Synthesis of M1-3xAl2O4:Eu2+x/Dy3+ 2x(M^2+= Sr^2+, Ca^2+ and Ba^2+) phosphors with long-lasting phosphorescence properties via co-precipitation method

The long afterglow fluorescent material of M1-3xAl2O4:Eu2+ x/Dy3+2x(M2+= Sr2+, Ca2+ and Ba2+) phosphors are successfully synthesized by calcining precursor obtained via co-precipitation method at 1300oC for 4 h with reducing atmosphere (20% H2 and 80% N2). The phase evolution, morphology and afterglow fluorescent properties are systematically studied by the various instruments of XRD, FE-SEM, PLE/PL spectroscopy and fluorescence decay analysis. The PL spectra shows that the Sr1-3xAl2O4:Eu2+x/Dy3+ 2x phosphors display vivid green emission at s519 nm (4f65d1!4f7 transition of Eu2+) with monitoring of the maximum excitation wavelength at s334 nm (8S7=2!6IJ transition of Eu2+), among which the optimal concentration of Eu2+ and Dy3+ is 15 at.% and 30 at.%, respectively. The color coordinates and temperature of Sr1-3xAl2O4:Eu2+ x/Dy3+ 2x phosphors are approximately at (s0.27, s0.57) and s6700 K, respectively. On the above basis, the M0:55Al2O4:Eu2+ 0:15/Dy3+ 0:3 (M2+= Ca2+ and Ba2+) phosphors is obtained by the same method. The PL spectra of these phosphors shows the strongest blue emission at s440 nm and cyan emission at s499 nm under s334 nm wavelength excitation, respectively, which are blue shifted comparing to Sr1??3xAl2O4:Eu2+ x/Dy3+ 2x phosphors. The color coordinates and temperatures of M0:55Al2O4:Eu2+ 0:15/Dy3+ 0:3 (M2+= Ca2+ and Ba2+) phosphors are approximately at (s0.18, s0.09), s2000 K and (s0.18, s0.42), s11600 K, respectively. In this work, long afterglow materials of green, blue and cyan aluminates phosphors with excellent properties have been prepared, in order to obtain wide application in the field of night automatic lighting and display.

Recent progress on electrochemical production of hydrogen peroxide

Hydrogen peroxide (H2O2), first synthesized in 1818 through the acidification of barium peroxide (BaO2) with nitric acid, is a clear and colorless liquid which is entirely miscible with water and variety of organic solvents such as carboxylic acid and esters. Anthraquinone process (an old production process of H2O2), a batch process carried out in large facilities is an energy demanding process that requires large facilities, and involves oxidation of anthraquinone molecules and sequential hydrogenation. Moreover, the direct synthesis method enables production in a continuous mode as well as it permits small scale, decentralized production. Many drawbacks associated with these processes such as, energetic inefficiency and inherent disadvantages have motivated researchers, industry and academia to find out alternative for synthesis of H2O2. Electrochemical route based on catalyst selectively reduce oxygen to hydrogen peroxide. O2 is cathodically reduced to produce H2O2 via 2-electron pathway or 4-electron pathway to get H2O. Electrolysis of water has an important place in storage and electrochemical energy conversion process where problem is to choose a sufficiently stable and active electrode for anodic oxygen evolution reaction. Most commonly used catalysts on the cathode are carbon based materials such as carbon black, carbon nanotubes, graphite, carbon sponge, and carbon fiber. In perspective of expanding demand of production and usage of hydrogen peroxide we review the past literature to summarize different production processes of H2O2. In this review, we mainly focus on electrochemical production of hydrogen peroxide along with other alternatives, such as anthraquinone method for industrial H2O2 production and direct synthesis process. We also review the catalytic activity, selectivity and stability for enhanced yield of H2O2. From revision of last two decade’s literature including experimental and theoretical data;we argue that successful implementation of electrochemical H2O2 production can be realized on the basis of stable, active and selective catalyst.

