Nm For Cr Research Articles

Novel spherical and homogeneous Alstonia Scholaris silver nanoparticles for dual applications: Detection of ultra-trace amounts of Cr(III) ions and MB discoloration sustained by 3-input AND gate

This study unveils an effective method for detecting Cr(III) and MB dye discoloration using biosynthesized silver nanoparticles obtained from leaves of Alstonia Scholaris (AS-AgNPs). HR-TEM images showed that the mean diameter of AS-AgNPs increased from 14.68 to 37.05 nm after the interaction with Cr(III) ions. The AS-AgNPs show an impressive detection limit of 2.1 nM for Cr(III) and demonstrate high efficacy in MB discoloration of 91.27% in 12 min. The discoloration reaction fitted pseudo-first-order kinetics with the R2 value of 0.9634. When comparing the kinetics of MB discoloration by NaBH4 alone, and addition of AS-AgNPs to NaBH4 resulted in a 102 fold decrease in t1/2 and a 102 fold increase in k values. This is the first report to use spherical AS-AgNPs for dual applications, supported by 3-Input AND gate logic, and also highlights AS-AgNPs' potential application for real sample analysis.

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).

Spatial distribution of paddy field’s heavy metals diversity contamination in Samarinda using remote sensing imagery

Abstract. Palupi NP, Hardi EH, Fahrunsyah, Rahayu DE, Nugroho RA, Darma S, Idris SD. 2023. Spatial distribution of paddy field’s heavy metals diversity contamination in Samarinda using remote sensing imagery. Biodiversitas 24: 6743-6752. The adverse effects of heavy metal contamination on rice fields posing a significant threat to food safety. This study, conducted from May to July 2023 in Samarinda East Kalimantan, Indonesia, aims to determine the distribution of active rice fields and heavy metal contamination through Kriging's interpolation method. Aerial photographic interpretations, facilitated by ArcGIS 10.4, were performed with 144 sample points within 4 Districts. The content of heavy metals was assessed by Atomic Absorption Spectroscopy at specific wavelengths: 248.3 nm for Fe, 228.8 nm for Pb, 283.3 nm for Cd, 357.9 nm for Cr, 279.5 nm for Mn, 213.9 nm for Zn, and 324.7 nm for Cu, following guidelines of SNI 8910:2021. The research showed that existing rice fields were concentrated in North Samarinda District (380,416 ha), Loa Janan Ilir District (210,133 ha), Sambutan District (404,682 ha), and Palaran District (188,617 ha) with Fe content ranged from 4.976,45 ppm to 16.800,485 ppm, exceeding the critical Fe limit in soil of 500 ppm set by SNI. Mn content ranged from 22.65 ppm to 564.88 ppm, surpassing the critical soil threshold of 0.15 ppm for Mn according to SNI. Cu content varied from 3.32 ppm to 121.75 ppm, exceeding critical Cu limit of 0.04 ppm. Zn content ranged from 8.61 ppm to 223.12 ppm, surpassing the critical limit of Zn's pollution in the soil (0.06 ppm). Pb content ranged from 10.72 ppm to 32,84 ppm, categorized as intermediate compared to the threshold of 0.07 ppm for Pb in soil. Cd content ranged from 0.04 ppm to 0.739 ppm, exceeding the critical limit of 0.01 ppm set by SNI. Cr content was detected to be less than 0.032 ppm, falling into a very low category, with the critical limit for Cr content in soil set at 0.5 ppm according to SNI.

Feasibility of a Low-Power, Low-Resolution Laser-Induced Breakdown Spectroscopy Instrument for Analysis of Nickel Alloys: Quantification of the Major Alloying Elements and Classification.

