Biswas Abhijit, Banerjee Arindam
Department of Biological Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata-700032, India.
Soft Matter. 2015 Jun 7;11(21):4226-34. doi: 10.1039/c5sm00359h.
In this study, sunlight was used for in situ preparation of gel-based various nanohybrid systems. A naturally occurring amino acid, l-phenylalanine derivative formed a hydrogel with graphene oxide (GO)/reduced graphene oxide (rGO) at physiological pH. This hydrogel was then used in the presence of silver ions and diffuse sunlight to form initially a tri-nanohybrid system consisting of six atom silver nanoclusters, nanosheets, and nanofibers. Interestingly, a time-dependent morphological transformation occurs in this nanohybrid system to form one tri-nanohybrid to another tri-nanohybrid with the appearance of a novel, nanoscopic intermediate tetra-nanohybrid system consisting of four distinctly different nanomaterials (nanofibers, nanosheets, nanospheres, and nanoparticles). UV-Vis and fluorescence spectroscopic analyses, transmission electron microscopic, X-ray photo electron spectroscopic and MALDI-TOF mass spectral analyses with time were applied to characterise these morphological transformations in gel based nanohybrids. Time-dependent X-ray photo electron spectroscopic (XPS) analysis was used to uncover the mechanism for the transformation of silver nanoclusters to silver nanoparticles in the hydrogel matrix. Sunlight was used to trigger time-dependent structural transformation in the nanohybrid systems. Interestingly, one of these tri-nanohybrid systems (silver nanoparticles containing rGO based hydrogel) shows a catalytic property of reducing nitroarenes to aminoarenes and the catalytic efficiency can be modulated by changing the size of the silver nanoparticles with time in diffuse sunlight. The mechanism for different catalytic activities for different hybrids with varying size of silver nanoparticles has also been deciphered.
在本研究中，利用阳光原位制备基于凝胶的各种纳米杂化体系。一种天然存在的氨基酸，即L-苯丙氨酸衍生物，在生理pH值下与氧化石墨烯（GO）/还原氧化石墨烯（rGO）形成水凝胶。然后在银离子存在和漫射阳光的条件下使用这种水凝胶，最初形成由六原子银纳米团簇、纳米片和纳米纤维组成的三纳米杂化体系。有趣的是，在这个纳米杂化体系中发生了随时间变化的形态转变，从一种三纳米杂化体系转变为另一种三纳米杂化体系，同时出现了一种由四种截然不同的纳米材料（纳米纤维、纳米片、纳米球和纳米颗粒）组成的新型纳米级中间四纳米杂化体系。利用紫外-可见光谱和荧光光谱分析、透射电子显微镜、X射线光电子能谱以及随时间进行的基质辅助激光解吸电离飞行时间质谱分析来表征基于凝胶的纳米杂化物中的这些形态转变。利用随时间变化的X射线光电子能谱（XPS）分析来揭示水凝胶基质中银纳米团簇向银纳米颗粒转变的机制。利用阳光触发纳米杂化体系中随时间变化的结构转变。有趣的是，这些三纳米杂化体系之一（含rGO基水凝胶的银纳米颗粒）表现出将硝基芳烃还原为氨基芳烃的催化性能，并且在漫射阳光中，催化效率可随时间通过改变银纳米颗粒的尺寸进行调节。还解读了具有不同尺寸银纳米颗粒的不同杂化物具有不同催化活性的机制。
