Photoelectrochemical glycerol oxidation on Mo-BiVO4 photoanodes shows high photocharging current density and enhanced H2 evolution.

Mo-doped BiVO4's lower efficiency can be attributed in part to exciton recombination losses. Recombination losses during photoelectrochemical water oxidation can be eliminated by using glycerol as a hole acceptor. This results in an enhanced photocurrent density. In this research, we present the synthesis of a Mo-doped BiVO4 photoelectrode with a greater photocurrent density than a traditional pristine photoanode system. Increased photon exposure duration in the presence of glycerol leads to 8 mA cm-2 increase in photocurrent density due to the creation of a capacitance layer and a decrease in charge transfer resistance on the photoelectrode in a neutral-phosphate buffer solution thus confirming the photo charging effect. Glycerol photooxidation improves the photoelectrode's rate of hydrogen evolution. Research into the effects of electrolyte and electrode potential on photoelectrodes has revealed that when the applied potential increases, the light absorbance behaviour changes following its absorption distribution over the applied potential. Under a transmission electron microscope (TEM), a unique dynamical crystal fringe pattern is found in the nanoparticles scratched from the photoelectrode.

Aerosol-Assisted Deposition for TiO2 Immobilization on Photocatalytic Fibrous Filters for VOC Degradation.

Atomization and spraying are well-established methods for the production of submicrometer- and micrometer- sized powders. In addition, they could be of interest to the immobilization of photocatalytic nanoparticles onto supports because they enable the formation of microporous films with photocatalytic activity. Here, we provide a comparison of aerosol-assisted immobilization methods, such as spray-drying (SD), spray atomization (SA), and spray gun (SG), which were used for the deposition of TiO2 dispersions onto fibrous filter media. The morphology, microstructure, and electronic properties of the structures with deposited TiO2 were characterized by SEM and TEM, BET and USAXS, and UV-Vis spectrometry, respectively. The photocatalytic performances of the functionalized filters were evaluated and compared to the benchmark dip-coating method. Our results showed that the SG and SA immobilization methods led to the best photocatalytic and operational performance for the degradation of toluene, whereas the SD method showed the lowest degradation efficiency and poor stability of coating. We demonstrated that TiO2 sprays using the SG and SA methods with direct deposition onto filter media involving dispersed colloidal droplets revealed to be promising alternatives to the dip-coating method owing to the ability to uniformly cover the filter fibers. In addition, the SA method allowed for fast and simple control of the coating thickness as the dispersed particles were continuously directed onto the filter media without the need for repetitive coatings, which is common for the SG and dip-coating methods. Our study highlighted the importance of the proper immobilization method for the efficient photocatalytic degradation of VOCs.

Multiple stressor effects on alpha, beta and zeta diversity of riverine fish.

We examined the effects of regional scale land use and local scale environmental and biotic stressors on alpha, beta and zeta diversities of native fish communities in wadeable streams and non-wadeable rivers in the Danube basin, Hungary. Relationships among land use and local scale environmental and biotic stressors were weak both in streams and rivers, suggesting that these stressors act relatively independently. Alpha diversity decreased strongly with increasing local scale environmental stressor intensity in rivers. On the contrary, its response to stressors was more obscure in streams, where the best-fit statistical model indicated the importance of the interaction between land use, local scale environmental and biotic stressors, while the secondly ranked model highlighted the negative impact of local scale environmental stressors. Analysis of variance using distance matrices provided evidence that stressors alone and in interactions explained compositional differences of pairs of study sites (beta diversity). Considering the degree of overall degradation, both local (alpha) and among-site (beta and zeta) diversity indices responded to increasing stressor intensity, generally negatively. Riverine fish communities showed higher degrees of similarity (lower beta and higher zeta) than stream fish communities. They also showed increasing similarity (i.e. homogenization) with increasing overall stressor intensity, unlike stream fish communities, which showed no relationship with overall stressor intensity. Our results suggest that the relationships between land use and local scale environmental and biotic stressors can be complex and so do their effects on biodiversity. While stressor specific indices can provide information on the role of specific stressors in some cases, the examination of overall stressor effects is needed to assess realistically the effects of anthropogenic disturbances on native fish diversity. Diversity indices that quantify among-site changes in species composition, such as measures of beta and zeta diversity, can be fruitful for better understanding the role of multiple stressors in structuring ecological communities.

Swiss Stakeholder Workshop for the SUNRISE H2020 FET-Flagship Project.

On 27 September 2019, a workshop for the Swiss stakeholders for the SUNRISE flagship project was held at Empa in Dübendorf. The workshop had the aim of community building and was attended by over 30 participants from Switzerland, France, and South Africa. The secondary purpose of the workshop was the inclusion of the previously competing ENERGY-X flagship project into a future joint project from SUNRISE and ENERGY-X. The workshop program had 20 technical presentations including posters, a panel discussion and an interactive session.

