SUPPLEMENTARY INFORMATION 1] Extra details on the procedure of fabrication of nanocomposite photocatalyst (NCPC) The nanocomposite fabrication was carried out using standard procedures and commercially available chemicals. Lead monoxide (PbO), Bismuth (III) oxide (Bi2O3), Niobium pentoxide (Nb2O5), Titanium dioxide (TiO2) and HPLC reagent ethanol were purchased from Aldrich. In a typical two step procedure of NCPC fabrication, PbBi2Nb1.9Ti0.1O9 (PBNTO) was prepared first by solid state reaction method and later W was deposited on PBNTO (obtained from first step) by CVD, followed by oxidation to WO3 in a controlled manner. Routinely, for the preparation of PBNTO by the conventional solid-state reaction, a stoichiometric mixture of PbO (99.999%), Bi2O3 (99.9%), Nb2O5 (99.999%), TiO2 (99.999%) were mixed and ground in a mortar in the presence of ethanol and dried in an oven. Pelletized powders were calcined at 1123 K for 24 h in static air and then sintered at 1323 K for 24 h to obtain PbBi2Nb2O9. A p-type PbBi2Nb1.9Ti0.1O9 (PBNTO) photocatalyst was fabricated by the Ti4+ substitution for Nb5+ in the PbBi2Nb2O9 perovskite lattice. In next step, the W on surfaces of PBNTO powders was deposited by using a cold-wall CVD chamber with a shower-head. The base pressure of the reactor was below 10-3 torr, and the operating pressure was in a range of 0.1-1 torr during the W deposition. The white colored tungsten salt viz. W (CO) 6 with a high vapor pressure was used as the source for metal oxide chemical vapor deposition (MOCVD). The solid tungsten hexacarbonyl source was contained in a stainless steel bubbler. During the W deposition, the bubbler temperature was maintained at 80 C. Delivery line was also heated to 110 C to prevent the source condensation. Argon was used as a carrier gas with the flow rate of 1.5mol/s. Deposition temperature was varied from 450 to 500C. Thus produced W metal-loaded PBNTO catalysts were then oxidized in air (25µmol/s) at 473 K for 1 h. The conceptual deposition procedure adopted for the entire PNCP fabrication is briefly illustrated in FIG. 1A.

2] Characterization Techniques The photocatalyst material was characterized for desired physico-chemical properties. The structural characterization was carried by High Resolution Transmission Electron Microscopy and X-ray diffraction analysis. High Resolution Transmission Electron Microscope (TEM Phillips Model CM 200) was used to examine the presence of nano crystals over the perovskite base material. The existence of single-phase, crystalline material was confirmed by the X-ray diffraction (XRD) analysis (not described) using Cu K  radiation. The band gap energy and optical property of these materials were measured by UV-Visible diffuse reflectance spectrometer (Shimadzu, UV 2401). The qualitative elemental analysis and electronic state of components on the surface of catalysts was studied by X-ray photoelectron spectroscopy (XPS, VG Scientific, ESCALAB220iXL) with Mg K radiation at 1253.6eV. The binding energy was calibrated using C 1s peak as the reference energy.

3] Details on the photocatalytic activity measurements The photocatalytic reactions in aqueous solution were carried out at room temperature in a closed system using a 450-Watt Xe-arc lamp (Oriel) with UV cut-off filter (420nm) placed in an inner irradiation-type pyrex reaction cell with a volume of 200 ml. The H 2 evolution was examined in an aqueous solution (H2O 170 ml + methanol 30 ml) containing 0.3g of WO3/W/PbBi2Nb1.9Ti0.1O9 catalyst. For the O2 evolution, the reaction was performed in an aqueous AgNO3 solution (0.05 mol/l, 200ml) containing 0.3g of the catalyst. The quantum yield (QY) was calculated using the following equation: QY = 2 × number of H2 or 4 × number of O2 generated per number of photon absorbed by photocatalyst. The number of absorbed photons was determined by light flux meter (1815-C, Newport) with the light sensor attached to the photocatalytic reactor. Thus, the light absorbed by the whole photocatalytic reactor system was obtained by the difference in light flux with and without the photocatalytic reactor between the light source and the light sensor. The loss of light intensity due to scattering and absorption by materials in the light path other than the photocatalyst was determined for the same reactor containing suspended La 2O3 powders (instead of the photocatalyst), which did not absorb visible light. The net absorption by the photocatalyst was obtained by the difference of these two values. About 200ppm of gaseous acetaldehyde or isopropyl alcohol was injected into a Pyrex reaction cell with a volume of 500 ml. The concentration of reaction products (H2, O2,

CO2) was determined by a gas chromatograph equipped with a thermal conductivity detector and a molecular sieve 5Å column. For photocurrent measurements, 25 mg of photocatalyst was suspended in distilled water (75ml) containing acetate (0.1 M) and Fe3+ (0.1 mM) as an electron donor and as an acceptor, respectively, and the suspension pH was adjusted to 1.4 with HClO4. A platinum plate (1x1 cm2, 0.125 mm thick, both sides exposed to solution), a saturated calomel electrode (SCE), and a platinum gauze was immersed in the reactor as working (collector), reference, and counter electrodes, respectively. With continuous N2 purging of suspension, photocurrents were measured by applying a potential (+0.6 V vs. SCE) to the Pt electrode using a potentiostat (EG&G). TiO2-xNx, known for its good photocatalytic activity in degradation of acetaldehyde under visible light was also prepared according to a standard reference.[*]

* R. Asahi, T. Morikawa, T. Ohwaki, K. Aoki, Y. Taga, Science, 293, 269 (2001)

4] Flat band potential measurements The slurry method1,2 was used to determine the positions of the flat-band potential (EFB) for PbBi2Nb1.9Ti0.1O9. For the photoelectrochemical measurement, the mixture of 25mg of photo catalyst and 0.5mM methylviologen dichloride was suspended in 100ml two-necked flask in 50mM KNO3. HNO3 and NaOH of 100mM were used to adjust the pH value. A Pt flat electrode (1x1 cm2, 0.125mm thickness, both sides exposed to solution), a saturated calomel electrode (SCE), a Pt gauze were immersed in the reactor as working (collector), reference and counter electrodes respectively. The study was performed by using a 450Watt Xe-arc lamp (Oriel) with UV cut-off filter (420nm). The stable photocurrents were recorded about 40min. after adjusting the pH value to desired value. With continuous N2 purging of suspension, photocurrents were measured (potentiostat EG&G) without applying any potential to Pt electrode. Initially the pH of the suspension was adjusted to pH 3.0-3.5 before measurement. The obtained pH0 values were converted to EFB at pH 7 by using the equation,1, 2 EFB= -0.6865 + (0.059 pH0) Reproducibility of pH0 values was better than 0.1 pH units.

Figure.SI1 Dependence of photo-current on pH value of electrolyte for PbBi2Nb1.9Ti0.1O9 photocatalyst. Inset shows the electrochemical potentials (vs. NHE) for band positions at pH=7.

[1] J.R. White, A.J. Bard, J.Phys.Chem., 89, 1947 (1985) [2] A.M. Roy, G.C. De, N. Sasmal, S.S. Bhattacharyya, Int. J. Hydrogen. Energy, 20, 627 (1995).

5] XPS analysis

Figure.SI2 XPS core level spectrum of W 4f 7/2 and 4f 5/2 for nanocomposite photocatalyst of WO3/W/PbBi2Nb1.9Ti0.1O9 after Ar+ etching of 12 min. The initial photocatalyst showed peaks only due to WO 3. The deconvoluted fit distinctly shows the components for pure and oxide of W.