Targeted Heating of Enzyme Systems Based on Photothermal Materials.

This study demonstrates that the enzymatic reaction rate can be increased significantly by targeted heating of the microenvironment around the enzyme, while maintaining the reaction system at environmental temperature. Enzyme molecules are covalently attached to the surface of Fe3 O4 @reduced graphite oxide (rGO). Under visible-light irradiation, the reaction rate catalyzed by the enzyme-Fe3 O4 @rGO system is clearly enhanced relative to that of the free enzyme and a mixture of free enzyme and Fe3 O4 @rGO. This local heating mechanism contributes to promotion of the enzymatic reactions of the targeted heating of the enzyme (THE) system, which has been validated by using different enzymes, including lipase, glucose oxidase, and organophosphorus hydrolase. These results indicate that targeted heating of the catalytic centers has the same effect on speeding up reactions as that of traditional heating methods, which treat the whole reaction system. As an example, it is shown that the THE system promotes the sensitivity of an enzyme screen-printed electrode by 14 times at room temperature, which implies that the THE system can be advantageous in improving enzyme efficiency, especially if heating the entire system is impossible or could lead to degradation of substrates or damage of components, such as in vitro bioanalysis of frangible molecules or in vivo diagnosis.

Conservative Sensor Error Modeling Using a Modified Paired Overbound Method and its Application in Satellite-Based Augmentation Systems.

Conservative sensor error modeling is of great significance in the field of safety-of-life. At present, the overbound method has been widely used in areas such as satellite-based augmentation systems (SBASs) and ground-based augmentation systems (GBASs) that provide integrity service. It can effectively solve the difficulties of non-Gaussian and non-zero mean error modeling and confidence interval estimation of user position error. However, there is still a problem in that the model is too conservative and leads to the lack of availability. In order to further improve the availability of SBASs, an improved paired overbound method is proposed in this paper. Compared with the traditional method, the improved algorithm no longer requires the overbound function to conform to the characteristics of the probability distribution function, so that under the premise of ensuring the integrity of the system, the real error characteristics can be more accurately modeled and measured. The experimental results show that the modified paired overbound method can improve the availability of the system with a probability of about 99%. In view of the fact that conservative error modeling is more sensitive to large deviations, this paper analyzes the robustness of the improved algorithm in the case of abnormal data loss. The maximum deviation under a certain integrity risk is used to illustrate the effectiveness of the improved paired overbound method compared with the original method.

A Gyroscope Bias Estimation Algorithm Based on Map Specific Information.

In an inertial navigation system, especially in a pedestrian dead-reckoning system, gyroscope bias can demonstrably reduce positioning accuracy. A novel gyroscope bias estimation algorithm is proposed, which estimates the bias of a gyroscope under any set of angle observations. Moreover, a method for obtaining Euler angles using map corridor information is proposed. The heading information obtained from a map is used to estimate the bias, and the estimated bias is used to correct the trajectories. Experimental results show that it is feasible for the algorithm to estimate the bias of the gyroscope.

An INS/WiFi Indoor Localization System Based on the Weighted Least Squares.

For smartphone indoor localization, an INS/WiFi hybrid localization system is proposed in this paper. Acceleration and angular velocity are used to estimate step lengths and headings. The problem with INS is that positioning errors grow with time. Using radio signal strength as a fingerprint is a widely used technology. The main problem with fingerprint matching is mismatching due to noise. Taking into account the different shortcomings and advantages, inertial sensors and WiFi from smartphones are integrated into indoor positioning. For a hybrid localization system, pre-processing techniques are used to enhance the WiFi signal quality. An inertial navigation system limits the range of WiFi matching. A Multi-dimensional Dynamic Time Warping (MDTW) is proposed to calculate the distance between the measured signals and the fingerprint in the database. A MDTW-based weighted least squares (WLS) is proposed for fusing multiple fingerprint localization results to improve positioning accuracy and robustness. Using four modes (calling, dangling, handheld and pocket), we carried out walking experiments in a corridor, a study room and a library stack room. Experimental results show that average localization accuracy for the hybrid system is about 2.03 m.

Immobilization of silver nanoparticles on exfoliated mica nanosheets to form highly conductive nanohybrid films.

Highly electrically conductive films were prepared by coating organic/inorganic nanohybrid solutions with a polymeric dispersant and exfoliated mica nanosheets (Mica) on which silver nanoparticles (AgNPs) had been dispersed in various components. Transmission electronic microscopy showed that the synthesized AgNPs had a narrow size distribution and a diameter of approximately 20 nm. Furthermore, a 60 µm thick film with a sheet resistance as low as 4.5 × 10(-2) Ω/sq could be prepared by controlling the heating temperature and by using AgNPs/POE-imide/Mica in a weight ratio of 20:20:1. During the heating process, the surface color of the hybrid film changed from dark golden to white, suggesting the accumulation of the AgNPs through surface migration and their melting to form an interconnected network. These nanohybrid films have potential for use in various electrically conductive devices.

