Valence State Of Cr Research Articles

A Solid‐Solution with Asymmetric Ni‐O‐Cr Sites for Boosting Protonation toward Anodic Oxidation

AbstractReplacing the slow protonation process of oxygen evolution reaction (OER) with the fast protonation of alcohol electro‐oxidation can decrease the driving potentials, thus improving overall efficiency of electrochemical devices. However, the formation of effective catalytic sites for alcohol oxidation remains challenging in accelerating protonation to inhibit metal leaching and improve catalyst stability. Herein, asymmetric Ni‐O‐Cr sites are constructed by alloying Cr into the NiO matrix to optimize coordination environments, showing significantly enhanced stability during alcohol electro‐oxidation. The asymmetric Ni‐O‐Cr can maintain constant valence states of Cr and Ni during alcohol oxidation, efficiently suppressing metal dissolution even at high oxidation potentials. In situ electrochemical characterizations combined with theoretical calculations indicate that asymmetric Ni‐O‐Cr can improve adsorption and activation of OH* and alcohol molecules compared to pure NiO, thus increasing anodic kinetics. The theoretical results also indicate that the smaller gap of Ni 3d‐O 2p in asymmetric Ni‐O‐Cr strengthens charge transfer, leading to fast protonation of catalytic sites with enhanced stability. This work gives insights into boosting anodic protonation using asymmetric sites‐enriched solid‐solution electrocatalysts.

Adsorption of Cr(VI) and Cr(III) on layered pipe scales and the effects of disinfectants in drinking water distribution systems

Pipe scales in drinking water distribution systems (DWDS) potentially adsorb chromium (Cr). Meanwhile, the fate of Cr in pipe scales and water could be influenced by the disinfectants used in DWDS since they might influence the valence state of Cr. Therefore, the adsorption of Cr (Cr(VI) and Cr(III)) on pipe scales, the transformation between different valence states, and the effects of disinfectants present in DWDS are important research topics for improving tap water quality but have not yet been sufficiently investigated. This study investigated the properties of layered pipe scales and conducted adsorption kinetic experiments in single and binary Cr(VI) and Cr(III) systems, as well as experiments related to the oxidation and adsorption of Cr(III) under the influence of decaying disinfectants. According to the results, pipe scales exhibited distinct layered structures with varying mechanisms for the adsorption of Cr(VI) and Cr(III). Cr(VI) was adsorbed through surface complexation on the surface and porous core layers, while redox reactions predominantly occurred on the shell-like layer. Furthermore, Cr(III) was adsorbed via surface precipitation on the three-layer pipe scales. Importantly, disinfectants promoted the transformation of Cr(III) to the less readily released Cr(VI) in pipe scales, reducing the Cr exposure risk from the pipe scale phase. Pipe scales also decreased the Cr(VI) concentration in water (almost 0 mg/L), enhancing the safety of DWDS. This study provides theoretical guidance on the safe operation of DWDS.

Construction and mechanistic insights of a novel ZnO functionalized rGO composite for efficient adsorption and reduction of Cr(VI).

A series of ZnO decorated reduced graphene oxide (rGO) (ZnrGOx) with different doping ratios were synthesized by the alkaline hydrothermal method using graphene oxide (GO) and Zn(NO3)2·6H2O as precursors, and subsequently used for the adsorption study of Cr(VI) in water. The morphology, crystalline phase structure, and surface elemental properties of ZnrGOx composites were revealed by XRD, SEM, BET, FT-IR, and XPS characterizations. The results showed that ZnO nanoparticles can be clearly seen on the surface of layered rGO. Meanwhile, as the doping rate increased, the C = C double bonds were broken and more carboxylic acid groups formed in ZnrGOx. In addition, the ZnrGO0.1 composite had the most excellent adsorption performance and good stability, and reusability. The adsorption removal rate of Cr(VI) can reach 99%, and the maximum adsorption amount of Cr(VI) was 68.9655mg/g in 3h. The isothermal and kinetic model simulations showed that Cr(VI) adsorption on ZnrGO0.1 composite is a chemical adsorption process, spontaneous and endothermic. Based on the concentrations of different valence states of Cr in the solid and liquid phases, 40% of Cr(VI) was reduced to Cr(III) on the surface of ZnrGO0.1 composite. Moreover, the adsorption-reduction mechanisms of Cr(VI) on ZnrGO0.1 composite were further elucidated. The ZnrGO0.1 composite manifested great potential as an efficient adsorbent for Cr(VI) removal.

