Specific Structural Defects Research Articles

Highly active nitrogen-doped biochar for catalytic reduction of 4-nitrophenol: Kinetic, thermodynamic and mechanism investigation

Biomass derived metal-free carbon catalysts are urgently needed in wastewater remediation and organic transformation, due to their environmental friendliness, low cost. In this respect, a series of nitrogen-doped hierarchically porous carbons (NHPCs) derived from cheap and abundant eggplant were fabricated via a one-pot strategy under different temperatures from 600 to 900°C, and employed as metal-free catalysts for the reduction of aromatic nitrophenols. Benefiting from the synergistic effects of the hierarchically porous structure, large specific surface area and abundant structural defects, NHPCs obtained from 800 °C has the highest reduction rate of 2.072 min−1 and maximal turnover frequency (TOF) for 4-nitrophenol of 1.23 × 10−2 mM·mg−1·min−1, which is superior to most of the reported metal-free catalysts. In addition, the NHPC-800 also exhibits satisfactory practicality and universality. The kinetic and thermodynamic studies were also conducted, finding that the obtained kinetics data over NHPC-800 fit well to L-H model with a low apparent activation energy (Ea = 18.96 kJ·mol−1). Furthermore, the mechanism was also elucidated by experimental investigation and theoretical calculations, which revealed that the pore creation and doping nitrogen can promote the adsorption of 4-NP and NaBH4 onto NHPC. This study make a significant contribution to the advancement of catalytic reduction of 4-NP by N-doped biochar catalysts.

Biochar, microbes, and biochar-microbe synergistic treatment of chlorinated hydrocarbons in groundwater: a review.

Dehalogenating bacteria are still deficient when targeted to deal with chlorinated hydrocarbons (CHCs) contamination: e.g., slow metabolic rates, limited substrate range, formation of toxic intermediates. To enhance its dechlorination capacity, biochar and its composites with appropriate surface activity and biocompatibility are selected for coupled dechlorination. Because of its special surface physical and chemical properties, it promotes biofilm formation by dehalogenating bacteria on its surface and improves the living environment for dehalogenating bacteria. Next, biochar and its composites provide active sites for the removal of CHCs through adsorption, activation and catalysis. These sites can be specific metal centers, functional groups or structural defects. Under microbial mediation, these sites can undergo activation and catalytic cycles, thereby increasing dechlorination efficiency. However, there is a lack of systematic understanding of the mechanisms of dechlorination in biogenic and abiogenic systems based on biochar. Therefore, this article comprehensively summarizes the recent research progress of biochar and its composites as a "Taiwan balm" for the degradation of CHCs in terms of adsorption, catalysis, improvement of microbial community structure and promotion of degradation and metabolism of CHCs. The removal efficiency, influencing factors and reaction mechanism of the degraded CHCs were also discussed. The following conclusions were drawn, in the pure biochar system, the CHCs are fixed to its surface by adsorption through chemical bonds on its surface; the biochar composite material relies on persistent free radicals and electron shuttle mechanisms to react with CHCs, disrupting their molecular structure and reducing them; biochar-coupled microorganisms reduce CHCs primarily by forming an "electron shuttle bridge" between biological and non-biological organisms. Finally, the experimental directions to be carried out in the future are suggested to explore the optimal solution to improve the treatment efficiency of CHCs in water.

3D-interconnected N-doped porous carbon with hierarchical pore structure as a high-efficiency catalyst for H2S oxidation at room temperature

Nitrogen-doped porous carbons (NPCs) have been regarded as an efficient metal-free catalyst for H2S oxidation. However, critical factors affecting their desulfurization ability are still unclear, making it difficult to accurately adjust their desulfurization performance to meet industrial requirements. Herein, a novel 3D-interconnected NPC with hierarchical pore structure was synthesized by one-step “leavening” strategy using rice husk and (NH4)2C2O4 as a carbon source and foaming agent, respectively, for H2S oxidation at room temperature. Pyrolysis temperature is the major factor for physicochemical properties of NPCs, and breakthrough sulfur capacity of the optimal NPC reaches up to 1036.68 mg/g, which can remain stable during three desulfurization-regeneration cycles. Comparative experiment shows that H2S capacity of NPC is 1.8 and 4.0 times those of PC and NC, respectively, revealing the excellent desulfurization performance of NPC. The structure-effect relationships between H2S and NPC reveal that both textural and chemical properties of NPC, especially specific surface area, structural defect, and pyrrolic N, play dominant roles in H2S removal. It is very necessary to balance the relationship between textural performances and pyrrolic N to synthesize optimal NPC catalyst. This work provides a valuable reference for rational design of high-efficiency carbon-based catalysts for persistent desulfurization at room temperature.