Enhanced conductivity of (110)-textured ScSZ films tuned by an amorphous alumina interlayer.

Herein a novel strategy to tune the crystallite orientation and the ionic conductivity of solid electrolyte films through interfacial control has been reported. 10 mol% Sc2O3-doped ZrO2 (10ScSZ) thin films were prepared with an amorphous alumina (AO) interlayer (AO/10ScSZ) using magnetron sputtering. It has been found that a (110)-preferred orientation develops in AO/10ScSZ films annealed at 1000 °C due to a strong interfacial interaction, while 10ScSZ films deposited without the AO interlayer are (111)-textured. The (110)-oriented AO/10ScSZ films show an ionic conductivity nearly 4 times higher than that of the (111)-oriented 10ScSZ films. This is explained by the fact that the (110)-texture provides faster migration pathways with lower energy barrier for oxygen vacancies. These results reveal the relationship between the crystal structure and the conductivity of AO/ScSZ heterostructured films, which can facilitate the development of high-performance multilayered electrolytes and enable the miniaturization of solid-state electrochemical devices operable at temperatures below 600 °C.

Defective NiFe2 O4 Nanoparticles for Efficient Urea Electro-oxidation.

Urea is an important organic pollutants in sewage and needs to be removed for environmental protection. Here, we report defective NiFe2 O4 (NFO) nanoparticles with excellent performance for urea electro-oxidation. The results show that defects can be effectively implanted at the surface of NFO nanoparticles by a facile and versatile lithium reduction method without affecting its main crystal structure and grain size. The defective NFO-5Li nanoparticles displayed a significantly improved urea electro-oxidation performance compared with NFO-Pristine nanoparticles. Particularly, the NFO-Pristine and NFO-5Li show a potential of 1.398 and 1.361 V at the current density of 10 mA cm-2 and Tafel slope of 37.3 and 31.4 mV dec-1 , respectively. In addition, the NFO-5Li nanoparticles also revealed outstanding electrocatalytic stability. The superior performance can be attributed to the designed tunable surface defect engineering. Furthermore, the defect engineering strategy as well as the defective NFO nanoparticles hold great potential for applications in other materials and areas.

Bifunctional nickel oxide-based nanosheets for highly efficient overall urea splitting.

Porous and hollow Ni0.9Fe0.1Ox microspheres assembled from 2D nanosheets exhibit excellent bifunctional activity for both urea oxidation reaction and hydrogen evolution reaction, in which the potential for overall urea splitting is 1.455 V at 10 mA cm-2.

Large Piezoelectric Strain in Sub-10 Nanometer Two-Dimensional Polyvinylidene Fluoride Nanoflakes.

Functional polymers such as polyvinylidene fluoride (PVDF) and its copolymers, which exhibit room-temperature piezoelectricity and ferroelectricity in two-dimensional (2D) limit, are promising candidates to substitute hazardous lead-based piezoceramics for flexible nanoelectronic and electromechanical energy-harvesting applications. However, realization of many polymers including PVDF in ultrathin 2D nanostructures with desired crystal phases and tunable properties remains challenging due to ineffective conventional synthesis methods. Consequently, it has remained elusive to obtain optimized piezoelectric performance of PVDF particularly in sub-10 nm regimes. Taking advantage of its high flexibility and easy processing, we fabricate ultrathin PVDF nanoflakes with thicknesses down to 7 nm by using a hot-pressing method. This thermo-mechanical strategy simultaneously induces robust thermodynamic α to electroactive ß-phase transformation, with ß fraction as high as 92.8% in sub-10 nm flakes. Subsequently, piezoelectric studies performed by using piezoresponse force microscopy reveal an excellent piezoelectric strain of 0.7% in 7 nm film and the highest piezoelectric coefficient ( d33) achieved is -68 pm/V for 50 nm-thick nanoflakes, which is 13% higher than the piezoresponse from 50 nm-thick PZT nanofilms. Our results further suggest thickness modulation as an effective strategy to tune the piezoelectric performance of PVDF and affirm its supremacy over conventional piezoceramics especially at nanoscale. This work aims not only to help understand fundamental piezoelectricity of pure PVDF in sub-10 nm regimes but also provides an opportunity to realize other polymer-based 2D nanocrystals.

Boosting the Electrocatalytic Water Oxidation Performance of CoFe2O4 Nanoparticles by Surface Defect Engineering.

