Cr2O3 Nanoparticles Research Articles

Polymerization of aniline derivatives by K2 Cr2 O7 and production of Cr2 O3 nanoparticles

Oxidative polymerization of aniline, anthranilic acid, and aniline-co-anthranilic acid by potassium dichromate Cr(VI) as an oxidant in acidic medium was investigated. In this study, the polymerization process of aniline, o-anthranilic acid as well as aniline/o-anthranlic acid using K2Cr2O7 produced, coordinated Cr(III)/polyaniline (PANI), Cr(III)/polyanthranilic acid (PAA) and Cr(III)/poly aniline-co-anthranilic acid (PANAA). The mechanism of polymerization reaction in the presence of dichromate was hypothesized. The precursor chromium doped polymers were characterized by TGA, FT-IR, UV-visible, XRD analyses. Cr2O3 nanoparticles size were determined using TEM analysis. The calcinations process of synthesized chromium doped PANI, PAA and PANAA yields Cr2O3 nanoparticles 26%, 31%, and 34% wt. respectively. Rhombohedral phase of Cr2O3 particles in the range from 33 to 61 nm was produced from chromium/polyanthranilic acid (PAA) and chromium/poly(aniline-co-anthranilic acid) PANAA. UV- visible analysis showed that optical band gaps (Eg) of doped poly aniline and its derivatives are in the range from1.55 to 1.80 using Tacu's law. The band gap values reveal that the doped chromium emeraldine base can be used as semiconductor materials. Copyright © 2016 John Wiley & Sons, Ltd.

Chromium oxide nanoparticles with controlled size prepared from hydrothermal chromium oxyhydroxide precursors

This work reports the preparation of morphologically well-defined chromium oxide nanoparticles with controlled sizes of 20–30nm. The synthetic procedure encompass two stages, the first one refers to the preparation of chromium oxyhydroxide nanoparticles by a hydrothermal approach of previously precipitated xerogels, followed by a thermal transformation of CrOOH nanoparticles to Cr2O3. The series of chromium oxyhydroxide particles sized over the range 15–50nm were prepared through the control of the pH of precipitation of the xerogels and the water/xerogel ratio of the hydrothermal aging. Results showed the formation of non-aggregated oxyhydroxide nanoparticles with two different trends: xerogels precipitated at pH 5 showed smaller particles for the higher amount of water (water/xerogel ratio in weight of 60/1); on the contrary, at pH 10 the size of oxyhydroxide nanoparticles increased with increasing the amount of water. The transformation from CrOOH to Cr2O3 took place at around 450°C; well-defined, non-aggregated crystalline nanoparticles of Cr2O3 with similar sizes, regardless of the precursors, were observed after treating the different oxyhydroxides at 600°C for one hour. Chromia nanocrystals obtained from precipitates at pH 10 displayed intense and better-defined absorption bands than those prepared at pH 5. Remarkable high reflectance intensity was shown by chromia nanocrystals prepared at pH 10 and the larger 60/1 water/xerogel ratio. The mechanisms of formation of both the CrOOH –grimaldite- and the Cr2O3 –eskolaite- nanoparticles by the two subsequent steps have been proposed based on the results arisen from the different characterization techniques.

Poly(o-toluidine dihydrochloride): Spectral Characterization and Synthesis of Eskolite Nanoparticles

ABSTRACTPoly(o-toluidine · 2HCl) and its doped polymers with Mn and Cr ions have been synthesized and characterized by FT-IR, UV–Vis. and thermogravimetrical analyses. Potassium dichromate has been used as an initiator and a dopant of chromium in CrPOT preparation. The effect of doping on thermal and optical properties of Poly(o-toluidine dihydrochloride) has been discussed.CrPOT has been used as a precursor of Cr2O3 nanoparticles through thermal decomposition rout. The obtained nanoparticles have been characterized by X-ray diffraction and high resolution transmission electron microscope. The results indicated that Cr2O3 exists in hexagonal structure as mesoporous Eskolit with average particle size of 48 nm. Optical band gap measurements indicated that Eskolite nanoparticles have wider band gap than the bulk.

