Modulating the afterglow time of Mn2+ doped double perovskites by size tuning and its applications in dynamic information display.

Mn2+ doped lead-free double perovskites are emerging afterglow materials that can avoid the usage of rare earth ions. However, the regulation of the afterglow time is still a challenge. In this work, the Mn doped Cs2Na0.2Ag0.8InCl6 crystals with afterglow emission at about 600 nm are synthesized by a solvothermal method. Then, the Mn2+ doped double perovskite crystals are crushed into different sizes. As the size decreases from 1.7 mm to 0.075 mm, the afterglow time decreases from 2070 s to 196 s. Steady-state photoluminescence (PL) spectra, time resolved PL, thermoluminescence (TL) reveal the afterglow time monotonously decreases due to the enhanced nonradiative surface trapping. The modulation on afterglow time will greatly promote their applications in various fields, such as bioimaging, sensing, encryption, and anti-counterfeiting. As a proof of concept, dynamic display of information is realized based on different afterglow times.

Hydrogen-assisted synthesis of Ni-ZIF-derived nickel nanoparticle chains coated with nitrogen-doped graphitic carbon layers as efficient electrocatalysts for non-enzymatic glucose detection.

Chains of nickel nanoparticles coated with few nitrogen-doped graphitic carbon layers (Ni@NC) are synthesized by hydrogen-assisted pyrolysis of Ni-ZIF. Hydrogen and temperature can play key roles in the formation of oriented Ni@NC nanoparticle chains, and carbon shells can protect Ni nanoparticles from external oxidation and aggregations. Under the optimized potential (0.60 V vs. Ag/AgCl), the Ni@NC7H nanoparticle chains obtained at 700 °C under H2/Ar atmosphere (Ni@NC7H) demonstrate outstanding performances, such as high sensitivity of 1.44 mA mM-1 cm-2 (RSD = 1.0%), low detection limit of 0.34 µM (S/N = 3), broad linear range from 1 µM to 1.81 mM, and excellent application potential in artificial sweat and human serum. Therefore, the findings above indicate that this study will provide a general methodology for the synthesis of chains-like core-shell nanoparticle electrocatalysts for non-enzymatic glucose detection.

Superresolution technology based on a heterodyne detection system.

Diffractive superresolution elements (DSEs) placed on a pupil plane can generate a diffractive main lobe whose width is smaller than that of an Airy disk, allowing for the realization of superresolution technology based on pupil filtering. However, the energy of the main lobe decreases dramatically with the decreasing of main lobe width, namely, the implementation of this superresolution technology is at the cost of effective signal power. This restricts greatly the development of this technology. In order to solve this problem, this study suggests the use of a heterodyne detection system (HDS) with this technology. The resolution characteristics of the HDS are analyzed through theoretical deduction. According to research results, HDS has the same longitudinal resolution and twice as high transverse resolution as a direct detection system (DDS). More significantly, the theoretical analyses show that HDS can increase detection sensitivity significantly compared with DDS. Hence, the proposed method makes it possible to detect extremely faint signals using this superresolution technology. In addition, because HDS lowers the requirements on main lobe energy due to its high sensitivity, the design of DSE can achieve a smaller width of main lobe, which can further improve the resolution of the superresolution technology based on pupil filtering.

High Performance of N-Doped Graphene with Bubble-like Textures for Supercapacitors.

Nitrogen-doped graphene (NG) with wrinkled and bubble-like texture is fabricated by a thermal treatment. Especially, a novel sonication-assisted pretreatment with nitric acid is used to further oxidize graphene oxide and its binding with melamine molecules. There are many bubble-like nanoflakes with a dimension of about 10 nm appeared on the undulated graphene nanosheets. The bubble-like texture provides more active sites for effective ion transport and reversible capacitive behavior. The specific surface area of NG (5.03 at% N) can reach up to 438.7 m2 g-1 , and the NG electrode demonstrates high specific capacitance (481 F g-1 at 1 A g-1 , four times higher than reduced graphene oxide electrode (127.5 F g-1 )), superior cycle stability (the capacitance retention of 98.9% in 2 m KOH and 99.2% in 1 m H2 SO4 after 8000 cycles), and excellent energy density (42.8 Wh kg-1 at power density of 500 W kg-1 in 2 m KOH aqueous electrolyte). The results indicate the potential use of NG as graphene-based electrode material for energy storage devices.

