# Surface Nanoengineering of Gold via Oxalic Acid Anodization: Morphology, Composition, Electronic Properties, and Corrosion Resistance in Artificial Saliva

## TL;DR

Oxalic acid anodization creates nanoporous gold surfaces with tunable properties, making them suitable for biomedical and dental applications.

## Contribution

A simple oxalic acid anodization method is introduced to tailor nanoporous gold surfaces for biomedical use.

## Key findings

- Oxalic acid anodization increases pore size, porosity, and layer thickness with higher acid concentration.
- Nanoporous gold surfaces exhibit altered electronic properties and work function.
- Anodization in 0.3 M oxalic acid provides optimal corrosion resistance and surface activity in artificial saliva.

## Abstract

What are the main findings?
Oxalic acid anodization enables controlled formation of nanoporous gold layers.Increasing acid concentration increases pore size, porosity, and layer thickness.Nanoporous gold shows altered electronic properties and work function.

Oxalic acid anodization enables controlled formation of nanoporous gold layers.

Increasing acid concentration increases pore size, porosity, and layer thickness.

Nanoporous gold shows altered electronic properties and work function.

What are the implications of the main findings?
Moderate anodization (0.3 M oxalic acid) offers optimal structural uniformity.Electronic and corrosion properties are tunable via anodization conditions.Nanoporous gold is promising for dental and biomedical surface applications.

Moderate anodization (0.3 M oxalic acid) offers optimal structural uniformity.

Electronic and corrosion properties are tunable via anodization conditions.

Nanoporous gold is promising for dental and biomedical surface applications.

Nanoporous gold (np-Au) has attracted significant attention for biomedical and electrochemical applications due to its high surface area, tunable morphology, and excellent biocompatibility. In this study, polycrystalline gold surfaces were modified by anodization in 0.3–0.9 M oxalic acid to produce np-Au layers. The influence of anodization conditions on surface morphology, chemical composition, electronic properties, and corrosion resistance in artificial saliva was systematically investigated. Surface morphology and porosity were analyzed by scanning electron microscopy combined with image analysis, revealing a transition from fine and uniform porosity to highly developed but structurally heterogeneous nanoporous structures with increasing oxalic acid concentration. Energy-dispersive spectroscopy confirmed surface oxidation and adsorption of oxygen- and carbon-containing species after anodization, while gold remained the dominant component. Scanning Kelvin probe measurements demonstrated significant modifications of surface electronic properties, including changes in contact potential difference, governed by nanostructure geometry and surface chemistry. Electrochemical tests in artificial saliva showed that increasing nanoporousness led to reduced thermodynamic stability, with the sample anodized in 0.3 M oxalic acid providing the most favorable balance between corrosion resistance and surface activity. These results demonstrate that oxalic acid anodization is a simple and effective approach for tailoring gold surfaces for biomedical applications, particularly in dentistry.