A strategy for ultrasensitive and selective detection of methylamine using p-type Cr2O3: Morphological design of sensing materials, control of charge carrier concentrations, and configurational tuning of Au catalysts

An ultrasensitive and selective trimethylamine (TMA) sensor was fabricated by the urea-assisted uniform loading of Au nanoparticles (∼5nm) on Cr2O3 yolk-shell spheres prepared by ultrasonic spray pyrolysis. The response (resistance ratio) of the Cr2O3 yolk-shell spheres uniformly loaded with fine Au nanoparticles to 5ppm TMA was 200.9 at 225°C, which was significantly higher than those of pure Cr2O3 yolk-shell spheres (24.6) and Cr2O3 yolk-shell spheres loaded with heavily agglomerated Au particles (9.2). The detection limit of Cr2O3 yolk-shell spheres uniformly loaded with Au nanoparticles was as low as 4.3ppb. The unprecedentedly high TMA response is explained and discussed in relation to the gas-accessible morphology of the yolk-shell spheres, and the catalytic and electronic promotion of the gas sensing reaction by both Cr2O3 and well-dispersed Au nanoparticles.

Crystal structure and electronic properties of facile synthesized Cr2O3 nanoparticles

We report on a facile method of synthesis of Cr2O3 nanoparticles by hydrothermal method. Chromium sulfate was used as a starting material whereas urea was used as a strong reducing agent. Cr2O3 nanoparticles, with rhombohedral crystal structure, have been synthesized, when the reaction solution was treated under hydrothermal condition at high pH (10). At pH = 8 amorphous Cr2O3 powders were obtained. Chromium oxide could not be synthesized in the absence of urea. Two different Raman modes have been detected for the final products synthesized at the high pH value. As-prepared Cr2O3 nanoparticles reveal agglomeration as evidenced from scanning electron microscope (SEM) images. Flake-like Cr2O3 nanoparticles, 20 to 50 nm in size, show clear lattice fringes through the high resolution transmission electron microscope (HRTEM) images. The electronic structure of the Cr2O3 nanoparticles has been studied employing x-ray photoelectron spectroscopy (XPS) and x-ray emission spectroscopy (XES) methods.

Prominent ethanol sensing with Cr2O3 nanoparticle-decorated ZnS nanorods sensors

ZnS nanorods and Cr2O3 nanoparticle decorated ZnS nanorods were synthesized using facile hydrothermal techniques and their ethanol sensing properties were examined. X-ray diffraction and scanning electron microscopy revealed the good crystallinity and size uniformity of the ZnS nanorods. The Cr2O3 nanoparticle decorated ZnS nanorod sensor showed stronger response to ethanol than the pristine ZnS nanorod sensor. The responses of the pristine and decorated nanorod sensors to 200 ppm of ethanol at 300oC were 2.9 and 13.8, respectively. Furthermore, under these conditions, the decorated nanorod sensor showed longer response time (23 s) and shorter recovery time (20 s) than those of the pristine one (19 and 35 s, respectively). Consequently, the total sensing time of the decorated nanorod sensor (42 s) was shorter than that of the pristine one (55 s). The decorated nanorod sensor showed excellent selectivity to ethanol over other volatile organic compound gases including acetone, methanol, benzene, toluene, whereas the pristine one failed to show selectivity to ethanol over acetone. The improved sensing performance of the decorated nanorod sensor is attributed to the modulation of the conduction channel width and the potential barrier height at the ZnS Cr2O3 interface accompanying the adsorption and desorption of ethanol gas as well as the greater surface to volume ratio of the decorated nanorods than the pristine one due to the existence of the ZnS Cr2O3 interface.

