Abstract
A new indium precursor, namely, indium(II) chloride, was tested as a precursor in the synthesis of ternary Ag–In–S and quaternary Ag–In–Zn–S nanocrystals. This new precursor, being in fact a dimer of Cl2In–InCl2 chemical structure, is significantly more reactive than InCl3, typically used in the preparation of these types of nanocrystals. This was evidenced by carrying out comparative syntheses under the same reaction conditions using these two indium precursors in combination with the same silver (AgNO3) and zinc (zinc stearate) precursors. In particular, the use of indium(II) chloride in combination with low concentrations of the zinc precursor yielded spherical-shaped (D = 3.7–6.2 nm) Ag–In–Zn–S nanocrystals, whereas for higher concentrations of this precursor, rodlike nanoparticles (L = 9–10 nm) were obtained. In all cases, the resulting nanocrystals were enriched in indium (In/Ag = 1.5–10.3). Enhanced indium precursor conversion and formation of anisotropic, longitudinal nanoparticles were closely related to the presence of thiocarboxylic acid type of ligands in the reaction mixture. These ligands were generated in situ and subsequently bound to surfacial In(III) cations in the growing nanocrystals. The use of the new precursor of enhanced reactivity facilitated precise tuning of the photoluminescence color of the resulting nanocrystals in the spectral range from ca. 730 to 530 nm with photoluminescence quantum yield (PLQY) varying from 20 to 40%. The fabricated Ag–In–S and Ag–In–Zn–S nanocrystals exhibited the longest, reported to date, photoluminescence lifetimes of ∼9.4 and ∼1.4 μs, respectively. It was also demonstrated for the first time that ternary (Ag–In–S) and quaternary (Ag–In–Zn–S) nanocrystals could be applied as efficient photocatalysts, active under visible light (green) illumination, in the reaction of aldehydes reduction to alcohols.
Highlights
The preparation of highly luminescent semiconductor nanocrystals, which do not contain toxic metals, is of great importance, especially in view of their application in medicine and biomedical sciences.[1−3] This necessity of eliminating toxic elements resulted in quick development of new preparation methods focused on cadmium- and lead-free nanocrystals of various binary, ternary and quaternary semiconductors.[4,5]Luminescent binary such as CuInS27−10 nanocrystals areInP6 and ternary AgInS2 especially interesting in and this respect
In the case of low zinc stearate concentrations, AgInS2 germs were formed as a consequence of high reactivities of silver and indium precursors, the resulting nanocrystal were spherical in shape
Increasing concentration of zinc stearate led to the formation of ZnIn2S4 germs and longitudinal quaternary Ag−In−Zn−S nanocrystals in the crystal growth step
Summary
The preparation of highly luminescent semiconductor nanocrystals, which do not contain toxic metals, is of great importance, especially in view of their application in medicine and biomedical sciences.[1−3] This necessity of eliminating toxic elements resulted in quick development of new preparation methods focused on cadmium- and lead-free nanocrystals of various binary, ternary and quaternary semiconductors.[4,5]. It is known that the dissolution of elemental sulfur in OLA results in a formation of an active precursor of the following chemical formula (C18H35NH3+)(C18H35NH-S8−), which can consecutively be transformed to carboxylic acids and thioacids.[103,104] It can be postulated that in the reaction mixture, a thiocarboxylic acid is formed of the formula R-CH2(C O)SH, which gives rise to a multiplet at 2.21 ppm corresponding to the methylene group (−CH2−) adjacent to the functional group, whereas the broadened signal appearing at 5.56 ppm has to be ascribed to −SH bound to the nanocrystal surface.[105] A detailed analysis of the 1H−13C heteronuclear multiple bond correlation (HMBC) NMR spectrum registered for the organic residue of A-4 is presented in Figure S17 in the Supporting Information in view of the unequivocal confirmation of the chemical structure of this thioacid-type ligand. Further investigations are needed leading to the optimization of the catalyst composition and reaction conditions
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