Preparation of ternary MnO2/Hydroxyapatite/ZIF-67 composite framework incorporating hydroxyapatite, MnO2 nanoflower and zeolitic imidazole framework (ZIF-67) for enhanced adsorptive elimination of Congo red dye

Abstract

Currently industrial activities produce a large amount of wastewater polluted with harmful dyes are endangering human health and aquatic ecosystems and requiring efficient treatment methods. In this context, a novel MnO 2 /Hydroxyapatite/ZIF-67 composite framework was developed by incorporating manganese dioxide (MnO 2 ) nanoflower, hydroxyapatite and zeolitic imidazole framework (ZIF-67) for Congo red dye elimination. The materials were examined using analytical methods viz. FE-SEM, HR-TEM, FT-IR, and BET. The FT-IR analysis shows that hydroxyapatite provides hydroxyl and phosphate groups that can interact with anionic CR species, whereas FE-SEM pictures show that MnO 2 nanoflowers impart a highly textured flower-like shape with numerous exposed sites. However, BET analysis shows that the ZIF-67 has the highest surface area, which provides easily accessible adsorption sites and encourages dye molecules to adhere to the composite structure. Various batch adsorption experiments were evaluated to optimize the adsorption efficiency. The study achieved the best results under the conditions such as the agitation time (180 min), adsorbent dose (0.6 g/L), temperature (40 °C), and initial concentration (100 mg/L) were all optimized, achieving maximum Congo red removal of 98.65 ± 0.15%. The maximum monolayer adsorption capacity (q max ) of the composite was estimated to be 304.87 mg/g. Among the isotherm and kinetic models, the Langmuir and PSO model were best fitted for adsorption studies respectively which indicates the involvement of strong chemical interactions perhaps electrostatic interaction and π-π interaction during the process of dye elimination. Thermodynamic study further reveals the endothermic nature and spontaneity of the process. Moreover, the composite exhibits 80.41 ± 0.44% removal efficiency even after 3rd reusability cycle. To evaluate the advantages and limitations of the current work, a comparative analysis between earlier studies and the current study was carried out.