3D-PHOTOCAT - Activities 2022

Although photocatalytic materials have advanced recently, titanium dioxide (TiO2) remains the most widely used photocatalyst. However, TiO2 nanoparticles can undergo aggregation due to the instability of the nanosized particles, which can hinder light incidence on the active centers and consequently reduce their catalytic activity. Additionally, a practical challenge is the recovery of TiO2 nanoparticles from treated water in terms of economics and environmental safety in aquatic environments.

The application of TiO2 is limited due to its relatively large bandgap (3.0 eV for rutile and 3.2 eV for anatase), making it effective only in the ultraviolet (UV) region between 315 and 400 nm, which represents only 5% of the solar spectrum. Any improvement in the photocatalytic efficiency of TiO2 by shifting its optical response to the visible range would have a positive effect. Another limitation is its weak affinity towards organic pollutants, especially hydrophobic molecules. The adsorption of organic pollutants onto TiO2 surfaces is relatively low, resulting in slow photocatalytic degradation rates. Currently, there are numerous methods to extend the photocatalytic response of titanium dioxide into the visible light range.

Activation strategies using the entire solar spectrum involve doping (with metal or non-metal ions) or coupling UV-active semiconductors (such as TiO2, ZnO) with narrow bandgap semiconductors (such as CuS).

The choice of photocatalyst depends on factors such as the band positions (VB, CB) of the photocatalyst in relation to the electrochemical potentials for water splitting, H2 transformation, and CO2 reduction. This means that the band position should be arranged such that the upper part of the VB is more positive than the O2/H2O redox potential (1.23 V), while the lower part of the CB is more negative than the H+/H2 redox potential (0 V versus NHE). Furthermore, the bandgap should be larger than 1.23 eV.

Another approach in photocatalysis involves using two photocatalysts and an electron mediator, known as a Z-scheme photocatalytic system. Natural photosynthesis inspires this system in green plants and can simultaneously fulfill the following three requirements that are not met by single-component photocatalysts or heterojunction photocatalysts: 1) small bandgap energy, 2) appropriate positions of VB and CB with a large potential difference, and 3) suppression of electron-hole recombination.