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

Adsorption of dyes and heavy metal ions by chitosan composites: A review

The research leading to these results has received funding (J.G., B.S.) from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement no. 335746, CrystEng-MOF-MMM. T.R. is grateful to TUDelft for funding. G.P. acknowledges the A. von Humboldt Foundation for a research grant. A.C., I.L. and F.X.L.i.X. thank Consolider-Ingenio 2010 (project MULTICAT) and the ‘Severo Ochoa’ programme for support. I.L. also thanks CSIC for a JAE doctoral grant.

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Metal–organic framework nanosheets in polymer composite materials for gas separation

Review of global 2.1-1.8 Ga orogens: implications for a pre-Rodinia supercontinent

The nanometer-scaled pore systems of gas shale reservoirs were investigated from the Barnett, Marcellus, Woodford, and Haynesville gas shales in the United States and the Doig Formation of northeastern British Columbia, Canada. The purpose of this article is to provide awareness of the nature and variability in pore structures within gas shales and not to provide a representative evaluation on the previously mentioned North American reservoirs. To understand the pore system of these rocks, the total porosity, pore-size distribution, surface area, organic geochemistry, mineralogy, and image analyses by electron microscopy were performed. Total porosity from helium pycnometry ranges between 2.5 and 6.6%. Total organic carbon content ranges between 0.7 and 6.8 wt. %, and vitrinite reflectance measured between 1.45 and 2.37%. The gas shales in the United States are clay and quartz rich, with the Doig Formation samples being quartz and carbonate rich and clay poor. Higher porosity samples have higher values because of a greater abundance of mesopores compared with lower porosity samples. With decreasing total porosity, micropore volumes relatively increase whereas the sum of mesopores and macropore volumes decrease. Focused ion beam milling, field emission scanning electron microscopy, and transmission electron microscopy provide high-resolution (∼5 nm) images of pore distribution and geometries. Image analysis provides a visual appreciation of pore systems in gas shale reservoirs but is not a statistically valid method to evaluate gas shale reservoirs. Macropores and mesopores are observed as either intergranular porosity or are confined to kerogen-rich aggregates and show no preferred orientation or align parallel with the laminae of the shale. Networks of mesopores are observed to connect with the larger macropores within the kerogen-rich aggregates.

Characterization of gas shale pore systems by porosimetry, pycnometry, surface area, and field emission scanning electron microscopy/transmission electron microscopy image analyses: Examples from the Barnett, Woodford, Haynesville, Marcellus, and Doig units

Three-dimensional (3D) data represent the basis for reliable quantification of complex microstructures. Therefore, the development of high-resolution tomography techniques is of major importance for many materials science disciplines. In this paper, we present a novel serial sectioning procedure for 3D analysis using a dual-beam FIB (focused ion beam). A very narrow and reproducible spacing between the individual imaging planes is achieved by using drift correction algorithms in the automated slicing procedure. The spacing between the planes is nearly of the same magnitude as the pixel resolution on scanning electron microscopy images. Consequently, the acquired stack of images can be transformed directly into a 3D data volume with a voxel resolution of 6 x 7 x 17 nm. To demonstrate the capabilities of FIB nanotomography, a BaTiO3 ceramic with a high volume fraction of fine porosity was investigated using the method as a basis for computational microstructure analysis and the results compared with conventional physical measurements. Significant differences between the particle size distributions as measured by nanotomography and laser granulometry indicate that the latter analysis is skewed by particle agglomeration/aggregation in the raw powder and by uncertainties related to calculation assumptions. Significant differences are also observed between the results from mercury intrusion porosimetry (MIP) and 3D pore space analysis. There is strong evidence that the ink-bottle effect leads to an overestimation of the frequency of small pores in MIP. FIB nanotomography thus reveals quantitative information of structural features smaller than 100 nm in size which cannot be acquired easily by other methods.

Three‐dimensional analysis of porous BaTiO3 ceramics using FIB nanotomography

FIB-nanotomography (FIB-nt) is applied to record high-resolution 3D pore networks from cementitious materials. Based on these data, it is examined as to why the pore size distribution (PSD), which is obtained from traditional analysis by mercury intrusion porosimetry (MIP), principally deviates from the findings that are achieved by common back-scattered electron image analysis. The paper does not reflect the vulnerability of the physical model assumptions, but merely focuses on the fundamental issues of the geometrical definition of a PSD. A computationally fast approach for the PSD assessment from 3D data as well as for the simulation of MIP is presented and the varying concepts for the definition of a PSD are compared with each other.

Contradicting Geometrical Concepts in Pore Size Analysis Attained with Electron Microscopy and Mercury Intrusion

Adsorption of polyelectrolytes and its influence on the rheology, zeta potential, and microstructure of various cement and hydrate phases.

This parametric study links the molecular structure of a carboxylate-type of superplasticizer with their performance in cement pastes with different C3A-contents. Beside the variation of the C3A-content, the experimental synthesized superplasticizers have been varied by polyethylene-oxide side chain density and length. The connection between the superplasticizers, their effect on workability properties and retardation phenomenon and the dependency of C3A-content in the cement paste has been investigated.

The characteristic interaction phenomenons between different PCE-architectures and different C3A-contents have been examined by calorimetric, rheological, adsorption, and zeta potential measurements. This study shows that with decreasing side chain density the PCE molecules adsorb stronger and thus, lower the yield stress of a cement paste by steric stabilization. It is also shown that PCE molecules with long side chains delaying the setting of the cement paste to less extend than PCE molecules with shorter side chains. Consequently, in terms of optimization of the molecular architecture, good workability can be achieved by addition of highly charged PCE with long side chains. The latter minimizes undesired retardation phenomena.

Interaction of polycarboxylate-based superplasticizers with cements containing different C3A amounts

A multi-method approach was used for the investigation and comparison of alkali-activated slag binders (AAS), pure slag and ordinary Portland cement (OPC). X-ray fluorescence, X-ray powder diffraction, granulometry, calorimetry, thermo-gravimetric analysis and environmental scanning electron microscope investigations of the microstructure with energy dispersive X-ray analyses were used to characterise the cements and their hydrate phases. In addition, the chemical composition of the pore solution, including the different sulphur-containing ions, was analysed. The precipitation mechanisms during binder hydration in the AAS and OPC systems exhibit significant differences: in AAS the formation of the ‘outer product’ C-S-H is much faster than in OPC. The high Si concentrations in the pore solution during the early hydration of AAS are related to the fast dissolution of Na-metasilicate. The fast reaction of Na is an important factor for the voluminous precipitation of C-S-H within the interstitial space alread...

Lorenz Holzer

Papers

Three‐dimensional analysis of porous BaTiO3 ceramics using FIB nanotomography

Contradicting Geometrical Concepts in Pore Size Analysis Attained with Electron Microscopy and Mercury Intrusion

Adsorption of polyelectrolytes and its influence on the rheology, zeta potential, and microstructure of various cement and hydrate phases.

Interaction of polycarboxylate-based superplasticizers with cements containing different C3A amounts

Hydration of alkali-activated slag: comparison with ordinary Portland cement