaffinity toward cells, long biostability under a cell culture adhesion condition (up to 108 h) is obtained, and with its inherent bio-mimetic enzymatic activity, the obtained nanoporous PB nanocubes (head segment) serve as robust substrates for site-selective cell adhesion and culture, which allows for sensitive detection of H2O2. Simultaneously, the single-crystalline TiO2 NWs (arm segment) provide efficient charge transport for electrode substrates. Compared with PB-functionalized planar electrochemical interfaces, the PB-TiO2 antenna NW biointerfaces exhibit a substantial enhancement in electrocatalytic activity and sensitivity for H2O2, which includes a low detection limit (∼20 nM), broad detection range (10−8 to 10−5 M), short response time (∼5 s) and long-term biocatalytic activity (up to 6 months). The direct cultivation of HeLa cells is demonstrated on the PB-TiO2 antenna NW arrays, which are capable of sensitive electrochemical recording of cellular activity in real time, where the results suggest the uniqueness of the biomimic PB-TiO2 antenna NWs for efficient cellular interfacing and molecular recognition. Insect tentacles have inspired researchers to make the first antenna-like nanosensor for the ultrasensitive detection of hydrogen peroxide at cell surfaces, and the creative concept of sensing and recognition could be adapted to detect other important biomolecules. Professor Dongyuan Zhao, Gengfeng Zheng and colleagues at Fudan University in China and Monash University in Australia made antenna-like structures from nanocubes of Prussian blue pigment attached to a titanium dioxide arm. The Prussian blue molecules catalyze electron transfer reactions that convert hydrogen peroxide into oxygen and water and the titanium dioxide arm carries the resulting electric current to a substrate surface where it is amplified and detected. The high surface area and porosity of the nanocubes allows much greater sensitivity and selectivity than traditional sensors. The antenna-like nanosensor also has remarkable affinity towards living cells and standout stability in cell cultures. Unconventional nanoporous antenna-like heterostructure arrays, inspired by insect tentacles, are developed for efficient interfacial sensing of biomolecules and cellular activities. The obtained nanoporous cubes (head segments) serve as a robust substrate for site-selective cell adhesion and culture, allowing for sensitive detection of biomolecules. Meanwhile, the single-crystalline nanowires (arm segment) provide efficient charge transport toward the electrode substrate. The inspired hetero-biointerfaces exhibit substantial enhanced electrocatalytic activity and sensitivity for biomolecules.

Evolution of self-oscillating polymer gels as autonomous polymer systems

Abstract: We developed ‘self-oscillating’ polymer gels that undergo spontaneous cyclic swelling–deswelling changes without any on–off switching of external stimuli like a heart muscle. Here, our recent progress on the self-oscillating polymer gels was summarized.

Aptamer-conjugated nanomaterials for specific cancer cell recognition and targeted cancer therapy.

Abstract: Based on their unique advantages, increasing interest has been shown in the use of aptamers as target ligands for specific cancer cell recognition and targeted cancer therapy. Recently, the development of aptamer-conjugated nanomaterials has offered new therapeutic opportunities for cancer treatment with better efficacy and lower toxicity. We highlight some of the promising classes of aptamer-conjugated nanomaterials for the specific recognition of cancer cells and targeted cancer therapy. Recent developments in the use of novel strategies that enable sensitive and selective cancer cell recognition are introduced. In addition to targeted drug delivery for chemotherapy, we also review how aptamer-conjugated nanomaterials are being incorporated into emerging technologies with significant improvement in efficiency and selectivity in cancer treatment. New methods of integrating aptamers with various types of nanomaterials are summarized, highlighting promising classes of aptamer-conjugated nanoparticles for efficient cancer cell recognition and the targeted delivery of drugs. In addition, emerging technologies for cancer treatment using nanomaterials as therapeutic drugs are discussed. These aptamer-conjugated nanomaterials will benefit cancer treatment through increased specificity and efficacy as well as reduced toxicity. A major challenge in cancer therapy is the selective targeting of cancerous cells to enhance treatment efficiency and reduce the side effects for patients. A variety of nanostructured materials have recently been developed that, when combined with ligands, are able to recognize the target cells through antigens or receptors. Qiaoling Liu from Hunan University and colleagues in China and the United States review the use of DNA aptamers as ligands. These short, synthetic oligonucleotide strands are cost-effective, exhibit low toxicity and can be attached to a range of nanomaterials - from liposomes and hydrogels to inorganic nanoparticles - to endow them with sensitive and selective cell-recognition abilities. Furthermore, the resulting hybrid nanomaterials can be used in conjunction with conventional treatments, such as photodynamic and photothermal therapies. Although hurdles in their toxicity and efficiency remain to be overcome before they are suitable for real-life cancer treatments, aptamer-conjugated nanomaterials have emerged as a promising theranostic platform.

