The Bionic Sunflower: A Bio-inspired Autonomous Light Tracking Photocatalytic System

Developing a self-adapting photocatalytic system that efficiently captures light all day is not only a dream but also a challenge. Here, we report a ‘bionic sunflower’ based on a light-responsive smart hydrogel, which can spontaneously track and orient itself directionally to a light source, mimicking phototropism in, e.g., plants. As a novel photocatalytic system, it can efficiently recover the oblique-incidence energy-density loss and maintain photocatalytic efficiency at the maximum level at any random incidence angle from 0 to 90°. By taking the photocatalysis of H2O2 generation as an example, the bionic sunflower displays a high H2O2 yield rate of 262.1 μmol g−1 h−1 under 90° irradiation, as compared with the same photocatalytic system without phototropism (83.5 μmol g−1 h−1). Theoretical analyses with COMSOL Multiphysics simulation and density functional theory (DFT) calculations reveal the mechanism behind the actuation motion that triggers the bending of the bionic sunflower and determine the active sites for H2O2 generation during photocatalysis. This work proposes a novel photocatalytic concept to boost any traditional photocatalytic reaction by optimally using the solar energy from the sun's passage.