Oxygen-defective ZnO films with various nanostructures prepared via a rapid one-step process and corresponding photocatalytic degradation applications (original) (raw)
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Applied Surface Science, 2018
The Solution Precursor Plasma Spray (SPPS) process is a novel, versatile and one-step route for building photocatalytic films. Herein, the influence of the precursor solution composition on the microstructure and on the properties of ZnO films prepared via the SPPS process was studied. Nanostructured ZnO particles (i.e. nanorods (NRs) and nanowires (NWs)) were obtained by using a solution of pure Zn(OAc) 2 rather than pure Zn(NO 3) 2. Upon adding urea to the Zn(NO 3) 2 solution, NRs structured ZnO films were formed as well. The addition of acetic acid into the Zn(OAc) 2 solution led to a damage of the nanostructured morphologies likely due to the inhibition of the zinc-containing clusters formation. UV-visible analyses demonstrate that all 2 samples exhibit narrower bandgaps than pure ZnO. The A02 and N03 samples prepared from Zn(OAc) 2 and Zn(NO 3) 2 solutions, respectively, exhibit photodegradation efficiency up to 100% under UV light irradiation. Moreover, A02 and N03 samples were able to bleach 46.2% and 54.6% of the Orange II dye under visible light, respectively. Trapping experiments revealed that hydroxyl radicals (• OH), holes (h +) and electrons (e −) play a key role in the photodegradation of Orange II. This study highlights the versatility of the SPPS process and demonstrates that the final nanostructured morphologies of ZnO can easily be controlled by adjusting the precursor solution composition. This result further revealed the potential strategy for optimizing the microstructure and photocatalytic performances of other metal oxide films.
Ceramics International, 2018
The development of efficient photocatalytic hierarchical coral-like ZnO films via a relatively simple, efficient, rapid and single-step process is essential for industrial development. Herein, we report a novel method for directly synthesizing well-shaped ZnO nanorods (NRs) by Solution Precursor Plasma Spray (SPPS) process rather than conventional spherical/ellipsoidal particles. In the prepared ZnO-NRs films, the ZnO NRs display an average diameter of 190 nm, and exhibit a preferential orientation growth along (002) plane compared to a reference ZnO films (called ZnO-P) containing spherical/ellipsoidal particles. ZnO-NRs films exhibit relative narrower bandgap (3.02 eV) probably due to the apparent non-equilibrium heating-cooling process and to the use of hydrogen in the SPPS method. Such ZnO-NRs films are capable of a quasi-quantitative (99%) decomposition of the Orange II dye within 150 min under Hg-Xe light irradiation, which is nearly 2.7 times of the reference sample ZnO-P (37% degradation). Besides, the ZnO-NRs films exhibit an excellent retention of performance (98.7% degradation in a second cycle). Moreover, these preliminary results demonstrate that SPPS process provides a promising alternative to conventional multi-step processes for the production of metal oxide photocatalytic films in practical applications.
Plasma Sources Science and Technology, 2019
The fast growth of ultrathin zinc oxide nanostructures is reported in this study, by using a flowing microwave plasma oxidation method: zinc films coated by a thin copper buffer layer are oxidized in low-pressure afterglow. This work highlights the versatility of plasma afterglow treatments and demonstrates that the morphology of ZnO nanostructures (nanowires, nanoribbons and nanocombs) can easily be controlled with good reproducibility by adjusting experimental parameters such as the working pressure during the oxidation process. The rapid growth of ultrathin nanostructures (∼1 min) is due to the afterglow area which is a very oxidizing medium since it contains high concentrations of oxygen atoms and excited oxygen molecules. The surface morphology and structural and optical properties of the as-synthesized nanostructures are studied by means of SEM, HRTEM and UV-visible absorption, respectively. Ultrathin ZnO nanowires and nanoribbons with high aspect ratios exhibit excellent photocatalytic activity for the degradation of a model organic dye: methyl orange (MO), by comparison with pure ZnO thin films without nanostructures and thick ZnO nanowires synthesized by thermal oxidation. These results are supported by photocurrent measurements. The enhancement in photocatalytic performance could be attributed to higher surface area and higher transfer efficiency of photoinduced charge carriers to the surface of ultrathin nanowires and nanoribbons. The reusability of ZnO nanowire samples is also investigated by recording the photoactivity after several cycles of photodegradation.
