Sacrificial Water Research Articles

Sunlight Selective Photodeposition of CoOx(OH)y and NiOx(OH)y on Truncated Bipyramidal BiVO4 for Highly Efficient Photocatalysis.

Facet-engineered monoclinic scheelite BiVO4 particles decorated with various cocatalysts were successfully synthesized by selective sunlight photodeposition of metal or metal oxy(hydroxide) nanoparticles onto the facets of truncated bipyramidal BiVO4 monoclinic crystals coexposing {010} and {110} facets. X-ray photoelectron spectroscopy, scanning electron microscopy, and scanning Auger microscopy revealed that metallic silver (Ag) and cobalt (oxy)hydroxide (CoOx(OH)y) particles were selectively deposited onto the {010} and {110} facets, respectively, regardless of the cocatalyst amount. By contrast, the nickel (oxy)hydroxide (NiOx(OH)y) photodeposition depends on the nickel precursor amount with an unprecedented selectivity for 0.1 wt % NiOx(OH)y/BiVO4 with a preferential deposition onto the {010} facets and the edges between the {110} facets. Moreover, these noble metal-free heterostructures led to remarkable photocatalytic properties for rhodamine B photodecomposition and sacrificial water oxidation reactions. For instance, 0.2 wt % CoOx(OH)y/BiVO4 led to one of the highest oxygen evolution rates, i.e., 1538 μmol h-1 g-1, ever described which is ten times higher than that found for bare BiVO4. The selective deposition of cobalt (oxy)hydroxide species onto the more electron-deficient facet of truncated bipyramidal monoclinic BiVO4 particles favors photogenerated charge carrier separation and therefore plays a key role for efficient photochemical oxygen evolution.

Temperature dependence of photoinduced hydrogen production and simultaneous separation in TiO2 nanotubes/palladium bilayer membrane

Temperature dependence of photoinduced hydrogen production and simultaneous separation was examined in a bilayer membrane comprised by an anodized TiO2 nanotube array (TNA) and a palladium layer. This membrane was fabricated by transferring a TNA embedded in a titanium sheet onto an electroless-plated palladium film. Sacrificial water splitting with methanol was photocatalytically performed under ultraviolet (UV) irradiation and only generated hydrogen gas was concurrently separated with the Pd layer. The H2 production rate (rH2) with the membrane at various temperatures was evaluated by using a home-made characterization system. The measured rH2 showed larger values at higher temperature of the membrane and increased abruptly after several hours of UV irradiation. This inflection behavior appeared earlier at the higher temperature of the membrane, which can be related to the permeation and adsorption characteristics of hydrogen in the Pd layer.

Synthesis and visible-light-induced sacrificial photocatalytic water oxidation of quinary oxynitride BaNb0.5Ta0.5O2N crystals

Quinary oxynitride BaNb0.5Ta0.5O2N crystals were fabricated through the partial nitridation and acidification of the KCl flux grown Ba5Nb2Ta2O15 crystals. The parameters of both the solute concentrations and cooling rates are optimized for the KCl flux growth of the larger Ba5Nb2Ta2O15 crystals with clearer crystal habits. Here, the optimal Ba5Nb2Ta2O15 crystals mainly have a hexagonal plate-like shape. After the partial nitridation and acidification, the porous BaNb0.5Ta0.5O2N crystals maintained the crystal shape of the oxide precursor and had a single-crystalline nature. For the Ba5Nb2Ta2O15 crystals, the wavelength of the absorption edge was about 707 nm. Especially, the CoOx-loaded BaNb0.5Ta0.5O2N photocatalyst demonstrated the comparatively high amount of O2 gas (150.7 μmol) during the 5 h visible-light-induced sacrificial water oxidation half-reaction, which might be achieved due to the high crystallinity and visible-light absorption property.

"The Easier the Better" Preparation of Efficient Photocatalysts-Metastable Poly(heptazine imide) Salts.

Cost-efficient, visible-light-driven hydrogen production from water is an attractive potential source of clean, sustainable fuel. Here, it is shown that thermal solid state reactions of traditional carbon nitride precursors (cyanamide, melamine) with NaCl, KCl, or CsCl are a cheap and straightforward way to prepare poly(heptazine imide) alkali metal salts, whose thermodynamic stability decreases upon the increase of the metal atom size. The chemical structure of the prepared salts is confirmed by the results of X-ray photoelectron and infrared spectroscopies, powder X-ray diffraction and electron microscopy studies, and, in the case of sodium poly(heptazine imide), additionally by atomic pair distribution function analysis and 2D powder X-ray diffraction pattern simulations. In contrast, reactions with LiCl yield thermodynamically stable poly(triazine imides). Owing to the metastability and high structural order, the obtained heptazine imide salts are found to be highly active photocatalysts in Rhodamine B and 4-chlorophenol degradation, and Pt-assisted sacrificial water reduction reactions under visible light irradiation. The measured hydrogen evolution rates are up to four times higher than those provided by a benchmark photocatalyst, mesoporous graphitic carbon nitride. Moreover, the products are able to photocatalytically reduce water with considerable reaction rates, even when glycerol is used as a sacrificial hole scavenger.

