DOI: 10.1002/cssc.201402173 New Hydrogen-Evolution Heteronanostructured Photocatalysts : Pt-Nb 3 O 7 (OH) and Cu-Nb 3 O 7 (OH) Mohamad Hmadeh, [a, b] Veronika Hoepfner, [a] Eduardo Larios, [c, d] Kristine Liao, [a] Jia Jia, [a] Miguel Jose-Yacaman, [c] and Geoffrey A. Ozin* [a] Nanorods of triniobium hydroxide heptaoxide, Nb 3 O 7 (OH), were synthesized by means of a hydrothermal method. Subse- quently, Pt and CuO nanoparticles were introduced on the sur- face of Nb 3 O 7 (OH) nanorods by a microwave-assisted solvo- thermal nucleation and growth technique. The resulting Pt- and CuO-decorated Nb 3 O 7 (OH) nanorods demonstrated uni- form particle dispersion and were fully characterized by X-ray diffraction, electron microscopy, and spectroscopic analysis. Furthermore, the solar-powered photocatalytic hydrogen pro- duction properties of these heteronanostructures were studied. The solar-driven H 2 formation rate over Pt-Nb 3 O 7 (OH) was de- termined to be 710.4  1.7 mmol g 1 h 1 with a quantum effi- ciency of f= 5.40 % at l = 380 nm. Interestingly, the as-pre- pared CuO-Nb 3 O 7 (OH) heteronanostructure was found to be inactive under solar irradiation during an induction phase, whereupon it undergoes an in situ photoreduction process to form the photocatalytically active Cu-Nb 3 O 7 (OH). This restruc- turing process was monitored by an in situ measurement of the time-evolution of the optical absorption spectra. The solar- powered H 2 production for the restructured compound was determined to be 290.3  5.1 mmol g 1 h 1 . Photocatalytic solar fuel production has attracted much atten- tion since Fujishima and Honda’s work using the TiO 2 photoca- talyst as a photoanode. [1] Following this initial discovery, nu- merous families of semiconductors (e.g. ZnO, ZrO 2 , CdS, ZnS, SiC) have been developed for solar fuel production. [2] At pres- ent, the main obstacle in the development of photocatalytic materials is their low efficiency. Several strategies have been employed in the design of novel materials to enhance the photocatalytic activity. [3, 4] The utilization of multi-component nanostructures rather than single semiconductors is one of the most efficient and practical approaches in achieving these highly sought-after characteristics. This is evidenced by semi- conductor-based heteronanostructures that have demonstrat- ed charge migration from one component, typically the semi- conductor absorbing irradiation, to the other component, which may be a noble metal, a transition metal or metal oxide, a metal sulfide, or another semiconductor with proper band- edge positions. [3–5] Because the Fermi energy levels of the noble and coinage metals such as Pt, Rh, Pd, Ru, Cu, Ag, and Au are typically lower than those of semiconductors, the metal nanoparticles can act as electron sinks, facilitating interfacial electron transfer and ultimately decreasing the electron-hole recombination rate as well as creating a new catalytic site for the reduction. [5,6] Although titania is the most commonly stud- ied photocatalyst, a series of niobium-based semiconductors (e.g. HNb 3 O 8 , HNbO 3 ,H 4 Nb 2 O 7 ,H 4 Nb 6 O 17 ) have attracted much attention recently due to their favorable properties such as high stability under light irradiation, chemical inertness, and non-toxicity. [7] Furthermore, it is believed that the protonic acidity in these semiconductors can promote adsorption of water, CO 2 , and some organic molecules. [7] Even though Nb 3 O 7 (OH) materials have been reported as photocatalysts used in dye degradation and dye-sensitized solar cells, the photocatalytic properties of Nb 3 O 7 (OH) nanorods and their het- eronanostructures towards hydrogen evolution remain unex- plored. [8] By combining the favorable properties of triniobium hydrox- ide heptaoxide, Nb 3 O 7 (OH), with the advantages associated with metal-semiconductor heteronanostructures, a novel and highly efficient photocatalyst can be created. Herein, the syn- thesis and characterization of Nb 3 O 7 (OH) nanorods as well as their Pt- and CuO-decorated heteronanostructures are report- ed. The photocatalytic hydrogen production properties of the pure Nb 3 O 7 (OH) nanorods and of the heteronanostructures (Pt- Nb 3 O 7 (OH) and CuO-Nb 3 O 7 (OH)) are investigated. Nanocrystals of Nb 3 O 7 (OH) were prepared via a hydrothermal method (see Experimental Section for more details). The powder X-ray diffraction (PXRD) pattern of the as-synthesized compound (Figure 1 A) was indexed as an orthorhombic struc- ture with lattice parameters of a = 20.74 , b = 3.82  and c = 3.93  (PDF, file No.: 00-031-0928) and no additional peaks were observed. The Nb 3 O 7 (OH) crystal structure is constructed [a] Dr. M. Hmadeh, + Dr. V. Hoepfner, + Dr. K. Liao, J. Jia, Prof. G. A. Ozin Materials Chemistry Research Group Department of Chemistry University of Toronto 80 St. George Street, Toronto, Ontario M5S 3H6 (Canada) E-mail : gozin@chem.utoronto.ca [b] Dr. M. Hmadeh + Department of Chemistry American University of Beirut Beirut 11-0236 (Lebanon) [c] E. Larios, Prof. M. Jose-Yacaman Physics Department University of Texas at San Antonio One UTSA Circle, San Antonio, TX 78249 (USA) [d] E. Larios Departamento de Ingeniería Química Universidad de Sonora 83000 Hermosillo, Sonora (MØxico) [ + ] These authors contributed equally to this work. 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