Hydroxyapatite incorporated geopolymer porous adsorbent for efficient removal of copper ions and ciprofloxacin

Abstract Sintering is a promising surface modification method for geopolymers in improving their ability to coadsorb heavy metals and antibiotics. However, geopolymer usually requires high sintering temperature (1000–1200°C), making it energy intensive. Therefore, researchers are paying more attention on the synthesis of low‐temperature sintered geopolymer adsorbents for heavy metals and antibiotics. In this regard, calcium‐based geopolymer can lower the sintering temperature due to its less thermal stability and exhibit more pores and wider cracks during heat exposure. However, no research has been done on the development of low‐temperature sintered geopolymer porous adsorbent using hydroxyapatite (Hap). Thus, this study aims to sinter geopolymer composed of 25% metakaolin, 75% silica fume and 2% Hap at varied sintering temperatures (300–800°C) for the coadsorption of copper ions (Cu 2+ ) and ciprofloxacin (CIP). The effects of different sintering temperatures on the phase stability, pore development of the geopolymer and on the removal efficiency of Cu 2+ and CIP were studied in both single and binary system. The characterization techniques, namely, X‐ray diffraction (XRD), Fourier‐transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), Brunauer–Emmett–Teller (BET), and X‐ray tomographic microscopy (XTM) were employed to characterize the physicochemical properties of the sintered geopolymer adsorbents. Based on the experimental results, the geopolymer sintered at 600°C obtained the highest removal efficiency of CIP (87%) and Cu 2+ (99.53%) in comparison to oven‐cured samples with CIP (61.5%) and Cu 2+ (96.62%). Besides, XTM results revealed that the total porosity of geopolymer sintered at 600°C increased by 60.1% when compared to oven‐cured sample. The complete dehydration of calcium aluminate silicate hydrate (C–A–S–H) gel and decomposition of calcite at 600°C created a microporous structure, enhancing Cu 2+ and CIP adsorption. Hence, a simple and effective strategy is developed in this study to improve the adsorption efficiency of geopolymer adsorbents for the treatment of wastewater that comprises Cu 2+ and CIP.