Heterostructured ZnO/RuO2 photocatalyst: influence of sputtering temperature on the photocatalytic and photoelectrochemical properties

Influence of thermal conditions on the performance of heterostructured ZnO/RuO2 in their photocatalytic and photoelectrochemical properties

Photocatalytic materials are highly investigated due its vital role in wide variety of applications that could help in tackling present day environmental problems. Inspite of wide and basic investigation for several decades on promising materials, the best photocatalyst is still under research. But the decades long research helped in better understanding of the materials and mechanisms involved. This led to the improvement of materials under examination from homostructured to modified materials. One of the major limiting factors of homostructured (single) photocatalyst is the fast recombination of excited charge carriers. Among several modification techniques used to enhance the lifetime of charge carriers, heterostructure formation with two different materials is very promising.

Here, we report the formation of ZnO/RuO2 by involving two steps: ZnO nanorods are grown on FTO by hydrothermal method, followed by physical deposition of RuO2 (At room temperature [RT], At RT followed by Insitu-Post Annealing at 250° & At High Temperature [HT] 400°), resulting in the formation of a heterostructure. The influence of different thermal conditions on the course of RuO2 deposition has been characterized by X-Ray Diffractometer (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-Ray Photoelectron Spectroscopy (XPS) and Photo Luminescence (PL).

The crystallinity of the material and its orientation was examined by XRD. Morphological studies by SEM revealed the growth of randomly oriented ZnO nanorods on FTO, whereas images of ZnO/RuO2 resulted in no structural difference. A very thin layer of RuO2 covering the surface of ZnO nanorods was observed through TEM. This displayed the core-shell type of heterostructure formation. XPS studies of ZnO/RuO2 under varying conditions implied the shift towards lower binding energy, which indicates the bond sharing between both materials. Interface studies by step-wise deposition of RuO2 on ZnO, showed the evidence for formation of band bending between two materials, which play an important role in enhancing the charge carrier separation. PL of homostructured and heterostructured materials led to the understanding with carrier recombination process. There was evidence of significant quenching for ZnO/RuO2, compared to that of ZnO. Among ZnO/RuO2 (At RT, RT-PAd, HT) – deposition at 400° disclosed higher quenching, i.e., reduced rate of recombination. Photocatalytic and Photoelectrochemical investigations was clearly correlating to the characterizational studies, confirming the enhancement in performance with heterostructure, especially with the ZnO/RuO2 (400°).