Epitaxial Growth and Characterization of Nanoscale Magnetic Topological Insulators: Cr-Doped (Bi0.4Sb0.6)2Te3.

The exploration initiated by the discovery of the topological insulator (BixSb1-x)2Te3 has extended to unlock the potential of quantum anomalous Hall effects (QAHEs), marking a revolutionary era for topological quantum devices, low-power electronics, and spintronic applications. In this study, we present the epitaxial growth of Cr-doped (Bi0.4Sb0.6)2Te3 (Cr:BST) thin films via molecular beam epitaxy, incorporating various Cr doping concentrations with varying Cr/Sb ratios (0.025, 0.05, 0.075, and 0.1). High-quality crystalline of the Cr:BST thin films deposited on a c-plane sapphire substrate has been rigorously confirmed through reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM) analyses. The existence of a Cr dopant has been identified with a reduction in the lattice parameter of BST from 30.53 ± 0.05 to 30.06 ± 0.04 Å confirmed by X-ray diffraction, and the valence state of Cr verified by X-ray photoemission (XPS) at binding energies of ~573.1 and ~583.5 eV. Additionally, the influence of Cr doping on lattice vibration was qualitatively examined by Raman spectroscopy, revealing a blue shift in peaks with increased Cr concentration. Surface characteristics, crucial for the functionality of topological insulators, were explored via Atomic Force Microscopy (AFM), illustrating a sevenfold reduction in surface roughness as the Cr concentration increased from 0 to 0.1. The ferromagnetic properties of Cr:BST were examined by a superconducting quantum interference device (SQUID) with a magnetic field applied in out-of-plane and in-plane directions. The Cr:BST samples exhibited a Curie temperature (Tc) above 50 K, accompanied by increased magnetization and coercivity with increasing Cr doping levels. The introduction of the Cr dopant induces a transition from n-type ((Bi0.4Sb0.6)2Te3) to p-type (Cr:(Bi0.4Sb0.6)2Te3) carriers, demonstrating a remarkable suppression of carrier density up to one order of magnitude, concurrently enhancing carrier mobility up to a factor of 5. This pivotal outcome is poised to significantly influence the development of QAHE studies and spintronic applications.

Effect of Ca2+/Cr3+doping ratio on the infrared radiation performance and Cr6+ formation in LaAlO3 ceramics

Ca2+/Cr3+ co-doped LaAlO3 has been considered as important ceramic to achieve energy-savings in thermal equipment due to excellent infrared radiation (IR) performance. However, following problems restricted its industrial applications: one is the correlation between emissivity and the valence state of Cr which is not clear, then there is no quantitative evaluation of Cr6+ content in ceramics. In this work, Ca2+/Cr3+ co-doping LaAlO3 ceramics have been fabricated. By adjusting Ca2+/Cr3+ doped ratio (0 ≤ n(Ca2+)/n(Cr3+) ≤ 0.75), the “Cr3+→(Cr4+/Cr6+)” transformation ratio has been controlled. The results show that a higher concentration of Cr4+ in the material can significantly enhance the emissivity, while Cr6+ has no such effect. In addition, the Cr6+ content was measured by leaching method and high-temperature volatilization methods, respectively. This work can be used to guide the fabrication of environment-friendly Ca2+/Cr3+ co-doped LaAlO3-based ceramics with high emissivity in the field of energy-saving for thermal equipment.

Exploration of temperature driven conduction process and ferroelectric properties of Mn doped GdCrO3

