Production of dye nanoparticles via a supercritical gas anti-solvent process and optimisation of the process conditions

Nanoparticles of dyes and pigments with high quality and efficiency can be successfully used in the supercritical dyeing process of the textile industries, which is introduced as a waterless and greener dyeing method. In this study, nanoparticles of the Quinoline yellow dye, known as colour index (CI) Solvent Yellow 33, were precipitated via the supercritical gas anti-solvent (GAS) process. This process was performed at various pressures (100, 130, and 150 bar), temperatures (308, 318, and 328 K), and solute concentrations (10, 30, and 50 mg/ml), designed by the Box–Behnken design (BBD) method. It was found that increasing the pressure, reducing the temperature, and reducing the initial concentration of the liquid solution provided favourable conditions for the production of nano-sized particles with narrow size distribution and uniform morphology. Accordingly, the optimum operating conditions of the GAS process which resulted in precipitation of the dye nanoparticles, with a mean particle size of 125 nm, were determined at a temperature of 318 K, pressure of 150 bar, and the initial concentration of 10 mg/ml. The characteristics of the precipitated particles were analysed with high-performance liquid chromatography (HPLC), field-emission scanning electron microscopy (FESEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), dynamic light scattering (DLS), and Fourier-transform infrared (FTIR) spectrometry analysis. Based on the DSC and XRD results, GAS processed samples have lower crystallinity and lower particle size. Also, nano-metric size and narrow size distribution of the precipitated dye particles were confirmed through the FESEM and DLS results.