The confirmation of colloid formation was achieved by observing the characteristic Willis-Tyndall scattering behavior when the solution was exposed to a 630 nm red laser. Notably, the colloidal solution obtained with the addition of aniline also exhibited remarkable stability, remaining unchanged even after 10 days since its synthesis (Figure ). The stability of the resulting colloid suggested the possible formation of nanoparticles, even though the catalyst concentration was high. To investigate the morphology of the colloidal aggregates generated in the yellow colloidal solution, we performed SEM analysis of the yellow powder obtained after subsequent flocculation, washing, and drying steps (see SI for further details of sample preparation). The data obtained revealed the presence of spherical-like particles with diameters below 40 nm, see Figure . In addition, the synchrotron and powder XRD patterns (Figure and S10, respectively) of this yellow powder exhibited clear similarities to those obtained for the COF-300 nanoparticles obtained with the micellar approach but without the addition of aniline (see Table ). Indeed, the chemical composition (Figure , S12, and S13) and surface area (Figure ) of this yellow powder were also found to be comparable to the COF-300 nanoparticles obtained with the micellar approach. Therefore, the data obtained confirm that the addition of aniline in the micellar media also facilitates the formation of COF-300 nanoparticles, even at the higher catalyst concentration. However, in sharp contrast to bulk synthetic approaches, the use of aniline in the micellar approach does not lead to an increased BET surface area or larger crystal sizes. Notably, these findings unequivocally illustrate the pivotal role of the CTAB/SDS mixed micelle core in the synthesis and controlled growth of COF-300 nanoparticles.