ZnO Nanostructures on Electrospun Nanofibers by Atomic Layer Deposition/Hydrothermal Growth and Their Photocatalytic Act
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ZnO Nanostructures on Electrospun Nanofibers by Atomic Layer Deposition/Hydrothermal Growth and Their Photocatalytic Activity Fatma Kayaci,1,2 Sesha Vempati,*1 Cagla Ozgit-Akgun,1,2 Necmi Biyikli1,2 and Tamer Uyar**1,2 1 UNAM-National Nanotechnology Research Center, Bilkent University, Ankara, 06800, Turkey 2 Institute of Materials Science & Nanotechnology, Bilkent University, Ankara, 06800, Turkey Authors for correspondence: *[email protected]; **[email protected] ABSTRACT A hierarchy of nanostructured-ZnO was fabricated on the electrospun nanofibers by atomic layer deposition (ALD) and hydrothermal growth, subsequently. Firstly, we produced poly(acrylonitrile) (PAN) nanofibers via electrospinning, then ALD process provided a highly uniform and conformal coating of polycrystalline ZnO with a precise control on the thickness (50 nm). In the last step, this ZnO coating depicting dominant oxygen vacancies and significant grain boundaries was used as a seed on which single crystalline ZnO nanoneedles (average diameter and length of ~25 nm and ~600 nm, respectively) with high optical quality were hydrothermally grown. The detailed morphological and structural studies were performed on the resulting nanofibers, and the photocatalytic activity (PCA) was tested with reference to the degradation of methylene blue. The results of PCA were discussed in conjunction with photoluminescence response. The nanoneedle structures supported the vectorial transport of photo-charge carriers, which is crucial for high catalytic activity. The enhanced PCA, structural stability and reusability of the PAN/ZnO nanoneedles indicated that this hierarchical structure is a potential candidate for waste water treatment. INTRODUCTION Development of novel materials with enhanced photocatalytic activity (PCA) along with stability is one of the intensely researched topics for water purification and waste treatment. The need for such research arises due to water pollution and ever increasing environmental issues threatening the human health severely [1-3]. Metal oxides such as ZnO in the structures of nanoparticles [4], nanorods [5, 6] and nanofibers [4] are widely studied for water purification purposes due to their well known PCA. On the other hand, electrospun polyacrylonitrile (PAN) nanofibers have been widely adopted in water filtration due to their unique properties including high surface area, nanoporous structure, low basis weight, easy permeability, good stability and chemical resistance [7-10]. Here we fabricated a hierarchy of nanostructured-ZnO depicting a synergy effect to enhance the PCA on electrospun PAN nanofibers using chemical vapor deposition and liquid phase deposition techniques, namely atomic layer deposition (ALD) and hydrothermal growth [11]. EXPERIMENTAL DETAILS N,N-dimethylformamide (Pestanal, Riedel) was used as a solvent to prepare 12% (w/v) PAN (Mw: 150,000, Scientific Polymer Products, Inc.) solution. For the electrospinning of the PAN solution; feed rate, applied voltage and tip-to-collector distance were 1 mL
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