Preparation of porous metakaolin-based geopolymer foam as an efficient adsorbent for dye removal from aqueous solution

Abstract

Dye removal from aqueous solutions as one of the dangerous and non-degradable pollutants is one of the critical environmental issues discussed today. In this research, metakaolin-based geopolymer foam adsorbent was fabricated using a templating emulsion/chemical foaming method, characterized, and utilized to remove methylene blue dye from an aqueous solution. Dye adsorption studies were performed using batch experiments and operational parameters such as contact time, initial pH solution, temperature, initial dye concentration, adsorbent dose, and pHPZC the adsorbent investigated. The various kinetic models (pseudo-first-order, pseudo-second-order, and intraparticle diffusion) and isotherms (Langmuir, Freundlich, and Temkin) were used to analyze the experiment results. The fabricated adsorbent surface includes the bulk porous structure consisting of novel flower-like hierarchical microstructures made up of dozens of nanorods building block units. The adsorption results were fitted to the pseudo-second-order kinetic with an equilibrium time of 120 min and Freundlich isotherm models. The highest methylene blue adsorption was obtained up to 90 %. Maximum adsorption capacity was obtained at 12.5 mg/g for 10 mg/L dye solution in 40 °C and pH = 13. According to the thermodynamic investigation, the methylene blue adsorption on the geopolymer foam adsorbent was performed as spontaneous and endothermic due to the negative value of the ΔG° and positive value of ΔH°. The prepared adsorbent could remove different cationic and anionic dyes from aqueous solutions but exhibited the highest adsorption efficiency towards cationic dyes. The prepared geopolymer exhibited good adsorption performance as a promising adsorbent for dye wastewater.