title: Facile, high yield ultrasound mediated protocol for ZnO hierarchical structures synthesis: Formation mechanism, optical and photocatalytic properties.
abstract: Hierarchical flowers-like zinc oxide structures have been successfully obtained by a simple and fast ultrasound-assisted method performed in a ordinary ultrasonic bath using an ammonia solution and zinc acetate, in the absence of any surfactant or template. The composition, structure, crystallinity, morphology and optical properties of the materials obtained at different ultrasound irradiation times were characterized by infrared, UV-Vis and photoluminescence spectroscopy, X-ray diffraction, scanning and transmission electron microscopy investigations. It was proved that the ultrasound irradiation time manipulates both the defect content (implicit the photoluminescent properties) and morphology of the ZnO materials: shorter irradiation times leads to the synthesis of high-defected ZnO structures of flower morphology with triangular-shaped petals, while higher irradiation times favours the formation of low-defected ZnO structures with tipped rod-like petals. A plausible growth mechanism of the architectures that implies aggregation via oriented attachment followed by an Ostwald ripening is advanced based on these results. The ZnO flower-like structures present high photocatalytic activities, a total phenol mineralization being registered in the case of visible light experiments. Electron-spin resonance measurements demonstrate the generation of reactive oxygen species, namely hydroxyl radicals but also C centred radicals adducts derived most probable from the residual acetate adsorbed on ZnO surface.
authors.affiliation: "Ilie Murgulescu" Institute of Physical Chemistry, Romanian Academy, Splaiul Independentei 202, 060021 Bucharest, Romania. Electronic address: ocarp@icf.ro.
authors.forename: Oana
authors.initials: O
authors.lastname: Carp
authors.affiliation: University of Bucharest, Physical Chemistry Department, Bd. Elisabeta 4-12, 030018 Bucharest, Romania.
authors.forename: Alina
authors.initials: A
authors.lastname: Tirsoaga
authors.affiliation: "Ilie Murgulescu" Institute of Physical Chemistry, Romanian Academy, Splaiul Independentei 202, 060021 Bucharest, Romania.
authors.forename: Ramona
authors.initials: R
authors.lastname: Ene
authors.affiliation: "Politechnica" University of Bucharest, Gh. Polizu Street no. 1-7, 011061 Bucharest, Romania.
authors.forename: Adelina
authors.initials: A
authors.lastname: Ianculescu
authors.affiliation: National Institute for Materials Physics, Atomistilor Street no. 105 bis, P.O. Box Mg-7, Bucharest-Magurele R-077125, Romania.
authors.forename: Raluca F
authors.initials: RF
authors.lastname: Negrea
authors.affiliation: "Ilie Murgulescu" Institute of Physical Chemistry, Romanian Academy, Splaiul Independentei 202, 060021 Bucharest, Romania.
authors.forename: Paul
authors.initials: P
authors.lastname: Chesler
authors.affiliation: "Ilie Murgulescu" Institute of Physical Chemistry, Romanian Academy, Splaiul Independentei 202, 060021 Bucharest, Romania.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Ionita
authors.affiliation: National Institute for Lasers, Plasma and Radiation Physics, P.O. Box Mg-27, Bucharest-Magurele, Romania.
authors.forename: Ruxandra
authors.initials: R
authors.lastname: Birjega
keywords: Crystal growth; Photocatalyst; Ultrasound; ZnO