Theoretical study on the optical and electronic properties of graphene quantum dots doped with heteroatoms.

The effects of four heteroatoms (B, N, P, and S) with three doping patterns on graphene quantum dots (GQDs) are systematically investigated using time-dependent density functional theory (TD-DFT). The absorption spectra and HOMO-LUMO gaps are quantitatively analyzed to study the correlations between the optical properties and heteroatom doping of doped GQDs. Heteroatom doping can endow GQDs with various new optical and structural properties, depending on the dopants and doping configurations. Compared with the absorption spectra of pristine GQD, both N and S surface doping demonstrate a slight blue shift, whereas B and P doping lead to a blue shift for edge-doped GQDs with heteroatoms in a pentatomic ring. The absorption process is investigated along with excited state analysis, which includes the density of state, natural transition orbital, and charge difference density. The results indicate that large radius atoms assist charge transfer in the excited state and play an important role in recombining the electron density distribution in the doped GQDs.

Analysis of false alarm in heterodyne coherence accumulation based on sequence shifting and the genetic algorithm.

As a new method, coherent accumulation based on sequence shifting and the genetic algorithm (GA) has been proposed to detect a weak heterodyne signal. The excellent performance of the new method was proved by an experiment in previous studies. In this paper, the phenomenon of false alarm caused by the method is revealed through numerical simulation. It is found that, when only noise exists or signal-to-noise ratio (SNR) is low, the false alarm will occur with a high probability. Based on the statistical property of the false alarm, a solution approach using multiple GA modules is proposed to avoid the false alarm. According to the approach, only when all search results of the modules are the same, can one determine that there is an actual heterodyne signal in the detection; otherwise, the inputs of the modules will be judged as noise. Thus, the false alarm can be eliminated completely even if the SNR is quite low. The studies of this paper promote the practical application of the new coherent accumulation method.

Experimental study of coherent accumulation based on sequence shifting and a genetic algorithm.

Because there is a certain phase difference between the two adjacent samples of an analog-to-digital converter for a heterodyne signal, we propose to eliminate the random phases in the coherent accumulation by shifting the sampling sequences with different steps. A genetic algorithm is used to determine the shifting steps of the sequences. An experiment has been conducted to verify the effectiveness of our approach. The results prove that the approach can greatly increase the strength of the heterodyne signal compared with the accumulation with random phases. Our approach is easier to implement in comparison with existing technologies.

Analysis of heterodyne detection in the frequency domain.

As opposed to previous works, our research on heterodyne detection is performed in the frequency domain. Based on the planar wave, it is pointed out that the current amplitude of a heterodyne signal is proportional to the spectrum value of the quantum efficiency function of a detector, and the frequency corresponding to the value is decided by the beam's incident angle. The spectrum of the quantum efficiency function has a low-pass characteristic, and its cut-off frequency is determined by the diameter of the photosensitive surface. Consequently, the strength of the heterodyne signal current depends on the position of a specific frequency in the passband. Our study method is extended to the arbitrary wave and proven to be still effective. According to our analyses, it is concluded that, in addition to the energy decline of interference field, the main cause of performance deterioration resulting from various influential factors can be generally explained as a spectrum mismatch between the interference field and the quantum efficiency function. Based on the Gaussian wave mode, the fact is illustrated by making theoretical deductions, in which the effects of the misaligned angle and beams' spot position offset are treated as examples. Our work provides the possibility of introducing frequency-domain theories into further studies on heterodyne detection.

Direct imaging of copper catalyst migration inside helical carbon nanofibers.

By using a double-aberration-corrected (scanning) transmission electron microscope (STEM/TEM) at an acceleration voltage of only 80 kV, we demonstrate that, due to the low solubility of copper (Cu) in carbon and its affinity with oxygen (O), single-crystal Cu catalysts dissociate into small cuprous oxide (Cu2O) nanoparticles after the growth of carbon nanofibers, and Cu2O nanoparticles ultimately localize on the fiber surfaces. This new finding is a step toward a better understanding of the interactions between Cu catalysts and carbon nanomaterials and could suggest a simple and effective method for eliminating Cu impurities from the fibers.

Influence of bovine serum albumin on biodegradation behavior of pure Zn.