A simple cost-effective laser-induced breakdown spectroscopy (LIBS) instrument was used for quantification of major elements in several nickel alloys and also sorting them. A compact low-power diode-pumped solid-state laser and a miniature low-resolution spectrometer were assembled for the LIBS instrument. Material properties of the nickel alloys depend mainly on the composition of the major elements, Ni, Cr, and Fe, ranging from a few to ∼60 wt%. The emission peaks at 547.7 nm, 520.4 nm, and 438.1 nm for Ni, Cr, and Fe, respectively, were chosen for this analysis. The analytical performance was found to be enough for the quantification of Ni, Cr, and Fe in the nickel alloys. Limits of detection and accuracy were estimated to be a few weight percent (wt%) and measurement precisions were less than 10% in terms of relative standard deviation. The calibration performance of this intensity-based method was compared with that of the "ratio method" which is used in conventional optical emission spectroscopy analyses. The comparison indicates that the intensity-based method is more appropriate with the low-performance LIBS instrument that detects emission peaks of only a few major elements. Also, multivariate modeling of the six different nickel alloy samples based on the emission peak intensities of Ni, Cr, and Fe was performed using k-nearest neighbors (KNN) and linear discriminant analysis (LDA). The KNN and ordinary LDA models showed 95.0% and 98.3% classification correctness for the separate test data set, respectively. To improve classification performance further, the two-step LDA model was trained. In this approach, the two closest sample classes responsible for the decrease in the classification correctness were separately modeled in the second step to exploit their difference effectively. The two-step LDA model showed 100% correctness in classifying the test objects. Our results indicate that such a low-performance LIBS instrument can be effectively utilized for quantitative analysis of the major elements in the nickel alloys and their rapid identification or sorting in combination with an appropriate multivariate modeling algorithm.

Atomically dispersed Fe-Zn dual-site nanozymes with synergistic catalytic effects for the simultaneous detection of Cr(VI) and 8-hydroxyquinoline.

Single-atom catalysts with atomically dispersed sites have been widely used as nanozymes for colorimetric sensing because their tunable M-Nx active centers are similar to those of natural enzymes. However, their low metal atom loading leads to insufficient catalytic activity and affects the sensitivity of colorimetric sensing, which limits their further applications. Herein, multi-walled carbon nanotubes (MWCNs) are selected as carriers to reduce the aggregation of ZIF-8 and improve the electron transfer efficiency of nanomaterials. Meanwhile, MWCN/FeZn-NC single-atom nanozymes with excellent peroxidase-like activity were prepared by pyrolysis on ZIF-8 doped with a second metal Fe. Based on the excellent peroxidase activity of MWCN/FeZn-NCs, a dual-functional colorimetric sensing platform for Cr(VI) and 8-hydroxyquinoline was established. The detection limits of the dual-function platform are 40 nM for Cr(VI) and 55 nM for 8-hydroxyquinoline. This work provides a highly sensitive and selective strategy for the detection of Cr(VI) and 8-hydroxyquinoline in hair care products, which has great application prospects in the field of pollutant detection and control.

The recovery of metals as high value powders and nanopowders from industrial wastewaters using potential-controlled electrolysis

The objective of the presented study was the recovery of Zn, Cr, Cu and Co in the form of powders and nanopowders from various types of industrial wastewaters. Powders and nanopowders as products of high added value find a wide applications in nanotechnology and material science and engineering. The metallic powders were obtained using potentiostatic electroreduction (potential-controlled electrolysis). The chosen method offers better control of the purity and structure of the products. The structure and size of crystallites depend on the value of electrolysis potentials and time, cathode material, concentrations of metal ions. In this investigation, the powders of different sizes ranging from 90 to 230 nm for Cr, 100–4000 nm for Zn, 25–100 nm for Co and 40–660 nm for Cu were deposited. The compositions, purity and size of the cathode deposits were confirmed by scanning electron microscopy and energy-dispersive X-ray spectroscopy. Presented metal recovery method is a promising technique for industrial application, given its simplicity, economic viability and environmental sustainability. It can be used on a wide range of solutions and help in reducing the problem of the growing amounts of industrial wastewater.

