I had samples of magnetite nanoparticles which was synthesized with the Coprecipitation method. I used it for adsorption of metallic ions in Aquas media at different pH. I read in a paper that in the alkaline range the surface charge of N.P is negative and in the acidic range, the surface charge will be positive. my question is during the synthesis pH determine the charge of N.P ? and this charge will not change for N.P ? or the surface charge is changing depending on the pH of the media? I mean when I change the pH of media during the adsorption tests the surface charge of N.P changes too?
Ali Hashemzadeh the synthesis method affect the surface charge of particles.
During the adsorption, surface charge greatly depend on pH of the medium. zeta potential can be used to infer charge on the surface of nanoparticles or you must calculate Point of zero charge of your nanoparticles by salt addition method.
I suggest you to have a look at the following papers:
1. Article The relationship between pH and zeta potential of 30 nm meta...
2. http://real.mtak.hu/22113/1/Tombacz_CollSurfA_2013_435_91_IAP2012.pdf
I agree to Dr. Zia Ullah Khan
The surface-charge very much depends on the synthetic procedure, used surfactants and pH of the medium. Although most nanoparticles acquire negative surface-charge, it can turn its sign depending on the environment.
Please conduct a number of DLS experiments using different solvents and at different pH levels.
I'll recommend the following articles:
1. Article DLS and zeta potential – What they are and what they are not?
2. Article Size-modulation of functionalized Fe3O4: Nanoscopic customiz...
Thank you, Dr. Zia Ullah Khan and Mr. Souvik Bhattacharjee , I will check the papers you recommended
Ali Hashemzadeh
The long range attractive magnetic forces will over-ride any short range attempted charge (electrostatic) stabilization. Van der Waals forces are always attractive, BTW. The only way to stabilize Fe3O4 magnetic particles is sterically with (say) 50 KDa PEG or PEI. The zeta potential then will be close to zero as the slipping plane is hidden in the protective 'cotton wool' of the polymer.
IMHO, zeta potential of magnetic particles is of little significance. The density (~ 5.5 g/cm3) and size are far more important in this regard. Carry out a Stokes' Law calculation to see what size of particles will remain in free Brownian motion for a material of this density (Table 1 in ASTM E2490-09 (15) shows such calculations).
And, yes, zeta potential and pH are intimately related but one must not forget the chemistry of the situation.
I would like to clarify the discussion. Sols (solid colloidal particles or dispersions of nanoparticles) have an adsorption potential and a charge arising from the adsorption of ions on the surface of nanoparticles. There is also kinetic or zeta potential. It arises on the slip plane in the diffuse layer of the micelle and is determined by the DLS method. These two different potentials are different from each other and should not be confused.