mM Of Cr Research Articles

Dual-responsive solvatochromic sensor for simultaneous detection and mechanism of Cr(III) and Co(II) cations by a new N2O4-donor tetrabenzodiaza-crown ether Macrocyclic ligand anchored to dipyridine moieties

The present study describes the chemosensing capability of an N2O4-donor tetrabenzodiaza-crown ether macrocyclic ligand derivatized by two pyridine side arms to afford the flexible macrocyclic ligand, 5,20-bis(pyridin-4-ylmethyl)-5,6,12,13,19,20,26,27octahydrotetrabenzo [e,i,o,s][1,4,11,14]tetraoxa[7,18]diazacycloicosine (PMHBOA). A selective colorimetric behavior of PMHBOA for the prompt detection of Cr(ΙΙΙ) and Co(ΙΙ) can be observed with naked eyes. The 1H, 13C{H} NMR, and infrared spectroscopy disclosed the ligand binding capability for selective metal ions, ascribed to a 1:1 complex formation with Cr(III) and Co(II) cations in isopropanol. The limit of detection (LOD) values were calculated as 580 and 850 nM for Cr(ΙΙΙ) and Co(ΙΙ), respectively, accompanied with suitable LOQs as 1.95 µM for Cr(III) and 2.85 µM for Co(II), respectively. The reusability was confirmed in the presence of ethylenediaminetetraacetic acid (EDTA). Moreover, a TLC-based fabricated paper strip successfully applied PMHBOA as a chemosensor for synchronous visible detection of Cr(III) and Co(II) in their alcoholic solution. Meanwhile, the observed color change along with the turn-off fluorescent of PMHBOA guaranteed a felicitous choice of candidate for Cr(III) in the presence of other library metal ions in isopropanol:H2O (9/1 v/v) solution. A fast separation test on the filter paper, impregnated with PMHBOA, was also employed to separate Cr(III) and Co(II) cations from aqueous solutions by recording UV–vis spectra. The 1H NMR spectroscopy supported the macrocycle ring and side arms as the parallel coordination site of PMHBOA with Cr(III) and Co(II).

In Situ Construction of a Type II Heterojunction UiO/BMO‐x for Improving the Photocatalytic Reduction of Cr (VI)

AbstractPhotocatalytic reduction of Cr(VI) to Cr(III) is one of the most promising technologies to remove Cr(VI) pollution because of its environmental friendliness, cost‐effective and energy saving. In this experiment, two‐dimensional Bi2MoO6(BMO) nanosheets and cerium‐based MOFs UiO‐66(Ce) were synthesized by solvent thermal method, and in the presence of BMO, the UiO/BMO‐x heterojunction composites were constructed in situ to explore its photocatalytic reduction properties of Cr(VI). The experiment showed that 4 mM of Cr (VI) solution could be reduced 100 % to Cr (VI) by 15 mg catalyst under optimal reaction conditions. The composite photocatalyst prepared in this experiment can realize the green treatment of Cr(VI) in the environment under photocatalytic conditions, and has potential application value in the remediation of heavy metal pollution.

A fluorescent probe based on carbon quantum dots with spectral selectivity for sensitive detection of Cr(VI) and Hg(II) in environmental waters

In this paper, fluorescent carbon dots were prepared by hydrothermal method using 3,5-dihydroxybenzoic acid and l-Arginine as precursors. The synthesized CDs have excitation-dependent emission with emission peaks at 354 nm and 460 nm, corresponding to the optimal excitation wavelengths of 295 nm and 330 nm, respectively. CDs have good dispersion and resistance to photobleaching in aqueous solution, and can maintain stable fluorescence in highly concentrated salt environment. Based on the inner filter effect, Cr(VI) with strong absorption can shield the excitation light of CDs at 295 nm and absorb the emission fluorescence at 354 nm simultaneously. Due to the intermolecular electrostatic interaction, Hg(II) can coordinate with CDs surface groups and cause static quenching, which significantly reduces the fluorescence intensity of CDs emitted at 460 nm. The linear ranges were 0.1–2 μM and 0.4–5 μM for Cr(VI) and Hg(II) detection, respectively, and limits of detection were 0.024 μM and 0.084 μM. Additionally, the probe was successfully applied to tap water and lake water samples. With high sensitivity and spectral selectivity, this sensing strategy realized the detection of two heavy metal ions by a single fluorescent probe, demonstrating its great potential in the field of environmental metal analysis.