Spinel oxides have attracted widespread interest for electrocatalytic applications owing to their unique crystal structure and properties. The surface structure of spinel oxides significantly influences the electrocatalytic performance of spinel oxides. Herein, we report a Li reduction strategy that can quickly tune the surface structure of CoFe2O4 (CFO) nanoparticles and optimize its electrocatalytic oxygen evolution reaction (OER) performance. Results show that a large number of defective domains have been successfully introduced at the surface of CFO nanopowders after Li reduction treatment. The defective CFO nanoparticles demonstrate significantly improved electrocatalytic OER activity. The OER potential observed a negative shift from 1.605 to 1.513 V at 10 mA cm-2, whereas the Tafel slope is greatly decreased to 42.1 mV dec-1 after 4 wt % Li reduction treatment. This efficient Li reduction strategy can also be applied to engineer the surface defect structure of other material systems and broaden their applications.

Room temperature Mg reduction of TiO2: formation mechanism and application in photocatalysis.

Defects in metal oxides can significantly improve their physical and chemical properties. However, the conventional methods to generate defects often require complex procedures and harsh conditions. In this study, we design a simple and room-temperature preparation route to prepare defective metal oxide nanoparticles with high yield. The formation of defects is attributed to the generation of oxygen vacancies (VO) and hydrogenation caused by charge transfer at a Mg-metal oxide junction structure. Defective TiO2 exhibits excellent performance toward wastewater cleaning and water splitting. The proposed route is promising in terms of convenience, low cost, and large-scale production.

Ultra-low-temperature growth of CdS quantum dots on g-C3N4 nanosheets and their photocatalytic performance.

CdS quantum dots deposited on carbon nitride (g-C3N4) nanosheets have been synthesized by ultra-low temperature (-60 °C) liquid phase precipitation reactions. The obtained CdS quantum dots were uniformly distributed on the surface of the g-C3N4 nanosheets with an average diameter of 5 nm. Correspondingly, CdS/g-C3N4 exhibits a highly enhanced photocatalytic performance.

Tuning defects in oxides at room temperature by lithium reduction.

Defects can greatly influence the properties of oxide materials; however, facile defect engineering of oxides at room temperature remains challenging. The generation of defects in oxides is difficult to control by conventional chemical reduction methods that usually require high temperatures and are time consuming. Here, we develop a facile room-temperature lithium reduction strategy to implant defects into a series of oxide nanoparticles including titanium dioxide (TiO2), zinc oxide (ZnO), tin dioxide (SnO2), and cerium dioxide (CeO2). Our lithium reduction strategy shows advantages including all-room-temperature processing, controllability, time efficiency, versatility and scalability. As a potential application, the photocatalytic hydrogen evolution performance of defective TiO2 is examined. The hydrogen evolution rate increases up to 41.8 mmol g-1 h-1 under one solar light irradiation, which is ~3 times higher than that of the pristine nanoparticles. The strategy of tuning defect oxides used in this work may be beneficial for many other related applications.

Enhanced enzymatic reactions by solar-to-thermal conversion nanoparticles.

In this study, we show that enzymatic reactions can be easily enhanced by visible light irradiation. It is a general method as demonstrated by several different types of enzymes, including amylase, cellulase and lipase, which are typically utilized in many industrial biocatalysis processes. Markedly different from conventional titanium dioxide (TiO2) nanoparticles which absorb UV light and generate little thermal energy, defect-rich Magnéli phase titanium oxide (Ti8O15) nanoparticles absorb solar light and provide a highly effective solar-to-thermal conversion, which greatly enhances enzymatic reactions. This accelerating effect, together with the biocompatibility, high chemical stability and easy preparation of Ti8O15 nanoparticles, makes this method appealing for enhancing the efficiency of biocatalysis.

Ultrathin two-dimensional metals with fully exposed (111) facets.

Large-size ultrathin two-dimensional (2D) metals with a fully exposed (111) surface have been synthesized by a heat-pressing process. As a result of the compact (111) surface arrangement, an ultrathin Pt 5 nm 2D metal exhibits a superior methanol electro-oxidation performance than an as-sputtered Pt 5 nm thin film (1.8, 2.2 and 5.0 times higher specific activity under different scanning cycles).

Ultralight, scalable, and high-temperature-resilient ceramic nanofiber sponges.

