Fly ash-based geopolymer as a novel photocatalyst for degradation of dye from wastewater

Abstract The geopolymer synthesized by alkali-activated fly ash was firstly used as a novel photocatalyst for degradation of methylene blue (MB) dye from wastewater. The geopolymer is composed of nanoparticulates with an average particle size of about 50 nm. More than 90% of pore volume in the fly ash-based geopolymer predominately centralized on the pore size in the range of 17−700 nm. The degradation efficiency of MB dye by fly ash-based geopolymer catalyst was up to 92.79% under UV irradiation due to the synergistic effect of adsorption and semiconductor photocatalysis. The pseudo-first-order and pseudo-second-order rate equations as well as intra-particle diffusion rate equation were employed to correlate analysis for the adsorption kinetics of MB dye. The experimental data agreed well with pseudo-second-order rate equation in both cases of with UV and without UV irradiations. The intra-particle diffusion process is not the rate determining step. The photocatalytic degradation of MB dye in solution obeys third-order reaction kinetics.