A team from Oak Ridge National Lab have found a good use for the much-maligned fizzy drink – it turns out that they are a great source of porous carbon!

Carbonated or fizzy drinks rarely make positive headlines, with countless studies linking them to conditions such as obesity, tooth decay and diabetes. But their combination of sugars and additives such as phosphoric acids and polyelectrolytes may actually be a good thing…. If you’re a scientist on the hunt for porous carbon materials, that is.

Ultrahigh surface area carbons (USACs) are in high demand, for use in everything from batteries to gas sensing. Generally, the carbon required for these applications is produced by the high-temperature carbonization of organic material (e.g. coconut shells), followed by exposure to a harsh oxidizing environment. Both of these processes are costly and energy intensive, but alternative routes have long resulted in carbon with sub-optimal surface area and poor chemical performance.

A paper in a recent issue of Carbon [DOI: 10.1016/j.carbon.2015.05.019] may change all that. Researchers from Oak Ridge National Lab reported on a low-cost process for synthesizing high-quality USACs, using fizzy drinks as the precursor. They have achieved this using hydrothermal carbonization (HTC) of the sugars in the drinks (mainly in the form of glucose, fructose and sucrose). This approach effectively speeds up the decomposition of the sugars, and forces them to polymerize at low temperatures and under a self-generated pressure.

The team selected a series of carbonated drinks with high sugar content (13 - 15 wt%) - Coca Cola©, Pepsi©, Dr. Pepper© and Fanta©. Small quantities of each beverage were heated at 200°C for 24 hours, and all yielded dark red solids when washed and filtered. Further heat treatment of these solids produced black carbon materials with remarkably high surface areas. Fanta produced carbon with the highest specific surface area (up to 3633 m2/g) but this reaction also resulted in the lowest yield (9 wt%). The relationship between yield and temperature varied non-linearly for each drink, but because most of the additives are patented, it was not possible to determine which individual molecule that may explain this observation.

The Oak Ridge team believe that these carbon structures have the potential to be used in a new generation of high-capacity supercapacitors, thanks to their huge surface area and low cost. So, while they might be bad for our teeth, fizzy drinks may be very good for carbon chemists!

P. Zhang et al, Carbon, 93 (2015) 39–47 “Ultrahigh surface area carbon from carbonated beverages: Combining self-templating process and in situ activation” DOI: 10.1016/j.carbon.2015.05.019