What is the reason for the origin of electrical charge on the colloidal particles?

The various reasons for the origin of electrical charge on the colloidal particles are as follows:

Frictional electrification:
It is caused by the mutual rubbing of colloidal particles with molecules of the dispersion medium.

Electron capture:
Electron capture by particles from air and during electro dispersion in Bredig’s arc method

Preferential adsorption ions from solutions:
The ions which have the same lattice structure are adsorbed by an ionic colloid. One example can be how AgCl particles adsorb Cl– ions from chloride solutions (solution will be charged negative) and Ag⁺ ions from the silver ion solutions (solution will be charged positive)

Dissociation of molecules followed by aggregation of ions:
For example: in case of soap the RCOO^– groups get dissociated from Na⁺ ions and have tendency to aggregate into a cluster carrying negative charge.

The particles of a dye have a tendency to dissociate to form aggregates carrying positive or negative charge depending upon its composition.

Dissociation of the molecular electrolytes adsorbed on surface of particles:
For example: H₂S molecules get adsorbed on colloidal particles of sulphide during precipitation. By dissociation of H₂S, H⁺ ions are lost thereby giving a negative charge to colloidal particles. Ferric hydroxide sol particles are positive due to self dissociation; OH^– ions are lost the solution giving positive charge to particles.