3D hierarchical nanostructures of iron oxides coatings prepared by pulsed laser deposition for photocatalytic water purification

3D hierarchical nanostructured hematite (alpha-Fe2O3) coatings containing various shapes were developed by pulsed laser deposition (PLD). A cold pressed, homogeneous mixture of Fe and H3BO3(Fe + H3BO3)was used as a target in PLD to deposit the coatings in O2 atmosphere. Phase explosion phenomenon provided by laser ablation on the target, allowed to form rough, porous and embedded metallic Fe particulates coating with H3BO3 as background on a glass substrate. Subsequent thermal annealing of theas deposited Fe + H3BO3coating at 600◦C, led to formation of crystalline, hierarchical 3D nanostructuredfeatures with nanowires, nanorods, and nanosheets grown from the spherical particulates. Characteri-zation by XRD, Micro-Raman, XPS, SEM and KPM analysis provided information on the systematic phaseand morphology transformation from metallic Fe to hierarchical Iron oxide. Stress-induced phase segre-gation and stress release process during thermal annealing are suggested as the growth mechanism forthe nanostructures. Photocatalytic activity measurements were studied with the coating in presence of Methylene Blue dye through Photo-Fenton process. To understand the effect of precursors, morphology,and synthesis technique (physical and chemical), similar hematite nanostructures were also preparedby thermal annealing of as deposited metallic Fe coating, hematite nanoparticles assembled coating by PLD, and by hydrothermal chemical method respectively. All these coatings showed less photocatalytic activity as compared to the hematite coating obtained from thermal annealing of Fe + H3BO3 sample. A series of various parameters such as effect of H2O2 concentration, effect of pH, water medium and recyclability tests for 10 times were performed, and all revealed promising results in terms of enhanced activity and high mechanical stability of the coatings. Presence of various 3D hierarchical nanostructures,high aspect ratio, more exposed active sites, increased interactions between catalyst surface and reactantdye molecules, and enhanced charge carrier separation, with immobilized stable coating form developedby PLD contributed to achieve the enhanced and stable photocatalytic activity.