Low-Temperature Ethanol Sensor via Defective Multiwalled Carbon Nanotubes.

This paper focuses on the fabrication of defective-induced nanotubes via the catalytic chemical vapor deposition method and the investigation of their properties toward gas sensing. We have developed defective multi-walled carbon nanotubes with porous and crystalline structures. The catalyst layer used in CNTs’ growth here was based on 18 and 24 nm of Ni, and 5 nm of Cr deposited by the dc-sputtering technique. The CNTs’ defects were characterized by observing the low graphite peak (G-band) and higher defect peaks (D-band) in the Raman spectrum. The defectives sites are the main source of the sensitivity of materials toward different gases. Thus, the current product was used for sensing devices. The device was subjected to various gases such as NO, NO2, CO, acetone, and ethanol at a low operating temperature of 30 °C and a concentration of 50 ppm. The sensor was observed to be less sensitive to most gas while showing the highest response towards ethanol gas. The sensor showed the highest response of 8.8% toward ethanol at 30 °C of 50 ppm, and a low response of 2.8% at 5 ppm, which was investigated here. The signal repeatability of the present sensor showed its capability to detect ethanol at much lower concentrations and at very low operating temperatures, resulting in reliability and saving power consumption. The gas sensing mechanism of direct interaction between the gas molecules and nanotube surface was considered the main. We have also proposed a sensing mechanism based on Coulomb dipole interaction for the physical adsorption of gas molecules on the surface.

Mn, Cu and Cr nanoparticles in Li2B4O7 glass: Radiation shielding and optical properties

Lithium tetraborate (Li2B4O7) glass matrices doped with Manganese (Mn), Copper (Cu) and Chromium (Cr) were synthesized, using the melt-quenching method. Radiation shielding and optical parameters are studied in this work. High-resolution Transmission Electron Microscopy confirms formation of Mn, Cu and Cr nanoparticles in the samples. Absorption spectra of the samples show the characteristic surface-plasmon bands of these transition-metals nanoparticles. Their bandgaps were calculated from the absorption spectra. The fluorescence bands of each transition-metal nanoparticle ensembles in the tetraborate glass matrices are identified by recording the fluorescence spectrum. Emission spectra under 405 nm pumping show bands with a peak at 591 nm from nanoparticles of Mn, a peak at 750 nm of Cu, and a peak at 735 nm of Cr. The fluorescence lifetimes are measured, and the stimulated emission and absorption cross-section are calculated. The theoretical values of radiation shielding parameters mass attenuation coefficient (MAC), half value layer (HVL), tenth value layer (TVL), mean free path (MFP) and effective atomic number (Zeff) were calculated for the glass samples to analyze which sample has the best radiation shielding response. It should be noted that the samples made in this work present a better response than high-performance heavyweight concrete mixes using the coarse aggregates of magnetite.

Comparative Study of Bulk and Nanoengineered Doped ZnSe

Chromium- and cobalt-doped zinc selenide nanoparticles were synthesized using a low-temperature reactive solution growth method. The morphological and optical characteristics were compared to those of doped zinc selenide (ZnSe) bulk crystals grown by the physical vapor transport (PVT) method. We observed agglomeration of particles; however, the thioglycerol capping agent has been shown to limit particle grain growth and agglomeration. This process enables doping by addition of chromium and cobalt salts in the solution. A slightly longer refluxing time was required to achieve cobalt doping as compared with chromium doping due to lower refluxing temperature. The nanoparticle growth process showed an average particle size of approximately 300 nm for both Cr- and Co-doped zinc selenide. The optical characterization of Co:ZnSe is ongoing; however, preliminary results showed a very high bandgap compared to that of pure ZnSe bulk crystal. Additionally, Co:ZnSe has an order of magnitude higher fluorescence intensity compared to bulk Cr:ZnSe samples.

