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Alloy nanoparticles (NPs) loaded TiO2 photocatalysts have attracted considerable attention in the recent years as a promoter of highly active photocatalysts under ultraviolet (UV) irradiation. Many synthetic techniques have been utilized in preparation of binary alloy NPs loaded TiO2. However, control of deposition site for alloy NPs on TiO2 is one of the challenging themes in TiO2 study. Herein, we present that site-selective Pt–Pb NPs deposition on rutile TiO2 nanorod by successive reduction in metal ions, photo-reduction of Pt4+ and followed by microwave assisted polyol reduction of Pb2+ (2-step method). The Pt–Pb NPs were site-selectively deposited on the reduction site on (1 1 0) surface of the rutile TiO2 nanorod. The photocatalytic activity of rutile TiO2 was significantly enhanced after Pt–Pb NPs loading for oxidative decomposition of AcOH in aqueous phase. The AcOH was completely oxide to CO2 and the CO2 evolution of the site-selectively Pt–Pb NPs deposited TiO2 was nearly six times higher than that of a bare rutile TiO2 and three times higher than randomly Pt–Pb NPs deposited TiO2. The well mating of the reduction reaction site on photocatalyst, TiO2, and deposition site for co-catalyst, Pt–Pb NPs, induces efficient electron injection from photocatalyst TiO2 to co-catalyst Pt–Pb NPs, promoting oxygen reduction reaction and reduction process of AcOH oxidative decomposition. The accelerated electron consumption in reduction process leads to smooth oxidative decomposition of AcOH at oxidation site. These findings suggest that the site-selective deposition of alloy NPs is a predominant way to bring out catalytic performance of co-catalyst alloy NPs on TiO2.

This study investigates the photocatalytic decomposition of acetic acid and its reaction mechanism over WO 3 -supported ordered intermetallic PtPb nanoparticle (NiAs-type structure, P63/mmc, a = 0.4259 nm; c = 0.5267 nm) (PtPb NPs/WO 3 ) co-catalysts under an oxygen-rich atmosphere and visible light. We rationally designed and synthesized the ordered intermetallic nanoparticle on WO 3 co-catalysts by a photodeposition and polyol method. Remarkably enhanced activities were observed for the synthesized PtPb NPs/WO 3 catalyst toward the decomposition of organic compounds compared to pure WO 3 and WO 3 -supported individual Pt co-catalysts.

The ordered intermetallic PtBi, which has a NiAs type structure (NiAs-type structure; P63/mmc, a = b = 0.431 nm; c = 0.549 nm), was prepared on the surface of tungsten oxide (WO3) using the photodeposition method and polyol method. The prepared ordered intermetallic PtBi nanoparticles (NPs) used as co-catalyst showed much higher photocatalytic activity towards the decomposition of acetic acid (AcOH) under visible light irradiation (λ > 420 nm) than that observed with photodeposited Pt NPs/WO3.

Tungsten oxide (WO 3 )-supported ordered intermetallic PtPb nanoparticles (PtPb NPs/WO 3 ) were prepared through a co-reduction of Pt and Pb precursors with sodium borohydride in anhydrous methanol containing WO 3 . The PtPb NPs/WO 3 were characterized based on the crystal structure obtained through powder X-ray diffraction ( p XRD) as well as X-ray photoemission spectroscopy (XPS) and transmission electron microscopy (TEM). The formation of an ordered PtPb intermetallic phase on the WO 3 surface was confirmed. The PtPb NPs/WO 3 were more efficient when decomposing acetic acid (AcOH) and acetaldehyde (AcH) with visible light irradiation compared to the same process over WO 3 loaded with Pt nanoparticles (Pt NPs/WO 3 ).

The site-selective deposition of PtPb nanoparticles (PtPb NPs) on oxidation sites and of Pt NPs on reduction sites as co-catalysts was attempted on tungsten oxide (WO3) using a photodeposition reaction and the chemical reduction of Pt and Pb precursors for photoexcited electrons and holes to be efficiently consumed without the recombination of photogenerated carriers during the photochemical decomposition of acetic acid (AcOH). The synthesized PtPb/Pt/WO3 exhibited higher photocatalytic performance for the decomposition of AcOH under visible light irradiation (λ > 420 nm) than that observed using the conventional photodeposited Pt/WO3 or chemically deposited PtPb/WO3. The results of this study highlight the importance of controlling the deposition site for co-catalysts on photocatalyst surfaces.

