Zr/Cu-TiO2 CATALYSTS FOR PHOTOCATALYTIC WATER TREATMENT

This work entitled «Zr/Cu-TiO2 catalysts for photocatalytic water treatment» tackles a problem of tons of dyes discharged everyday mainly from textile industries. This is a huge concern because of dyes persistence, toxicity and potential to the bioaccumulation in living organisms. Here, a small contribution to overall problem is presented. The research work consists of three main parts: Theoretical background, Experimental and Results and discussion. In the Theoretical background chapter the overall problem is identified and discussed. The main water treatment techniques are presented briefly with their advantages and drawbacks. Photocatalysis assisted with TiO2 is shown as an alternative additional technique with its own pros and cons. Further, a cursory overview of TiO2 modification techniques is made and advantages in using copper and zirconium oxides for TiO2 modification are presented. The reason and possible positive effect of using of two oxides simultaneously for TiO2 modification is indicated. Additionally, a positive impact of solar light for overall rate of dyes degradation assisted with TiO2 is discussed. Within the framework of photosensitization effect, the problem of using dyes for assessment of photocatalytic properties of materials under the visible light is touched on. Photothermal methods as possible beneficial techniques for this purpose are proposed. In the Experimental chapter, all experimental techniques used in current research work with the technical details specific for the research work are presented. There are methods of materials preparation, photocatalytic tests under different conditions and varying model pollutants, and physico-chemical characterization techniques. The Results and discussion chapter is divided by three subchapters. Each chapter is dedicated to one hypothesis, which was checked and confirmed or disproved. The first hypothesis is about beneficial loading of copper and zirconium oxides to TiO2. After numerous experiments held, it was concluded that the pair of copper and zirconium oxides is beneficial for simultaneous application on TiO2 surface to promote its performance. The second subchapter is about zirconium distribution and its impact on the activity of studied materials towards the antraquinone dye Reactive Blue 19. Different techniques such as XRD, TEM, EXAFS and many others were used in order to characterize the materials and to understand the details of the processes taking place. The existence of upper limit of copper oxide loading for its beneficial effect on TiO2 performance was demonstrated. It was observed that zirconium species loading leads to improvement in performance of materials with higher copper loading, which otherwise lowers activity of TiO2 – this is in case when copper only above its optimal level is present. It was concluded that zirconium oxide containing species occupy rutile surface sites in mixed phase TiO2 and this way beneficially influence the material performance towards the dye removal. The third subchapter is about the visible light TiO2 assisted dye degradation. It is well known that photosensitization mechanism of dye degradation appears under the visible and as a consequence under the solar light irradiation. This leads to the overall enhancement of dyes degradation, which is positive and may be used as a benefit for faster pollutant destruction. However, this fact leads to mishmash in the determination of real photocatalytic activity of materials towards the dye. It was hypothesized that the impact of photosensitization mechanism on the overall material performance against Reactive blue 19 dye (RB19) descends with the dye concentration lowering. Thermal lens spectrometry (TLS) which is sensitive to chemicals at low concentrations was used for hypothesis evaluation. To summarize the research work achievements, the conclusions of the thesis are given at the end

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

Study of water adsorption on EDTA-modified LTA zeolites

The present work deals with the study of water adsorption on acid-modified zeolites A. Commercial zeolites 4A (Na form) and 5A (Ca form) were subjected to EDTA dealumination, and their structure, textural properties and stability were checked by XRD, EDX, NMR and N2 physisorption analyses. The water adsorption isotherms of the parent zeolites and their modified forms were measured at a temperature of 25 °C and up to a relative pressure of 0.9. The results show that the treatment with EDTA drastically changes the structural properties of the zeolites and increases the water adsorption capacity by up to 10%. The changes depend on the type of extra-framework cations (Na+ and Ca2+) and the EDTA concentration

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