Ultralight and resilient porous nanostructures have been fabricated in various material forms, including carbon, polymers, and metals. However, the development of ultralight and high-temperature resilient structures still remains extremely challenging. Ceramics exhibit good mechanical and chemical stability at high temperatures, but their brittleness and sensitivity to flaws significantly complicate the fabrication of resilient porous ceramic nanostructures. We report the manufacturing of large-scale, lightweight, high-temperature resilient, three-dimensional sponges based on a variety of oxide ceramic (for example, TiO2, ZrO2, yttria-stabilized ZrO2, and BaTiO3) nanofibers through an efficient solution blow-spinning process. The ceramic sponges consist of numerous tangled ceramic nanofibers, with densities varying from 8 to 40 mg/cm3. In situ uniaxial compression in a scanning electron microscope showed that the TiO2 nanofiber sponge exhibits high energy absorption (for example, dissipation of up to 29.6 mJ/cm3 in energy density at 50% strain) and recovers rapidly after compression in excess of 20% strain at both room temperature and 400°C. The sponge exhibits excellent resilience with residual strains of only ~1% at 800°C after 10 cycles of 10% compression strain and maintains good recoverability after compression at ~1300°C. We show that ceramic nanofiber sponges can serve multiple functions, such as elasticity-dependent electrical resistance, photocatalytic activity, and thermal insulation.

Graphene-based Recyclable Photo-Absorbers for High-Efficiency Seawater Desalination.

Today's scientific advances in water desalination dramatically increase our ability to transform seawater into fresh water. As an important source of renewable energy, solar power holds great potential to drive the desalination of seawater. Previously, solar assisted evaporation systems usually relied on highly concentrated sunlight or were not suitable to treat seawater or wastewater, severely limiting the large scale application of solar evaporation technology. Thus, a new strategy is urgently required in order to overcome these problems. In this study, we developed a solar thermal evaporation system based on reduced graphene oxide (rGO) decorated with magnetic nanoparticles (MNPs). Because this material can absorb over 95% of sunlight, we achieved high evaporation efficiency up to 70% under only 1 kW m(-2) irradiation. Moreover, it could be separated from seawater under the action of magnetic force by decorated with MNPs. Thus, this system provides an advantage of recyclability, which can significantly reduce the material consumptions. Additionally, by using photoabsorbing bulk or layer materials, the deposition of solutes offen occurs in pores of materials during seawater desalination, leading to the decrease of efficiency. However, this problem can be easily solved by using MNPs, which suggests this system can be used in not only pure water system but also high-salinity wastewater system. This study shows good prospects of graphene-based materials for seawater desalination and high-salinity wastewater treatment.

Enhanced Electrocatalytic Activity for Water Splitting on NiO/Ni/Carbon Fiber Paper.

Large-scale growth of low-cost, efficient, and durable non-noble metal-based electrocatalysts for water splitting is crucial for future renewable energy systems. Atomic layer deposition (ALD) provides a promising route for depositing uniform thin coatings of electrocatalysts, which are useful in many technologies, including the splitting of water. In this communication, we report the growth of a NiO/Ni catalyst directly on carbon fiber paper by atomic layer deposition and report subsequent reduction and oxidation annealing treatments. The 10-20 nm NiO/Ni nanoparticle catalysts can reach a current density of 10 mA·cm-2 at an overpotential of 189 mV for hydrogen evolution reactions and 257 mV for oxygen evolution reactions with high stability. We further successfully achieved a water splitting current density of 10 mA·cm-2 at 1.78 V using a typical NiO/Ni coated carbon fiber paper two-electrode setup. The results suggest that nanoparticulate NiO/Ni is an active, stable, and noble-metal-free electrocatalyst, which facilitates a method for future water splitting applications.

Defective SrTiO3 synthesized by arc-melting.

Defective perovskite SrTiO3 has been synthesized by rapid solidification of its melts obtained from arc-melting treatment. As a result of rich and stable defects implanted in SrTiO3, the bandgap was narrowed from 3.29 eV to 3.08 eV. Correspondingly, the defective SrTiO3 powders exhibit highly enhanced photocatalytic performance.

Suppressed phase transition and giant ionic conductivity in La2Mo2O9 nanowires.

Improving the ionic conductivity of solid electrolytes at low temperatures represents a major challenge and an opportunity for enabling a variety of solid-state ionic devices for energy conversion and storage, as well as for environmental protection. Here we report a giant ionic conductivity of 0.20 Scm(-1), achieved at 500 °C, in the La2Mo2O9 nanowires with a bamboo-wire morphology, corresponding to a 1000-fold enhancement in conductivity over conventional bulk material. Stabilization of the high-temperature phase is observed to account for about a 10-fold increase in the conductivity. We further demonstrate that fast surface conduction in ∼3 nm thick, partially ordered, surface 'amorphous' films, under strain on the curved surfaces of the nanowires (as a non-autonomous surface phase or complexion), contributes to an enhancement of the conductivity by another two orders of magnitude. Exemplified here by the study of the La2Mo2O9 nanowires, new possibilities for improvement of conductivity and for miniaturization of solid-state ionic devices by the careful use of one-dimensional nanomaterials can be envisioned.