Pure Crystal Phase Research Articles

Photocatalytic performance of Soot/TiO2 nanocomposite against toxic dye

Nowadays, composing semiconductors with carbon structures to enhance their optical properties shows huge interest as a nanophotocatalyst for trending applications (i.e., photodegrading pollutants). In this study, TiO2 and soot/TiO2 nanocomposites were prepared via a one-step sol-gel assisted hydrothermal method, using a temperature of 220 °C and a reaction time of 6 h. Characterization by X-ray diffraction and Raman spectroscopy confirmed that the resulting TiO2 and soot/TiO2 materials exhibited a pure anatase crystal phase, without the presence of other TiO2 polymorphs. Soot composition on TiO2 showed enhanced photocatalysis properties, such as a lower combination rate of electron-hole pairs than pure TiO2. Crystal violet (CV) was applied as a pollutant model to examine the photocatalytic degradation of synthesized TiO2 and soot/TiO2. The photodegradation experiments of CV dye in its aqueous media by UV light interaction showed 26.63 % and 89.09 % in the presence of TiO2 and soot/TiO2 nanocomposite, respectively. In the basic media (pH 11), maximum photodegradation (97.95 %) is attained when 0.004 g of Photocatalyst (soot/TiO2) is used. Using the recycled photocatalyst, the dye's photodegradation efficiency remained high throughout the reusability cycles, even after four consecutive cycles.

Engineering of Soft Urea Synthesized Ni3n Nanomaterials for Oxygen Evolution Reaction

Most active electrocatalysts include platinum-group metals (PGMs) and their alloys for electrochemical water splitting, but they are strongly limited by material cost and scarcity. [1] On the other hand, transition metal nitrides overcome this bottleneck and show high electrical conductivity, making them catalytically active for water electrolysis. The high conductivity is based on the incorporation of nitrogen atoms into the unit cell of metal, leading to their d-band contraction with electron density enhancement below Fermi level. [2] For instance, metallic nickel nitride (Ni3N) has been widely reported as a promising electrocatalyst material to accelerate the oxygen evolution reaction (OER) by in-situ forming a nickel (oxy)hydroxide [Ni(OH)2 and NiOOH] layer. [3] The Ni3N materials can be prepared by single step soft-urea route to obtain pure crystal phase [4] or a composite with carbon [5], which rises the following two research questions: 1. What are the optimal synthesis parameters of the soft-urea route to control the structure of Ni3N? 2. What is the relationship between structure and OER activity for Ni3N materials?In this work, we used the soft-urea route to prepare Ni3N materials by varying the ratios of NiCl2, urea and ethanol as precursor chemicals. The precursors were made into a gel by magnetic stirring having metal:urea ratio of 1:5, and then heated up to 400 ºC in a tubular furnace with constant flow of argon. The as-prepared Ni3N were then characterized by X-ray diffraction (XRD), elemental analysis (CHN), transmission electron microscopy (TEM) equipped with an energy-dispersive X-ray spectroscopy (EDX) and X-ray absorption spectroscopy (XAS).Based on the quantitative Rietveld refinement, the formation of pristine Ni3N materials is strongly controlled by the annealing temperature. In addition to the Ni3N phase, we observed the formation of the fcc Ni phase (0 – 10 wt.%) as a minor phase. The TEM images show individual particles of below 100 nm in size. Rotating disc electrode (RDE) technique was employed to establish the electrochemical OER activity of Ni3N materials by sweeping the potential from 1.3 to 1.8 VRHE at 10 mV s-1 in Ar-saturated 0.1 M KOH. Polycrystalline Ni and Ni particles are taken as reference materials. We observed an improvement of the OER activity as the overpotential at 10 mA cm-2 (normalized by the geometric surface area) reduced from 379 mV (poly-Ni) to 358 mV (Ni3N). Furthermore, in-situ XAS studies were performed to better understand the nature of the redox reactions between Ni species and the in-situ formation of nickel (oxy)hydroxide [Ni(OH)2 and NiOOH] layers before and during the OER as a function of the applied potential. Based on the in-situ XANES data, we correlated the structure of Ni3N/fcc-Ni/carbon composite with observed OER activity under alkaline conditions.To summarize, we were able to prepare a composite of Ni3N/fcc-Ni/carbon material with improved OER activity via soft-urea route. The in-situ formation of the layered nickel (oxy)hydroxide [Ni(OH)2 and NiOOH] layers as the catalytically active OER species were probed by in-situ XANES data.