This work delivers the research findings of the temperature dependent DC resistivity, AC impedance and ferroelectric polarization of GdCr1−xMnxO3 (x = 0 and 0.3). Mixed valence states of Cr (Cr3+ and Cr4+) are explored using the x-ray photoelectron spectroscopy analysis. The exponential decay of DC resistivity on escalating the temperature advocates the semiconducting-like nature for the probed samples. The DC resistivity data of these samples fit well into small-polaron hopping and variable range hopping models. The impedance attributes of these samples were scrutinized over a broad spectrum of temperatures at selected frequencies. The values of the real and imaginary parts of impedance unveil substantial reduction on raising the temperature, thereby signifying the increase in conductivity of the samples. Pristine sample displays an electrical relaxation peak at 65 °C, which translates towards the lower temperature at higher frequencies. Further, the semicircular behavior of Nyquist plots at higher temperatures indicates the reduction of the charge transfer resistance. The equivalent circuits of Nyquist plots are generated using Z-view software. From these plots, it is perceived that grain boundary resistance upsurges while the grain resistance and capacitance drops upon doping. The ferroelectric measurements reveal that the coercive field (Ec) values decrease whereas the values of maximum polarization (Pm), remnant polarization (Pr) and energy storage increase in 30% doped GdCrO3. These observations establish that electrical and ferroelectric properties of GdCrO3 system can be tuned with appropriate Mn doping.

Structural transition and magnetization reversal in rare earth doped R0.5Sr0.5Fe0.5Cr0.5O3 (R[dbnd]La, Nd and Sm) perovskite oxides containing mixed valent cations at B site: Magnetic, optical and transport properties

In the current paper, the effect of lanthanide metal cation substitution on structural, magnetic, optical and transport properties of R0.5Sr0.5Fe0.5Cr0.5O3 (RLa, Nd and Sm) perovskite oxides have been investigated. Structural investigations reveal that there is a phase transition from cubic to orthorhombic symmetry with the doping of heavier rare earth ion. The findings of XPS studies point to the existence of mixed valence states of Cr and Fe ions. The change in magnetization in response to an external magnetic field reveals that the phases have a mostly antiferromagnetic character with some trace amounts of ferromagnetic components. In temperature dependent magnetization studies, magnetic reversal has been observed in Nd doped sample, while La and Sm doped samples only show positive magnetization. The band gap energies of the synthesized materials determined from the UV–vis reflectance spectroscopy lie in the range of 1.60–1.78 eV indicating the semi-conducting nature of the samples. The temperature-dependent resistivity measurements show semi-conducting behaviour of the samples with decreasing temperature which finally become insulating at low temperature. It has been shown that the VRH model provides the best fit for the resistivity data when compared to the other transport mechanism models that were used to describe the electrical conduction process of synthesized phases.

Molecular toxicity of Cr(III) and Cr(VI) to defensive protein lysozyme and their differential mechanisms

Chromium (Cr) poses potential threats on human and ecological health through both food and environmental pathways. However, the response mechanisms of Cr to function-related proteins in human subjects and the differential effects in the case of different valence states of Cr are still lacking. Herein, the binding interactions and mechanisms of lysozyme to Cr(III) and Cr(VI) were investigated by isothermal titration microcalorimetry, multi-spectroscopy, enzyme activity assay, and molecular simulations. Our results indicated that the binding of Cr in different valence states with lysozyme was a relatively affinity process and mainly driven by hydrophobic forces. Both Cr species induced the looseness of backbone for lysozyme and the enhancement of hydrophilicity around the backbone microenvironment. Otherwise, the α-helix of lysozyme was decreased with different valence states of Cr, while Cr(III) showed a greater degree of influence and a stronger regularity. Interestingly, no significant changes in the microenvironment around aromatic amino acid residues were observed under the exposure of different valence states of Cr. Differential structural changes of lysozyme resulted in activity alterations. At 80 mg·L−1 of Cr, Cr (VI) reduced the lysozyme activity to 81.44% of the control, while the lysozyme activity was significantly reduced to 24.45% under the exposure of Cr (III). Further molecular docking showed that amino acids near the binding sites of different valence states of Cr with lysozyme were not identical, but the enzyme active site, Asp52, was all within the binding pocket. This study elucidates the differential toxicity effects and interaction mechanisms of Cr in different valence states, and offers a comprehensive strategy for exploring the in vitro responses of toxicants exposure.

Early oxidation stages of austenitic stainless steel monitored using Mn as tracer

Understanding the mechanism of oxide layer growth on 316 L requires knowledge, e.g., about the reaction front position, oxide phase formation and diffusion paths of the elements involved. We gain essential information for the early stages of oxidation up to 600 °C, utilizing Mn as tracer in a novel experimental approach. Reasoning is based on monitoring implanted Mn in a Mn-free 316 L before and after oxidation. The reaction front is located inside each oxide grain at ∼400 °C but shifts towards the surface at ∼600 °C. Detection of Cr6+ at 600 °C suggests a so far undocumented role of Cr valence state during oxide growth.

