# Tuning the color of high-karat gold in Au-TiO2 nanoparticle composites all the way to black

## TL;DR

Scientists developed a new method to create high-karat gold composites with a range of colors, including black, by combining gold nanoparticles with TiO2.

## Contribution

The study introduces a novel fabrication technique using TiO2 nanowires and gold nanoparticles to produce high-karat gold with tunable optical properties.

## Key findings

- 18k gold composites with black, red, and purple hues were successfully fabricated.
- TiO2 nanowires stabilize gold nanoparticles, preventing coalescence and ripening.
- Oxygen vacancies and Ti3+ ions in TiO2 allow for precise modulation of color while preserving mechanical properties.

## Abstract

For centuries, artisans have harnessed gold nanoparticles to imbue their creations with the vibrant hues that captivate the eye through interactions with visible light. In modern times, these distinct optoelectronic characteristics have pivoted toward the forefront of innovative technologies, finding their niche in advanced applications from solar energy to medicine, overshadowing their artistic heritage. This investigation reimagines the utilitarian scope of gold by innovating the optical characteristics of gold-titania nanostructures. This allows for an expanded palette of colors that retain the value of the precious metal. We employ nanostructured TiO2 in a high-pressure-high-temperature sintering technique that stabilizes Au nanoparticles, thwarting coalescence, and Oswald ripening. Further refinement is possible by engineering TiO2 color centers through the introduction of oxygen vacancies and Ti3+ ions, which aid in creating an opulent high-karat black-gold, but preserve the mechanical attributes essential to the integrity and function of the final product.

•Fabrication of 18k gold composites exhibiting distinctive hues of black, red, and purple•TiO2 nanowires gold nanoparticles–based composites for high-karat hard gold materials•Two synthesis pathways for the precise property modulation of TiO2-Au composites

Fabrication of 18k gold composites exhibiting distinctive hues of black, red, and purple

TiO2 nanowires gold nanoparticles–based composites for high-karat hard gold materials

Two synthesis pathways for the precise property modulation of TiO2-Au composites

Physics; Optics; Materials science