Stabilization of various structural phases and magnetic properties of chemically synthesized Co-Ni-Ga nanoparticles

Polycrystalline Co-Ni-Ga ferromagnetic shape memory alloy nanoparticles with phase single austenite (A), martensite (M) and gamma (γ) structures have been obtained for the first time through a facile template-less chemical method. Average crystallite size of A, M and γ phase nanoparticles are 25 nm, 22 nm and 21 nm, respectively. All the synthesized nanoparticles exhibit soft ferromagnetic behavior with saturation magnetization varying from 21.22 to 77.65 emu/g and effective magnetic anisotropy of ∼105 J/m3 at 5 K. Ab initio studies have been performed to evaluate the magnetic moments of single A, M and γ phase. All the single phase nanoparticles have been ascertained to be in single-domain regime by estimating the single-domain size limit. This work showcases a simple methodology to prepare pure crystal phases in these nanoparticles. It also provides insight on the role of elemental precursors and processing conditions in designing Co-Ni-Ga nanoparticles for ferromagnetic shape memory applications.

Investigation of structural, photo and thermoluminescence properties of YAGG:Ce nanogarnet for medical dosimetry application

Cerium-doped yttrium aluminum gallium garnet (YAGG:Ce3+) nanophosphors were synthesized using the sol-gel method. Mixed garnet of Y2.97Al5-xGaxO12:Ce0.03 was prepared with varying gallium content: x = 0, 1, 2 and 3 Ga. The effect of gallium substitutions on the structural, photo and thermoluminescence properties of the prepared nanophosphors were studied by X-ray diffraction (XRD), photoluminescence (PL) and thermoluminescence (TL) techniques. XRD results indicated that the single and pure cubic crystal phase was formed for all nanophosphor samples regardless of the Ga content. The PL spectra of all the samples exhibited a green-yellow emission band centered at 522 nm attributed to the 5d → 4f transitions of Ce3+ ions. The TL glow curve spectra recorded after β-particle irradiation showed a strong dependence in terms of position, shape and intensity, of all temperature peaks with the Ga content. The highest TL sensitivity was observed for the sample prepared with x = 2 Ga, with main peak arising at low temperature (85 °C). The sample prepared at x = 1 Ga exhibited also high TL sensitivity with a simple glow curve spectrum showing a main peak at high temperature (∼158 °C). Thus, the linear dose response of this sample has been investigated in the wide dose range from 0.125 to 100 Gy in order to evaluate the potentiality of this material for radiation dosimetry applications.

Impacts of Ce3+ doping on temperature sensing characteristics of LuAG: Yb3+/Ho3+ up-conversion fluorescent materials

A series of LuAG: 5 mol%Yb3+/0.5 mol%Ho3+/x mol%Ce3+ (x = 0, 0.2, 0.5, 1.0, 2.0) up-conversion (UC) fluorescent materials were prepared using CO2 laser heating zone melting method. The X-ray diffraction (XRD) patterns confirm that the prepared samples have a pure LuAG crystal phase. Under excitation of a 980 nm laser, the up-conversion luminescence (UCL) spectra of the prepared samples were obtained. Two UCL emission bands of Ho3+ ions were observed, including green emission band of the 5F4/5S2→5I8 transition, and red emission band of the 5F5→5I8 transition. Due to the cross-relaxation (CR) processes between Ce3+ ions and Ho3+ ions, the doping of Ce3+ ions can effectively improve the UCL efficiency of Ho3+ ions, and the emission intensity reaches maximum when doped with 1 mol% Ce3+. The temperature sensing characteristics of LuAG: Yb3+/Ho3+ and LuAG: Yb3+/Ho3+/Ce3+ from 303 K to 723 K were studied by fluorescence intensity ratio (FIR) method. By doping 1 mol% Ce3+ ions, the absolute sensitivity of the sample has been significantly improved, with the maximal absolute sensitivity of 0.0951 K−1 (303 K), and the maximal relative sensitivity of 0.0103 K−1 (343 K). The high sensitivity and wide measurement range make LuAG: Yb3+/Ho3+/Ce3+ UCL material ideal for temperature sensing.

