Optical properties of ferroic Fe2O(SeO3)2 and Fe2(SeO3)3·3H2O.

Ferroic compounds Fe2O(SeO3)2 (FSO) and Fe2(SeO3)3·3H2O (FSOH) prepared by the hydrothermal method are characterized and their optical properties are investigated by combining with first-principles calculations. The results show that (i) FSO is antiferromagnetic below ∼110 K and becomes ferromagnetic at elevated temperatures, while FSOH is antiferromagnetic at low temperatures probably due to a change in the spin state from Fe3+ (S = 5/2) to Fe2+ (S = 2); (ii) the optical bandgap is determined to be ∼2.83 eV for FSO and ∼2.15 eV for FSOH, consistent with the theoretical calculation; and (iii) the angle-resolved polarized Raman spectroscopy results of both crystals demonstrate the strong anisotropic light absorption and birefringence effects, and the unconventional symmetricity of some Raman modes is observed, which can be interpreted from the variation of Raman scattering elements. This work can provide not only an understanding of the structure and physical properties of iron selenites, but also a strategy for exploring the anomalous Raman behaviors in anisotropic crystals, facilitating the design and engineering of novel functional devices with low-symmetry ferroic materials.

Treating waste with waste: Adsorption of anionic dyes in wastewater with surfactant-modified phosphogypsum.

Phosphogypsum (PG) is a solid waste generated during the wet process of phosphoric acid production. The environmental-friendly disposal and recycling of PG is vital in the field of environmental solid waste treatment. In this study, PG is used for adsorbent of dyes in wastewater to achieve the goal of recycling waste with waste. Surfactant-modified phosphogypsum (ODBAC@PG) was prepared using octadecyl dimethyl benzyl ammonium chloride (ODBAC) as modifier. ODBAC@PG exhibits high adsorption capability for anionic dyes (methyl blue (MeB) and indocyanine carmine (IC)). The pseudo-second-order kinetic model fits the kinetic experimental data for the adsorption of two organic anionic dyes. Langmuir adsorption isotherm fits the adsorption characteristics of MeB and IC on ODBAC@PG, exhibiting a monolayer adsorption pattern. Thermodynamic parameters indicate the spontaneous and exothermic properties of MeB and IC on ODBAC@PG. MeB and IC have antagonistic effects on each other in binary adsorption system. High adsorption capacity after six cycles of experiments demonstrates the high reusability of ODBAC@PG. The nature for the adsorption includes electrostatic interaction, hydrogen bond and hydrophobic interaction. Using ODBAC@PG for dyes wastewater treatment can accomplish the goal of treating waste with waste and turning waste into treasure.

Surface Reconstruction of CsPbBr3 Nanocrystals by the Ligand Engineering Approach for Achieving High Quantum Yield and Improved Stability.

Oleylamine/oleic acid (OAm/OA) as the commonly used ligand is indispensable in the synthesis of perovskite nanocrystals (PNCs). Unfortunately, poor colloidal stability and unsatisfactory photoluminescence quantum yield (PLQY) are observed, resulting from a highly dynamic binding nature between ligands. Herein, we adopt a facile hybrid ligand (DDAB/ZnBr2) passivation strategy to reconstruct the surface chemistry of CsPbBr3 NCs. The hybrid ligand can detach the native surface ligand, in which the acid-base reactions between ligands are suppressed effectively. Also, they can substitute the loose capping ligand, anchor to the surface firmly, and supply sufficient halogens to passivate the surface trap, realizing an exceptional PLQY of 95% and an enhanced tolerance toward ambient storage, UV irradiation, anti-solvents, and thermal treatment. Besides, the as-fabricated white light-emitting diode (WLED) utilizing the PNCs as the green-emitting phosphor has a luminous efficiency around 73 lm/W; the color gamut covers 125% of the NTSC standard.

Constructing Chromium Multioxide Hole-Selective Heterojunction for High-Performance Perovskite Solar Cells.