A pH-responsive smart surface for the continuous separation of oil/water/oil ternary mixtures

Abstract: To handle the serious issue of increasing oil spill accidents, many strategies have been proposed to either clean spilt oil or separate water/oil mixture. Especially, superhydrophilic/underwater superoleophobic smart materials have recently shown advantages in overcoming problems of oil blocking and water barriers during conventional oil/water-separating process of oil-rich mixtures with superhydrophobic/superoleophilic materials. However, to the best of our knowledge, no prior reports have detailed smart materials with the wetting properties of superhydrophobic/superoleophilic that can be applied in continuous in situ separations of oil/water/oil ternary mixtures, which are common in practical oil spill cases. Herein, we describe the fabrication and efficacy of a pH-responsive smart device for continuous in situ separations of such oil/water/oil ternary mixtures without the need for ex situ treatments. In air, the superhydrophobic/superoleophilic surface of the device allowed dichloromethane to permeate through while preventing water from passing. The superhydrophilicity/underwater superoleophobicity of the device surface following alkaline treatments prevented the passage of hexane while allowing water to penetrate the device. Recent efforts to find quick and simple ways to remediate oil spills have focused on bio-inspired membranes that selectively filter either oil or water from a mixture. Real-world oil pollution, however, often contains complex, oil–water–oil emulsions that can clog single-purpose membranes. Now, a team led by Feng Shi from Beijing University of Chemical Technology in China has developed a pH-responsive ‘smart’ device that can separate three component oil–water mixtures on demand. Their device — a porous copper foam cube coated with silver aggregates and self-assembled organic films — initially absorbs oil while blocking water. Increasing the mixture's pH transforms the device wettability from superhydrophobic to superhydrophilic, meaning that only water can now be absorbed. Sequential pH changes enable efficient separation of tertiary oil spills without additional treatments. By fabricating a pH-responsive smart device with tunable surface-wetting properties, we have realized continuous in situ separations of oil/water/oil ternary mixtures without ex situ treatments of cleaning or drying. In air, the superhydrophobic/superoleophilic surface of the smart device allowed heavy oil to permeate through while preventing water from passing. When exposed to alkaline water, the superhydrophilicity/underwater superoleophobicity of the smart device surface prevented the passage of hexane while allowing water to penetrate. In this way, efficient separation and collection of the individual components of a complex oil/water/oil mixture was realized in a continuous process with no ex situ treatments. This method could provide a strategy for continuous separations of oil/water/oil ternary mixtures, which are common in practical oil spill cases.

A superconducting joint for GdBa2Cu3O7−δ-coated conductors

Abstract: Researchers in South Korea have solved the problem of how to join two high-temperature superconducting materials together while preserving their electrical and magnetic properties. Superconducting materials are pivotal for a range of scientific instruments including MRI machines and particle accelerators. Established connection methods, however, have resulted in high resistance at the join. Haigun Lee and colleagues at Korea University have developed a technique that does not have this problem. When their ‘superconducting joint’ is added to a coil arrangement, the induced magnetic field remains unchanged, further indicating the lack of resistance and maintenance of superconductivity. The multi-step process includes the partial melting of the conductor and annealing under high-pressure oxygen. The join could be incorporated in high-temperature superconducting materials that form closed circuits and operate without the need for an external power supply for applications ranging from analytical instruments to medical scanners.

