A single probe of an Au nanocluster–CdTe quantum dots nanocomposite has been developed by using tripeptide‐capped CdTe quantum dots (QD) and bovine serum albumin (BSA) protein‐conjugated Au25 nanocluster (NC) for detection of both Hg2+ ion and F? ion. The formation of Au‐NC–CdTe QD nanocomposite has been confirmed by TEM, steady state and time resolved spectroscopy, CD and FTIR studies. A significant signal off (74 % PL quenching at 553 nm) phenomenon of this nanocomposite is observed in presence of 6.56×10?7 M Hg2+ ion, due to salt‐induced aggregation. However, a dramatic PL enhancement (128 %) of the Au‐NC–CdTe QD nanocomposite is observed in presence of 8.47×10?7 M F? anion. The calculated limit of detections (LOD) of Hg2+ ion concentration and F? ion concentration are found to be 9 and 117 nM , respectively, which are within the safety range set by the United States Environment Protection Agency. Thus, the simple Au‐NC–CdTe QD optical‐based sensor is very useful to detect both toxic cations and anions. 相似文献
Abstract Polymerizations of methyl methacrylate (MMA) and acrylonitrile (AN) were carried out in aqueous nitric acid at 30°C with the redox initiator system ammonium ceric nitrate-ethyl cellosolve (EC). A short induction period was observed as well as the attainment of a limiting conversion for polymerization reactions. The consumption of ceric ion was first order with respect to Ce(IV) concentration in the concentration range (0.2–0.4) × 10?2 M, and the points at higher and lower concentrations show deviations from a linear fit. The plots of the inverse of pseudo-first-order rate constant for ceric ion consumption, (k1)?1 vs [EC]?1, gave straight lines for both the monomer systems with nonzero intercepts supporting complex formation between Ce(IV) and EC. The rate of polymerization increases regularly with [Ce(IV)] up to 0.003 M, yielding an order of 0.41, then falls to 0.0055 M and again shows a rise at 0.00645 M for MMA polymerization. For AN polymerization, Rp shows a steep rise with [Ce(IV)] up to 0.001 M, and beyond this concentration Rp shows a regular increase with [Ce(IV)], yielding an order of 0.48. In the presence of constant [NO?3], MMA and AN polymerizations yield orders of 0.36 and 0.58 for [Ce(IV)] variation, respectively. The rates of polymerization increased with an increase in EC and monomer concentrations: only at a higher concentration of EC (0.5 M) was a steep fall in Rp observed for both monomer systems. The orders with respect to EC and monomer for MMA polymerization were 0.19 and 1.6, respectively. The orders with respect to EC and monomer for AN polymerization were 0.2 and 1.5, respectively. A kinetic scheme involving oxidation of EC by Ce(IV) via complex formation, whose decomposition gives rise to a primary radical, initiation, propagation, and termination of the polymeric radicals by biomolecular interaction is proposed. An oxidative termination of primary radicals by Ce(IV) is also included. 相似文献
Polymerization of methyl methacrylate was carried out in aqueous nitric acid in the temperature range 26–40°C, with the redox initiator system ceric ammonium nitrate–isopropyl alcohol. A short induction period was observed, as well as the attainment of a limiting conversion, and the total ceric ion consumption with reaction time. The reaction orders were 1/2 and 3/2 with respect to the IPA and monomer concentration, respectively, within the range (3–5) × 10?3M of Ce(IV). But at lower Ce(IV) concentration (≤ 1 × 10?3M), the order with respect to monomer and Ce(IV) changed to 1 and 1/2, respectively. The rate of ceric ion disappearance was first order with respect to Ce(IV) concentration and (RCe)?1 was proportional to [IPA]?1. Both the rate of polymerization and the rate of ceric ion consumption increase with rise in temperature. The average-molecular weight can be controlled by variations in IPA, Ce(IV), and monomer concentrations, and in temperature. A kinetic scheme involving oxidation of IPA by Ce(IV) via complex formation, whose decomposition gives rise to a primary radical, initiation, propagation, and termination of the polymeric radicals by bimolecular interaction is proposed. An oxidative termination of primary radicals by Ce(IV) is also included. 相似文献