Coordinatively unsaturated cobalt single-atom nanozymes for visual pesticides detection by smartphone-based platform

By adjusting the coordination environment of single-atom catalysts,the enzyme-like activity can be finely tuned for highly sensitive biosensing.Herein,we demonstrated that coordinatively unsaturated cobalt-nitrogen sites doped within porous carbon(SA-CoN_(3))could serve as highly efficient oxidase mimic.Compared with the typical planar four-coordination structure(SA-CoN_(4)),the as-obtained single-atom Co nanozymes anchored by three nitrogen atoms are found to display much higher oxidase-like catalytic efficiency.Combined theoretical and experimental analysis revealed that the coordinatively unsaturated Co sites could facilitate adsorption and activation of O_(2) molecule and thus improve their oxidase-like activity.Based on the enhanced oxidase-like activity of SA-CoN_(3),a paper/smartphone sensor for organophosphorus pesticides(OPs)was successfully constructed and used to quantify glyphosate in environmental and food samples with a low detection limit of 0.66μM.This work not only highlights the important role of coordination unsaturation of SA nanozymes for promoting oxidase-like activity,but also provides an easy and cost-effective way to conduct effective quantification of OPs in the field.

Highly exposed Cu active sites as efficient peroxidase mimics for colorimetric analysis

Nanozymes are nanomaterials with intrinsic enzyme-mimic activity,but their large-scale application is generally limited by their low catalytic activity.Herein,we demonstrated that highly exposed Cu active sites on two-dimensional(2D)nitrogen-doped carbon(Cu_(x)/NC)can serve as efficient peroxidase-like(POD)catalysts with high atomic utilization.Specially,the uniformly distributed Cu active sites could react with H_(2)O_(2)to produce singlet oxygen(^(1)O_(2))under acidic conditions,which can efficiently oxidizes colorless 3,3',5,5'-tetramethylbenzidine(TMB)to blue oxidized TMB(oxTMB).Among various Cu_(x)/NC nanozymes studied,the Cuo.14/NC exhibited smaller maximum catalytic velocities(V_(max))and Menten constant(K_(m))for TMB and H_(2)O_(2).Benefiting from the highly active peroxidase-like activity,the Cu_(0.14)/NC nanozyme could be successfully applied for the hydroquinone(HQ)and ascorbic acid(AA)detection applications through the inhibitory effect of HQ and AA.More interestingly,α-glucosidase(α-Glu)detection sensing platform could be constructed based on HQ as a signal transmitter,with the detection range ranging from O to 12 U/L and the minimum detection limit being 0.68 U/L.This work provides not only an idea for the rational design of highly exposed Cu active sites but also fabricate an effective detection sensing platform forHQ,AA,andα-Glu detection.

Structure characteristics and microwave dielectric properties of Pr_(2)(Zr_(1-x)Ti_(x))_(3)(MoO_(4))_(9) solid solution ceramic with a stable temperature coefficient

Pr_(2)(Zr_(1−x)Ti_(x))_(3)(MoO_(4))_(9)(x=0.1-1.0)ceramics were prepared via a conventional solid-state method,the dependence of crystal structure and bond characteristics on microwave dielectric properties was investigated systemically.The X-ray diffraction patterns indicated that the single-phase Pr_(2)Zr_(3)(MoO_(4))_(9)structure was formed in all the specimens.As the Ti^(4+)content increased,the lattice volume gradually decreased,which was ascribed to the fact that the ionic radius of Ti^(4+)was smaller than that of Zr^(4+).Notably,outstanding microwave dielectric properties withεr of 10.73-16.35,Q·f values of 80,696-18,726 GHz and minorτ_(f) values−14.1-−2.6 ppm/℃were achieved in Pr_(2)(Zr_(1−x)Ti_(x))_(3)(MoO_(4))_(9)ceramics.Theε_(r) increased with the rising x values,which was associated with the increase ofα/Vm values.The decreasing Q·f was affected by the decline of lattice energy of[Zr/TiO_(6)]octahedral.Theτf value was dominated by[Zr/TiO_(6)]octahedral distortion,Mo-O bond energy,bond strength and B-site bond valence.Furthermore,infrared reflection spectra suggested that the properties were mainly caused by the absorption of phonon,and the dielectric loss could be further reduced by optimizing the experimental process.