Anelastic Internal Friction and Mechanical Spectroscopy of SiO2/Si Wafers

In this work, after electron irradiation and X-ray, the outcomes of the evaluation dynamic characteristics of interstitial atoms Si j , vacancy V, and O-complexes were evaluated to account for the annealing conditions to derive specific structural defects in the SiO2/Si wafer. A non-destructive method, which allows the determination of the internal friction difference ΔQ −1 /Q −1 0 of the elastic vibration of structural defects of dislocations with density N D and the depth of the broken layer h b , is offered for the SiO2/Si wafer. The method was developed, the installation was designed and manufactured for the excitation and registration of damped bending resonant oscillations in a SiO2/Si disc-shaped wafer with a thickness h SiO2 ≈ 100 nm, h is = 300 ÷ 500 × 103 nm, and diameter D = 60 ÷ 100 × 10−3 m to measure the structurally sensitive internal friction Q −1 in vacuum P ≈ 10−2 Pa. Measurement of the internal friction background Q −1 0 at harmonic frequencies f 0 and f 2 allowed us to experimentally determine the nodal lines of the oscillating disks.

Defects in layered boron nitride grown by Metal Organic Vapor Phase Epitaxy: luminescence and positron annihilation studies

Defects in two-dimensional boron nitride (BN) are candidates for a manifold of applications, for example, as single-photon emitters or optically addressable spin defects. However, the topic has proven to be complex and despite extensive research efforts, knowledge on midgap defects and their signature in photoluminescence (PL) remains fragmentary. Mass production of high-quality layered BN by Metal Organic Vapor Phase Epitaxy (MOVPE) is possible and effective, thus understanding the conditions of formation and identifying defects that arise in the material grown by this method is extremely important. Here, we present an analysis of the influence of the MOVPE growth conditions of layered BN on the occurrence of specific structural defects. PL spectra in the visible range were analysed involving the Huang-Rhys theory implemented in the fitting procedure for polycrystalline samples grown under various conditions. Such an approach allowed us to separate bands from individual entities. Two bands at 1.57 eV and 2.6 eV with phonon replicas were observed. The three additional bands are characterized by a broad emission centered at 1.38 eV, 1.9 eV and 2.24 eV. Further properties, including an analysis of the surface morphology, the impact of annealing and laser bleaching on the PL spectra and Positron Annihilation Spectroscopy (PAS) were considered to draw conclusions about the nature of the examined defects. The PAS analysis correlated with the PL of the BN layers allows us to classify the studied samples in terms of the concentrations of boron vacancies and their complexes. Based on the obtained results, we propose that the rich family of PL bands observed in various sp2-BN layers is associated with different defect complexes build of boron vacancies (VB), boron antisite defects (BN), substitutional carbon defects (CB, CN) and their donor-acceptor pairs. The main value of this paper is the transfer of knowledge gained about defects and the corresponding luminescent bands to characterize high-quality continuous epitaxial sp2-BN layers. The presented results constitute an important step toward the deterministic manipulation of defect concentrations in two-dimensional boron nitride, which opens up new pathways for future optoelectronic device application.

APPLICATION OF ACOUSTIC EMISSION METHOD FOR DETECTING DIFFUSION INTERLAYERS IN DIFFERENT WELDED JOINTS

The paper investigates the possibility of detecting specific structural defects of dissimilar welded joints by the method of acoustic emission (AE). Carbide and decarburized interlayers are formed in dissimilar welded joints of austenitic and pearlitic steels during welding and subsequent operation. Diffusion interlayers, as a structural defect, are usually small in size and cannot be detected by traditional non-destructive testing (NDT) methods, while the AE method is promising for detecting such defects. In the present work, we studied the AE data obtained during testing of defect-free specimens of a welded joint and specimens with diffusion interlayers. It has been established that the AE parameters for defective and defect-free welded joints have significant differences, which makes it possible to identify the presence of diffusion interlayers in dissimilar welded joints.