Optical, electrical, and EPR studies of polycrystalline Al:Cr:ZnSe gain elements

Transition metal-doped II-VI (TM:II-VI) chalcogenides are well-known laser materials for optically pumped middle-infrared lasers. Cr:ZnSe is a key representative of this class of transition metal doped II-VI gain media and is arguably considered the material of choice for optically pumped middle-infrared lasers. In addition to effective mid-IR lasing under optical excitation, these crystals, being wide-band semiconductors, hold the potential for direct electrical excitation. One way to form n-type conductivity in ZnSe crystals is by annealing them in a melt of Zn-Al alloy. However, this annealing of Cr:ZnSe crystals results in their purification and transfer of chromium to the melt of Zn-Al alloy. In this article, we report on optimizing the doping technique for providing n-type conductivity in Al:Cr:ZnSe crystals while preserving the chromium concentration. Al:Cr:ZnSe samples with resistivities ranging from 10.8 to 992 Ω-cm were fabricated. While the 2 + valence state of Cr is typically dominant in Cr:ZnSe, both Cr2+ and Cr+ were detected in Al:Cr:ZnSe samples. The maximum level of Cr+ concentration was measured to be 4 × 1018 cm-3.

Toxicity mechanisms and remediation strategies for chromium exposure in the environment

Chromium (Cr) is the seventh most abundant chemical element in the Earth’s crust, and Cr(III) and Cr(VI) are common stable valence states of Cr. Several Cr-containing substances, such as FeOCr2O3 and stainless-steel products, exist in nature and in life. However, Cr(VI) is toxic to soil, microorganisms, and plants and poses a serious threat to human health through direct and indirect exposure. By collecting published journal literature, we found that Cr(VI) can cause acute and chronic toxicity in organisms and has carcinogenic effects, and the mechanisms causing these toxicity include endoplasmic reticulum stress, autophagy and apoptosis. However, the relationship between these mechanisms remains unclear. Many methods have been researched to purify chromium, but each of these methods has its own advantages and disadvantages. Therefore, this review summarizes the hazards of chromium and the mechanisms of chromium toxicity after entering cells and provides a number of methods for chromium contamination management, providing a direction for the next step in chromium toxicology and contamination decontamination research.

An environmental-friendly process for efficient recovery of Cr and harmless utilization of stainless steel slag via supergravity

Stainless steel slag is classified as a hazardous waste owing to the presence of soluble poisonous Cr(VI), which is harmful to the surrounding environment and human health. In this study, an environmental-friendly process was proposed for efficient recovery of Cr resources and harmless utilization of stainless steel slag. Cr element was selectively enriched from molten slag into the Cr-spinel crystal with the decrease of temperature and efficiently immobilized into the Cr-spinel with a stable valence state of Cr(III) at the temperature of 1573 K in molten stainless steel slag. In addition, almost all Cr-spinel crystals were fully recovered from the molten slag under the supergravity field, where the recovery rate of Cr was up to 95.24 % and the mass fraction of Cr2O3 in Cr-spinel phase reached 19.96 wt%. Moreover, the total leaching amount of Cr in both Cr-spinel and residue phases is as low as 0.67 mg/L and 0.13 mg/L and both products were further recycled, which indicated that Cr elements were completely immobilized in both green and environmental-friendly products.

Detection of chromium in different valence states in water and soil using laser-induced breakdown spectroscopy combined with an ion enrichment chip

IEC–LIBS could rapidly and sensitively detect different valence states of Cr in water and soil.

Formation of rutile (Cr,Ta,Ti)O2 oxides during oxidation of refractory high entropy alloys in Ta-Mo-Cr-Ti-Al system

The chemical identity of rutile oxides formed during oxidation of alloys with different Ti content within the Ta-Mo-Cr-Ti-Al system at 1200 °C for 24 h was determined. Rutile-type oxide (Cr,Ta,Ti)O2 was observed on 20Ta20Mo20Cr20Ti20Al and 67.5(TaMoCr)10Ti22.5Al (at%). Based on the experimental results, the valence states of Cr, Ta and Ti were unequivocally determined. Higher concentrations of Ti in (Cr,Ta,Ti)O2 lead to the formation of thinner oxide scales and zones of internal corrosion. It is concluded that the occupation of higher-valent Ti4+ cations on the Cr3+ sub-lattice reduces the oxygen vacancy concentration and thus improves the oxidation behavior of n-type conducting (Cr,Ta,Ti)O2-forming alloys.

