Chromium Species Research Articles

Evaluation and Assessment of Trivalent and Hexavalent Chromium on Avena sativa and Soil Enzymes.

Chromium (Cr) can exist in several oxidation states, but the two most stable forms-Cr(III) and Cr(VI)-have completely different biochemical characteristics. The aim of the present study was to evaluate how soil contamination with Cr(III) and Cr(VI) in the presence of Na2EDTA affects Avena sativa L. biomass; assess the remediation capacity of Avena sativa L. based on its tolerance index, translocation factor, and chromium accumulation; and investigate how these chromium species affect the soil enzyme activity and physicochemical properties of soil. This study consisted of a pot experiment divided into two groups: non-amended and amended with Na2EDTA. The Cr(III)- and Cr(VI)-contaminated soil samples were prepared in doses of 0, 5, 10, 20, and 40 mg Cr kg-1 d.m. soil. The negative effect of chromium manifested as a decreased biomass of Avena sativa L. (aboveground parts and roots). Cr(VI) proved to be more toxic than Cr(III). The tolerance indices (TI) showed that Avena sativa L. tolerates Cr(III) contamination better than Cr(VI) contamination. The translocation values for Cr(III) were much lower than for Cr(VI). Avena sativa L. proved to be of little use for the phytoextraction of chromium from soil. Dehydrogenases were the enzymes which were the most sensitive to soil contamination with Cr(III) and Cr(VI). Conversely, the catalase level was observed to be the least sensitive. Na2EDTA exacerbated the negative effects of Cr(III) and Cr(VI) on the growth and development of Avena sativa L. and soil enzyme activity.

Separation, speciation and quantification of both chromium (VI) and chromium (III) in tanned leather samples: a comparative study and validation of analytical methods

In the present work, a comparative study of analytical methods for the simultaneous and quantitative determination of trivalent and hexavalent chromium is presented. For the analysis by ion chromatography-inductively coupled plasma-mass spectrometry, two different columns were tested, as well as different mobile phases and different pH of the samples. The optimized analytical method permitted the separation of Cr(III) and Cr(VI) using 75 mmol/L NH4NO3 pH 3 as chromatographic eluent. The method was validated and applied to real samples, allowing the determination of both species simultaneously, even when there is a huge difference of concentration between Cr(III) and Cr(VI). Limit of detection and limit of quantification for Cr(III) were found to be 0.016 and 0.054 upmug/L (0.3 and 1.1 upmug/kg), respectively, and for Cr(VI) 0.13 and 0.43 upmug/L (7 and 22 upmug/kg), respectively. Possible species interconversions were monitored through the use of chromium isotopic standards, which confirmed that the optimized methodology preserves chromium speciation during extraction and analysis. Fourier-transform ion cyclotron resonance-mass spectrometry permitted the structure elucidation of the complex formed during ethylenediaminetetraacetic acid extraction.Graphical

Computational Modeling for Cr and S Poisoning Pathways on La0.6Sr0.4Co0.2Fe0.8O3 Surfaces

Solid oxide fuel cells (SOFCs) are highly efficient devices for energy conversion. However, their performance is hindered by the poisoning of their oxygen electrode materials by chromium and sulfur species. While previous studies have proposed a nucleation theory of Cr and S poisoning as a mechanism, little is known about the adsorption behaviors and compound formation steps during the poisoning process. This knowledge is critical for understanding the poisoning mechanisms and developing effective mitigation strategies. In this study, the state-of-the-art SOFC oxygen electrode material, La0.6Sr0.4Co0.2Fe0.8O3 (LSCF), is used as a modeling system. A realistic surface structure will be constructed by grand canonical Monte Carlo (GCMC) simulation. Then, the adsorption energies as a function of surface chemistry will be calculated using density functional theory (DFT). The results revealed the importance of surface chemistry in determining the energetics and kinetics of precursor adsorption and compound formation.