Perovskite solar cells (PSCs) suffer from significant nonradiative recombination at perovskite/charge transport layer heterojunction, seriously limiting their power conversion efficiencies. Herein, solution-processed chromium multioxide (CrOx ) is judiciously selected to construct a MAPbI3 /CrOx /Spiro-OMeTAD hole-selective heterojunction. It is demonstrated that the inserted CrOx not only effectively reduces defect sites via redox shuttle at perovskite contact, but also decreases valence band maximum (VBM)-HOMO offset between perovskite and Spiro-OMeTAD. This will diminish thermionic losses for collecting holes and thus promote charge transport across the heterojunction, suppressing both defect-assisted recombination and interface carrier recombination. As a result, a remarkable improvement of 21.21% efficiency with excellent device stability is achieved compared to 18.46% of the control device, which is among the highest efficiencies for polycrystalline MAPbI3 based n-i-p planar PSCs reported to date. These findings of this work provide new insights into novel charge-selective heterojunctions for further enhancing efficiency and stability of PSCs.

Rational Construction of a Ni/CoMoO4 Heterostructure with Strong Ni-O-Co Bonds for Improving Multifunctional Nanozyme Activity.

Due to the lack of a general descriptor to predict the activity of nanomaterials, the current exploration of nanozymes mainly depended on trial-and-error strategies, which hindered the effective design of nanozymes. Here, with the help of a large number of Ni-O-Co bonds at the interface of heterostructures, a prediction descriptor was successfully determined to reveal the double enzyme-like activity mechanisms for Ni/CoMoO4. Additionally, DFT calculations revealed that interface engineering could accelerate the catalytic kinetics of the enzyme-like activity. Ni-O-Co bonds were the main active sites for enzyme-like activity. Finally, the colorimetric signal and intelligent biosensor of Ni/CoMoO4 based on deep learning were used to detect organophosphorus and ziram sensitively. Meanwhile, the in situ FTIR results uncovered the detection mechanism: the target molecules could block Ni-O-Co active sites at the heterostructure interface leading to the signal peak decreasing. This study not only provided a well design strategy for the further development of nanozymes or other advanced catalysts, but it also designed a multifunctional intelligent biosensor platform. Furthermore, it also provided preferable ideas regarding the catalytic mechanism and detection mechanism of heterostructure nanozymes.

Activated biochar derived from peanut shells as the electrode materials with excellent performance in Zinc-air battery and supercapacitance.

The use of activated biochar-based electrode derived from waste biomass in energy technologies, such as metal-air batteries and supercapacitors, is an important strategy for realizing energy and environmental sustainability in the future. Herein, peanut shells (waste biomass) were employed to prepare activated biochar materials by pyrolysis in molten KCl and heat-treatment. The effective dispersion and corrosion effects of molten salt for the pyrolysis products during pyrolysis obviously increase defects and specific surface area of the activated biochar materials. The prepared activated biochar material (PS-800-1000) by pyrolysis in molten KCl at 800 °C and heat-treatment at 1000 °C exhibits excellent catalytic activity with half-wave potential of 0.84 V vs. RHE, comparable to commercial Pt/C for oxygen reduction reaction (ORR) in 0.1 M KOH and outstanding supercapacitance performance in 6 M KOH with high specific capacitance (355 F g-1 at 0.5 A g-1), which exceeds all reported biochar derived from peanut shells. The PS-800-1000-based zinc-air battery (ZAB) displays higher peak power density (141 mW cm-2), specific capacity (767 mAh gZn-1) and cycling stability than Pt/C-based ZAB. The activated biochar prepared by pyrolysis in molten KCl and heat-treatment method from peanut shells can be a promising candidate for replacing precious metals in energy conversion/storage devices.

The Evolution of Amitraz and Its Metabolic Degradation Products in Human Blood over 90 Days for Use in Forensic Determination.