High rate capability and long cycle stability of Cr2O3 anode with CNTs for lithium ion batteries

The present study describes the synthesis of nanocomposite materials based on chromium oxide (Cr2O3) nanoparticles and carbon nanotubes (CNTs) (Cr2O3–CNT(x%)) by in-situ chemical co-precipitation method. The physical studies of these materials using a wide range of analytical techniques reveal high surface area and narrow pore size distribution of these nanocomposite materials, indicating homogenous dispersion of Cr2O3 nanoparticles (particle sizes ∼20-30nm) on the surface of CNTs. The first cycle discharge capacity of 1120mAhg-1 for electrodes fabricated from Cr2O3 alone, which is improved for Cr2O3–CNT(0.08%) nanocomposite (1199mAhg-1). This nanocomposite material achieved an overall reversible capacity of 995.3mAhg-1 after 200 cycles, which can be attributed to the high surface area and the large mesoporous volume of Cr2O3 nanoparticles interconnected with highly conducting network of CNTs. At higher current densities, the Cr2O3–CNT(x%) nanocomposite electrodes exhibited high lithium storage capacity compared to the electrode fabricated from Cr2O3 nanoparticles alone. Overall, the Cr2O3–CNT(0.08%) nanocomposite electrode displayed high stability under varying current rates with overall high capacity retention and highest reversible capacity of 719mAhg-1 at a current rate of 2000mAhg-1. This highly enhanced rate capability and excellent cycling stability of Cr2O3–CNT(0.08%) nanocomposite electrode can be ascribed to the synergistic effect of CNTs (anchored with the Cr2O3 nanoparticles). The outcome of this study offers a possibility of improving lithium ion storage of Cr2O3 nanoparticles by carefully controlling their size and shape along with the use of a suitable buffering matrix like CNTs.

Synthesis, structural and optical properties of Eskolaite nanoparticles derived from Cr doped polyanthranilic acid (CrPANA)

Cr doped polyanthranilic acid (Cr PANA) has been used as a molecular precursor of Cr2O3 nanoparticles. Potassium dichromate acted as an oxidant and a dopant in Cr PANA synthesis. The spectral, optical and thermal properties of the precursor have been described. Thermogravimetric Analysis (TGA) and differential scanning calorimetric (DSC) were used to clarify the thermal stability of Cr PANA. The optical band gap (Eg) measurements indicated that Cr PANA has wider optical band than the pure PANA. Calcination of Cr PANA at 600 °C produced Eskolaite (Cr2O3) nanoparticles. The obtained nanoparticles have been characterized by XRD and TEM. The average size of the nanoparticles was found to be 70 nm. The measured optical band gap of Eskolaite nanoparticles is 0.35 eV wider than the bulk.

Structural and magnetic phase transition of sol–gel-synthesized Cr2O3 and MnCr2O4 nanoparticles

Cr2O3 and MnCr2O4 spinel chromite nanoparticles were synthesized using chemically derived sol–gel technique. Crystal structure was analyzed using X-ray diffraction, and phase transition from a rhombohedral symmetry (R-3c) for Cr2O3 to a spinel cubic symmetry (Fd3 m) for MnCr2O4 has been observed. Data obtained from diffraction were also utilized to evaluate the lattice parameters, crystallite size and unit cell volume. Micrographs obtained using a field emission scanning electron microscope exhibited well-shaped, homogenously distributed 30–70-nm-sized nanoparticles, with well-defined grain. Stoichiometric composition of all the elements present in the samples was confirmed using energy-dispersive X-ray spectroscopy. Dynamic light scattering measurement was performed to corroborate the hydrodynamic diameter and distribution of Cr2O3 and MnCr2O4 nanoparticles. The magnetic behavior of samples was scrutinized as a function of temperature and applied field. It was observed that Cr2O3 exhibited paramagnetic behavior both at room temperature and at 5 K, while a magnetic phase transition from ferro to para was observed in MnCr2O4 with a Curie temperature, T c ~ 50 K.

Progress on Synthesis and Applications of Cr2O3 Nanoparticles.

As is known to us that nanosized chromic oxide (Cr2O3) is an important transition metal oxide. Because it has many excellent properties, it can be used in many fields such as pigment, catalyst, Lithium material etc. This article briefly reviewed the preparation and applications of Cr2O3 nanoparticles. In this paper, some specific applications will be listed according to different fields. Nanosized chromic oxide (Cr2O3) can be obtained via many methods. A summary of the methods have been made. The preparation methods are divided into three main types, including vapor phase method, solid phase method and liquid phase method. Simultaneously, different types of methods have been simply evaluated in this paper. And the advantage and disadvantage are simply noted.

