Solution combustion synthesis (SCS) is shown to be versatile for the rapid-one-pot synthesis of three compounds and four polymorphs in the Cu−V−O ternary family: α-CuV 2 O 6 , αand β-Cu 2 V 2 O 7 , and γ-Cu 3 V 2 O 8. These compounds feature copper/vanadium stoichiometric ratios ranging from 1:1 to 3:1; their structural, electronic, optoelectronic, and photoelectrochemical attributes were comprehensively characterized by a combination of theoretical and experimental techniques. The main contribution of the present study is the demonstration that a range of stoichiometries in this compound family can be derived simply by tuning the precursor mole ratio in the SCS procedure. The Cu−V−O family of samples, derived by SCS, is shown to exemplify the strong effect of compound stoichiometry on the optoelectronic and photoelectrochemical properties. Overall, α-CuV 2 O 6 showed the best performance, rooted in the direct nature of the optical transition in this material. Finally, SCS is very timeefficient and the various compositions can be obtained in a matter of minutes, as opposed to hours or even days in classical solution-based or ceramic synthesis routes.

This review article addresses areas where solid-state chemistry concepts can contribute to the on-going search for a "magic bullet" inorganic semiconductor that can efficiently split water or reduce CO 2 . First, a methodology to visualize complex ternary oxide combinations is outlined using 31 examples based on copper in both +1 and +2 oxidation states. Then the synthetic aspects are reviewed followed by a discussion of the structural characteristics. The optoelectronic aspects are considered next, culminating the review with the state-of-the-art in the practical applicability of these materials in solar fuels photogeneration and environmental (e.g., azo dye) remediation.

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The ternary compound, CuBi2O4, a 1:1 stoichiometric derivative of the two component oxides CuO and Bi2O3, has attracted attention from the solar water splitting and photocatalysis communities as a p-type semiconductor responsive to visible light. This study demonstrates that solution combustion synthesis (SCS) can be used to prepare powders not only of this compound but also nanocomposites with either CuO or Bi2O3 in excess. This was simply done by tuning the SCS precursor mixture composition. The synthesized crystalline samples were characterized by powder X-ray diffraction (with Rietveld refinement for phase purity), diffuse reflectance UV–visible spectroscopy, electron microscopy, and photoelectrochemical (PEC) techniques. The band structure and photoactivity of these oxides were probed by linear sweep voltammetry and by measuring their photoaction spectra (internal photon-to-electron conversion efficiency vs wavelength). The photoactivity (attributed to hydrogen evolution and CO2 photoreduction) was considerably improved in the CuO/CuBi2O4 nanocomposites because of electron transport of the photogenerated charge carriers between the CuBi2O4 and the CuO nanoparticles.

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Centrifuge model tests and finite element (FE) analysis have been conducted to study the penetration of spudcan foundations in uniform clay with nominally constant strength with depth. In particular, the transition between shallow penetration, with soil heaving to the ground surface, and deep penetration, with a localised flow-round mechanism, has been investigated. This transition governs the onset of back-flow and hence the depth of soil lying on the installed spudcan, which in turn influences the bearing capacity and also the potential for suction to develop and hence the uplift capacity and moment resistance of the foundation. The maximum cavity depth above the spudcan prior to any back-flow is therefore a critical issue for spudcan assessment in clay. In the centrifuge model tests, a half-spudcan model penetrating against a transparent window has been used to visualise the soil flow mechanisms around the spudcan during penetration. The formation of a cavity above the spudcan is revealed by both centrifuge modelling and FE analysis. It is found that there are three distinct penetration mechanisms during spudcan installation: during initial penetration, an open cavity is formed with vertical walls; with further penetration, soil flows partially around the spudcan into the cavity; during deep penetration, the spudcan is fully embedded and the soil flow mechanism is entirely localised. Over the wide range of normalised soil strengths explored, the soil back-flow in the second stage was shown to be due to a flow failure that was triggered by the spudcan penetration and not by wall failure, that is, the collapse of the vertical sides of the soil cavity. This observation is supported by FE analysis. The cavity depth due to flow failure is much shallower than the criterion for wall failure that is incorporated in current design guidelines. Instead, a new design chart and expression is suggested with the normalised cavity depth expressed as a function of the soil shear strength, normalised by the effective unit weight of the soil and the spudcan diameter.

This study addresses a perennial problem in the synthesis of copper vanadates, namely, that of phase purity. A time-efficient solution combustion synthesis (SCS) was employed for obtaining α-CuV2O6 in a polycrystalline powder form in a matter of minutes. Admixture of the final product with α-Cu2V2O7 or V2O5 was avoided by a combination of careful pH control of the SCS precursor mixture and by a postsynthesis NaOH wash. The phase purity of the resultant product was demonstrated by Rietveld refinement of the X-ray diffraction data, energy-dispersive X-ray analyses, and laser Raman spectroscopy. Photoelectrochemical (PEC) measurements showed the material to be an n-type semiconductor. Possible applicability of α-CuV2O6 in PEC devices designed for solar water splitting hinges on a comprehensive study of its structural, optical, magnetic, and optoelectronic attributes; this was done by a combination of theory and experiment. Intensity-modulated photocurrent spectroscopy on thin film samples permitted an assessment of the balance between charge transfer and surface recombination, underlining that the charge separation efficiency determined the photocurrent magnitude. Finally, experiments on the PEC stability of this material on prolonged (∼4 h) irradiation revealed self-healing behavior induced by incipient photocorrosion product layer formation on the oxide semiconductor surface.

Installation of independent-legged jack-up rigs in sea-bed sediments where a strong layer overlays weaker soil can lead to catastrophic ‘punch-through', with potential leg buckling or toppling of the unit. Although approximate methods of analysis exist for estimating the penetration resistance, these do not account for the distortion of the upper layer as it punches through into the lower layer and there has been only limited visual depiction of the failure mechanism that occurs for the case of strong clay overlying weaker soil. This paper reports results of centrifuge model tests undertaken to provide insight into spudcan foundation behaviour during undrained vertical penetration through a stronger clay layer into weaker material, varying the strength ratio between lower and upper soil layers, the thickness of the upper layer relative to the spudcan diameter and the strength gradient of the lower layer. The model tests included half-spudcan tests against a transparent window, allowing the soil flow to be captured continuously by a digital camera and subsequently quantified through particle image velocimetry (PIV) analysis, and separate full-spudcan tests to measure the penetration resistance. Four interesting aspects of the soil flow mechanisms were identified: (a) vertically downwards motion of the soil and consequent deformation of the layer interface; (b) trapping of the stronger material beneath the spudcan, with this material being carried down into the underlying soft layer; (c) delayed back-flow of soil around the spudcan into the cavity formed above the spudcan; (d) eventual localised flow around the embedded spudcan. The effect of normalised layer soil properties and geometry on the soil flow mechanisms and the form of the penetration resistance profile is discussed in the context of the likelihood and severity of punch-through failure. Typical critical failure modes involved punching shear, with clear shear planes in the shape of a truncated cone forming in the upper layer below the spudcan. Potential punch-through, with a peak in penetration resistance followed by some reduction, occurred for almost all cases investigated. The reduction in resistance became more severe as the strength ratio of the underlying layer to the upper layer reduced, and also as the upper layer thickness increased. The failure modes assumed by the currently available recommended practices are not consistent with those observed from the study, suggesting a more rational approach is needed.