A comprehensive overview of the process of digestive ripening that is known to convert polydisperse nanocrystals to monodisperse ones is presented. Apart from highlighting the role of organic molecules (ligands) in achieving size control, the roles of other parameters such as the nanocrystal-ligand binding strength and the temperature at which the reaction is carried out in accomplishing size control are also delineated. The generality of the procedure is illustrated by providing examples of how it is used to prepare monodisperse nanocrystals of different metals, alloy systems, and ultrasmall nanocrystals and also to narrow the size distribution in complex binary and ternary nanocrystal systems. Finally, the current status as far as the theoretical understanding of how size control is being achieved by digestive ripening is laid out, emphasizing at the same time the necessity to undertake more systematic studies to completely realize the full potential of this practically very useful procedure.

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Synthesis of amphi-functional mesoporous silica nanoparticles (~80 nm) by stepwise chemical modifications of outer and inner pore surfaces and their utilization for the separation of hydrophobic dyes from hydrophilic ones is reported.

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.

A rational synthetic method that produces monodisperse and air-stable metal sulfide colloidal quantum dots (CQDs) in organic nonpolar solvents using octyl dithiocarbamic acid (CDTCA) as a sulfur source, is reported. The fast decomposition of metal-CDTCA complexes in presence of primary amines is exploited to achieve this purpose. This novel technique is generic and can be applied to prepare diverse CQDs, like CdS, MnS, ZnS, SnS, and InS, including more useful and in-demand PbS CQDs and plasmonic nanocrystals of CuS. Based on several control reactions, it is postulated that the reaction involves the in situ formation of a metal-CDTCA complex, which then reacts in situ with oleylamine at slightly elevated temperature to decompose into metal sulfide CQDs at a controlled rate, leading to the formation of the materials with good optical characteristics. Controlled sulfur precursor's reactivity and stoichiometric reaction between CDTCA and metal salts affords high conversion yield and large-scale production of monodisperse CQDs. Tunable and desired crystal size could be achieved by controlling the precursor reactivity by changing the reaction temperature and reagent ratios. Finally, the photovoltaic devices fabricated from PbS CQDs displayed a power conversion efficiency of 4.64% that is comparable with the reported values of devices prepared with PbS CQDs synthesized by the standard methods.