Application of TiO2-loaded fly ash-based geopolymer in adsorption of methylene blue from water: Waste-to-value approach

This paper aims to explore the removal of methylene blue from wastewater using fly ash-based geopolymer (FAG) modified with titanium dioxide (TiO2) nanoparticles referred to as FAG-TiO2. Using several analytical techniques, the modified geopolymer was physically and chemically characterized. Additionally, it was investigated how pH, MB concentration, and temperature affected the MB adsorption process utilizing FAG-TiO2. Scanning electron microscopy images exhibited a porous morphology. Furthermore, transmission electron microscopy images revealed a nanostructured shape, with nanoparticles clumping together to form small channels suitable for MB adsorption. The stretching vibration of the alumina silicate was seen using the Fourier transform infrared, indicating that geopolymerization was successfully conducted. The developed FAG-TiO2 showed a remarkable capacity for MB adsorption from the aqueous phase. The Langmuir isotherm model was the bestfitting adsorption model, with a maximum adsorption capacity of 103.19 mg/g at pH 6 and 35 degrees C. The thermodynamics investigations revealed negative values for Gibbs free energy (Delta Go), emphasizing the spontaneous nature of the processes. While the positive entropy (Delta So) indicated a significant affinity between the two phases, static interactions between MB and FAG-TiO2 facilitated the adsorption process. Furthermore, desorption studies with two different chemicals were used to investigate MB retention onto FAG-TiO2. The adsorbents were desorbed using an HCl (0.5 M) reagent where the maximum MB desorption reached 41.95%. Real wastewater samples were also tested, and promising results were found, indicating the possible use of the prepared adsorbent in industrial applications.