The removal of chromium(VI) from an acidic (HCl) medium through non-dispersive extraction with strip dispersion (NDXSD) was investigated using a microporous PVDF membrane support in a permeation cell. The ionic liquid Cyphos IL102 (phosphonium salt) in Solvesso 100 was used as an organic phase. In NDXSD, the stripping phase (NaOH) is dispersed in the organic phase on the cell side with an impeller stirrer adequate to form a strip dispersion. This pseudo-emulsion phase (organic + strip solutions) provides a constant supply of the Cyphos IL102/Solvesso 100 to the membrane phase. Various hydrodynamic and chemical parameters, such as variation in the feed and pseudo-emulsion stirring speeds, HCl and Cr(VI) concentrations in the feed phase, and carrier concentration, were investigated. Results indicated that the best chromium(VI) transport was obtained under the following conditions: feed and pseudo-emulsion stirring speeds of 1000 min-1 and 600 min-1, respectively; an HCl concentration in the feed phase of 0.1 M; a chromium concentration of 0.01 g/L in the same phase; and carrier concentration in the organic phase in the 2-5-10% v/v range. From the experimental data, several mass transfer coefficients were estimated: a bulk diffusion coefficient of 3.1·10-7 cm2/s and a diffusion coefficient of 6.1·10-8 cm2/s in the membrane phase and mass transfer coefficients in the feed (5.7·10-3 cm/s) and membrane phases (2.9·10-6 cm/s). The performance of the present system against other ionic liquids and the presence of base metals in the feed phase were investigated.

BACKGROUND: In response to growing concerns regarding heavy metal contamination in food, particularly chromium (Cr)(VI) contamination, this study presented a simple, sensitive and practical method for Cr(VI) detection.
RESULTS: A magnetic separation-based capture-exponential enrichment ligand system evolution (SELEX) method was used to identify and characterize DNA aptamers with a high affinity for Cr(VI). An aptamer, Cr-15, with a dissociation constant (Kd) of 4.42 ± 0.44 μmol L-1 was obtained after only eight rounds of selection. Further innovative methods combining molecular docking, dynamic simulation and thermodynamic analysis revealed that CrO4 2- could bind to the 19th and 20th guanine bases of Cr-15 via hydrogen bonds. Crucially, a label-free fluorometric aptasensor based on SYBR Green I was successfully constructed to detect CrO4 2-, achieving a linear detection range of 60-300 nmol L-1 with a lower limit of detection of 44.31 nmol L-1. Additionally, this aptasensor was able to quantitatively detect CrO4 2- in grapes and broccoli within 40 min, with spike recovery rates ranging from 89.22% to 108.05%. The designed fluorometric aptasensor exhibited high selectivity and could detect CrO4 2- in real samples without sample processing or target pre-enrichment.
CONCLUSIONS: The aptasensor demonstrated its potential as a reliable tool for monitoring Cr(VI) contamination in fruit and vegetable products. © 2024 Society of Chemical Industry.

A new type of polyethyleneimine-protected copper nanoclusters (PEI-CuNCs) is favorably developed by a one-pot method under mild conditions. The obtained PEI-CuNCs is characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, Fourier-transform infrared (FTIR) spectroscopy and other techniques. It is worth noting that the proposed PEI-CuNCs demonstrate a selective response to chromium(VI) over other competitive species. Fluorescence quenching of PEI-CuNCs is determined to be chromium(VI) concentrations dependence with a low limit of detection of 8.9 nM. What is more, the as-developed PEI-CuNCs is further employed in building a detection platform for portable recognition of chromium(VI) in real samples with good accuracy. These findings may offer a distinctive strategy for the development of methods for analyzing and monitoring chromium(VI) and expand their application in real sample monitoring.