The results of the influence of electrodeposition conditions on the structural, compositional, optical, and photoelectrochemical properties of CdTe thin films deposited in one-step electrochemical method are presented. The CdTe films were prepared electrochemically from aqueous acidic solution with low ratios of Cd2+ ions to Te(IV) ions concentration. Instead of commonly used TeO2, water-soluble Na2TeO3 was used as a source of tellurium ions. The cathodic deposition of CdTe was performed at different constant potentials from solutions containing different cadmium and tellurium ions concentration. As-deposited CdTe thin films were studied by different analytical techniques. The X-ray photoelectron spectroscopy spectra exhibited CdTe formation on the electrode with some amount of tellurium oxides and cadmium oxides. The best quality CdTe deposits, free of TeO2, were formed in bath containing excess of Cd2+ ions and at the potential of ?0.65 V vs. saturated calomel electrode, slightly more positive than Eeq of Cd/Cd2+ system. Structural X-ray diffraction studies revealed polycrystallinity of deposits with the highest content of the (111)-oriented cubic (111) form. Optical band gap energy values were found in the range from 1.36 to 1.6 eV for CdTe films prepared at various synthesis conditions. The preliminary photoelectrochemical studies have shown that the variation of the deposition potential as well as bath composition leads to the formation of p- or n-type CdTe films. As-deposited CdTe films were not stable in polysulfide solution under illumination. 相似文献
The extraction of Ce (IV) by di-(2-ethylhexyl)-phosphoric acid (HDEHP) has been studied as a function of nitric acid concentration. Using the distribution coefficient data, the optimum conditions for recovery of Ce (IV) from nitric acid medium were arrived at. Under the conditions employed for Ce(IV), a small percentage of Ru was also found to be extracted. Cerium could be selectively stripped from the organic phase with 8M HNO3/30% H2O2 solution. This procedure led to the recovery of144Ce free of106Ru. Based on the solvent extraction data, an extraction-chromatographic procedure employing HDEHP (40% w/w) loaded on Amberlite XAD-7 as the stationary phase was developed for the isolation of pure, carrier-free144Ce from the spent fuel solution. 相似文献
The redox potential of the Ce(IV)/Ce(III) DOTA is determined to be 0.65 V versus SCE, pointing out a stabilization of ~13 orders of magnitude for the Ce(IV)DOTA complex, as compared to Ce(IV)aq. The Ce(III)DOTA after electrochemical oxidation yields a Ce(IV)DOTA complex with a t1/2 ~3 h and which is suggested to retain the “in cage” geometry. Chemical oxidation of Ce(III)DOTA by diperoxosulfate renders a similar Ce(IV)DOTA complex with the same t1/2. From the electrochemical measurements, one calculates logK (Ce(IV)DOTA2?) ~ 35.9. Surprisingly, when Ce(IV)DOTA is obtained by mixing Ce(IV)aq with DOTA, a different species is obtained with a 2 : 1(M : L) stoichiometry. This new complex, Ce(IV)DOTACe(IV), shows redox and spectroscopic features which are different from the electrochemically prepared Ce(IV)DOTA. When one uses thiosulfate as a reducing agent of Ce(IV)DOTACe(IV), one gets a prolonged lifetime of the latter. The reductant seems to serve primarily as a coordinating ligand with a geometry which does not facilitate inner sphere electron transfer. The reduction process rate in this case could be dictated by an outer sphere electron transfer or DOTA exchange by S2O32?. Both Ce(IV)DOTA and Ce(IV)DOTACe(IV) have similar kinetic stability and presumably decompose via decarboxylation of the polyaminocarboxylate ligand. 相似文献
In the present study, a nanocomposite consisting of magnetic reduced graphene oxide decorated with thioglycolic-acid-capped CdTe quantum dots (TGA/CdTe QDs/Fe3O4/rGO) was synthesised using simple ‘hydrothermal method’ and applied as a nanosorbent for extraction and preconcentration of cerium (Ce)(III) from aqueous solutions prior to inductively coupled plasma-optical emission spectroscopy detection. Under the optimised extraction conditions, the calibration graph for Ce(III) was linear in a concentration range of 0.1–511.0 μg L?1 with a correlation coefficient of 0.9986. A detection limit of 0.1 μg L?1 Ce(III) with an enrichment factor of 125 was obtained. Precisions, expressed as relative standard deviation for single-sorbent repeatability and sorbent-to-sorbent reproducibility, were 3.6% and 9.1% (n = 5), respectively. Finally, spiked sea, mineral and tap waters were analysed to evaluate the performance of the proposed method. The high recoveries indicated that the suggested protocol was acceptable for determination of Ce(III) ions in the water samples. The use of QDs and study of their ability for preconcentration of metal ions is an important achievement towards designing novel adsorbents with high efficiency. 相似文献
