Adsorption efficiency and photocatalytic activity of fly ash-based geopolymer foam mortar

Abstract

Fly ash-based geopolymer foam mortar (GFM) was used as an adsorbent material to methylene blue (MB) and also the dye removal material using the photocatalytic mechanism. The GFM, containing 50 wt% river sand aggregate, was prepared to have approximately 46% open porosity, pore size distribution between 0.01 and 3.5 mm, and water permeability of 0.2 cm/s. The variation of adsorption efficiency and adsorption capacity with the contact time of the GFM was first evaluated using various GFM dosages (10, 20, 50, 80, and 100 g/L). The adsorption efficiency at equilibrium (AEe) was found to linearly increase, while adsorption capacity (qae) exponentially decayed, with an increase of loading dosages. The photocatalytic removal efficiency of ~100% was obtained with 50, 80, and 100 g/L GFM loading dosages, with a shorter time at higher dosages. The GFM could be reused, without regeneration, for 5 cycles. The AEe and qae for each reused cycle did not noticeably change suggesting the reusability. The photocatalytic removal efficiency, however, was found to decrease with an increase of the reused cycle. After the 5th cycle, the highest removal efficiency was reduced to ~70%. The attempts to treat the GFMs with hydrochloric (HCl) and phosphoric (H3PO4) acid to reduce the excess alkaline did not give satisfactory results as expected. The photocatalytic removal efficiency had subsided after the treatment with both acids.