Introducing band gap states to TiO2 photocatalysts is an efficient strategy for expanding the range of accessible energy available in the solar spectrum. However, few approaches are able to introduce ...band gap states and improve photocatalytic performance simultaneously. Introducing band gap states by creating surface disorder can incapacitate reactivity where unambiguous adsorption sites are a prerequisite. An alternative method for introduction of band gap states is demonstrated in which selected heteroatoms are implanted at preferred surface sites. Theoretical prediction and experimental verification reveal that the implanted heteroatoms not only introduce band gap states without creating surface disorder, but also function as active sites for the CrVI reduction reaction. This promising approach may be applicable to the surfaces of other solar harvesting materials where engineered band gap states could be used to tune photophysical and ‐catalytic properties.
Band gap state engineering: Band gap states are introduced to the surface electronic structure of rutile TiO2 by substituting the in‐plane oxygen atoms of the (110) facet with nitrogen atoms without creating surface disorder. The modified material is able to reduce CrVI, which suggests that adsorption and heteroatom sites create an active surface that promotes charge transfer.
This study investigated the use of 10 (M1), 17 (M2) and 27wt.% (M3) electric arc furnace steel slag (EAFS) as a raw material in the production of calcium ferroaluminate belite cement clinker, after ...firing at 1320°C. The thermal behavior of the raw meals was studied by TG/DSC and XRD whereas for the analysis of the clinkers, XRD/QXRD, SEM/EDS and EPMA were employed. The resulting clinker was co-grinded with 5 and 20wt.% Flue Gas Desulfurization (FGD) gypsum and the properties were determined by a series of tests in accordance to EN standards. The evolution of hydration was investigated by SEM and the development of compressive strength. The results revealed that the formed phases in the clinkers were C2S, C4AF and C4A3Ŝ. The main hydration products were ettringite, AFm and hydrogarnet. The leached CrVI was below 1ppm in M3. Compressive strength in cements with 5wt.% FGD gypsum was (in MPa): 18.3 for M1, 14.3 for M2 and 7.8 for M3 at 28days, whereas for 20wt.% FGD gypsum, the values were almost doubled.
A new nanocomposite, CeO2–MoO3–SiO2(CH2)3-(Alg)2, has been synthesized via a simple synthesis method using a microwave irradiation technique. The morphological characterization indicated that the ...average particle size of the nanocomposite is 94.26–141.54 nm.The adsorptive remediation was established for MnII and CrVI ions by the nanocomposite under the influence of the microwave sorption process. Additionally, remediation of 51Cr and 56Mn radioactive nuclides was established using column technique. In this study, all the adsorption controlling parameters were explored like, solutions pH, contact time, amount of nanocomposite, and ionic concentration of the target metals. The maximum metal up-take capacities were estimated as 122.06 mg/g for MnII and 151.96 mg/g for CrVI by utilizing 5.0 mg of the nanocomposite at pH values 7.0 for MnII, and 2.0 for CrVI, while the equilibrium time at 25, and 20 s for MnII, and CrVI ions, respectively. The adsorption kinetics of MnII, and CrVI ions onto the CeO2–MoO3–SiO2(CH2)3-(Alg)2 nanocomposite proved to fit with the pseudo-second-order kinetics model and the adsorption mechanism fitted to the Langmuir and Freundlich isotherm models compared to the other models.
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•Synthesis of assembly of CeO2–MoO3–SiO2(CH2)3-(Alginate)2 microcomposite sorbent.•The microcomposite has been characterized by diverse techniques.•Remediation of MnII/CrVI and 56Mn/51Cr radionuclides from water.•The solution pH, reaction time, solid amount, radionuclides concentration, has been examined during the remediation.•Maximum capacity was estimated as 122.06 mg/g for MnII, 151.96 mg/g for CrVI, 92.3% for 56Mn, and 97.4% for 51Cr.
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•Triamino-anchored fibrous silica nanospheres adsorbent is prepared via facile route.•Removal of CrVI from aqueous solution by this adsorbent is investigated.•Adsorption isotherms, ...kinetics, and possible pathways were discussed.•Physical adsorption (electrostatic attractions) are responsible for CrVI removal.•This functionalized material act as a potential adsorbent for aqueous CrVI removal.
