The effects of time and temperature on the gold nanoparticle sizes obtained by digestive ripening have been investigated. In digestive ripening, a polydisperse colloid, upon refluxing with a surface-active ligand in a solvent, gets converted to a nearly monodisperse one. In this study, a polydisperse gold nanoparticle system was heated in 4-tert-butyltoluene with hexadecanethiol at different temperatures, viz., 60, 90, 120, 150, and 180 °C for different time periods, and the trends in particle size variations were recorded. At lower temperatures such as 60 and 90 °C, after the initial narrowing of the size distribution, the particle sizes remain constant even though the refluxing step is continued for 24 h, substantiating the prevalence of the digestive ripening process. However, at elevated temperatures (120, 150, and 180 °C) particle sizes grow continuously, indicating a deviation from the digestive ripening behavior to an Ostwald ripening-type phenomenon.

It is demonstrated that a fine control over the size and size distribution of nanoparticles could be achieved using digestive ripening at different temperatures. Such variations in size and size distributions hugely influence the self-assembled processes in nanoparticles, and result in superlattice structures that are controlled by subtle interplay between ligand orientational entropy and their interdigitation and the van der Waals attraction between the metal cores.

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In the wurtzite phase, asymmetric growths of nanocrystals are typically observed along the polar [001] direction. Polarity driven layerwise alternative depositions of cations and anions on seed dots mostly drive such directional growths. However, while the reaction condition favored the asymmetric growth for 2D seeds, it breaks the symmetry of the basal plane and allowed the growth along one of the three symmetric directions. Considering Cu 2 S disks as seeds, the diffusion induced asymmetric growth leading to 2D tadpole shaped (2d-tadpole) ternary CuGaS 2 nanostructures is reported here. The formation mechanism of these asymmetric unique ternary nanostructures is elaborately discussed with tailoring the growth patterns via tuning the interface or introducing a dopant. The entire formation process is also compared with standard tadpoles obtained from 0D Cu 2 S particles, and the parameters for obtaining such anomalous architectures were established. The most exciting chemistry tuned here is the exploration of specific reactivity of a dual sulfur source which led to highly monodisperse nanostructures observed self-assembled on microscopic grids. The entire study from the reaction chemistry to structural transformation are correlated and compared in both 2D and 0D seeded asymmetric growths leading along [100] and [001] directions, respectively.

The efficiency of multidentate ligands as digestive ripening (DR) agents for the preparation of monodisperse Au nanoparticles (NPs) was investigated. This systematic investigation was performed using ligands possessing one, two, or three thiol moieties as ligands/DR agents. Our results clearly establish that among the different ligands, monodentate ligands and the use of temperature in the range of 60-120 °C offer the best conditions for DR. In addition, when DR was carried out at lower temperatures (e.g., 60 °C), the NP size increased as the number of thiol groups per ligand increased. However, in the case of ligands possessing two and three thiol moieties, when they were heated with polydispersed particles at higher temperatures (120 or 180 °C), the etching process dominated, which affected the quality of the NPs in terms of their monodispersity. We conclude that the temperature-dependent strength of the interaction between the ligand headgroup and the NP surface plays a vital role in controlling the final particle sizes.