Investigation and mitigation of reagent ageing during the continuous flow synthesis of patchy particles

• Published in: Chemical engineering research & design 2022-05, Vol.181, p.133-143
• Main Authors: Völkl, Andreas, Klupp Taylor, Robin N.
• Format: Article
• Language: English
• Subjects: Absorption of carbon dioxide by aqueous ammonia; Ammonia; Ammonium nitrate; Atoms & subatomic particles; Carbon dioxide; Chemical equilibrium; Continuous flow; Continuous flow synthesis; Flow velocity; Heterogeneous nucleation and growth; Localized surface plasmon resonance; Mixers; Nitric acid; Reagents; Scanning electron microscopy; Silica; Static T-mixer; Synthesis
• ISSN: 0263-8762; 1744-3563
• DOI: 10.1016/j.cherd.2022.03.016

Patchy particles, which comprise a core particle of one material partially covered by a thin layer of another, offer great promise for tailored particle-based materials and devices in the future. This study concerns the investigation and improvement of a potentially gram-scalable continuous flow process based on a cascade of two T-mixers for the synthesis of thin, conformal silver patches on colloidal silica particles. The starting point of the work is the observation that on seemingly random occasions the process results in patches having undesired spiky protrusions. Through a systematic study of reagent ageing supported by scanning electron microscopy, optical spectroscopy and chemical equilibrium calculations it can be ascertained that the desired product morphology is only obtained through carbon dioxide absorption by the dilute ammonia solution used in the reaction. It is shown that the ageing process can be emulated for fresh reagents by addition of ammonium nitrate or nitric acid. [Display omitted] •Silver patches on colloidal silica particles produced in a cascade of two T-mixers.•Random formation of unwanted spiky silver protrusions demands closer investigation.•The ageing of ammonia reagent solution is found to improve product morphology.•Equilibrium calculations show that CO2 absorption leads to reduced reaction rate.•Product similar to that from ammonia ageing obtained by reagent acidification.