Zinc is emerging as a promising biodegradable metal for temporary implant applications. In this work, we investigate the influence of bovine serum albumin (BSA)-the most abundant blood protein in simulated body fluid (SBF) on degradation of pure Zn via electrochemical measurements and long-term immersion. Electrochemical experiments indicate a decrease of the corrosion rate of bare Zn with increasing BSA concentration in solution for short-term exposures. Samples were characterized with scanning electron microscope (SEM) (including energy dispersive spectroscopy [EDS], X-ray photoelectron spectroscopy [XPS], Fourier transform infrared spectroscopy [FTIR], and time-of-flight secondary ion mass spectrometry [TOF-SIMS]) after immersion up to 21 days. Presence of BSA in the electrolyte, decrease the amount of Ca-phosphate precipitation on Zn surface. However, a more compact surface layer formed in the presence of BSA in solution. Most noteworthy, in long-term exposures, BSA enhances localized corrosion of Zn-such detrimental localized attack was not observed in BSA-free solution. We suggest that a sealed space forming between the Zn substrate and a protein adsorption layer restricts mass transport, thus triggering localized corrosion of Zn.

A self-floating and integrated bionic mushroom for highly efficient solar steam generation.

Solar desalination is considered as a promising approach to solve the shortage of fresh water resources. In this work, inspired by the transpiration of trees, a self-floating and integrated bionic mushroom solar steam generator (BMSSG) is proposed for highly efficient water evaporation. A wooden strip is used to mimic the stipe of the mushroom for water transportation, meanwhile polyvinyl alcohol (PVA) modified graphene aerogels (GA) is used to imitate the pileus of the mushroom for photothermal conversion. After optimizing compositions of the aerogel and sizes of the wooden strip, a high evaporation rate of 1.67 kg m-2h-1 is obtained, outcompeting most of other wood-based evaporators. Compared to traditional interfacial evaporation devices, BMSSG is an integrated structure without a thermal insulation layer and an absorbent wick, which not only increases the compactness that is good for stability and reliability, but also reduces the manufacturing cost. Moreover, the BMSSG can self-float on the water like a roly-poly. These advantages indicate that BMSSG will play a significant role in seawater desalination. The feasibility as well as stability and recyclability of the BMSSG for seawater desalination are demonstrated. This bioinspired design provides a low-cost and scalable SSG, which will have a profound impact in future practical applications.

Construction of 2D-layered quantum dots/2D-nanosheets heterostructures with compact interfaces for highly efficient photocatalytic hydrogen evolution.

The emergence of two dimensional (2D) nanosheets provides flexible platforms for the construction of semiconductor heterostructures for photocatalytic hydrogen evolution. However, the compact and conformal contact between the components with different dimensions remains challenge. Herein, we anchor the 2D layered black phosphorous quantum dots (BPQDs) onto the 2D ZnIn2S4 nanosheets with sulfur vacancies (V-ZIS). This unique interface between 2D layered QDs and 2D nanosheets ensures a sufficient contact area between the BPQDs and the V-ZIS, which is conducive to the transport and the spatial separation of photogenerated electrons and holes. A synergistic effect of sulfur vacancies and type-Ⅱ heterojunction results in an excellent photocatalytic hydrogen evolution performance of the BPQDs/V-ZIS composites. The hydrogen evolution rate by the BPQDs/V-ZIS without any noble-metal as cocatalyst is up to 5079 µmol g-1h-1 under visible light irradiation with an apparent quantum yield (AQY) of 12.03% at 420 nm, which is dramatically higher than most other photocatalysts reported previously.

Carbon-based 0D/1D/2D assembly with desired structures and defect states as non-metal bifunctional electrocatalyst for zinc-air battery.

