Gangwar Chinky, Yaseen Bushra, Kumar Indresh, Singh Narendra Kumar, Naik Radhey Mohan
Department of Chemistry, Lucknow University, Lucknow, Uttar Pradesh 226007, India.
ACS Omega. 2021 Aug 19;6(34):22344-22356. doi: 10.1021/acsomega.1c03100. eCollection 2021 Aug 31.
The complex process of nanoparticle formation in an aqueous solution is governed by kinetics and thermodynamic factors. This paper describes a room-temperature growth kinetic study and evaluation of thermodynamic activation parameters of monodispersed silver nanoparticles (AgNPs) synthesized in alkaline medium by chemical reduction method using AgNO as a source of Ag ions and tannic acid (TA) as a reductant (reducing agent) as well as a capping or stabilizing agent in the absence of any other external stabilizer. A simple and conveniently handled reaction process was monitored spectrophotometrically to study the growth kinetics in an aqueous solution as a function of the concentration of silver ion, hydroxide ion, and TA, respectively. The neutral nucleophilic group donates the electron density via a lone pair of electrons to Ag ions for the reduction process, i.e., for the nucleation of AgNPs colloid. Also, a few silver ions form a silver oxide, which also facilitates the nucleation center to enhance the growth of AgNPs colloid. The decrease and increase in rate constant on varying the TA concentration showed its adsorption onto the surface of metallic AgNPs and stabilized by polygalloyl units of TA and were the main elements to control the growth kinetics. Consequently, stabilized TA-mediated AgNPs are formed using the electron donated by quinone form of TA followed by a pseudo-first-order reaction. Apart from this, nanoparticles formed were characterized using UV-visible spectrophotometry, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and powder X-ray diffraction techniques to confirm its formation during the present kinetic study.
水溶液中纳米颗粒形成的复杂过程受动力学和热力学因素控制。本文描述了在室温下对通过化学还原法在碱性介质中合成的单分散银纳米颗粒（AgNPs）的生长动力学研究以及热力学活化参数的评估，该方法使用AgNO作为银离子源，单宁酸（TA）作为还原剂（还原试剂）以及封端或稳定剂，且不存在任何其他外部稳定剂。通过分光光度法监测一个简单且易于操作的反应过程，以分别研究水溶液中作为银离子、氢氧根离子和TA浓度函数的生长动力学。中性亲核基团通过孤对电子将电子密度提供给银离子用于还原过程，即用于AgNPs胶体的成核。此外，一些银离子形成氧化银，这也促进了成核中心以增强AgNPs胶体的生长。改变TA浓度时速率常数的降低和增加表明其吸附在金属AgNPs表面，并由TA的聚没食子酰单元稳定，这是控制生长动力学的主要因素。因此，利用TA醌形式提供的电子形成稳定的TA介导的AgNPs，随后发生准一级反应。除此之外，使用紫外可见分光光度法、傅里叶变换红外光谱法、场发射扫描电子显微镜、能量色散X射线光谱法、透射电子显微镜和粉末X射线衍射技术对形成的纳米颗粒进行表征，以确认其在当前动力学研究过程中的形成。
