Application of TiO2-loaded fly ash-based geopolymer in adsorption of methylene blue from water: Waste-to-value approach
Johaina Alahmad, Amina BiBi, Mohammad A. Al‐Ghouti
Abstract
This paper aims to explore the removal of methylene blue from wastewater using fly ash-based geopolymer (FAG) modified with titanium dioxide (TiO 2 ) nanoparticles referred to as FAG-TiO 2 . 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-TiO 2 . 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-TiO 2 showed a remarkable capacity for MB adsorption from the aqueous phase. The Langmuir isotherm model was the best-fitting adsorption model, with a maximum adsorption capacity of 103.19 mg/g at pH 6 and 35 °C. The thermodynamics investigations revealed negative values for Gibbs free energy (ΔG o ), emphasizing the spontaneous nature of the processes. While the positive entropy (ΔS o ) indicated a significant affinity between the two phases, the positive enthalpy (ΔH o ) implies an endothermic reaction. Additionally, hydrogen bonds , n -π, and electrostatic interactions between MB and FAG-TiO 2 facilitated the adsorption process. Furthermore, desorption studies with two different chemicals were used to investigate MB retention onto FAG-TiO 2 . 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. • Fly ash-based geopolymer modified with titanium dioxide was successfully prepared. • A nanostructured shape with clumping that forms small channels was identified. • The maximum MB Langmuir adsorption capacity was 103.19 mg/g at pH 6 and 35 °C. • H-bond, n -π, and electrostatic interactions facilitated the adsorption process.