Tunable transport properties of dual-gated InAs/GaSb core/shell nanowires

Dual-gate structures were fabricated on a single high-quality InAs/GaSb core/shell nanowire, enabling control of the band structure and Fermi level in the crossed bandgap heterostructure. The nanowire was grown using the molecular-beam-epitaxy method in a pure crystal phase for both the core and the shell. We demonstrated clear ambipolar transport characteristics derived separately from n-type InAs and p-type GaSb. A relatively high resistance region was found between n- and p-type conduction regions; the entrance to an energy gap was thus indicated. The gap's size varied with the electric fields of dual gates and could even be closed; after closure, a weak and non-vanishing energy gap appeared. The reopened energy gap was considerably suppressed in an in-plane magnetic field only when the field was perpendicular to the axis of the nanowire (i.e., the current direction) and was identified as an electron–hole interaction induced hybridization gap.

Upconversion luminescence and optical thermometry of Gd3BWO9: Yb3+, Er3+ phosphors

Rare earth upconversion (UC) luminescent materials have important application prospect in the field of optical thermometry due to the unique fluorescence properties. To search for new and efficient UC luminescent materials for optical temperature measurement, a series of Gd3BWO9: Yb3+, Er3+ UC phosphors were prepared through a high temperature solid-state reaction process. X-ray diffraction data show that all of the Gd3BWO9: Yb3+, Er3+ phosphors have pure Gd3BWO9 crystal phase. Under the excitation of 980 ​nm pump laser, all of the Gd3BWO9: Yb3+, Er3+ phosphors exhibit bright green emission at 522 ​nm and 543 ​nm. The UC luminescence mechanism and energy transfer (ET) processes were revealed by studying the power dependency of the UC emission intensities, and the green emission lifetimes of 4S3/2-2H15/2 were also measured to prove the existence of ET between Yb3+ and Er3+ ions. Moreover, the optical thermometry performance of Gd3BWO9: 0.20 ​Yb3+, 0.02 Er3+ was investigated by using fluorescence intensity ratio techniques. At 303 ​K, the relative sensitivity of phosphor is 0.94% K−1. The results manifest that Yb3+- Er3+ co-doped Gd3BWO9 phosphors can be used in optical temperature measurement.

Engineering of Nanostructured WO3 Powders for Asymmetric Supercapacitors

Transition metal oxide nanostructures are promising materials for energy storage devices, exploiting electrochemical reactions at nanometer solid-liquid interface. Herein, WO3 nanorods and hierarchical urchin-like nanostructures were obtained by hydrothermal method and calcination processes. The morphology and crystal phase of WO3 nanostructures were investigated by scanning and transmission electron microscopy (SEM and TEM) and X-ray diffraction (XRD), while energy storage performances of WO3 nanostructures-based electrodes were evaluated by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) tests. Promising values of specific capacitance (632 F/g at 5 mV/s and 466 F/g at 0.5 A/g) are obtained when pure hexagonal crystal phase WO3 hierarchical urchin-like nanostructures are used. A detailed modeling is given of surface and diffusion-controlled mechanisms in the energy storage process. An asymmetric supercapacitor has also been realized by using WO3 urchin-like nanostructures and a graphene paper electrode, revealing the highest energy density (90 W × h/kg) at a power density of 90 W × kg-1 and the highest power density (9000 W/kg) at an energy density of 18 W × h/kg. The presented correlation among physical features and electrochemical performances of WO3 nanostructures provides a solid base for further developing energy storage devices based on transition metal oxides.

Synthesis of Platinum-Rare Earth Metal Alloy Catalysts for Proton Exchange Membrane Fuel Cells

Electrocatalysts for low temperature fuel cells are based on noble metals and can be promoted by development of alloys of platinum with e.g. late transition metals such as Ni and Co.[1,2] It has been reported that Pt alloys with rare earth (RE) metals exhibit remarkable activity and high stability towards the oxygen reduction reaction.[3] Due to the very low standard reduction potentials and high oxophilicity of rare earth metals, preparation platinum alloys in form of nanoparticles meets great challenges for chemical routes of co-reduction. A one-step method is recently developed to prepare Pt−RE nanoalloys from a mixture of solid state precursors consisting of metal halides in their hydrate forms, a suitable nitrogen-rich compound and a carbon support.[4,5] The synthesis involves in situ formation of a carbon-nitrogen network, onto which the two metals are atomically dispersed. The coordination with nitrogen sites stabilizes the metals, which, upon thermal decomposition under a mild reducing atmosphere, leads to the formation of Pt-RE nanoalloys. The carbon support is introduced either as carbon blacks or carbon supported platinum powder. The pre-formed, either in or ex situ, platinum nanoparticles, facilitates the reduction of rare earth metals thermodynamically driven by the negative alloying free energy. A series of pure crystal phases such as Pt5RE (e.g. La, Ce, Nd), and Pt3RE (e.g. Y, Gd, Tb) have been synthesized in form of carbon supported nanoparticles with tunable metal loadings and alloy particle sizes. One of the typical catalysts is the Pt5Ce/C in a metal to carbon ratio of 30 wt% and an average alloy particle size of ca. 5.5 nm which exhibits an area specific activity of 3.7 times and a mass activity of 1.9 times higher than those of the Pt/C analogue. Further understanding and improvement of the process are in progress and the updated results will be presented in this talk.[1]. J. K. Norskov et al., Nature Chemistry 1, 37-46 (2009)[2]. X. Q. Huang et al., Science 348, 1230-1234 (2015)[3]. M. Escudero-Escribano et al., Science 352, 73-76 (2016)[4]. Y. Hu et al., J. Am. Chem. Soc. 142, 953–961 (2020)[5]. Y. Hu et al., Chem. Mater. 33, 2, 535–546 (2021)

