. Surface interactions during the removal of emerging contaminants by hydrochar based adsorbents from biomass

Abstract

This work investigates the capability of the activated hydrochars (HC) described in ref. [3] as adsorbents of two emergent contaminants, namely fluoxetine and nicotinic acid, in aqueous solution. Provided the structural differences between these two compounds, this study was aimed to elucidate how the dissimilar surface characteristics of the adsorbents might influence their adsorption process mechanisms. To the best of the authors´s knowledge, the removal of none of these adsorbates has been studied before by adsorption onto HC-based ACs. Adsorption studies showed that the adsorption capacity was mainly determined by the chemical nature of the adsorbents, namely the presence of specific functional groups and their ionization in aqueous solutions, while the porous structure had a secondary role. The activated carbons produced by air activation showed a higher adsorption capacity of fluoxetine, whilst the samples produced by carbon dioxide had a better performance for the removal of nicotinic acid. In general, surface acidity was advantageous for fluoxetine and detrimental for nicotinic acid removal. The adsorption mechanisms involved in each case were discussed and related to the adsorbents characteristics. The maximum adsorption capacity, Q0, given by the Langmuir model was 44.1 and 91.9 mg g-1 for fluoxetine and nicotinic acid adsorption, respectively