A modified fly ash-based geopolymer as a sustainable solution for ammonia storage by sorption

The aim of the work was to evaluate the influence of three selected additives and their proportions on the sorption of ammonia on fly ash based geopolymer composites. The fly ash was alkali activated with a 10 M sodium hydroxide (NaOH) solution. Charred spent coffee grounds were used as an additive at 0.1 %, 1 %, 2 % and 3 % by weight of the dry ingredients. Hydrogen peroxide (H 2 O 2 ) was used as a foaming agent and calcium chloride (CaCl 2 ) as an active salt. The raw materials and the prepared geopolymers were characterised by X-ray diffraction, XRF, SEM and FT-IR. The results of the NH 3 -TPD test showed that among all the tested samples, four showed higher sorption compared to the reference sample. The sorption of ammonia on the reference sample was 2.43 mmol⸱g −1 . The measured NH 3 sorption showed no correlation with the surface area of the solids. Furthermore, in the case of H 2 O 2 and CaCl 2 , the measured surface area values were very similar. The results of XRD, XRF and FT-IR showed no significant difference in chemical composition when different additives were introduced, except for the sample with 30 % salt addition. The novelty of this study lies in the demonstration of the potential to prepare geopolymeric composites using fly ash and coffee waste as additives, which could be used as effective ammonia sorbents or host matrices. • NH 3 sorption on modified geopolymer composites was analyzed by NH 3 -TPD. • Addition of charred coffee grounds and H 2 O 2 increased ammonia sorption in fly ash based geopolymers. • The sample with 0.1 % of H 2 O 2 by weight of fly ash absorbed the most ammonia.