Hexavalent chromium inhibits myogenic differentiation and induces myotube atrophy

Hexavalent chromium [Cr(VI)] is extensively used in many industrial processes. Previous studies reported that Cr(VI) exposures during early embryonic development reduced body weight with musculoskeletal malformations in rodents while exposures in adult mice increased serum creatine kinase activity, a marker of muscle damage. However, the impacts of Cr(VI) on muscle differentiation remain largely unknown. Here, we report that acute exposures to Cr(VI) in mouse C2C12 myoblasts inhibit myogenic differentiation in a dose-dependent manner. Exposure to 2 μM of Cr(VI) resulted in delayed myotube formation, as evidenced by a significant decrease in myotube formation and expression of muscle-specific markers, such as muscle creatine kinase (Mck), Myocyte enhancer factor 2 (Mef2), Myomaker (Mymk) and Myomixer (Mymx). Interestingly, exposure to 5 μM of Cr(VI) completely abolished myotube formation in differentiating C2C12 cells. Moreover, the expression of key myogenic regulatory factors (MRFs) including myoblast determination protein 1 (MyoD), myogenin (MyoG), myogenic factor 5 (Myf5), and myogenic factor 6 (Myf6) were significantly altered in Cr(VI)-treated cells. The inhibitory effect of Cr(VI) on myogenic differentiation was further confirmed in freshly isolated mouse satellite cells, a stem cell population essential for adult skeletal muscle regeneration. Furthermore, Cr(VI) exposure to fully differentiated C2C12 myotubes resulted in a decrease in myotube diameter, which was exacerbated upon co-treatment with dexamethasone. Together, our results demonstrate that Cr(VI) inhibits myogenic differentiation and induces myotube atrophy in vitro.

Chromium (VI) induced physiological and metabolic responses and metal accumulation in Vigna mungo L cv. BVN-3

Present study investigates chromium induced toxicity and metal accumulation in plant black gram (Vigna mungo L.) under different concentrations of Cr (VI) treatment. Phytotoxicity in black gram was assessed by evaluating growth responses, foliar symptoms, biochemical changes enzyme activities and nutrient uptake at different concentration of chromium (VI) viz. 0.0, 0.05, 0.10 and 0.25 mM. Chlorosis followed by necrosis was observed in the leaves with tapered lamina at higher concentration of chromium (0.25 mM) treatment. Similarly, reduction in biomass, decrease in photosynthetic and metabolic activities, imbalances in nutrient uptake were recorded in Cr (IV) treated plants at higher concentration (0.25 mM). Maximum Cr accumulation was recorded in leaves (166.5 μg g-1 dw) followed by root (123.4 μg g-1 dw) and shoot (46.6 μg g-1 dw) after 29 d of treatment at 0.25 mM of Cr(VI). Present study concludes that growing black gram in Cr contaminated soil may lead to poor yield and health hazards.

The effect of FeS on the fate of Cr(VI) in the presence of organic matters under dynamic anoxic/oxic conditions.

The reduction of Cr(VI) by FeS under anoxic conditions has been studied extensively. However, when the redox environments alternate from anoxic to oxic, the effect of FeS on the fate of Cr(VI) in the presence of organic matters still remains unknown. Therefore, this study investigated the effect of FeS coupled with humic acids (HA) and alga on the transformation of Cr(VI) under dynamic anoxic/oxic conditions. HA could promote the reduction of Cr(VI) from 86.6% to 100% under anoxic conditions due to the enhancement of the dissolution and dispersibility of FeS particles by HA. However, the strong complexing and oxidizing properties of alga inhibited the reduction of FeS. Reactive oxygen species (ROS) generated from FeS oxidation under oxic conditions could oxidize 3.80μM of Cr(III) to aqueous Cr(VI) at pH 5.0, while aqueous Cr(VI) reached to 4.83μM in the presence of HA, which was ascribed to the increasing amount of free radicals. In addition, acidic conditions and excess FeS would increase strong reducing Fe(II) and S(-II) species, and improve the efficiency of Fenton reaction. The findings provided new insights into the fate of Cr(VI) in aquatic systems containing FeS and organic matters under dynamic anoxic/oxic conditions.

