The use of activated carbon in water works and wastewater treatment plants is one way of eliminating organic micropollutants in the water cycles. In this way, the increasing pollution of the environment with drug residues, pesticides and other chemicals can be minimized. However, the large number of substances adsorb to varying degrees on activated carbon, depending on their properties which are decisive for the adsorption performance. They are mainly determined by the source material (carbon, wood, coconut husk, etc.) and the activation conditions during the manufacturing process. The actual removal of organic micropollutants, however, takes place under complex interactions with the water matrix.
The large number of interacting substances and complex mechanisms can only be determined to a limited extent by adsorption tests in the laboratory, since activated carbon is only considered as the sum of its properties, as a "black box". With the present publication we propose a different approach, in which the activated carbon is analyzed rather than the removal of micropollutants in the water. For this purpose, the ubiquitous substance carbamazepine, an anti-epileptic drug, was adsorbed onto various activated carbons, dried and then characterized with thermoanalytic methods. For this purpose, the samples were heated to 600 °C in an inert nitrogen atmosphere and the resulting gaseous pyrolysis products were analyzed.
Carbamazepine as a pure substance decomposed into two decomposition products when heated. In the adsorbed state, however, more than 55 decomposition products were formed, which are characteristic for the activated carbons, also in terms of quantity. Furthermore, these pyrolysis products were assigned to nine groups and states such as multilayer and pore-filling effects were described. Specific decomposition products for preferred adsorption sites as well as the interaction with inorganic components of the activated carbon could be detected. Furthermore, it can be assumed that the availability of hydrogen in the carbon structure of the activated carbon has a great influence on micropollutant adsorption and its thermal decomposition. A thermodynamic hypothesis has been proposed. This and future investigations with more complex adsorption systems may help to better describe and finally predict adsorption processes on activated carbons.
In addition to this Open Access publication, all raw data collected were published in a Zenodo repository.
Specific adsorption sites and conditions derived by thermal decomposition of activated carbons and adsorbed carbamazepine
Daniel Dittmann, Paul Eisentraut, Caroline Goedecke, Yosri Wiesner, M Jekel, A S Ruhl, Ulrike Braun, published in Scientific Reports 10, article no. 6695
BAM, division Physical and Chemical Analysis of Polymers