ChemSusChem

The cover picture illustrates the use of switchable water, an aqueous solution with a CO₂-switchable ionic strength, to expedite the settling of clay solids without making the process water permanently salty. In strip mining operations, the settling of fine solids such as clay particles from aqueous suspensions is often a time- and material-intensive process. In their Full paper on page 132, Horton and Jessop describe how calcium salts can be used to promote the settling of the solids; however, the liberated salts must then be desalinated before recycling. Using switchable water, the introduction of CO₂ increases the ionic strength of the aqueous solution by reacting with an amine additive, thus promoting clay settling. The later removal of CO₂ from the liberated water decreases the ionic strength, allowing the water to be recycled.

“If one had an easy way to decontaminate water, a method that allows the water to be recycled without expensive purification steps, then water might really live up to its green potential.” This and more about the story behind the front cover research can be found on p. 2.

The back cover picture shows the sequential steps for the conversion of wheat straw to isosorbide: organosolv pretreatment of wheat straw to delignified pulp followed by one-pot hydrolytic hydrogenation and dehydration to isosorbide with heteropoly acids and Ru/C, as described by Sels et al. on page 199. The carbon cycle is tentatively closed via CO₂ uptake from the end products (e.g. polymers, surfactants) by the wheat plants.

In this Editorial we look back on 2012 and forward to what 2013 has to offer. ChemSusChem grew very strongly in 2012, and a number of topical issues further defined the journal′s scope. From 2013 onwards, Licheng Sun will take the reigns as one of our three Chairmen, while we introduce new features aimed at making the journal more attractive. Outside of ChemSusChem, the Smart Article debuts at Chemistry–An Asian Journal while Angewandte Chemie celebrates the publication of its 125th volume!

All good things come in threes: Addition of a third component in bulk heterojunction solar cells (sensitizer or fullerene derivative) may increase the short-circuit current through enhanced light harvesting and/or can increase the open-circuit voltage through enhanced carrier mobility and modification of HOMO/LUMO energy levels. Such ternary organic solar cell systems will be reviewed in this article.

Fuel for the future? 2,5-Dimethylfuran has been the subject of many recent studies since its potential as a ‘green next-generation’ biofuel was highlighted in 2007. The chemistry of this compound is characterised by unusually strong ring-carbon-to-hydrogen bonds, and some of its derivatives are distinguished by extremely weak bonds. This combination makes the task of unravelling their chemistry, and the impacts on the environment and human health, both interesting and challenging.

Syngas as a versatile hydrogen source: Using readily available and economically favorable syngas as a convenient hydrogen source, an efficient and sustainable aqueous reduction of bio-based carboxylic acids has been achieved over a highly robust catalyst system consisting of gold nanoparticles supported on acid-tolerant single-phase monoclinic zirconia (Au/m-ZrO₂). A range of bio-based multifunctional carboxylic acids have been selectively converted into their corresponding lactones or diols in high to excellent yields.

One divided into two combined into one: The catalytic conversion of furfural into a 2,5-furandicarboxylic acid-based polyester, linked by the disproportionation of furoate to furan and 2,5-furandicarboxylate, is reported. In this manner, all carbons are utilized, demonstrating the success of combining a platform molecule from C₅ sugars (furfural) to one from C₆ sugars (2,5-FDCA).

Crosstown traffic: Further development of Li–O₂ batteries may eventually lead to their use in transportation applications. One problem that needs to be addressed is electrolyte decomposition, which has been partially mitigated by using ether- rather than carbonate-based solvents. The influence of oxygen crossover from the cathode to the anode on electrolyte, and lithium anode, decomposition in ether-based Li-O₂ batteries is investigated.

Between the sheets: Sodium-ion batteries are an attractive, low-cost alternative to lithium-ion batteries. Nitrogen-doped porous carbon sheets are prepared by chemical activation of polypyrrole-functionalized graphene sheets. When using the sheets as anode material in sodium-ion batteries, their unique compositional and structural features result in high reversible capacity, good cycling stability, and high rate capability.

It′s nano: Small and uniform chromium nanoparticles, either preformed or generated in situ, effectively catalyze the conversion of glucose into 5-hydroxymethyl furfural. The results compare favorably with those achieved by using a catalyst system based on divalent CrCl₂ in ionic liquids (ILs). In addition, the chromium nanoparticles are found in the CrCl₂/IL system, and the implications of their presence in that system is investigated.

Down to the core: A soluble molecular model of a cobalt-based oxygen-evolving catalyst has been appended to Re^I photosensitizers, giving rise to an unusual coordination complex consisting of an inorganic metal-oxo core tethered to two photo-sensitising oxidants. Substantial emission quenching of the Re^I photocentres is evident upon irradiation at 355 nm.

Sensitive dyes absorb it all: Co-sensitization of three spectrally complementary dyes on a TiO₂ film in a well-designed sequence significantly improves the photovoltaic performance of the device, and an efficiency of 8.2 % is achieved. The devices demonstrate a panchromatic response with an incident photon-to-current conversion efficiency >80 % over the entire visible spectral region from 400 to 700 nm.

