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ZnSe/ZnS Core/shell Quantum Dots with Superior Optical Properties through Thermodynamic Shell Growth
摘要： Epitaxial growth of a protective semiconductor shell on a colloidal quantum dot (QD) core is the key strategy for achieving high fluorescence quantum efficiency and essential stability for optoelectronic applications and bio-tagging with emissive QDs. Herein we investigate the effect of shell growth rate on the structure and optical properties in blue-emitting ZnSe/ZnS QDs with narrow emission linewidth. Tuning the precursor reactivity modifies the growth mode of ZnS shells on ZnSe cores transforming from kinetic (fast) to thermodynamic (slow) growth regimes. In the thermodynamic growth regime, enhanced fluorescence quantum yields and reduced on-off blinking are achieved. This high performance is ascribed to the effective avoidance of traps at the interface between the core and the shell, which are detrimental to the emission properties. Our study points to a general strategy to obtain high-quality core/shell QDs with enhanced optical properties through controlled reactivity yielding shell growth in the thermodynamic limit.
关键词： thermodynamic,core/shell QDs,heavy-metal-free,ZnSe/ZnS,kinetic
更新于2025-09-19 17:13:59
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Quantitative analysis of Pb in soil by femtosecond-nanosecond double-pulse laser-induced breakdown spectroscopy
摘要： The effects of inter-pulse delay on the quantitative analysis of femtosecond-nanosecond double-pulsed laser-induced breakdown spectroscopy (fs-ns DP-LIBS) for assessing Pb in soil have been systematically studied in this work. A femtosecond pulse laser was focused to produce a filament, which was used to ablate the soil sample and produce an appreciable amount of aerosol particles ejected from the soil surface at a low density. Scattering images of the soil particles ejected from the soil surface were obtained, and the soil particles were found to have a delay of 800 μs. After an inter-pulse delay, a nanosecond Nd:YAG laser re-ablated the soil particles and obtained a spectral enhancement and a narrow line width. The quantitative analysis based on DP-LIBS for Pb in soil was strongly dependent on the inter-pulse delay time. With an inter-pulse delay time of 10 μs for DP-LIBS, the R-square factor (R2), relative standard deviation (RSD), root mean square error of cross-validation (RMSECV), and limit of detection (LOD) were 99.42%, 2.99%, 0.42 wt.%, and 8.13 mg/kg, respectively. These findings demonstrate that DP-LIBS can be applied as an efficient spectroscopic tool to improve the quantitative analysis of Pb heavy metal in soil.
关键词： fs-ns DP-LIBS,quantitative analysis,limit of detection,Pb heavy metal
更新于2025-09-19 17:13:59
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Quantitative Analysis of Heavy Metal Components in Soil by Laser-Induced Breakdown Spectroscopy Based on Principal Component Analysis
摘要： The calibration curves of heavy metal elements Cd and Ni were established based on laser induced breakdown spectroscopy of standard soil and soil to be tested. The plasma excitation test was carried out on the soil by laser induced breakdown spectroscopy to obtain a plasma spectrum with a wavelength of 300-1000 nm. By comparing the characteristic peaks in the obtained spectrum with the National Institute of Standards and Technology database, it is found that the test samples contain heavy metal elements such as Cd, Cr, Cu, Hg, Ni and W, and the Cd and the measured standard soil. The main method analysis of the peak of Ni element is carried out, and the principal component regression model is established to obtain the calibration curve of Cd and Ni elements, and then the content of Cd and Ni elements in the soil to be tested is estimated. Based on the concentration of the national standard soil sample and the measured spectral intensity, the linear correlation coefficients between the predicted and actual values of the Cd and Ni element contents were established to be 1 and 0.99443. Compared with the commonly used methods, laser-induced breakdown spectroscopy can quickly detect samples to be tested, and sample pretreatment is simple and less damage to the sample.
关键词： Principal component analysis,Soil heavy metal pollution,Laser induced breakdown spectroscopy,Qualitative and quantitative analysis
更新于2025-09-16 10:30:52
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Detection of heavy metal containment of soil pollution due to waste of paper industry using Nd:YAG laser induced breakdown spectroscopy
摘要： Detection of heavy metal containment of soil pollution has been made by using laser-induced breakdown spectroscopy (LIBS). A pulsed Nd:YAG laser (1064 nm, 8 ns, 200 mJ) was focused on to a soil sample, which is prepared in the form of pellet, at atmospheric pressure. Emission spectra taken from the waste-contaminated soil and uncontaminated soil were obtained. Plasma emissions are then detected using a multichannel analyzer (OMA) to obtain the emission line spectrum that represents the content of atoms and molecules in the target material. The spectrum is recorded and compared with the spectrum of reference standards of atoms, ions and molecules (National Institute of Standards and Technology/NIST) so that the atomic and molecular content in the sample can be known. From the results of the study it was found that there are elements of heavy metals in the form of Fe, Cd, and Mg in polluted soils.