Tremella-like hierarchical carbon derived from carbon dots through sponge-templated synthesis for supercapacitor electrodes

Carbon-based electrical double-layer capacitors have considerable attention due to their long cycle life and high power density. However, it remains a challenge to prepare desirable electrode materials for electrical double layer capacitors through simplified methods. Herein, a tremella-like hierarchical porous carbon material is synthesized via a simple, versatile, and eco-friendly template method using ultra-small and low-cost carbon dots as the carbon source and the sponge as the scaffold. Due to the high specific surface area (2144.6 m2/g), unique structure, and abundant structural defects, the resulting tremella-like hierarchical porous carbon show a high specific capacitance of 148 F/g at 1 A/g and long-term cycling stability with 86.2% of the initial capacitance retention after 10,000 cycles at 5 A/g. The study provides a facile and efficient strategy for the construction of electrode materials in supercapacitors.

(Digital Presentation) Internal Friction, Mechanical Spectroscopy in SiO2/Si Wafers

In this work, after X-ray and electron irradiation, the outcomes of the evaluation dynamic characteristics of interstitial atoms Sij , vacancy V, and O-complexes were evaluated to account for the annealing conditions to derive specific structural defects in the SiO2/Si wafer. A non-destructive method, which allows the determination of the internal friction difference ΔQ-1/Q-1 0 of the elastic vibration structure defect density Nd and the depth of the broken layer hb , is offered for the SiO2/Si wafer. The method was developed, the installation was designed and manufactured for the excitation and registration of damped bending resonant oscillations in a SiO2/Si disc-shaped wafer with a thickness hSiO2 ≈ 100 nm, his = 300÷500×103 nm, and diameter D = 60÷100×10-3 m to measure the structurally sensitive internal friction Q-1 . Measurement of the internal friction background Q-1 0 at harmonic frequencies f0 and f2 allowed us to experimentally determine the nodal lines of the oscillating disks.

Internal Friction and Mechanical Spectroscopy of SiO2/Si, Nanocomposites of Multiwalled Carbon Nanotubes and Polyamide, Polyethylene, Polyvinyl Chloride, Expanded Polystyrene

