Point of zero charge, isoelectric point, and potential of zero charge on activated carbons: A comprehensive interpretation about their interrelation

Abstract

Recent advances in the characterization of carbon-based materials for cutting-edge applications have highlighted the importance of understanding their physical, chemical, and electrochemical properties. These insights have led to the development of specific interrelations key surface-related parameters. Of particular interest is the relation between porous and non-porous carbon materials and their interfacial interactions with surrounding environments. For over two decades, the difference between the point of zero charge (pH_PZC) and the isoelectric point (pH(I)) has been considered indicative of the surface charge distribution in porous carbons. Simultaneously, the increasing relevance of carbon materials in electrochemical systems has driven interest in the potential of zero charge (E_PZC), which provides information on how the surface charge of an electrode responds to an applied electric potential, and how the surface potential responds to changes in the surface chemistry of the electrode. Considering the substantial influence of the surface chemistry on these three parameters, they are certainly correlated, which can be established based on theoretical and experimental fundamentals of pH(I), pH_PZC, and E_PZC. Unfortunately, to date, no single study has addressed all three parameters simultaneously; only partial correlations have been reported. This review aims to provide a comprehensive interpretation of these three physical properties using activated carbon (AC) as a reference material, given its extensive use in technological applications. Insights derived from AC provide a robust conceptual framework that can be extended to other carbonaceous systems, particularly in adsorption and electrochemical applications. Notably, the review contends that, although the parameters may not correlate directly, they can still be used together to more effectively explain interfacial phenomena in various carbon-based materials.