Interfacial charge transfer induced antiferromagnetic metals and magnetic phase transition in (CrO2) m /(TaO2) n superlattices

As a class of remarkable spintronic materials, intrinsic antiferromagnetic (AFM) metals are rare. The exploration and investigation of AFM metals are still in its infancy. Based on first-principles calculations, the interface-induced magnetic phenomena in the (CrO2) m /(TaO2) n superlattices are investigated, and a new series of AFM metals is predicted. Under different ratios of with varying valence states of Cr, the (CrO2) m /(TaO2) n superlattices exhibit three different phases, including the AFM metal, the AFM semiconductor, and the ferromagnetic (FM) metal. In the AFM semiconducting phases, the intra-CrO2-monolayer magnetic exchange interaction is systematically discussed, corresponding to m = 1 or m = 2. Both the localization of the Cr 3 d orbitals and the crystal-field splitting are crucial for magnetic ordering in super-exchange interactions. Based on the analyses of the AFM semiconducting phases with m = 1 and m = 2, the mechanisms of AFM metallic phases with radios of and are discussed in detail. Additionally, the AFM metallic superlattices can be tuned into a FM metallic phase by applying strain in the c-direction, such as a compression of 7% in the (CrO2)1/(TaO2)3 superlattice, and a tensile strain of 7% in the (CrO2)2/(TaO2)3 superlattice. The phase diagram of the (CrO2) m /(TaO2) n superlattices is obtained as a function of the layer thickness. This work provides new insights about realizing and manipulating AFM metals in artificial superlattices or heterostructures in experiments.

Quantification and the sources identification of total and insoluble hexavalent chromium in ambient PM: A case study of Aktobe, Kazakhstan

Hexavalent chromium (Cr(VI)), a known carcinogen, emanates from both anthropogenic and natural sources. A pilot study of the ambient Cr(VI) concentrations was conducted at the center of Aktobe which is a few kilometers away from major industrial chromium plants. Total Cr(VI) concentrations were measured in the fall and winter seasons with mean values (S.D) of 5.30 (2.16) ng/m3 and 2.26 (1.80) ng/m3, respectively. Insoluble Cr(VI) levels were 4.80 (1.96) and 2.19 (1.75) ng/m3 for the fall and winter, respectively. The total and insoluble Cr(VI) concentrations in the fall season were significantly higher than in winter, likely due to the higher rate of Cr(III) oxidation in the presence of ozone and ROS in fall compared to the rate of Cr(VI) reduction in the presence of VOCs at higher temperatures. On average, total Cr(VI) constituted 34.49% of the total Cr concentrations suggesting that the dominant valence state of Cr in the atmosphere is Cr(III). The previous reference values of exposure to Cr(VI) must be revisited by taking into account the insoluble Cr(VI) concentration since it is more prevalent in the atmosphere compared to soluble Cr(VI). The influence of the chromium plants as potential sources was not obvious in this study.

Effects of Cr and Fe substitution at Mn-sites of GdMn1-xTxO3 (x = 0, 0.10) on its structural and complex dielectric properties

The observation of insulators to metallic conduction leads to vigorous study in transition metal-doped GdMnO3. Present study reveals the detailed study of structural correlation to electrical properties of transition metal element doped polycrystalline GdMn1-xTxO3 (where T = Cr, Fe; x = 0, 0.10) solid solution. The structural properties and phase purity of the synthesized samples have been analyzed by XRD. The Rietveld refinement of XRD patterns shows that the samples are crystallized in orthorhombic symmetry having the Pnma space group. However, the doping of Cr and Fe affects the octahedral distortion and structural parameters. The Mn–O octahedral distortion in Cr and Fe doped GdMn1-xTxO3 is reduced compared to pure GdMnO3, which is confirmed by the Raman spectroscopy. The X-ray photoelectron spectroscopy study is further observed to study the multiple valence state of Cr, Fe, and Mn in the material, which affects the structural and electrical properties of doped GdMn1-xTxO3. The low-temperature complex dielectric, complex Impedance, and ac conductivity study reveal the anomalous change in the dielectric behavior of Cr and Fe doped GdMn1-xTxO3 compared to pure GdMnO3. Dielectric constant and impedance show a relatively high value in GdMnO3, but the values decrease after Cr and Fe doping. A rapid change with decreased dielectric constant values in GdMn0.9Cr0.1O3 is observed compared to GdMn0.9Fe0.1O3 and GdMnO3 in the temperature range of 300 K–80 K. The ac conductivity and activation energy study of polycrystalline GdMn1-xTxO3 reveal the transformation from insulator to semiconducting nature of the material.