Exogenous hydrogen sulfide alleviates chromium toxicity by modulating chromium, nutrients and reactive oxygen species accumulation, and antioxidant defence system in mungbean (Vigna radiata L.) seedlings

Chromium (Cr), a highly toxic redox-active metal cation in soil, seriously threatens global agriculture by affecting nutrient uptake and disturbing various physio-biochemical processes in plants, thereby reducing yields. Here, we examined the effects of different concentrations of Cr alone and in combination with hydrogen sulfide (H2S) application on the growth and physio-biochemical performance of two mungbeans (Vigna radiata L.) varieties, viz. Pusa Vishal (PV; Cr tolerant) and Pusa Ratna (PR; Cr sensitive), growing in a pot in hydroponics. Plants were grown in the pot experiment to examine their growth, enzymatic and non-enzymatic antioxidant levels, electrolyte balance, and plasma membrane (PM) H+-ATPase activity. Furthermore, root anatomy and cell death were analysed 15 days after sowing both varieties in hydroponic systems. The Cr-induced accumulation of reactive oxygen species caused cell death and affected the root anatomy and growth of both varieties. However, the extent of alteration in anatomical features was less in PV than in PR. Exogenous application of H2S promoted plant growth, thereby improving plant antioxidant activities and reducing cell death by suppressing Cr accumulation and translocation. Seedlings of both cultivars treated with H2S exhibited enhanced photosynthesis, ion uptake, glutathione, and proline levels and reduced oxidative stress. Interestingly, H2S restricted the translocation of Cr to aerial parts of plants by improving the nutrient profile and viability of root cells, thereby relieving plants from oxidative bursts by activating the antioxidant machinery through triggering the ascorbate-glutathione cycle. Overall, H2S application improved the nutrient profile and ionic homeostasis of Cr-stressed mungbean plants. These results highlight the importance of H2S application in protecting crops against Cr toxicity. Our findings can be utilised to develop management strategies to improve heavy metal tolerance among crops.

Chemical Speciation of Arsenic and Chromium in Seafood by LC-ICP-MS

Two methods were developed for the As and Cr species determination in different kinds of seafood, exploring the LC-ICP-MS potential and chemometric approach to define the extraction conditions. Adequates separation and sensitivity data by LC-ICP-MS were obtained with 0.01 mol L-1 (NH4)2HPO4 in 1% ethanol (pH 8.0) for arsenic, and 0.015 mol L-1 Na2SO4, 0.005 mol L-1 EDTA, and 0.005 mol L-1 NaH2PO4 (pH 7.0) for chromium. The Doehlert matrix and Box-Behnken design defined the ideal extraction conditions for arsenic and chromium species. For As extraction, the optimized conditions employed 0.1 g of sample and 30 mmol L-1 HNO3 at 90°C for 45 min, and Cr, 0.1 g of sample and 0.045 mol L-1 [EDTA] at 90°C for 40 min. Recoveries from 88 to 106% of arsenobetaine (AsB), arsenite [As(III)], dimethylarsinic acid (DMA), monomethylarsonic acid (MMA), arsenate [As(V)], Cr(III) and Cr(VI) were obtained for all evaluated samples. The limits of quantification provided by the proposed methods were 5.3; 52.1; 16.4; 2.8; 83.3; 113.8; 53.9 ng g-1 for AsB, As(III), DMA, MMA, As(V), Cr(III) and Cr(VI) respectively. The trueness was evaluated using certified reference materials and addition and recovery procedures. The sum of the species agreed with the total concentration of arsenic and chromium contents.

Bi-functional photocatalytic heterostructures combining titania thin films with carbon quantum dots (C-QDs/TiO2) for effective elimination of water pollutants

In this study, carbon quantum dots (C-QDs), prepared via hydrothermal-microwave procedures, were successfully combined with nanostructured titania (TiO2). The photocatalytic oxidation/reduction activity of the C-QDs/TiO2 composite films was evaluated in the decomposition of organic-inorganic contaminants from aqueous solutions under UV illumination. Physicochemical characterizations were applied to investigate the crystal structure of the carbon quantum dots and the composites. It was found that the prepared C-QDs/TiO2 composites had great contribution to the photocatalytic reduction of hexavalent chromium (Cr+6) species and 4-Nitrophenol (PNP) as well as to the photocatalytic oxidation of methylene blue (MB) and Rhodamine B (RhB) dyes. The mechanism of the photocatalytic reaction was studied with trapping experiments, revealing that the electron (e−) radical species were powerfully supported for the photocatalytic reduction of Cr+6 and PNP and the holes (h+) are the main active species for the photocatalytic oxidation reactions.

