The photochemical behavior of solutions containing a mixture of CdS and CdTe nanoparticles under pulsed irradiation conditions was investigated. It was shown that electron transfer from the CdS particles to the CdTe nanoparticles occurs during the photoexcitation of such systems. The effectiveness of the process is increased with increase in the size of the CdTe nanoparticles. Such behavior is due to decrease in the potential of the CdTe conduction band with increase in the size of the nanoparticles as a result of the appearance of quantum-dimensional effects. 相似文献
Electropolymerization of 3,3′-diaminobenzidine on a gold surface gave an adherent, stable film of poly(3,3′-diaminobenzidine) (PDAB). This polymer film retained the complexational functionalities of its monomer, demonstrating preconcentration abilities for several ions, including Se(IV) and Te(IV). In particular, in this work, continuous flow and flow injection methods were developed for the sensitive and selective determination of Te(IV). The optimized method for the continuous flow mode had a detection limit of 5.6×10−9 mol l−1 for 10 min preconcentration. Typical relative standard deviations for six consecutive determinations were 1.82 and 2.56% for Te(IV) concentrations of 1.0×10−6 and 5.0×10−8 mol l−1, respectively (10 min preconcentration). The method was applied to the determination of Te(IV) in real samples. 相似文献
Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are considered highly toxic contaminants and the environmental and biological monitoring of these compounds is of great concern. Immunoassays may be used as screening methods to satisfy the growing demand for rapid and low cost analysis. In this work, we describe the application of an immunoassay that uses 2,3,7-trichloro-8-methyldibenzo-p-dioxin (TMDD) as a surrogate standard for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to sediment and human serum samples. Sample extraction and preparation methods were developed with the aim to establish the simplest, cost-effective and efficient removal of the matrix interferences in the enzyme-linked immunosorbent assay (ELISA). The overall method for sediments is based on a hexane extraction; clean up by a multilayered silica gel column and an activated carbon column; an organic solvent exchange with DMSO–Triton X-100 and ELISA measurement. The gas chromatography–high resolution mass spectrometry (GC–HRMS) validation studies (n = 13) revealed that the method is suitable for the toxic equivalents (TEQ) screening of dioxin in sediments with a method detection limit of about 100 pg g−1 dry sediment with a precision of 13–33% R.S.D. The analysis of a large number of samples originating from different sources would be required to establish more precisely the screening level, as well as the number of false positives and negatives of dioxin TEQ by the immunoassay for sediments. The immunoassay method for sediment analysis offers improvement in speed, sample throughput, and cost in comparison to GC–HRMS. Dioxins were determined in serum samples after a simple liquid–liquid extraction and solvent exchange into DMSO–Triton X-100 without further dilution. The current method (approximate method LOQ of 200 pg ml−1 serum) is not sufficiently sensitive for the determination of dioxins in serum to measure acceptable exposure limit. 相似文献
A simple and effective chemically modified carbon paste electrode (CMCPE) for the simultaneous determination of lead(II) and cadmium(II) was developed in this work. The electrode was prepared by the addition of diacetyldioxime into a carbon paste mixture. Pb2+ and Cd2+ were preconcentrated on the surface of the modified electrode by complexing with diacetyldioxime and reduced at a negative potential (−1.10 V). Then the reduced products were oxidized by differential pulse stripping. The fact that two stripping peaks appeared on the voltammograms at the potentials of −0.65 V (Cd2+) and −0.91 V (Pb2+) demonstrates the possibility of simultaneous determination of Pb2+ and Cd2+. Under the optimized working conditions, calibration graphs were linear in the concentration ranges of 1.0×10−7-1.5×10−5 mol l−1 (Pb2+) and 2.5×10−7-2.5×10−5 