Removal of Fluoride from water through bacterial-surfactin mediated novel hydroxyapatite nanoparticle and its efficiency assessment: Adsorption Isotherm, Adsorption kinetic and Adsorption Thermodynamics

Fluoride contamination in water due to natural and anthropogenic activities has been documented as serious problems worldwide commanding a major threat to the environment. In present study focuses to synthesis bacterial-surfactin (Bacillus subtilis) mediated nano-hydroxyapatite (HAp), novel adsorbents for defluoridation. HAp particle size and morphology were controlled by varying temperature of 90–150°C and pH of 7-11 respectively. The TEM and SEM micrographs reveal that the short-rod particle is observed 20–30nm at 90°C and pH 11. The ratio between the length (nm) and width (nm) of nanoparticle are decreased from 4.17 to 1.65 with increasing pH (7-11). The selected area diffraction (SAD) of particles are indicated uniform rod-like monocrystals. The XRD and FTIR observations were indicated the synthesized HAp nanoparticles were well-crystallized with purity phase and high quality. The study reflected that the fluoride removal from contaminated water by HAp was increased significantly (R2=99) with the increasing adsorbent concentration, temperature and time, with two-step adsorption process as the first portion a rapid adsorption occurs during first 90min after which equilibrium is slowly achieved. The adsorption process is closer to Freundlich isotherm (R2>98) in compare to Langmuir isotherm (R2≈92), indicating HAp as a good adsorbent (n >3). Above 97% of fluoride removal were noticed at a HAp dose of 0.06g/10mL. The adsorption kinetics more fit with pseudo-second-order (R2 99) in compare to pseudo-first-order (R2≈91). The slope and intercept of Arrhenius equation were indicated the activation/adsorption energy (Ea) of 3.199kJ/mol and frequency factor (A) of 1.78 1/s. Adsorption thermodynamic parameters (free energy (ΔG <0), enthalpy (ΔH> 0) and entropy (ΔS>0)) indicates the spontaneous and endothermic reactions of the adsorption process. Thus, newly synthesized HAp nanoparticles exhibit as a good adsorbent for fluoride removal, theoretically and experimentally, and it’s applicable for environmental pollution control.