Temperature dependent reduction of Cr(VI) to Cr(V) aroused by CaO during thermal treatment of solid waste containing Cr(VI)

Cr(VI) compounds at high temperature usually tend to decompose and reduce into Cr(III) due to thermodynamically instability for Cr(VI). This study found Cr(VI) could be reduced into Cr(V) instead of Cr(III) in the presence of CaO during heating solid waste containing Cr(VI). CaCrO4 is prepared and mixed with CaO as simulated solid waste containing Cr(VI). It was found that CaCrO4 reacted with CaO and formed a new product Ca5(CrO4)3O0.5 at temperature range of 800 and 1000 °C. The valence state of Cr in Ca5(CrO4)3O0.5 is determined to be +5 b y XPS analysis, and the color for new formed Cr(V) is observed in green, similar to Cr(III) compounds. The temperature and CaO are two keys to arouse the reduction reaction of Cr(VI) into Cr(V). In particular, the reduction of Cr(VI) into Cr(V) is strongly depended on temperature (800–1000 °C), this reaction can be balanced within 10 min, while prolonging sintering time has little help for promoting the reduction of Cr(VI) to Cr(V). Additionally, it was found Cr(V) can keep stable and not be re-oxidized into Cr(VI) at 800–1000 °C. Above results offers some new understanding and knowledge about the formation of Cr(V) in presence of much CaO or CaCO3 during heating solid waste containing Cr(VI).

Ruthenium containing perovskites as electrode materials for 4-nitrophenol detection

In this paper, the relationship of structure, type of oxygen defects, valence states of Cr and Ru, and electrochemical properties of La0.7Sr0.3Cr1-XRuXO3 (0 < x < 0.1) perovskite-type oxides were studied. The samples were synthesized by a conventional solid-state reaction method and characterized by powder X-ray diffraction, X-ray fluorescence spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and electron paramagnetic resonance spectroscopy. The electrochemical performance of these samples was evaluated towards the detection of 4-nitrophenol and strongly depends on the concentration of ruthenium incorporated in the crystal lattice. A new La0.7Sr0.3Cr0.925Ru0.075O3 electrocatalyst with a wide linear concentration range (25–5000 mM) and a detection limit of 8 mM was obtained. These results provide an opportunity for its application in the analysis of real water samples.

Role of manganese superoxide dismutase (Mn-SOD) against Cr(III)-induced toxicity in bacteria

The toxicity of Cr(VI) was widely investigated, but the defense mechanism against Cr(III) in bacteria are seldom reported. Here, we found that Cr(III) inhibited bacterial growth and induced reactive oxygen species (ROS). After exposure to Cr(III), loss of sodA not only led to the excessive generation of ROS, but also enhanced the level of lipid peroxidation and reduced the GSH level, indicating that the deficiency of Mn-SOD decreased the bacterial resistance ability against Cr(III). The adverse effects of oxidative stress caused by Cr(III) could be recovered by the rescue of Mn-SOD in the sodA-deficient strain. Besides the oxidative stress, Cr(III) could cause the bacterial morphology variation, which was distinct between the wild-type and the sodA-deficient strains due to the differential expressions of Z-ring division genes. Moreover, Mn-SOD might prevent Cr(III) from oxidation on the bacterial surface by combining with Cr(III). Taken together, our results indicated that the Mn-SOD played a vital role in regulating the stress resistance, expression of cell division-related genes, bacterial morphology, and chemistry valence state of Cr. Our findings firstly provided a more in-depth understanding of Cr(III) toxicity and bacterial defense mechanism against Cr(III).