A cellulose-based material as a fluorescent sensor for Cr(VI) detection and investigation of antimicrobial properties of its encapsulated form in two different MOFs

It is crucial to detect toxic chromium ions quickly, reliably, sensitively and at low concentrations. In recent years, fluorescence-based methods have been developed for the rapid detection and determination of toxic ions such as chromium. In present work, we focused on the development of a cellulose-based fluorescent probe (Cel-Nap) for the determination of Cr(VI). The fluorescent probe bearing the 1,8-naphthalimide group displayed a low LOD of 1.07 μM for Cr(VI) in the working range of 0.33 × 10−5–3.22 × 10−5 M. The fluorescence and antibacterial properties of UiO-66-Cel-Nap and ZIF-8-Cel-Nap materials prepared by encapsulating Cel-Nap with 2 different MOF types (UiO-66 and ZIF-8) were investigated. While it was found that ZIF-8-based materials had better antimicrobial properties compared to those of UiO-66, it was determined that materials containing Ag+ were more effective against microbial than those containing AgNPs. It was found that the most effective material was ZIF-8-Cel-Nap-Ag+ and it had a significant antibacterial effect against E. coli at a MIC value of 0.0024 mg/mL.

The influence of Pd4Cr6@(NH2)M-MOF(Cr) catalyst on components of formic acid dehydrogenation gaseous products

ABSTRACT In the dehydrogenation of formic acid, catalyst has a great influence on the composition and formation rate of gaseous products. However, the hydrogen used in fuel cells has strict requirements on the content of carbon monoxide impurities. Therefore, it is very important to study the relationship between catalyst components and their synergistic effects and the composition of gaseous products. The role of Pd-Cr bimetallic nanoparticles supported on amino modified Cr-based metal-organic framework catalyst (Pd4Cr6@(NH2)M-MOF(Cr)) in the formic acid dehydrogenation was explored through comparative experiments and catalyst characterization. Results show that both Cr-based metal-organic framework (MOF(Cr)) and amino-modified Cr-based metal-organic framework ((NH2)M-MOF(Cr)) have no effect on promoting the generation of gaseous products. The presence of Cr and NH2 groups in Pd4Cr6@(NH2)M-MOF(Cr) greatly improves the formation rate of H2 and CO2 products, the gas production rate of Pd4Cr6@(NH2)M-MOF(Cr) is 2.89 times that of Pd4@(NH2)M-MOF(Cr), and the gas production rate of Pd4Cr6@(NH2)M-MOF(Cr) is 6.26 times of Pd4Cr6@MOF(Cr). However, the formation rate of H2 increases more in the presence of Cr. Synergy of Pd-Cr and Pd-NH2 in the Pd4Cr6@(NH2)M-MOF(Cr) catalyst promotes CO formation.

Four octamolybdate compounds with properties of organic dye adsorption and photocatalytic reduction of Cr(VI).

Hydrothermal synthesis was used to create four different POM-based compounds, namely {[Co(Hptpm)2(β-Mo8O26)0.5(ξ-Mo8O26)0.5]}·H2O (1), [Co(Hptpm)2(δ-Mo8O26)]·H2O (2), [Co(Hptpm)2(β-Mo8O26)] (3) and [Zn(Hptpm)2(β-Mo8O26)] (4) (ptpm = 4-[3-(3-pyridine-2-yl-[1,2,4]triazol-4-yl)-propyl]-morpholine). 1-4 containing different octamolybdate isomers were characterized. Compounds 1-4 showed good electrochemical performance and can be utilized as bifunctional sensors for NO2-, H2O2, Cr(VI) and Fe(III). Taking compound 1 as an example, the detection limits are 0.081 μM for NO2-, 0.072 μM for H2O2, 0.054 μM for Cr(VI) and 0.063 μM for Fe(III), respectively. Compounds 1-4 have good capacitance. Moreover, compounds 1-4 also show good adsorption properties for organic cationic dyes. The cationic dyes include methylene blue (MB), crystal violet (CV) and neutral red (NR). In addition, 1-4 have excellent characteristics that can reduce Cr(VI) to Cr(III) by photocatalytic technology. Within 30 min, the reduction rates were 95.85% for 1, 93.99% for 2, 90.29% for 3 and 88.18% for 4.