Water splitting using a particle photocatalyst with visible light has attracted interest, because this will realize efficient conversion of the solar energy to hydrogen fuels for sustainable energy managements. Many water-splitting photocatalysts, such as metal-doped oxides, metal-(oxy)nitrides, and metal-oxysulfides, exhibit water reduction and oxidation ability when absorbing visible light. However, in such water-splitting photocatalysts, solely doping and/or replacement of foreign element at host material has been attempted to prepare visible-light-driven photocatalysts. The doping and/or replacement induces defect sites and charge imbalance into photocatalyst, resulting in the formation of recombination centers between excited electron and holes, in return to create new valence state. Therefore, the development of new native visible-light-sensitive photocatalyst for water splitting without doping of foreign elements is a major challenge for photocatalyst research. Herein, we report that an undoped metal oxide, Sn3O4, can efficiently catalyze Hydrogen (H2)-evolution in the presence of a sacrifice agent and, furthermore, can split water to H2 and O2 under irradiation of visible light by two-step photoexcitation (Z-scheme) systems using Sn3O4 as H2-evolving photocatalyst, combined with an appropriate O2-evolving photocatalyst in the presence of iodate/iodide (IO3 −/I−) as an electron mediator. We prepared nanocrystals of Sn3O4 by hydrothermal synthesis using sodium citrate as a ligand [1]. The Sn3O4 significantly catalyzed hydrogen evolution in aqueous solution in the presence of sacrifice agent under irradiation of visible light (λ>420nm), even without Pt co-catalyst. Pt co-catalyst was critical for Sn3O4 material to exhibit higher photocatalytic activity, so far in this study. The apparent quantum yield was 0.2% for high purity Sn3O4 and 1.5% for Pt loaded-Sn3O4, competitive to that of visible-light-sensitive doped metal oxide and (oxy)nitrides photocatalyst. Simultaneous evolution of H2 and O2 was attempted by using Sn3O4 as H2-evolving photocatalyst, combined with an appropriate O2-evolving photocatalyst (BiVO4, WO3 etc.,). By employing the appropriate combination of Sn3O4 and the redox couple (IO3 −/I−), simultaneous evolution of H2 and O2 stably proceeded with higher rates. [1] M. Maidhily, T. Tanabe, et al., ACS Appl. Mater. Interfaces 2014, 6, 3790.

Alloy nanoparticles (NPs) loaded TiO2 photocatalysts have attracted considerable attention in recent years as a promoter of highly active photocatalysts under ultraviolet (UV) irradiation [1]. Many synthetic techniques have been utilized in preparation of binary alloy NPs loaded TiO2. However, control of deposition site for alloy NPs on TiO2 is one of a challenging theme in TiO2 study. Herein, we present that site-selective Pt-Pb NPs deposition on rutile TiO2 nanorod by successive reduction of metal ions, photo-reduction of Pt4+ and followed by microwave assisted polyol reduction of Pb2+ (2-step method). The Pt-Pb NPs were site-selectively deposited on the reduction site on (110) surface of the rutile TiO2 nanorod. The photocatalytic activity of rutile TiO2 was significantly enhanced after Pt-Pb NPs loading for oxidative decomposition of AcOH in aqueous phase as shown in following figure. The AcOH was completely oxide to CO2 and the CO2 evolution of the site-selectively Pt-Pb NPs deposited TiO2 was nearly six times higher than that of a bare rutile TiO2 and three times higher than randomly Pt-Pb NPs deposited TiO2. The well mating of the reduction reaction site on photocatalyst, TiO2, and deposition site for co-catalyst, Pt-Pb NPs, induces efficient electron injection from photocatalyst TiO2 to co-catalyst Pt-Pb NPs, promoting oxygen reduction reaction, reduction process of AcOH oxidative decomposition. The accelerated electron consumption in reduction process leads to smooth oxidative decomposition of AcOH at oxidation site. These findings suggest that the site-selective deposition of alloy NPs is a predominant way to bring out catalytic performance of co-catalyst alloy NPs on TiO2. [1] T. Gunji, A. J. Jeevagan, M. Hashimoto, T. Nozawa, T. Tanabe, S. Kaneko, M. Miyauchi, F. Matsumoto, Appl. Catal B 181 (2016) 475-480. Figure 1

