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What problem was the article looking to address?

 

In order to convert biomass to biofuel, a process called depolymerization needs to take place, where the chemical bonds that link each of the glucose molecules together, called glycosidic bonds, can be broken to produce individual sugars from a cellulose molecule. This crucial process is the most expensive step in the production of biofuels and has recently become the major challenge for scientists to overcome as they search for an economical, efficient, and renewable source of energy to replace fossil fuels. This paper hopes to introduce a much cheaper depolymerization method by using a renewable silica surface, which is much less costly than enzymes and does not need strongly acidic conditions to activate the glycosidic bonds.

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Research synopsis & accomplishments

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Drawing inspiration from biological catalysts, the Katz group found that a solid silica surface, which presents an ensemble of reactive groups known as silanols, mimics the essential active groups within an enzyme. By having this “pseudo-continuum of active sites on a surface,” the group was able to do reactions similar to those done in nature, without complex and intricate positioning of atoms that enzymes facilitate. Essentially, if a strand of cellulose can get close to the silica surface, then activation and hydrolysis of the glycosidic bonds will occur. Postdoctoral Scholar in the Katz Group, Oz Gazit, determined a method to get the cellulose strands close enough for the reaction to take place. His project involved synthesis of a new class of materials that were the first composites between molecular strands of cellulose absorbed on the surface of silica. He saw that as the interaction between the silica surface and the cellulose strands increased, the rate of hydrolysis of the glycosidic bonds increased because those bonds by the surface were being activated.  Thus, the more silanol groups on the silica--the more efficient the depolymerization process. The observed hydrolysis rate was over a hundred times more reactive than cellulose conventionally pretreated. As Professor Katz explained, “This presented a new mechanism by which we could breakup biomass under very mild conditions––using pH of 4 which is very very mild compared to concentrated sulfuric acid breaking up the same bonds.”

One problem to this initial approach is that it requires high temperature of 100 ºC, which they determined also breaks the bonds that comprise the silica, thus degrades the catalyst. Currently, the group is looking towards other types of materials that function similar to silica, but are less prone to degradation, such as carbon. Carbon materials also adsorb these long cellulose chains, and by decorating the carbon materials with acid groups you can actually make glucose by just having water as the medium. Despite this drawback when using silica for biomass depolymerization, the Katz group is continuing to develop and commercialize their cellulose-coated silica surface technology, as it is a convenient way to make the silica surface repel water with many potential applications.