Hydrothermal Preparation and Photocatalytic Activity of Hierarchically Sponge-like Macro-/Mesoporous Titania

The evolution of self-sustained reaction-rate oscillations in the catalytic oxidation of propane over a nickel foil has been studied in situ using X-ray photoelectron spectroscopy coupled with on line mass spectrometry and gas chromatography. Changes in the effective surface area and in the catalyst morphology under reaction conditions have been examined by scanning electron microscopy and a krypton adsorption technique. It is shown that the regular kinetic oscillations arise under oxygen-lean conditions. CO, CO 2 , H 2 , H 2 O, and propylene are detected as products.The conversion of propane oscillates in a range from 1% to 23%. During the half-periods with high activity, the main reaction pathway is the partial oxidation of propane: selectivity toward CO achieves 98%. In contrast, during the half-periods with low activity, the reaction proceeds through three competitive pathways: the partial oxidation of propane, the total oxidation of propane, and the dehydrogenation of propane to propylene. The driving force for the selfsustained kinetic oscillations is the periodic reoxidation of nickel. According to the Ni2p and O1s core-level spectra measured in situ, the high-active catalyst surface is represented by metallic nickel, whereas during the inactive half-periods the catalyst surface is covered with a thick layer of NiO. The intensity of O1s spectra follows the oscillations of O 2 in the gas phase during the oxidation of propane. It is found that during the induction period before the regular oscillations appear, a rough and porous structure develops because of strong reconstruction of the catalyst surface. The thickness of the reconstructed layer is approximately 10-20 µm. This process is accompanied with at least an 80-fold increase in the effective surface area compared with a clean, non-treated nickel foil, which undoubtedly leads to a drastic increase in the number of active sites. We believe that it is the main reason for the induction period always being  Corresponding author.E-mail address: vvk@catalysis.ru (V.V. Kaichev) 2 observed before the appearance of self-sustained oscillations in the catalytic oxidation of light hydrocarbons over catalysts with a low specific surface area (single crystals, foils, or wires).Moreover, without such reconstruction, the oscillations cannot arise due to low activity of such catalysts.

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“…6a,b,c). This structure is similar to a metal foam [48,49] or to hierarchically sponge-like macro-/mesoporous titania [50].…”

Section: Ex Situ Surface Morphology and Effective Surface Area Measurmentioning

confidence: 78%

Evolution of self-sustained kinetic oscillations in the catalytic oxidation of propane over a nickel foil

Каичев

Teschner

Saraev

et al. 2016

Journal of Catalysis

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“…The most commonly used organic templates were amphiphilic poly(alkylene oxide) block copolymers, such as HO-(CH 2 CH 2 O) 20 (CH 2 CH(CH 3 )O) 70 ( 17 and cetyltrimethylammonium bromide (CTAB) ( Table 1). [29][30][31][32]43,[45][46][47]87,100 TiO 2 is an interesting material for photocatalytic applications and it is regarded as the most efficient and environmentally benign photocatalyst, and it has been most widely used for photodegradation of various pollutants such as methylene blue (MB), 30,37,52,55,57 methyl orange (MO), 30,39 Escherichia coli (E. coli), 57,60 Rhodamine B (RhB) 36,[46][47][48] Rhodamine 6G (Rh6G) 29 and phenol 27,47 (Table 1). The principle of the semiconductor photocatalytic reaction is straightforward.…”

Section: Synthetic Methods For Mesoporous Titania Photocatalystmentioning

confidence: 99%

“…Many groups have used the hydrothermal method to prepare mesoporous TiO 2 nanoparticles. [41][42][43][44][45][46][47][48][49][50][51] Formation mechanism of stable porous TiO 2 . TiO 2 crystallites with low crystallinity are first prepared by a hydrolysis process in the acid system, and it can be expected that they easily form agglomerations because of the existence of some amorphous phase resulting from Ti(OH)n. 41 Subsequently, the CTAB introduction during the hydrothermal process under basic conditions can effectively disperse the agglomeration and further induce the assembly of the as-prepared crystallites.…”