Amitraz is a pesticide that is often involved in poisoning cases. In determination process of poisoning cases, a problem often encountered is that when the evidence samples were examined, the poison had already decomposed, thus posing significant difficulty for obtaining evidences. In this study, we qualitatively and quantitatively tracked the metabolic degradation products of amitraz and ascertained that the metabolic degradation products were N,N'-bisdimethylphenylformamidine, N'-(2,4-dimethylphenyl)-N-methylformamidine (DMPF), 2,4-dimethylformamidine (DMF) and 2,4-dimethylaniline (DMA). It was found that although amitraz decomposed rather rapidly, the metabolic degradation products of amitraz persisted for quite a long time. This study demonstrates that forensic evidence in poisoning cases of amitraz can be obtained by the determination of DMPF, DMF and DMA. This study can provide insights on obtaining forensic evidences in poisoning cases.

3D Graphene-Carbon Nanotube Hybrid Supported Coupled Co-MnO Nanoparticles as Highly Efficient Bifunctional Electrocatalyst for Rechargeable Zn-Air Batteries.

The development of high-efficiency and low-cost catalysts is one of the core and important issues to improve the efficiency of electrochemical reactions on electrodes, and it is also the goal we ultimately pursue in the commercialization of large-scale clean energy technologies, such as metal-air batteries. Herein, a nitrogen-doped graphene oxide (GO)-carbon nanotube (CNT) hybrid network supported coupled Co/MnO nanoparticles (Co/MnO@N-C) catalyst was prepared with a hydrothermal-pyrolysis method. The unique three-dimensional network structure of substrate allowed for the uniform dispersion of Co-MnO nanoparticles in the carbon skeleton. These characters enable the Co/MnO@N-C to possess the excellent bifunctional electrocatalysts. In alkaline electrolyte, the Co/MnO@N-C presents the outstanding oxygen evolution reaction (OER) performance comparable to the commercial RuO2 catalyst and the exceedingly good oxygen reduction reaction (ORR) activity with positive half-wave potential of 0.90 V vs. RHE outperforming commercial Pt/C (0.84 V vs. RHE) and the recently reported analogous electrocatalysts. When it is applied to homemade Zn-air batteries, such a non-noble metal electrocatalyst can deliver a better power density, specific capacity and cycling stability than mixed Pt/C and RuO2 catalyst, and exhibits a wide application prospect and great practical value.

Determination of capsaicinoids by magnetic solid phase extraction coupled with UPLC-MS/MS for screening of gutter oil.

Capsaicinoids, including capsaicin, dihydrocapsaicin and N-vanillylnonanamide have been identified as characteristic markers for gutter oil. In this study, the nanocomposite of graphene oxide-Fe3O4 (GO-Fe3O4) was synthesized by a co-precipitation method, and applied to magnetic solid phase extraction (MSPE) process. The capsaicin, dihydrocapsaicin and N-vanillylnonanamide extracted in gutter oil were analyzed by ultrahigh performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). Under the optimized pretreatment conditions, the limit of detection (LOD) and limit of quantification (LOQ) are 0.15 and 0.4 µg L-1, respectively. The linear range is 0.4-200 µg L-1, and the correlation coefficients (R2) are over 0.996 for all three compounds. The recoveries range from 81.2% to 103.3% for soybean oil and 71.2% to 84.3% for rapeseed oil. The values of matrix effect range in 87.6%-105.5% and 83.4%-110.6% and the intra-day RSDs range from 2.8%-4.6% to 4.8%-6.1% for soybean oil and rapeseed oil, respectively. The adsorbent can be reused for multiple times with no appreciable loss of adsorption capability. The present methodology has high potential for screening of gutter oil in food samples, thus having importance for food safety monitoring.

A dual-readout nanosensor based on biomass-based C-dots and chitosan@AuNPs with hyaluronic acid for determination of hyaluronidase.

