Toward sustainable energy: photocatalysis of Cr-doped TiO<Subscript>2</Subscript>: 2. effect of defect disorder

The present chain of five papers considers the concept of solar-to-chemical energy conversion using TiO₂-based semiconductors. The series reports the effect of chromium on the key performance-related properties of polycrystalline TiO₂ (rutile), including electronic structure, photocatalytic activity, intrinsic defect disorder, electrochemical coupling and surface versus bulk properties. In this work, we show that the effect of chromium on photocatalytic performance of TiO₂ depends on its elemental content and the related defect disorder that is determined by oxygen activity in the oxide lattice. At high oxygen activity, chromium leads to enhanced photocatalytic performance only for dilute solid solutions (up to 0.04–0.043 at.% Cr). Higher chromium content results in a decrease of photocatalytic activity below that for pure TiO₂, despite the observed substantial decrease of the band gap. The photocatalytic performance of Cr-doped TiO₂ annealed in reducing conditions is low within the entire studied range of compositions. The obtained results led to derivation of a theoretical model representing the mechanism of the light-induced reactivity of TiO₂ with water and the related charge transfer. The photocatalytic performance is considered in terms of a competitive effect of several key performance-related properties. The performance is predominantly influenced by the concentration of titanium vacancies acting as reactive surface sites related to anodic charge transfer.

Open image in new window

Graphical abstract ?

     

Crystal Structure of a Rearranged Cage Compound, 3-Hydroxy-4-aza-8-oxoheptacyclo [9.4.1.0<Superscript>2,10</Superscript>.0<Superscript>3,14</Superscript>.0<Superscript>4,9</Superscript>.0<Superscript>9,13</Superscript>.0<Superscript>12,15</Superscript>]tetradecane

Abstract  Polycyclic hydrocarbon compounds exhibit a wide variety of biological activities, ranging from antiviral to Parkinson’s disease. Several structures such as the adamantanes have reached clinical status and are used therapeutically to treat, amongst others, neurodegenerative disorders such as Alzheimer’s. Polycyclics have also been utilised as carrier molecules to facilitate entry of drugs into the brain. The synthesis, molecular and crystal structure of a new polycyclic compound, 3-hydroxy-4-aza-8-oxoheptacyclo[9.4.1.0^2,10.0^3,14.0^4,9.0^9,13.0^12,15]tetradecane, are reported. NMR spectroscopy was applied for structure elucidation of the novel compound and a rearrangement mechanism is proposed for its formation. This compound crystallises in the orthorhombic system, space group Pbca (no. 61). The unit cell parameters are: a = 12.3763 (7), b = 11.6597 (6), c = 15.0539 (8) ?, V = 2172.3 (2) ?³ , and Z = 8 molecules in the unit cell. The reported structure was confirmed by X-ray analysis, which showed that the title molecules associate into centrosymmetric dimers via N–H···O hydrogen bonding. Index Abstract  The synthesis and structure of a new polycyclic compound, 3-hydroxy-4-aza-8-oxoheptacyclo[9.4.1.0^2,10.0^3,14.0^4,9.0^9,13.0^12,15]tetradecane, are reported in this article.      

Mechanical response of a small swimmer driven by conformational transitions

A conformation space kinetic model is constructed to drive the deformation cycle of a three-sphere swimmer to achieve propulsion at low Reynolds number. We analyze the effect of an external load on the performance of this kinetic swimmer and show that it depends sensitively on where the force is exerted, so that there is no general force-velocity relation. We discuss how the conformational cycle of such swimmers should be designed to increase their performance in resisting forces applied at specific points.     

Investigation of gain ripple in two-pump fiber optical parametric amplifiers

By using the four-sideband theory, we analyze the gain spectrum in wideband two-pump fiber optical parametric amplifiers and predict gain ripples over the flat gain region. We derive an approximation of their pseudo-periods and discuss methods for reducing their amplitudes.     