Morphological effects of ordered Cr2O3 nanorods and Cr2O3 nanoparticles on fluorination of 2-chloro-1,1,1-trifluoroethane

Ordered Cr2O3 nanorods (Cr2O3-R) and Cr2O3 nanoparticles (Cr2O3-P) were prepared by a hard template method with SBA-15 and a deposition–precipitation method, respectively. These catalysts were tested for the fluorination of 2-chloro-1,1,1-trifluoroethane (HCFC-133a) to synthesize 1,1,1,2-tetrafluoroethane (HFC-134a). It was found that both catalysts were very selective, with a HFC-134a selectivity of 98 %. However, the Cr2O3-R catalyst had an area specific reaction rate of 0.012 μmol m−2 s−1 at 320 °C, which was much higher than that on the Cr2O3-P (0.005 μmol m−2 s−1). The enhanced activity of the Cr2O3-R was attributed to its higher content of Cr(VI) species compared to that in the Cr2O3-P, which was evidenced by the hydrogen temperature-programmed reduction and X-ray photoelectron spectroscopy results. Besides, the Cr2O3-R catalyst had a higher surface acid density (0.076 mmol m−2) than the Cr2O3-P (0.068 mmol m−2), which could be another reason for its better performance.

Metal-Carbon Hybrid Electrocatalysts Derived from Ion-Exchange Resin Containing Heavy Metals for Efficient Hydrogen Evolution Reaction.

Transition metal-carbon hybrids have been proposed as efficient electrocatalysts for hydrogen evolution reaction (HER) in acidic media. Herein, effective HER electrocatalysts based on metal-carbon composites are prepared by controlled pyrolysis of resin containing a variety of heavy metals. For the first time, Cr2 O3 nanoparticles of 3-6 nm in diameter homogeneously dispersed in the resulting porous carbon framework (Cr-C hybrid) is synthesized as efficient HER electrocatalyst. Electrochemical measurements show that Cr-C hybrids display a high HER activity with an onset potential of -49 mV (vs reversible hydrogen electrode), a Tafel slope of 90 mV dec(-1) , a large catalytic current density of 10 mA cm(-2) at -123 mV, and the prominent electrochemical durability. X-ray photoelectron spectroscopic measurements confirm that electron transfer occurs from Cr2 O3 into carbon, which is consistent with the reported metal@carbon systems. The obtained correlation between metals and HER activities may be exploited as a rational guideline in the design and engineering of HER electrocatalysts.

Exchange bias effect in CuCr2O4/Cr2O3 nanogranular systems

We have successfully synthesized the CuCr2O4/Cr2O3 nanogranular system through a high-temperature phase separation route from Cu doped Cr2O3 nanoparticles, which are confirmed by X-ray diffraction measurements. Magnetic susceptibility shows two magnetic transitions at 130 K and 310 K corresponding to the ferrimagnetic and antiferromagnetic phases of CuCr2O4 and Cr2O3, respectively. Significant exchange bias behavior could be observed in the field cooling magnetic hysteresis loop at low temperatures. Both exchange bias field (HEB) and coercive field (HC) decrease with increasing temperature and disappear near 200 K. This exchange bias behavior is discussed in terms of the existence of exchange coupling between the ferrimagnetic CuCr2O4 and antiferromagnetic Cr2O3. The uncompensated spins in antiferromagnetic phase frozen along field cooling direction provide the pinning force on the ferrimagnetic spins leading to the exchange bias effect.

