Method for removing impurities from nanoparticles

A method for removing at least one impurity from at least one metal-based nanoparticle, comprising at least two heating steps:

• heating step 1 during which the at least one nanoparticle is heated to a temperature that is between 50° C. and 500° C. and remains or is maintained at a heating temperature that is between 50° C. and 500° C. for a heating time that is between 1 second and 1 month, and
• heating step 2 during which the at least one nanoparticle is heated to a heating temperature that is between 350° C. and 1600° C. and remains or is maintained at the temperature that is between 350° C. and 1600° C. for a heating time that is between 1 second and 1 month,
• wherein each of the heating step 1 and the heating step 2 comprises at least two phases:
• (i) a second phase of each of the heating step 1 and heating step 2 during which the temperature of the at least one nanoparticle remains or is maintained at the heating temperature, which is:
• a) between 50° C. and 500° C. for heating step 1, and
• b) between 350° C. and 1600° C. for the heating step 2, and
• (ii) at least one other phase selected from the groups consisting of:
• a first phase during which the temperature of the at least one nanoparticle increases or is increased from an initial temperature to the heating temperature of the second phase, wherein the initial temperature is smaller than 102° C. or smaller than the heating temperature of the second phase, and
• a third phase during which the temperature of the at least one nanoparticle decreases or is decreased from the heating temperature of the second phase to a final temperature,
• wherein the at least one nanoparticle has a crystalline structure, and the heating temperature of the second phase and the final temperature reached by the at least one nanoparticle of the third phase do not induce one of the following modifications selected in the group consisting of:
• i) the entire or part of the melting of the at least one nanoparticle,
• ii) the destruction of the at least one nanoparticle or of its crystalline structure, partly or fully,
• iii) the denaturation or disassembly of the at least one nanoparticle or of at least one or two of its atom(s) or ion(s), partly or fully,
• and
• iv) the partial or total modification of the crystalline structure of the at least one nanoparticle that is different from that resulting from oxidation or that differs from a change in an oxidation state of the at least one nanoparticle,
• wherein the at least one nanoparticle has at least one property selected from the group consisting of magnetic, diamagnetic, ferromagnetic, ferrimagnetic, superparamagnetic, non-zero magnetization or remanent magnetization, non-zero coercivity and paramagnetic, and
• wherein the at least one impurity is removed from the at least one nanoparticle by the method.