Nanoparticles in photocatalysis

Photocatalysis has emerged as an attractive means to promote chemical transformations that are generally performed with expensive chemical treatments. It can contribute to the remediation and degradation of pollutants. Interesting applications are also found in pursuing the synthesis of compounds rather than the degradation and destruction of them.

Photocatalysts are the substances that modify the rate of chemical reactions. Chlorophyll is a natural photocatalyst. This green pigment helps plants to capture sunlight to turn water and carbon dioxide into oxygen and glucose. Man-made photocatalysts like nanoparticles use light to excite conduction electrons. The enhanced electric fields in close proximity to the nanoparticles help convert solar energy into chemical energy.

Scientists working on the EU-funded project NANOPHOCAT (Nanoparticles as photocatalysts: Understanding their interaction with light) focused on gold nanoparticles and what are known as upconverting nanoparticles. These nanomaterials have surface area per weight greater than larger particles and, therefore, can be particularly reactive to other molecules.

Determining the optimum strategy for the formation of stable water-dispersible upconverting nanoparticles was the first step. The nanoparticles prepared with enhanced emissive properties were decorated with different dyes to build nanohybrids able to produce oxygen under near-infrared light. The final nanohybrids proved particularly efficient for inducing cancer cell death.

On the other hand, for the synthesis of water-dispersible gold nanoparticles, the scientists used a new protocol based on laser ablation. These nanoparticles were covered with cucurbituril in the absence of metal cations and metal-binding organic ligands. The ultraclean gold nanoparticles offered a highly sensitive assay for sensing cancerous tumour biomarkers.

Further applications in sensors and biosensors are foreseen. However, catalytic applications had not been fully explored by the end of the NANOPHOCAT project. Much research remains to be done, as nanoparticle photocatalysts promise numerous applications in environmental control and fine chemicals processing thanks to their strong absorption of light.