Surface Of Microcrystals Research Articles

Pioneering preparation and analysis of a clean surface on a microcrystal, mined by a focused ion beam

We demonstrate a series of procedures to prepare a clean surface of micro-sized graphite, mined from a bulk flake and securely affixed onto a macroscopic Si plate by focused ion beam scanning electron microscope. Analyses of structure and electronic (chemical) states were made using micro-beam X-ray photoelectron spectroscopy and angle-resolved photoemission spectroscopy. At the surface of the micro graphite, the band dispersion from a single-domain structure was observed. The proposed methodology showcases its capability to produce clean and high-quality micro samples suitable for surface-sensitive analyses. This technique paves the way to investigate surfaces of unexplored microcrystals embedded in complex materials.

In Situ Loading of Cu Nanocrystals on CsCuCl3 for Selective Photoreduction of CO2 to CH4.

Rational design and facile synthesis of efficient environmentally friendly all-inorganic lead-free halide perovskite catalysts are of great significance in photocatalytic CO2 reduction. Aiming at photogenerated charge carrier separation and CO2 reaction dynamics, in this paper, a CsCuCl3 /Cu nanocrystals (NCs) heterojunction catalyst is designed and synthesized via a simple acid-etching solution process by using Cu2 O as the sacrificed template. Due to the disproportionation reaction of Cu2 O induced by concentrated hydrochloric acid, Cu NCs can be deposited onto the surface of CsCuCl3 microcrystals directly and tightly. As revealed by photoelectrochemical analysis, in situ Fourier transform infrared spectra, etc., the Cu NCs contribute a lot to extracting photoelectrons of CsCuCl3 to improve the charge separation efficiency, regulating the CO2 adsorption and activation, and also stabilizing the reaction intermediates. Therefore, CsCuCl3 /Cu heterojunction exhibits a total electron consumption rate of 58.77µmol g-1 h-1 , which is 2.9-fold of that of single CsCuCl3 . Moreover, high CH4 selectivity of up to 92.7% is achieved, which is much higher than that of CsCuCl3 (50.4%) and most lead-free halide perovskite-based catalysts. This work provides an ingenious but simple strategy to rationally design cocatalysts in situ decorated perovskite catalysts for manipulating both the catalytic activity and the product selectivity.

Adsorption Kinetics of Type-III Antifreeze Protein on Ice Crystal Surfaces.

The spatio-temporal distribution of type-III antifreeze protein (AFP-III) molecules labeled with fluorescent isocyanate (FITC) was visualized at the interfaces between ice and solutions with an FITC-labeled AFP-III (F-AFP-III) concentration of 20-800 μg/mL by fluorescence microscopy. The number density of F-AFP-III on the surface of ice microcrystals was calculated from the calibrated fluorescence intensity. The adsorption of F-AFP-III molecules on the ice crystal surfaces proceeded at a finite rate and then reached the saturation level. The time course of the number density of adsorbed F-AFP-III molecules could be well represented by Langmuir's model. The characteristic adsorption time of F-AFP-III, the adsorption coefficient k1 = (0.5 ± 0.05) × 10-4 (μg/mL)-1 s-1, and the desorption coefficient k2 = 0.005 ± 0.002 s-1 were determined using the Langmuir's model and obtained experimental data. We found that the adsorption of F-AFP-III could have different kinetics depending on the solution conditions and the type of fluorescence molecules conjugated with AFP-III.

Self-powered white light photodetector with enhanced photoresponse using camphor sulphonic acid treated CsPbBr3 perovskite in carbon matrix

The surface modification of CsPbBr3 perovskite provides an effective way of defect passivation for device applications. In this work, Camphor sulfonic acid (CSA) was used to modify the surface of CsPbBr3 microcrystals (MCs) and helped in enhancement of Photoluminescence (PL) emission, photoresponse, and photodetectivity. We fabricated the perovskite FTO/c-TiO2/CsPbBr3-CSA/Carbon composite self-powered photodetector. The device exhibited higher photo responsivity and detectivity of 1.523 mA/W and 2.1454 × 109 Jones, respectively, under white light with excellent stability on high ON/OFF cycles.

S-Scheme BiOCl/MoSe2 Heterostructure with Enhanced Photocatalytic Activity for Dyes and Antibiotics Degradation under Sunlight Irradiation.

