Heterostructured photocatalytic material and the influence of its architecture

HETEROSTRUCTURED PHOTOCATALYTIC MATERIAL AND THE INFLUENCE OF ITS ARCHITECTURE

The unending usage of fuels and polluting the water bodies around the world have consequently led to the decline of the health of environment. In order to mitigate the repercussions in future, one of the few serious environmental issues like energy and water crises are being addressed from several decades with wide research on photocatalysts and photocatalysis. A typical photocatalysis reaction involves three vital steps associated with charge kinetics: charge generation, transfer and consumption. They are interdependent and each of these steps needs to be improved to realize higher efficiencies. Recent advancements and developments in identifying the working mechanisms, synthesis techniques and characterizations have paved the way for gaining attentiveness towards structure engineering (Energy band + Surface + Interface engineering). Efforts taken towards the enhancement of structure engineering can capably improve efficiencies of the steps involved in charge kinetics. In this work, we have embraced the structure engineering for the preparation of metal oxide heterostructured films with controlled architecture, to enhance its photocatalytic properties.

Heterostructured architecture of a photocatalyst, which consists in combining two different materials at the nanoscale, has always shown better performance than the homostructured metal oxide semiconductors. Despite the beneficial factors of an individual metal oxide - like favorable electronic configuration, ability to absorb light and excite the electrons- the major limiting factor is usually fast recombination of the excited charge carriers, which makes it a less performing photocatalyst. Here, we have prepared heterostructured photocatalysts composed by two metal oxide semiconductors, in order to favor charge separation in each component and thereby limit recombination.
The material was prepared as supported thin films in three steps, to attain the heterostructure formation. First, one dimensional Zinc Oxide material (component I) was prepared using a two step wet chemical route on FTO substrates [Step 1 – spin coating the seeds layer; Step 2 – growing the nanorods by hydrothermal method]. The concentration of seeding solution and number of seeds layers, was varied to optimize the desired morphology before deposition of component II. This resulted in the growth of ZnO nanorods arrays with predominent normal orientation. The Nickel Oxide (component II) was deposited on top of the ZnO nanorods using the direct current sputtering method, using a Nickel target in presence of Oxygen. With component II – the oxygen partial pressure, deposition temperature and time were varied to study the influence of those parameters on the heterostructure formation as well as the photocatalytic activity. AFM analysis was done to investigate the adherence of material to the FTO surface and the roughness before and after deposition was compared. The formation of heterostructure between the two components was confirmed with the help of characterizations like XRD, SEM, and XPS. The XRD peak intensity of NiO was influenced by the rate of deposition, and the morphology by temperature during sputtering. At a lower rate of deposition, the layer thickness was reduced such that it was not visible anymore by SEM, but its presence was confirmed through XPS. Photocatalytic tests were performed with UV light source to analyze the photocatalyst’s degradation efficiency on Methylene Blue.