Enhanced oxidase-like activity of g-C_(3)N_(4) nanosheets supported Pd nanosheets for ratiometric fluorescence detection of acetylcholinesterase activity and its inhibitor

The undesirable enzymatic activity of nanozymes under near neutral p H condition and the traditional single signal output always restrict the analytical application of nanozyme-based biosensors.Herein,graphitic carbon nitride nanosheets supported palladium nanosheets composite (Pd/g-C_(3)N_(4)) with both oxidase-like activity and fluorescent property is synthesized.Notably,Pd/g-C_(3)N_(4)exhibits enhanced oxidase-like activity compared to Pd NSs under p H 7.4.By combining Pd/g-C_(3)N_(4)with o-phenylenediamine(OPD),a ratiometric fluorescence assay for acetylcholinesterase (ACh E) activity detection is developed.Pd/g-C_(3)N_(4)can catalyze oxidation of nonfluorescent OPD to fluorescent oxidized OPD (ox OPD,Em=565nm),which can quench fluorescence of g-C_(3)N_(4)supporter (Em=441 nm) through fluorescence resonance energy transfer (FRET).However,in presence of ACh E,acetylthiocholine can be hydrolyzed into thiocholine,which will block the oxidase-like activity of Pd/g-C_(3)N_(4)and then hamper the FRET process.This ratiometric fluorescence assay is also viable to screen ACh E inhibitor.This work will guide design of ratiometric fluorescence assay based on nanozymes with improved enzymatic activity.

Bimetallic synergistic Pd-Pt icosahedra as highly active peroxidase-like mimics for colorimetric analysis

Thanks to the synergistic effect,the bimetallic catalysts show better catalytic activity than the single metal cat-alysts and become a focus of research in heterogeneous catalysis.In this study,we successfully prepared Pd-Pt icosahedra which show high peroxidase-like activity under the synergistic effects of Pd and Pt.V max of the Pd-Pt icosahedra was significantly enhanced by 1.66 times for 3,3’,5,5’-tetramethylbenzidine(TMB)as the substrate and 1.23 times for H_(2)O_(2) as the substrate,compared to that of the Pd icosahedra alone.By harnessing the supe-rior peroxidase-like activity of Pd-Pt icosahedra,we successfully utilized Pd-Pt icosahedral nanozymes in various biological analyses based on colorimetry.In most cases,using a Pd-Pt icosahedra/H_(2)O_(2)/TMB system,glucose,glutathione(GSH),acid phosphatase(ACP),and alkaline phosphatase(ALP)were detected over a wide range of 0.05∼0.20 mM,0∼20 mM,0∼10 U/L and 0∼12 U/L.In this study,we prepared a novel bimetallic nanozyme that exhibited excellent peroxidase-like activity owing to the bimetallic synergistic effect,thus demonstrating the promising potential of Pd-Pt icosahedra in the field of bioanalysis.

Red color Sr_(2)NaMg_(2)V_(3)O_(12):Eu^(3+)phosphor with high thermal stability for w-LEDs

Sr_(2)NaMg_(2)V_(3)O_(12):xEu phosphors with uniform particle size/morphology and good dispersion can be synthesized via solid state reaction.Under the optimum excitation wavelength of ~340 nm,the Sr_(2)NaMg_(2)V_(3)O_(12):xEu phosphor displays the broad emission band at ~500 nm(blue-green emission,^(3)T_(1,2)→^(1)A_(1) transition of[VO_(4)]^(3-))and sharp emission peak at~610 nm(red emission,^(5)D_(0)→^(7)F_(2) transition of Eu^(3+)),respectively.With the Eu^(3+)content increasing,the emission intensity of[VO_(4)]^(3-)decreases gradually while the emission intensity of Eu^(3+)increases,which is ascribed to the energy transfer from[VO_(4)]^(3-)to Eu^(3+)ions.The decay time of[VO_(4)]^(3-)(-500 nm)increases gradually with the Eu^(3+)content increasing.The energy transfer efficiency and mechanism of[VO_(4)]^(3-)→Eu^(3+)ions were analyzed,respectively.The emission color of Sr_(2)NaMg_(2)V_(3)O_(12):xEu phosphor was regulated from green to red via altering the Eu^(3+)ions concentration.It is delightful for us that the white color emission can be just achieved when the Eu^(3+)content is 5 at%(x=0.05),and the w-LED can be assembled.By studying the luminescence temperature dependence and activation energy of Sr_(2)NaMg_(2)V_3O_(12):xEu phosphor,it is shown that the phosphor has good thermal stability.The Sr_(2)NaMg_(2)V_3O_(12):xEu powder is expected to be a new type of phosphor widely used in light and display areas.