Semiconductor photocatalysis is considered to be a promising technique to completely eliminate the organic pollutants in wastewater. Recently, S-scheme heterojunction photocatalysts have received much attention due to their high solar efficiency, superior transfer efficiency of charge carriers, and strong redox ability. Herein, we fabricated an S-scheme heterostructure BiOCl/MoSe2 by loading MoSe2 nanosheets on the surface of BiOCl microcrystals, using a solvothermal method. The microstructures, light absorption, and photoelectrochemical performances of the samples were characterized by the means of SEM, TEM, XRD, transient photocurrents, electrochemical impedance, and photoluminescence (PL) spectra. The photocatalytic activities of BiOCl, MoSe2, and the BiOCl/MoSe2 samples with different MoSe2 contents were evaluated by the degradation of methyl orange (MO) and antibiotic sulfadiazine (SD) under simulated sunlight irradiation. It was found that BiOCl/MoSe2 displayed an evidently enhanced photocatalytic activity compared to single BiOCl and MoSe2, and 30 wt.% was an optimal loading amount for obtaining the highest photocatalytic activity. On the basis of radical trapping experiments and energy level analyses, it was deduced that BiOCl/MoSe2 follows an S-scheme charge transfer pathway and •O2−, •OH, and h+ all take part in the degradation of organic pollutants.

Eroding the Surface of Rare Earth Microcrystals through Vanadate Ions for Considerable Improvement of Luminescence

Developing an efficient approach to improve the luminescence of the phosphors without heating processing is a challenge, but attracts much attention. In the present paper, prismatic microcrystals of RE4O(OH)9NO3 (RE = Y, Eu) were synthesized by a hydrothermal reaction at 180 °C for 24 h. The reaction with VO3− did not change the crystal structure of the microcrystals and VO3− substituting for NO3− anions did not take place. However, it contributed to the formation of amorphous particles containing VO3− on the surface of a prism, which is similar to the surface corrosion of a metal, called “surface eroding”. Therefore, surface modification was successfully achieved by eroding the surface of the microcrystals through the reaction with vanadate ions. As a result of VO3−→Eu3+ energy transfer and the light-harvesting ability of VO3−, the red emission intensity at 617 nm of the modified microcrystals greatly increased. Eroding the surface of rare earth microcrystals recommends a new paradigm for luminescence improvement of rare earth compounds.

Morphological features and phase composition of W-containing coatings formed on diamond via its interaction with WO3

In the present work, W-containing coatings were deposited on the surface of diamond microcrystals. The coatings formed as diamond reacted with a WO3 powder in the die of a hot press at elevated temperatures. The morphology and phase composition of the coatings were studied as functions of the treatment temperature and treatment time. The coated diamond crystals were investigated by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. After treatment of the mixture at 850 °C for 15 min, WO2 and W18O49 were found on the diamond surface. After treatment at 950 °C (15 min), tungsten was the dominant phase of the coating. Treatment at 1150 °C (15 min) led to the formation of the WC and W2C phases; no metallic tungsten was present in the coating obtained at this temperature. The reaction sequence describing the coating formation process was proposed. During the coating formation, the deposition selectivity with regard to the diamond facet was observed. The {100} facets of diamond were preferentially coated. The coating developed through the formation and coalescence of islands, which were of square shape on the {100} facets and of triangular shape on the {111} facets of diamond.

Preparation of Ag3PO4/α-Fe2O3 hybrid powders and their visible light catalytic performances.

The inefficiency of conventional photocatalytic treatment for removing rhodamine B is posing potential risks to ecological environments. Here, we construct a highly efficient photocatalyst consisting of Ag3PO4 and α-Fe2O3 hybrid powders for the treatment of rhodamine B. Ag3PO4 nanoparticles (nanoparticles, about 50 nm) are uniformly dispersed on the surface of α-Fe2O3 microcrystals (hexagonal sheet, about 1.5 μm). The Ag3PO4-deposited uniformity on the α-Fe2O3 surface first increased, then decreased on increasing the hybrid ratio of Ag3PO4 to α-Fe2O3. When the hybrid ratio of Ag3PO4 to α-Fe2O3 is 1 : 2, the distribution of Ag3PO4 particles on the sheet α-Fe2O3 is more uniform with excellent Ag3PO4/α-Fe2O3 interface performance. The catalytic degradation efficiency of hybrids with the introduction of Ag3PO4 nanoparticles on the α-Fe2O3 surface reached 95%. More importantly, the hybrid material exhibits superior photocatalytic stability. Ag3PO4/α-Fe2O3 hybrids have good reusability, and the photocatalytic efficiency could still reach 72% after four reuses. The excellent photocatalytic activity of the as-prepared hybrids can be attributed to the heterostructure between Ag3PO4 and α-Fe2O3, which can effectively inhibit the photoelectron–hole recombination and broaden the visible light response range.

