Anna Zielińska-Jurek

Progress, challenge, and perspective of bimetallic TiO 2 -based photocatalysts

Bimetallic TiO2-based photocatalysts have attracted considerable attention in recent years as a class of highly active catalysts and photocatalysts under both UV and Vis light irradiation. Bimetallic noble metal structures deposited on TiO2 possess the ability to absorb visible light, in a wide wavelength range (broad LSPR peak), and therefore reveal the highest level of activity as a result of utilization of a large amount of incident photons. On the other hand they can enhance the rate of trapping photoexcited electrons and inhibit the recombination process due to the capability of the storage of photoexcited electrons. Based on literature two groups of bimetallic photocatalysts were distinguished. The first group includes bimetallic TiO2 photocatalysts (BMOX), highly active under UV and Vis light irradiation in a variety of oxidation reactions, and the second group presents bimetallic photocatalysts (BMRED) exceptionally active in hydrogenation reactions. This review summarizes recent advances in the preparation and environmental application of bimetallic TiO2-based photocatalysts. Moreover, the effects of various parameters such as particle shape, size, amount of metals, and calcination on the photocatalytic activity of bimetallic TiO2-based photocatalysts are also discussed.

Nanoparticles Preparation Using Microemulsion Systems

A wide range of techniques have been developed for the preparation of nanomaterials. These techniques include physical methods such as mechanical milling (Arbain et al., 2011) and inert gas condensation (Perez-Tijerina et al., 2008), along with chemical methods such as chemical reduction (Song et al., 2009), photochemical reduction (Ghosh et al., 2002), electrodeposition (Mohanty, 2011), hydrothermal (Hayashi & Hakuta, 2010), and sol-gel synthesis (Sonawane & Dongare, 2006). Among all chemical methods the microemulsion has been demonstrated as a very versatile and reproducible method that allows to control over the nanoparticle size and yields nanoparticles with a narrow size distribution (LopezQuintela, 2003).

UV-Vis-Induced Degradation of Phenol over Magnetic Photocatalysts Modified with Pt, Pd, Cu and Au Nanoparticles

The combination of TiO2 photocatalyst and magnetic oxide nanoparticles enhances the separation and recoverable properties of nanosized TiO2 photocatalyst. Metal-modified (Me = Pd, Au, Pt, Cu) TiO2/SiO2@Fe3O4 nanocomposites were prepared by an ultrasonic-assisted sol-gel method. All prepared samples were characterized by X-ray powder diffraction (XRD) analysis, Brunauer-Emmett-Teller (BET) method, X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), Mott-Schottky analysis and photoluminescence spectroscopy (PL). Phenol oxidation pathways of magnetic photocatalysts modified with Pt, Pd, Cu and Au nanoparticles proceeded by generation of reactive oxygen species, which oxidized phenol to benzoquinone, hydroquinone and catechol. Benzoquinone and maleic acid were products, which were determined in the hydroquinone oxidation pathway. The highest mineralization rate was observed for Pd-TiO2/SiO2@Fe3O4 and Cu-TiO2/SiO2@Fe3O4 photocatalysts, which produced the highest concentration of catechol during photocatalytic reaction. For Pt-TiO2/SiO2@Fe3O4 nanocomposite, a lack of catechol after 60 min of irradiation resulted in low mineralization rate (CO2 formation). It is proposed that the enhanced photocatalytic activity of palladium and copper-modified photocatalysts is related to an increase in the amount of adsorption sites and efficient charge carrier separation, whereas the keto-enol tautomeric equilibrium retards the rate of phenol photomineralization on Au-TiO2/SiO2@Fe3O4. The magnetization hysteresis loop indicated that the obtained hybrid photocatalyst showed magnetic properties and therefore could be easily separated after treatment process.

Characterization of TiO 2 Modified with Bimetallic Ag/Au Nanoparticles Obtained in Microemulsion System

Abstract Titanium dioxide modified with silver-gold bimetallic nanoparticles were prepared by simultaneously formation of Ag/Au and TiO2 nanoparticles in water-in-oil microemulsion system (water/AOT/cyclohexane). Silver nitrate (AgNO3) and tetrachloroauric(III) acid (HAuCl4) were taken as the precursors and sodium borohydride (NaBH4) was used as a reducing agent. The photocatalysts samples were characterized by X-ray powder diffraction (XRD), BET surface area measurements, scanning electron microscopy (SEM) and energy dispersive spectroscopy analysis (EDS). The photocatalytic activity of bimetallic nanoparticles deposited at the TIP-TiO2 surface under visible light irradiation was estimated by measuring the decomposition rate of phenol in aqueous solution. The highest photocatalytic activity was obtained for the photocatalyst containing 1.5 mol % of silver and 0.5 mol % of gold.