硼掺杂石墨烯耦合双金属氧化物作为高效氧气析出电催化剂

开发高效价廉的氧气析出反应电催化剂对于制备多种可再生能量转化和存储器件至关重要.本文中,我们设计合成了一系列硼掺杂石墨烯负载的钴镍双金属氧化物,并研究了其氧气析出电催化性能.研究结果表明适当温度下退火后的Co-Ni-Ox/BG(Co/Ni比为1:1)在碱性条件下表现出非常高的氧气析出电催化性能.在电流密度为10 mA cm-2时,该电催化剂对氧气析出反应的过电位仅为310 mV,优于绝大多数已报道的基于单金属氧化物的催化剂,甚至可与商业RuO2电催化剂的性能相媲美.该双金属氧化物复合材料中,电荷分布的微调控及协同耦合效应都对该材料的电催化性能起到了促进作用.另外,本文还提出了几种可有效提高氧化物材料氧气析出电催化活性的方法.

abrication of CDs hybrid MIL-68(In) derived In2O_(3)eIn_(2)S_(3) hollow tubular heterojunction and their exceptional self-powered PEC aptasensing properties for ampicillin detecting

A visible-light-driven self-powered photoelectrochemical(PEC)aptasensor was developed for ampicillin(AMP)detecting based on carbon dots(CDs)hybrid MIL-68(In)-derived In2O_(3)eIn_(2)S_(3) hollow tubular heterojunction(CDs/In2O_(3)eIn_(2)S_(3)).In_(2)S_(3) nanosheets uniformly grew in-situ on the surface of In2O_(3) hollow tubes,forming a close contact heterogeneous interface,which significantly promoted the transfer and separation of photo-generated carriers,and provided a large specific surface area and rich active sites for the PEC aptasensing platform.Furthermore,the CDs/In2O_(3)eIn_(2)S_(3)/ITO electrode,which was obtained by dipping assembly,showed remarkable and stable photoelectric signals at zero-bias under visible light irradiation.The amino-functionalized AMP aptamer was fixed on the working electrode as a biological recognition element,and the concentration of AMP was determined by observing the change in photocurrent intensity caused by the specific capture of AMP molecules in solution.Under optimized conditions,the developed PEC aptasensor displayed a relatively wide linear range from 0.001 ng mL^(-1) to 300 ng mL^(-1),as well as a low detection limit(LOD)of 0.06 pg mL^(-1).Besides,the novel self-powered PEC AMP-aptasensor exhibited excellent reproducibility,good stability and selectivity,which open a potential avenue for antibiotic residues detection in environmental media.

Spontaneous Deposition of Uniformly Distributed Ruthenium Nanoparticles on Graphitic Carbon Nitride for Quantifying Electrochemically Accumulated H_(2)O_(2)

Highly dispersed ultrasmall ruthenium nanoparticles with a clean surface are deposited onto graphitic carbon nitride(C_(3)N_(4)-Ru)through spontaneous redox reaction between the C_(3)N_(4) sheets and Ru salt without the use of any reductant.The as-prepared C_(3)N_(4)-Ru exhibits distinct peroxidase-like activity.A nanozyme based method is successfully developed for detecting the H_(2)O_(2) generated in-situ by the two-electron oxygen reduction strategy.The C_(3)N_(4)-Ru nanozyme can realize the detection of H_(2)O_(2) with a wide linear range and a low detection limit.The testing results are also compared with the conventional modified titration method,and show greater possibility for the practical detection of H_(2)O_(2) produced via the electrochemical oxygen reduction for its higher selectivity.