: In this work after X-ray irradiation outcomes of the evaluation of dynamic characteristics interstitial atoms Sij, vacancy V and O-complexes was applied for account of a condition of an annealing with the purpose of deriving specific structural defects in SiO2/Si wafer-plate. The nondestructive method, which is allow to determine from internal friction difference ΔQ-1/Q-1 0 of elastic vibrations structure defects density Nd and the depth of broken layer hb, is offered for SiO2/Si wafer-plates. 1. Introduction Defect annealing leads to a change in the shape of the internal friction (IF) temperature spectrum Q-1(T) [1]. IF method allows to set the spectrum of structural defects on the analysis of positions of maximums IF, on duration of relaxation time τ and on their deposit in attenuation of elastic vibrations [2]. A non-destructive method for the technological control of the structure defects by measuring internal friction (IF) and elastic modulus E after laser radiation was developed. 2. Experimental procedure Ultrasonic (US) pulse-phase method using USMV-LETI, modernized USMV-KNU and computerized “KERN-4” with frequencies f║ ≈ 1 MHz and f┴ ≈ 0,7 MHz, US invariant-polarization method for determining the effective acoustic μil and elastic constants Cijkl were used [3,4]. The measured velocity error was equal to ΔV/V = 0,5÷1,5%.The study of influence of structure defects on damping of vibrations in Si/SiO2 wafer-plates by the diameter of D = 100÷60 mm and by the thickness of hSiO2 ≈ 600 nm, hSi ≈ 470 000 nm, allows to estimate the degree of perfection of crystalline structureMetallography optical supervision of microstructure by means of the microscope ”LOMO MVT”, atomic-force microscopy (AFM) were used. 3. Results and discussion The quasi-longitudinal US velocity V║[001] = 5870 m/s, elastic modulus E001 = ρV║[001] 2 = 80,28 GPa for SiO2/Si from the oscillogram were determined. Temperature dependence of internal friction Q-1(T) in SiO2/Si wafer-plate p-type, doped with B, KDB-7.5(100) diameter D ≈ 76∙10-3 m, thickness hSi ≈ 460∙103 nm with SiO2 layer thickness hSiO2 ≈ 100 nm after X-ray irradiation with dose Dγ ≈ 102 Gy is showed. 4. Conclusions 1. The growth of internal friction maximum height QM -1 testifies the growth of the structural defects concentration n, and the broadening of internal friction maximum ΔQM -1 here represents the relaxation process of structural defects new types in SiO2/Si wafer-plate.2. It was found that as the result of the structural defect annealing IF background Q0 -1 significantly decreases during measuring of IF temperature dependence Q-1(T), which indicates the improvement of SiO2/Si crystal structure.3. The elastic modulus Е, the shear modulus G, Poisson coefficient μ, IF Q-1 are dependent from SiO2/Si wafer-plate anisotropy.4. The value of IF background Q-1 0 after temperature T, mechanical treatments describes the changes of the elastic stress σi fields in SiO2/Si wafer-plate.5. The study of vibrations of disk wafer-plate Si/SiO2 at different harmonic frequencies f0, f2 made it possible to develop the technique for determining the structural defects density nD for semiconductor wafers-substrates.6. The relationship between IF Q-1 value, the logarithmic decrement of ultrasound damping δ and the dislocations density nD was established for disk-shaped semiconductor wafers-substrates. Acknowledgements This work has been supported by Ministry of Education and Science of Ukraine: Grant of the Ministry of Education and Science of Ukraine for perspective development of a scientific direction "Mathematical sciences and natural sciences" at Taras Shevchenko National University of Kyiv.

(Digital Presentation) Adsorption Characteristics of SiO2/Si, Nanocomposites of Multiwalled Carbon Nanotubes and Polyamide, Polyvinyl Chloride, Polyethylene, Porous Polystyrene

Kyiv national university, Kyiv-01601, Ukraineonanko@i.ua : In this work nondestructive method, which is allow to determine from internal friction difference ΔQ-1/Q-1 0 of elastic vibrations structure defects density Nd and the depth of broken layer hb, is offered for SiO2/Si wafer-plates. Outcomes of the evaluation of dynamic characteristics interstitial atoms, vacancy and O-complexes can be applied for account of a condition of an annealing with the purpose of deriving specific structural defects in SiO2/Si wafer-plates. Introduction The leading factor of the elastic anisotropy forming is a crystallography orientation and the orientation of grains on the form with the orientation of miсrocracks, pores [1]. Acoustic emission (AE) allow to receive the additional information about the process of miсrocracks [2]. A non-destructive method for the technological control of the structure defects by measuring internal friction (IF) and elastic modulus E after laser radiation was developed. Experimental procedure The study of influence of structure defects on damping of vibrations in Si/SiO2 plates by the diameter of D = 100÷60 mm and by the thickness of hSiO2 ≈ 600 nm, hSi ≈ 470 000 nm, allows to estimate the degree of perfection of crystalline structure. Brief thermal influence is created by the powerful impulsive nanosecond neodymium laser resulted to local surface tissue fusion. After stopping of the laser radiation action of fusion solidification begun exactly from the surface, but the crater underbody is extended (molten) and created the additional squeezing mechanical tension σi, that „pull” the central part of crater surface in depth with the liquid crater fusion.The pressure dynamics Рi(t) is following: at the beginning of destruction Рi grows quickly, and on the completion of impulse action diminishes instantly on the value of the light pressure created by the laser. Then the diminishing pressure Рi becomes slower, for nanosecond times of laser influence the appearance of acoustic emission (AE) review is important in time range τ ≈ 0.2 nanosec [3,4]. Results and discussion Effects of AE after nanosecond neodymium and ruby laser irradiation in fluid SiO2 are investigated. The fusion depth as the result of relaxation of photothermal elastic strains Ϭi at the large time ∂T/∂t = (55±100).109 K/sec and spatial ∂T/∂x = (1±2).104 K/sm temperature gradients on the SiO2 surface was appraised Δh ≈ 10000 nm. The quantity of reflections N = τ/t ≈ 0.2 nsec/0.02 nsec = 10, approximately 10 times forward-back in specimen. There was a small value of IF background in SiO2 Qo -1 ≈ 2.10-6 to T ≈ 385 K. AE method was measured the group longitudinal wave velocity in fluid SiO2 by water solution of NaCl with the concentration ρ ≈ 38.125 g/l there was v║ = l/τ » 0.03032 m/10.7 mcsec » 2830 m/sec; shear wave velocity v┴ » 2300 m/sec. Oscilloscopegramma of impulses with transversal polarization, which are reflected in SiO2/Si wafer-plate is represented in Figure 1. Figure 1. Oscilloscopegramma of impulses with transversal polarization, which are reflected in SiO2/Si wafer-plate.Taking into account the value of density ρ ≈ 2.63.103 kg/m3, shear modulus G = ρ.v┴ 2 » 13.91 GPa and elastic modulus E = ρ.v║ 2 » 21.06 GPa were determined. Conclusions The value of internal friction background Q-1 0 after temperature, mechanical treatments describes the changes of the elastic stress σi fields in SiO2/Si wafer-plate after laser radiation.After laser radiation outcomes of the evaluation of dynamic characteristics interstitial atoms Sij, vacancy V and O-complexes can be applied for account of a condition of an annealing with the purpose of deriving specific structural defects in SiO2/Si. Acknowledgements This work has been supported by Ministry of Education and Science of Ukraine: Grant of the Ministry of Education and Science of Ukraine for perspective development of a scientific direction "Mathematical sciences and natural sciences" at Taras Shevchenko National University of Kyiv.

