Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

Titanium Dioxide Nanomaterials: Synthesis, Properties, Modifications, and Applications

2.3. Evaluation of Photocatalytic Water Splitting 6507 2.3.1. Photocatalytic Activity 6507 2.3.2. Photocatalytic Stability 6507 3. UV-Active Photocatalysts for Water Splitting 6507 3.1. d0 Metal Oxide Photocatalyts 6507 3.1.1. Ti-, Zr-Based Oxides 6507 3.1.2. Nb-, Ta-Based Oxides 6514 3.1.3. W-, Mo-Based Oxides 6517 3.1.4. Other d0 Metal Oxides 6518 3.2. d10 Metal Oxide Photocatalyts 6518 3.3. f0 Metal Oxide Photocatalysts 6518 3.4. Nonoxide Photocatalysts 6518 4. Approaches to Modifying the Electronic Band Structure for Visible-Light Harvesting 6519

Semiconductor-based Photocatalytic Hydrogen Generation

A fundamental aim in the field of catalysis is the development of new modes of small molecule activation. One approach toward the catalytic activation of organic molecules that has received much attention recently is visible light photoredox catalysis. In a general sense, this approach relies on the ability of metal complexes and organic dyes to engage in single-electron-transfer (SET) processes with organic substrates upon photoexcitation with visible light.

Many of the most commonly employed visible light photocatalysts are polypyridyl complexes of ruthenium and iridium, and are typified by the complex tris(2,2′-bipyridine) ruthenium(II), or Ru(bpy)32+ (Figure 1). These complexes absorb light in the visible region of the electromagnetic spectrum to give stable, long-lived photoexcited states.1,2 The lifetime of the excited species is sufficiently long (1100 ns for Ru(bpy)32+) that it may engage in bimolecular electron-transfer reactions in competition with deactivation pathways.3 Although these species are poor single-electron oxidants and reductants in the ground state, excitation of an electron affords excited states that are very potent single-electron-transfer reagents. Importantly, the conversion of these bench stable, benign catalysts to redox-active species upon irradiation with simple household lightbulbs represents a remarkably chemoselective trigger to induce unique and valuable catalytic processes.






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Figure 1


Ruthenium polypyridyl complexes: versatile visible light photocatalysts.

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Visible Light Photoredox Catalysis with Transition Metal Complexes: Applications in Organic Synthesis

As a fascinating conjugated polymer, graphitic carbon nitride (g-C3N4) has become a new research hotspot and drawn broad interdisciplinary attention as a metal-free and visible-light-responsive photocatalyst in the arena of solar energy conversion and environmental remediation. This is due to its appealing electronic band structure, high physicochemical stability, and “earth-abundant” nature. This critical review summarizes a panorama of the latest progress related to the design and construction of pristine g-C3N4 and g-C3N4-based nanocomposites, including (1) nanoarchitecture design of bare g-C3N4, such as hard and soft templating approaches, supramolecular preorganization assembly, exfoliation, and template-free synthesis routes, (2) functionalization of g-C3N4 at an atomic level (elemental doping) and molecular level (copolymerization), and (3) modification of g-C3N4 with well-matched energy levels of another semiconductor or a metal as a cocatalyst to form heterojunction nanostructures. The constructi...

Graphitic Carbon Nitride (g-C3N4)-Based Photocatalysts for Artificial Photosynthesis and Environmental Remediation: Are We a Step Closer To Achieving Sustainability?

Overall water splitting to form hydrogen and oxygen over a heterogeneous photocatalyst using solar energy is a promising process for clean and renewable hydrogen production on a large-scale. The ZnGeN2–ZnO solid solution photocatalyst shows photocatalytic activity under visible irradiation. This paper deals with results of photocatalytic reactions over the (Zn1+xGe)(N2Ox) photocatalyst for overall water splitting. The photocatalyst shows high rates for overall water splitting under visible irradiation, with notable deactivation with time. This study focuses on measuring rates for H2 and O2 evolution to elucidate the cause of the deactivation. Our results showed negligible changes in the structure and the composition of the photocatalyst after the photocatalytic reaction, and thus the changes undetectable by the techniques employed should be the cause of deactivation. This paper also discusses two strategies to improve the photocatalytic activity: metal doping in the oxynitride formulation and post-calcination after nitridation. Several characterization carried out in this study led us to conclude, at the current point, that the improvement of photocatalytic activity is ascribed to the reduction in the number of defects in the photocatalyst materials.

