Chemical and thermal modification of geopolymer for efficient dye removal

In the pursuit of advancing sustainable wastewater treatment solutions in the industry, this study investigates the effect of chemical and thermal modifications on adsorbent geopolymer (GP) structure. Optimal conditions of sulfuric acid treatment and calcination temperature were determined to enhance the adsorption of the direct red dye 28 (DR28). Functional groups (FTIR), mineralogical composition (DRX), morphology (SEM–EDS), and physical properties (BET/BJH) were employed to study the effect of attack with H₂SO₄ and calcination on GP characteristics. The modified GP exhibited a high specific area (190 m² g⁻¹). Adsorption tests indicated that the Elovich model satisfactorily describes the kinetics, while the Sips model represents the isotherms. The maximum adsorption capacity achieved was 107.5 mg g⁻¹. Remarkably, the adsorption capacity was doubled with GP regeneration, allowing reuse for three cycles. Furthermore, the selectivity profile uncovers a pronounced affinity hierarchy for dyes, with direct dyes manifesting a superior attraction, followed by acid, reactive, and disperse dye categories. Analyzing the efficiency of GPAT and comparing it with other GPs, it is evident that GPAT is an efficient and versatile adsorbent, featuring a simplified production process and requiring milder temperatures than those needed for activated carbon. Additionally, the cost–benefit analysis highlights geopolymers as a more economical and efficient alternative compared to conventional adsorbents.