The interfacial electrochemistry of goethite (α-FeOOH) especially the effect of CO2 contamination

The surface charge density/pH function of goethite is shown to be very similar to the surface charge density/surface potential functions reported for mercury. This finding differs from all other reports and we attribute the difference to the experimental method. This paper describes a method of titrating oxide suspensions which reduces pH drifts and suspension and stirring effects to negligible values and also a method for effectively removing CO₂ from oxide suspensions. When goethite which had been stored as a suspension in contact with air was titrated in N₂-purged NaI solution the point of zero charge (pzc) was within the range found by previous workers, i.e. pH 8.75 and the σ/pH function did not resemble reported σ/ψ₀ functions of mercury but when goethite from the same preparation was purged with N₂ for 2 months and then titrated in N₂-purged NaI the pzc was pH 9.3 and the σ/pH function did resemble the σ/ψ₀ function of mercury.