This study investigated the genotoxic effects of chromium (Cr) in Hsd:ICR mice, considering factors such as oxidative state, apoptosis, exposure pathway, duration, pregnancy, and transplacental exposure. Genotoxicity was assessed using the erythrocytes\' micronucleus (MN) assay, while apoptosis was evaluated in nucleated blood cells. The results showed that Cr(III) (CrK(SO4 )2 and CrCl3 ) did not induce any marked genotoxic damage. However, Cr(VI) (CrO3 , K2 Cr2 O7 , Na2 Cr2 O7 , and K2 CrO4 ) produced varying degrees of genotoxicity, with CrO3 being the most potent. MN frequencies increased following 24-h exposure, with a greater effect in male mice. Administering 20 mg/kg of CrO3 via gavage did not lead to significant effects compared to intraperitoneal administration. Short-term oral treatment with a daily dose of 8.5 mg/kg for 49 days elevated MN levels only on day 14 after treatment. Pregnant female mice exposed to CrO3 on day 15 of pregnancy exhibited reduced genotoxic effects compared to nonpregnant animals. However, significant increases in MN levels were found in their fetuses starting 48 h after exposure. In summary, data indicate the potential genotoxic effects of Cr, with Cr(VI) forms inducing higher genotoxicity than Cr(III). These findings indicate that gender, exposure route, and pregnancy status might influence genotoxic responses to Cr.

Heavy metals (HMs) in water are highly poisonous and carcinogenic agents for human health. To alleviate the toxic impacts of HMs, green remediation technologies are the need of the hour. In this regard, different nanosorbents (CMCG@ORP, ORAC, NiO/NPs, and NiO@ORAC/NCs) were synthesized in the present study, and the percentage removal of heavy metals [chromium(VI) and cadmium(II) ions] was evaluated. The nanosorbents were characterized by using FTIR, SEM, UV-Vis spectroscopy, and XRD. UV-Vis spectroscopy confirmed the synthesis of nanosorbents such as NiO/NPs and NiO@ORAC/NCs at 330.5 nm and 352.55 nm, respectively. The characterization studies show that the surface of synthesized nano-sorbents was highly coarse, uneven, and abrasive. XRD pattern deduced that the sample was of single phase, and no other impurity was detected except the face-centered cubic-phase peak of NiO. The maximum adsorption of Cd (91%) and Cr (92%) was found at initial concentrations of 100 and 60 ppm respectively at contact time = 180 min, temperature 25 °C, and with an adsorbent dose of 0.5 g. Isothermal, kinetic, and thermodynamic studies were also performed to evaluate the adsorption mechanisms and feasibility of the process. Adsorption mostly followed Freundlich isotherm which indicates the multilayer adsorption phenomenon and the negative value of Gibb\'s free energy showed the spontaneous nature and feasibility of the adsorption reaction. Surface complexation, ion exchange, surface precipitation, and the phenomenon of physical adsorption occurred on the sorbent surface which led to the attachment of Cd and Cr to the tested nanosorbents. In conclusion, NiO@ORAC/NCs were the most effective in the alleviation of Cd(II) and Cr(VI) ions in contaminated water.

In this study, first time the combination of composites with Phytic acid (PA) as the organic binder cross-linker is reported. The novel use of PA with single and double conducting polymers (polypyrrole (Ppy) and polyaniline (Pani)) were tested against removal of Cr(VI) from wastewater. Characterizations (FE-SEM, EDX, FTIR, XRD, XPS) were performed to study the morphology and removal mechanism. The adsorption removal capability of Polypyrrole - Phytic Acid - Polyaniline (Ppy-PA-Pani) was deemed to be higher than Polypyrrole - Phytic Acid (Ppy-PA) due to the mere existence of Polyaniline as the extra polymer. The kinetics followed 2nd order with equilibration at 480 min, but Elovich model confirmed that chemisorption is followed. Langmuir isotherm model exhibited maximum adsorption capacity of 222.7-321.49 mg/g for Ppy-PA-Pani and 207.66-271.96 mg/g for Ppy-PA at 298K-318K with R2 values of 0.9934 and 0.9938 respectively. The adsorbents were reusable for 5 cycles of adsorption-desorption. The thermodynamic parameter, ΔH shows positive values confirmed the adsorption process was endothermic. From overall results, the removal mechanism is believed to be chemisorption through Cr(VI) reduction to Cr(III). The use of phytic acid (PA) as organic binder with combination of dual conducting polymer (Ppy-PA-Pani) was invigorating the adsorption efficiency than just single conducting polymer (Ppy-PA).

