Surface Functionalization of Grown-on-Tip ZnO Nanopyramids: From Fabrication to Light-Triggered Applications

We report on a combined chemical vapor deposition (CVD)/radio frequency (RF) sputtering synthetic strategy for the controlled surface modification of ZnO nanostructures by Ti-containing species. Specifically, the proposed approach consists in the CVD of grown-on-tip ZnO nanopyramids, followed by titanium RF sputtering under mild conditions. The results obtained by a thorough characterization demonstrate the successful ZnO surface functionalization with dispersed Ti-containing species in low amounts. This phenomenon, in turn, yields a remarkable enhancement of photoactivated superhydrophilic behavior, self-cleaning ability, and photocatalytic performances in comparison to bare ZnO. The reasons accounting for such an improvement are unravelled by a multitechnique analysis, elucidating the interplay between material chemico-physical properties and the corresponding functional behavior. Overall, the proposed strategy stands as an amenable tool for the mastering of semiconductor-based functional nanoarchitectures through <i>ad hoc</i> engineering of the system surface

XAS studies of Sn modified TiO2\mathrm{TiO_{2}} coatings

Coatings based on $\mathrm{TiO_{2}}$ are extensively investigated material for the preparation of surfaces which are referred as self-cleaning. Under solar illumination these coatings catalyze pollutants degradation and enhance their removal from the surface due to photoinduced superhydrophilicity [1]. There are two main drawbacks of using pure $\mathrm{TiO_{2}}$ (anatase) as a photocatalyst; i) its band gap lies in the UVA region so it can exploit only a part of the sunlight spectrum, and ii) it has a high degree of recombination between photo generated electrons and holes on the surface. There are various strategies to improve the photocatalytic efficiency of $\mathrm{TiO_{2}}$, one of them is the modification with transition metals. Based on our previous experiences with sol-gel synthesis of low-temperature $\mathrm{TiO_{2}}$ thin films [2], we prepared a series of Sn modified $\mathrm{TiO_{2}}$ photocatalysts. As a starting material only organic (Ti and Sn alkoxide) precursors were used. The loadings of Sn cations were varied in the range of 0.05 to 20 mol.%. The coatings, deposited on glass substrates by dip-coating technique, were dried at 150 oC. In addition, another set of photocatalyst coatings was prepared by further calcination at 500 °C in air. The comparison of photocatalytic activities of Sn modified $\mathrm{TiO_{2}}$ to unmodified $\mathrm{TiO_{2}}$ showed that Sn loadings in the range of 1-10 mol.% improved photocatalytic activity up to 8 times. At lower loadings of Sn, the photocatalytic activity was improved only by 30 %. After the coatings are calcined, their photocatalytic activity was significantly reduced.The objective of the research was to examine the mechanism responsible for photocatalytic properties of Sn modified $\mathrm{TiO_{2}}$ and to to clarify the role of Sn cations in the $\mathrm{TiO_{2}}$ photocatalytic process. For this purpose, Sn and Ti K-edge XANES and EXAFS analysis was used to precisely determine the local structure and the site of incorporation of Sn cations on titania nanoparticles in the coatings. We examined the hypothesis that the solid-solid interface was a crucial structural feature that facilitates charge separation and enhances photocatalytic efficiency of titania

Structural analysis of sunlight efficient Cu and Zr modified TiO2\mathrm{TiO_{2}} photocatalyst

Solving of the renewable energy as well as environmental sustainability issues is on the top ofconsideration nowadays. Using abundant, inexpensive, nontoxic and efficient material,photocatalysis can be a great alternative and promising approach for many important processes [1].The most known (due to its availability and appropriate properties) photocatalyst is TiO2. However,it is only activated by irradiation at wavelengths shorter than 400 nm. To effectively utilize lightwith longer wavelength (visible spectrum) metal and non-metal doping were explored [2].Nevertheless, quantum yield of electronic process under visible light in doped materials is muchlower than under UV, due to crystal defects and generation of recombination centers. On the otherhand the surface modification process is very attractive because the visible-light activity can beinduced without changes in crystal structure. Most probably, visible light sensitivity can beachieved by the interfacial charge transfer process of excited TiO2 electrons to the modifier [3].Evonik Degussa P25 is one of the most efficient photocatalyst, showing photocatalytic activity evenunder the visible light [4]. The surface modification of TiO2 with two different elementssimultaneously finds its place among different approaches. The improvement in the activity of TiO2modified with appropriate combination of two or more elements is assigned to the existence ofsynergistic effect. The promising combination for sunlight driven TiO2 photocatalysis is acombination of Cu and Zr for TiO2 surface modification [5].The objective of our research is to improve photocatalytic properties of P25 by facile surfacemodification method with Cu and Zr, to find the correlation between catalytic and structuralproperties of modified P25 materials, and to identify the synergistic role of the two elements. Wereport on the results of Cu and Zr K-edge EXAFS (Extended X-ray Absorption Fine Structure)analysis of Cu and Zr chemical state and local environment in the surface modified P25photocatalyst

Contribution of Cu and Zr to the properties of TiO2TiO_{2} for photocatalytic watertreatment