Triamino-anchored monodispersed fibrous silica nanospheres (Triamino-KCC-1) was successfully fabricated, for the first time, via anchoring 3-2-(2 Aminoethylamino) ethylamino propyltrimethoxysilane by a facile and effective post-grafting approach. Triamino-KCC-1 with fibrous silica nanosphere morphology showed large pore volume (1.15 m3 g–1) and surface area (∼536 m2 g−1) containing the micro-mesostructured silica fibers. The adsorption behaviors of hexavalent chromium (CrVI) from aqueous media on the Triamino-KCC-1 adsorbent were monitored as a function of initial pH solution, adsorbent dose, initial CrVI concentration, and contact time. The Triamino-KCC-1, as a novel functionalized fibrous silica adsorbent, had high adsorption efficiency at acidic pH and the adsorption rate was fast. The adsorption data for Triamino-KCC-1 was consistent with the Langmuir isotherm model with a calculated maximum uptake capacity of ∼316 mg g−1, which was in reasonable agreement with experimental adsorption capacity (∼317 mg g−1). According to the results obtained by applying isotherm and kinetic parameters, we can conclude that the most active sites of Triamino-KCC-1 are easily accessible. The results obtained in the present study indicate that it is of great practical and research interest to develop functionalized fibrous silica-based adsorbents for effective heavy metals removal.
Although it has been demonstrated that exposure of lactating rats to CrVI delays tooth eruption, the effects of CrVI exposure on bone remodeling in the developing alveolus during tooth eruption ...remain unknown. Our purpose was to analyze the effect of CrVI in the alveolus of the first lower molar of rats. Thirty-two suckling Wistar rats were divided into two groups. The experimental group received 12.5 mg/kg body weight/day of potassium dichromate dissolved in saline solution by oral gavage as of day 4 of the experiment; the control group received an equal dose of saline solution. Each group was divided into two sub-sets and euthanized at the ages of 9 and 15 days, respectively. Histochemical and histomorphometric studies of the bone surfaces of the developing tooth alveolus were performed. The percentage of bone formation surfaces was lower in experimental animals than in age-matched controls. The percentage of bone resorption surfaces was significantly lower in 9-day-old experimental rats than in controls and significantly higher in 15-day-old experimental rats than in controls. Exposure to CrVI during lactation alters the sequence of bone resorption and formation in the walls of the developing alveolus, both of which are necessary for tooth eruption, thus causing a delay.
The main aim of the research was to evaluate the impact of the type and color of container and the type of stored water on the concentration of toxic As, Cr and Sb species. The applicability of the ...method previously developed in our laboratory for the multielemental speciation analysis of five toxic species: AsIII, AsV, CrVI, SbIII and SbV in drinking water samples using HPLC/ICP-DRC-MS was extended to ensure that it would apply to drinking water samples characterized by mineralization up to 7390mgL−1. Two point standard addition calibration was developed to compensate for matrix effects in the samples. Extended procedure was characterized by precision in the range from 1.8% to 5.6% for all analytes. Recovery, calculated based on the analysis of spiked real water samples at concentration level of analytes — 0.5μgL−1, was in the range from 84% to 117%. All other parameters validated previously were recognized as valid for the extended scope procedure. 35 bottled water samples were analyzed for the presence of: AsIII, AsV, CrVI, SbIII and SbV. In most cases, samples stored in glass containers contained a higher concentration of AsIII and AsV in comparison to PET bottles. Antimony exhibits the opposite trend, therefore a higher concentration of SbV was determined in the same water stored in PET bottles than in glass bottles. CrVI was observed mainly in water stored in green bottles regardless of its material which points to the leaching of chromium from the green containers. The maximum concentrations of AsV, AsIII, SbV, CrVI in the tested samples were (3.759±0.474) μgL−1, (1.121±0.091) μgL−1, (0.721±0.040) μgL−1 and (2.222±0.084) μgL−1 respectively. SbIII was not detected in any of the samples.
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•Multielemental speciation by HPLC/ICP-DRC-MS•Quantification of AsIII, AsV, CrVI, SbIII and SbV in one analytical run•Analysis of drinking water samples•Uncertainty budget estimation and method validation•The impact of color and material of the container on the toxic species leaching
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•Few-layer MoS2 nanosheets decorated on the TiO2 NTAs via a facile hydrothermal method.•The composites possess a stable construction benefiting to the utilization of sunlight and ...electron transfer.•High concentration CrVI can be fast reduced over MoS2@TiO2 in the presence of appropriate LOAs and applied voltage.•Effect of LOAs, applied voltages and initial concentrations were performed.
