The removal of toxic and harmful heavy metal contaminants from wastewater is of great importance for global environmental health. The development of efficient photocatalysts is attracting increasing ...interest with a current focus on material design for improved efficiency. Accordingly, this study aims to optimize the conformation of nanocomposite prepared from a CdS/ZnO heterojunction on reduced graphene oxide (RGO) for boosting the photocatalytic removal of heavy metal contaminants of aqueous systems. Under visible light, the candidate nanocomposites exhibited a range of photocatalytic activity in reducing hexavalent chromium Cr(VI) to trivalent chromium Cr(III) at room temperature. Among these different nanocomposites, the photocatalytic removal rate constant of Cr(VI) ranged as follows: ZnO/CdS6:5/RGO6 (0.106 min−1) > ZnO/CdS6:5 (0.0630 min−1) > CdS (0.0335 min−1) > ZnO (0.00121 min−1). Moreover, after five cycles of use, the photocatalytic reduction rate of ZnO/CdS6:5/RGO6 was 93.2 %, which signifies its strong re-cycling performance. These results reveal the feasibility of using CdS/ZnO6:5/RGO6 to reduce heavy metal ions from wastewater and provide insights for efficiently removing heavy metal ions without additional chemical trapping agents in the photocatalytic process.
•ZnO/CdS/RGO photocatalyst was successfully prepared by a simple, one-step hydrothermal method.•ZnO/CdS/RGO shows enhanced visible-light photocatalytic removal of Cr(VI).•The prepared photocatalyst exhibited good stability and reusability.•Possible photocatalytic mechanism of ZnO/CdS/RGO removal of Cr(VI) under visible light.
Clinobisvanite (monoclinic scheelite BiVOsub.4, S.G.I2/b) has garnered interest as a wide-band semiconductor with photocatalyst activity, as a high NIR reflectance material for camouflage and cool ...pigments and as a photoanode for PEC application from seawater. BiVOsub.4 exists in four polymorphs: orthorhombic, zircon-tetragonal, monoclinic, and scheelite-tetragonal structures. In these crystal structures, V is coordinated by four O atoms in tetrahedral coordination and each Bi is coordinated to eight O atoms from eight different VOsub.4 tetrahedral units. The synthesis and characterization of doped bismuth vanadate with Ca and Cr are studied using gel methods (coprecipitated and citrate metal-organic gels), which are compared with the ceramic route by means of the UV-vis-NIR spectroscopy of diffuse reflectance studies, band gap measurement, photocatalytic activity on Orange II and its relation with the chemical crystallography analyzed by the XRD, SEM-EDX and TEM-SAD techniques. The preparation of bismuth vanadate-based materials doped with calcium or chromium with various functionalities is addressed (a) as pigments for paints and for glazes in the chrome samples, with a color gradation from turquoise to black, depending on whether the synthesis is by the conventional ceramic route or by means of citrate gels, respectively; (b) with high NIR reflectance values that make them suitable as fresh pigments, to refresh the walls or roofs of buildings colored with them; and (c) with photocatalytic activity.
The impacts of hexavalent chromium (Cr) contamination on the microbiome, soil physicochemistry, and heavy metal resistome of a tropical agricultural soil were evaluated for 6 weeks in field-moist ...microcosms consisting of a Cr-inundated agricultural soil (SL9) and an untreated control (SL7). The physicochemistry of the two microcosms revealed a diminution in the total organic matter content and a significant dip in macronutrients phosphorus, potassium, and nitrogen concentration in the SL9 microcosm. Heavy metals analysis revealed the detection of seven heavy metals (Zn, Cu, Fe, Cd, Se, Pb, Cr) in the agricultural soil (SL7), whose concentrations drastically reduced in the SL9 microcosm. Illumina shotgun sequencing of the DNA extracted from the two microcosms showed the preponderance of the phyla, classes, genera, and species of
Actinobacteria
(33.11%),
Actinobacteria
_class (38.20%),
Candidatus Saccharimonas
(11.67%), and
Candidatus Saccharimonas aalborgensis
(19.70%) in SL7, and
Proteobacteria
(47.52%),
Betaproteobacteria
(22.88%),
Staphylococcus
(16.18%),
Staphylococcus aureus
(9.76%) in SL9, respectively. Functional annotation of the two metagenomes for heavy metal resistance genes revealed diverse heavy metal resistomes involved in the uptake, transport, efflux, and detoxification of various heavy metals. It also revealed the exclusive detection in SL9 metagenome of resistance genes for chromium (
chrB, chrF, chrR, nfsA, yieF
), cadmium (
czcB/czrB, czcD
), and iron (
fbpB, yqjH, rcnA, fetB, bfrA, fecE
) not annotated in SL7 metagenome. The findings from this study revealed that Cr contamination induces significant shifts in the soil microbiome and heavy metal resistome, alters the soil physicochemistry, and facilitates the loss of prominent members of the microbiome not adapted to Cr stress.