Диагностирование непрерывных динамических систем с использованием структурных функций чувствительности

The paper considers an algorithm for searching for single defects of structural blocks of a diagnostic object in the form of an arbitrary change in the parameters of one dynamic block as part of a continuous dynamic system. This approach corresponds to the real picture of the manifestation of a specific structural defect in the unit and its influence on the dynamics of the system. The use of known algorithms of this kind is complicated by the need to use models with trial deviations of parameters, or by the need to analyze the signs of signal transmissions. The algorithm based on trial deviations of model parameters uses the specification of these changes in the model, which is a laborious task. The algorithm for analyzing transmission signs using a normalized diagnostic feature, as well as using a binary diagnostic feature, requires additional calculations of the signs of signal transmissions from block outputs to checkpoints. An algorithm for searching for single defects in the form of changes in the parameters of dynamic blocks is considered, based on the use of a model of the structural sensitivity of integral estimates of the output signals of an object to changes in the dynamic properties of a block. The algorithm allows you to move from the analysis of time functions to the analysis of the numerical values of their integral estimates. This approach allows you to identify a faulty dynamic unit without determining the actual parameters of its transfer function. The procedure for obtaining normalized diagnostic features and calculating a quantitative measure of the distinguishability of defects has been determined. The results of the implementation of the algorithm for the gas pressure stabilization system at a straight-tube furnace for heating oil products of an oil refinery are presented. The implementation of the algorithm shows that the considered algorithm gives acceptable values of the distinguishability of all single defects.

In ovo exposure to cadmium causes right ventricle hyperplasia due to cell proliferation of cardiomyocytes

Cadmium (Cd) is an environmental and occupational pollutant inhaled through smoking or ingested through contaminated food. Yet, little is known about its teratogenicity. In this study, the effects of Cd on embryonic heart development were investigated by exposing Cd to chicken embryos in ovo. Fertilized eggs were treated with Cd at Hamburger-Hamilton Stage (HH)16 and collected at HH35 for histological evaluation of the heart. Cd treatment of 100 μM at HH16 increased embryo mortality at HH35. Specific structural heart defects were not observed in any Cd treatment group, but the relative myocardial tissue area of the right ventricle was increased with Cd exposure.When the HH31 hearts were stained with p-H3S10, the right ventricle had an increased number of cells undergoing proliferation, which was associated with upregulation of Cdk1, Cdk6, CycA, CycD, and CycE detected by qPCR. These findings suggest that Cd exposure from HH16 upregulates proliferation genes and drives overgrowth of the right ventricle. These results grant further attention to Cd teratogenicity on embryonic heart development. Such morphological changes in the heart can potentially affect cardiac function and increase the risk for future cardiovascular diseases, such as heart failure.