This paper reports the effect of spray flux density on the photocatalytic activity of sprayed ZnO thin films towards the Rhodamine B (RhB) degradation, for the first time. In addition, the influence of annealing on the photocatalytic activity of ZnO film is studied and reported. It was found that, the change in spray flux density helps in tuning the surface morphology, crystalline quality and the concentration of oxygen vacancies (V O ) and zinc interstitials (Zn i ) which are crucial factors that can control the photocatalytic activity of deposited samples. The photocatalytic study shows that the samples prepared from higher spray flux density possess high efficiency for degradation of RhB. As these samples require only lower deposition time, this result may be useful in reducing the time consumed in large area production of photocatalytic thin films.
Applied Catalysis B: …, 2010
The aim of this study was to evaluate the effectiveness of using a range of innovative nanostructured high surface area zinc oxide (ZnO) thin films as photocatalysts, and thereafter to systematically relate initial and reacted surface morphology and irradiated surface area to photocatalytic activity under both limited and rich oxygen conditions. The thin films were produced using an innovative combination of magnetron sputtered surfaces and hydrothermal solution deposition that allows the morphology, porosity and thickness to be controlled by varying the composition and processing conditions. Methylene Blue (MB) was chosen as the model compound and the reaction was performed with ultra violet light (UV) at 254 nm. The thin film morphology and surface area before and after reaction was determined by scanning electron microscopy (SEM). The photocatalytic activity (measured as the rate and extent of MB degradation) was determined for seven different ZnO nanostructured thin films: three different ZnO hydrothermal solution depositions on bare glass slides (S1-CG, S2-CG and S3-CG films), the same three ZnO hydrothermal solution depositions but on glass slides coated with a magnetron sputtered ZnO film (S1-MS, S2-MS and S3-MS films), and glass slides coated with just a magnetron sputtered ZnO film (MS films).
Importance of precursor type in fabricating ZnO thin films for photocatalytic applications
Materials Science in Semiconductor Processing, 2018
Here, the importance of choosing an appropriate precursor with right molarity for the fabrication of zinc oxide (ZnO) films by spray pyrolysis for the photocatalytic application is reported. Films were grown on glass substrates by using three different zinc precursors such as zinc acetate, zinc chloride, and zinc acetylacetonate. The structural, morphological, and optical characterizations were performed on the ZnO films. A preferential orientation along (002) plane, crystallite size distribution in the range 21-59 nm, and the nanostructures such as nanothorns, hexagonal nanorods, hexagonal layers and elongated grains, were acquired from the characterization studies. Further, the photocatalytic activity was tested using indigo carmine dye, obtaining 100% of dye degradation using the ZnO thin films deposited with zinc acetate, whereas films from zinc chloride and zinc acetylacetonate precursors showed 20% and 10% of degradation respectively.
Applied Catalysis B-environmental, 2010
The aim of this study was to evaluate the effectiveness of using a range of innovative nanostructured high surface area zinc oxide (ZnO) thin films as photocatalysts, and thereafter to systematically relate initial and reacted surface morphology and irradiated surface area to photocatalytic activity under both limited and rich oxygen conditions.The thin films were produced using an innovative combination of magnetron sputtered surfaces and hydrothermal solution deposition that allows the morphology, porosity and thickness to be controlled by varying the composition and processing conditions. Methylene Blue (MB) was chosen as the model compound and the reaction was performed with ultra violet light (UV) at 254 nm. The thin film morphology and surface area before and after reaction was determined by scanning electron microscopy (SEM). The photocatalytic activity (measured as the rate and extent of MB degradation) was determined for seven different ZnO nanostructured thin films: three different ZnO hydrothermal solution depositions on bare glass slides (S1-CG, S2-CG and S3-CG films), the same three ZnO hydrothermal solution depositions but on glass slides coated with a magnetron sputtered ZnO film (S1-MS, S2-MS and S3-MS films), and glass slides coated with just a magnetron sputtered ZnO film (MS films).A clear relationship between surface morphology (and the related thin film preparation method) and photocatalytic activity was observed for ZnO thin film supported catalysts: the tallest, most aligned structure had the highest photocatalytic activity, whilst the smallest, least aligned structure had the lowest photocatalytic activity. Thus, MB degradation rate was the fastest for the 1 μm thick ZnO thin film with a uniform arrayed structure from the S2-MS deposition technique. The degradation rates of the ZnO thin films were comparable to commercially available ZnO powder on a surface area basis. Photocatalytic degradation of MB under oxygen rich conditions increased for all other films except one film (S1-CG). This was most effective for thin film structure S2-MS, whose reaction rate was increased by 15%. Adding oxygen made the films more stable: in oxygen limited conditions, SEM and atomic absorption spectroscopy indicated zinc leaching had occurred. However, with additional oxygen the zinc leaching was minimised under the same reaction conditions. It is thought that this additional oxygen is either minimising the release of or replacing lost ZnO lattice oxygens, indicating that this ZnO photocatalytic oxidation could be occurring via a Mars Van Krevelen type redox mechanism.