Biodegradation of dispersed Macondo crude oil by indigenous Gulf of Mexico microbial communities

Because of the extreme conditions of the Deepwater Horizon (DWH) release (turbulent flow at 1500m depth and 5°C water temperature) and the sub-surface application of dispersant, small but neutrally buoyant oil droplets <70μm were formed, remained in the water column and were subjected to in-situ biodegradation processes. In order to investigate the biodegradation of Macondo oil components during the release, we designed and performed an experiment to evaluate the interactions of the indigenous microbial communities present in the deep waters of the Gulf of Mexico (GOM) with oil droplets of two representative sizes (10μm and 30μm median volume diameter) created with Macondo source oil in the presence of Corexit 9500 using natural seawater collected at the depth of 1100–1300m in the vicinity of the DWH wellhead. The evolution of the oil was followed in the dark and at 5°C for 64days by collecting sacrificial water samples at fixed intervals and analyzing them for a wide range of chemical and biological parameters including volatile components, saturated and aromatic hydrocarbons, dispersant markers, dissolved oxygen, nutrients, microbial cell counts and microbial population dynamics. A one phase exponential decay from a plateau model was used to calculate degradation rates and lag times for more than 150 individual oil components. Calculations were normalized to a conserved petroleum biomarker (30αβ-hopane). Half-lives ranged from about 3days for easily degradable compounds to about 60days for higher molecular weight aromatics. Rapid degradation was observed for BTEX, 2–3 ring PAHs, and n-alkanes below n-C23. The results in this experimental study showed good agreement with the n-alkane (n-C13 to n-C26) half-lives (0.6–9.5days) previously reported for the Deepwater Horizon plume samples and other laboratory studies with chemically dispersed Macondo oil conducted at low temperatures (<8°C). The responses of the microbial populations also were consistent with what was reported during the actual oil release, e.g. Colwellia, Cycloclasticus and Oceanospirillales (including the specific DWH Oceanospirillales) were present and increased in numbers indicating that they were degrading components of the oil. The consistency of the field and laboratory data indicate that these results could be used, in combination with other field and model data to characterize the dissipation of Macondo oil in the deepwater environment as part of the risk assessment estimations.

Non-destructive functionalisation for atomic layer deposition of metal oxides on carbon nanotubes: effect of linking agents and defects.

The hybridisation of metal oxides and nanocarbons has created a promising new class of functional materials for environmental and sustainable energy applications. The performance of such hybrids can be further improved by rationally designing interfaces and morphologies. Atomic layer deposition (ALD) is among the most powerful techniques for the controlled deposition of inorganic compounds, due to its ability to form conformal coatings on porous substrates at low temperatures with high surface sensitivity and atomic control of film thickness. The hydrophobic nature of the nanocarbon surface has so far limited the applicability of ALD on CNTs. Herein we investigate the role of structural defects in CNTs, both intrinsic and induced by acid treatment, on coverage, uniformity and crystallinity of ZnO coatings. Furthermore, we demonstrate the potential of small aromatic molecules, including benzyl alcohol (BA), naphthalene carboxylic acid (NA) and pyrene carboxylic acid (PCA), as active nucleation sites and linking agents. Importantly, only PCA exhibits sufficiently strong interactions with the pristine CNT surface to withstand desorption under reaction conditions. Thus, PCA enables a versatile and non-destructive alternative route for the deposition of highly uniform metal oxide coatings onto pristine CNTs via ALD over a wide temperature range and without the typical surface corrosion induced by covalent functionalisation. Importantly, preliminary tests demonstrated that the improved morphology obtained with PCA has indeed considerably increased the hybrid's photocatalytic activity towards hydrogen evolution via sacrificial water splitting. The concept demonstrated in this work is transferable to a wide range of other inorganic compounds including metal oxides, metal (oxy)nitrides and metal chalcogenides on a variety of nanocarbons.