Electrochemical Fe(III) mediation for reducing hexavalent chromium Cr(VI) on templated copper-nickel foam electrode

Hexavalent chromium (Cr(VI)) is highly toxic and migratory, rapidly transported between water bodies. This study synthesized a Cu/Ni electrode which the polyhedral copper crystallites were electroplated on the nickel foam for direct and indirect reduction of Cr(VI). The micromorphology of Cu/Ni in respect to the grain size and crystal facets Cu(200) and Cu(111) was manipulated by the cationic surfactant in specific critical micelle concentrations (CMC). Behaviors of electron transfer between the soluble Cr(VI) and Fe(III) on Cu/Ni as affected by the facet ratio (FCu(200)) were analyzed. Voltammetry showed that the preference of Cu(111) system aided the cathode in the transfer coefficient of Fe(III)/Fe(II) couple. Under electrochemical conditions: current density = 5 mA cm−2, FeCl3 = 3 mM, pH 3.0, Cr(VI) removal and yield of soluble Cr(III) attained 99% and 90%, respectively. Cu(111) exposed on the electrode which catalytically generated the surface-adsorbed Fe2+ was positively correlated to the rate constant of indirectly reducing Cr(VI).

Shewanella sp. T2.3D-1.1 a Novel Microorganism Sustaining the Iron Cycle in the Deep Subsurface of the Iberian Pyrite Belt.

The Iberian Pyrite Belt (IPB) is one of the largest deposits of sulphidic minerals on Earth. Río Tinto raises from its core, presenting low a pH and high metal concentration. Several drilling cores were extracted from the IPB’s subsurface, and strain T2.3D-1.1 was isolated from a core at 121.8 m depth. We aimed to characterize this subterranean microorganism, revealing its phylogenomic affiliation (Average Nucleotide Identity, digital DNA-DNA Hybridization) and inferring its physiology through genome annotation, backed with physiological experiments to explore its relationship with the Fe biogeochemical cycle. Results determined that the isolate belongs to the Shewanella putrefaciens (with ANI 99.25 with S. putrefaciens CN-32). Its genome harbours the necessary genes, including omcA mtrCAB, to perform the Extracellular Electron Transfer (EET) and reduce acceptors such as Fe3+, napAB to reduce NO3− to NO2−, hydAB to produce H2 and genes sirA, phsABC and ttrABC to reduce SO32−, S2O32− and S4O62−, respectively. A full CRISPR-Cas 1F type system was found as well. S. putrefaciens T2.3D-1.1 can reduce Fe3+ and promote the oxidation of Fe2+ in the presence of NO3− under anaerobic conditions. Production of H2 has been observed under anaerobic conditions with lactate or pyruvate as the electron donor and fumarate as the electron acceptor. Besides Fe3+ and NO3−, the isolate also grows with Dimethyl Sulfoxide and Trimethyl N-oxide, S4O62− and S2O32− as electron acceptors. It tolerates different concentrations of heavy metals such as 7.5 mM of Pb, 5 mM of Cr and Cu and 1 mM of Cd, Co, Ni and Zn. This array of traits suggests that S. putrefaciens T2.3D-1.1 could have an important role within the Iberian Pyrite Belt subsurface participating in the iron cycle, through the dissolution of iron minerals and therefore contributing to generate the extreme conditions detected in the Río Tinto basin.

Influence of potassium dichromate on the reduction of sulfur, nitrate and nitrite ions by bacteria Desulfuromonas sp.

