Synthesis and characterization of ZnO and TiO 2 powders, nanowire ZnO and TiO 2 /ZnO thin films for photocatalyc applications (original) (raw)
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Materials Science in Semiconductor Processing, 2014
The crystallographic phase, surface features and photocatalytic properties in the reaction of decolorization of Malachite Green dye over TiO 2 (0-100 mol%) doped ZnO films have been investigated. The films have been prepared by polymer modified spray pyrolysis. The crystallization degree and the size of the crystallites comprising the films have been found to be influenced by the TiO 2 content in the spraying solution. The undoped ZnO film has little porosity. The titania dopant causes formation of hexagonal nanorods on the ZnO surface. The increase in TiO 2 content results in enhancement of both size and crystallization degree of the nanorods. When the TiO 2 content is increased (i) the Zn2p, O1s and Ti2p peaks are shifted to lower binding energies, (ii) the atomic ratio of O L /Zn is decreased and (iii) the amount of adsorbed hydroxyl (OH À ) species is increased. All the TiO 2 doped ZnO films manifested higher photocatalytic activity than that of the undoped ZnO and TiO 2 samples. The films obtained from solutions with 50 mol% TiO 2 showed the fastest decoloration of the dye.
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.
Optical and photocatalytic properties of composite TiO2/ZnO thin films
Catalysis Today, 2014
Pure TiO 2 and ZnO thin films named Ti100 and Zn100 were prepared via sol-gel technique using Ti alkoxide and Zn acetate as metal precursors and dip coating deposition on quartz substrate. Different vol.% ratios of the initial Ti and Zn solutions were used to obtain composite TiO 2 /ZnO films nominated as Ti25, Ti50 and Ti75. The XRD patterns of pure TiO 2 and ZnO films revealed the formation of anatase TiO 2 and wurtzite hexagonal ZnO, respectively. The patterns of the composite film Ti75 were similar to the pure TiO 2 , while the composite films Ti25 and Ti50 revealed amorphous structure. The XPS analysis proved presence of TiO 2 and ZnO oxide phases in the pure and composite films that is in accordance with XRD analysis. The UV-vis transmission spectra of the films showed that absorption edges of the composite films were blue shifted in comparison with the pure films. The largest shift was attained in the Ti25 composite film. The Forouhi-Bloomer (FB) and Tauc-Lorentz (TL) dispersion models were used for description of the complex refractive index of the films and for estimation of their thickness and energy band gap. The refractive index in the films' transparency region and high energy region increased with the increase of TiO 2 phase content. The thickness of the films also increased with the increase of TiO 2 content. The pure TiO 2 film was approximately 2.5 times thicker (145 nm) than the pure ZnO film (60 nm). The estimation of the energy gaps showed comparable gap value of ∼3.2 eV for the pure oxide films. The largest value of ∼3.8 eV was calculated for the Ti25 composite film. A good agreement between the two models was observed in the estimation of gap and thickness values. For pure ZnO film, better accordance between experimental and theoretical transmittance spectra was achieved via FB model simulations in the region above the band gap. The photocatalytic properties of the films in air purification were investigated via standard NO oxidation procedure. The Ti100 and Ti75 films exhibited improved performance in comparison to Ti25 and Zn100 films. The highest photocatalytic efficiency of 1.6 × 10 −2 mol/einstein in NO oxidation was recorded for pure TiO 2 film. Also, the latter showed the highest hydrophylicity without and under UV illumination.
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.
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.
Applied Surface Science, 2012
Fe 3+ and Ce 3+ codoped titanium dioxide films with high photocatalytic activity were successfully obtained via the improved sol-gel process. The as-prepared specimens were characterized using X-ray diffraction (XRD), high-resolution field emission scanning electron microscopy (FE-SEM), X-ray energy dispersive spectroscopy, Brunauer-Emmett-Teller (BET) surface area, X-ray photoelectron spectroscopy, photoluminescence (PL) spectra, and UV-Vis diffuse reflectance spectroscopy. The photocatalytic activities of the films were evaluated by degradation of various organic dyes in aqueous solutions. The results of XRD, FE-SEM, and BET analyses indicated that the TiO 2 film had nanostructure. With the codoping of Fe 3+ and Ce 3+ , TiO 2 photocatalysts with smaller crystal size, larger surface area, and larger pore volume were obtained. Moreover, codoped ions could obviously not only suppress the formation of brookite phase but also inhibit the transformation of anatase to rutile at high temperature. Compared with pure TiO 2 film, Fe 3+ doped or Ce 3+ doped TiO 2 film, the Fe 3+ /Ce 3+ codoped TiO 2 film exhibited excellent photocatalytic activity. It is believed that the surface microstructure of the films and the doping methods of the ions are responsible for improving the photocatalytic activity.
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).
TiO2-Coated ZnO Nanowire Arrays: A Photocatalyst with Enhanced Chemical Corrosion Resistance
Catalysts, 2021
Photocatalysis is proven to be the most efficient and environmentally friendly method for the degradation of organic pollutants in water purification. To meet the requirement of large-scale water treatment, there are two important points: One is the lifetime and chemical stability of the photocatalyst material, especially in the complex and harsh aqueous conditions. The other is the ease of synthesis of such photocatalysts with specific nano-morphology. In this work, two common photocatalyst materials, zinc oxide (ZnO) and titanium dioxide (TiO2), are selected to form more sustainable photocatalysts with high chemical stability. This involves the combination of both TiO2 and ZnO in a two-step simple synthesis method. It appears advantageous to exploit the conformal deposition of atomic layer deposition (ALD) to achieve nanometer-thick TiO2 coating on ZnO nanowires (NWs) with a high aspect ratio, which are firmly anchored to a substrate and exhibit a large specific surface area. The ...
ZnO ratio-induced photocatalytic behavior of TiO2–ZnO nanocomposite
Superlattices and Microstructures, 2013
The aim of this study is to examine the photocatalytic activity of TiO 2 (P25)-ZnO nanocomposite. The precursors of the TiO 2 -ZnO nanocomposite were deposited on a low cost ceramic substrate using the simple roll-coating method. We seek to improve the photocatalytic performance and the mechanical adherence of the TiO 2 nanoparticles by adding ZnO. The photocatalytic properties of the nanocomposite were tested through the bleaching of polluted water. These properties were optimized by varying the composition of the nanocomposite precursors, deposition conditions and temperature annealing. A systematic study of the nanocomposites was made using ultraviolet-visible spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). These characterizations allowed us to establish a relationship between the photocatalytic performances and the ZnO ratio using an azo-dye (methyl orange). It was found that the kinetic degradation increases with the increasing of the ZnO ratio. The Photodegradation of the dye using the sole ZnO was found to be more efficient than the P25 TiO 2 and the TiO 2 -ZnO nanocomposite itself. The discussions were based on the mobility and lifetime of the charge carriers generated in the ZnO or in TiO 2 -ZnO nanocomposite.