Section: Hydrothermal Methodsmentioning

confidence: 99%

Mesoporous titania photocatalysts: preparation, characterization and reaction mechanisms

2011

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Titanium dioxide is a very important semiconductor with a high potential for applications in photocatalysis, solar cells, photochromism, sensoring, and various other areas of nanotechnology. Increasing attention has recently been focused on the simultaneous achievement of high bulk crystallinity and the formation of ordered mesoporous TiO 2 frameworks with high thermal stability. Mesoporous TiO 2 has continued to be highly active in photocatalytic applications because it is beneficial for promoting the diffusion of reactants and products, as well as for enhancing the photocatalytic activity by facilitating access to the reactive sites on the surface of photocatalyst. This steady progress has demonstrated that mesoporous TiO 2 nanoparticles are playing and will continue to play an important role in the protection of the environment and in the search for renewable and clean energy technologies. This review focuses on the preparation and characterisation of mesoporous titania, noble metals nanoparticles, transition metal ions, non-metal/doped mesoporous titania networks. The photocatalytic activity of mesoporous titania materials upon visible and UV illumination will be reviewed, summarized and discussed, in particular, concerning the influence of preparation and solid-state properties of the materials. Reaction mechanisms that are being discussed to explain these effects will be presented and critically evaluated.

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“…Last but not the least, the suitable electronic property and morphology with enlarged specific surface areas may also contribute to the increased photocatalytic performance. The former ensures the moderate band gap energy that can be easily excited and trigger photocatalytic process and the later ensures the efficient access of contaminant molecules to active sites and the subsequent escape of mineralized products or intermediates [37,38]. As a result, a synergistic effect of the strengthened light harvesting ability, efficient separation of charge carriers by LSPR effect, and the favorable electronic structure and morphology enables these Ag-containing bismuth-based composites to exhibit an excellent photocatalytic performance.…”

Section: Fig 3 Sem Images Of Composites Ab0 (A) and Ab4(b) And Thementioning

confidence: 99%

Ag/Bi12O17Cl2 composite: A case study of visible-light-driven plasmonic photocatalyst

Chang

Wang

Luo

et al. 2017

Molecular Catalysis

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a b s t r a c tIn this investigation, novel Ag/Bi 12 O 17 Cl 2 plasmonic composites with different Ag contents were constructed through a solvothermal and subsequent photoreduction route and fully characterized by a collection of analytical techniques. Spectroscopic results confirmed the presence and uniform dispersion of Ag nanoparticles on the 2D nanosheets of Bi 12 O 17 Cl 2 . The Ag content in composites exerted considerable influence on the extension of light-adsorption range and the enlargement of specific surface areas. The photocatalytic abilities of these Ag/Bi 12 O 17 Cl 2 composites were evaluated toward the degradation of rhodamine B (RhB) and 2,4-dichlorophenol (2,4-DCP) under the visible-light irradiation. The results demonstrated that the Ag/Bi 12 O 17 Cl 2 composites showed much higher photocatalytic efficiencies than that of pure Bi 12 O 17 Cl 2 , especially the sample with an optimal Ag content showing the best photocatalytic behavior among all tested samples. The remarkable enhancement of Ag/Bi 12 O 17 Cl 2 photocatalytic efficiency could be mainly attributed to the efficient charge separation that was induced by the localized surface plasmon resonance effect of metallic Ag, strong visible-light adsorption and the favorable morphology with enlarged specific surface areas. Eventually, the photocatalysis mechanism over Ag/Bi 12 O 17 Cl 2 composites was preliminarily proposed on the base of reactive species trapping experiments.

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Hydrothermal Preparation and Photocatalytic Activity of Hierarchically Sponge-like Macro-/Mesoporous Titania

Cited by 453 publications

References 52 publications

Evolution of self-sustained kinetic oscillations in the catalytic oxidation of propane over a nickel foil

Evolution of self-sustained kinetic oscillations in the catalytic oxidation of propane over a nickel foil

Mesoporous titania photocatalysts: preparation, characterization and reaction mechanisms

Ag/Bi12O17Cl2 composite: A case study of visible-light-driven plasmonic photocatalyst

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