In recent years, there is a high demand on utilizing heterogeneous nanocatalysts in organic synthetic routes because of their green approach, facile purification of the products, and reusability of the catalyst. Herein, we introduced trihydrazinotriazine (THDT)-coated Fe3O4@SiO2 as a novel amino-functionalized magnetic nanocompostie. We fully characterized the nanocatalyst and proved the morphology and magnetic property of the nanoparticles by using essential analyses. The basic attribute of the amino-rich porous surface of the nanocomposite provides a desirable environment for enhancing various reaction conditions. To examine the applicability of the nanocatalyst in organic reactions, we synthesized several benzoxanthenes using Fe3O4@SiO2-THDT nanocatalysts. The nanocomposite successfully improved the reaction conditions and provided the benzoxanthenes in an environmentally friendly procedure, which afforded product in excellent yields (80–96%) and reduced time. The nanomagnetic catalyst was easily recovered after each trial by using an external magnet. After six successive runs, the loss of catalytic activity of the nanocomposite was negligible. Finally, we propounded a plausible mechanism for the preparation of the benzoxanthenes derivatives using the THDT-functionalized core-shell magnetic nanocatalyst. 相似文献
This study introduces a low temperature surfactant-free hydrothermal method to synthesize mesoporous Nb2O5 photocatalysts using NbCl5 and H2O2 as precursors that are subsequently calcinated at 300, 400 and 450 °C and are assigned as mNb2O5-300, mNb2O5-400 and mNb2O5-450, respectively. Commercial niobia sample was used as reference sample for comparison purpose. All of materials were characterized by XRD, SEM, UV–Vis DRS, FTIR, TG/DTG and BET techniques. The synthesized Nb2O5 particles especially mNb2O5-300 sample shows a high surface area (240 m2/g), a large pore volume (0.21 cm3/g) and an identifying morphology of these features. Photocatalytic decomposition of terephthalic acid was evaluated using UV–Vis spectrophotometer. The photocatalytic reactions followed pseudo-first-order kinetics with an apparent rate constant of k = 105 × 10?3 min?1 for mNb2O5-300 sample with the highest activity among all samples at natural pH (pH = 6). Meanwhile, it was observed that optimum pH of 4 resulted in fast photocatalytic reaction for mNb2O5-300 sample. 相似文献
Determination of near-surface residual stresses is challenging for the available measurement techniques due to their limitations. These are often either beyond reach or associated with significant uncertainties.
Objective
This study describes a critical comparison between three methods of surface and near-surface residual stress measurements, including x-ray diffraction (XRD) and two incremental central hole-drilling techniques one based on strain-gauge rosette and the other based on electronic speckle pattern interferometry (ESPI).
Methods
These measurements were performed on standard four-point-bend beams of steel loaded to known nominal stresses, according to the ASTM standard. These were to evaluate the sensitivity of different techniques to the variation in the nominal stress, and their associated uncertainties.
Results
The XRD data showed very good correlations with the surface nominal stress, and with superb repeatability and small uncertainties. The results of the ESPI based hole-drilling technique were also in a good agreement with the XRD data and the expected nominal stress. However, those obtained by the strain gauge rosette based hole-drilling technique were not matching well with the data obtained by the other techniques nor with the nominal stress. This was found to be due to the generation of extensive compressive residual stress during surface preparation for strain gauge installation.
Conclusion
The ESPI method is proven to be the most suitable hole-drilling technique for measuring near-surface residual stresses within distances close to the surface that are beyond the penetration depth of x-ray and below the resolution of the strain gauge rosette based hole-drilling method.
A simple synthesis of 2‐hydrazinylidene‐3‐hydroxy‐4H‐furo[3,2‐c]pyran‐4‐ones is described. A mixture of (isocyanoimino)(triphenyl)phosphorane, an aromatic aldehyde, and dehydroacetic acid (=3‐acetyl‐2‐hydroxy‐6‐methyl‐4H‐pyran‐4‐one) undergo a 1 : 1 : 1 addition reaction under mild conditions to afford the title compounds in excellent yields. 相似文献
Extending work by Hernandez, Labate and Weiss, we present a sufficent condition for a generalized shift-invariant system to
be a Bessel sequence or even a frame for . In particular, this leads to a sufficient condition for a wave packet system to form a frame. On the other hand, we show
that certain natural conditions on the parameters of such a system exclude the frame property.