Facile synthesis of copper oxide nanoparticles and their applications in the photocatalytic degradation of acyclovir

Copper oxide nanoparticles were synthesized by a simple sol-gel route using copper (II) acetate monohydrate as a precursor at varying temperatures (300 °C, CuO(300); 350 °C, CuO(350) and 400 °C, CuO(400)), and were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and UV–visible absorption spectroscopy. While the lowest temperature of calcination (300 °C) yielded mixed phases of CuO and Cu2O, the higher temperature (350 °C and 400 °C) gave pure monoclinic crystal phase of CuO. The microscopic analysis revealed that both CuO samples exhibited spherical shape with the average particle size of 47.15 nm (350 ᵒC) and 47.67 nm (400 ᵒC). The crystallite size estimated from the XRD pattern showed average crystalline sizes of 32.16 and 32.45 nm at 350 and 400 °C respectively. Photocatalytic degradation of acyclovir (ACV) was conducted using the nanoparticles and the effect of process variables such as catalyst dosage and solution pH were evaluated in order to establish the efficiency of the CuO nanoparticles in the photocatalytic process. The photo-enhanced degradation of ACV using both CuO nanoparticles demonstrated high and comparable removal efficiency of greater than 81%, within 120 min irradiation time. The results also showed that the performance of both CuO is dependent. The efficient performance achieved with both CuO photocatalysts, without further modification, suggests that the synthesized CuO nanoparticles could be a potential photocatalyst to remove ACV-laden water.

Role of Capping Molecule L-Cysteine on Synthesis and Characterization of Silver Oxide (Ag2O) Nanoparticles by Co-Precipitation Method

Biocompatible Ag2Onanoparticles have been developed using L-Cysteine biomolecule as a capping molecule via the elementary co-precipitation method resulting in a stable, efficient, and pure crystal phase of silver oxide nanoparticles at room temperature. Optical, structural, morphological, and compositional measurements indicated that L-Cysteine plays a crucial role in the synthesis because of the better surface passivation and stability of Ag2O nanoparticles. The face-centered cubic phase structure is evident from the XRD pattern, and the particle size was calculated using the Scherrer formula, which is obtained in the range of 50 nm and 76 nm. The present synthetic approach is simple, eco-friendly (non-toxic), and as obtained, silver oxide nanoparticles can be used for photocatalytic and display applications.

Photocatalytic removal of sulfamethoxazole using yeast biomass-derived NixP/biocarbon composites in the presence of dye sensitizer

Photocatalysis represents an environmental-benign approach for organic pollutant treatment. Herein, a photocatalytic system composed of NixP/biocarbon composite as reactive center and erythrosine B (ErB) as sensitizer was constructed for the removal of sulfamethoxazole (SMX) antibiotic under visible light irradiation. NixP/biocarbon composites were fabricated via a facile impregnation-pyrolysis approach using baker’s yeast as both phosphorus and carbon precursor. It was found that NixP with pure Ni12P5, almost pure Ni2P or mixed crystal phases could be obtained by simply adjusting Ni:P molar ratio in precursor and pyrolysis temperature. Interestingly, the variation of NixP crystal phases remarkably affected photocatalytic removal efficiency of SMX. The obtained NixP(1:4)− 900 sample with mixed phases of Ni12P5 and Ni2P displayed excellent photodegradation performance with 98.71% removal efficiency for SMX (C0 = 20 mg L−1) in ErB-sensitized photocatalytic system. Moreover, the reusability of NixP/biocarbon composite was confirmed by four consecutive runs. The slight loss of activity in recycle study could be fully recovered after thermal regeneration. Further investigation indicated that photo-generated electrons from excited ErB molecules could be transferred to NixP/biocarbon, triggering a series of reactions to form various reactive oxygen species (eg., •O2−, H2O2, •OH) for SMX degradation. The better photocatalytic activity of NixP mixed crystal phases should be ascribed to its faster electron transfer ability. Overall, this study provides useful guidance in terms of the development of transition metal phosphide and efficient photocatalytic system.