mol l−1 (Cd2+), respectively. For 5 min preconcentration, detection limits of 1×10−8 mol l−1 (Pb2+) and 4×10−8 mol l−1 (Cd2+) were obtained at the signal noise ratio (SNR) of 3. To evaluate the reproducibility of the newly developed electrode, the measurements of 5×10−7 mol l−1 Pb2+ and Cd2+ were parallel carried out for six times at different electrodes and the relative standard deviations were 2.9% (Pb2+) and 3.2% (Cd2+), respectively. Interferences by some metals were investigated. Only Ni2+ and Hg2+ apparently affected the peak currents of Pb2+ and Cd2+. The diacetyldioxime modified carbon paste electrode was applied to the determination of Pb2+ and Cd2+ in water samples. The results indicate that this electrode is sensitive and effective for the simultaneous determination of Pb2+ and Cd2+. 相似文献
Simple catalytic systems for cross-coupling reactions of acyl chlorides with arylboronic acids under microwave conditions were tested. Microwave irradiation facilitated the reaction course. Mild reaction conditions afford the symmetrical and unsymmetrical aryl ketones in reasonable to high yields within a short time. A wide range of substrates bearing an electron-donating or an electron-withdrawing substituent on aryl ring of acid chloride as well as on boronic acid were examined and high yields of ketones were produced. 相似文献
The emulsifier-free emulsion polymerization of styrene (St) and N-isopropylacrylamide (NIPAAm) was successfully carried out with microwave irradiation, and the monodisperse thermoresponsive
poly(styrene-co-N-isopropylacrylamide) (poly(St-co-NIPAAm)) particles with diameters in the range 100–130 nm were prepared. The morphology, size and size distribution of the
poly(St-co-NIPAAm) particles were characterized by transmission electron microscopy, scanning electron microscopy (SEM) and photon correlation
spectroscopy (PCS), respectively. The results showed that poly(St-co-NIPAAm) particles had spherical morphology, and the poly(St-co-NIPAAm) particles prepared by emulsifier-free emulsion polymerization with microwave irradiation were smaller, more uniform
than those obtained with conventional heating. The hydrodynamic diameters of poly(St-co-NIPAAm) particles were decreased as the temperature increased from 25 °C to 40 °C, and poly(St-co-NIPAAm) particles collapsed remarkably at 32 °C, which is the lower critical solution temperature of the poly(N-isopropylacrylamide). The morphology of the assembled poly(St-co–NIPAAm) particles was observed by SEM, it was found that monodisperse poly(St-co-NIPAAm) particles could assemble to form the two-dimensional order structures. 相似文献
has been determined by gas electron diffraction (GED) combined with microwave (MW) spectroscopic data. Ab initio calculations at the HF/3–21G* level were carried out and used as structural constraints in the data analysis. The torsional vibration of the methyl group was treated as a large-amplitude motion. The structural parameters were determined to be: rg(S---C2) = 1.719(2) Å, rg(C2=C3) = 1.370(3) Å, rg(C3---C6) = 1.497(6) Å, rg(C2---H) = 1.101(5) Å, CSC = 91.6(2)°, SC2C3 = 113.3(5)°, SC5C4 = 111.3(3)°, C2C3C6 = 123.2(11)° and C3C6H = 112(2)°. The values of r(S---C2) − r(S---C5) and r(C2=C3) − r(C4=C5) were fixed at the 3–21G* value of 0.002Å. Parenthesized values are the estimated limits of error (3σ) referring to the last significant digit. 相似文献
The molecular structure of 3-methylthiophene
has been determined by gas electron diffraction (GED) combined with microwave (MW) spectroscopic data. Ab initio calculations at the HF/3–21G* level were carried out and used as structural constraints in the data analysis. The torsional vibration of the methyl group was treated as a large-amplitude motion. The structural parameters were determined to be: rg(S---C2) = 1.719(2) Å, rg(C2=C3) = 1.370(3) Å, rg(C3---C6) = 1.497(6) Å, rg(C2---H) = 1.101(5) Å, CSC = 91.6(2)°, SC2C3 = 113.3(5)°, SC5C4 = 111.3(3)°, C2C3C6 = 123.2(11)° and C3C6H = 112(2)°. The values of r(S---C2) - r(S=C5) and r(C2=C3)-r(C4 =C5) were fixed at the 3–21G* value of 0.002 Å. Parenthesized values are the estimated limits of error (3σ) referring to the last significant digit. 相似文献