The polymerization of acrylonitrile (M) initiated by the sorbitol (R)-Ce(IV) redox system has been studied in sulphuric acid in the range 30–40° under nitrogen. At moderately high concentrations of Ce(IV) (0.00015-0.02 M), the rate of polymerization (Rp) is proportional to and and the rate of Ce(IV) disappearance is proportional to [R] and [Ce(IV)]. At lower concentration of Ce(IV) (0.00005–0.00015 M) Rp is proportional to [M], [R]1/2 and [Ce(IV)]1/2 and rate of Ce(IV) disappearance is proportional to [R] and [Ce(IV)]. The effects of certain salts, acid, solvent and temperature on both rates have been investigated. A kinetic scheme involving mutual termination has been proposed and various rate and energy parameters evaluated. At still higher concentration of Ce(IV) (0.02 M), a linear mode of termination seems to operate. 相似文献
Quantum dots (QDs) are preferred as high-resolution biological fluorescent probes because of their inherent optical properties
compared with organic dyes. This intrinsic property of QDs has been made use of for sensitive detection of methylparathion
(MP) at picogramme levels. The specificity of the assay was attributed to highly specific immunological reactions. Competitive
binding between free MP and CdTe QD bioconjugated MP (MP-BSA-CdTe) with immobilized anti-MP IgY antibodies was monitored in
a flow-injection system. The fluorescence intensity of MP-BSA-CdTe bioconjugate eluted from the column was found to be directly
proportional to the free MP concentration. Hence, it was possible to detect MP in a linear range of 0.1–1 ng mL−1 with a regression coefficient R2 = 0.9905. In this investigation, IgY proved advantageous over IgG class immunoglobulins in terms of yield, stability, cost
effectiveness, and enhancement of assay sensitivity. The photo-absorption spectrum of bioconjugated CdTe QD (λmax = 310 nm) confirmed nano-biomolecular interactions. The results suggest the potential application of bioconjugation and nano-biomolecular
interactions of QDs for biological labeling and target analyte detection with high sensitivity. 相似文献
A chemiluminescence (CL) method is presented for the flow injection determination of norfloxacin (NFLX). It is based on the fact that the weak CL of the Ce(IV)-Na2SO3 redox system is strongly enhanced in the presence of silver nanoparticles. UV-visible and fluorescence spectroscopy was carried out and showed that the energy of the intermediate SO2*, originating from the reaction of Ce(IV) with Na2SO3, was transferred to Tb3+ via NFLX, and that the silver nanoparticles (AgNPs) accelerate the process due to the electric activity of AgNPs. Norfloxacin was detected by measuring the CL intensity which increases linearly with the concentration of NFLX in the range from 10 nM to 50 μM. The detection limit is lowered to 2.0 nM. The method was successfully applied to the determination of NFLX in eyedrops. 相似文献
Cellulose-MMA graft copolymers have been produced using aqueous-based, Ce(IV)-initiated and periodate-initiated systems and also photochemical initiation. The reaction variables studied include the effect on grafting of varying the MMA monomer concentration, the initiator type and concentration, and also the reaction time. Of the three initiator types examined, the Ce (IV)-initiated and the photochemically-initiated systems are comparable in their effects on graft copolymer formation. Concurrent homopolymer formation was in the region of 50% by weight. Periodate-initiation leads to less efficient grafting of MMA onto cellulose, although homopolymer formation is also lower (typically <20% by weight). The characterization of the copolymeric products through their properties as solids and, as their carbanilated derivatives, through their solution properties has been undertaken. Values of the activation onergy of decomposition (EA) of the cellulose-MMA graft copolymers decrease with increasing MMA content, ranging between 227 and 155kJ mol?1. There is also a dependence on initiator type and grafting reaction conditions used (EA (cellulose wood pulp) = 239 kJ mol?1; EA (PMMA) = 115 kJ mol?1). Quantitative zeta-potential (ζ) determinations for cellulose-MMA graft copolymer samples produce negative surface charge density (σ) values. At a comparable MMA grafting level of 70–80%, values are of the order: photochemical (?730 esu/cm2) > periodate (?470 esu/cm2) > Ce (IV)-initiation (?351 esu/cm2). Characterization of carbanilate solutions (by rheological examination) and of dry, carbanilate films (by study of surface wetting behavior) highlighted differences in the physical conformation of copolymers prepared by the different initiation routes. The highly degradative effect on cellulose of a periodate initiator, in comparison with the Ce (IV)-initiation system, is reflected in significantly reduced molar mass values (typically, Mn 65,000 as opposed to 130,000 for Ce (IV)-initiated graft copolymer carbanilates). 相似文献