For the design of electrocatalysts, the combination between components and the regulation of material structures tend to be neglected, giving rise to the constraint of catalytic performance and durability. Herein, we developed a graphene oxide quantum dots (GOQDs) with enhanced oxygen content by a one-step cutting method. Then, one-dimensional (1D) carbon nanotubes and two-dimensional (2D) reduced graphene oxide are crosslinked and self-assembled, thus attracting unsaturated-bond-riches GOODs (0D) to uniformly attach to the skeleton, simultaneously achieving nitrogen and sulfur co-doping. To the best of our knowledge, there is no report to prepare bifunctional electrocatalyst with GOQDs. Electrochemical tests show that even without metal-doping, the novel non-metal bifunctional electrocatalyst (N,S-GOQD-RGO/CNT) exhibits a higher half-wave potential (0.84 V) and enhanced limiting current density (5.88 mA cm-2) than commercial Pt/C catalyst. The density functional theory is implemented to reveal the coordination of nitrogen and sulfur co-doping on GOQDs, which results in the improvement of overall catalytic active sites. Furthermore, the rechargeable zinc-air battery based on N,S-GOQD-RGO/CNT exhibits a maximum power density of 134.3 mW cm-2, open circuit potential of 1.414 V, which is better than Pt/C+Ru/C mixed material. The obtained N,S-GOQD-RGO/CNT will provide a perspective application in fuel cells.

Colloidal Cu2ZnSn(S1-x,Sex)4-Au nano-heterostructures for inorganic perovskite photovoltaic applications as photocathode alternative.

We concretely report feasible synthesis procedures of colloidal Cu2ZnSn(S1-x,Sex)4-Au (CZTSSe-Au) nano-heterostructured composites, and creatively employ them as the counter electrodes (CEs) of all-solid-state solar cells with inorganic CsSnI2.95F0.05 perovskite hole conductor. Acquired optical characterization indicates that integration of noble metal nanoparticles with cuprum-chalcogenide could heighten light absorption within visible-band due to localized surface plasmon resonance (LSPR) generated by Au, and the forbidden gap of nanocomposites gets adjustment accordingly. It is demonstrated that this novel photocathode alternative with favorable conductivity can not only match the energy level within the device band structure construction, but also restrain recombination so that accelerate charge transfer and extraction occurring on the photocathode. The photocurrent and photoelectric conversion efficiency (PCE) of cells conjugating CZTS-Au photocathodes turn to be respectively 43% and 25% higher than those using pure CZTS. Moreover, it has been demonstrated that CZTS-Au, coupling very well with inorganic perovskite, owns comparable electrocatalytic performance and even higher output photocurrent with respect to platinum CEs, which portends a potential substitution for conventional costly photocathodes. A comprehensive analysis on impedance spectroscopy data is subsequently carried out for the sake of deep understanding charge accumulation and transfer response at CsSnI2.95F0.05/CE interface, attempting to orient further optimization of device performance.

High-Performance Supercapacitor of Graphene Quantum Dots with Uniform Sizes.

Graphene quantum dots (GQDs) with uniform sizes of less than 5 nm are synthesized by a novel top-down strategy. Nitric acid as a strong oxidant can be used to cut graphene oxide via sonication and hydrothermal processes. Moreover, purified GQDs are obtained from removing oxygen-containing functional groups in a heat treatment process. Both nanoscale size and edge effect of GQDs improve their abundant active sites and restrain the restack of graphene nanosheets. Meanwhile, their electrochemical performance demonstrates the properties of the GQDs for practical application in energy storage. The GQD electrode material shows an ideal electric double-layer capacitance behavior such as a high specific capacitance of 296.7 F g-1, a satisfactory energy density of 41.2 W h kg-1 at 1 A g-1, a low internal resistance, a small relaxation time, and an excellent cycling stability. The results illustrate excellent electrochemical activity, high conductivity, and enhanced ion transport rate on the surface of electrolyte and electrode. The advantages of GQDs confirm their unique characteristics for potential applications in the field of electrode materials for supercapacitors.

Porous stable poly(lactic acid)/ethyl cellulose/hydroxyapatite composite scaffolds prepared by a combined method for bone regeneration.

A major challenge in bone tissue engineering is the development of biomimetic scaffolds which should simultaneously meet mechanical strength and pore structure requirements. Herein, we combined technologies of high concentration solvent casting, particulate leaching, and room temperature compression molding to prepare a novel poly(lactic acid)/ethyl cellulose/hydroxyapatite (PLA/EC/HA) scaffold. The functional, structural and mechanical properties of the obtained porous scaffolds were characterized. The results indicated that the PLA/EC/HA scaffolds at the 20wt% HA loading level showed optimal mechanical properties and desired porous structure. Its porosity, contact angle, compressive yield strength and weight loss after 56days were 84.28±7.04%, 45.13±2.40°, 1.57±0.09MPa and 4.77±0.32%, respectively, which could satisfy the physiological demands to guide bone regeneration. Thus, the developed scaffolds have potential to be used as a bone substitute material for bone tissue engineering application.

