Studies on Cr(VI) Removal from Aqueous Solutions by Nanoalumina

Abstract

The current study deals with Cr(VI) removal using unmodified alumina nanoparticles 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 of Cr(VI)/g of adsorbent, were noted for NA1 and NA2, respectively, under optimized conditions (pH 7.0, temperature = 27 °C, initial Cr(VI) concentration = 20 mg L −1 , adsorbent dosage = 0.1g L −1 ) but different contact times (120 min for NA1, 180 min for NA2). For both sorbents, the equilibrium adsorption data fitted well with the Langmuir isotherm model. The adsorbent NA1 followed a pseudo-second-order kinetics, whereas NA2 followed pseudo-firstorder kinetics. Surface characterization studies (zeta potential measurement, scanning electron microscopy (SEM), energydispersive X-ray spectroscopy (EDX), and Fourier transform infrared (FTIR) spectroscopy) substantiated oxyanionic binding on the sorbent surface. The EPR and XRD spectroscopy confirmed the existence of reduced Cr(III) on the adsorbent surface. The applicability of the sorbent in Cr(VI)-contaminated water was studied.

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“…During first 60 min of interaction, removal was facilitated possibly due to the excess availability of empty sites. After 60 min, the remaining vacant surface sites may not have been occupied due to the increased competition between the solute molecules . Therefore beyond 60 min, the Cr(VI) removal remained constant.…”

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“…[7] Nanoparticles like zero-valent iron (Fe 0 ), Fe 2 O 3 , Fe 3 O 4 , TiO 2 , Al 2 O 3 , and SiO 2 are quite commonly employed for the removal of heavy metals. [4,[9][10][11][12] High energy is a prerequisite to excite the TiO 2 and ZnO nanoparticles which are semiconductors in nature. Generally, ultra-violet (UV) light is used to irradiate them.…”

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“…R L values between 0 and 1 indicates favorable adsorption, while R L N 1, R L = 1, and R L = 0 indicate unfavorable, linear, and irreversible adsorption isotherms, respectively [31,32].…”

One-pot mass self-assembly of MnO2 sponge-like hierarchical nanostructures through a limited hydrothermal reaction and their environmental applications

“…Transition metal oxide-based nanomaterials have been explored for wide applications in catalysis, water splitting, and optoelectric devices, due to their available features such as rich valence states, vast surfaces and special electronic structures [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Among them, hierarchically nanostructured materials have been paid much attention because of their unique properties [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33], compared to nanomaterials with single dimension (such as nanoparticles, nanowires, nanotubes and nanofilms).…”