Distinct chromium removal mechanisms by iron-modified biochar under varying pH: Role of iron and chromium speciation

Iron-modified biochar (Fe-biochar) has been widely developed to attenuate Cr(VI) pollution in both acid and alkaline environments. However, there are few comprehensive studies on how the iron speciation in Fe-biochar and chromium speciation in solution influencing the removal of Cr(VI) and Cr(III) under varying pH. Here, multiple Fe-biochar containing Fe3O4 or Fe(0) were prepared and applied to remove aqueous Cr(VI). Kinetics and isotherms suggested that all Fe-biochar could efficiently remove Cr(VI) and Cr(III) via adsorption-reduction-adsorption. The Fe3O4-biochar immobilized Cr(III) by forming FeCr2O4, while amorphous Fe–Cr coprecipitate and Cr(OH)3 was formed when using Fe(0)-biochar. Density functional theory (DFT) analysis further indicated that pH increase caused more negative adsorption energies between Fe(0)-biochar and the pH-dependent Cr(VI)/Cr(III) species. Consequently, the adsorption and immobilization of Cr(VI) and Cr(III) species by Fe(0)-biochar was more favored at higher pH. In comparison, Fe3O4-biochar exhibited weaker adsorption abilities for Cr(VI) and Cr(III), which were in consistent with their less negative adsorption energies. Nonetheless, Fe(0)-biochar merely reduced ∼70% of adsorbed Cr(VI), while ∼90% of adsorbed Cr(VI) was reduced by Fe3O4-biochar. These results unveiled the importance of iron and chromium speciation for chromium removal under varying pH, and might guide the application-oriented design of multifunctional Fe-biochar for broad environmental remediation.

Speciation of chromium in water samples and lettuce extracts in the unified bioaccessibility method (UBM) saliva solution by vortex assisted-dispersive solid phase microextraction

In this study, a new sulfonamide based polymeric adsorbent (5ATT-CSPS) was prepared with reaction between 5-Amino-1,3,4-thiadiazole-2-thiol and chlorosulfonated polystyrene resin and characterized by FT-IR, FESEM-EDX, zeta potential. It was used for the first time as an adsorbent for speciation of chromium in various water samples and lettuce extracts in UBM saliva by dispersive solid phase micro extraction (d-SPµE). The total chromium concentration was determined by F AAS. The parameters affecting the recovery of Cr(III) such as pH, contact times, elution conditions, sample volume, co-existing ions and adsorption capacity were optimized. The adsorbent demonstrated a good performance for adsorption of Cr(III) (R%≥95). It was quantitatively adsorbed in the range of pH 2.0–4.0 whereas Cr(VI) was not adsorbed in the pH range of 2.0-8.0. Therefore Cr(VI) concentration was calculated indirectly. The elution was achieved by 5 mL of 2 mol L-1 HNO3. Adsorption and elution contact times of the adsorbent were 3 min and 2 min, respectively. The preconcentration factor of the method was found to be 8. Considering optimal conditions, limit of detection was found to be 2.9 µg L-1, and precision of the method (as RSD%) was found to be ≤4.3%. The adsorption capacity of the 5ATT-CSPS for Cr(III) was 25 mg g−1.The accuracy of this method was verified by analyzing TMDA-70 certified reference material and by recovery studies in spiked water samples and lettuce extracts in the unified bioaccessibility method (UBM) saliva.

Mechanistic insights into collaborative removal of NOx and chromium from flue gas in denitrifying biotrickling filter

