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1.
In this paper, we report the mild sonochemical synthesis of hexagonal (β) NaYF4:Yb,Er mesocrystals at low temperature of 40 °C. The nucleation and transformation of crystal structures is investigated in the course of time, and it is shown that the pure β phase is obtained after 2 h of pulsed sonication. The crystallization of orthorhombic YF3:Yb,Er and cubic (α) NaYF4:Yb,Er precedes the appearance of a thermodynamically stable β NaYF4:Yb,Er phase. Based on the evolution of the nanoparticle morphology, it is concluded that the transition from α to β phase is consistent with the dissolution-recrystallization process, while the final shape of mesocrystals is a consequence of the oriented attachment growth in the newly formed β phase nanocrystallites along two planes. The structural properties of all compounds are analyzed and correlated with their thermal and optical characteristics. The pump power dependence of green and red emissions confirms that only two-photon process is involved in up-conversion, which is superior in β phase mesocrystals.  相似文献   
2.
This review covers an ultrasound assisted synthesis of polymer nanocomposites using in situ emulsion polymerization. First of all, surface modification of core nanoparticles with a coupling agent and surfactant has been employed for the synthesis of core–shell polymer nanocomposites. In addition to application of ultrasound for the synthesis of core–shell polymer nanocomposites, due to its influential efficiency, sonochemistry has been extensively used not only as an aid of dispersion for inorganic nanoparticles and organo-clay, but also acts as an initiator to enhance polymerization rate for synthesis of polymer nanocomposites. In situ emulsion polymerization of hydrophobic monomers, such as methyl methacrylate, butyl acrylate, aniline, vinyl monomers and styrene, using surfactant and water soluble initiator were carried out for a synthesis of core–shell polymer nanocomposite. This technique assists in preparation of stable and finely dispersed polymer nanocomposite with the loading of inorganic particles up to 5 wt.%. Recent developments in the preparation of core–shell polymer nanocomposites using an ultrasound assisted method with their physical characteristics such as morphology, thermal, and rheological properties and their potential engineering applications have been discussed in this review.  相似文献   
3.
A novel synthesis methodology is reported for the preparation of NiS submicron particles in a green solvent 1-butyl-3methylimidazolium tetrafluoroborate (BMImBF4) ionic liquid (IL), using ultrasonic sonochemical technique. Structural, morphological and optical properties of nickel sulfide powders were obtained by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and diffuse reflectance spectroscopy (DRS). Composition was corroborated by energy dispersive X-ray spectroscopy (EDXS), both in the SEM and in the TEM. Regular shape particles were obtained under high-intensity ultrasonic irradiation for 105 min from the reaction between nickel nitrate and thioacetamide in ethanol/BMImBF4 (80:20), respectively. After vacuum annealing treatment at 180 °C overnight, spherical crystalline NiS particles were observed. The powders showed a band gap of 0.74 eV.  相似文献   
4.
随着纳米科技的飞速发展,合成纳米材料的新方法层出不穷。由于在纳米材料合成中的特殊效应,超声化学法用于制备特殊功能的纳米材料引起了材料科学界的极大关注,并取得了显著的进展。本文介绍了超声化学法制备纳米材料的原理和合成形态的控制纳米材料。  相似文献   
5.
Preparations of PbS-coated titanium dioxide (TiO2) and lead sulfide (PbS) nanoparticles under ultrasonic field at the multibubble sonoluminescence (MBSL) conditions were tested in water solutions. Under the optimal MBSL conditions (20 kHz and 220 W power input), PbS nanoparticles (diameter = 40-50 nm) were prepared by treating lead nitrate and thioacetamide for 20 min in water solutions. The size of PbS nanoparticles was found to be easily increased to about 90 nm in diameter by increasing the reactant concentration twice. A similar sonochemical reaction with TiO2 nanoparticles (about 20-30 nm in diameter) gave rise to PbS-coated TiO2 nanoparticles with a core/shell structure. The PbS thin film coating was quite uniform and the average coating depth of PbS on the TiO2 nanoparticles was about 2-3 nm under the described conditions. It is interesting to note that the coating depth was found to be controlled to 2-10 nm range by increasing the amounts of reactants for Pb and S twice with a sonication time of 30 min.  相似文献   
6.
