Studies on Cr(VI) Removalfrom Aqueous Solutions byNanoalumina.

The current study deals with Cr(VI) removal using unmodifiedaluminananoparticles of two different sizes (NA1: mean hydrodynamic diameter= 75.3 ± 2.8 nm; NA2: mean hydrodynamic diameter = 229.8 ±3.3 nm). The equilibrium adsorption capacities, 73.2 and 59.4 mg ofCr(VI)/g of adsorbent, were noted for NA1 and NA2, respectively, underoptimized conditions (pH 7.0, temperature = 27 °C, initial Cr(VI)concentration = 20 mg L–1, adsorbent dosage = 0.1gL–1) but different contact times (120 min for NA1,180 min for NA2). For both sorbents, the equilibrium adsorption datafitted well with the Langmuir isotherm model. The adsorbent NA1 followeda pseudo-second-order kinetics, whereas NA2 followed pseudo-first-orderkinetics. Surface characterization studies (zeta potential measurement,scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy(EDX), and Fourier transform infrared (FTIR) spectroscopy) substantiatedoxyanionic binding on the sorbent surface. The EPR and XRD spectroscopyconfirmed the existence of reduced Cr(III) on the adsorbent surface.The applicability of the sorbent in Cr(VI)-contaminated water wasstudied. [ABSTRACT FROM AUTHOR]