Nitrogen oxides (NOx) and chromium can cause harm to human health and ecological environment. An aerobic denitrifying biotrickling filter (DBTF) for simultaneous removal of NOx and chromium from flue gas was investigated. NOx and chromium removal efficiency could reach up to 98 % and 88 %, respectively. Halomonas, Stappia, Pseudomonas and UG_Peptococcaceae were the core chromium-resistance- denitrifying genus. Anti-oxidative stress proteins (RpoS, SOD, OxyR and catalase) and anti-heavy metal proteins (MntA, FbpA, TorB and ChrE etc.) and the denitrifying enzymes (NarH, NarI, NapA, NapB, NirK, NirS and NorB) involved in the regulation of chromium stress and the reduction of NOx, as shown by 16 S rDNA, metagenomic and metaproteomic sequencing. The biofilm was characterized by FTIR, XPS, EEM, and SEM-EDS. XPS spectra indicated the formation of a chromium carbonate by microbial induced carbonate precipitation. Chromium speciation in biofilm mainly consisted of 52.8 % organic matter bound state, 35.1 % carbonate bound state and 10.7 % exchangeable state. Flue gas chromium could be removed in the form of chromium carbonate bioprecipitate and HA-Cr via complexation of humic acids in extracellular polymeric substances (EPS), biosorption and biodeposition. DBTF was capable of NOx reduction and chromium removal by denitrification. The results provide a new potential for the collaborative control of NOx and heavy metals from flue gas by the DBTF.

Amorphous silica-alumina as robust support for catalytic dehydrogenation of propane: Effect of Si/Al ratio on nature and dispersion of Cr active sites

The effect of amorphous silica-alumina (ASA) with Si/Al ratios of 0.01, 0.1, 1, and 3 on the catalytic performance of chromium catalysis in the propane dehydrogenation reaction were studied. The characterization results reveal that the Si/Al ratio significantly affects the nature and dispersion of chromium species, reducibility, the surface concentration of Cr3+, and acidity. ASA catalysis with Si/Al ratios of 0.1 and 0.01 showed a remarkable increase in Cr6+ species and the lowest α-Cr2O3, which have the highest propane conversion (with initial propylene yield of 60 and 57, respectively) due to the reduction of surface monochromate Cr6+ species, which are the precursor of coordinatively unsaturated active sites (c.u.s.) to active Cr3+ species. Si/Al increase to the values of 1 and 3 can restrict the access of reactants to active Cr species due to the decrease in chromium reduction and increase in α-Cr2O3.

All-solid-state MoS2/WO3 photoelectrodes as high-efficiency catalysts for reductive/sorptive/recycling of hexavalent chromium

Photoelectrocatalysis (PEC) is an effective approach to eliminate carcinogen hexavalent chromium (Cr(VI)) in wastewater, in which high-performance catalysts are crucial. Herein, controlled growth of thin molybdenum disulphide (MoS2) nanosheets on self-supported tungsten trioxide (WO3) created an all-solid-state MoS2/WO3 heterojunction serving as electrode and catalyst simultaneously for removing Cr(VI). Countless small and thin MoS2 nanoflakes build in a huge and porous interface for harvesting lights and adsorbing chromium species. And the highly conductive WO3 substrate facilitates the transfer of those photoexcited-electron and therefore suppresses the recombination between electrons and holes. Furthermore, assisted by bias potential, electron streams from external circuit render an electron-rich interface at the MoS2/WO3 cathode, accelerating the Cr(VI) reduction by PEC. At −1.2 V, the PEC reduction efficiency of Cr(VI) reaches 100% within 30 min, surpassing the pristine WO3 by 2.7 times. The generated Cr(III) ions can be immobilized on the porous MoS2/WO3 cathode through electrostatic attraction, enabling removal of total chromium. More importantly, the Cr(III) anchored to the catalyst can be effortlessly recovered by eluting with clean water, which also refreshes the MoS2/WO3 cathode. This study provides a new approach to fabricating photoelectrodes for sustainable PEC reduction and treatment of Cr(VI) containing wastewater.

Construction of bubbles enrichment sites and gas-diffusion-microchannel to assist Cr(VI) electrochemical reduction in a flow-through electrochemical system