Optical and structural studies of PVP capped silver oxide nanoparticles

Biocompatible silver oxide (Ag2O) nanoparticles have been developed using Polyvinylpyrrolidone (PVP) as a capping molecule via elementary co-precipitation method resulting in a stable, efficient and pure crystal phase of silver oxide nanoparticles at room temperature. Optical, structural, morphological and compositional measurements clearly indicated that PVP plays a crucial role in the synthesis of Ag2O nanoparticles, because of better surface passivation and stability. The optical absorption measurements show clear blue shift, The photoluminescence study confirms the emission in the blue region. The results from the X-ray diffraction (XRD) and selected area electron diffraction (SAED) evident that Ag2O nanoparticles have better crystallinity and purity, the average particle size is 18 nm. The present method of synthesis of Ag2O nanoparticles is simple, eco-friendly (non-toxic) and can be used for photocatalytic, humidity sensor and display applications.

White light emission and energy transfer processes in LaInO3 doped with Bi3+, Tb3+ and Eu3+

A series of LaInO3 bulk materials doped with Bi3+, Tb3+ and Eu3+ ions have been synthesized via a flux solid-state reaction technique, characterized by powder X-ray diffraction (PXRD) and investigated by luminescence spectroscopy. The compounds exhibit the pure crystal phase of LaInO3 (JCPDS No. 08-0148), and the structure is not affected by the presence of the dopants. The Bi3+ → Tb3+ and Tb3+ → Eu3+ energy transfer phenomena have been studied by means of luminescence spectroscopy and decay kinetics of Bi3+ excited state and of the 5D4 excited state of Tb3+. White light emission is attained via altering the concentration of dopant, and the obtained color coordinate (0.3248, 0.3030) is close to standard white light (0.313, 0.329). The energy transfer process is crucial, in order to tune the color of the emitted light.

All-Inorganic p-n Heterojunction Solar Cells by Solution Combustion Synthesis Using N-type FeMnO3 Perovskite Photoactive Layer.

This study outlines the synthesis and physicochemical characteristics of a solution-processable iron manganite (FeMnO3) nanoparticles via a chemical combustion method using tartaric acid as a fuel whilst demonstrating the performance of this material as a n-type photoactive layer in all-oxide solar cells. It is shown that the solution combustion synthesis (SCS) method enables the formation of pure crystal phase FeMnO3 with controllable particle size. XRD pattern and morphology images from TEM confirm the purity of FeMnO3 phase and the relatively small crystallite size (∼13 nm), firstly reported in the literature. Moreover, to assemble a network of connected FeMnO3 nanoparticles, β-alanine was used as a capping agent and dimethylformamide (DMF) as a polar aprotic solvent for the colloidal dispersion of FeMnO3 NPs. This procedure yields a ∼500 nm thick FeMnO3 n-type photoactive layer. The proposed method is crucial to obtain functional solution processed NiO/FeMnO3 heterojunction inorganic photovoltaics. Photovoltaic performance and solar cell device limitations of the NiO/FeMnO3-based heterojunction solar cells are presented.

Structural and dielectric studies of MgAl2O4–TiO2 composites for energy storage applications

Nanostructured MgAl2O4 and TiO2 were successfully synthesized in phase pure form using well know co-precipitation method. The composites of MgAl2O4 with various concentrations of TiO2 (5 %, 10 %, 20 %, and 50 %) were prepared by vertexing technique. The pure crystal phase of both TiO2 and MgAl2O4 have hexagonal and spinel crystal structures, respectively as confirmed from x-rays diffraction analysis. The sheet-like morphology with some agglomeration was shown for pure MgAl2O4 and spherical for TiO2 with clear boundaries are obtained from FESEM micrographs. Energy dispersive x-rays confirmed the presence of expected elements in corresponding percentages in all compositions. These compositions present enhanced ferroelectric and dielectric responses in synthesized composite materials. The improvement in saturation polarization Ps, electric-remanence polarization Pr, and the electric-coercivity Ec parameters confirm that these can be used as a good dielectric medium and can consider highly efficient material for energy storage device applications.