Enhancement of photocatalytic activity of zinc-germanium oxynitride solid solution for overall water splitting under visible irradiation

Utilizing solar energy to convert CO2 into fuels and chemicals represents a promising solution to reduce reliance on fossil fuels, but it is hampered by the lack of highly-efficient catalysts. Herein, we report unique cobalt nitride/nitrogen-rich carbons (Co4N/NCs), which can work as noble-metal-free catalysts for CO2-to-CO conversion. The mass activity of Co4N/NCs is two orders of magnitude higher than those of previously reported CO2 photoreduction catalysts. The quantum yield for CO production at 450 nm reaches 7.2% with a turnover frequency per Co atom of 0.97 s-1. The electronic structure and coordinated environment of catalysts are analyzed by X-ray absorption fine structure spectroscopy and X-ray photoelectron spectroscopy. The reaction processes are investigated by in-situ diffuse reflectance infrared fourier transform spectroscopy and density functional theory calculations. Results suggest that the synergetic effects between the Co4N and the NCs can consolidate the adsorption and activation of CO2 and accelerate the interfacial electron-transfer kinetics between the Co4N/NCs catalysts and light-harvesting antenna, thereby resulting in the outstanding activity for synthesizing CO from CO2. This work offers the possibility to design Co-based host-guest topology for highly-efficient CO2 reduction.

Cobalt Nitride Anchored on Nitrogen-Rich Carbons for Efficient Carbon Dioxide Reduction with Visible Light

Boron carbon nitride (BCN) is a promising earth-abundant photocatalyst for solar energy conversion. However, the photocatalytic activities of BCN materials remain moderate because of the fast electron-hole recombination. Herein, an ordered BCN structure is fabricated by a facile one-step thermal treatment strategy. The ordered structure of BCN is directly evident from powder X-ray diffraction and high-resolution transmission electron microscopy. Importantly, it is found that the long-period ordered structure can intrinsically accelerate the separation and transfer kinetics of photogenerated charge carriers. Benefiting from these advantages, the ordered BCN structure exhibits remarkable performance for photoinduced selective oxidation of benzyl alcohol compared with the pristine BCN counterpart. This work highlights the important role of the crystal structure of light-harvesting materials in affecting electron-hole separation and at the same time points to the ample potential for improving the photocatalytic performance.

Structure‐Mediated Charge Separation in Boron Carbon Nitride for Enhanced Photocatalytic Oxidation of Alcohol

Polymeric carbon nitrides (PCNs) are a species of metal-free semiconductors that consists of only Earth-abundant carbon and nitrogen elements. The semiconducting properties of PCN were first realiz...

Diverse Polymeric Carbon Nitride-Based Semiconductors for Photocatalysis and Variations

A suitable protocol for the photocatalytic decarboxylation of carboxylic acids was developed with metal-free ceramic boron carbon nitrides (BCN). With visible light irradiation, BCN oxidize carboxy...

Xinchen Wang

Papers

Enhancement of photocatalytic activity of zinc-germanium oxynitride solid solution for overall water splitting under visible irradiation

Cobalt Nitride Anchored on Nitrogen-Rich Carbons for Efficient Carbon Dioxide Reduction with Visible Light

Structure‐Mediated Charge Separation in Boron Carbon Nitride for Enhanced Photocatalytic Oxidation of Alcohol

Diverse Polymeric Carbon Nitride-Based Semiconductors for Photocatalysis and Variations

Metal-Free Heterogeneous Semiconductor for Visible-Light Photocatalytic Decarboxylation of Carboxylic Acids