Due to characteristics of the forced convection and enhanced mass transfer, graphite felt cathode based flow-through electrochemical system presented high electroreduction efficiency for aqueous Cr(VI). However, disadvantage is that bubbles generated by water electrolysis cannot pass through the liquid filled microchannel in time, which is easy to cause gas accumulation and an unstable electrochemical operation. Herein, we demonstrated graphite felt flow-through cathode designed with hydrophobic polytetrafluoroethylene (PTFE) as bubbles enrichment sites and construction of gas-diffusion-microchannel to assist in Cr(VI) electrochemical reduction. Cr(VI) reduction kinetics constant by graphite felt flow-through cathode increased 4.6 times after loading PTFE and was 2.6 ∼ 5.7 times higher than parallel-plate electrodes system. Typical electrochemical analysis suggested that PTFE can enrich and accelerate the dissolved oxygen mass transfer rate at PTFE-electrode-solution micro-interface, realizing oxygen digestion via two-electron reduction reaction. The unconsumed bubbles were transported out of electrochemical cell along gas-diffusion-microchannel to avoid gas accumulation and maintained a stable operation. Batch experiments indicated the ∼ 99.9% Cr(VI) reduction efficiency when the initial pH 2 and 100 mg/L Cr(VI) feed was treated under a single-pass pattern with flow rate of 1.5 mL/min and current density of 12.74 mA/cm2. Mechanism study revealed that faraday reaction was the main driving force for Cr(VI) reduction, while Cr(VI)-induced activation of in-situ electro-generated H2O2 contributed to formations of •OH and intermediate chromium species. This work also shows the feasibility of remediation for Cr(VI)-organic coexistence environment by a catalyst-free flow-through electrochemical system.

Chromium Speciation by HPLC-DAD/ICP-MS: Simultaneous Hyphenation of Analytical Techniques for Studies of Biomolecules

The first element legislated adopting chemical speciation was chromium (Cr) for differentiation between the highly toxic Cr(VI) from the micronutrient Cr(III). Therefore, this work aimed to develop a new analytical method through the coupling of High-Performance Liquid Chromatography with Diode-Array Detection (HPLC-DAD) with inductively coupled plasma mass spectrometry (ICP-MS) to obtain molecular and elemental information simultaneously from a single sample injection. In the first step, a low-cost flow split made of acrylic was developed aiming at optimally directing the sample to the detectors, enabling the HPLC-DAD/ICP-MS coupling. After the extraction of Certified Reference Materials (CRM of natural water NIST1640a and sugar cane leaf agro FC_012017), the recoveries determined by ICP-MS were 99.7% and 85.4%, respectively. Then, the method of HPLC-DAD/ICP-MS was applied for real samples of the CRMs. The presence of possible biomolecules associated with Cr(III) and Cr(VI) species was evaluated, with the simultaneous response detection of molecular (DAD) and elementary (ICP-MS) detectors. Potential biomolecules were observed during the monitoring of Cr(VI) and Cr(III) in sugar cane leaves, water samples and a supplement of Cr picolinate. Finally, the article also discusses the potential of the technique applied to biomolecules containing other associated elements and the need of more bioanalytical methods to understand the presence of trace elements in biomolecules.

Thermal treatment of municipal solid waste incineration fly ash and nanofiltration membrane concentrate co-processing: Speciation of chromium and its leachability

The thermal treatment of municipal solid waste incineration fly ash (MSWI FA) has raised serious concerns due to the increasing leaching concentration of Cr, and Cl severely limits the reuse and utilization of MSWI FA. A nanofiltration membrane concentrate (NF-MC) is utilized in this study to leach the MSWI FA to remove Cl and the fate of Cr in the leaching MSWI FA by NF-MC (L-MSWI FA) is investigated. The results showed that Cl in the MSWI FA was effectively removed at a removal rate greater than 95%. After the thermal treatment of the proportion of the MSWI FA based on the L-MSWI FA (P-MSWI FA), it was revealed that Cr primarily as Cr2O3 hexagonally shaped flake-like crystallites, was oxidated first to Cr(VI), and the leaching concentration reached the maximum (1.17±0.05 mg/L) at 800°C. Cr(VI) was then reduced, and the chemical valence of Cr between Cr(III) and Cr(VI) confirmed that the leachability of the Cr-containing materials rose after the thermal treatment. In addition, it was believed that Cr(VI) was reduced when the temperature was greater than 1000°C. The results of this study provide theoretical guidance for controlling the enhancement of Cr leachability during the thermal treatment process.