High electrical conductivity and breakdown current density of individual monolayer Ti3C2Tx MXene flakes

High electrical conductivity and breakdown current density of individual monolayer Ti3C2Tx MXene flakes

Odd spin frustration in Cr(001) films thinner than three nanometers revealed by spin-polarized scanning tunneling microscopy

We have studied the surface structure and morphology of epitaxial Cr films on Au(001) substrate with Cr thickness (${d}_{\mathrm{Cr}}$) below 3 nm. We have characterized the films prepared under various growth conditions by using scanning tunneling microscopy and spectroscopy (STM/STS), low-energy electron diffraction, and Auger electron spectroscopy. The good growth conditions of the Cr(001) films, which have atomically flat terraces without surface segregation of Au and with distinct surface states, are obtained by the following two methods. (I) ${d}_{\mathrm{Cr}}=3$ nm film realized by two-step growth, i.e., first 1.5 nm of Cr deposited at room temperature ($\ensuremath{\sim}290$ K) and an additional 1.5 nm Cr deposition at 570 K and (II) ${d}_{\mathrm{Cr}}=1.5$ nm film by room temperature growth and subsequently post-annealing at 470 K. The magnetic imaging of (I) ${d}_{\mathrm{Cr}}=3$ nm Cr(001) film was performed by means of spin-polarized STM/STS. The observed magnetic image indicates that the topological antiferromagnetic (AF) order appears in a series of adjacent terraces and two types of spin frustration caused by screw dislocations lead to modifications of the topological AF order. One type of spin frustration is accompanied by narrow domain walls between two screw dislocations. The other type is a complex spin frustration caused by a cluster of an odd number of screw dislocations. The difference of the two types of spin frustration is explained through a micromagnetic simulation. We have also identified a large spin-frustrated area, consisting of a cluster of multiple number of screw dislocations.

Highly sensitive detection of Cr(VI), Pb(II) and Cd(II) ions by a new fluorescent sensor based on 4-amino-3-hydroxynaphthalene sulfonic acid-doped polypyrrole

A new electrosynthesized, fluorescent 4-amino-3-hydroxynaphthalene-1-sulfonic acid-doped polypyrrole (AHNSA-PPy) was used for the detection of Cr(VI), Pb(II) and Cd(II) heavy metallic ions. The optical properties of AHNSA-PPy were studied by UV-VIS absorption and fluorescence spectrometry in diluted DMSO solutions. UV-VIS spectrum showed a main band at 260 nm, a moderate band at 240 nm, and shoulders at 285, 295, 320 and 360 nm, whereas the fluorescence spectrum presented an excitation peak at 330 nm and a main emission peak at 390 nm with a shoulder at 295 nm. The effects of heavy metallic ions, including Cr(VI), Pb(II), and Cd(II), on the AHNSA-PPy UV-VIS absorption and fluorescence spectra were investigated. AHNSA-PPy fluorescence spectra were strongly quenched upon increasing the Cr(VI), Pb(II) and Cd(II) concentrations. Linear Stern-Volmer relationships were established, and polynomial equations for Pb(II) and Cd(II) were obeyed, indicating the existence of a AHNSA-PPy dynamic fluorescence quenching mechanism for Cr(VI) and a combination of dynamic and static fluorescence quenching for Pb(II) and Cd(II). The AHNSA-PPy sensor showed high sensitivity for fluorescence detection of the three heavy metallic ions, with very low limits of detection (3σ) of 1.4 nM for Cr(VI), 2.7 nM for Cd(II) and 2.6 nM for Pb(II). Therefore, this very sensitive quenching fluorimetric sensor is proposed for the detection of trace, toxic heavy metallic ions in the environment.

A potent multifunctional Ag/Co-polyvinylpyrrolidone nanocomposite for enhanced detection of Cr(III) from environmental samples and its photocatalytic and antibacterial applications.

