Photocatalytic Nanocomposites for Hydrogen Production from Water Splitting and Environmental Purification

ナノダイナミクス国際シンポジウム 平成22年1月21日(木) 於長崎大学Nagasaki Symposium on Nano-Dynamics 2010 (NSND2010), January 21, 2010, Nagasaki University, Nagasaki, Japan, Invited Lectur

Effect of Oxide Composition of Spinel-type Copper Chromites on the Catalytic Activity for the Simultaneous Removal of NOx and Soot Particulate

The catalytic activity of Cu-Cr oxides for the simultaneous removal of NO_x and diesel soot particulate has been investigated with special attention being placed on effects of the composition of oxide catalysts. The temperature programmed reaction technique in which the mixture of a catalyst and soot was heated at a constant rate in an NO+O_2 gas stream was used to evaluate the catalytic performance. Spinel-type CuCr_2O_4 was superior to CuO, Cr_2O_3 and their mechanical mixture in terms of the selectivity to NO_x reduction. The catalytic performance of Cu-Cr oxides depended significantly but complicatedly on the Cr/Cu molar ratio as well as the partial substitution of transition metal and alkali metal cations. The effect of preparation method of CuCr_2O_4 was also studied. As compared with the conventional acetate process, the citric acid-aided process gave the monophasic CuCr_2O_4 spinel at lower temperatures, and the oxides prepared by the citric acid-aided process were more active than those prepared by the acetate process

TiO 2 /SiO 2 Composite Films Immobilized on Foam Nickel Substrate for the Photocatalytic Degradation of Gaseous Acetaldehyde

The photocatalyst anatase titanium dioxide (TiO 2 ) films were immobilized via sol-gel technique on foam nickel modified with SiO 2 films as transition layer (indicated as TiO 2 /SiO 2 films). The structural properties of TiO 2 /SiO 2 composite films were characterized using TG-DSC, XRD, FE-SEM, and BET. The photocatalytic activities of immobilized TiO 2 /SiO 2 films were tested through photocatalytic degradation reactions of gaseous acetaldehyde under ultraviolet (UV) light irradiation. The substrate modification with transition layer of SiO 2 films improved the specific surface area (SSA) of substrate and the acetaldehyde adsorption on photocatalyst film enormously and resulted in great enhancement of photocatalytic activity and stability. The degradation ratio of gaseous acetaldehyde (concentration of 100 ppmv) on TiO 2 /SiO 2 photocatalysts reached 100% after 100 minutes of irradiation. The photocatalytic activity of TiO 2 /SiO 2 films reduced about 15% after 9 consecutive runs, which was more stable than that of TiO 2 films, and was completely recovered after heating at 30

Hydrogen evolution from water splitting on nanocomposite photocatalysts

The photocatalytic production of H2 in one step is potentially one of the most promising ways for the conversion and storage of solar energy. The paper overviews our recent studies on the photocatalysts splitting water into hydrogen under irradiation. The attention was mainly focused on the promotion effects of nanosized modifications in the interlayer and surface of photocatalysts for hydrogen evolution with visible light. The photocatalytic activity depended significantly on modification techniques, such as loading, proton exchange, and intercalation. The formation of a "nest" on the particle surface promoted a uniform distribution and strong combination of the nanosized particles on the surface of catalysts. By the methods of intercalation and pillaring as well as by selecting both host and guest, a large variety of molecular designed host–guest systems were obtained. Cadmium sulfide (CdS)-intercalated composites showed higher activity and stability. This activity of K4Ce2M10O30 (M=Ta, Nb) evolving H2 under visible light irradiation was enhanced by the incorporation of Pt, RuO2 and NiO as co-catalysts. Especially, the nanosized NiOx (Ni–NiO double-layer structure) greatly prompted the photocatalytic H2 evolution significantly

Effect of Oxide Composition of Spinel-type Copper Chromites on the Catalytic Activity for the Simultaneous Removal of NOx and Soot Particulate

The catalytic activity of Cu-Cr oxides for the simultaneous removal of NO_x and diesel soot particulate has been investigated with special attention being placed on effects of the composition of oxide catalysts. The temperature programmed reaction technique in which the mixture of a catalyst and soot was heated at a constant rate in an NO+O_2 gas stream was used to evaluate the catalytic performance. Spinel-type CuCr_2O_4 was superior to CuO, Cr_2O_3 and their mechanical mixture in terms of the selectivity to NO_x reduction. The catalytic performance of Cu-Cr oxides depended significantly but complicatedly on the Cr/Cu molar ratio as well as the partial substitution of transition metal and alkali metal cations. The effect of preparation method of CuCr_2O_4 was also studied. As compared with the conventional acetate process, the citric acid-aided process gave the monophasic CuCr_2O_4 spinel at lower temperatures, and the oxides prepared by the citric acid-aided process were more active than those prepared by the acetate process

Low-temperature catalysis for VOCs removal in technology and application: a state-of-the-art review

VOCs pollution is a complex issue involving a wide variability of pollutants that threatens human health and environment. Owing to the effective and economic characters, low-temperature (293–673 K) catalytic oxidation (CO) has been extensively studied for VOCs removal in research and application fields. This review examines recent progress on the VOCs catalytic oxidation with noble metal and metal oxides catalysts, and the engineering features of regenerative catalytic oxidizer (RCO), recuperative catalytic oxidizer (CO), photocatalytic oxidizer (PCO) and hybrid treatment combining adsorptive concentration/ozonation/plasma with catalytic oxidizer. The aim was to analyze the factors that relate to the low-temperature activity of catalysts, and the efficiency and economy of manifold catalytic oxidizers. It can be concluded that improving low-temperature activity of catalysts, increasing thermal recovery efficiency of oxidizers and developing hybrid treatment technologies are most effective means to control practical VOCs pollution

Recent advances in visible-light-driven photoelectrochemical water splitting: catalyst nanostructures and reaction systems

Photoelectrochemical (PEC) water splitting using solar energy has attracted great attention for generation of renewable hydrogen with less carbon footprint, while there are enormous challenges that still remain for improving solar energy water splitting efficiency, due to limited light harvesting, energy loss associated to fast recombination of photogenerated charge carriers, as well as electrode degradation. This overview focuses on the recent development about catalyst nanomaterials and nanostructures in different PEC water splitting systems. As photoanode, Au nanoparticle-decorated TiO2 nanowire electrodes exhibited enhanced photoactivity in both the UV and the visible regions due to surface plasmon resonance of Au and showed the largest photocurrent generation of up to 710 nm. Pt/CdS/CGSe electrodes were developed as photocathode. With the role of p–n heterojunction, the photoelectrode showed high stability and evolved hydrogen continuously for more than 10 days. Further, in the Z-scheme system (Bi2S3/TNA as photoanode and Pt/SiPVC as photocathode at the same time), a self-bias (open-circuit voltage V oc = 0.766 V) was formed between two photoelectrodes, which could facilitate photogenerated charge transfers and enhance the photoelectrochemical performance, and which might provide new hints for PEC water splitting. Meanwhile, the existing problems and prospective solutions have also been reviewed