This article presents the regularities of reduction of sulfur, nitrate and nitrite ions by sulfur reducing bacteria Desulfuromonas sp., which were isolated from the water of the man-made Yavorivske Lake (Lviv Region, Ukraine), under the influence of potassium dichromate. This bacteria in the process of anaerobic respiration can use and reduce different electron acceptors, such as sulfur, nitrates, nitrites, oxidized forms of heavy metals, in particular, hexavalent chromium. Technogenically altered ecotopes are characterized by complex pollution, so several electron acceptors are available to bacteria at the same time. Strains of microorganisms isolated from such ecotopes are adapted to unfavourable conditions and therefore have high biotechnological potential. The purpose of this work was to investigate the regularities of elemental sulfur, nitrate or nitrite ion usage by sulfidogenic bacteria of Desulfuromonas genus in conditions of simultaneous presence in the medium of another electron acceptor – Cr(VI), to establish the succession of reduction of electron acceptors by strains of these bacteria and to evaluate the efficiency of their possible application in technologies of complex purification of the environment from metal compounds and other inorganic toxicants. Bacteria were grown under anaerobic conditions in Kravtsov-Sorokin medium without SO42– and without Mohr’s salt for 10 days. To study the efficiency of sulfur, nitrate or nitrite ions’ reduction at simultaneous presence in the medium of Cr(VI) bacteria were sown in media with elemental sulfur, NaNO3, NaNO2 or K2Cr2O7 to final S0, NO3–, NO2–or Cr(VI) concentration in the medium of 3.47 (concentration of SO42– in medium of standard composition) or 1.74, 3.47, 5.21, 6.94 and 10.41 mM. Biomass was determined by the turbidimetric method, and the concentrations of nitrate, nitrite, ammonium ions, hydrogen sulfide, Cr(VI), Cr(ІІІ) in cultural liquid were determined spectrophotometrically. It has been established that Cr(VI) inhibits the biomass accumulation and hydrogen sulfide production by bacteria of Desulfuromonas sp. after simultaneous addition into the medium of 3.47 mM S0 and 1.74–10.41 mM Cr(VI). In the medium with the same initial content (3.47 mM) of S0 and Cr(VI) bacteria produced Cr(III) at concentrations 3.3–3.4 times higher than that of hydrogen sulfide. It has been shown that K2Cr2O7 inhibits biomass accumulation, nitrate ions’ reduction and ammonium ions’ production by bacteria after simultaneous addition into the medium of 3.47 mM NO3– and 1.74–10.41 mM Cr(VI) or 1.74–10.41 mM NO3– and 3.47 mM Cr(VI). In the medium with the same initial content (3.47 mM) of NO3– and Cr(VI) bacteria reduced up to 1.2 times more nitrate ions than Cr(VI) with the production of ammonium ions at concentrations the same times higher than those of Cr(III). It has been established that K2Cr2O7 inhibits biomass accumulation, nitrite ions’ reduction and ammonium ions’ production by bacteria after simultaneous addition into the medium of 3.47 mM NO2– and 1.74–10.41 mM Cr(VI) or 1.74–10.41 mM NO2– and 3.47 mM Cr(VI). In the medium with the same initial content of (3.47 mM) NO2– and Cr(VI) the reduction of Cr(VI) by bacteria was only slightly, up to 1.1 times, lower than the reduction of nitrite ions, almost the same concentrations of trivalent chromium and ammonium ions were detected in the cultural liquid. The processes of nitrate and nitride reduction carried out by bacteria of Desulfuromonas genus were revealed to be less sensitive to the negative influence of sodium dichromate, as compared with the process of sulfur reduction, because in the media with the same initial content (3.47 mM) of NO3– or NO2– and Cr(VI) bacteria produced 1.1–1.2 times more NH4+ than Cr(III), but in the medium with the same initial content (3.47 mM) of S0 and Cr(VI) ) bacteria produced over than three times more Cr(III) than hydrogen sulfide. Our data allow us to conclude that bacteria of Desulfuromonas genus, the investigated strains of which are adapted to high concentrations (up to 10.41 mM) of inorganic toxicants, play an important role in the geochemical cycles of sulfur, nitrogen and chromium in aquatic environments that have been under anthropogenic influence.