A dual-signal strategy is proposed based on fluorescent biomass-based carbon dots (BC-dots) and chitosan stabilized AuNPs (CS@AuNPs) to determine hyaluronidase (HAase). BC-dots can induce aggregation of CS@AuNPs nanoparticles with a colour change from red to blue. Positively charged CS@AuNPs interacted with the negatively charged hyaluronic acid (HA) through electrostatic adsorption, and CS@AuNPs maintained stability due to the semirigid coil conformation of HA. However, in the presence of HAase, due to enzymatic hydrolysis of HA by HAase, the CS@AuNPs agglomerated. Based on the change of fluorescence and colour, quantitative analysis of HAase was achieved. Linear ranges for the fluorometric and colorimetric determinations were 2.0-70 U mL-1 and 8-60 U mL-1 , respectively, with a detection limit of 0.27 U mL-1 . This dual-signal sensing system possesses high potential for determination of HAase in biological matrices.

Graphene oxide-Fe3O4 nanocomposite magnetic solid phase extraction followed by UHPLC-MS/MS for highly sensitive determination of eight psychoactive drugs in urine samples.

Graphene oxide-Fe3O4 (GO-Fe3O4) nanocomposite was synthesized by a facile chemical co-precipitation method. The GO-Fe3O4 was used as magnetic sorbent to extract the eight psychoactive drugs from urine samples. The analytes are morphine (MOR), 6-monoacetylmorphine (6-MAM), amphetamine (AMP), methamphetamine (MAMP), codeine, cocaine, dolantin and benzoylecgonine (BZE), which were determined by ultrahigh performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). This method has high selectivity for the target analytes. The limit of detection (LOD) and limit of quantification (LOQ) were 0.02-0.2 µg L-1 and 0.05-0.5 µg L-1, respectively. The Mandel's fitting test revealed good linearity within all linear ranges. The linear ranges were calculated as 0.05-1000 µg L-1 for AMP, MAMP, cocaine and dolantin; 0.1-1000 µg L-1 for 6-MAM and codein; and 0.5-1000 µg L-1 for MOR and BZE. The recoveries ranged in 80.4-105.5%. The intra-day and inter-day RSDs are in the range of 2.7-13.1% and 3.9-13.7%, respectively. Magnetic solid phase extraction (MSPE) with GO-Fe3O4 provides a convenient, rapid and green sample pretreatment method for extracting the target psychoactive drugs from urine. This methodology can be used for simultaneous or individual detection of eight major psychoactive drugs with high sensitivity. This method has high potential in clinical and forensic areas for psychoactive drugs analysis.

Nitrogen-doped carbon frameworks decorated with palladium nanoparticles for simultaneous electrochemical voltammetric determination of uric acid and dopamine in the presence of ascorbic acid.

A glassy carbon electrode (GCE) was modified with nitrogen-enriched carbon frameworks decorated with palladium nanoparticles (Pd@NCF/GCEs). The modified GCE is shown to be a viable tool for determination of uric acid (UA) and dopamine (DA) in the presence of ascorbic acid (AA). The Pd@NCF was fabricated though one-step pyrolysis and characterized by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy and nitrogen-adsorption/desorption analysis. The Pd@NCF/GCE was characterized by differential pulse voltammetry (DPV). Both UA and DA have pronounced oxidation peaks (at 360 mV for UA and 180 mV for DA, all vs. Ag/AgCl) in the presence of AA. Response is linear in the 0.5-100 µM UA concentration range and in the 0.5-230 µM DA concentration range. The detection limits are 76 and 107 nM, respectively (at S/N = 3). This electrode is stable, reproducible and highly selective. It was used for UA and DA determination in spiked serum samples. Graphical abstractSchematic representation of nitrogen-enriched carbon frameworks decorated with palladium nanoparticles co-modified glassy carbon electrode for simultaneous determination of dopamine and uric acid in the presence of ascorbic acid.

Simultaneous determination of 16 alkaloids in blood by ultrahigh-performance liquid chromatography-tandem mass spectrometry coupled with supported liquid extraction.