A stable MoS2 nanosheets@TiO2 NTAs composite was prepared via a simple hydrothermal process. Few-layer MoS2 nanosheets distributed on the TiO2 nanotube top surface and the inner walls rather than filling in the tubes, allowing abundant tubular channels open to environment and benefiting for efficient mass transport. Photocatalytic (PE) and photoelectrocatalytic (PEC) performance of the composite were evaluated on CrVI reduction, with variable low molecule weight organic acids (LOAs) added as sacrificial electron donor to form a charge-transfer-complex (CTC) between LOAs and TiO2/MoS2, which is sensitive to the visible light illumination and could induce the photo-reduction of CrVI and photo-oxidation of LOAs. The overall trend of CrVI PEC rates are in the order as: L(+)-Tartaric acid>oxalic acid>citric acid>malic acid>amber acid, which is 103.9>62.5>31.2>21.6>2.5mg/Lmin−1cm−2, respectively. The improved catalytic performance and excellent stability of the composite can be attributed to the abundant active adsorption and reaction sites on MoS2 nanosheets and the formation of a heterojunction between TiO2 and MoS2. Moreover, the appropriate application of LOAs and voltage also have a great contribution to the utilization of sunlight and efficient separation of photogenerated carriers.
Given the serious harm of CrVI to human health, development of efficient techniques for its degradation and subsequent in situ adsorptive removal is highly desirable. Herein, UiO‐66 type ...metal–organic frameworks (MOFs) integrated with various hydroxyl groups (UiO‐66, UiO‐66‐OH, and UiO‐66‐(OH)2) were successfully explored for the efficient decontamination of CrVI from aqueous solution. The abundant hydroxyl groups in organic ligands not only served as reductive sites for the degradation of CrVI to less toxic CrIII but also acted as inherent anchorages for the efficient capture of CrIII. Thanks to their inherent hydroxyl groups and high porosity, UiO‐66‐(OH)2 presented almost complete removal of Cr species in simulated industrial wastewater. The total Cr content could be reduced from 5 ppm to 48 ppb under optimized adsorption conditions, which is much lower than the limits of total Cr in drinking water established by the US Environmental Protection Agency (EPA). These outstanding CrVI decontamination features, combined with the exceptional chemical stability as well as high porosity prefigured the great potentials of the current adsorbents for the remediation of real‐world CrVI‐containing industrial wastewater.
Zr‐based metal–organic frameworks (MOFs) of UiO‐66‐(OH)2 were successfully explored to simultaneously degrade and remove toxic CrVI, which presented almost complete removal of Cr species in simulated industrial wastewater even at a high concentration of background electrolytes (see scheme).
The level and distribution of chromium (as total chromium and CrVI) and other trace elements were investigated from surface and groundwater samples collected over three periods (n = 155) from Mersin ...(Turkey) in terms of their origins and potential health risk. The maximum total chromium is 41 µg/L and some of the samples have CrVI contents above 5 µg/L, which is the maximum permissible level of CrVI under Italian regulations. The dominant water facies are Ca–HCO
3
and Mg–HCO
3
types based on the Piper diagram. The Ca–HCO
3
type waters originate mainly from interaction with carbonate rocks, and the Mg–HCO
3
type waters originate from serpentinite dissolution. Chromium contents are higher in Mg–HCO
3
water types and the highest concentrations are found in samples from ophiolitic rocks and industrial areas. The As, Fe, Pb, Al, and Ni contents of some samples are above the EU limits in industrial areas.
California, the first state in the nation to regulate hexavalent chromium (CrVI) in drinking water, has set a maximum contaminant level (MCL) of 10 μg/L. To comply with the MCL, a California utility ...conducted extensive pilot studies to determine the best-performing ion exchange resin, empty bed contact time (EBCT), and hydraulic loading rate (HLR). The CrVI removal capacities of four strong base anion exchange resins were tested at seven wells. Results showed that between 12,000 and 37,000 bed volumes of treatment can be expected before an 8-μg/L breakthrough threshold. HLR was shown to have little effect on CrVI removal within the range tested (7.5 to 30 gpm/ft2), whereas longer EBCTs (>45 s) appeared to improve performance. The presence of co-occurring anions in the raw water—namely, sulfate and nitrate—had substantial effect on the resin's chromium loading capacity.
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