Ultrafast catalytic reduction of toxic nitroaromatics and organic colouring dyes by using Au/ZIF-11: Efficient wastewater treatment

An ultrafast catalytic method to reduce various toxic nitrophenols, nitroaniline and organic dyes by using gold nanoparticles decorated-ZIF-11 (Au/ZIF-11) composite for wastewater treatment has been described. Three new Au/ZIF-11 composites (abbreviated as Au0.1Z, Au0.2Z and Au0.3Z) have been synthesized via direct reduction of HAuCl4 (0.1 to 0.3 mM) using sodium borohydride (NaBH4) in the suspension of pre-synthesized ZIF-11 and characterized by various spectroscopic and morphological/surface techniques. TEM images confirmed the formation of spherical and uniformly distributed gold NPs, having average particle size of 7.35 ± 0.95 nm, on the surface of ZIF-11 microcrystals. Au0.2Z displayed exceptionally high catalytic efficiency towards the reduction of nitrophenols (2-NPhenol, 3-NPhenol and 4-NPhenol), 4-nitroaniline (4-NANI) and 2,4,6-triNPhenol at substrate's concentration: 1.58 × 10−4 M in the presence of NaBH4 (0.04 M) at ambient condition. k̅app, (apparent rate constant) was (4.64/3.24/1.90) × 10−2 s−1 having activity coefficient k′ (k′ = k̅app/M) value of 928.83, 647.59 and 380.61 s−1 g−1 for 3-NPhenol, 4-NPhenol and 2-NPhenol, respectively, using Au0.2Z ([catalyst] = 15.87 μg/mL). Further, Au0.2Z can be re-used up to 5 cycles with more than 90% conversion efficiency. Moreover, Au0.2Z also reduced organic colouring dyes (methylene blue (MB), rhodamine B (RhB), congo red (CR) and methyl orange (MO)) in the presence of NaBH4 and the corresponding k̅app was 7.88 × 10−3–9.22 × 10−4 s−1 with k′ value of 157.71–9.22 s−1 g−1. The probable mechanism involving Langmuir-Hinshelwood apparent first-order kinetics model described that Au nanoparticles immobilized onto ZIF-11 may serve as antenna to transfer electrons and hydrogen from borohydride (BH4−) ions to the acceptor (nitro group/organic dye). Therefore, Au0.2Z can effectively be used for environmental remediation application to remove organic pollutants from the industrial wastewater.

Chemical Stability of Framboidal Pyrite Containing Geogenic Arsenic in Alluvial Sediments

The number of underground construction projects is increasing worldwide, resulting in the production of a huge amount of waste excavated material. Excavated soils from alluvial plains are rich in pyrite. When these soils are exposed to air, the pyrite oxidizes, resulting in the generation of H2SO4, which acidifies the soil and releases potentially harmful trace metals and metalloids such as arsenic into the environment. Polarized light microscopy and field‐emission scanning electron microscopy (FE‐SEM) revealed the presence of framboidal pyrite within the shells of microorganisms in alluvial soil samples collected in Japan. Analysis with FE‐SEM/energy‐dispersive X‐ray spectrometry and electron probe microanalysis (EPMA) revealed that this framboidal pyrite contained As. When soaked in distilled water for 6 h or in 1 M HCl for 2 h, the framboidal pyrite remained unchanged; however, when it was soaked in 10% H2O2 for 6 h, it was oxidized and swelling was observed on the surface of pyrite microcrystals. A 1 M HCl extraction test indicated that arsenic release from framboidal pyrite would be difficult under acidic conditions. Framboidal pyrite in alluvial sediment is stable at low pH; however, it is unstable under oxidative conditions, suggesting that waste alluvial soil should be kept under reducing conditions. The chemical stability of geogenic arsenic in pyrite in soils and sediments provides a useful way to determine a correct handling of the soils for reclamation or as a covering material.Core Ideas Chemical stability of framboidal pyrite in acidic or oxidative conditions was examined. Geogenic As was accumulated mostly in framboidal pyrite. Framboidal pyrite was stable in acidic conditions but was unstable in oxidative conditions.

Mechanical Exfoliation Assisted by Molecular Tweezers for Production of Sulfur-Based Semiconducting Two-Dimensional Materials

The liquid and mechanical exfoliation techniques, used to produce two-dimensional materials (2DM), are merged in a mechanical exfoliation assisted by molecular tweezers technique (MEAMT). Sulfur-based semiconducting materials, that is, WS2 or MoS2 microcrystals dispersed in a liquid, are functionalized with thiolated long chain polymers. The polymer chains bound to the surface of microcrystals are stretched by ultrasonication, which generates a strong mechanical force. The force of the polymer tweezers overcomes the van der Waals force that holds the sheets of the crystals. By changing the chain length of polymer tweezers, the dimensions and the yield percentage of the MoS2 and WS2 sheets produced by MEAMT are controlled. The prepared 2DM functionalized with polymer improve their applicability and stability. Upon comparison to the typical liquid exfoliation technique, the WS2 and MoS2 sheets produced by MEAMT resulted in a higher yield percentage and higher photoluminescence (PL) quantum efficiency. The h...