Probing the mystery of Liesegang band formation: revealing the origin of self-organized dual-frequency micro and nanoparticle arrays.

Periodic precipitation processes in gels can result in impressive micro- and nanostructured patterns known as periodic precipitation (or Liesegang bands). Under certain conditions, the silver nitrate-chromium(vi) system exhibits the coexistence of two kinds of Liesegang bands with different frequencies. We now present that the two kinds of bands form independently on different time scales and the pH-dependent chromate(vi)-dichromate(vi) equilibrium controls the formation of the precipitates. We determined the spatial distribution and constitution of the particles in the bands using focused ion beam-scanning electron microscopy (FIB-SEM) and scanning transmission X-ray spectromicroscopy (STXM) measurements. This provided the necessary empirical input data to formulate a model for the pattern formation; a model that quantitatively reproduces the experimental observations. Understanding the pattern-forming process at the molecular level enables us to tailor the size and the shape of the bands, which, in turn, can lead to new functional architectures for a range of applications.

A self-assembled, multicomponent water oxidation device.

Langmuir-Blodgett (LB) and drop-cast (DC) films prepared from [Ru(1)3][PF6]2 and Co4POM (1= 4,4'-bis((n)nonyl)-2,2'-bipyridine, Co4POM = K10[Co4(H2O)2(α-PW9O34)2]) have been evaluated as water oxidation catalysts and their electrocatalytic performances are reported; DC films evolve more O2 per unit area than LB films and the catalyst is stable on an FTO surface for ≈500-600 minutes.

Growth of nanoparticles and microparticles by controlled reaction-diffusion processes.

The synthesis of different sizes of nanoparticles and microparticles is important in designing nanostructured materials with various properties. Wet synthesis methods lack the flexibility to create various sizes of particles (particle libraries) using fixed conditions without the repetition of the steps in the method with a new set of parameters. Here, we report a synthesis method based on nucleation and particle growth in the wake of a moving chemical front in a gel matrix. The process yields well-separated regions (bands) filled with nearly monodisperse nanoparticles and microparticles, with the size of the particles varying from band to band in a predictable way. The origin of the effect is due to an interplay of a precipitation reaction of the reagents and their diffusion that is controlled in space and time by the moving chemical front. The method represents a new approach and a promising tool for the fast and competitive synthesis of various sizes of colloidal particles.

Maze solving using fatty acid chemistry.

This study demonstrates that the Marangoni flow in a channel network can solve maze problems such as exploring and visualizing the shortest path and finding all possible solutions in a parallel fashion. The Marangoni flow is generated by the pH gradient in a maze filled with an alkaline solution of a fatty acid by introducing a hydrogel block soaked with an acid at the exit. The pH gradient changes the protonation rate of fatty acid molecules, which translates into the surface tension gradient at the liquid-air interface through the maze. Fluid flow maintained by the surface tension gradient (Marangoni flow) can drag water-soluble dye particles toward low pH (exit) at the liquid-air interface. Dye particles placed at the entrance of the maze dissolve during this motion, thus exhibiting and finding the shortest path and all possible paths in a maze.

Formation of an electron hole doped film in the α-Fe2O3 photoanode upon electrochemical oxidation.

Solar hydrogen generation by water splitting in photoelectrochemical cells (PEC) is an appealing technology for a future hydrogen economy. Hematite is a prospective photoanode material in this respect because of its visible light conjugated band gap, its corrosion stability, its environmentally benign nature and its low cost. Its bulk and surface electronic structure has been under scrutiny for many decades and is considered critical for improvement of efficiency. In the present study, hematite films of nominally 500 nm thickness were obtained by dip-coating on fluorine doped tin oxide (FTO) glass slides and then anodised in 1 molar KOH at 500, 600, and 700 mV for 1, 10, 120 and 1440 minutes under dark conditions. X-ray photoelectron spectra recorded at the Fe 3p resonant absorption threshold show that the e(g) transition before the Fermi energy, which is well developed in the pristine hematite film, becomes depleted upon anodisation. The spectral weight of the e(g) peak decreases with the square-root of the anodisation time, pointing to a diffusion controlled process. The speed of this process increases with the anodisation potential, pointing to Arrhenius behaviour. Concomitantly, the weakly developed t(2g) peak intensity becomes enhanced in the same manner. This suggests that the surface of the photoanode contains Fe(2+) species which become oxidized toward Fe(3+) during anodisation. The kinetic behaviour derived from the experimental data suggests that the anodisation forms an electron hole doped film on and below the hematite surface.

