Evaluation of phosphate removal from aqueous solution using metal organic framework; isotherm, kinetic and thermodynamic study.

BACKGROUND

Phosphate (PO ) is the main etiological factor of eutrophication in surface waters. Metal organic frameworks (MOFs) are novel hybrid materials with amazing structural properties that make them a prominent material for adsorption.

METHODS

Zeolitic imidazolate framework 67 (ZIF-67), a water stable member of MOFs, with a truncated rhombic dodecahedron crystalline structure was synthesized in aqueous environment at room temperature and then characterized using XRD and SEM. PO adsorption from synthetic solutions using ZIF-67 in batch mode were evaluated and a polynomial model (R: 0.99, R : 0.98, LOF: 0.1433) developed using response surface methodology (RSM).

RESULTS

The highest PO removal (99.2%) after model optimization obtained when ZIF-67 dose, pH and mixing time adjusted to 6.82, 832.4 mg/L and 39.95 min, respectively. The optimum PO concentration in which highest PO removal and lowest adsorbent utilization occurs, observed at 30 mg/L. PO removal eclipsed significantly in the presence of carbonate. The equilibrium and kinetic models showed that PO adsorbed in monolayer (q: 92.43 mg/g) and the sorption process controlled in the sorption stage. Adsorption was also more favorable at higher PO concentration, according to the separation factor (K) graph. Thermodynamic parameters (minus signs of ∆G°, ∆H° of 0.179 KJ/mol and ∆S° of 44.91 KJ/mol.K) demonstrate the spontaneous, endothermic and physisorption nature of the process.

CONCLUSION

High adsorption capacity and adsorption rates, make ZIF-67 a promising adsorbent for PO removal from aqueous environment.