Controlled solvothermal flow synthesis and spray-drying of fluorescent carbon-based nanomaterials based on phenylenediamines

Continuous solvothermal syntheses of carbon-based nanomaterials (CBNs) provide an efficient route to generate optically active substances compared to batchwise synthesis. In this study, technical process control and in-line analytical data acquisition was applied. Both facilitated immediate insight into the product’s properties in correlation to the process parameters. As a second continuous step, spray-drying, converted the CBNs dispersions into powder materials to increase the density and simplify product handling, in addition minimizing self-quenching of the fluorescent properties. As starting materials, phenylenediamine regioisomers were chosen which are conventionally explored via autoclave synthesis. For each regioisomer, two emission wavelength regions appeared in the visible wavelength range. The residence time, temperature, acidic component and initial starting concentration played a significant role in the relative emission intensities concluded from systematic screening. While the resulting materials need further improvement concerning their photo stability and absolute emission intensity, the technological combination presented here is a step towards the tailor-made manufacturing chain of CBNs based on micro-process engineering and continuous flow syntheses at safe high-pressure conditions.