Trivalent chromium (Cr(III)) is considered to exhibit hormesis (bi-phasic dose-response) property, where low dose be beneficial and high dose shows toxic effect. The present work describe the development of a bimetallic Ag/Co-polyvinylpyrrolidone nanocomposite (Ag/Co-PVP NPs) probe to detect and quantify Cr(III) ions from aqueous samples. The hydrodynamic size and zeta potential of the particle was determined to be 29±1.3nm and -37.19±2.4 mV respectively. The interaction of Cr(III) with Ag/Co-PVP probe showed drastic change in colour of NPs from dark brown to pale yellow, with corresponding blue shift, tapering width and increased peak intensity. The probe showed high specificity towards Cr(III) among the tested metal ions. A linearity was observed between various dilutions of Cr(III) ions (10 to 50nM) and the absorbance of Ag/Co-PVP NPs at 428nm with R2 value of 0.998. The minimum detectable limit of Cr(III) was calculated to be 0.6nM. The influence of salinity, temperature and pH on detection was studied. The probe was found to detect Cr(III) at acidic pH effectively. Competitive metal ions did not interfere the detection of Cr(III). The water sample collected from Noyyal river was taken to estimate Cr(III) by using the prepared probe to ensure practical applicability. The sample contains 9.3nM of Cr(III) that was cross verified with AAS analysis. Hence, it is understood that the reported probe can be used to detect Cr(III) selectively with high accuracy from aqueous samples. In addition, the particles also exhibited excellent photocatalytic activity under visible light. Ag/Co-PVP nanocomposites exhibited excellent antibacterial activity against both gram +ve (B. subtilis) and gram -ve (E. coli) bacteria.

Enhanced room temperature ferromagnetism in Cr and Fe co-doped SnO2 nanoparticles synthesized by sol-gel method

The Cr and Fe atoms incorporated into SnO2 matrix by sol-gel method have been studied for enhancement in ferromagnetism and emission properties at room temperature. X-ray diffraction studies confirms the enrichment in crystallinity and pure rutile type tetragonal structure of SnO2 with co-doping of (Cr, Fe). Crystallite size from XRD analysis of co-doped SnO2 nanoparticles was found to decrease from 15 nm for pure SnO2 to 8 nm for (Cr, Fe) co-doped SnO2 nanoparticles. The particle size of prepared nanoparticles was exposed by transmission electron microscopy images and found to be in the range of 5–10 nm. A sharp photoluminescence peak marked at 425 nm with change in peak intensity was observed for all the compositions. Further, room temperature magnetic investigation for pure and modified SnO2 samples was done using Vibrating Sample Magnetometer. The value of saturation magnetization was found to increase from 4 × 10 −3emu/g for Cr doped SnO2 to 6 × 10 −2emu/g for (Cr, Fe) co-doped SnO2 which might be due to presence of oxygen vacancies in the system.

Hydrothermal Synthesis of a Novel Mesoporous Silica Fluorescence Carbon Dots and Application in Cr(VI) and Folic Acid Detection

Highly blue fluorescence carbon dots (CDs-MCM) were successfully prepared via a simple hydrothermal method with citric acid and ethylene diamine tetraacetic acid doped mesoporous silica MCM-41. The CDs-MCM exhibited uniform particle size and possessed good excitation-dependent characteristic. It showed highly selectivity and sensitivity in detection of Cr(VI), folic acid and good linear ranges of 0–37.5[Formula: see text][Formula: see text]M ([Formula: see text]) and 0–50[Formula: see text][Formula: see text]M ([Formula: see text]). The low detection limits were 79.31[Formula: see text]nM and 118.73[Formula: see text]nM for Cr(VI) and folic acid, respectively. It revealed that inner filter effect dominated in Cr(VI) quenching of the CDs-MCM fluorescent, while that of folic acid belonged to static quenching. The CDs-MCM were successfully used to detect the Cr(Vl) and folic acid in water and vegetable samples with satisfactory results. It provided new insight into environmental Cr(VI) and folic acid detection.

