Synthesis of nanoZrO2via simple new green routes and its effective application as adsorbent in phosphate remediation of water with or without immobilization in Al-alginate beads

Abstract

Nano particles of ZrO2of average size 10.91 nm are successfully synthesized via green routes from a solvent blend of water and ethylene glycol (4:1 v/v). Bio-extract of seeds of Sapindus plant is employed as stabilizing and/or capping agent and homogeneous method of precipitation is adopted to generate the precipitating agent. The nZrO2particles are immobilized in aluminum alginate beads (nZrO2-Al- alig). Nano-ZrO2and beads are investigated as adsorbents for the extraction of phosphate from water. The controlling physicochemical parameters are studied for the maximum phosphate removal using simulate water. The optimum conditions are: pH: 7; sorbent dosage: 0.1 g/100 mL for nZrO2and 0.08 g/100 mL for beads; equilibration time: 30 min.for nZrO2and 35 min for beads; initial phosphate concentration: 50 mg/L; temperature: 30 ±1 °C; 300 rpm. The adsorption capacities are: 126.2 mg/g for nZrO2and 173.0 mg/g for 'nZrO2-Al- alig' and they are higher than many reported in literature. The beads, besides facilitating the easy filtration, are exhibiting enhanced cumulative phosphate-adsorption nature of nanoZrO2and Al-alginate. X-ray diffraction (XRD), Fourier transform infrared (FTIR), field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray (EDX) investigations are employed in characterizing the adsorbents. Of the various isotherm models analyzed to assess the nature of adsorption, Freundlich model provides the best correlation (R2 = 0.99 for nZrO2and R2 = 0.99 for 'nZrO2-Al-alig'), indicating the heterogeneous and multi-layered adsorption process. Thermodynamic studies reveal the endothermic and spontaneous nature of sorption. Pseudo-second-order model of kinetics describes the adsorption well. Spent adsorbents can be regenerated with marginal loss of adsorption capacity until five cycles. The sorbents are successfully applied to remove phosphate from polluted lake water samples.