CHCl3-Dependent Emission Color and Jumping Behavior of Cyclic Chalcone Single Crystals: The Halogen Bond Network Effect

As a conventional strategy to modulate the structure and properties of inorganic single crystals, hydration/solvation is rarely found to function in pure organic single crystal. Herein, we report chalcone single crystals with CHCl3-dependent emission color and jumping behavior. Two crystals: a pure crystal phase (1) with green-yellow emission and a CHCl3-containing co-crystal phase (1•2CHCl3) with orange-red emission were constructed by fine-controlling the crystallization conditions. The special halogen bond network in the crystal packing structure effectively narrows the bandgap and thereby redshift the emission of 1•2CHCl3. 1•2CHCl3 would revert to 1 together with emission color change when losing CHCl3. These findings are similar to the effect of H2O in hydrated inorganic crystals. Notably, owing to a special pre-organized “molecular pair” structure for [2 + 2] cycloaddition, the pure crystal phase 1 exhibits violently photo-induced jumping phenomenon, indicating large potentials in intelligent devices. This work would overturn the previous perception that the structurally simple solvent molecules without conjugation cannot greatly affect the structure and properties of pure organic single crystals and provide a new strategy to construct multi-colored organic fluorescent crystals.

Effect of preparation methods on the structure and naphthalene hydrogenation performance of Ni2P/SiO2 catalyst

Ni2P/SiO2 catalysts were prepared by temperature-programmed reduction method and hypophosphite disproportionation method to investigate their naphthalene hydrogenation performance. The prepared catalysts were characterized by ICP-OES, X-ray diffraction, H2 temperature-programmed reduction, N2 adsorption-desorption method and transmission electron microscopy, etc. Results showed that Ni2P/SiO2 catalyst with pure Ni2P crystal phase could be successfully prepared by the temperature-programmed reduction method and hypophosphite disproportionation method. When the naphthalene hydrogenation reaction was performed at 340°C, 4 MPa, H2/oil volume ratio of 600, and a weight hourly space velocity (WHSV) of 20.8 h–1, Ni2P/SiO2 catalyst prepared by the temperature-programmed reduction method possessed superior hydrogenation activity. This result was ascribed to the advantages of temperature-programmed reduction method. It not only installed the higher number of Ni2P species (CO adsorption amount 21.6 μmol/g) over SiO2, but also obtained more weak acid sites on the catalyst surface, which promoted the adsorption of aromatic hydrocarbons and subsequently resulted in the higher hydrogenation activity. Furthermore, when the temperature-programmed reduction method was used to prepare Ni2P/SiO2 catalyst, the lower Ni/P molar ratio was more beneficial to enhance the naphthalene hydrogenation activity of the as-prepared catalyst.

Facile synthesis of Bi5O7NO3 with enhanced photocatalytic activity by a molten salt strategy and its photocatalytic performance

Photocatalysis is a promising technology for wastewater treatment as it is a low-cost environmentally friendly method with a high reaction rate. Bi5O7NO3 possesses superb catalytic properties and excellent cycling stability, and can be synthesized by a molten salt method, which has been systematically investigated. The results show that high temperature (≥500 °C) leads to the decomposition of Bi5O7NO3, while low temperature (≤400 °C) causes formation of a pure crystal phase of Bi5O7NO3, which shows excellent photocatalytic performance. The facile synthesis strategy and superior catalytic activity may shed a light on the synthesis of novel catalysis for wastewater treatment.

Large Graphene Oxide Flakes: From Isotopic to Nematic Liquid Crystal Phase Transition

Herein, graphene oxide (GO) with large flakes of average size 38 μm is studied, following the isotropic–nematic phase transition over time and determining the critical concentration, i.e., the minimum value for the formation of the pure liquid crystal (LC) phase. The GO flakes in aqueous suspensions can form LC phases, which are attractive for various applications because of their exceptional properties. Stability over time is very important for their applications, especially, if the GO suspension is in the biphase concentration region in which a crucial change can occur—the isotropic LC phase separation. GO LCs have a wide biphase region, and even very low concentration suspensions appear purely nematic when prepared. However, over time, they appear to be biphasic and higher concentrations are needed for pure LC phase. The changes in the critical concentration were followed for over 4 months, and the findings indicate that it increases with time until it reaches a stable value that is, nevertheless, very low in concentration, 0.7 mg mL−1 (0.035 vol%). From the stable threshold volume fraction, the effective flake thickness, relevant in the LC phase formation behavior, is estimated. This value is almost double than what is measured by atomic force microscopy.