超声波在聚合物合成中的研究   总被引:1,自引:0,他引:1  
综述了超声波在聚合物降解及合成中的最新进展。  相似文献   
7.
Unsupported MoS2 particles, which were produced in the preparation of MoS2/Al2O3 using a sonochemical method, were successfully separated from the prepared sample catalyst by adding oleylamine as an agent for dispersing the unsupported particles. The fraction of the unsupported MoS2, which was estimated based on Mo balance, varied between 0.03 and 0.4, independent of the Mo loading levels investigated (6–54 wt% of Mo). The activity of the unsupported MoS2 for the hydrodesulfurization of dibenzothiophene was nearly the same as that of the Al2O3-supported MoS2, indicating that the activity of the prepared catalyst was not affected by the presence of the unsupported MoS2 particles.  相似文献   
8.
The performance of a new type of CoMoS/Al2O3 catalyst, with added fluorine and prepared by sonochemical and chemical vapor deposition (CVD) methods, was investigated in the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). The catalyst, which was designed to contain optimum amounts of fluorine and cobalt, exhibited a higher activity, ca. 4.6 times higher activity particularly in the HDS of 4,6-DMDBT, than a fluorine-free catalyst prepared by a conventional impregnation method. The enhanced activity of the new catalyst can be attributed to the cumulative effects of individual factors involved in the catalyst preparation. That is, the use of a sonochemical synthesis led to a high dispersion of small MoS2 crystallites on the alumina, and the addition of the Co species to the catalyst by CVD caused a close interaction between the Co species and the MoS2 crystallites to produce numerous CoMoS species, which are the catalytically active species for HDS. The addition of fluorine increased the amounts of acidic sites in the catalyst, which promoted hydrogenation (HYD) route to a greater extent than the direct desulfurization (DDS) route in DBT HDS and both HYD and DDS routes to similar extents in the case of 4,6-DMDBT HDS. Accordingly, the addition of fluorine led to a greater increase in catalytic activity for 4,6-DMDBT HDS than for DBT HDS.  相似文献   
9.
Among the cleanest combustibles, hydrogen represents the energy carrier of the near future, thereby, techniques for hydrogen synthesis have been the subject of several research studies. The integration of ultrasound to several techniques as a promising combination has known in recent years an increasing interest owing to the physical and chemical roles of sonication and the eventual created synergetic effects. The present review aims to inspect the various techniques using ultrasound as a direct or auxiliary pathway for the generation of hydrogen. Experimental and numerical studies related to the use of power ultrasound as an isolated technique are reviewed in terms of approaches, configurations, and qualitative and quantitative observations. The combination of power ultrasound with other techniques such as electrolysis, catalysis, and photolysis, is then examined and discussed, particularly in regards to the role of ultrasound in the “ultrasound-assisted” hydrogen production, but also the expected magnitude of the kinetics enhancement and energy-saving when integrating ultrasound. It was reported in several works that the use of ultrasound for hydrogen generation may lead to an increase in the rate of produced hydrogen achieving 25%, and an improvement in energy efficiency in the range of 5–18%, while some other studies reported limited enhancement in the order of 1%. Overall, ultrasound irradiation has the advantages of enhancing mass transport, bubbles detachment from catalysts and electrodes surfaces, efficient degassing, and cleaning effect. The technological state of the art and the engineering designs are also reported with the perspective of adopting the sono-production of hydrogen at the industrial scale.  相似文献   
10.
This paper presents a study on the effect of ultrasonic frequency on both the nucleation and the degradation of paracetamol under sonication. The effect of ultrasonic irradiation was investigated for frequencies ranging from 41 to 1140 kHz. The results obtained in this paper show that the lower ultrasonic frequencies are preferable, both to enhance the nucleation rate and to limit degradation. A reduction of the metastable zone width was observed in all experiments when applying ultrasound. The highest reduction was achieved at a frequency of 41 kHz and a decrease of the reduction was observed with increasing ultrasonic frequencies. Degradation was limited at a frequency of 41 kHz, while significantly higher levels of degradation are observed at higher frequencies. Radical formation seems to be the main degradation mechanism for all frequencies.  相似文献   
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