Therapeutic applications of low-toxicity spherical nanocarbon materials

Abstract: Nanocarbon materials have received considerable attention due to their unique structure and properties, which make them promising candidate materials for use in biomedical applications. In this review, we discuss the therapeutic applications of spherical nanocarbon materials, including fullerene nanoparticles, carbon nanohorn aggregates, nanodiamonds and porous carbon nanospheres, and their toxicology in biological systems. We put special emphasis on the antitumor effects of these multifunctional nanoparticles, which operate via novel mechanisms in a highly efficient manner. The low toxicities of these spherical nanocarbon materials as well as the possible effects of shape on toxicity are discussed. Various spherical nanocarbon materials, including fullerenes, carbon nanohorn aggregates, nanodiamonds etc., have shown potential anti-cancer effects. Fullerenes and metallofullerenes possess outstanding ROS-scavenging capability, as well as other biological effects like immunity enhancement etc., affording promising tumor suppression potential. Carbon nanohorn aggregates and nanodiamond particles have demonstrated effective drug delivery ability for cancer therapy. Moreover, it is noteworthy that these spherical nanocarbon materials show positive toxicological evaluation results, encouraging possible practical usage for biomedical applications. Since the discovery of fullerenes in 1985 with the report of a football-shaped C60 molecule, a variety of carbon nanostructures have emerged, the most familiar of which are carbon nanotubes and graphene sheets. Owing to some intriguing properties and an ever-increasing range of potential applications, these ‘nanocarbons’ have attracted a great deal of attention from the scientific and technology communities. Jianxun Xu and Yuliang Zhao from the National Center for Nanosciences and Technology, China, and co-workers review both the pharmaceutical activity and toxicity of spherical nanocarbons. Such materials—which include fullerenes, the ‘nanohorn’ clusters formed from aggregated horn-shaped carbon nanotubes, nanodiamonds and porous nanospheres—are less toxic than their non-spherical counterparts in biomedical applications. In particular, Xu, Zhao and colleagues focus on the potential of these species for anticancer treatments that arise from their effects, including tumor metastasis and drug-resistance suppression.

Metal oxide mesocrystals with tailored structures and properties for energy conversion and storage applications

Abstract: Mesocrystals (MCs) are superstructures with a crystallographically ordered alignment of nanoparticles Owing to their organized structures, MCs posses some unique characteristics such as a high surface area, pore accessibility, and good electronic conductivity and thermal stability; thus, MCs could be beneficial for many areas of research and application This review begins with a description of the common synthesis strategies for, and characterization and fundamental properties of metal oxide MCs Newly developed analytical methods (that is, photoconductive atomic force microscopy and single-molecule, single-particle fluorescence microscopy) for unraveling the charge transport and photocatalytic properties of individual MCs are then introduced Further, recent developments in the applications of various metal oxide MCs, especially in the fields of energy conversion and storage, are also reviewed Finally, several perspectives in terms of future research on MCs are highlighted Mesocrystals are superstructures with a crystallographically ordered alignment of nanoparticles and posses unique characteristics such as a high surface area, pore accessibility, and good electronic conductivity and thermal stability This review summarizes the recent developments of metal oxide mesocrystals in the fields of energy conversion and storage Mesocrystals are periodic arrangements of nanoparticles that form larger structures of several hundreds of nanometers, or even micrometers, in size Takashi Tachikawa and Tetsuro Majima from Osaka University in Japan review the potential of metal oxide mesocrystals for applications in energy generation and energy storage Nanoparticles can have very different properties compared to the regular bulk material from which they originate For example, the larger surface area of mesocrystals is more efficient for water splitting or catalysis Additionally, the nanoparticles in mesocrystals are held in place, which can further improve their properties — such as the ability to transport electrical charges Mesocrystals containing titanium dioxide nanoparticles are of particular interest for use in catalytic processes or as electrodes in lithium batteries Nevertheless, the assembly of these nanoparticle superstructures, which can require complex fabrication processes, has hampered technological applications so far

Facile synthesis of chain-like LiCoO2 nanowire arrays as three-dimensional cathode for microbatteries

