Microwave-Assisted Green Synthesis of Fluorescent Graphene Quantum Dots: Metal Sensing, Antioxidant Properties, and Biocompatibility Insights
Parul SinghHitasha VithalaniAditya AdhyapakTinodaishe SemwaNihal SinghMukesh DhankaDhiraj BhatiaJhuma Saha
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PVF film prepared by means of extruding casting was cooled in water bath at different temperature,the crystallinity of the film sample was tested by XRD,the desolvation of the PVF film was made at different given temperature and got the curves of the desolvation rate.The results showed the higher the cooling temperature of water bath,the higher the initial crystallinity would be; the lower the initial crystallinity of film,the faster the desolvation rate would be; the crystallinity of film would increase during the desolvation,and the increase of the crystallinity would decrease the desolvation rate simultaneous.
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Biological hydroxyapatite (BHAp) derived from thermally-treated fish bones was successfully produced. However, the obtained biological HAp was amorphous and thus making it unfavorable for medical application. Consequently, this research exploits and engineers the crystallinity of BHAp powders by addition of CaCO3 and investigates its degree of crystallinity using XRD and IR spectroscopy. On XRD, the HAp powders with [Ca]/[P] ratios 1.42, 1.46, 1.61 and 1.93 have degree of crystallinity equal to 58.08, 72.13, 85.79, 75.85% and crystal size equal to 0.67, 0.74, 0.75, 0.72 nm, respectively. The degree of crystallinity and crystal size of the obtained calcium deficient biological HAp powders increase as their [Ca]/[P] ratio approaches the stoichiometric ratio by addition of CaCO3 as source of Ca2+ ions. These results show the possibility of engineering the crystallinity and crystal size of biological HAp by addition of CaCO3. Moreover, the splitting factor of PO4 vibration matches the result with % crystallinity on XRD. Also, the area of phosphate-substitution site of PO4 vibration shows linear relationship (R2 = 0.994) with crystal size calculated from XRD. It is worth noting that the crystallinity of the biological HAp with [Ca]/[P] ratios 1.42 and 1.48 fall near the range 60-70% for highly resorbable HAp used in the medical application.
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In this work, we present a detailed investigation of the low temperature emission properties of ZnSeO alloys by means of photoluminescence, micro-photoluminescence, and time-resolved photoluminescence. We show that the low temperature broad photoluminescence spectrum of ZnSeO attributed to the recombination of localized excitons is composed of sharp lines related to individual trapping states. Based on studies of photoluminescence thermal quenching from individual trapping states and photoluminescence dynamics, the mechanism of nonradiative recombination in ZnSeO alloys is discussed. Moreover, an unexpected decrease of the low temperature Stokes shift with increasing oxygen content is observed in contrast to what has been reported for GaAs based highly mismatched alloys. The possible origin of this effect is proposed.
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We examined the change in photoluminescence spectra of porous Si when it is oxidized then deoxidized chemically. After both steps, photoluminescence shifted to higher frequencies and increased in intensity. These shifts to higher frequencies indicate the photoluminescence is a result of the quantum size effect. Moreover, the increase in photoluminescence intensity after oxidation suggests that termination by hydrogen on the porous Si surface does not always play a key role in the photoluminescence mechanism.
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This study investigates the photoluminescence quantum yield for co‐sputtered solid‐state dispersions of Si nanocrystals in SiO 2 with different size and density, and concludes that the absolute value of the photoluminescence quantum yield shows a varied dependence on the excitation energy. Physical mechanisms influencing the photoluminescence quantum yield at different excitation energy ranges are considered. Based on the experimental evidence, this study proposes a generalized description of the excitation dependence of photoluminescence quantum yield of Si nanocrystals in SiO 2 , and concludes on the important role of impact excitation by hot carriers and parasitic absorption at high and low excitation energy ranges, respectively.
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Measurements of friction and wear were made on poly (ethylene-terephthalate) (PET) sliding against a smooth steel disk. The friction was little dependent upon crystallinity, while the wear rate increased with increase in crystallinity, especially remarkable in the range above about 40%. It was found that the reciprocal of wear rate was closely related to the Vickers hardness in PET of different crystallinity. The wear of PET with a low crystallinity as small as 8% was mainly due to transfer. On the other hand, wear of high crystallinity PET is different from that of the low crystallinity PET and seemed to be mainly due to a surface fatigue during sliding. The differnce between the mechanisms in PET of low and high crystallinity was essentially due to the differnce in morphological structures.
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Polypropylene specimens were made by the injection molding experiments under different processing conditions. The crystallinity of each polypropylene specimen was obtained using the X-ray diffraction method. The effects of the injection molding processes on the crystallinity of polypropylene were revealed: (1) the crystallinity decreases as the melt temperature increases, and the higher the melt temperature, the slower the crystallinity decreases, (2) the crystallinity decreases as the mould temperature increases, and the higher the mould temperature, the faster the crystallinity decreases, (3) the crystallinity increases as the injection speed increases, and the larger the injection speed, the faster the crystallinity increases. By the tensile experiments of the injection molded specimens, it is also found that the crystallinity has a major impact on the mechanical properties of polypropylene. The yield strength and tensile strength of polypropylene specimens increase as the crystallinity increases.
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Abstract Crystallinity is an important parameter of thermoplastic polymers. Furthermore, crystallinity is closely related to processing conditions such as temperature and applied shear stress. However, determining the degree of crystallinity is very complicated because of the different interpretations of crystallinity according to each technique. In this paper, we analyze the crystallinity of polyethylene glycol-based composites using two instruments, i.e., X-Ray Diffraction (XRD) and wide-angle X-Ray Scattering (WAXS). The results showed that with the addition of 60 wt.% silica, the degree of crystallinity revealed by XRD was 81.24%, while WAXS showed a degree of crystallinity of 80.93%. In general, the crystallinity results obtained with WAXS were almost identical, only 0.31% different from the XRD results. This difference in results was due to more presence as a consequence of the broad amorphous halo and background instrumentation exhibited by the higher background from XRD. Thus, the instrument effect must first be removed from the XRD data and it is possible that the amorphous region of the sample will also be reduced and result in a slightly higher crystallinity. At the same time WAXS with the transmission technique will minimize the possibility of background instrumentation. Therefore, WAXS was recommended to analyze the crystallinity of polymer-based and amorphous materials.
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Abstract The crystalline-amorphous ratio, and consequently the degree of crystallinity of polychlorotrifluoroethylene was measured by use of the ratio of observed absorbance of crystalline band at 440 cm.−1 to that of amorphous band at 760 cm.−1. The crystallinity as a function of temperature was measured by this method, and it was in good agreements with that obtained by specific heat methd. Furthermore, a linear relationship between the degree of crystallinity and the specific volume was found, and it leads to extrapolated values of film and 0.4901 and 0.4575 for the specific volumes of completely amorphous and crystalline meterials, respectively.
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