Efficient solid-state and dual-mode photoluminescence of carbon-dots/NaLuF4 microcrystals for multifunctional applications

The carbon-dots/NaLuF4 microcrystals have been synthesized by the hydrothermal method and bright blue emission from carbon dots is observed in aqueous and solid state under 365 nm excitation. Self-quenching property of the carbon-dots/NaLuF4 microcrystals under solid state was deeply investigated, by changing the ratio of citric acid (CA) and ethylenediamine (DHE). The results indicate that the carbon dots can be effectively adsorbed and dispersed on the surface of NaLuF4 microcrystals, suppressing the aggregation of carbon dots. Furthermore, the upconversion luminescence can also be realized under 980 nm laser excitation. From the above observations, the carbon-dots/NaLuF4 microcrystals not only reveal emission property of carbon dots and NaLuF4, respectively, but also optimize the property of carbon dots. It provides a promising new strategy to prevent the carbon dots quenching in solid state and the carbon-dots/NaLuF4 microcrystals may have potential multi-applications in different fields including temperature sensing, solid-state display lighting as well as security inks.

Hierarchical nano-on-micro copper with enhanced catalytic activity towards electro-oxidation of hydrazine

The electrochemical properties of catalyst materials are highly dependent on the materials structure and architecture. Herein, nano-on-micro Cu electrodes are fabricated by growing Cu microcrystals on Ni foam substrate, followed by introducing Cu nanocrystals onto the surface of the Cu microcrystals. The introduction of Cu nanocrystals onto the surface of Cu microcrystals is shown to dramatically increase the electrochemically active surface area and thus significantly enhances the catalytic activity of the catalyst electrode towards electro-oxidation of hydrazine. The onset potential (-1.04 V vs. Ag/AgCl) of the nano-on-micro Cu electrode is lower than those of the reported Cu-based catalysts under similar testing conditions, and a current density of 16 mA·cm-2, which is 2 times that of the microsized Cu electrode, is achieved at a potential of -0.95 V vs. Ag/AgCl. Moreover, the nano-on-micro Cu electrode demonstrates good long-term stability.

Properties of Resistive Hydrogen Sensors as a Function of Additives of 3D-Metals Introduced in the Volume of Thin Nanocrystalline SnO2 Films

Analysis of the results of studying electrical and gas sensitive characteristics of the molecular hydrogen sensors based on thin nanocrystalline SnO2 films coated with dispersed Au layers and containing Au+Ni and Au+Co impurities in the bulk showed that the characteristics of these sensors are more stable under the prolonged exposure to hydrogen in comparison with Au/SnO2:Sb, Au films modified only with gold. It has been found that introduction of the nickel and cobalt additives increases the band bending at the grain boundaries of tin dioxide already in freshly prepared samples, which indicates an increase in the density Ni of the chemisorbed oxygen. It is important that during testing, the band bending eφs at the grain boundaries of tin dioxide additionally slightly increases. It can be assumed that during crystallization of films under thermal annealing, the 3d-metal atoms in the SnO2 volume partially segregate on the surface of microcrystals and form bonds with lattice oxygen, the superstoichiometric tin atoms are formed, and the density Ni increases. If the bonds of oxygen with nickel and cobalt are stronger than those with tin, then, under the prolonged tests, atomic hydrogen will be oxidized not by lattice oxygen, but mainly by the chemisorbed one. In this case, stability of the sensors’ characteristics increases.

Synthesis of Ag-coated TiNb2O7 composites with excellent electrochemical properties for lithium-ion battery

Ag/TiNb2O7 composites are synthesized by a facile and effective solid state method and following solvothermal process. It is found that Ag nanoparticles are deposited on the surfaces of TiNb2O7 microcrystals. When Ag/TiNb2O7 is used as the anode for lithium-ion battery, its 2nd discharge capacity is 275.3mA·h·g−1 at 1C, larger than that of pure TiNb2O7 (234.2mA·h·g−1); moreover, Ag/TiNb2O7 exhibits better rate capacity performance than TiNb2O7. The electronic conductivity of the Ag/TiNb2O7 electrode is increased for the incorporation of Ag nanoparticles, which can effectively improve the electron transport in the Li+ insertion/extraction process and accordingly enhance the electrochemical performance.