Alkaloids are widely present in food and medicine. However, many alkaloids have poisoning effect. Thus, a sensitive and rapid method for determination of alkaloids is highly desired. In this study, a convenient, reliable and accurate method is developed for the simultaneous determination of 16 poisonous alkaloids in human blood by ultrahigh performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) coupled with supported liquid extraction (SLE). The 16 alkaloids include colchicine, anisodamine, scopolamine, atropine, sinomenine, dicaine, thebaine, papaverine, strychnine, brucine, aconitine, hypaconitine, yunaconitine, deoxyaconitine, bullatine A and bullatine B. Low limits of detection (LODs) were obtained ranging in 0.002-0.03 µg L-1. The linear ranges are 0.005-200 µg L-1 for colchicine, papaverine, brucine, aconitine, hypaconitine, yunaconitine and deoxyaconitine, 0.01-200 µg L-1 for anisodamine and scopolamine, 0.05-200 µg L-1 for atropine, strychnine, bullatine A and bullatine B, 0. 1-200 µg L-1 for other target analytes, all with correlation coefficients (R2) higher than 0.995. The recoveries range from 79.2% to 95.8%. The relative standard deviation (RSD) values are lower than 15% and the values of matrix effect (ME) range in 86.3%-118.2%. This method of UPLC-MS/MS coupled with SLE has high potential for analyzing multiple alkaloids in blood samples.

CuCo2O4/N-Doped CNTs loaded with molecularly imprinted polymer for electrochemical sensor: Preparation, characterization and detection of metronidazole.

CuCo2O4 nanoparticles modified with nitrogen doped carbon nanotubes (CuCo2O4/N-CNTs) have high specific surface area and good electrical conductivity. Herein, a novel electrochemical sensor based on CuCo2O4/N-CNTs loaded molecularly imprinted polymer (MIP) modified glassy carbon electrode (GCE) is proposed for rapid and ultrasensitive detection of metronidazole (MNZ). The composite of CuCo2O4/N-CNTs with MIP significantly enhances the electrical signal. The electrochemical polymerization was performed with MNZ as template and aniline as functional monomer by cyclic voltammetry (CV), and differential pulse voltammetry (DPV) was used to detect MNZ. Factors that affect sensor response were optimized. Under the optimal experimental conditions, the DPV current response shows two linearity ranges for MNZ in the range of 0.005-0.1 µM and 0.1-100 µM with very low limit of detection (LOD) of 0.48 nM (S/N = 3). This electrochemical sensing system has high sensitivity, selectivity, excellent reproducibility, repeatability and stability. The recovery (95.9%-100.9%) and reasonable relative standard deviation (RSD) (3.2%-4.8%) for determination of real samples indicate the practicality of the sensing system. This sensing system has high potential for rapid determination of MNZ in samples such as metronidazole tablets, human serum and urine.

Molecularly imprinted polydopamine modified with nickel nanoparticles wrapped with carbon: fabrication, characterization and electrochemical detection of uric acid.

An electrochemical sensor is described for determination of uric acid (UA). Carbon-enwrapped nickel nanoparticles (Ni@BC) were coated with polydopamine (PDA) that was molecularly imprinted with UA. The biomass carbon (BC) was synthesized by one-step solid-state pyrolysis from leaves of Firmiana platanifolia. The imprinted polymer was obtained by electrodeposition of DA as the monomer. The amount of monomer, the scan cycles, pH value and adsorption time were optimized. Furthermore, the selectivity of the MIP for UA on a glassy carbon electrode (GCE) was evaluated by selectivity tests. The differential pulse voltammetric responses to UA with and without interferents were consistent. The modified GCE has a linear response in the 0.01-30 µM UA concentration range, and the limit of detection is 8 nM. The MIP electrode was applied to the analysis of UA in urine for which the initial concentrations were determined by the phosphotungstic acid kit. Recoveries ranged from 91.3 to 113.4%, with relative standard deviations between 1.3 and 9.7% (n = 3). Graphical abstract Schematic presentation of electrochemical detection of uric acid by molecularly imprinted polydopamine modified with nickel nanoparticles wrapped with carbon (Ni@BC-MIP).