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•A novel MXenes based composite material was successfully constructed.•Waterenvironment conditions played a vital role in adsorption of U(VI)/Cr(VI).•U(VI)/Cr(VI) adsorbed on ...Ti3C2@FeS-PDA/PEI was chemically controlled.•Removal mechanism was associated with surface complexation reaction.
Herein, a MXenes decorated nanoscale FeS composites were developed via electrostatic self-assembly strategy to achieve efficient U(VI)/Cr(VI) adsorption-reduction. Different analytical techniques were applied to adequately characterize all as-prepared materials to determine the formation of species with the desired morphology and properties. Results revealed that the special chemical structure of MXenes could improve the dispersion of FeS nano-particles and suppress its aggregation. Meanwhile, the adsorption data closely well tailored with the Langmuir isotherm and Pseudo-second-order equation, and the maximum removal efficiencies were 88.5 and 107.2 mg/g for uranium(VI) and chromium(VI). It was also found that the presence of other cations and anions had no obvious influence on removal of U(VI)/Cr(VI), whereas the elimination process was a spontaneous endothermic reaction. More importantly, according to the spectroscopic analysis and DFT calculation, both FeS and surface functional groups on Ti3C2@FeS-PDA/PEI exhibited strong chemical affinities to the targeted pollutants, while FeS could effectively reduce Uranium(VI) to Uranium(IV) and Chromium(VI) to Chromium(III). This work facilitated the omnidirectional improvement of MXenes-based materials for the de-pollution of practical radionuclide or heavy metals wastewater.
A colorimetric-electrochemical dual-mode analytical method based on bismuth metal-organic framework nanozyme was developed for label-free and trace/ultra-trace Cr6+ detection. 3D ball-flower shaped ...bismuth oxide formate (BiOCOOH) was used as the precursor and template to facilely construct the metal-organic framework nanozyme BiO-BDC-NH2, which possesses intrinsic peroxidase-mimic activity to effectively catalyze the colorless 3,3′,5,5′-tetramethylbenzidine into blue oxidation products in the presence of hydrogen peroxide. Based on Cr6+ to promote the peroxide-mimic activity of BiO-BDC-NH2 nanozyme, a colorimetric method for Cr6+ detection was developed with the detection limit of 0.44 ng mL−1. Cr6+ can be electrochemically reduced to Cr3+ that would specifically inhibit the peroxidase-mimic activity of BiO-BDC-NH2 nanozyme. Thus, the colorimetric system for Cr6+ detection was converted into a low-toxic and signal-off electrochemical sensor. The electrochemical model showed upgraded sensitivity and a lower detection limit of 9.00 pg mL−1. The dual-model method was developed for selective appropriate sensing instruments in different detection scenarios, which can provide built-in correction for environmental effects, as well as the development and utilization of dual-signal sensing platforms for trace to ultra-trace Cr6+ rapid assay.
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•A bismuth-based MOF nanozyme with 3D ball-flower shape was constructed.•The MOF showed Cr6+-promoted and Cr3+-inhibited peroxidase-mimic activity.•A dual-model colorimetric-electrochemical sensor for trace to ultra-trace Cr6+ detection.•The colorimetric model can convert into sensitive electrochemical model.
Biochar derived from waste water hyacinth was prepared and modified by ZnO nanoparticles for Cr(VI) removal from aqueous solution with the aim of Cr(VI) removal and management of waste biomass. ...The effect of carbonization temperature (500–800 °C), ZnO content (10–50 wt%) loaded on biochar and contact time (0.17–14 h) on the Cr(VI) removal were investigated. It was found that higher than 95% removal efficiency of Cr(VI) can be achieved with the biochar loaded 30 wt% ZnO. The adsorption kinetics of the sorbent is consistent with the pseudo-second-order kinetic model and adsorption isotherm follows the Langmuir model with maximum adsorption capacity of 43.48 mg g−1 for Cr(VI). Multiple techniques such as XRD, XPS, SEM, EDX and FT-IR were performed to investigate the possible mechanisms involved in the Cr (VI) adsorption. The results show that there is precipitation between chromium ions and Zn oxide. Furthermore, the ZnO nanoparticles acts as photo-catalyst to generate photo-generated electrons to enhance the reduction of Cr(VI) to Cr(III). The as-prepared ZnO/BC possess good recyclability and the removal ratio remained at about 70% in the fifth cycle, which suggests that both contaminants removal and effective management of water hyacinth can be achieved by the approach.