Ozone Decomposition on Defective Graphene: Insights from Modeling

We propose via first-principles calculations that graphene tailored with specific structural or foreign-atom defects can be used as catalysts for O3 decomposition. Compared to the pristine graphene, we show that introduction of thermodynamically stable surface defects, that is, Stone-Wales, 555–777 divacancy or nitrogen atoms to graphene, can drastically lower the chemisorption energy barrier of O3. The ozonides once formed can evolve into epoxide or ketone-like intermediate structures on graphene, which assist in the sustainable conversion of O3 to O2. The minimal energy needed to complete the O3 decomposition cycle on different graphene substrates has the order of E555–777 (0.22 eV) < EN-doping (0.33 eV) < EStone-Wales (0.61 eV) < Epristine graphene (1.08 eV). As two most promising catalysts, 555–777 divacant and N-doped graphene shows a clear adsorption selectivity to O3 under the ambient conditions. N-doped graphene outperforms 555–777 divacant graphene at the stage of physisorption in that the former catalyst separates O3 from the ambient gases by a much larger adsorption energy. These results and conclusions are a pivotal and necessary step that should stimulate both the proof-of-principle experiments and the computational search of metal-free catalysts for O3 decomposition.

Effect of the addition of the natural and treated açaí stone in structural mortars

&lt;abstract&gt; &lt;p&gt;The açaizeiro is a palm tree present on a large scale in the northern region of Brazil and in others countries, such as Colombia and Peru, its fruit constitutes one of the main forest products of great economic potential to exportation. However, a generation of large amounts of waste during its processing represents a serious environmental problem, since about 365 tons of açaí stone are discarded in landfills daily in Brazil. The objective of this work was to evaluate the potential of using açaí stone as a substitute of 25% in mass natural sand with filler function, in the development of structural mortars with reference mixture of ratio 1:2:0.45 (cement:sand:water) and waste mixture with1:1.5:0.5:0.45 (cement:sand:açai stone:water), that both mixtures are relationship adopted for structural mortar in the literature. Three different types of mortar were made for evaluation, the reference (without adding stones) and with the addition of natural stone (without treatment and treated with NaOH). After the incorporation of the stones, consistency, water retention, incorporated air content and density in fresh mortars were analyzed, in the fresh state. For evaluation in a hardened state, cylindrical specimens (50 mm × 100 mm) were molded, for compression strength and density tests. The optimum composition was also analyzed with confocal microscopy. It can be seen that in the compression strength tests, mortars with the addition of natural and treated stone showed a reduction, decreasing from 6.25 MPa (reference), to 5.55 MPa (natural stone) and 1.89 MPa (treated stone), this showed that the natural stone mortar was above the minimum of 5.00 MPa reported in the literature. As for density, the evaluations demonstrate a beneficial effect to the incorporation of the stone, which formed lighter mortars, decreasing from 2.12 to 1.79 g/cm&lt;sup&gt;3&lt;/sup&gt; in the natural composition and 1.85 g/cm&lt;sup&gt;3&lt;/sup&gt; in the treated composition, in both situations with additions, the values were within the maximum limit of 2 g/cm&lt;sup&gt;3&lt;/sup&gt; that the literature suggests for structural mortars. In addition, the results of water retention showed an increase in the treated composition (97.28%) in relation to the reference (95.84%), an increase characterized by the treatment in NaOH that reduced the hygroscopic characteristics of the stones, the mixture mortar with treated seed, as well as the reference, presented values above 95%, which is recommended by other studies. The evaluations show that there is a potential for specific structural applications of these mortars, since in all tests the composition with natural stone is within the ideal parameters by Brazilian standard, in addition to helping to solve the environmental impacts caused by discard this waste. As it is a mortar with low compressive strength, its application is suggested for the purpose of repairing specific structural defects that arise in the molding stage of beams, slabs and columns, located in regions with low load demand.&lt;/p&gt; &lt;/abstract&gt;

Correlation between Microstructure and Chemical Composition of Zinc Oxide Gas Sensor Layers and Their Gas-Sensitive Properties in Chlorine Atmosphere.

