Scientists have designed a photosensitive hydrogel that can orient towards a light source. The hydrogel mimics phototropism in plants and was used to maximise the energy-harvesting ability of a photocatalyst.
Phototropism allows plants and other organisms to adapt to changing light conditions and maximise energy harvesting throughout the day. Man-made photocatalytic systems, however, typically require direct irradiation from a light source. There are only a few examples of scientists achieving artificial phototropism that are independent of an external control and automatically track the direction of light.
Now, a team led by Feili Lai of KU Leuven in Belgium and Tinaxi Liu of Jiangnan University in China has devised a system that combines artificial phototropism with photocatalytic hydrogen peroxide production. Modelled on a sunflower, the system contains two poly(N-isopropylacrylamide)-based hydrogels. One hydrogel is temperature-sensitive and forms a stem. It also contains reduced graphene oxide (rGO) to absorb light. On top of the stem sits the second hydrogel, which mimics a flower head. It contains a photocatalyst for generating hydrogen peroxide that is made from a cadmium sulfide and reduced graphene oxide composite.
When light is shone on the stem, it bends and tracks the light source. This orientates the floral disk towards the light to maximise light absorption so it can maintain a high photocatalytic efficiency regardless of the incidence of light.
The team compared their hydrogen peroxide yield rate to a system without phototropism and saw that while the light-responsive system’s yield remained constant, the yield of the control decreased as the incident angle increased from 0° to 90°.
J Qin et al, Energy Environ. Sci., 2021, DOI: 10.1039/d1ee00587a