Microstructure, Mechanical and Tribological Properties of the Rapidly Solidified NiAl/Cr(Mo,Dy) Hypoeutectic Alloy

The NiAl/Cr (Mo,Dy) hypoeutectic alloy was fabricated by rapid solidification. The microstructure and mechanical properties as well as tribological properties for the alloy at different temperatures were investigated. The results revealed that the rapidly solidified NiAl/Cr (Mo,Dy) hypoeutectic alloy was composed of primary NiAl, fine NiAl/Cr (Mo) eutectic lamella, Ni5Dy phase and Cr7Ni3 precipitate. The compression test showed that the rapid solidification improved the mechanical properties of the NiAl/Cr (Mo,Dy) hypoeutectic alloy obviously. The dry sliding test results showed that alloy had excellent tribological properties at about 1073 K, which obtained wear rate of 4.9 10-14m3/m·N and friction coefficient of 0.16 μ. The excellent tribological properties at high temperature may be attributed to the continuous and intact protecting lubricant film which was composed of amorphous, Cr2O3 and Al2O3 nanoparticles. Between 700 K to 900 K, the alloy demonstrated bad tribological properties, especially the high wear rate, which may be ascribed to the softening of NiAl and Cr (Mo) phases.

PREPARATION AND INVESTIGATION OF ELECTRODEPOSITED Ni–NANO-Cr2O3 COMPOSITE COATINGS

The electrodeposition of Ni–nano-Cr2O3 composite coatings was studied in electrolyte containing different contents of Cr2O3 nanoparticles (Cr2O3 NPs) on mild steel surfaces. Some techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), microhardness, the potentiodynamic polarization curves (Tafel) and electrochemical impedance spectroscopy (EIS) were used to compare pure Ni coatings and Ni–nano-Cr2O3 composite coatings. The results show that the incorporation of Cr2O3 NPs resulted in an increase of hardness and corrosion resistance, and the maximum microhardness of Ni-nano-Cr2O3 composite coatings reaches about 495 HV. The coatings exhibit an active-passive transition and relatively large impedance values. Moreover, the effect of Cr2O3 NPs on Ni electrocrystallization is also investigated by cyclic voltammetry (CV) and EIS spectroscopy, which demonstrates that the nature of Ni-based composite coatings changes attributes to Cr2O3 NPs by offering more nucleation sites and less charge transfer resistance.

Synergistic Effects of a Combination of Cr2O3-Functionalization and UV-Irradiation Techniques on the Ethanol Gas Sensing Performance of ZnO Nanorod Gas Sensors.

There have been very few studies on the effects of combining two or more techniques on the sensing performance of nanostructured sensors. Cr2O3-functionalized ZnO nanorods were synthesized using carbothermal synthesis involving the thermal evaporation of a mixture of ZnO and graphite powders followed by a solvothermal process for Cr2O3-functionalization. The ethanol gas-sensing properties of multinetworked pristine and Cr2O3-functionalized ZnO nanorod sensors under UV illumination were examined to determine the effects of combining Cr2O3-ZnO heterostructure formation and UV irradiation on the gas-sensing properties of ZnO nanorods. The responses of the pristine and Cr2O3-functionalized ZnO nanorod sensors to 200 ppm of ethanol at room temperature by UV illumination at 2.2 mW/cm(2) were increased by 3.8 and 7.7 times, respectively. The Cr2O3-functionalized ZnO nanorod sensor also showed faster response/recovery and better selectivity than those of the pristine ZnO nanorod sensor at the same ethanol concentration. This result suggests that a combination heterostructure formation and UV irradiation had a synergistic effect on the gas-sensing properties of the sensor. The synergistic effect might be attributed to the catalytic activity of Cr2O3 for ethanol oxidation as well as to the increased change in conduction channel width accompanying adsorption and desorption of ethanol under UV illumination due to the presence of Cr2O3 nanoparticles in the Cr2O3-functionalized ZnO nanorod sensor.

Biotransformation of hexavalent chromium into extracellular chromium(III) oxide nanoparticles using Schwanniomyces occidentalis.

To demonstrate biotransformation of toxic Cr(VI) ions into Cr2O3 nanoparticles by the yeast Schwanniomyces occidentalis. Reaction mixtures containing S. occidentalis NCIM 3459 and Cr(VI) ions that were initially yellow turned green after 48 h incubation. The coloration was due to the synthesis of chromium (III) oxide nanoparticles (Cr2O3NPs). UV-Visible spectra of the reaction mixtures showed peaks at 445 and 600 nm indicating (4)A2g → (4)T1g and (4)A2g → (4)T2g transitions in Cr2O3, respectively. FTIR profiles suggested the involvement of carboxyl and amide groups in nanoparticle synthesis and stabilization. The Cr2O3NPs ranged between 10 and 60 nm. Their crystalline nature was evident from the selective area electron diffraction and X-ray diffraction patterns. Energy dispersive spectra confirmed the chemical composition of the nanoparticles. These biogenic nanoparticles could find applications in different fields. S. occidentalis mediated biotransformation of toxic Cr(VI) ions into crystalline extracellular Cr2O3NPs under benign conditions.

