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. 2020 Mar 18;5(12):6666-6675.
doi: 10.1021/acsomega.9b04448. eCollection 2020 Mar 31.

DBU-Catalyzed One-Pot Synthesis of Nearly Any Metal Salt of Fatty Acid (M-FA): A Library of Metal Precursors to Semiconductor Nanocrystal Synthesis

Siddhant Basel  1 , Karishma Bhardwaj  1 , Sajan Pradhan  1 , Anand Pariyar  1 , Sudarsan Tamang  1
Affiliations

DBU-Catalyzed One-Pot Synthesis of Nearly Any Metal Salt of Fatty Acid (M-FA): A Library of Metal Precursors to Semiconductor Nanocrystal Synthesis

Siddhant Basel et al. ACS Omega. .

Abstract

The metal salts of fatty acid (M-FA) are the most widely used metal precursors to colloidal semiconductor nanocrystals (NCs). They play a key role in controlling the composition, shape, and size of semiconductor NCs, and their purity is essential for attaining impeccable batch-to-batch reproducibility in the optical and electrical properties of the NCs. Herein, we report a novel, one-pot synthesis of a library of highly pure M-FAs at near-quantitative yields (up to 91%) using 1,8-diazabicyclo[5.4.0]undec-7-ene or the related nonionic/noncoordinating base as an inexpensive and ecofriendly catalyst in a green solvent medium. The method is highly general and scalable with vast academic and industrial potential. As a practical application, we also demonstrate the use of these high-quality M-FAs in the synthesis of the spectrum of colloidal semiconductor NCs (III-V, II-VI, IV-VI, I-VI, I-III-VI, and perovskite) having absorption/emission in visible to the near-infrared region.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Scheme 1
Scheme 1. Reaction of Stearic Acid (1a) with Indium Trichloride (2a) to Obtain Indium Stearate (3a)
Figure 1
Figure 1
Fourier transform infrared (FTIR) spectrum of stearic acid (1a, black) and the indium stearate (3a, red) prepared from 1a. The characteristic stretching and bending signatures related to carboxylic and carboxylate groups are marked for clarity.
Scheme 2
Scheme 2. Synthesis of Metal Carboxylates (3) from Fatty Acid (1) and Metal Salt (2)
Figure 2
Figure 2
(a) FTIR spectra of the starting compound stearic acid (1a, black), the pristine DBU catalyst (red), a mixture of stearic acid and DBU heated to the reaction temperature for 5 min (intermediate A, blue) and the aqueous part of the reaction mixture after 13 h of reaction (intermediate B, green) and (b) proposed mechanistic pathway for the DBU-catalyzed synthesis of M-FAs.
Figure 3
Figure 3
(a) Scheme for reaction between ZnCl2 (2i) and stearic acid (1a) to yield zinc stearate (3i); (b) FTIR spectrum zinc stearate (3i, red) showing lower carbonyl stretching compared to the stearic acid (1a); and (c) photographic image of 19.7 g zinc stearate (3i).
Figure 4
Figure 4
(a) UV–vis (red) and PL spectra (blue) of CsPbBr3 perovskite NCs (excitation: 400 nm, emission: 515 nm, fwhm = 28 nm); (b) UV–vis spectrum of CuFeS2 NCs exhibiting a typical surface plasmon resonance band (HWHM: 156 nm); (c) UV–vis (red) and PL (blue) spectra of CdSe NCs (excitation: 480 nm, emission: 552 nm, fwhm: 33 nm); (d) UV–vis–NIR (red) and PL Spectra (blue) PbS NCs (excitation: 950 nm, emission: 1102 nm, fwhm: 149 nm); (e) UV–vis–NIR (red) and PL spectra (blue) of Ag2S NCs (excitation: 800 nm, emission: 1206 nm, fwhm: 186 nm); and (f) UV–vis spectra of InP NCs (HWHM: 37 nm).
Figure 5
Figure 5
PXRD of (a) CsPbBr3 perovskite (cubic phase, JCPDS 00-054-0752); (b) CuFeS2 NCs (tetragonal, JCPDS 00-037-0471); (c) CdSe NCs (zinc blende, JCPDS 65-2891); (d) PbS NCs (rock salt, JCPDS 05-0592); (e) Ag2S NCs (monoclinic, JCPDS 00-014-0072); and (f) as-synthesized InP (pristine, red color) and corresponding spectrum (blue color) of the annealed (270 °C, 4 h) InP film (zinc blende, JCPDS 96-101-0147). Spectra in (a–e) have been obtained from the as-prepared samples without any annealing step to improve crystallinity.
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