关键词： LIBS,laser-induced breakdown spectroscopy,soil pollution,heavy metal,Nd:YAG laser
更新于2025-09-16 10:30:52
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Near-Infrared Spectroscopic Study of Heavy-Metal-Contaminated Loess Soils in Tongguan Gold Area, Central China
摘要： Loess soil is a kind of widespread soil type in northwest China. Human engineering activities such as mining have caused numerous problems related to heavy metal pollution in soils, which threaten people’s health. The band formation mechanism of the near-infrared (NIR) spectral features in loess soils forms the theoretical basis for the study of the soil environment by hyperspectral remote sensing. Some NIR features of loess soils will shift because of the variations of the soil composition and microstructure after they adsorb heavy metal cations. In this study, we focused on the heavy metal adsorption of the illite, smectite, and illite–smectite (I/S) mixed layer in loess soils; evaluated the pollution by Nemerow indexing; applied X-ray diffraction (XRD), mid-infrared (MIR) spectral analysis, and inductively coupled plasma mass spectrometry (ICP-MS); and carefully observed the shift behavior of the MIR and NIR features. Then, the NIR bands were assigned to MIR bands according to the vibration behavior. Furthermore, the relationships between the NIR band positions and the six heavy metal cations as well as the Nemerow index were investigated via multiregression and simple linear correlation methods. Finally, the relationship obtained from the experiments was analyzed using the physical and chemical mechanisms of the heavy metal cations in the clay minerals. These findings may benefit the application of NIR and remote sensing techniques for detecting heavy-metal-polluted soils.
关键词： loess soil,combination band,Nemerow index,heavy metal contamination,near infrared
更新于2025-09-16 10:30:52
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Bifunctionalized Silver Nanoparticles as Hg2+ Plasmonic Sensor in Water: Synthesis, Characterizations, and Ecosafety
摘要： In this work, hydrophilic silver nanoparticles (AgNPs), bifunctionalized with citrate (Cit) and L-cysteine (L-cys), were synthesized. The typical local surface plasmon resonance (LSPR) at λ max = 400 nm together with Dynamic Light Scattering (DLS) measurements (<2RH = 8 ± 1 nm) and TEM studies (? = 5 ± 2 nm) confirmed the system nanodimension and the stability in water. Molecular and electronic structures of AgNPs were investigated by FTIR, SR-XPS, and NEXAFS techniques. We tested the system as plasmonic sensor in water with 16 different metal ions, finding sensitivity to Hg2+ in the range 1–10 ppm. After this first screening, the molecular and electronic structure of the AgNPs-Hg2+ conjugated system was deeply investigated by SR-XPS. Moreover, in view of AgNPs application as sensors in real water systems, environmental safety assessment (ecosafety) was performed by using standardized ecotoxicity bioassay as algal growth inhibition tests (OECD 201, ISO 10253:2006), coupled with determination of Ag+ release from the nanoparticles in fresh and marine aqueous exposure media, by means of ICP-MS. These latest studies confirmed low toxicity and low Ag+ release. Therefore, these ecosafe AgNPs demonstrate a great potential in selective detection of environmental Hg2+, which may attract a great interest for several biological research fields.
关键词： silver nanoparticles,heavy metal sensing,Hg2+ sensors,optical sensors,ecosafety,plasmonic sensors
更新于2025-09-12 10:27:22
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Fabrication & Characterization of Simple Structure Self-Assembled Graphene Oxide Based Heavy Metal Ion Sensor
摘要： The simple structure and high robustness of heavy metal sensors were developed by implementing a GO/Au/FR4 Substrate configuration. In this study, the sensing characteristics of an in-house fabricated heavy-metal-ion sensor (HMS) with graphene oxide (GO) as the sensing element was presented. The HMS employed a three electrodes configuration architecture, while GO of various concentrations ranging from 0.1 to 1 mg/ml would serve as the sensing medium. The surface of the working electrode was decorated with GO through drop-casting technique. Several types of heavy metal ions such as lead (Pb), mercury (Hg), and cadmium (Cd) were used in this study. The concentration of each was prepared according to the maximum exposure limit imposed by the World Health Organization, with Pb (10 ppm), Hg (1 ppm), and Cd (5 ppm). The sensing performance was found to be proportionate to GO concentration when the sensor was exposed to 10 ppm of Pb. On selectivity test using 1 mg/ml of GO, the sensor exhibited superior sensitivity towards 10 ppm of Pb, ～ 1666.6%; followed by 5 ppm of Cd, ～ 512.8%, while 1 ppm of Hg being the least detected, ～ 10.5%. This signified GO shows greater affinity towards Pb ions detection in comparison to others.