Fabrication of Porous Semiconductor Interfaces by pH-Driven Assembly of Carbon Nanotubes on Honeycomb Structured Membranes

Semiconductor hybrid structures are achieved by interfacing single-walled carbon nanotubes (CNTs) with microstructured porous membranes. Interconnectivity and interplay of nanotubes are achieved by the assistance of adaptive polymers on 3D ordered honeycomb membranes. The buildup of semiconductor interfaces is based on the nanoassembly concept, which includes (a) self-assembly of sacrificial water droplets for tailoring 3D ordered polymeric platforms; (b) directed assembly of carbon nanotubes by sequential layer-by-layer (LBL) deposition; and (c) improvement of the electrical contact between nanotubes and stabilization of the organic–inorganic interface by pH-directed forces. Unprecedented better-quality charge-transfer pathways are achieved by making a large number of connections between nanotubes rather than increasing the adsorption of conductive inorganic materials onto the membrane platforms. Electrical current transfer is generated in hybrid interfaces, wherein fine conductivity function (σ 102 S/m) is associated with high-defined porous structure, through a rationalization of the role of intermolecular forces in the assembly process.

Photocatalytic oxygen evolution using BaNbO2N modified with cobalt oxide under photoexcitation up to 740 nm

BaNbO2N was activated for photocatalytic sacrificial water oxidation and reduction by modifying the starting material for nitridation and loading appropriate cocatalysts. Addition of BaCO3 to the Ba5Nb4O15 precursor improved the crystallinity and uniformity of BaNbO2N as a nitridation product, leading to higher oxygen evolution activity. BaNbO2N generated oxygen from an aqueous AgNO3 solution under illumination up to 740 nm.

Photocatalytic Hydrogen Production and Oxygenate Photoreforming

In this perspective the current state of photo-catalytic hydrogen production is considered, focusing especially on photo-reforming reactions. There are fundamental thermodynamic and kinetic limitations to direct water splitting and a number of strategies have been developed to overcome them. These include the development of catalysts which have little activity for the back reaction of hydrogen oxidation, systems with spatially separated H2 and O2 production and the interception of the oxygen species by sacrificial water reductants. Success has been achieved in these areas over the last 20 years or so, but more needs to be done in terms of the development of high quantum efficient photo-absorbers which operate over the useable light range, and of two-photon efficient processes which can extend the useable range further. There is also an urgent need for fundamental investigations of the nature of the range of surface processes which occur during photocatalysis, and which have to occur in synchrony. Solar inputs, combined with photocatalytic technology, can drive the creation of hydrogen as a clean, sustainable fuel for the 21st century.

High quantum efficiency Pt/TiO2 catalyst for sacrificial water reduction

Platinum photodeposition on TiO2 from methanolic solution of chloroplatinic acid (CPA) is investigated to determine the conditions that give optimum photocatalytic activity towards dehydrogenation of methanol. Conditions favoring nucleation of Pt islets rather than their autocatalytic growth enhance the catalytic activity. Photoplatinization from idoplatinic acid, adsorbing more strongly on TiO2 than CPA produced more active Pt/TiO2 catalysts. The best catalyst prepared from CPA yielded H2 from 12.5% methanol solution at a quantum efficiency of 23.9% whereas for idoplatinic acid based catalysts, the quantum efficiency increased to 42.5%.

Sacrificial water photocleavage using Nb-doped TiO2 fine particles under band gap irradiation

Ultrafine powders of TiO2 doped with Nb5+ up to 10 mol% are produced by the hydrothermal procedure at 150–180 C and 1–4 MPa. Aqueous suspensions of these powders do not produce H2 on band gap irradiation, even after Pt-loading. H2 is evolved only in presence of a hole scavenger, such as EDTA. H2-evolution capacity of TiO2 is enhanced up to ∼0.3 mol% Nb and reverses the trend at higher Nb-concentrations. H2-yield is not related to anatase/rutile phase content. The decrease in H2 production with TiO2:Nb is due to the Schottky type of defect centres with donor character, that are charge-compensatively formed in TiO2 and act as electron traps. The accumulation of electrons in Nb-doped TiO2 is supported by the electron paramagnetic resonance and the current potential measurements under illumination of the slurry electrode cells.

Zum Mechanismus der Photoreduktion von Wasser mit Ruthenium‐trisbipyrazil als Sensibilisator

On the Mechanism of the Photoreduction of Water with Ruthenium‐trisbipyrazil as SensitizerOxidative and reductive primary steps can be differentiated in using Ru(bipy) and Ru(bipz), respectively, as sensitizers in a photochemically induced, Pt‐catalyzed sacrificial water reduction. Experimental evidence for the reductive primary step and kinetic data are given for the electron transfer to methylviologen as relay compound.