Study on Initial Kinetics of CdSe Nanocrystals by a Combination of in Situ X-ray Absorption Fine Structure and Microfluidic Reactor

Abstract

The initial nucleation and growth processes of CdSe nanocrystals in a microfluidic reactor are studied by in situ extended X-ray absorption fine structure (EXAFS) in conjunction with UV−visible absorbance and photoluminescence spectra. On the basis of a surface reaction kinetics equation, the analytical expressions of the particle size and concentration are proposed. The surface reaction rate constant calibrated by UV−visible absorbance spectra at longer reaction time (>2.4 s) was used to estimate the particle size and concentration within the first 2.4 s of reaction. A burst of nucleation at 1−2 s with the smallest nucleus size of ∼1.3 nm was observed after rapidly heating the reaction solution in the microfluidic reactor. This initial nucleation burst was associated with a rapid particle size increase within ∼3 s, and after that the growth rate was slowed. It is demonstrated that the combination of in situ EXAFS with a microfluidic reactor provides a valuable way for studying the kinetics of nanocrystals synthesis in solution.

In situXAFS experiments using a microfluidic cell: application to initial growth of CdSe nanocrystals

“…The formation of CdSe particles observed by EXAFS at 1.1 s (Sun et al, 2009) is confirmed by UV-vis absorption after 2.4 s (Fig. 5b).…”

“…6b) clearly indicates good correlation of the two components, i.e. Se-Cd and Se-P pairs (Sun et al, 2009).…”

“…This phenomenon may be explained by the removal (a) Magnitude of the Fourier transform (FT) of the k 2 -weighted experimental EXAFS data measured with elapsed time in seconds. Solid lines represent the experimental data (Sun et al, 2009) and open circles show the fitting results. (b) FT magnitude of the k 2 -weighted EXAFS simulation for a two-component model with various compositions of CdSe together with reference CdSe and Se-TOP.…”

The Core/Shell Structure of CdSe/ZnS Quantum Dots Characterized by X‐Ray Absorption Fine Spectroscopy

“…There are two peaks at approximately 1.7Å and 2.3Å without a phase shift. Based on previous results [21,31,[39][40][41], the Cd-Se bond has a peak between 2.0 and 3.2Å in the Cd K-edge RSF function. In our results, there is a peak at approximately 2.3Å without a phase shift, which was confirmed to be from the Cd-Se bond.…”

In Situ Synchrotron X‐Ray Techniques for Real‐Time Probing of Colloidal Nanoparticle Synthesis

“…Due to the advance in instrumentation and data analysis, in situ XAFS spectroscopy has been employed by several research groups to study the nucleation and growth of colloidal nanoparticles made of metals, semiconductors, and oxides . For example, Harada and co‐workers have extensively studied the synthesis of different metal nanoparticles through photoreduction of the corresponding metal precursors (e.g., H 2 PtCl 6 and K 2 PtCl 4 for Pt, RhCl 3 for Rh, PdCl 2 for Pd, AgClO 4 for Ag, HAuCl 4 for Au in an aqueous ethanol solution in the presence of poly( N ‐vinly‐2‐pyrrolidone) (PVP).…”