TiO2 Nanoparticles Co-Sensitized with Graphene Quantum Dots and Pyrocatechol Violet for Photoelectrochemical Detection of Cr(VI)

Photoactive electrodes with high photon-to-electron conversion efficiency are key to achieving sensitive photoelectrochemical sensors. Among all the photoactive materials, titanium dioxide (TiO2) nanoparticles have attracted much attention due to their unique electronic and optical properties. However, the large bandgap of TiO2 results in limited photocurrent signal generation under visible irradiation, which is important for its use in many applications including sensing. Herein, we modified TiO2 nanoparticles with both pyrocatechol violet and graphene quantum dots to obtain high photocurrents at visible light excitation while also improving TiO2 nanoparticle dispersion and film-forming properties. This material system enhances photocurrent by 5 times compared to TiO2 nanoparticles that are modified with only pyrocatechol violet and 60 times compared to TiO2 nanoparticles modified with graphene quantum dots. Additionally, the optimized photoelectrodes were used to detect hexavalent chromium (Cr(VI)), which has been reported as a toxic carcinogen. Under visible light irradiation, the fabricated sensor offered a low limit-of-detection of 0.04 μM for Cr(VI), with selectivity against Na, Mg, Cu, and Cr (III) ions, paving the route toward photoelectrochemical Cr(VI) sensing.

Individual and Combined Effects of Manganese and Chromium on a Freshwater Chlorophyceae.

Manganese (Mn), an essential metal in trace amounts, and chromium (Cr), a nonessential metal to algae, are often found in effluent discharges and may co-occur in contaminated aquatic environments. Therefore, we investigated the effects of Mn and Cr, and their mixtures, on a freshwater Chlorophyceae, Raphidocelis subcapitata, using a multiple endpoint approach. Regarding the single exposure of metals, Mn was 4 times more toxic (median inhibitory concentration at 72 h [IC5072 h ] = 4.02 ± 0.45 µM Mn) than Cr (IC5072 h = 16.42 ± 4.94 µM Cr) for microalgae, considering the effects on the relative growth rate. Moreover, this species was the most sensitive to Mn, according to the species sensitivity distribution curve. Overall, the tested metals did not lead to significant changes in reactive oxygen species production, cellular complexity, and cell relative size but significantly decreased the algal growth and the mean cell chlorophyll a (Chl a) fluorescence at the highest concentrations (3.64-14.56 µM of Mn and 15.36-19.2 µM of Cr). The decreased mean cell Chl a fluorescence indicates an impact on pigment synthesis, which may be related to the observed growth inhibition. In the mixture tests, the reference models concentration addition and independent action were used to analyze the data, and the independent action model was the best fit to describe our results. Therefore, the Mn and Cr mixture was noninteractive, showing additive effects. This is the first study to address the combined toxicity of Mn and Cr regarding freshwater Chlorophyceae. Environ Toxicol Chem 2022;41:1004-1015. © 2022 SETAC.

The low-cost and high-efficient photoreduction of Cr(VI) by oxalic acid synergized with the iron-loaded rice straw

In the view of the possible synergy between the Fe(III)-induced photochemical reduction and the photocatalytic role of agriculture waste rice straw(RS), the iron-loaded rice straw (Fe-RS) was firstly prepared and successfully used in the photoreduction removal of Cr(VI) by oxalic acid (Ox). 1 mM of Cr(VI) in aqueous solution was completely removed in 6 min in Fe-RS/Ox/UV system. The Cr(VI) removal of Fe-RS/Ox/UV system was investigated through the effect of Ox concentration, initial Cr(VI) concentration, Fe-RS dosage and reusability of Fe-RS. The Cr(VI) removal mechanism of Fe-RS/Ox/UV system was discussed in detail, and the role of Fe-RS in Fe-RS/Ox/UV system was further revealed. The results showed that Fe-RS significantly enhanced the Cr(VI) photoreduction by Ox, and the loaded Fe component and the contained Si components on Fe-RS played an important synergized photocatalytic action for Cr(VI) removal in Fe-RS/Ox/UV system. The continuously photo-generated Fe(II) and CO2·- in the system reduced most Cr(VI). The separated electron (e-) and the produced CO2·- from the oxidation of Ox by hole (h+), which was due to the photocatalyzed SiO2 on Fe-RS, reduced some Cr(VI).