Digested metals reduce oxygen: A nanoporous PdTi (NP-PdTi) alloy characterized by a 3D bicontinuous network nanostructure can be easily fabricated by a one-step mild dealloying process of PdTiAl (precursor alloy). With a ligament size as small as 6 nm, NP-PdTi shows superior electrocatalytic activity in the oxygen reduction reaction with enhanced specific and mass activities as well as higher methanol tolerance and structure stability relative to Pt/C.

Ruthenium and phosphor work wonders: Air-stable ruthenium phosphomide complexes are active catalysts in the hydrogenation of sodium bicarbonate, carbon dioxide, and carbonyl compounds. Hydrogenation proceeds with high catalyst turnover numbers in the absence of amines or other additives. The application range of these new ruthenium catalysts also includes the hydrogenation of cinnamaldehyde and benzaldehyde.

Teamwork 2.0: A highly active system for photocatalytic water reduction consisting of an Ir photosensitiser and a Pd dichloro complex as the source of catalytically active Pd⁰ is described. Additionally, the introduction of a hitherto unknown dinuclear Co complex as a water reduction centre resulted in a system with a comparably high initial activity.

Tin best or tin pest? The role of Sn extrinsic dopants in chalcopyrite AgInS₂ is investigated to understand their effects on the optical, electronic, and photoelectrochemical properties of this promising photoanode material. We found that at low amounts, Sn increased the AgInS₂ carrier concentration and photocurrent, but was detrimental at higher dopant concentrations.

Green fuels and chemicals: The enzymatic digestibility of cellulose in lignocellulosic biomass towards fermentable glucose can be increased significantly by hydrothermal pretreatment in pure water under relatively mild conditions. Appropriate selection of the pretreatment temperature and time also leads to a process liquid that can be enriched in xylose or in furfural and acetic acid.

From HMF to surfactants: Precursors of surfactant molecules are obtained by a two-step one-pot selective acetalization and transacetalization of 5-hydroxymethylfurfural with long-chain alkyl alcohols by controlling the zeolite acidity and polarity.

The use of inorganic salts to enhance clay settling in aqueous suspensions is a common industrial process. Recycling and/or treatment of this high salinity water after use are necessary environmental and economical practices but are often energetically costly. We propose the use of switchable water, a reversible ionic strength aqueous solvent, as a means to settle clays rapidly with easy recycling of the process water.

This way or that? Monoclinic zirconia has great potential as a catalyst for ketonic decarboxylation of carboxylic acids (see picture). A combined experimental and DFT study shows a route involving a β-keto acid intermediate as the kinetically preferred reaction pathway.

To sensitise and encapsulate: Ru dye-sensitised TiO₂ is encapsulated with plasma-polymerised polyallylamine to improve long-term stability under ambient conditions for photocatalytic water splitting. Using a Pd dichloro complex as the reduction catalyst and triethylamine as the electron source, a highly stable long-term performance as well as a small improvement in catalytic activity is achieved. The nanostructure is characterised by TEM as well as UV/Vis and ATR-FTIR spectroscopy.

From waste to fuel: Liquefaction bio-oils can be used as fuel in engines to produce heat and electricity or be upgraded as replacements for diesel and gasoline fuels. An integrated approach based on NMR spectroscopy and MS data is used to characterize a bio-oil obtained from the hydrothermal liquefaction of municipal organic wastes (see picture).

Platinum replacement: The phase-controlled synthesis of tungsten carbide nanoparticles from the nanoconfinement of a mesoporous graphite C₃N₄ (mpg-C₃N₄) reactive template is shown. The nanomaterials catalyze hydrogen evolution/oxidation reactions, but are inactive in the oxygen reduction reaction. Tungsten carbide is an effective cocatalyst for photocatalytic overall water splitting (see picture).

Making metathesis plus nanofiltration POSS-ible: New molecular-weight-enlarged metathesis catalysts, which bear polyhedral oligomeric silsesquioxane (POSS) tags, have been synthesized and characterized. The catalysts can be recovered from the reaction mixture by using nanofiltration techniques and can be reused. The membranes Starmem 228 and PuraMem 280 can be used to successfully separate the catalyst from the post-reaction mixtures.

Having a ball with milling: The reversible cycling of CaO adsorbents to CaCO₃ for high-temperature CO₂ capture is substantially improved by a mechanochemical approach. MgO has been used as an inert binder to help mitigate CaCO₃ sintering. Wet planetary milling of MgO into CaCO₃ allows for efficient particle size reduction and effective dispersion of MgO throughout the particles, yielding the most stable sorbents during several cycles of carbonation–calcination.

Biomass to isosorbide: A promising direct route from cellulose to isosorbide is investigated, relying on a joined action of heteropoly acids and Ru on carbon. This strategy enables fast conversions of pure microcrystalline cellulose and impure cellulose pulps into over 50 % and 60 % isosorbide, respectively.