High temperature continuous flow synthesis of CdSe/CdS/ZnS, CdS/ZnS, and CdSeS/ZnS nanocrystals

Abstract

Continuous flow reactors show great promise for large-scale synthesis of quantum dots. Here, we discuss results for the synthesis of multi-layered Cd-based hybrid nanocrystals - CdSe/CdS/ZnS, CdS/ZnS, and CdSeS/ZnS - in a continuous flow reactor. The simple reactor design and liquid-phase chemistry obviate the need for preheating or in-line mixing, and the chosen reactor dimensions and operating conditions allow for high flow rates (∼10 mL min(-1)). Additionally, the simple reactor design is well suited for scale-up. The CdSe/CdS/ZnS particles synthesized at elevated temperatures in the reactor exhibit quantum yields of over 60% at longer wavelengths (red region). The shell growth for these particles is conducted without the need for complex dropwise addition or SILAR shell growth procedures used in batch reactors. CdS-based particles were shown to have a higher performance when using octadecene-S instead of TOP-S, which improved the quality of shell growth. In addition, stoichiometric synthesis of the alternate CdSeS/ZnS alloy particles was conducted, removing the need for a large excess of S to offset the lower S reactivity. CdSeS/ZnS alloy nanoparticles exhibit quantum yields of about 50% in the intermediate wavelength range (500-600 nm).

Optimization of the recipe for the synthesis of CuInS2/ZnS nanocrystals supported by mechanistic considerations

“…Furthermore, the emission bandwidth was not significantly narrowed. The broad FWHM and blue-shift properties of CIS/ZnS PL emission were different from the reported narrow FWHM and red-shift properties of CdSe and CdS QDs because of excitonic emissions [9,48,49].…”

A Millifluidic Reactor System for Multistep Continuous Synthesis of InP/ZnSeS Nanoparticles

“…A major advantage of using millifluidic reactors rather than microfluidic reactors for nanoparticle synthesis is the ability to produce high quality nanoparticles at high production rate for large scale synthesis ,,. The overall reaction yield in our millifluidic reactor set up ranges from 60 to 80% based on calculation for three different flow rate conditions.…”

“…Moreover, the synthesized nanoparticles were reported to exhibit a maximum PL QY of only 37% and 20% for particles emitting in the red and green regions respectively, which is still significantly less than what has been achieved via batch synthesis. Previously, we have reported large‐scale synthesis of CdSe with PL QYs over 60% using a continuous flow stainless steel tube reactor . However, the reactor configuration, comprised of a 2.2 mm diameter coiled stainless steel tube, used in this study is not suitable for air‐sensitive reactions (for instance, InP synthesis) and the maximum operating temperature is limited by the decomposition temperature of the oil used for heating.…”

Multistage Microfluidic Platform for the Continuous Synthesis of III–V Core/Shell Quantum Dots

“…Compared to traditional batch‐based processes, flow‐based configurations can improve mass and heat transfer and precisely control reaction parameters, which is ideal for large‐scale nanomanufacturing . Despite extensive research on the synthesis of nanocrystals with a homogeneous structure, few studies have focused on the preparation of nanocrystals with heterostructures (like core/shell morphologies) in flow . One possible reason is that the synthesis of heterogeneous structures often requires slow additions of the overcoating precursors to avoid secondary nucleation of the shell material, which is challenging to achieve using tubular reactors or droplet‐based systems …”