Cr2O3 Nanoparticles on Ba5Ta4O15 as a Noble‐Metal‐Free Oxygen Evolution Co‐Catalyst for Photocatalytic Overall Water Splitting

AbstractThe (1 1 1)‐layered perovskite material Ba5Ta4O15 represents a suitable photoabsorber with remarkable photocatalytic activity in overall water splitting. We are the first to demonstrate overall water splitting without the presence of a noble‐metal‐based co‐catalyst over this catalyst. The photocatalytic activity of Ba5Ta4O15 was investigated by overall water splitting after reductive photodeposition of amorphous Cr2O3. The formation of Cr2O3 nanoparticles for water splitting was evidenced by X‐ray photoelectron spectroscopy and transmission electron microscopy. The reductive photodeposition of very low amounts of Cr2O3 on Ba5Ta4O15 induces stable rates in overall water splitting up to 465 μmol h−1 H2 and 228 μmol h−1 O2.

Cytogenetic studies of chromium (III) oxide nanoparticles on Allium cepa root tip cells

The current study evaluates the cytogenetic effects of chromium (III) oxide nanoparticles on the root cells of Allium cepa. The root tip cells of A. cepa were treated with the aqueous dispersions of Cr2O3 nanoparticles (NPs) at five different concentrations (0.01, 0.1, 1, 10, and 100μg/mL) for 4hr. The colloidal stability of the nanoparticle suspensions during the exposure period were ascertained by particle size analyses. After 4hr exposure to Cr2O3 NPs, a significant decrease in mitotic index (MI) from 35.56% (Control) to 35.26% (0.01μg/mL), 34.64% (0.1μg/mL), 32.73% (1μg/mL), 29.6% (10μg/mL) and 20.92% (100μg/mL) was noted. The optical, fluorescence and confocal laser scanning microscopic analyses demonstrated specific chromosomal aberrations such as—chromosome stickiness, chromosome breaks, laggard chromosome, clumped chromosome, multipolar phases, nuclear notch, and nuclear bud at different exposure concentrations. The concentration-dependent internalization/bio-uptake of Cr2O3 NPs may have contributed to the enhanced production of anti oxidant enzyme, superoxide dismutase to counteract the oxidative stress, which in turn resulted in observed chromosomal aberrations and cytogenetic effects. These results suggest that A. cepa root tip assay can be successfully applied for evaluating environmental risk of Cr2O3 NPs over a wide range of concentrations.

An experimental investigation into the effects of Cr2O3 and ZnO2 nanoparticles on the mechanical properties and durability of self-compacting mortar

Abstract In this paper, the effects of using Cr2O3 and ZnO2 nanoparticles on the mechanical properties and durability of self-compacting mortars are investigated. A fraction of Portland cement was replaced with 1, 2, 3, 4 or 5 wt.% of either Cr2O3 or ZnO2 nanoparticles, and 25 wt.% fly ash. The rheological properties of these mortars were determined through the mini-slump flow diameter and V-funnel flow time tests. The mechanical and durability characteristics were evaluated by compressive and flexural strength, water absorption, electrical resistivity and rapid chloride permeability tests. The microstructure of the mortars was assessed through the use of scanning electron microscopy. The inclusion of 2 wt.% Cr2O3 or 4 wt.% ZnO2 nanoparticles had the best result in compressive and flexural strength tests. Also, mixtures containing either 3 wt.% of Cr2O3 or 5 wt.% of ZnO2 nanoparticles obtained the best result in terms of durability. It can be deduced that the properties of these mixtures are significantly improved by the addition of Cr2O3 and ZnO2 nanoparticles.