Experimental Data Contributing to the Elusive Surface Charge of Inert Materials in Contact with Aqueous Media

We studied the charging of inert surfaces (polytetrafluoroethylene, i.e., PTFE; graphite; graphene; and hydrophobic silica) using classical colloid chemistry approaches. Potentiometric titrations showed that these acquired less charge from proton-related reactions than oxide minerals. The data batch-type for PTFE powder did not show an effect ionic strength, which was also in contrast with results colloids. In agreement colloids, electrokinetic typical salt level dependence. some cases, point zero net proton as determined mass tentatively acid–base titration differed isoelectric points, has been previously observed, example by Chibowski co-workers ice electrolyte interfaces. Finally, we found no evidence surface contaminations our particles before after immersion aqueous solutions. Only presence NaCl-containing solutions cryo-XPS detect oxygen water. believe low points were due to impurities. Moreover, measured buffering at pH 3 could be explained sub-micromolar concentrations contaminants. most comprehensive explanation various sets is hydroxide ion accumulation occurred interfaces between