Rose-like Nanocomposite of Fe-Ni Phosphides/Iron Oxide as Efficient Catalyst for Oxygen Evolution Reaction.

In order to accelerate the reaction rate of water splitting, it is of immense importance to develop low-cost, stable and efficient catalysts. In this study, the facile synthesis of a novel rose-like nanocomposite catalyst (Ni2 P/Fe2 P/Fe3 O4 ) is reported. The synthesis process includes a solvothermal step and a phosphatization step to combine iron oxides and iron-nickel phosphides. Ni2 P/Fe2 P/Fe3 O4 performs well in catalyzing oxygen evolution reaction, with a very low overpotential of 365 mV to reach 10 mA cm-2 current density. The Tafel slope is as low as 59 mV dec-1 . Ni2 P/Fe2 P/Fe3 O4 has a large double-layer capacitance that contributes to a high electrochemically active area. Moreover, this catalyst is very stable for long-term use. Therefore, the Ni2 P/Fe2 P/Fe3 O4 catalyst has a high potential for use in oxygen evolution reactions.

Ultrathin films of a metal-organic framework prepared from 2-methylimidazole, manganese(II) and cobalt(II) with strong oxidase-mimicking activity for colorimetric determination of glutathione and glutathione reductase activity.

Nanosheets (NSs; type ZIF-67) of a metal organic framework (MOF) that was prepared from 2-methylimidazole, manganese(II) and cobalt(II) were obtained by an ultrasonic hydrothermal method. Their Mn(II) doping reached as much as 11.3%. The NSs inherit high porosity, a large specific surface, and a large number of active sites. They display superior oxidase-mimicking activity and can catalyze the oxidation of tetramethylbenzidine (TMB) by molecular oxygen to form blue oxTMB. Glutathione (GSH) can reduce oxTMB, so that less blue oxTMB will be present. A simple and rapid method was established for the colorimetric determination of GSH and of the activity of GSH reductase (GR), best at a wavelength of 652 nm. The response to GSH drops linearly in the 0.1-25 µM concentration range. The activity of GR can be quantified in the 0.1 - 3 mU⋅mL-1 activity range. The respective detection limits are 0.07 µM and 0.18 mU⋅mL-1. Graphical abstract Schematic presentation of colorimetric detection of glutathione and glutathione reductase activity by the oxidase-mimicking activity of Mn-Co nanosheets in a metal organic framework.

A fluorometric and colorimetric method for determination of trypsin by exploiting the gold nanocluster-induced aggregation of hemoglobin-coated gold nanoparticles.

A dual-signal assay is described for the determination of trypsin based on the use of gold nanoparticles (AuNPs) that aggregate in the presence of gold nanoclusters (AuNCs) due to electrostatic interaction. This is accompanied by a color change from red to blue. However, if hemoglobin (Hb) is present in the solution, it will attach to the surface of AuNPs, thus preventing aggregation. The Hb-coated AuNPs quench the fluorescence of AuNCs. Trypsin can hydrolyze Hb and destroy the protective coating of Hb on the AuNPs. As a result, AuNP aggregation will occur after the addition of AuNCs, and the blue fluorescence of the AuNCs with 365 nm excitation and 455 nm maximum emission peak is recovered. Thus, trypsin can be determined by measurement of fluorescence emission intensity. Additionally, trypsin can be determined by the maximum absorption peak wavelength between 530 nm and 610 nm. Fluorescence increases linearly in the 10-2500 ng⋅mL-1 concentration range, and absorbance in the 20-2000 ng·mL-1 concentration range. The limits of detection are 4.6 ng·mL-1 (fluorometry) and 8.4 ng·mL-1 (colorimetry), respectively. The assay is sensitive and selective, and can be applied to the determination of trypsin in serum. Graphical abstract Schematic presentation of a fluorometric and colorimetric method for determination of trypsin. The presence of hemoglobin (Hb) protects AuNPs from agglomeration after adding AuNCs and the fluorescence of AuNCs is quenched. With trypsin present, trypsin destroys the coating of AuNPs by Hb. AuNPs aggregate again and the fluorescence recovers after the addition of AuNCs.

