Zeta potential measurements the zeta potentials were measured on a ZetaSizer Nano ZS from Malvern via M3-PALS technique with a laser beam at 633 nm. The detection angle was 13°. The electrophoretic mobilities (u) were converted into ζ-potentials via the Smoluchowski equation. where η denotes the viscosity and ε the permittivity of the solution.