The highly enhanced Cr(VI) photoreduction removal by oxalic acid coordinated with iron-loaded waste Loofah

In order to remove high toxic Cr(VI) from the water with low cost and high efficiency, iron-loaded Loofah (Loofah-Fe) was prepared from agriculture waste Loofah and was applied in the Cr(VI) photoreduction remvoal by oxalic acid (Ox). The Cr(VI) removal of Loofah-Fe/Ox/UV system were investigated by the effect of initial Cr(VI) concentration, Ox concentration and Loofah-Fe dosage. The Cr(VI) removal mechanism in Loofah-Fe/Ox/UV system were discussed through the study of initial pH, the change (pH, Ox concentration, Fe(II) and Fe(III) concentration) in solution during the reaction, and the free radicals scavenging test. The role of Loofah-Fe in Loofah-Fe/Ox/UV system was further deduced by the analysis of XPS, EIS and Mott-Schottky. The results showed that Loofah-Fe remarkably enhanced the Cr(VI) photoreduction by Ox, 1 mM of Cr(VI) in aqueous solution was completely removed in 30 min by Loofah-Fe/Ox/UV system at pH = 3.0. The loaded Fe(III) and the contained SiO2 on Loofah-Fe played an important synergized photocatalytic role for Cr(VI) removal in Loofah-Fe/Ox/UV system. Fe(II) and CO2·-, which was continuously generated by photoactive Fe(III)-(C2O4)3 formed between Ox and Fe(III) dissolved from Loofah-Fe, reduced a large amounts of Cr(VI) in solution. The separated electron (e−) and the produced CO2·-, generated from the oxidized Ox by the hole (h+) through photoactive SiO2 on Loofah-Fe, also reduced part of Cr(VI).

Bifunctional photoelectrochemical sensor based on Bi/Bi2S3/BiVO4 for detecting hexavalent chromium and hydrogen peroxide

In this study, a bifunctional photoelectrochemical (PEC) sensor based on Bi/Bi2S3/BiVO4 (Bi-BSV) is prepared by one-step hydrothermal method. Firstly, the results from experiments show that the PEC performances of Bi2S3/BiVO4-X (BSV-X, X = m(Bi2S3)/m(Bi2S3 + BiVO4)) are higher than those of Bi2S3 and BiVO4, and BSV-15% has the highest PEC performance. To further improve the PEC properties of BSV-15%, metal-Bi was introduced to the synthesis of Y-Bi-BSV-15% (Y represents the amount of glucose added). Moreover, UV–visible diffuse reflectance spectrum (UV–vis DRS) and photoluminescence (PL) demonstrate that 0.3-Bi-BSV-15% has the widest visible light absorption range and strongest photogenerated carriers separation capability among all composites. Based on the above results, the PEC sensor based on the 0.3-Bi-BSV-15% for detecting hexavalent chromium (Cr (VI)) and hydrogen peroxide (H2O2) is built. The results exhibit that 0.3-Bi-BSV-15% has a wider detection range of 2–230 µM and a lower detection limit of 0.094 µM for Cr (VI) detection. While for H2O2 detection, the detection range and detection limit are 1–130,000 µM and 0.089 µM, respectively. Therefore, 0.3-Bi-BSV-15% has potential application in Cr (VI) and H2O2 detection.

Effects of metals on activity and community of sulfate-reducing bacterial enrichments and the discovery of a new heavy metal-resistant SRB from Santos Port sediment (São Paulo, Brazil).

