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Examination of Fluorescent Molecules as in situ Probes of Polymerization Reactions
Published in Raphael M. Ottenbrite, Sung Wan Kim, Polymeric Drugs & Drug Delivery Systems, 2019
Francis W. Wang, Deborah G. Sauder
The intensity of anthracene fluorescence from liquid methyl methacrylate was examined over a wide range of concentrations. The fluorescence intensity measured following excitation at 350 nm was observed to be linear with anthracene concentration up to a mass fraction of 3 × 10−5% anthracene in MMA. Experimental measurements were made with this concentration of anthracene in the liquid component of the cement. Fluorescence spectra taken as single scans at three different times after mixing a 2:1 powder: liquid (mass ratio) sample are shown in Figure 1. These uncorrected fluorescence spectra have a ±5% relative standard uncertainty in the maximum intensity of the individual fluorescence features. The excitation wavelength was 350 nm. In addition to the sharp features between 370 and 470 nm, which were attributed to fluorescence from isolated anthracene molecules in a polar solvent, there was a broad band centered at ≈540 nm that shifted to the blue as the cure proceeded. In considering previous studies [10] we attributed this band to an exciplex interaction between anthracene probe molecules and the dimethyltoluidine initiator in the cement. In the dilution studies of fluorescence intensity from the liquid component of the cement, the excimer intensity showed a linear dependence on anthracene concentration over the range where the intensity of anthracene monomer feature depended linearly on anthracene concentration.
A Novel Type of Tetradentate Dipyridyl-Derived Bis(pyrazole) Ligands for Highly Efficient and Selective Extraction of Am3+ Over Eu3+ From HNO3 Solution
Published in Solvent Extraction and Ion Exchange, 2023
Lianjun Song, Xueyu Wang, Long Li, Zhuang Wang, Lanlan He, Qiuju Li, Qingjiang Pan, Songdong Ding
UV–vis spectrophotometric titration of BPzBPy ligand with Eu3+ was conducted in chromatographic-grade methanol by recording the absorption spectra in the region 210 − 390 nm at 15 °C, 20 °C, 25 °C, 30 °C, and 35 °C, respectively, to give the complexation thermodynamic parameters. A solution of 2.0 × 10−5 mol/L BPzBPy was kept in a 4.0 mL cuvette and titrated with 4.0 × 10−4 mol/L Eu(NO3)3. A certain amount of tetraethylammonium nitrate (Et4NNO3) was added into the cuvette as the background electrolyte to keep the ionic strength of all the stock solutions at 0.10 mol/L. For each titration, about 10 μL aliquot of Eu(NO3)3 solution was added into the cuvette and mixed for about 5.0 min. And then UV–vis spectra were recorded in the wavelength region of 220 − 350 nm. The titration was carried on until further spectral variations in absorbance were barely detectable. The overall constant of the Eu3+/L complexes was obtained by employing the HypSpec program from the obtained spectral data.[35–37] When dealing with the data, the spectroscopic data was imported into the HypSpec software first. Instrument absorbance data files are ASCII data files typically produced by a spectrophotometer, that is, they contain an absorbance spectrum. And then a complete spectrum in HYPERQUAD format was recorded and saved after entering relevant experimental conditions, such as the volume and concentration of the titrant. At last, the wavelength in the HYPERQUAD formatted file, which is most suitable for the calculation, was chosen and fit to calculate the stability constant using the program.
Green synthesis of strongly luminescent Si/SiO2 nanoparticles using Actinidia deliciosa
Published in Radiation Effects and Defects in Solids, 2021
Sweta Gurung, Nimmala Arun, Ajay Tripathi, Anand P. Pathak, Archana Tiwari
The addition of AD to APTES has been responsible for the synthesis of APTES-AD nanoparticles, their oxidation and creation of defects. Owing to this, we have also examined the effects of prolonged reaction of APTES with AD in water and its consequent effects on the PL spectrum of APTES-AD. This has been performed by mixing APTES and AD and keeping the mixture solution for few days. In order to stop the reaction process, purification of APTES-AD by repeated centrifugation was performed on the day when PL measurements were performed. For these measurements, excitation wavelength of 350 nm was utilized. As mentioned earlier, a broad PL peak centered at 458 nm is seen as shown in Figure 5(a). With the variation in the reaction time, an increase in the emission around 458 nm is seen. The maximum emission was recorded on the 5th day. The PL intensity remains invariant with further increase in the reaction time suggesting that APTES has been completely reduced by AD on the 5th day. In addition, we also observe a blue shift of approximately 0.039 eV in the emission by varying the reaction time (as seen in Figure 5b where normalized PL intensity is plotted for different reaction times). The blue shift in PL peaks is often attributed to the surface oxidation of Si NPs to Si/SiO NPs which induces the defect states near the band edge (as shown on Figure 5 e). We have fitted the emission peaks obtained on day 1 and day 5 as shown in Figure 5(c,d) where two peaks are observed centered at 451 nm and 498 nm and are labeled as P1 and P2. The presence of P1 and P2 suggests that these Si NPs have different extent of surface oxidation and also there are two prominent defect bands with different local environment of the defect sites near the band-edge (33). On day 1, the intensity of P2 is higher than P1 as shown in Figure 5(c). Contrary to that, on day 5, we observed the depletion in the intensity of P2 and enhancement in that of P1 as shown in Figure 5(d). This could be attributed to increase in the number of defect states closer to the edge as the reaction progresses to day 5. No peak shift is observed after 5th day of the reaction suggesting that the oxidation of Si NP took place for initial 5 days post which either all NPs are oxidized or are stabilized with the limited surface oxidation. Such self-limiting oxidation has been reported previously for Si NP to Si/SiO NPs in air at room temperature (34).