Abstract: Three-dimensional microbatteries have emerged as a new direction for powering microelectronic devices, where the three-dimensional nanostructured electrode is the key component for microbatteries to achieve high power density and high energy density in a small footprint. In this work, we present a novel approach for fabrication of LiCoO2 nanowire arrays as three-dimensional cathode for microbatteries. Mesoporous low-temperature LiCoO2 nanowire arrays can be directly prepared by a two-step hydrothermal method and they can be easily converted into chain-like high-temperature LiCoO2 nanowire arrays through further calcination. The layered LiCoO2 nanowire arrays exhibit both high gravimetric capacity and areal capacity, while maintaining good cycling stability and rate capability. The facile synthesis and superior electrochemical performance of the three-dimensional LiCoO2 cathode make it promising for application in microbatteries. Hui Xia from Nanjing University of Science and Technology in China and colleagues report a three-dimensional (3D) nanowire battery cathode that packs high power and energy into a tiny framework. The team turned lithium cobalt oxide - a compound widely used for lithium-ion battery cathodes - into freestanding, 3D nanowire arrays on metal substrates using a simple two-step hydrothermal synthesis technique. Further heat treatment transformed the nanowires into chain-like structures with first-rate electrochemical and recharging properties thanks to the material's short ion transport lengths and large surface area for energy storage. The cathode helps solve problems associated with delivering sufficient power and high storage capacities for on-chip battery applications - a finding that can aid in the design of advanced microscale devices such as drug delivery systems and wireless sensors. Mesoporous low-temperature LiCoO2 nanowire arrays can be directly prepared by a two-step hydrothermal method and they can be easily converted into chain-like high-temperature LiCoO2 nanowire arrays through further calcination. The layered LiCoO2 nanowire arrays exhibit both high gravimetric capacity and areal capacity, while maintaining good cycling stability and rate capability, make them promising for application in microbatteries.

Discotic liquid crystal-nanoparticle hybrid systems

Abstract: Discotic liquid crystals (DLCs) are nanomaterials with sizes ranging from 2 to 6 nm, and they are emerging as one-dimensional organic semiconducting materials. Recently, hybridization of these materials with various metallic and semiconducting nanoparticles (NPs) to alter and improve their properties has been realized. This article provides an overview of the developments in the field of newly immersed discotic nanoscience, a sub-field of liquid crystal (LC) nanoscience. As this field is also of great interest to readers without an LCs background, a brief introduction of the LC field is given first, with special emphasis on DLCs. This is followed by various DLC-NP hybrid systems. Finally, an outlook into the future of this newly emerging, fascinating and exciting field of discotic nanoscience research is provided. Liquid crystals are intriguing molecules that exhibit aspects of both liquids (in particular, the manner in which they flow) and crystalline solids (such as their molecular ordering). Owing to their interesting properties, liquid crystals and their derivatives have practical applications — in electronic displays, for example. Sandeep Kumar from the Raman Research Institute in Bangalore, India, reviews recent developments in blending nano-objects with a particular type of ‘discotic’ liquid crystal. These consist of disc-shaped molecules — typically an aromatic core decorated with pendant alkyl chains — that self-assemble into a columnar arrangement through stacking interactions. By covalently grafting nanoparticles to the chains and non-covalently incorporating other materials, including carbon nanotubes or quantum dots, the properties of the liquid crystals can be altered — increasing their electrical conductivity, for instance. The hierarchical self-organization of appropriately functionalized disc-shaped molecules leads to the formation of discotic liquid crystals (DLCs). Columnar phases formed by these intriguing materials are emerging as one-dimensional organic semiconducting materials. Recently, their hybridization with various metallic and semiconducting nanoparticles has been realized to alter and improve their properties. This article provides an overview on the development in the field of newly immersed discotic nanoscience, a sub-field of liquid crystal (LC) nanoscience.

Stretchable organic memory: toward learnable and digitized stretchable electronic applications

Abstract: A stretchable organic digital information storage device has been developed, which potentially advances the development of future smart and digital stretchable electronic systems. The stretchable organic memory with a buckled structure was configured by a mechanically flexible and elastic graphene bottom electrode and polymer compound. The current–voltage curve of the wrinkled memory device demonstrated electrical bistability with typical write-once-read-many times memory features and a high ON/OFF current ratio (∼105). Even under repetitive stretching, the stretchable organic memory exhibited excellent electrical switching functions and memory effects. We believe the first proof-of-concept presentation of the stretchable organic nonvolatile memory may accelerate the development of information storage device in various stretchable electronic applications, such as stretchable display, wearable computer and artificial skin. Stretchable and foldable electronic devices are very attractive, not only for their practicality but also for their potential in as-yet-undeveloped applications, such as artificial electronic skin. Now, Yang-Fang Chen from the National Taiwan University and co-workers have constructed a stretchable organic memory device. Although a variety of flexible organic electronic devices have already been built, which include transistors or solar cells, building stretchable memory devices has remained a challenge. This is because they typically contain a brittle metal electrode, and their fabrication also involves processes — such as spin coating — that are incompatible with flexible substrates. The researchers circumvented these issues by buckling both a graphene, rather than metallic, electrode and the active memory layers over a pre-stretched poly(dimethylsiloxane) elastomer. When the pre-strain was released, the materials adopted a wrinkled structure that endowed them with flexibility. The resulting device showed good electrical switching behavior and memory effects after several stretch/release cycles. A stretchable wrinkled organic memory has been successfully demonstrated. The stretchable organic memory with a graphene bottom electrode possesses rippled structures. The stretchable organic memory exhibits excellent electrical switching behaviors and memory effects even under repetitive stretching. It is believed that this stretchable organic memory may be beneficial for digital information storage in future stretchable electronic systems.