Sulfate-reducing bacteria (SRB) can be used to remove metals from wastewater, sewage, and contaminated areas. However, metals can be toxic to this group of bacteria. Sediments from port areas present abundance of SRB and also metal contamination. Their microbial community has been exposed to metals and can be a good inoculum for isolation of metal-resistant SRB. The objective of the study was to analyze how metals influence activity and composition of sulfate-reducing bacteria. Enrichment cultures were prepared with a different metal (Zn, Cr, Cu, and Cd) range concentration tracking activity of SRB and 16S rRNA sequencing in order to access the community. The SRB activity decreased when there was an increase in the concentration of the metals tested. The highest concentration of metals precipitated were 0.2 mM of Cd, 5.4 mM of Zn, 4.5 mM of Cu, and 9.6 mM of Cr. The more toxic metals were Cd and Cu and had a greater community similarity with less SRB and more fermenters (e.g., Citrobacter and Clostridium). Meanwhile, the enrichments with less toxic metals (Cr and Zn) had more sequences affiliated to SRB genera (mainly Desulfovibrio). A new Desulfovibrio species was isolated. This type of study can be useful to understand the effects of metals in SRB communities and help to optimize wastewater treatment processes contaminated by metals. The new Desulfovibrio species may be important in future studies on bioremediation of neutral pH effluents contaminated by metals.

Ultrastructural evidences for chromium(III) immobilization by Escherichia coli K-12 depending on metal concentration and exposure time

Microorganisms can mediate in heavy metal sequestration through several cellular strategies and pathways. This offers an efficient way to remediate heavy metal polluted environments.This paper describes the ability of Escherichia coli K-12 to capture chromium(III) (Cr(III)) and the ultrastructural effects of this metal on cells, as well as the cellular metal localization and the possible sequestration strategy uses for it. The study was mainly performed by using several electron microscopy techniques and is based on the chromium trivalent concentration and the related exposure time. Transmission electron microscopy (TEM) assay was performed along with field emission scanning electron microscopy (FESEM) for morphological responses. Furthermore, TEM was coupled with an energy dispersive X-ray (TEM-EDX) and TEM with selected area electron diffraction (TEM-SAED) to conduct analytical assays. The exposed cultures to 10 and 12 mM Cr(III) at 12 h and to 5, 7, 10, 12, 13, and 15 mM of Cr(III) at 24 h indicated the presence of multiple electrodense granules that were significantly enriched in chromium and phosphorus content via EDX analysis. Moreover, these granules were observed to be attached to external membrane and/or surrounding cells in the respective ultrathin sections analyzed under TEM. According to these results, E. coli K-12 possesses the ability to immobilize Cr(III) in external polyphosphate granules through a strategy of accumulation, where cell response to Cr(III) toxicity seems to have a dose-dependent and time-dependent relation, thereby offering significant potential for bioremediation in Cr(III)-contaminated areas.

Fluorescent nitrogen-doped Ti3C2 MXene quantum dots as a unique “on-off-on” nanoprobe for chrominum (VI) and ascorbic acid based on inner filter effect

The MXene quantum dots (MQDs) derived from two-dimensional MXene nanosheets is a kind of rising-star nanomaterial recently, exhibiting important applications in many fields, while the investigation of element-doping MQDs with better performances for chem/biosensing is jut beginning. In this work, by cutting Ti3C2 MXene nanosheets with a simple method, we synthesized firstly nitrogen-doping Ti3C2 MQDs (N-Ti3C2 MQDs) which displays remarkable excitation-dependent photoluminescence and photobleaching resistance. Interestingly, the fluorescence of N-Ti3C2 MQDs can be quenched by chromium (VI) (Cr(VI)) owing to the existence of Inner filter effect and static quenching, triggering a fluorescent “on-off” signal; on account of the oxidation-reduction reaction between ascorbic acid (AA) and Cr(VI), the related fluorescence of N-Ti3C2 MQDs can be further recovered in the presence of AA, inducing an “off-on” fluorescence response. Thus, N-Ti3C2 MQDs was then used as nanoprobe for the fluorescent detection of Cr(VI) and AA, and the developed sensing method was verified to possess great sensitivity with the wide linear ranges from 0.1–500.0 μM toward both Cr(VI) and AA as well as low detection limits of 0.012 μM for Cr(VI) and 0.02 μM for AA. Furthermore, the investigation about the selectivity and practical application demonstrated N-Ti3C2 MQDs has important actual values for Cr(VI) and AA sensing.