Nanoparticle dispersions and methods of forming

A method for preparing a dispersion of nanoparticles, the method comprising:

• providing:
• a solid organic dye or pigment in a liquid carrier;
• a first solution or slurry comprising a reactant precursor for the solid organic dye or pigment in an organic or other solvent;
• a counter current or concurrent mixing reactor comprising a first inlet for at least the first solution or slurry, a second inlet for at least the solid inorganic dye or pigment in the liquid carrier, and an outlet;
• wherein the second inlet is co-axially disposed with and/or diametrically opposed to the first inlet;
• continuously mixing the first solution or slurry with the solid organic dye or pigment in the liquid carrier within the counter current or concurrent mixing reactor at a pressure of 10 MPa to 25 MPa and a temperature of 100° ° C.to 250° C., wherein the first solution or slurry is fed through the first inlet and the solid organic dye or pigment in the liquid carrier is fed through the second inlet, whereby to obtain reaction of the reactant precursor with the solid organic dye or pigment and formation of the solid organic dye or pigment as a dispersion of nanoparticles in the liquid carrier and solvent mixture;
• wherein the first solution or slurry and/or the solid organic dye or pigment in the liquid carrier have a residence time of between 1 second and 5 minutes;
• optionally, removing unreacted reactant precursor and/or by-product from the dispersion of nanoparticles when present;
• and
• optionally, concentrating the dispersion of nanoparticles.