Effect of iodine doping in the deposition solution and iodine vapor pressure in the sensitization treatment on the properties of PbSe films

Effect of iodine-doping in the deposition solution and iodine vapor pressure during the sensitization process on the morphological, microstructural, electrical, and optical properties of PbSe films was studied. Undoped and iodine-doped PbSe films of polycrystalline particles were coated on thermally oxidized silicon substrates by chemical bath deposition. The PbSe films were oxidized at 380°C for 30 min and then iodinated at different iodine vapor pressures at 380°C for 5 min. When the iodine vapor pressure was below 20 Pa, PbSeO3 was the main phase formed on the surface of PbSe microcrystals for both undoped and iodine-doped films. As the iodine vapor pressure was increased above 20 Pa, Pb3I2O2 and PbI2 phases were formed in both types of films and PbSeO3 disappeared in the undoped film. Only the iodine-doped films showed photo response. The sheet resistance and IR signal-to-noise ratio had maximum values at the iodine vapor pressure of 17.5 Pa in the iodine-doped film. The x-ray diffraction spectra, scanning electron microscopy morphologies, and EDS analyses of the sensitized PbSe films show that the main role of iodine in the sensitization is helping solid-state sintering of PbSe microcrystals which may lead to redistribution of oxygen atoms in the effective atomic sites.

Trapping gases in metal-organic frameworks with a selective surface molecular barrier layer.

The main challenge for gas storage and separation in nanoporous materials is that many molecules of interest adsorb too weakly to be effectively retained. Instead of synthetically modifying the internal surface structure of the entire bulk—as is typically done to enhance adsorption—here we show that post exposure of a prototypical porous metal-organic framework to ethylenediamine can effectively retain a variety of weakly adsorbing molecules (for example, CO, CO2, SO2, C2H4, NO) inside the materials by forming a monolayer-thick cap at the external surface of microcrystals. Furthermore, this capping mechanism, based on hydrogen bonding as explained by ab initio modelling, opens the door for potential selectivity. For example, water molecules are shown to disrupt the hydrogen-bonded amine network and diffuse through the cap without hindrance and fully displace/release the retained small molecules out of the metal-organic framework at room temperature. These findings may provide alternative strategies for gas storage, delivery and separation.

The effect of oxygen on sensitization of AgBrI crystals with anionic dye

A mechanism is suggested for the effect of oxygen on spectral sensitization of AgBrI microcrystals (MCs) with anionic dye adsorbed on the surface, which adequately describes the changes of both luminescent and spectral-sensitometric properties of this system. It is shown that the effect of oxygen on the spectral sensitization of AgBrI MC with anionic dye cannot be explained only by desensitization of the AgBrI MC sensitivity as has been suggested in the literature, but rather its effect on the spectral sensitization of AgBrI MC was not so unambiguous. In the framework of the suggested mechanism such ambiguity is due to the fact that the Ag+ and Ag2+ silver centers that participate in the generation recombination processes and are different in structure, interact on the surface of the AgBrI MC with different aggregate forms of the dye, which are in turn differently affected by oxygen. Understanding physicochemical processes occurring in the considered system allows using the obtained results in holographic and spectrozonal photographic materials, gas-phase sensors, and in solar-energy systems.

Dye sensitization of photoconductivity of polycrystalline silicon

The DC photoconductivity of powder silicon samples with organic dyes applied to the surface of microcrystals was studied. Effective sensitization of photoconductivity in the absorption band of the dyes in the visible part of the spectrum was found.

Formation of Cu-related emission centers under thermal doping of ZnS powders with CuCl and CuCl2

The photoluminescence (PL), PL excitation and electron paramagnetic resonance spectra of powderlike ZnS doped with Cu from CuCl and CuCl2 compounds at 800°C with restricted access of atmospheric air or in He flow were investigated. It is shown that the contribution of blue and green PL bands to PL spectra depends on the compounds used for doping and on the annealing conditions. The appearance of Cu clusters on the surface of ZnS microcrystals for both doping compounds is found. These clusters manifest themselves in the presence of broad line in electron paramagnetic resonance spectra and are the additional source for the doping of ZnS powder. The chemical reactions upon doping are analyzed. It is shown that these reactions control the concentration of the recombination centers responsible for blue and green PL bands and are also the reason of Cu clusters appearance. Under annealing in He flow when volatile components are removed by flowing gas, the dominant process can be the doping of ZnS from Cu clusters. This allows obtaining the blue band mainly. The localization of recombination centers responsible for blue and green emissions is discussed.