Chemical and spectroscopic characteristics of humic acid from a clay loam soil in Ontario after 52 years of consistent fertilization and crop rotation

Long-term fertilization and crop rotation can influence both organic C sequestration as well as the C composition of soils and the more resistant organic C compounds contained in humic acid(HA). This study examined the effects of fertilization and cropping type(monoculture corn(MC) and Kentucky bluegrass sod(KBS) and corn-oat-alfalfa-alfalfa rotation(RC)) on the HA composition of soil from a 52-year field study in southern Ontario, Canada. Humic acid samples were extracted from soil, and elemental analysis, infrared spectroscopy, solid state 13C nuclear magnetic resonance spectra, and electron paramagnetic resonance methods were used to determine the influence of the cropping type on the characteristics of HA. Both fertilization and cropping type affected the chemical characteristics of HA. Fertilization led to a 5.9% increase in C, a 7.6% decrease in O, and lower O/C and(N + O)/C ratios in HA as compared to the corresponding non-fertilized treatments. Rotation resulted in a lower proportion of C(48.1%) and a greater(N + O)/C ratio(0.7) relative to monoculture cropping. Infrared spectroscopy analysis showed that HA contained more C-O groups in fertilized soil than in non-fertilized soil under MC and KBS. Fertilization increased the O-alkyl-C, phenolic-C, and free radical contents of HA relative to non-fertilization treatments. Rotation decreased the aliphatic and carboxyl groups and increased the O-alkyl, carbohydrate, aryl, and phenolic groups and free radicals, relative to MC and KBS. Both long-term crop rotation and fertilization dramatically modified the soil HA composition. Significant relationships were observed between the molecular composition of HA and soil organic C. Hence, humic acid characterization could be used as an indicator of the long-term sustainability of crop management practices.

Single-atom Pd catalysts as oxidase mimics with maximum atom utilization for colorimetric analysis

Pd-based nanomaterials have shown great promise as potential mimic enzymes,but conventional catalysts use only a small fraction of the Pd content that located on the catalyst's surface.Herein,we demonstrated that maximum atom utilization could be achieved by using single-atom Pd catalysts as oxidase mimic.The single-atom Pd nanozymes exhibit significantly enhanced catalytic efficiency,with a catalytic rate constant(Kcat)and the catalytic efficiency(Kcat/Km)values more than 625 and 4,837 times higher than those of horseradish peroxidase,respectively.A combined experimental and theoretical calculation reveals reactive oxygen species involved catalytic mechanism which endows single-atom Pd catalysts with excellent colorimetric analysis performance.Benefiting from the maximum atom utilization efficiency and well-defined structural features,the single-atom Pd nanozymes could be successfully applied for the total antioxidant capacity of fruit,determining the serum acid phosphatase activity as well as constructing NAND logic gate.This finding not only provides an effective strategy to maximize the noble-metal atom utilization efficiency as enzyme mimics,but also provides a new idea for extending their possible applications.

Highly efficient hydrogen peroxide electrosynthesis on oxidized carbon nanotubes by thermally activated-persulfate

Electrochemical synthesis of hydrogen peroxide(H_(2)O_(2))through two-electron oxygen reduction represents an attractive alternative for on-site H_(2)O_(2) generation.Here,we develop a facile thermally activatedpersulfate approach to obtain oxidized carbon nanotubes(O-CNTs-x,x represents oxidation time)with enhanced H_(2)O_(2) electrosynthesis performance.Electrochemical studies have demonstrated that the optimized O-CNTs-6(i.e.,oxidation time is 6 h)could deliver a sustained high selectivity of around 92%for H_(2)O_(2) over a wide voltage window in 0.1 mol/L KOH and a high H_(2)O_(2) production rate of 296.84 mmol/L g^(-1) cat h^(-1).Compared with pristine CNTs,the enhanced catalytic activity primarily stems from the newly-generated oxygen-containing functional groups and some defects created on the surface of O-CNTs-x.Importantly,the proposed oxidation process is proved to be valid for promoting H_(2)O_(2) electrosynthesis performance of the Ketjen black.This study provides an universal oxidation method to obtain highly active carbon-based catalysts and initiates new opportunities for the exploration of highperformance electrosynthesis H_(2)O_(2) catalysts.