An investigation of chromium(VI) transport across a supported liquid membrane containing the phosphine oxides Cyanex 921 and Cyanex 923 dissolved in Solvesso 100 as carrier phases was carried out in batch operation mode. Chromium(VI) transport was investigated as a function of different variables: hydrodynamic conditions in the feed (1000-1600 min-1) and stripping (600-1500 min-1) phases, HCl (0.25-2 M) and indium (0.01-0.1 g/L) concentrations in the feed phase, and carrier (0.01 M-0.75 M) concentration in the membrane phase. Indium was recovered in the stripping phase using hydrazine sulphate solutions, and, at the same time, chromium(VI) was reduced to the less harmful Cr(III) oxidation state. Models describing the transport mechanism comprising a diffusion process through the feed aqueous diffusion layer, fast interfacial chemical reaction, and diffusion of the respective chromium(VI)-phosphine oxide complexes across the membrane were developed. The equations describing the rate of transport correlate the membrane permeability coefficient with diffusion and equilibrium parameters, as well as the chemical compositions of the respective metal-carrier phases. The models were used to calculate diffusional parameters for each metal-carrier system, and the minimum thickness of the feed boundary layer was calculated as 1 × 10-3 cm and 6.3 × 10-4 cm for the Cr(VI)-Cyanex 921 and Cr(VI)-Cyanex 923 systems, respectively.

The toxicity and carcinogenicity of Cr(VI) makes it a major threat to the health of animals and people. However, how to efficiently remove Cr(VI) still faces important challenges. In this study, a new metal-free polypyrrole-red phosphorus (PPy-RP) composite is successfully synthesized by in-situ oxidation polymerization for Cr(VI) removal from wastewater. The maximum adsorption capacity (qm) of Cr(VI) on PPy-RP-1 is 513.2 mg/g when the pH value is 2, which is far superior to RP nanosheets (207.8 mg/g) and PPy (294.9 mg/g). The improved qm can be ascribe to the good dispersion and increased specific surface area of PPy-RP adsorbent. Encouragingly, PPy-RP adsorbent still exhibits excellent stability after 7 cycles tests without a significant decline in removal efficiency, and remain above 81.4%. Based on the fittings of adsorption isotherms and kinetics, the process conforms to the pseudo-first-order kinetic model and the single-layer adsorption of the Langmuir model with an R2 value of 0.98533. The adsorption process is chemical and monolayer. The experimental result demonstrates that the PPy-RP can efficient removal Cr(VI) by electrostatic attraction and complexation reaction (formation of N-Cr(VI) bond) through the PPy on the surface. The results of this study indicate that PPy-RP is a promising adsorbent to remove the Cr(IV).

Iron minerals, which exert excellent biocompatibility and reactivity with redox-active microorganisms, have attracted attention as a precursor to synthesizing composite materials with higher catalytic efficiency in driving redox-active microorganisms to reduce Cr(VI). However, researches on the effective preparation method of composites, the interaction between bacteria and composite materials and the mechanism of electron transfer are still scarce. In this work, Fe-complex@BC prepared by a one-step method using goethite was used for chromium treatment together with soil microorganisms. The composite was the best-performing in promoting Cr(VI) bioreduction (up to 3.48 mg (L·h)-1) than Fe-complex (2.26 mg (L·h)-1) and biochar (0.5 mg (L·h)-1), even about 19 times higher than that of bioreduction without materials. Specifically, Fe-complex@BC shortened the electron transfer distance due to its excellent adsorption properties for bacteria and Cr(VI). Its high redox activity also promoted Cr(VI) bioreduction by directly enhancing electron transfer. In addition, the presence of the Fe(III)/Fe(II) cycle proved that the active sites of composite could be regenerated to reduce Cr(VI) persistently by receiving extracellular electrons from bacteria. High-throughput 16 S rDNA gene sequencing indicated the composite could promote the proliferation of electrochemically active bacteria, which directly enhanced bioreduction. This study developed the low-cost Fe@BC material prepared by a one-step co-pyrolysis method, which exerts a synergistic effect with soil microorganisms and presents a promising potential for chromium pollution treatment.