Photocatalytic efficiency of reusable ZnO thin films deposited by sputtering technique
Applied Surface Science, 2014
The photocatalytic activity of ZnO thin films with different physicochemical characteristics deposited by RF magnetron sputtering on glass substrate was tested for the decolorization of orange G dye aqueous solution (OG). The crystalline phase, surface morphology, surface roughness and the optical properties of these ZnO films were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM) and UV-visible spectroscopy (UV-Vis), respectively. The dye photodecolorization process was studied at acid, neutral and basic pH media under UV irradiation of 365 nm. Results showed that ZnO films grow with an orientation along the c-axis of the substrate and exhibit a wurtzite crystal structure with a (002) preferential crystalline orientation. A clear relationship between surface morphology and photocatalytic activity was observed for ZnO films. Additionally, the recycling photocatalytic abilities of the films were also evaluated. A promising photocatalytic performance has been found with a very low variation of the decolorization degree after five consecutive cycles at a wide range of pH media.
Photocatalytic activity of ZnO nanoparticles prepared via submerged arc discharge method
Applied Physics A, 2010
Zinc oxide nanoparticles (ZnO Nps) were prepared using zinc nitrates and succinic acid as a fuel through low temperature solution combustion method (LCS) at 500 0 C. The obtained materials were characterized by XRD, FTIR, UV-Vis and SEM. The XRD result shows that synthesized ZnO was hexagonal wurtzite stracture. FTIR indicates a significant band at ~ 380 cm −1 is assigned to the characteristic stretching mode of Zn-O. UV-Vis spectroscopy of ZnO Nps shows the band gap of 3.29 eV. SEM images show that the product is agglomerated and almost spherical in shape. The Photocatalytic activity of the synthesized ZnO Nps was examined for the degradation of methylene blue dye under both UV and Sunlight and the results shows it is a good photocatalytic materials.
Journal of Sol-Gel Science and Technology, 2012
Nanostructure single ZnO, SnO 2 , In 2 O 3 and composite ZnO/SnO 2 , ZnO/In 2 O 3 and ZnO/SnO 2 /In 2 O 3 films were prepared using sol-gel method. The obtained composite films were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-Vis spectroscopy. The photocatalytic activities of composite films were investigated using phenol (P), 2,4-dichlorophenol (2,4-DCP), 4-chlorophenol (4-CP) and 4-aminophenol (4-AP) as a model organic compounds under UV light irradiation. Hybrid semiconductor thin films showed a higher photocatalytic activity than single component ZnO, SnO 2 and In 2 O 3 films. The substituted phenols degrade faster than phenol. The ease of degradation of phenols is different for each catalyst and the order of catalytic efficiency is also different for each phenol. The use of multiple components offered a higher control of their properties by varying the composition of the materials and related parameters such as morphology and interface. It was also found that the photocatalytic degradation of phenolic compounds on the composite films and single films followed pseudo-first order kinetics. Keywords Zinc oxide Á Composite film Á Photocatalytic activity Á Phenolic compounds Á-, HO 2 Á). Among these species, holes and Á OH radicals play the most important roles in the photodegradation of organic pollutants.