Specific adsorption sites and conditions derived by thermal decomposition of activated carbons and adsorbed carbamazepine

Abstract

The adsorption of organic micropollutants onto activated carbon is a favourable solution for the treatment of drinking water and wastewater. However, these adsorption processes are not sufficiently understood to allow for the appropriate prediction of removal processes. In this study, thermogravimetric analysis, alongside evolved gas analysis, is proposed for the characterisation of micropollutants adsorbed on activated carbon. Varying amounts of carbamazepine were adsorbed onto three different activated carbons, which were subsequently dried, and their thermal decomposition mechanisms examined. The discovery of 55 different pyrolysis products allowed differentiations to be made between specific adsorption sites and conditions. However, the same adsorption mechanisms were found for all samples, which were enhanced by inorganic constituents and oxygen containing surface groups. Furthermore, increasing the loadings led to the evolution of more hydrated decomposition products, whilst parts of the carbamazepine molecules were also integrated into the carbon structure. It was also found that the chemical composition, especially the degree of dehydration of the activated carbon, plays an important role in the adsorption of carbamazepine. Hence, it is thought that the adsorption sites may have a higher adsorption energy for specific adsorbates, when the activated carbon can then potentially increase its degree of graphitisation. Increasing amounts of pharmaceuticals enter the water bodies and are detected all over the world 1-3. Many of them are persistent and may accumulate within water cycles 4-6. These organic micropollutants already show adverse effects in aquatic ecosystems despite their comparably low concentrations 7-9. Therefore, technical measures are introduced as advanced wastewater treatment 10. One of the favoured techniques is the removal by adsorption onto activated carbon 11,12. Activated carbon has been used in water purification for more than hundred years. In modern times, we face more ecological and economical challenges that require the accurate prediction of removal efficiencies prior to the upgrade of wastewater treatment plants. Hence, several approaches have been applied to gain fast and efficient predictions through laboratory experiments and the optimization of operating parameters through data driven modeling 13-16. The removal of the target substances has been shown to be strongly influenced by the composition of the waters and that of the activated carbons used in the removal 17,18. The underlying adsorption processes have been extensively described in theory and investigated experimentally 19,20. However, adsorption in the liquid phase has been proven to be much more complicated than adsorption in gas phases, especially in complex water matrices that are governed by the presence of dissolved organic matter, the ionic strength and the pH value 21-23. Hence, both the adsorbate solution and the adsorbent, are mutually influenced. Moreover, activated carbon has a highly heterogeneous pore stru...

Lignin activated carbon obtained by a environmentally friendly green production process using deep eutectic solvents

“…The results of this study are consistent with those reported by Dittmann et al ., 71 who found that activated carbon prepared by chemical activation with zinc chloride had higher thermal stability than those prepared by physical activation. However, they are different from those reported by Kaya et al 72 .…”

“…The results of this study are consistent with those reported by Dittmann et al, 71 who found that activated carbon prepared by chemical activation with zinc chloride had higher thermal stability than those prepared by physical activation. However, they are different from those reported by Kaya et al 72 who found that activated carbon prepared from pistachio shells by chemical activation with zinc chloride had lower thermal stability than those prepared by physical activation.…”

Characterization of activated carbons for water treatment using TGA-FTIR for analysis of oxygen-containing functional groups

“…It is therefore most likely that the dominant adsorption interactions are dispersive forces. They occur between the aromatic carbon structures (graphite, graphene) present in high content in all PACs and the dibenzazepine moiety of the adsorbate molecule with a flat structure (Dittmann et al 2020).…”

Porous sulfur polymers for effective aqueous-phase organic contaminant removal – a low-cost sustainable material

“…In addition, the amide group of caffeine molecule can form NH/π geometries of face-on type with benzene rings with energies higher than 40 kJ mol − 1 52 and therefore benzene rings can interact strongly with amide groups wing to their higher π-π stack bonding energies and hydrogen bonding 53,54 . However, due to the high free adsorption energy, it is expected that caffeine molecules had integrated into the PSPs structure, as Dittmann et al 55 observed in their studies with carbamazepine and activated carbons. Nevertheless, further studies should be conducted to investigate the adsorption mechanisms of caffeine and other organic pollutants into PSPs and also the effects of using other monomers on the adsorption properties.…”