Insights into interactions of Cr(III) and organic matters during adsorption onto titanate nanotubes: Differential absorbance and DFT study

Organic Matter (OM) with different molecular weight and functional groups can impact the adsorptive removal of metal ions, and the influence trend can be facilitated, inhibited or unchanged. However, the association capabilities of different ligands were superficially expounded. Based on the sorption behavior of Cr(III) onto titanate nanotubes (TNTs) with coexisting citric acid (CA), humic acid (HA) and fulvic acid (FA), this study highlighted differential absorbance and DFT simulations to quantitatively detect the mutual effect. As results, adsorption capacities of Cr(III) obviously enhanced from ca. 60 mg/g to 85 mg/g with CA or FA; while HA can slightly promote Cr(III) adsorption. UV spectra scanning proved that FA and HA led to the remarkable red shift of peak A1 (232 nm), A2 (262 nm), A3 (295 nm), A4 (431 nm) of Cr(III), and the area ratio of A2/A3 followed the order Cr-HA > Cr-FA > Cr-CA ≈ Cr. DFT calculations further confirmed that the simultaneous formation of ligand-metal-adsorbents complex and electrostatic effect promoted Cr(III) adsorption, with binding energies of −202.9 ~ −420.8 kJ/mol and − 3958 kJ/mol, respectively. Meanwhile, the bridge connection of OM mainly appeared in the outer sphere of TNTs, as the larger molecular scale prevented their insertion into the inner spacing of TNTs, especially for HA and FA. Therefore, the adsorption mechanism was the combined actions of electrostatic attraction, bridge connection of OM and steric effect. This study can give insights into OM effects on metal adsorption, and quantificationally describe the junction state of ternary complex.

Monitoring graphene oxide’s efficiency for removing Re(VII) and Cr(VI) with fluorescent silica hydrogels

Supported carbon quantum dots (CQDs), used as fluorescent sensors for the detection of metal ions, have rarely been used to remove heavy metals from water. Nitrogen-doped CQDs immobilized in hydrophilic silica hydrogels exhibited a more superior sensitivity and selectivity for the detection of Re(VII) and Cr(VI) than other metal ions, including Fe(III), Fe(II), Zn(II), Cu(II) and Mn(II). For the first time, low limits of detection (LOD) of 2.3 μM for Re(VII) detection and 65 nM for Cr(VI) detection were reported by a facile method. Based on the high selectivity of fluorescent silica hydrogels for Re(VII) and Cr(VI) detection, the removal of Re(VII) and Cr(VI) by graphene oxide (GO) in water was monitored with the hydrogels used as a turn-off fluorescent sensing platform. The consistent results of the sorption isotherms of each metal on GO, which were obtained from the fluorescence spectra and by UV absorption, further verified the possibility of monitoring metal removal by fluorescence detection. Remarkably, GO removed 1186 mg/g of Re(VII) but only 178 mg/g of Cr(VI). The density functional theory (DFT) calculations indicated that both Re(VII) and Cr(VI) formed stable bonds with silica hydrogels, confirming that the interactions between the metal ions and the substrate would promote the fluorescence quenching of the supported CQDs. On the other hand, Re(VII) interacted more strongly with the carboxyl groups of GO than Cr(VI). In addition, a real-time detection system was designed to alarm the service life of a GO filter used for Re(VII) removal.