Distribution of Chromium Species and Physico-Chemical Analysis of Various Industrial Effluents in Hyderabad and Jamshoro, Pakistan

This research aimed to quantify the speciation of chromium in different industrial effluent samples of Hyderabad and Jamshoro, Pakistan. The hexavalent chromium (Cr(VI)) was determined by microsample injection system flame atomic absorption spectroscopy (MIS-FAAS). The total chromium was measured by MIS-FAAS after the oxidation of trivalent chromium (Cr(III)) to hexavalent chromium (Cr(VI)) by Ce(SO4)2 in an acidic medium (0.07 M H2SO4). The content of Cr(III) was measured by the difference method (total chromium – hexavalent chromium). In the effluent samples of textile and fabrics industries, the total Cr was observed 400 to 1600 times higher than the US-EPA and WHO regulatory limit (0.10 mg/L) in the industrial discharge. In the effluent of food and plastic industries, the Cr(VI) was found to be high as compared to the Cr(III), and the Cr(III) was observed high in the effluent samples of chemical as well as textile and fabrics industries. The Cr(VI) was higher than the US-EPA and WHO regulatory limit (0.05 mg/L) in the effluent samples of all selected industries, but the Cr(III) was within the US-EPA and WHO regulatory limit (170 mg/L) in the industrial discharges.

Selenium toxicity and bioaccumulation in selenium-enriched fly (Chrysomya megacephala) maggots.

Selenium (Se) is an essential trace element for human health, and as a potential animal feed, the Chrysomya megacephala (Fabricius) fly is rich in protein and fat. By using different concentrations of sodium selenite (0, 30, 50, 70mgkg-1), the possibility of biological Se enrichment in C. megacephala (Fabricius) maggots (CMMs) was investigated. The accumulation, Se speciation, enzymatic activity, and concentrations of copper (Cu), zinc (Zn), chromium (Cr), and cadmium (Cd) in the maggots were also determined. Transcriptomics was also used to investigate the mechanism of the Se response to CMM genes. The results showed that the CMMs had a survival rate of > 80% at Se exposure concentrations ranging from 0 to 100mgkg-1. The optimal concentration of sodium selenite for CMM growth was 50mgkg-1, and the weight, protein content, and total Se accumulation of the larvae (10.8g, 53.5%, and 72.6 ± 3.36mgkg-1 (DW), respectively) were considerably higher than the control and other exposure doses (p < 0.05). In addition, Se improved the ability of maggots to absorb Cu and Zn, decreased malondialdehyde (MDA) and lipid peroxidation, but improved the antioxidant activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX). Furthermore, Se negatively affected the absorption of Cd and Cr. According to the transcriptomic findings, Se supplementation can boost protein synthesis and control both antioxidant and non-antioxidant enzyme activity in CMMs. Therefore, our findings showed that Se-enriched CMMs may counteract the toxicity of Cd and Cr, and Se is an effective supplement for improving the consumption safety of cultured animals fed containing CMMs.

The effect mechanism of HCl on chromium removal by CaO sorbent

A combination of experiments and density functional theory (DFT) calculations was conducted to explore the effect mechanism of HCl on Cr adsorption over CaO surface. The experimental results suggested that CaO showed good removal performance for Cr. The best Cr adsorption efficiency was 74.51% at 1000 °C in N2. HCl had an adverse effect on Cr removal due to the competition with Cr for active sites and the promotion effect on Cr volatilization by HCl. O2 can offset the inhibitory effect of HCl on Cr capture by CaO with the coexistence of HCl. The XPS results suggested that Cr capture by CaO contained adsorption and oxidation. The combined action of HCl and O2 can further promote the oxidation of chromium on CaO. DFT calculations demonstrated that HCl, CrCl3, and CrO2Cl2 adsorptions on CaO (001) surface were chemisorptions with the adsorption energies of −170.32, −288.25 and −125.56 kJ/mol, respectively. CrCl3 (Cr(III)) was formed on CaO surface via a five-step reaction pathway (Cr → Cr(ads) → CrCl(ads) → CrCl2(ads) → CrCl3(ads) → CrCl3). CrCl2 formation was the rate-determining step, and the energy barrier was 160.81 kJ/mol. CrO2Cl2 (Cr(VI)) preferred to form via chlorination-oxidation process with four steps (Cr → Cr(ads) → CrCl2(ads) → CrO2Cl2(ads) → CrO2Cl2). The rate-determining step of CrO2Cl2 formation on CaO surface in the pathway was CrCl2(ads) → CrO2Cl2(ads). The activation energy barrier of CrO2Cl2 formation on CaO surface was 238.60 kJ/mol. This study of reaction mechanism contributed to deeply understand the effect of HCl on the transformation of chromium species over CaO surface.