Self-organised microdots formed by dewetting in a highly volatile liquid.

Dewetting induced self-organisation was used to prepare an ordered microstructure from a highly volatile liquid. Dewetting of an evaporating iron oxide precursor solute on silicon substrate resulted in arrays of microdots with nearly hexagonal and tetragonal symmetries. Ordered structures form either by stick-slip motion or fingering instability at the receding contact line of evaporating droplets. Subsequent thermal treatment at 550 °C yields crystalline Fe(2)O(3) microdots with a diameter range of 1-4 µm. The size, density and shape of the microdots can be changed by using patterned substrates with different surface energies.

Implementation of glider guns in the light-sensitive Belousov-Zhabotinsky medium.

In cellular automata models a glider gun is an oscillating pattern of nonquiescent states that periodically emits traveling localizations (gliders). The glider streams can be combined to construct functionally complete systems of logical gates and thus realize universal computation. The glider gun is the only means of ensuring the negation operation without additional external input and therefore is an essential component of a collision-based computing circuit. We demonstrate the existence of glider-gun-like structures in both experimental and numerical studies of an excitable chemical system-the light-sensitive Belousov-Zhabotinsky reaction. These discoveries could provide the basis for future designs of collision-based reaction-diffusion computers.

Spiral formation and degeneration in heterogeneous excitable media.

Spontaneous spiral formation occurs when an excitation wave is input to a heterogeneous network of low- and high-light-intensity cells projected onto a light-sensitive Belousov-Zhabotinsky reaction. The range of network conditions where spirals form is increased if two waves are input at critical time intervals. Spirals degenerate to form multiple spirals and spirals trapped within excitable cells. Spiral formation and degeneration is dependent on network excitability, cell size, and network size. Results exhibit parallels with spiral formation in excitable biological systems such as the heart.

Dynamic control and information processing in the Belousov-Zhabotinsky reaction using a coevolutionary algorithm.

We propose that the behavior of nonlinear media can be controlled dynamically through coevolutionary systems. In this study, a light-sensitive subexcitable Belousov-Zhabotinsky reaction is controlled using a heterogeneous cellular automaton. A checkerboard image comprising of varying light intensity cells is projected onto the surface of a catalyst-loaded gel resulting in rich spatiotemporal chemical wave behavior. The coevolved cellular automaton is shown to be able to either increase or decrease chemical activity through dynamic control of the light intensity within each cell in both simulated and real chemical systems. The approach is then extended to construct a number of simple logical functions.

Clusters and switchers in globally coupled photochemical oscillators.

We experimentally investigate the transition to synchronization in a population of photochemical oscillators with weak global coupling. Above a critical coupling strength the oscillators join a one-phase group or two-phase clusters. The number of oscillators in each cluster depends on the initial phase distribution, and irregular switching of oscillators between clusters is observed. The fully synchronized state emerges above a second critical coupling strength. In agreement with earlier theory, the experiments demonstrate the importance of population heterogeneity in cluster multistability.

Loss of coherence in a population of diffusively coupled oscillators.

The authors investigate the relationship between the natural frequency distribution of diffusively coupled chemical oscillators and their entrainment by pacemakers. The system consists of micrometer-sized catalyst beads which are coupled to their neighbors by diffusion of the activator/inhibitor species through the catalyst-free Belousov-Zhabotinsky (BZ) reaction solution. The frequency distribution is measured as a function of the beads' number of neighbors. With the maximum number of neighbors, either target waves or disordered patterns are observed in the reaction domain and there is a shift to higher frequencies than those observed in the natural frequency distribution. The loss of coherence between neighbor oscillators is quantified by a decrease in the phase synchronization index. The experimental results are reproduced in simulations which demonstrate that the decrease in the degree of synchronization is correlated with the appearance of a small fraction of permanently excited beads in BZ populations of high mean frequency and/or large width.

Collective behavior of a population of chemically coupled oscillators.

Experiments are performed in which a large number (approximately 10(4)) of relaxation oscillators are globally coupled through the concentration of chemicals in the surrounding solution. Each oscillator consists of a microscopic catalyst-loaded particle that displays oscillations in the concentrations of chemical species when suspended in catalyst-free Belousov-Zhabotinsky (BZ) reaction solution. In the absence of stirring, the uncoupled particles display a range of oscillatory frequencies. In the well-stirred system, oscillations appear in the surrounding solution for greater than a critical number density of particles (n(crit)). There is a growth in the amplitude of oscillations with increasing n, accompanied by a slight increase or no change in frequency. A model is proposed to account for the behavior, in which the transfer of activator and inhibitor to and from the bulk medium is considered for each particle. We demonstrate that the appearance and subsequent growth in the amplitude of oscillations may be associated with partial synchronization of the oscillators.