This work reported for the first time the use of flow injection electrochemiluminescence (FI-ECL) sensor for the determination
of durabolin in an aqueous system based on CdTe quantum dot (QD) films. Aqueous CdTe colloidal solutions were prepared using
thioglycolic acid as a capping agent. Zetasizer Nano ZS (Malvern, UK) was employed to characterize the size of CdTe QDs. The
UV–vis and photoluminescence spectra of samples were systematically characterized. Indium tin oxide (ITO) slide glass was
modified with CdTe QDs by layer-by-layer self-assembly. CdTe QD films were packed into a homemade cell and used as a recognizer
of the FI-ECL sensor to determine durabolin. The intensive anodic ECL emission was obtained at a starting potential of +1.3 V
(vs. Ag/AgCl) in a carbonate bicarbonate buffer solution with a pH of 9.93 at an ITO electrode. The ECL intensity was correlated
linearly with the concentration of durabolin over the range of 1.0 × 10−8–1.0 × 10−5 g mL−1, and the detection limit was 2.5 × 10−9 g mL−1. The relative standard deviation for the determination of 1.0 × 10−6 g mL−1 durabolin was 1.04% (n = 11). This simple and sensitive sensor revealed good reproducibility for ECL analysis. As a result, the new FI-ECL sensor
had been successfully applied to the determination of durabolin in food samples. This strategy could be easily realized and
opened new avenues for the applications of QDs in ECL biosensing. 相似文献
A direct adsorption method for the synthesis of Cu2+-doped CdTe quantum dot (QD)-sensitized TiO2 nanotubes (TNTAs) for use as a photoanode is reported in this study. The influences of the molar concentration of Cu2+, the sensitization temperature, the sensitization time, and the loop index on the photovoltaic performance of the CdTe:Cu2+/TNTAswas investigated. Scanning electron microscopy images showed that the CdTe:Cu2+ QDs are well dispersed on the TNTA surface. UV–vis adsorption measurements showed that the visible absorption of the TNTAs was enhanced by the CdTe:Cu2+ QD sensitization. Whereas the power conversion efficiency (PCE) of the bare TNTAs was 0.11%, the maximum PCE of the CdTe:5%Cu2+/TNTAs was 3.70% with a sensitization time of 5.0 h, a sensitization temperature of 60 °C, and a loop index of 2. Therefore, CdTe:5%Cu2+/TNTAs may be employed in quantum-dot-sensitized solar cells.
Graphical abstract The conversion efficiency of the CdTe: 5%Cu2+/TiO2 nanotube arrays can reach a maximum of 3.7%, which is enhanced by 33-fold, on comparison with bare TiO2 nanotube arrays (0.11%).
The influence of NaClO4, Na2SO4, Ce2(SO4)3, H2SO4, and HClO4 on the oxidation of Tl(I) by Ce(IV) in the presence of Mn(IV) as a catalyst was investigated. It was found that in the presence of NaClO4 and HClO4 the existence of CeSO42+ facilitated the reaction progress. An increase of the SO42– concentration favours the formation of negative complexes of Ce(IV) and Ce(III) such as Ce(SO4)32–, HCe(SO4)3-, and Ce(SO4)2- inhibiting the course of the reaction.Mit 2 Abbildungen 相似文献
The redox-initiated polymerization of methyl methacrylate (MMA) by the Ce(IV)-malic acid system has been carried out in aqueous medium under an inert atmosphere. The rate of polymerization was found to be proportional to [MMA]3/2 [MA]1/2 [Ce(IV)]1/2 and the rate of ceric ion disappearance was proportional to [Ce(IV)] but independent of [MMA]. The rate increased linearly up to a certain range of [MA], above which it remained constant. Increasing [H2SO4] decreased the rate. The activation energy was found to be 57.44 kJ/mol. 相似文献
In this paper, the electrogenerated chemiluminescence (ECL) from thiol-capped CdTe quantum dots (QDs) was reported. The ECL emission was occurred at −1.1 V and reached a maximum value at −2.4 V when the potential was cycled between 0.0 and −2.5 V. The reduced species of CdTe QDs could react with the coreactants to produce the ECL emission. The CdTe QD concentration (6.64 × 10−7 mol L−1) of ECL is lower than that (1.0 × 10−3 mol L−1) of chemiluminescence (CL). Based on the enhancement of light emission from thiol-capped CdTe QDs by H2O2 in the negative electrode potential, a novel method for the determination of H2O2 was developed. The light intensity was linearly proportional to the concentration of H2O2 between 2.0 × 10−7 and 1.0 × 10−5 mol L−1 with a detection limit of 6.0 × 10−8 mol L−1. Compared with most of previous reports, the proposed method has higher sensitivity for the determination of H2O2. In addition, the ECL spectrum of thiol-capped CdTe QDs exhibited a peak at around 620 nm, which was substantially red shifted from the photoluminescence (PL) spectrum, suggesting the surface states play an important role in this ECL process. 相似文献