Ru/SrTiO 3 :Rh photocatalyst powder for H 2 evolution and varied photocatalyst powders for O 2 evolution such as BiVO 4 and WO 3 were suspended in acidified aqueous solutions, resulting in showing activities for water splitting into H 2 and O 2 in a stoichiometric ratio without an electron mediator under visible light irradiation. The photocatalytic activities were dependent on pH. The highest activity was obtained at pH 3.5. An optical microscope observation of the aqueous suspension containing Ru/SrTiO 3 :Rh and BiVO 4 powders at pH 3.5 revealed that these powders aggregated with suitable contact. The condition of Rh doped in SrTiO 3 also affected strongly the photocatalytic activity and quenching of the photoluminescence of BiVO 4 . The high photocatalytic activity was obtained and the luminescence was remarkably quenched, when SrTiO 3 :Rh containing Rh species with reversible redox properties was used and mixed. These results indicated that the photocatalytic water splitting and quenching of the photoluminescence occurred through interparticle electron transfer from the conduction band of BiVO 4 to impurity level consisting of the reversible Rh species doped in SrTiO 3 . Thus, we succeeded in constructing unique and simple Z-scheme photocatalysis systems driven by interparticle electron transfer under visible light irradiation. In addition, the (Ru/SrTiO 3 :Rh)-(BiVO 4 ) system split water under simulated sunlight (AM-1.5).

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Co(bpy) 3 ] 3+/2+ and [Co(phen) 3 ] 3+/2+ redox couples were revealed to play as electron mediators for Z-scheme photocatalyst systems composed of Ru/SrTiO 3 :Rh and BiVO 4 powders for overall water splitting under visible light irradiation. These electron mediators were effective for only the combination of SrTiO 3 :Rh with BiVO 4 . They did not work when nondoped SrTiO 3 and TiO 2 of H 2 -evolving photocatalysts and WO 3 of O 2 -evolving photocatalysts were employed. These results indicated that the affinity between photocatalysts and the Co-complex electron mediators was important. The photocatalytic activity depended on pH. Neutral pH conditions gave the highest activity for overall water splitting. Overall water splitting by the present system steadily proceeded for a long time. The Z-scheme photocatalyst system was also confirmed to split water under sunlight irradiation at the rates depending on weather. Moreover, overall water splitting by the Z-scheme photocatalyst system with the Co-complex electron mediator using a reaction cell in which the Ru/SrTiO 3 :Rh suspension was divided from BiVO 4 suspension by a membrane filter resulted in H 2 evolution separated from that of O 2 .

Two-step excitation photocatalytic systems called Z-scheme systems are attractive to achieve overall water splitting under visible light irradiation. The low activity of SrTiO 3 :Rh as a H 2 -evolving photocatalyst suppresses the overall efficiency of the Z-scheme system composed of SrTiO 3 :Rh modified with a Pt or Ru cocatalyst, BiVO 4 , and an Fe 3+ /Fe 2+ electron mediator. In this study, improvement of efficiency for water splitting over the Z-scheme system has been achieved through the preparation of highly efficient SrTiO 3 :Rh photocatalysts by hydrothermal and polymerizable complex methods. It has also been revealed that excess amounts of Sr are necessary to obtain highly active SrTiO 3 :Rh photocatalysts.Apparent quantum yields of the Z-scheme systems were improved from 0.4% to 3.9-4.2% at 420 nm when SrTiO 3 :Rh prepared by HT and PC methods was used as a H 2 -evolving photocatalyst instead of that prepared by a solid state reaction. The efficiency of the improved Z-scheme system for solar energy conversion was determined to be 0.1%.

A combination system consisting of a H2 production photocatalyst, Pt/SrTiO3:Rh, and an O2 production photocatalyst, BiVO4 or WO3, decomposed water into H2 and O2 under visible light irradiation in the presence of an Fe3+/Fe2+ redox couple as an electron mediator. O2 evolution on the BiVO4 photocatalyst was inhibited by Fe2+ ions, because of the oxidation of Fe2+ instead of water. In contrast, H2 evolution on the Pt/SrTiO3:Rh photocatalyst was enhanced when Fe3+ ions co-existed. It is due to the back-reactions between H2 and O2 to form water, and the reduction of Fe3+ by H2, which easily proceeded on the bare Pt cocatalyst surface, being efficiently suppressed by adsorption of [Fe(SO4)(H2O)5]+ and/or [Fe(OH)(H2O)5]2+ on the Pt surface. Overall water splitting was achieved with the suppression of the back-reactions even using a Pt cocatalyst. Thus, it clears that iron ions contributed to the present Z-scheme systems not only as an electron mediator but also as an inhibitor of the back-reactions.

ABSTRACTars, the With the increase monitor tr a ffi c sur volume roundii have to constantly mo ng conditions and passi n g vehicles, and low t ake extreme care operating ad urin g of a high l s evePl are which has va accuracy preca u tions demanded e nsure re q uired . In n add ition, Also, e xtreme high levelca r e of a Design Conditions for Development of the EquipmentThe conditions for the design of the equipment are given below. 1 Model of the Base MachineA two stage , 200 PS class of rotary snowplow, widely sold in the market , was taken as the model. 2 Restrictions imposed on the Base MachineWe have given priority to manual operability , considering safety aspects. Automation of Snow Throwing Operation