# Carbon Impurity Entrapping and Charge Localization within TiO2 Nanoparticle Films

## TL;DR

This study explores how carbon impurities affect the electronic properties of TiO2 nanoparticle films used in photocatalysis.

## Contribution

The discovery of carbon-related defects acting as electron traps in TiO2 nanostructures is a novel finding in photocatalyst defect engineering.

## Key findings

- Carbon impurities become embedded in TiO2 nanoparticle films despite cleaning processes.
- These carbon defects act as electron traps and influence the photoelectronic properties of TiO2.
- Paramagnetic properties vary based on film architecture and preparation methods.

## Abstract

Titanium dioxide
(TiO2) particle systems are well-established
photocatalysts with high performance under UV irradiation. They are
often used as supported nanostructured thin films composed of interconnected
TiO2 nanoparticles. During the film preparation, a variety
of defects can be introduced, which can have a significant influence
on the material performance. This can be used for defect engineering
to enhance charge generation and separation within photocatalysts.
We report here a study of the paramagnetic properties of four different
TiO2 nanoparticle architectures. The spin concentrations
measured on supported films and free-standing nanoparticles, in the
presence or absence of dense TiO2 thin films prepared via
sputtering, are compared. Organic additives are typically used for
the immobilization of powdered photocatalyst materials or the production
of photoelectrodes. Despite extensive cleaning and oxidative treatment
for all cases where nanoparticle aggregation can occur or interfaces
can form between the particles and the silicon substrate, paramagnetic
carbon-related defects appear and become part of the lattice. In the
concentration range of a few parts per million, underlying carbonecks act as electron traps and represent a previously
overlooked defect type that may determine the photoelectronic properties
of TiO2-based nanostructures.