In this article, we present results concerning the impact of structural and chemical properties of zinc oxide in various morphological forms and its gas-sensitive properties, tested in an atmosphere containing a very aggressive gas such as chlorine. The aim of this research was to understand the mechanism of chlorine detection using a resistive gas sensor with an active layer made of zinc oxide with a different structure and morphology. Two types of ZnO sensor layers obtained by two different technological methods were used in sensor construction. Their morphology, crystal structure, specific surface area, porosity, surface chemistry and structural defects were characterized, and then compared with gas-sensitive properties in a chlorine-containing atmosphere. To achieve this goal, scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and photoluminescence spectroscopy (PL) methods were used. The sensing properties of obtained active layers were tested by the temperature stimulated conductance method (TSC). We have noticed that their response in a chlorine atmosphere is not determined by the size of the specific surface or porosity. The obtained results showed that the structural defects of ZnO crystals play the most important role in chlorine detection. We demonstrated that Cl2 adsorption is a concurrent process to oxygen adsorption. Both of them occur on the same active species (oxygen vacancies). Their concentration is higher on the side planes of the zinc oxide crystal than the others. Additionally, ZnO sublimation process plays an important role in the chlorine detection mechanism.

High-temperature annealing effect on photoluminescence of ZnO nanoparticles produced by laser ablation in hydrogen peroxide

Zinc oxide nanoparticles were for the first time produced by laser ablation of a solid zinc target in 35% liquid hydrogen peroxide. As-produced nanoparticle-based films on Si substrates were visualized by scanning electron microscopy (SEM) and energy-dispersion x-ray micro-spectroscopy (EDX) as amorphous, containing highly defective mixed oxide/hydroxide structures and crystallization-water molecules. Specific structural defects, damping the photoluminescence band of the nanoparticles peaked near 550 nm for the 488 nm pump laser wavelength, were annealed in air at temperatures 200-400 °C over 1-2 hours, with the accompanying strong photoluminescence yield and the appearance of the absorption cut-off near 350 nm. However, the following annealing at higher temperatures up to 1200 °C for time periods variable in the range of 1-3 hours, resulted in the damping of the photoluminescence. According to x-ray diffraction (XRD) characterization of the nanoparticle-based films on fluorite substrates, high-temperature annealing at 800 C for 1 hour induce crystallization of the common hexagonal ZnO phase (wurzite structure) via loss of peroxide bridges, crystallization water molecules and other structural defects. Meanwhile, annealing at 1200 °C yields in another distinct crystalline phase of ZnO, which appears to be a sphalerite.

Identifying Structural Defects in Hematite Photoanodes through Structure-Property Analysis

Hematite photoanodes continue to exhibit highly variable photoelectrocatalytic water oxidation performance across the literature despite over two decades of intensive research. Studies have advanced the understanding of fundamental photophysical behavior of key electron transfer and enriched material design in hematite photoanodes, but poor photoelectrocatalytic performance and high variability in reported behavior indicate missing information. We believe that a lack of the chemical nature of structural defects in hematite and their specific impacts on material properties and photoelectrocatalytic water oxidation is a key problem. We target this issue with a structure-property analysis using photoelectrochemical, X-ray diffraction, Raman and UV-visible spectroscopic data on a series of hematite photoanodes. The analysis reveals a formally Raman inactive vibrational mode in hematite films prepared by annealing lepidocrocite films whose intensity varies with annealing protocols. Correlations between the intensity of this feature in the Raman spectrum with photocurrent density, semiconductor band structure, and the onset of photoelectrocatalysis signifies systematic changes in the magnitude of a crystal lattice distortion. Analysis of the nature of these key Raman vibrations and the synthetic conditions lead us to conclude that the observed defects are iron vacancies induced by trapped protons within the crystal lattice. This finding provides a means to rapidly diagnose a specific structural defect and will aid in the optimization of fabrication protocols for hematite photoanodes. Figure 1

