No abstract

The outstanding potential of mesoporous carbonaceous materials [1] requires a methodology that grants control over their surface chemistry and the distribution of pore sizes. The best current method that achieves control over pore-size distribution is the templating method. A typical procedure [1c] involves filling mesoporous silica with a carbon precursor (e.g. sucrose), which is subsequently carbonized through a series of high-temperature processes. The template is then removed by using hydrofluoric acid or caustic soda. The resultant activated carbons produced by this method possess wellordered mesoporous structures with a large specific volume and physical properties amenable to a broad range of applications.[2] However, highly aggressive chemicals involved limit this approach to the production of stable graphitic carbons with inert hydrophobic surfaces. [3] To functionalize and open up new chemistry, further difficult chemical modifications are required. This is at the cost of reducing the availability of the mesopores.[4]Herein we report a novel approach for the generation of a new family of mesoporous carbonaceous materials with surfaces ranging from hydrophilic to hydrophobic, which is controlled by the degree of carbonization. The method utilizes the natural ability of the amylose and amylopectin polymer chains within the starch granules to assemble into an organized nanoscale lamellar structure, which consists of crystalline and amorphous regions.[5] Our strategy was to synthesize mesoporous carbons (hereinafter referred to as "starbons") by using mesoporous expanded starch [6] as the precursor without the need for a templating agent. This process is gentle and provides the opportunity to produce a whole range of mesoporous carbon-based materials from starch to activated carbon, including amorphous oxygencontaining carbons that have many applications, [7] such as catalysis, [7a, b] adsorption, [7c] and medicine, [7d, e] owing to their varied surface functionalities.The approach described is illustrated in Scheme 1. First, a simple process of gelatization in water opens up and disorders the dense biopolymer network, [8] after which it partially recrystallizes during a process of retrogradation.[9] Exchanging water with a lower-surface-tension solvent (usually ethanol) prevents collapse of the network structure during the drying process. After drying, the expanded mesoporous starch is obtained. In the final stage of the process, mesoporous starch is doped with a catalytic amount of organic acid (e.g. para-toluenesulfonic acid) and heated under vacuum. This enables fast carbonization and fixing of the mesoporous structure. Heating at different temperatures, ranging from 150 to 700 8C has produced a variety of mesoporous materials from amorphous carbons to graphite-like activated carbons. Native starch granules do not produce mesoporous materials when carbonized. This indicates that the formation of expanded starch as a precursor to starbon is crucial.

Research into renewable bioresources at York and elsewhere is demonstrating that by applying green chemical technologies to the transformation of typically low value and widely available biomass feedstocks, including wastes, we can build up new environmentally compatible and sustainable chemicals and materials industries for the 21st century. Current research includes the benign extraction of valuable secondary metabolites from agricultural co-products and other low value biomass, the conversion of nature's primary metabolites into speciality materials and into bioplatform molecules, as well as the green chemical transformations of those platform molecules. Key drivers for the adoption of biorefinery technologies will come from all stages in the chemical product lifecycle (reducing the use of non-renewable fossil resources, cleaner and safer chemical manufacturing, and legislative and consumer requirements for products), but also from the renewable energy industries (adding value to biofuels through the utilisation of the chemical value of by-products) and the food industries (realising the potential chemical value of wastes at all stages in the food product lifecycle).

Novel supported palladium catalysts have been developed based on chitosan as a support. These catalysts display excellent activity in the Suzuki and Heck reactions.

A new concept is demonstrated for an integrated close to zero waste wheat straw biorefinery combining two novel green technologies, CO 2 extraction and low temperature microwave pyrolysis, to produce a variety of products, including energy and CO 2 which can be internally recycled to sustain the processes. CO 2 adds value to the process by extracting secondary metabolites including fatty acids, wax esters and fatty alcohols. Low temperature microwave pyrolysis (<200 C) is shown to use less energy and produce higher quality oils and chars than conventional pyrolysis. The oils can be fractionated to produce either transport fuels or platform chemicals such as levoglucosan and levoglucosenone. The chars are appropriate for co-firing. The quality of the chars was improved by washing to remove the majority of the potassium and chlorine present, lowering their fouling potential. The economic feasibility of a wheat straw biorefinery is enhanced by intergrating these technologies.