Always look on the "light" side of life: sustainable carbon aerogels.

The production of carbon aerogels based on the conversion of inexpensive and abundant precursors using environmentally friendly processes is a highly attractive subject in materials chemistry today. This article reviews the latest developments regarding the rapidly developing field of carbonaceous aerogels prepared from biomass and biomass-derived precursors, highlighting exciting and innovative approaches to green, sustainable nanomaterial synthesis. A review of the state-of-the-art technologies will be provided with a specific focus on two complimentary synthetic approaches developed upon the principles of green chemistry. These carbonaceous aerogel synthesis strategies, namely the Starbon and carbogel approaches, can be regarded as "top-down" and "bottom-up" strategies, respectively. The structural properties can be easily tailored by controlling synthetic parameters such as the precursor selection and concentration, the drying technique employed and post-synthesis temperature annealing. In addition to these parameters, the behavior of these sustainable carbon aerogel platforms in a variety of environmental and energy-related applications will also be discussed, including water remediation and fuel cell chemistry (i.e., the oxygen reduction reaction). This Review reveals the fascinating variety of highly porous, versatile, nanostructured, and functional carbon-based aerogels accessible through the highlighted sustainable synthetic platforms.

A sweet killer: mesoporous polysaccharide confined silver nanoparticles for antibacterial applications.

Silver nanoparticles (AgNP) confined within porous starch have been prepared in a simple, green and efficient manner, utilising the nanoporous structure of predominantly mesoporous starch (MS) to act as nanoparticle stabiliser, support and reducing surface. MS/AgNP materials present high surface areas (S(BET) > 150 m(2) g(-1)) and mesopore volumes (V(meso) > 0.45 cm(3) g(-1)). The interaction of the AgNP precursor and forming nanoparticle nuclei with the mesoporous domains of the porous polysaccharide, direct porosity to increasingly narrower and more defined pore size distributions, indicative of a degree of cooperative assembly. Transmission electron microscopy images indicated the presence of spherical AgNP of a size reflective of the porous polysaccharide mesopore diameter (e.g., 5-25 nm), whilst XPS analysis confirmed the metallic Ag(0) state. Materials were prepared at relatively low Ag loadings (<0.18 mmol g(-1)), demonstrating excellent antimicrobial activity in solid and liquid phase testing against Gram negative (E. coli) and positive (S. aureus) model bacteria. The resulting materials are biocompatible and present a useful solid porous carbohydrate-based polymer vehicle to control the AgNP size regime and facilitate transference to a biological environment.

Microwave assisted decomposition of cellulose: A new thermochemical route for biomass exploitation.

A microwave assisted low temperature decomposition process has been developed for production of high quality fuels from biomass. 180 degrees C was identified as key in the process mechanism, as the amorphous region of cellulose softens allowing a microwave induced rearrangement. Proton transfer is then possible under the microwave field resulting in acid catalysed decomposition. This low temperature process has been shown to be suitable for scale-up, producing a high quality char for use as a coal replacement and bio-oil suitable for upgrading to liquid fuel.

Pectin-derived porous materials.

Porous forms of pectin, a major industrial waste biomass polysaccharide, have been prepared by aqueous phase expansion routes (S(BET)>200 m(2) g(-1); V(pore)>0.80 cm(3) g(-1)). It was demonstrated that the aqueous phase acidity crucially influenced the properties of the porous pectin form. Preparation route selection allows direction of material textural and morphological properties, thought to be the result of polysaccharide configuration, and methyl ester group hydrolysis, believed to alter the lowest energy accessible metastable polysaccharide state during gel recrystallisation. The resulting low density amorphous powders or mouldable monoliths (rho(powder) approximately 0.20 g cm(-3)/rho(monolith) approximately 0.07 g cm(-3)) can be directly transformed by thermal carbonisation into low density mesoporous carbonaceous materials (e.g. rho approximately 0.27 g cm(-3) (T(p)=550 degrees C)), which possess textural and nanoscale material morphology reflective of the porous pectin precursor employed. Acidic gelation promotes methyl ester groups hydrolysis of the polysaccharide structure, generating carbons with unusual interdigitated rod-like nanoscale morphology. Importantly, the materials presented herein are produced directly from the parent porous pectin material, without the need for additive catalyst (or template) to yield highly mesoporous products (e.g. V(meso) > or = 0.45 cm(3) g(-1); polydispersity (PD)>10 nm), with accessible tuneable functionally rich surfaces. Due to the high mesoporosity (>85%), materials have potential application in chromatography, heterogeneous catalysis and large molecule adsorption strategies.

The preparation of high-grade bio-oils through the controlled, low temperature microwave activation of wheat straw.

The low temperature microwave activation of biomass has been investigated as a novel, energy efficient route to bio-oils. The properties of the bio-oil produced were considered in terms of fuel suitability. Water content, elemental composition and calorific value have all been found to be comparable to and in many cases better than conventional pyrolysis oils. Compositional analysis shows further differences with conventional pyrolysis oils including simpler chemical mixtures, which have potential as fuel and chemical intermediates. The use of simple additives, e.g. HCl, H(2)SO(4) and NH(3), affects the process product distribution, along with changes in the chemical composition of the oils. Clearly the use of our low temperature technology gives significant advantages in terms of preparing a product that is much closer to that which is required for transport fuel applications.

Versatile mesoporous carbonaceous materials for acid catalysis.

Starbon mesoporous materials were synthesized after pyrolysis of expanded starch and subsequently functionalised with sulfonated groups, providing highly active and reusable materials in various acid catalysed reactions.