A research team at the Institute for Structural and Engineering Materials, part of the National Institute of Advanced Industrial Science and Technology (AIST), has made water-soluble nanometer-sized carbon disks by oxidation of the raw material carbon black with nitric acid, to form hydrophilic functional groups on the periphery of carbon nanodisks. For the purposes of this article, we have called this material water-soluble activated carbon. When dry, the water-soluble activated carbon has an extremely small surface area, and cannot adsorb other substances. The substance is not soluble in aqueous solutions at acid pH, but is highly soluble in aqueous solutions of neutral or alkaline pH. When in solution under these conditions, or when the material has precipitated out of such solutions, the water-soluble activated carbon can adsorb many organic compounds. The researchers have confirmed that the saturation adsorption capacity for the water-soluble activated carbon is equivalent to that of normal activated carbon. The team discovered that, when in solution, the water-soluble activated carbon can adsorb the agrochemical TPN (1,3-dicyano-2,4,5,6-tetrachlorobenzene) and reduce its toxicity against the Japanese medaka fish (Oryzias latipes). From this research and a separate adsorption study, the researchers observed that the reduction in toxicity was equivalent to the adsorption of the agrochemical by the water-soluble activated carbon, thereby confirming that the toxicity of the agrochemical was eliminated through its adsorption by the water-soluble activated carbon.

The water-soluble activated carbon have an adsorption capacity equivalent to that of commercially available activated carbon, but their lack of a micropore structure means they are not as strongly adsorbent as conventional activated carbon. The structure and the characteristics of the water-soluble activated carbon are significantly different from conventional activated carbon. As the new material is water soluble and capable of reducing chemical toxicity, as shown in this research, it is expected to have a wide range of applications, such as in environmental clean-up operations.