Substrate temperature induced effect on microstructure, optical and photocatalytic activity of ultrasonic spray pyrolysis deposited MoO3 thin films

"Accepted Manuscript"In this work, the substrate temperature (TS) effect on the microstructure, optical and photocatalytic activity of spray pyrolysis deposited transparent molybdenum trioxide (MoO3) thin films is studied. Microstructure analysis reveals the coexistence of hexagonal and orthorhombic phases when TS ≤ 300 °C and the existence of the orthorhombic phase only when TS ≥ 400 °C. The SEM analysis suggests that the films consist of rod and spherical shaped grains. The dimensions of rods and spheres are found to be sensitive to TS and can be correlated to strain. The band gap is increased from 3.06 to 3.46 eV with TS. Photoluminescence analysis reveals that the emission corresponds to defects increased with Ts. The photocatalytic activity of MoO3 films deposited at various TS is evaluated by using 0.5 mM Rhodamin-B (Rh-B) dye aqueous solution as a template. The film deposited at 500 °C shows the maximum photodegradation efficiency due to its high structural sensitivity, surface selectivity and catalytic anisotropy. The variation in efficiency with TS is discussed based on the band bending effect, crystallographic orientation, surface morphology, defects concentration and light absorption capacity. The effect of irradiation time on photodegradation efficiency is also investigated. The MoO3 film shows photodegradation efficiency of 91% after two hour illumination and makes it suitable for photocatalytic applications.This work was financially supported by UGC and DST-SERB, Govt. of India through Grants No. F.4-5(59-FRP/2014(BSR)) and ECR/2017/000068. This work was partially supported by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2019. The author Kevin V Alex acknowledges DST, Govt. of India for the Inspire fellowship (IF170601). A R Jayakrishnan acknowledges Central University of Tamil Nadu, India for his PhD fellowship. J P B S is grateful for the financial support through the FCT Grant SFRH/BPD/92896/2013. Authors acknowledge Mr Akshay Govind for his help during the deposition of films