A carbon dot-based ratiometric fluorometric and colorimetric method for determination of ascorbic acid and of the activity of ascorbic acid oxidase.

A dual-mode method was developed for the determination of ascorbic acid (AA) and of ascorbic acid oxidase (AA-Ox) activity. It combines the advantages of ratiometric fluorometry and colorimetry. The assay is based on the oxidation of o-phenylenediamine (OPDA) by permanganate (KMnO4). A yellow substance (referred to as oxOPDA) with an absorption peak at 425 nm is rapidly produced in the presence of the oxidant. oxOPDA reduces the blue fluorescence of carbon dots (C-dots) peaking at 450 nm (upon 380-nm excitation), and a new emission peak is found at 565 nm. If AA is pesent, it consumes a certain fraction of KMnO4, so that less OPDA will be oxidized. This is accompanied by a decrease in the intensity of the fluorescence at 565 nm and an increase in the intensity at 450 nm. In parallel, the color of the solution changes from yellow to colorless. The determination of the activity of ascorbic acid oxidase (AA-Ox) is performed as follows: AA is oxidized by AA-Ox. This causes the fluorescence and colors to change in the opposite directions compared with AA detection. The ratio of fluorescences (I565/I450) becomes larger if the color the solution turns from colorless to yellow. Thus, the fluorescence intensity ratio (I565/I450) and colorimetric "bare-eye" readout can be used for determination of both the concentration of AA and the activity of AA-Ox. The fluorometric assay for AA has a linear range that extends from 0.6 to 40 µM, and the colorimetric assay from 0.2 to 70 µM. The respective data for AA-Ox activity are 0.04 ~ 5 mU·mL-1 and 0.04 ~ 8 mU·mL-1, respectively. The limits of detection for AA are 9 and 40 nM, and the LODs for AA-Ox activity are 0.017 and 0.012 mU·mL-1. Graphical abstract Schematic presentation of the assay. Permanganate (KMnO4) rapidly oxidizes ortho-phenylenediamine oxide to form a product (oxOPDA) having a yellow fluorescence peaking at 565 nm. The yellow color of oxOPDA can be detected visually. It also reduces the intensity of the blue fluorescence of carbon dots (C-dots) peaking at 450 nm. Ascorbic acid (AA) can consume permanganate, and this results less oxidation of OPDA. Ascorbic acid oxidase (AA-Ox) catalyzes the oxidization of AA by oxygen, and this - in turn - causes the changes in absorbance and fluorescence to change in the opposite directions.

Single-Composition White Light Emission from Dy3+ Doped Sr2CaWO6.

A series of Dy3+ ion doped Sr2CaWO6 phosphors with double perovskite structure were synthesized by traditional high temperature solid-state method. It was found that there is significant energy transfer between Dy3+ and the host lattice, and the intensities of emission peaks at 449 nm (blue), 499 nm (cyan), 599 nm (orange), 670 nm (red), and 766 nm (infra-red) can be changed by adjusting the concentration of dopant amount of Dy3+ ion in Sr2CaWO6. The correlated color temperature of Dy3+ ion doped Sr2CaWO6 phosphors can be tuned by adjusting the concentration of Dy3+ ion. Upon optimal doping at 1.00 mol% Dy3+, white light with chromaticity coordinate (0.34, 0.33) was emitted under excitation at 310 nm. Thus, single composition white emission is realized in Dy3+ doped Sr2CaWO6.