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Discontinuous molecular dynamics simulations, together with the protein intermediate resolution model, an intermediate-resolution model of proteins, are used to carry out several microsecond-long simulations and study folding transition and stability of alpha-de novo-designed proteins in slit nanopores. Both attractive and repulsive interaction potentials between the proteins and the pore walls are considered. Near the folding temperature T(f) and in the presence of the attractive potential, the proteins undergo a repeating sequence of folding/partially folding/unfolding transitions, with T(f) decreasing with decreasing pore sizes. The unfolded states may even be completely adsorbed on the pore's walls with a negative potential energy. In such pores the energetic effects dominate the entropic effects. As a result, the unfolded state is stabilized, with a folding temperature T(f) which is lower than its value in the bulk and that, compared with the bulk, the folding rate decreases. The opposite is true in the presence of a repulsive interaction potential between the proteins and the walls. Moreover, for short proteins in very tight pores with attractive walls, there exists an unfolded state with only one alpha-helical hydrogen bond and an energy nearly equal to that of the folded state. The proteins have, however, high entropies, implying that they cannot fold onto their native structure, whereas in the presence of repulsive walls the proteins do attain their native structure. There is a pronounced asymmetry between the two termini of the protein with respect to their interaction with the pore walls. The effect of a variety of factors, including the pore size and the proteins' length, as well as the temperature, is studied in detail. 相似文献
Dicloran pesticide is used to inhibit the fungal spore germination for different crops. Because of the increasing application of pesticides, reliable and accurate analytical methods are necessary. The aim of this work is designing the highly selective sensor to determine the dicloran in biological and environmental samples. Multi-walls carbon nanotubes and a molecularly imprinted polymer (MIP) were used as modifiers in the sensor composition. A dicloran MIP and a nonimprinted polymer (NIP) were synthesized and applied in the carbon paste electrode. After the optimization of electrode composition, it was used to determine the concentration of analyte. Parameters affecting the sensor response were optimized, such as sample pH, electrolyte concentration and its pH, and the instrumental parameters of square wave voltammetry. The MIP-CP electrode showed very high recognition ability in comparison with NIP-CP. The obtained linear range was 1 × 10?6 to 1 × 10?9 mol L?1. The detection limit was 4.8 × 10?10 mol L?1. This sensor was used to determine the dicloran in real samples (human urine, tap and river water samples) without special sample preparation before analysis. All important parameters were optimized, improving the sensor response considerably. 相似文献
Headspace solid phase microextraction (HS-SPME) followed by gas chromatography–mass spectrometry was developed for the determination of paraquat in urine. The volatile product resulting from reduction of paraquat by sodium borohydride–nickel chloride was used for HS-SPME. The calibration curve was linear from 10–1000 ng/mL and the limit of detection was 0.1 ng/mL. The optimized methods were validated using 500 and 750 ng/mL concentrations of paraquat in the spiked urine samples. The recoveries obtained in this study were 98.2% for intra-day (n = 6) and 99.2% for inter-day (n = 6), respectively, with RSD lower than 1.1%. 相似文献
This research has been conducted to study extraction of an anionic dye, Alizarin Red S (ARS), from the aqueous phase into the organic phase in a T-junction microchannel. The organic phase included Aliquat 336 and 1-octanol. Equal volumetric flow rates of aqueous and organic phases were adjusted in all the experiments. Designing the experiments and analyzing of the parameters that affect the extraction percentage of ARS were carried out using response surface methodology. The parameters were feed pH, feed concentration, extractant concentration and flow rate of aqueous and organic phases. The maximum extraction percentage of 98.7 was obtained at the feed pH of 3, feed concentration of 5000 mg L?1, extractant concentration of 4 vol.% and flow rate of 2.5 mL min?1. Under the optimum conditions obtained from the experimental design analysis, ARS extraction was performed in a batch system, too. The two-phase contact times to reach the extraction percentage of 98.7 in the microchannel and batch system were 2.4 s and 5.5 min, respectively. 相似文献