•Effect of carbonization temperature on the characteristics of biochar was examined.•.The biochar derived from water hyacinth was modified by ZnO nanoparticles.•.Higher than 95% removal efficiency of Cr(VI) was achieved even at natural pH.•Possible mechanisms involved in the Cr (VI) adsorption by ZnO/BC were investigated.
In National Toxicology Program 2-year studies, hexavalent chromium Cr(VI) administered in drinking water was clearly carcinogenic in male and female rats and mice, resulting in small intestine ...epithelial neoplasms in mice at a dose equivalent to or within an order of magnitude of human doses that could result from consumption of chromium-contaminated drinking water, assuming that dose scales by body weight3/4 (body weight raised to the 3/4 power). In contrast, exposure to trivalent chromium Cr(III) at much higher concentrations may have been carcinogenic in male rats but was not carcinogenic in mice or female rats. As part of these studies, total chromium was measured in tissues and excreta of additional groups of male rats and female mice. These data were used to infer the uptake and distribution of Cr(VI) because Cr(VI) is reduced to Cr(III) in vivo, and no methods are available to speciate tissue chromium. Comparable external doses resulted in much higher tissue chromium concentrations following exposure to Cr(VI) compared with Cr(III), indicating that a portion of the Cr(VI) escaped gastric reduction and was distributed systemically. Linear or supralinear dose responses of total chromium in tissues were observed following exposure to Cr(VI), indicating that these exposures did not saturate gastric reduction capacity. When Cr(VI) exposure was normalized to ingested dose, chromium concentrations in the liver and glandular stomach were higher in mice, whereas kidney concentrations were higher in rats. In vitro studies demonstrated that Cr(VI), but not Cr(III), is a substrate of the sodium/sulfate cotransporter, providing a partial explanation for the greater absorption of Cr(VI).
Broadband near‐infrared (NIR) phosphor‐converted light emitting diode (pc‐LED) is demanded for wearable biosensing devices, but it suffers from low efficiency and low radiance. This study reports a ...broadband NIR Ca3‐xLuxHf2Al2+xSi1−xO12:Cr3+ garnet phosphor with emission intensity enhanced by 81.5 times. Chemical unit co‐substitution of Lu3+−Al3+ for Ca2+−Si4+ is responsible for the luminescence enhancement and further alters the crystal structure and electronic properties of the garnet. Using the optimized phosphor, a NIR pc‐LED with photoelectric efficiencies of 21.28%@10 mA, 15.75%@100 mA and NIR output powers of 46.09 mW@100 mA, 54.29 mW@130 mA is fabricated. The high power NIR light is observed to penetrate upper arms (≈8 cm). For application in NIR spectroscopy, the NIR pc‐LED is used as light source to measure transmission spectra of water, alcohol, and bovine hemoglobin solution. These results indicate the NIR garnet phosphor to be a promising candidate for NIR pc‐LED.
Luminescence enhancement of 81.5 times is achieved in Ca3‐xLuxHf2Al2+xSi1‐xO12:0.08Cr3+ garnet phosphor by chemical unit co‐substitution. The near‐infrared phosphor‐converted light emitting diode fabricated by the optimized phosphor shows 46.09 mW output under 100 mA current and is capable of penetrating the upper arm.
•A multi-layer multi-track 3D transient numerical model was built.•Thermal behavior during SLM of CoCr powder was displayed.•Thermal mechanisms of SLM parameters on molten pool behavior were ...predicted.•Corresponding experiments were implemented to provide verification for molten pool behavior.
In this study, the ANSYS19.0 (APDL) was used to build a finite element model of Selective Laser Melting (SLM) forming cobalt-chromium alloy. The model parameters included the conversion of material properties, convective heat transfer, physical properties with different temperatures, and so on. Based on this model, the dimension of molten pool, temperature gradient, liquid lifetime and cooling rate were predicted at different processing parameters. In addition, the reliability of the model was checked by conducting relevant experiments and studying the micro-hardness and microstructure of specimens. The metal parts with high density and excellent forming quality could be acquired with the scanning speed of 750 mm/s and laser power in the range of 160–200 W. Especially, when the laser power was 160 W, the molten pool existed for a suitable time (0.3133 ms), and the liquid phase acquired good fluidity which was beneficial to the overlap of adjacent molten pools.
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