Small copper nanoparticles have a better antibacterial activity compared to big nanoparticles.
Smaller particles have a greater surface area than the same mass of larger particles. Since the release of ions comes from the surface, the greater the surface area, the greater the release of ions. Presumably the reason why the smaller particles have greater antibacterial effect is that they release more ions than the larger particles per unit mass.
Smaller particles have a greater surface area than the same mass of larger particles. Since the release of ions comes from the surface, the greater the surface area, the greater the release of ions. Presumably the reason why the smaller particles have greater antibacterial effect is that they release more ions than the larger particles per unit mass.
In addition to mass transfer in heterophase processes, this phenomenon can also be explained from a microbiological point of view. There are at least two main mechanisms of nanoparticles’ antibacterial activity: direct or indirect one; both of them depends on size of particle. The first occurs when nanoparticle contact with bacterial wall directly, damaging the membranes and/or penetrating into cytoplasm (via endocytosis or diffusion) and destroying internal cellular components. Obviously, a smaller particle will diffuse through the wall faster. If even the direct contact is absent, the second (indirect) mechanism is possible, when a particle can produce the secondary damaging factors (for instance, reactive oxygen species), or release toxic contents (in molecular or ionic form). According to Ostwald–Freundlich equation, particle's solubility (S) drastically (exponentially) depends on the radius of curvature of particle: S=S0*exp(α/r), where S0 is solubility of bulk (flat) material, α – capillary length (constant for each type of material immersed in each type of liquid), r – particle’s radius.
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I think that Adam is right. The better performance of the smaller particle size is as a result of the large surface area.
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