A versatile bio-based material for efficiently removing toxic dyes, heavy metal ions and emulsified oil droplets from water simultaneously.

Developing versatile materials for effective water purification is significant for environment and water source protection. Herein, a versatile bio-based material (CH-PAA-T) was reported by simple thermal cross-linking chitosan and polyacrylic acid which exhibits excellent performances for removing insoluble oil, soluble toxic dyes and heavy metal ions from water, simultaneously. The adsorption capacities are 990.1mgg-1 for methylene blue (MB) and 135.9mgg-1 for Cu2+, which are higher than most of present advanced absorbents. The adsorption towards organic dyes possesses high selectivity which makes CH-PAA-T be able to efficiently separate dye mixtures. The stable superoleophobicity under water endows CH-PAA-T good performance to separate toluene-in-water emulsion stabilized by Tween 80. Moreover, CH-PAA-T can be recycled for 10 times with negligible reduction of efficiency. Such versatile bio-based material is a potential candidate for water purification.

Effect of Cs-Ce-Zr Catalysts/Soot Contact Conditions on Diesel Soot Oxidation.

Cs-Ce-Zr catalysts with various weight ratios are prepared by the sol-gel method in this paper. The main crystalline phases were identified by X-ray diffraction. The activities of catalysts during soot combustion were tested by thermogravimetric and differential scanning calorimetry. The contact conditions of soot/catalysts (sintered at 450 and 380 °C, respectively, under loose and tight contact conditions) were observed by scanning electron microscopy to study the effect of contact conditions on catalytic activity, and it was determined that the catalytic activities under tight contact conditions are superior to those under loose contact conditions. However, the soot oxidation rate speeds up after the peak temperature of about 450 °C under loose contact conditions, which is due to the fact that the contact condition is enhanced by melting CsNO3. The soot onset ignition temperature is lower for the catalysts with more Cs content under loose contact conditions. The minimum gaps of the soot onset ignition temperature and soot oxidation rates under the two contact conditions are 32 and 7 °C, which shows that the gap of catalytic activities under the respective contact conditions can be decreased by the formation of different crystalline phases.

Bi-directional controlled release of ibuprofen and Mg(2+) from magnesium alloys coated by multifunctional composite.

Two major problems for magnesium alloy implant are the high degradation rate and easy infection associated with implantation. Herein, a surface drug delivery system (Mg/Epoxy resin-ZnO/PCL-Ibuprofen) which can realize bi-directional controlled release of ibuprofen and Mg(2+) was designed via a dip coating process followed by spraying. The in vitro test demonstrated that the ibuprofen in drug-eluting compound material showed sustained release profiles for 22days, which can effectively solve the local cellular rejection and inflammation during the early stage of implantation. Besides, the drug carrier also exhibited improved corrosion resistance duel to the high combining strength between Epoxy resin-ZnO coating and magnesium alloy, so Mg(2+) can release slowly at first and then speeded up later. This approach may be suitable for coating other implant materials such as stainless steel, titanium alloy etc.

One-Step Electrodeposition of Co/CoP Film on Ni Foam for Efficient Hydrogen Evolution in Alkaline Solution.

The development of high-efficiency catalysts for hydrogen evolution via water splitting has been an effective strategy to solve the energy environmental problems and energy crisis. The abundant-reserving transition metals and their phosphides are becoming attractive Pt alternatives for hydrogen evolution reaction (HER). Herein, a crystalline/amorphous Co/CoP film was facilely prepared on nickel foam (NF) by a one-step electrodeposition technique at room temperature, named Co/CoP-NF. The as-prepared Co/CoP-NF electrocatalyst exhibits excellent electrocatalytic activity for HER, on par with Pt/C, showing a low overpotential of 35 mV at a current density of 10 mA·cm-2 and small Tafel slope of 71 mV·dec-1 in 1.0 M NaOH solution. More importantly, the Co/CoP-NF catalyst presents good long-term durability at an overpotential of 60 mV. Moreover, the influence of the electrodeposition parameters on the catalytic performance of the catalyst was discussed. This study offers an effective strategy to develop a non-noble-metal HER catalyst for industrial production of hydrogen.