Effective adsorbents based on nano mixed (Al-Fe-Zr) oxide synthesised by new green methods: for the simultaneous extraction of phosphate and chromate from contaminated water

Abstract

ABSTRACT Nanoparticles of Al2O3, ZrO2, Fe3O4 and their mixed oxides are synthesized adopting new green methods. Aloe-vera gel is identified as a capping agent for controlling the size of particles. The slow generation of precipitating agent, NH3, and increase in viscosity of medium, assist the synthesis. The mixed nanoparticles are found to be very effective in the simultaneous extraction of phosphate (qe:112.14 mg/g) and chromate (qe:122.6 mg/g) from water atpH: 4, equilibration time: 60 min and dosage: 0.12 g/150 mL. These particles when doped in calcium alginate beads to make the filtration easy, the effective pH is increased to 10 for the simultaneous removal of both the pollutants with enhancement in adsorption capacities for phosphate (qe:130.01 mg/g) and chromate(qe:144.12 mg/g) at the equilibration time: 90 min and dosage: 0.10 g/150 mL. The nano mixed oxide as well as beads are characterized by FTIR, XRD, FESEM and EDX techniques. Spontaneous and endothermic nature of sorption is revealed by thermodynamic investigations. The adsorbents are robust and effective up to six regeneration cycles. The experimental data are best fitted with the Langmuir isotherm and pseudo-second-order kinetic models with R2 values > 0.99 for both the adsorbates. The methodology developed is applied to water remediation for phosphate and chromate. The importance of the present investigation is that the adsorbents based on nanomaterials synthesised by new green methods are identified to have high adsorption capacities for the simultaneous extraction of chromate and phosphate from polluted water.