Microwave-polyol process for Pt and Ag nanoparticles
Microwave-polyol process for Pt and Ag nanoparticles
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DOI：
10.1021/la025741n
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发表时间：
2002-07-23
期刊：
影响因子：
3.9
通讯作者：
Bhalla, AS
中科院分区：
文献类型：
--
作者：
Komarneni, S;Li, DS;Bhalla, AS
具有许多技术应用的纳米相金属粉末已经通过各种技术制备，包括从水溶液或有机溶液中化学沉淀。最近有一种使用液体多元醇如乙二醇制备金属粉末的创新，称为多元醇法。多元醇法是一种低温工艺，由于反应在封闭系统条件下进行，因此对环境无害。在这里，我们使用微波与多元醇工艺相结合，即微波多元醇（MrP）工艺，以非常快速地生产纳米相金属粉末。我们的研究小组一直非常积极地在液态下使用微波8 r13来加速反应速率，包括使用微波辅助多元醇工艺合成微米级金属。13微波是电磁频谱的一部分，频率在300兆赫至300千兆赫之间。这些频率对应的波长为1 m ~ 1 mm，最常用的频率为2.45 GHz。微波与电介质的相互作用程度与材料的介电常数和介电损耗有关。当微波穿透并传播通过介电溶液或悬浮液时，在受影响体积内产生的内部电场引起自由或束缚电荷（例如电子或离子）的平移运动，并使电荷复合体（例如偶极子）旋转。14由于惯性力、弹性力和摩擦力引起的这些感应运动的阻力（这些阻力是频率相关的）导致损耗并衰减电场。由于这些损失，导致体积加热。14超声波的频率范围约为15 kHz至10 MHz，波长为10 r 0。01厘米。15超声波的化学效应是由于不同的物理机制，其中最重要的是空化，即气泡的形成。空腔或气泡的崩溃导致巨大的局部温度（约10000 K）和压力（约10000 atm），这是化学反应的原因。[15]在微波加热过程中没有类似的气泡形成，但过热发生在局部点，这一点还没有得到很好的理解。在合成中，微波辅助反应相对于常规方法的主要优点是（a）反应动力学增加了1 r2个数量级，8 r13，16 r30（B）形成新相，8，10（c）初始加热快速，这可以导致能量节省，11和（d）发生一种相相对于另一种相的选择性形成。31微波诱导效应的一个可能假设是在反应位点产生局部高温，以类似于超声波15的方式提高反应速率，其中在反应期间报告了高温和高压。结晶的增强动力学（其可导致高达90%32的能量节省）和MrP工艺的环境友好的封闭系统条件对于纳米相的合成是理想的。
Nanophase metal powders which have numerous technological applications have been prepared by various techniques including chemical precipitation from aqueous or organic solutions. 1r4 There has been a recent innovation to prepare metal powders using liquid polyols such as ethylene glycol, 5r7 which was named the polyol process. The polyol method is a low-temperature process and is environmentally benign because the reactions are carried out under closed system conditions. Here we used microwaves in combination with the polyol process, that is, the microwaverpolyol (MrP) process, to produce nanophase metal powders very rapidly. Our group has been very active in using microwaves in the liquid state8r13 to accelerate reaction rates including the synthesis of micrometer-sized metals using the microwave-assisted polyol process. 13 Microwaves are a portion of the electromagnetic spectrum with frequencies in the range of 300 MHz to 300 GHz. The corresponding wavelengths of these frequencies are 1 m to 1 mm. The most commonly used frequency is 2.45 GHz. The degree of interaction of microwaves with a dielectric medium is related to the material’s dielectric constant and dielectric loss. 14 When microwaves penetrate and propagate through a dielectric solution or suspension, the internal electric fields generated within the affected volume induce translational motions of free or bound charges such as electrons or ions and rotate charge complexes such as dipoles. 14 The resistance of these induced motions due to inertial, elastic, and frictional forces, which are frequency dependent, causes losses and attenuates the electric field. As a consequence of these losses, volumetric heating results. 14 The frequency range of ultrasound is roughly 15 kHz to 10 MHz with wavelengths of 10r0. 01 cm. 15 The chemical effects of ultrasound are due to different physical mechanisms, the most important of which is cavitation, that is, bubble formation. The collapse of cavities or bubbles leads to enormous local temperatures (∼ 10 000 K) and pressures (∼ 10 000 atm) which are responsible for the chemical reactions. 15 There is no similar bubble formation during microwave heating but superheating occurs in localized spots and this is not well understood. The main advantages of the microwave-assisted reactions over conventional methods in synthesis are (a) the kinetics of the reaction are increased by 1r2 orders of magnitude, 8r13, 16r30 (b) novel phases are formed, 8, 10 (c) the initial heating is rapid which can lead to energy savings, 11 and (d) selective formation of one phase over another occurs. 31 One possible hypothesis for the microwaveinduced effects is the generation of localized high temperatures at the reaction sites to enhance reaction rates in an analogous manner to that of ultrasonic waves15 where both high temperatures and pressures have been reported during reactions. The enhanced kinetics of crystallization which can lead to energy savings of up to 90% 32 and the environmentally benign closed system condition of the MrP process are ideal for the synthesis of nanophase