Determination of Chromium in Contaminated Water Samples Using Chemically Modified Nanoadsorbent: A Computational and Experimental Study

AbstractIn the reported work, a solid phase extraction method for speciation of chromium species in contaminated industrial and river water samples has been studied by using both experimental and computational methods. Multiwalled carbon nanotubes (MWCNTs) functionalized with tris(2‐aminoethyl)amine (TREN) was used as a solid phase extractant for the hyphenated preconcentration of chromium species. The characterization of the immobilized MWCNTs was done by FTIR and SEM analysis. This hyphenated system significantly improves the overall analytical performance by reducing sample consumption and sampling time. The computational results supported the experimental findings. The negative adsorption energy (−2.71 eV) suggested that the interaction process between chromium and modified nanoadsorbent is spontaneous. The system showed a limit of detection of 0.07 μg L−1 at optimized condition with an RSD value of 1.2 %. Adsorption capacity was measured using Lagergren's equation which showed that adsorption kinetics follows pseudo second‐order. The suggested method was applied to contaminated real water samples by performing spike recovery tests. The validation of the reported system was done by analysing NIST Standard Reference Material Trace Elements in Natural Water 1640a.

Chromium-Catalyzed syn-Selective Ring-Opening Aryl-/Alkylation of 7-Oxabenzonorbornadiene Derivatives with Grignard Reagents

Chromium(III) trichloride in combination with aryl/alkyl Grignard reagents under ligand-free conditions exhibited extremely high catalytic activity (turnover number of up to 2.4 × 104) toward the syn-selective ring-opening aryl/alkylation of 7-oxabenzonorbornadiene derivatives, producing syn-2-aryl/alkyl-1,2-dihydronaphthalen-1-ols in high yields. The superior catalytic activity of the chromium catalyst under the ring-opening arylation conditions enabled us to use unstable aryl Grignard reagents with esters and N-protecting groups synthesized from the corresponding aryl iodides and turbo-Grignard reagent. Control experiments to elucidate the reactivity of arylchromium species such as neutral triarylchromium(III) and anionic tetraarylchromate(III) suggested that in situ formed diarylchromate(I) from tetraarylchromate(III) served as the active species in this catalytic reaction. The magnetic susceptibility of the in situ generated chromium species from CrCl3(thf)3 and excess amounts of p-tolylmagnesium bromide was reasonable for the low-spin Cr(I) species (μ = 1.93 μB).

Speciation and distribution of chromium (III) in rice root tip and mature zone: The significant impact of root exudation and iron plaque on chromium bioavailability

Evidence on the contribution of root regions with varied maturity levels in iron plaque (IP) formation and root exudation of metabolites and their consequences for uptake and bioavailability of chromium (Cr) remains unknown. Therefore, we applied combined nanoscale secondary ion mass spectrometry (NanoSIMS) and synchrotron-based techniques, micro-X-ray fluorescence (µ-XRF) and micro-X-ray absorption near-edge structure (µ-XANES) to examine the speciation and localisation of Cr and the distribution of (micro-) nutrients in rice root tip and mature region. µ-XRF mapping revealed that the distribution of Cr and (micro-) nutrients varied between root regions. Cr K-edge XANES analysis at Cr hotspots attributed the dominant speciation of Cr in outer (epidermal and sub-epidermal) cell layers of the root tips and mature root to Cr(III)-FA (fulvic acid-like anions) (58–64%) and Cr(III)-Fh (amorphous ferrihydrite) (83–87%) complexes, respectively. The co-occurrence of a high proportion of Cr(III)-FA species and strong co-location signals of 52Cr16O and 13C14N in the mature root epidermis relative to the sub-epidermis indicated an association of Cr with active root surfaces, where the dissolution of IP and release of their associated Cr are likely subject to the mediation of organic anions. The results of NanoSIMS (poor 52Cr16O and 13C14N signals), dissolution (no IP dissolution) and µ-XANES (64% in sub-epidermis >58% in the epidermis for Cr(III)-FA species) analyses of root tips may be indicative of the possible re-uptake of Cr by this region. The results of this research work highlight the significance of IP and organic anions in rice root systems on the bioavailability and dynamics of heavy metals (e.g. Cr).