Energy harvesting from organic liquids in micro-sized microbial fuel cells

Abstract: Micro-sized microbial fuel cells (MFCs) are miniature energy harvesters that use bacteria to convert biomass from liquids into usable power. The key challenge is transitioning laboratory test beds into devices capable of producing high power using readily available fuel sources. Here, we present a pragmatic step toward advancing MFC applications through the fabrication of a uniquely mobile and inexpensive micro-sized device that can be fueled with human saliva. The 25-μl MFC was fabricated with graphene, a two-dimensional atomic crystal-structured material, as an anode for efficient current generation and with an air cathode for enabling the use of the oxygen present in air, making its operation completely mobile and free of the need for laboratory chemicals. With saliva as a fuel, the device produced higher current densities (1190 A m−3) than any previous air-cathode micro-sized MFCs. The use of the graphene anode generated 40 times more power than that possible using a carbon cloth anode. Additional tests were performed using acetate, a conventional organic material, at high organic loadings that were comparable to those in saliva, and the results demonstrated a linear relationship between the organic loading and current. These findings open the door to saliva-powered applications of this fuel cell technology for Lab-on-a-Chip devices or portable point-of-care diagnostic devices. A micro-sized (75 ml) MFC with graphene anode and air cathode fueled by human saliva producing higher current densities (1190 A m−3) than any previous air-cathode micro-sized MFCs and generated 40 times more power than that possible with a carbon cloth anode. In microbial fuel cells, microorganisms in the anode compartment carry out a biochemical reaction that oxidizes the fuel. The electrons produced are transferred to the cathode compartment through an external circuit, generating an electrical current. The development of micro-sized microbial fuel cells is attractive owing to their potential for use in portable devices, such as point-of-care diagnostic units. A team of researchers led by Muhammad M. Hussain at the King Abdullah University of Science and Technology, Saudi Arabia, has now shown that multi-layered graphene serves as an efficient anode material for these devices. The graphene anode was prepared through chemical vapor deposition and combined with an air cathode — which enables the use of oxygen from the air — to produce a mobile 25-microliter microbial fuel cell. When saliva was used as a fuel, good power generation (of nearly 1 microwatt) was observed, holding promise for the development of biointegrated electronics.

Au/Ni 12 P 5 core/shell nanocrystals from bimetallic heterostructures: in situ synthesis, evolution and supercapacitor properties

Abstract: Chinese researchers have designed a simple and efficient route to fabricating nanoparticles comprised of a gold core coated with a single-crystal-thick layer of a nickel phosphide semiconductor. Synthesis of this type of core-shell nanoparticle was previously problematic. Sibin Duan and Rongming Wang from Beihang University and University of Science and Technology Beijing in China examined the nanoparticles created using their new scheme under the microscope and by X-ray and found they contained few defects. They then assessed the electrochemical properties of the particles and showed that they have better supercapacitor properties than both nickel phosphide alone and gold-nickel phosphide nanoparticles without the core-shell design. The researchers' new synthesis could be used to make core-shell nanoparticles for a wide range of applications including energy storage materials, such as lithium-ion batteries, and electrochemical sensors.

Rechargeable-hybrid-seawater fuel cell

Abstract: A novel energy conversion and storage system using seawater as a cathode is proposed herein. This system is an intermediate between a battery and a fuel cell, and is accordingly referred to as a hybrid fuel cell. The circulating seawater in this opencathode system results in a continuous supply of sodium ions, which gives this system superior cycling stability that allows the application of various alternative anodes to sodium metal by compensating for irreversible charge losses. Indeed, hard carbon and Sn-C nanocomposite electrodes were successfully applied as anode materials in this hybrid-seawater fuel cell, yielding highly stable cycling performance and reversible capacities exceeding 110 mAh g-1 and 300 mAh g-1, respectively.