Dear Ali,

One of the main antibacterial mechanisms of metal oxide nanoparticles is this: they enhance the local release of reactive oxygen species (ROS) such as hydrogen peroxide, hydroxyl radical and superoxide anion, in their vicinity. For low doses, ROS induce oxidative stress in bacteria and eventually kill them.

You can find a good example in this paper regarding nanoparticles made of a metallic core (Te) and a shell with Te oxide:

Article Citric Juice-mediated Synthesis of Tellurium Nanoparticles w...

1- Size and Shape

2-Surface and Zeta potential

3- Chemical doping

Ali Hussein Al-Marzoqi It depends.

Dear Sir

Please check the following link which my be useful for you

https://id.elsevier.com/as/authorization.oauth2?platSite=SD%2Fscience&scope=openid%20email%20profile%20els_auth_info%20urn%3Acom%3Aelsevier%3Aidp%3Apolicy%3Aproduct%3Ainst_assoc&response_type=code&redirect_uri=https%3A%2F%2Fwww.sciencedirect.com%2Fuser%2Fidentity%2Flanding&authType=SINGLE_SIGN_IN&prompt=none&client_id=SDFE-v3&state=retryCounter%3D0%26csrfToken%3Dc9d3a42e-a2ff-4b3e-91c5-dca2ec63d34f%26idpPolicy%3Durn%253Acom%253Aelsevier%253Aidp%253Apolicy%253Aproduct%253Ainst_assoc%26returnUrl%3D%252Fscience%252Farticle%252Fpii%252FS0928493114005165%26uuid%3D7798b446-f205-46e0-ad28-ba1fa66b1aa8%26prompt%3Dnone%26cid%3Darp-2104e6ba-95ed-4c85-b31f-731f863d8215

Depending on the size and type of semiconductor, the antimicrobial activity can differ. However, the underlying mechanism remains the same; i.e. by the formation of active (highly reactive) species on the surface of semiconductors. For instance; TiO2 absorbs light, and exciton (electron-hole pair) is generated. This exciton is highly reactive in nature, hence it can oxidize/reduce the surrounding air/water. This red/ox reaction produces nascent hydrogen/O3 etc. These gaseous species are strong enough to react with the surface of microbes and break their cell wall/degrade them. Usually, the semiconductors with low bandgap or broader light spectrum absorption show higher antimicrobial activity because of higher excitons generated in them. However, it is important to note that such of antimicrobial activity works only in the presence of light (specifically of energy higher than the bandgap of semi-conductor).

other type of semiconductors like carbon quantum dots/graphene sometimes show antimicrobial activity due to their exceptionally high surface charge. The oppositely charges microbes stick on their surface and surface charge do not allow them to detach/inhale. The surface charge-dependent degradation cannot be refreshed and is one-time use (like face mask also has charge based separation, so cannot be used repeatedly). However, these types of semiconductors can work under dark conditions.

In some cases, the antimicrobial activity is imparted by the superhydrophobicity. for instance in the case of hydrophobic silica nano-particles (h-Si NPS). As, h-Si NPS are not semiconductors in nature and don't have high surface charge, however by grafting hydrophobic molecules ( hexadecyl trimethoxy silane etc) make them extremely water repellent. If we coat such materials on any substrate, we can make that substrate water repellent. If there is no water, no microorganisms can survive on it.

Hello Ali Hussein Al-Marzoqi, Herein a good article that demonstrates the antimicrobial activity of metal oxide nanomaterials like ZnO, CuO, and Fe2O3 nanoparticles against Gram-positive and Gram-negative bacteria (A comparative study):

Article Antimicrobial activity of metal oxide nanoparticles against ...

Dear Ali,

One of the main antibacterial mechanisms of metal oxide nanoparticles is this: they enhance the local release of reactive oxygen species (ROS) such as hydrogen peroxide, hydroxyl radical and superoxide anion, in their vicinity. For low doses, ROS induce oxidative stress in bacteria and eventually kill them.

You can find a good example in this paper regarding nanoparticles made of a metallic core (Te) and a shell with Te oxide:

Article Citric Juice-mediated Synthesis of Tellurium Nanoparticles w...

1. nature of the metal oxide (nano particles)

2. size and shape

3. surface and zeta potential

-doping of molecules

- electrical and dielectric proprieties

Silver Nanoparticles add anti microbiological properties, e.g. to paints. Efficiency allegedly is improved by addition of Zirconium hydrogen phosphate. More information might be available from sunshine / Zirco Tech Limited http://en.yaolongchem.com/plus/list.php?tid=36 @lillian