Progress in nanoscale material chemistry in general, and in TiO2 photocatalysis particularly goes on. The past 10 years achievements in the enhancement of photocatalytic activity, hardening of materials, chemical and biological resistance and other unique characteristics contributed to the ability of controlling nanoparticles size and shape, particles organization and their surface chemistry. However, the drawbacks of wide band gap (3,2 eV) and fast electron/hole recombination rate of TiO2, which are limiting TiO2 application in sunlight driven photocatalysis and photocatalytic ability in general, still attract the scientists’ attention. In frame of these, there has been great interest for doping and surface modification of TiO2 with transition metals as a possibility for photoexcitation in the visible region and charge separation [1]. A lot of work in the field of TiO2 modification with copper and zirconium separately has been done. Both elements showed beneficial results in TiO2 modification [2]. However, double metal modification can lead to additional achievements [3].Copper and zirconium modified photocatalysts were obtained by wet impregnation method of P25 (Evonik Degussa). In order to follow the changes in photocatalytic properties in conjunction with local structure and origin of modified photocatalysts, two types of metal precursors (organic: copper(ll) acetyl acetonitrile, zirconium(lV) isopropoxide, and inorganic: copper nitrate, zirconyl nitrate hydrate) were used. Concentration of metals varied as well. Photocatalytic properties and surface chemistry of obtained materials were investigated. Changes in the quality and quantity of acidic sites on the surface of TiO2 were shown. Durability of photocatalytic films based on obtained powders was checked by pencil hardness test. Obtained results suggest employment of two metals simultaneously for catalyst characteristics improvement

Cu and Zr surface sites in photocatalytic activity of TiO2\mathrm{TiO_{2}} nanoparticles: The effect of Zr distribution

The present work is focused on the role of $\mathrm{TiO_{2}}$ modification in theperformance of CuO modified $\mathrm{TiO_{2}}$. Zirconia loading leads to formationof more resistant photocatalytic layers compared to samples modifiedwith only copper containing species. Surface modification of mixedphase $\mathrm{TiO_{2}}$ with CuO/ZrO$_2$ improves the degradation of Reactive blue 19 dye under simulated solar irradiation. An in-depth investigation of thecatalysts showed that in case of CuO/ZrO$_2$ modification, the covering ofthe $\mathrm{TiO_{2}}$ surface with zirconium containing species preventsmorphological and harmful energetic changes induced by copper speciesformed on the rutile $\mathrm{TiO_{2}}$ phase at a higher copper loading

Cu and Zr surface sites in photocatalytic activity of TiO2_{2} nanoparticles: the effect of Zr distribution

TiO$_{2}$ is the most studied photocatalyst for environmental application. The industrial scale application of TiO$_{2}$ is facing numerous problems andimmobilization of active and stable layers is among them. There is always a compromise between good mechanical stability and good photocatalytic activity ofimmobilyzed layers. Since zirconium oxide is claimed to have outstanding mechanical properties and in some cases causing the increase in catalytic activityof metal modified TiO$_{2}$., we have studied influence of Zr modification of TiO$_{2}$. and Cu modified TiO$_{2}$ photocatalysts, with the goal to improve their photocatalyticand mechanical properties.Copper/zirconium surface modified photocatalysts were prepared by modification of commercial titanium dioxide Aeroxide Degussa P25.Hardness test (Fig. 1) of active layers obtained from modified TiO$_{2}$ showed that Zr loading leads to improvement of mechanical properties compared to onlyCu modified samples. Microscopic investigation of copper modified powders (Fig. 4) showed formation of copper nanoclusters about 1-2 nm size on thesurface of TiO$_{2}$. EXAFS results (Figs. 5 and 6) suggest formation of separate ZrO$_2$ and CuO species attached to TiO$_{2}$ surface. The surface acidity titrationshowed, that Zr modification, leads to covering of all rutile acidic sites (Fig. 3). Thus, while combined Cu/Zr modification, Zr acts as a shield, covering rutilesurface, that results in preferably copper/anatase interaction. Thus, zirconium modification prevents formation of harmful copper/rutile interactions, whichappear at higher copper loading, and improves photocatalytic activity of combined Cu/Zr modified TiO$_{2}$ photocatalyst

Multi-functional MnO2 nanomaterials for photo-activated applications by a plasma-assisted fabrication route

Supported MnO2-based nanomaterials were fabricated on fluorine-doped tin oxide substrates using plasma enhanced-chemical vapor deposition (PE-CVD) between 100 \ub0C and 400 \ub0C, starting from a fluorinated Mn(II) diamine diketonate precursor. Growth experiments yielded \u3b2-MnO2 with a hierarchical morphology tuneable from dendritic structures to quasi-1D nanosystems as a function of growth temperature, whose variation also enabled a concomitant tailoring of the system fluorine content, and of the optical absorption and band gap. Preliminary photocatalytic tests were aimed at the investigation of photoinduced hydrophilic (PH) and solid phase photocatalytic (PC) performances of the present nanomaterials, as well as at the photodegradation of Plasmocorinth B azo-dye aqueous solutions. The obtained findings highlighted an attractive system photoactivity even under visible light, finely tailored by fluorine content, morphological organization and optical properties of the prepared nanostructures. The results indicate that the synthesized MnO2 nanosystems have potential applications as advanced smart materials for anti-fogging/self-cleaning end uses and water purification