Probing of the interaction of natural dye with transition metal oxide nanoparticles using small angle neutron scattering

Different transition metal oxide nanoparticles such as zinc oxide, copper oxide, titanium dioxide, iron oxide etc posses the advantage of being used in biomedical applications, solar energy conversion, field emission emitters. Zinc oxide nanoparticles are used as catalysts, nanosensors, ultraviolet absorber; copper oxide nanoparticles have antibacterial and antioxidant properties, iron oxide is used as contrast material in bio-imaging and titanium dioxide nanoparticles are widely used in optoelectronic devices, photo-catalysis, protective coating and photovoltaic devices to energy accumulators. It has been reported that all such nanoparticles have the capability of interacting with bio chemicals and molecular constituents of biological origin such as chlorophyll, carotenoid, anthocyanin, betalain etc. Chlorophyll functions as a photocatalyst in plants as well as a photo-sensitizer in dye-sensitized solar cells and organic photovoltaic devices. Similarly carotenoids functions as light harvesting as well as photoprotective agents. They also have high extinction coefficient and hence act as sensitizers. Overall, the sensitization process involving natural dye molecules like chlorophyll, carotenoids, anthocyanin, betalain etc and semiconductor nanoparticles like zinc oxide, copper oxide, titanium dioxide, and iron oxide are highly fruitful for photoelectric energy conversion processes in dye sensitized solar cells (DSSCs). However, the performance of the DSSC is based mainly on surface structure of visible light absorbing dye/sensitizer. Hence, in order to understand the conformation structure and aggregation behaviour of natural dyes in solution, neutron scattering technique such as small angle neutron scattering (SANS) can be used. The technique can be used to probe the structure and dynamics of dye aggregates in solutions. This will help in understanding the nanoscale organization of molecular aggregation in solutions of these conjugated molecules at atomic level resolution and provide the mechanism for the enhancement of the efficiency of the photo-conversion devices. (author)