The lithium ions storage behavior of heteroatom-mediated echinus-like porous carbon spheres: From co-doping to multi-atom doping

This study proposed a facile method to prepare echinus-like porous carbon spheres (PCS) with different heteroatom doping for lithium ions battery (LIBs). A metal-organophosphine framework (MOPF) was synthesized by employing riboflavin sodium phosphate as an organic ligand to conjugate with metal ions and then carbonized at mild temperature, leading to the formation of heteroatom doped PCS (H-PCS). As a result, (N, P) co-, (N, P, Ni) tri-, (N, P, Co) tri- and (N, Ni, Co, P) tetra-doped PCS were obtained to examine the insight into lithium-ion storage behavior of H-PCS. It was found that the specific surface area, pore texture and structural defects of H-PCS were dependent on doping of heteroatoms as well as the charge transfer resistance and Li-ion diffusion coefficient. Significantly, the redox reaction potential during the charge/discharge could be mediated upon the doping. Thus, when evaluated as anode for LIBs, the (N, Ni, Co, P) tetra-doped PCS exhibited highly reversible capacity of 680 mAh g−1 at 0.1 A g−1, excellent rate capability (115.9 mAh g−1 at 1.0 A g−1) and superior cycling performance (399.6 mAh g−1 at 0.1 A g−1). Moreover, the cyclic voltammogram measurements demonstrated that the doping of metal atoms was favorable for improving the capacitive contribution of surface limited diffusion. Thus, this work highlighted the importance of HCP with defined doping which could be considered as one of the prominent candidates for high-performance LIBs’ anode.

Low temperature specific heat anomaly with boson peak in isotope-enriched boron carbides B4·3C – B10C

The low temperature specific heat of boron carbide exhibits characteristic deviations from the classical Debye model (c ∝ T3). Including α-rhombohedral boron, the degree of deviations from this model is proportional to the concentration of B(3) voids in the structure and to the content of B11C icosahedra, respectively. The observed effects of specific structural defects can be described in accordance with the model of voids in amorphous Si proposed by Nakhmanson and Drabold. Results of β-rhombohedral boron, largely corresponding to the Debye model, are used for comparison.

G-C3N4 synthesized from NH4SCN in a H2 atmosphere as a high performance photocatalyst for blue light-driven degradation of rhodamine B.

Graphitic carbon nitride (g-C3N4) was prepared by a simple thermal polymerization method in this work. The effects of precursor type, thermal polymerization temperature, constant temperature time and atmosphere on the crystal structure, morphology, elemental composition, valence distribution, light absorption properties and photocatalytic activity of the prepared photocatalytic materials were investigated. Taking rhodamine B (RhB) as the target degradant, the blue light catalytic activity of the photocatalytic material was studied in detail. The experimental results showed that the final pyrolysis temperature and constant temperature time are positively related to the adsorption characteristics and photocatalytic ability of the prepared materials. In addition, the adsorption capacity and photocatalytic activity of the products obtained in Ar and H2 atmospheres are better than those produced in CO and CH4, which can be attributed to the combined effect of large specific surface area and structural defects of the materials. The sample's large specific surface area, wide band gap, and excellent photogenerated carrier separation and transfer capabilities make the adsorption performance and photocatalytic performance of the products obtained with ammonium thiocyanate and thiourea as precursors better than those prepared from melamine and dicyandiamide. g-C3N4 prepared by using ammonium thiocyanate as precursor at 550 °C for 5 h under a hydrogen atmosphere showed the best catalytic activity for the degradation of RhB under blue light. It was demonstrated that g-C3N4 prepared exhibited good stability and reusability after four repeat experiments. The active components that play major roles in the degradation of RhB described herein were holes and superoxide radicals, which was inferred by free radical trapping experiments. This work provides a theoretical basis for the idea of converting the mixed salts of desulfurization waste liquid containing ammonium thiocyanate into an excellent photocatalyst g-C3N4 with visible light response.