Oxide supported metal catalysts are widely recognized as an important photocatalyst because of its peculiar chemical and physical behaviors. Owing to its high reactivity, low cost and stability, TiO2 is one of the most extensivley studied photocatlaysts.1 However, for indoor applications, the faction of UV light available is very low. Hence, visble light photocatalysts are needed as an alternative of UV light photocatalysts. Recently, it hase been reported that Pt loaded WO3 exhibits high photocatalytic activity for the degradation of organic compounds under visible light.2 However, the high cost of Pt has been the primary impediment for the use of Pt loaded WO3 in indoor applications. The loading of other noble metals, such as Au, Pd, and Ag can also used as cocatalysts to enhance the photocatalytic activity of WO3. Among them Pd is one of the most effective cocatalyst because of the cost of the Pd is approximately one-fifth that of Pt and also shows enhanced charge separation lead to effective photocatalytic activity towards volatile organic compounds. In this study, Pd and Pd based binary cocatalysts were prepared and subsequently characterized and we have demonstrated the enhancement of visible light photocatalytic activity of WO3in the decomposition of organic compounds. The details about the synthesis, characterization and photocatalytic activity of catalysts would be discussed in the presentation. References 1. M.R. Hoffman, S.T. Martin, W. Choi and D.W. Bahnemann, Chem. Rev., 95, 69, (1995). 2. R. Abe, H. Takami, N. Murakami and B. Ohtani, J. Am. Chem. Soc., 130, 7780, (2008)

1. Introduction Photocatalytic decomposition of organic pollutants is one of the promising method for environmental purification. Most of the researchers focused on efficient decomposition of environmental organic contaminants under visible light irradiation or indoor fluorescent light.1 Oxide-supported metal catalysts are widely acknowledged as important catalysts that are related to versatile key in photochromism, chemical sensing and photocatalytic activity. Tungsten trioxide (WO3) acts as a ideal visible light photocatalyst owing to its small band gap energy (2.4-2.8 eV) and high oxidation power of vanlence band holes. But, WO3 exhibits low photocatalytic activity due its high recombination rate of photoexcited electrons and holes. In order to suppress the recombination of photoexcited carriers and significantly increase the photocatalytic efficiency, most research has focused to prepare WO3 doping constituent or WO3 composites.2,3 In the present study, we have synthesized PtPb/WO3 and PtAu/WO3 alloy catalysts, demonstrated to exhibit the efficiency for the decompostion of organic pollutants under visible light irradiation. 2. Experimental A simple one-pot synthesis approach to obtain WO3 supported PtAu catalyst is as follows. In the synthesis, 0.5 g of WO3was suspended in 15 mL of anhyrous methanol for 15 min in a two neck round bottom flask. Pt (0.0075 g) and Au (0.0045 g) precursors were dissolved in 15 mL anhydrous methanol in the shielded vial uder Ar atmosphere and transferred to the suspensions. Then, the solution was stirred for 30 min to yield homogeneous color soluion. Required amount of NaBH4 in mehtanol was injected into the suspensions. The product were washed and centrifuged with anhydrous methanol for three times and dried under vacuum. Similar procedure was followed to synthesis the PtPb/WO3 catalyst. 3. Results and Discussion Figure 1 shows the TEM images of (a) Pt/WO3 (b) PtPb/WO3 and (c) PtAu/WO3 photocatalysts. Pt and PtPb and PtAu NPs are showed monodispersity and homogeneity on the WO3 supports. The average particle size of the three catalysts can be ranked as PtPb/WO3~PtAu/WO3 > Pt/WO3. The TEM results show that the addition of Pb and Au increases the size of NPs. Figure 2 depicts that the CO2 formation profile over different photocatalysts under visible light irradiation time. PtPb/WO3 photocatalyst (1 wt %) shows the higher rate of CO2formation over other photocatalysts. The details about the characterization and photocatalytic activity of catalysts would be discussed in the presentation. 4. References 1. M.R. Hoffmann, S.T. Martin, W. Choi and D.W. Bahnemann, Chem. Rev., 95, 69, (1995). 2. R. Abe, H. Takami, N. Murakami and B. Otani, J. Am. Chem. Soc., 130, 7780, (2008). 3. M. Miyauchi, Phys. Chem. Chem. Phys., 10, 6258, (2008).

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