EPR investigations of SiC and SiOC nanometric powders

EPR investigations are performed in SiC and SiOC nanometric powders annealed between 1200 and 1800°C. By using different EPR frequency bands and a suitable spectra analysis, three quite different paramagnetic defects with well defined $\tilde g_i $ (i=1, 2, 3) and hyperfine $\tilde A_i $ (i=1, 2) tensors account for the EPR signal in these materials. The defects are characterized by $\tilde g_1 $ (g ₁ ^‖ =2.0046(3), g ₁ ^? =2.0023(3)), $\tilde g_2 $ (g ₂ ^‖ =2.0037(3), g ₂ ^? =2.0028(3)) and isotropic $\tilde g_3 $ (2.0030(3)) tensors. In SiC powders, the defects assignment is discussed with respect to the different SiC forms, namely α-SiC and β-SiC polytypes as well as amorphous SiC and carbon present in minor concentration in the network. In SiOC powders, the above defects are evidenced only at high annealing temperature (T _a≥1200°C) when the oxygen contained is highly reduced.     

A Novel Side-Chain Liquid Crystal Elastomer Exhibiting Anomalous Reversible Shape Change

Liquid crystalline elastomers (LCEs) have been actively investigated as stimuli-controlled actuators and soft robots. The basis of these applications is the ability of LCEs to undergo a reversible shape change upon a liquid crystalline (LC)-isotropic phase transition. Herein, we report the synthesis of a novel LCE based on a side-chain liquid crystalline polymer (SCLCP). In contrast to known LCEs, this LCE exhibits a striking anomalous shape change. Subjecting a mechanically stretched monodomain strip to LC-disorder phase transition, both the length and width of the strip contract in isotropic phase, and both elongate in LC phase. This thermally induced behaviour is the result of a subtle interplay between the relaxation of polymer main chain oriented along the stretching direction and the disordering of side-group mesogens oriented perpendicularly to the stretching direction. This finding points out potential design of LCEs of this peculiar type and possible applications to exploit.     

One-dimensional geometric random graphs with nonvanishing densities II: a very strong zero-one law for connectivity

We consider a collection of n independent points which are distributed on the unit interval [0,1] according to some probability distribution function F. Two nodes communicate with each other if their distance is less than some given threshold value. When F admits a density f which is strictly positive on [0,1], we give conditions on f under which the property of graph connectivity for the induced geometric random graph obeys a very strong zero–one law when the transmission range is scaled appropriately with n large. The very strong critical threshold is identified. This is done by applying a version of the method of first and second moments.     

Local Convergence Analysis of a Primal–Dual Method for Bound-Constrained Optimization Without SOSC

Journal of Optimization Theory and Applications - We propose a local convergence analysis of a primal–dual interior point algorithm for the solution of a bound-constrained optimization...     

Energy Storage Materials Synthesized from Ionic Liquids

The advent of ionic liquids (ILs) as eco‐friendly and promising reaction media has opened new frontiers in the field of electrochemical energy storage. Beyond their use as electrolyte components in batteries and supercapacitors, ILs have unique properties that make them suitable as functional advanced materials, media for materials production, and components for preparing highly engineered functional products. Aiming at offering an in‐depth review on the newly emerging IL‐based green synthesis processes of energy storage materials, this Review provides an overview of the role of ILs in the synthesis of materials for batteries, supercapacitors, and green electrode processing. It is expected that this Review will assess the status quo of the research field and thereby stimulate new thoughts and ideas on the emerging challenges and opportunities of IL‐based syntheses of energy materials.     

Phonon dispersion relations and mean correlated displacement for the (111) face of f.c.c. crystal

The generating coefficients of lattice Green functions have been calculated for the (111) face of f.c.c. crystal. The crystal model takes account of only central force between nearest neighbours. Phonon dispersion relations and mean correlated displacement value between nearest and next-nearest neighbours are given.