A novel multifunctional fluorescent sensor based on N/S co-doped carbon dots for detecting Cr (VI) and toluene

The construction of a novel multifunctional fluorescence platform is of great significance to detect different toxic pollutions. In this work, multifunctional nitrogen and sulfur doped fluorescence carbon dots (N, S-CDs) were synthesized with citric acid monohydrate and thiosemicarbazide as raw materials. The quantum yield (QY) of N, S-CDs was calculated as 12%. The fluorescence intensity of N, S-CDs could be quenched obviously by Cr (VI) due to the inner filter effect, achieving a low detection limit of 0.33 nM for Cr (VI). While excessive Ba2+ was added, the fluorescence intensity could be restored. Meanwhile, based on the fact that the fluorescence of the N, S-CDs could be enhanced by toluene, the detection of toluene was achieved and the detection limit was low as 0.03 μM. Furthermore, the practical application of the N, S-CDs was assessed in the river water. The proposed N, S-CDs could provide a promising fluorescence platform for detecting different toxic pollutions.

Dynamics and diagenesis of trace metals in sediments of the Changjiang Estuary

The seasonal dynamics and diagenesis of trace metals at two contrasting coastal sites were studied to determine the mechanism that drove the diffusive release of trace metals from sediments in the Changjiang Estuary. Porewater trace metal concentrations were 53.4–4829 nM for Zn, 11.0–344 nM for Cu, 7.75–221 nM for Cr, 2.71–61.1 nM for Co, 0.822–42.7 nM for Pb and 0.037–4.22 nM for Cd. The concentrations and profiles of trace metals in the porewater and solid phase displayed obvious regional and seasonal variations. This variation was mainly reflected in the surface layer and the depth of the suboxic and anoxic layers. Regionally, surface porewater trace metal concentrations in the seasonal hypoxic region were higher than those in the aerobic region due to changes in the redox conditions being beneficial to the release of trace metals. Seasonally, surface porewater trace metal concentrations decreased in summer compared to spring due to their removal by forming metal sulfides in summer. Solid profiles of the trace metals supported their dynamic variations in the porewater. The partition coefficient suggested that the formation of Fe/Mn (hydr)oxides was effective for the removal of trace metal in oxidizing condition, while the formation of sulfides was conducive to the removal of trace metals in reducing condition. The combination of porewater with solid phase data suggested that the dynamics of Cu, Zn, Cr and Co were mainly controlled by Fe and Mn diagenesis, the dynamics of Cd were affected by S cycling, and the dynamics of Pb were disturbed by anthropogenic inputs and benthic organism activities. Estimation of benthic fluxes indicated that sediments were an important source of trace metals in the water column. The contributions of trace metals by sediments to the water column of the Changjiang Estuary were only one order of magnitude lower than those by riverine fluxes.

Structural, photoluminescence and magnetic properties of Mn, Cr dual-doped ZnS quantum dots: Influence of Cr concentration

Mn-doped ZnS and Mn, Cr dual-doped ZnS quantum dots were prepared using a simple co-precipitation method. The synthesized samples were analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-rays (EDX), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), UV–visible spectroscopy, photoluminescence (PL) spectra and vibrating sample magnetometer (VSM). Cr doping reduced the crystallite size. The reduction of activation energy due to the incorporation of Cr is responsible for the increase of micro-strain and the suppression of crystallite size. The change in lattice parameters by Cr doping is attributed to the replacement of Cr3+/Cr2+ ions instead of Zn2+ ions in the ZnS host lattice. Doping concentration of the samples was confirmed by energy dispersive X-ray (EDX) spectra. Occurrence of higher intensity in absorption and a shift in absorption edge towards the lower angle side were supported by the proper substitution of Cr2+ ions instead of Zn2+ ions in the ZnS host. The diminishment of absorption intensity for Cr doping beyond 2% can be ascribed to defect states caused by imperfections in the lattice structure due to the different sizes of Cr2+/3+, Mn2+ and Zn2+. When Cr is introduced into the Zn-Mn-S assembly, a shift in UV emission is observed from 392 nm to 379 nm for Cr = 2% and 382 nm for Cr = 4%; these peak shifts were due to the size effect and the change in crystal structure by Cr doping. Nevertheless, the magnetic moment is enhanced because of the increase in number of spins by Cr incorporation; all samples retained their paramagnetic nature.