关键词： graphene oxide,sensors and working electrode,Electrochemical,IDE,heavy metal ions
更新于2025-09-12 10:27:22
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Fluorescence Characteristics of Aqueous Synthesized Tin Oxide Quantum Dots for the Detection of Heavy Metal Ions in Contaminated Water
摘要： Tin oxide quantum dots were synthesized in aqueous solution via a simple hydrolysis and oxidation process. The morphology observation showed that the quantum dots had an average grain size of 2.23 nm. The rutile phase SnO2 was confirmed by the structural and compositional characterization. The fluorescence spectroscopy of quantum dots was used to detect the heavy metal ions of Cd2+, Fe3+, Ni2+ and Pb2+, which caused the quenching effect of photoluminescence. The quantum dots showed the response of 2.48 to 100 ppm Ni2+. The prepared SnO2 quantum dots exhibited prospective in the detection of heavy metal ions in contaminated water, including deionized water, deionized water with Fe3+, reclaimed water and sea water. The limit of detection was as low as 0.01 ppm for Ni2+ detection. The first principle calculation based on the density function theory demonstrated the dependence of fluorescence response on the adsorption energy of heavy metal ions as well as ion radius. The mechanism of fluorescence response was discussed based on the interaction between Sn vacancies and Ni2+ ions. A linear correlation of fluorescence emission intensity against Ni2+ concentration was obtained in the logarithmic coordinates. The density of active Sn vacancies was the crucial factor that determined fluorescence response of SnO2 QDs to heavy metal ions.
关键词： heavy metal ion,tin oxide,fluorescence,quantum dot,sensing mechanism,water pollution
更新于2025-09-11 14:15:04
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Robust Remote Sensing of Trace-Level Heavy-Metal Contaminants in Water Using Laser Filaments
摘要： Water is the major natural resource that enables life on our planet. Rapid detection of water pollution that occurs due to both human activity and natural cataclysms is imperative for environmental protection. Analytical chemistry–based techniques are generally not suitable for rapid monitoring because they involve collection of water samples and analysis in a laboratory. Laser-based approaches such as laser-induced breakdown spectroscopy (LIBS) may offer a powerful alternative, yet conventional LIBS relies on the use of tightly focused laser beams, requiring a stable air–water interface in a controlled environment. Reported here is a proof-of-principle, quantitative, simultaneous measurement of several representative heavy-metal contaminants in water, at ppm-level concentrations, using ultraintense femtosecond laser pulses propagating in air in the filamentation regime. This approach is straightforwardly extendable to kilometer-scale standoff distances, under adverse atmospheric conditions and is insensitive to the movements of the water surface due to the topography and water waves.
关键词： filamentation,heavy-metal pollution,femtosecond laser pulse,remote sensing
更新于2025-09-11 14:15:04
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Spectroscopic and thermal analysis of lead-free multipurpose radiation shielding glasses
摘要： The genetic algorithm was used to identify glasses, of the composition 50Bi2O3-(50-x) B2O3-xBaO with wt.%, that have a similar half-value layer (HVL) and neutron removal cross-section. The structure of these glasses was further explored using a combination of spectroscopic and thermal analysis in order to ascertain whether they possess advantageous physical properties comparable to traditional materials used in nuclear reactor design. Differential scanning calorimetry (DSC) analysis was used to examine the thermal profile of the glass system and to identify glass transition temperature Tg and softening temperature Ts. Glass of the composition 50Bi2O3-30B2O3-20BaO had exhibited the highest thermal stability. Analysis of the Raman spectra of the samples confirmed the presence of BiO6 octahedrons and B-O-B bonds in poly borate chains. A deconvolution of the IR spectra was carried out to determine the relative proportions of BO3 triangles to BO4 tetrahedral units in the glass network that would affect the density and bulk modulus. Optical absorption spectrum of the samples exhibited absorption peaks in the blue region along with a broad band of absorption at longer red wavelengths associated with excitation of bismuth ions. When compared to traditional heavy concretes used in radiation shielding, the bismuth-barium borate glasses exhibited superior performance over conventional barite concrete as a gamma-radiation shield and was comparable to limonite concrete as a neutron radiation shield. The bulk modulus of the glass series was also found to be comparable to that of regular concrete at approximately to 30 GPa.
关键词： Half-value layer,Heavy metal oxide,Neutron removal cross-section,Genetic algorithm
更新于2025-09-10 09:29:36