Enhanced Adsorption of Arsenic onto Maghemites Nanoparticles:  As(III) as a Probe of the Surface Structure and Heterogeneity

Abstract

When normalized per unit of surface area, the quantity of arsenic adsorbed at the maghemite surface remains constant for particles between 300 and 20 nm. However, nanoparticles smaller than 20 nm exhibit enhanced adsorption capacity. The origin of this observed size-dependence for adsorption or "nano effect" is unclear. Arsenic was chosen as a probe of the surface structure to explore adsorption mechanisms occurring at the surface of maghemite nanoparticles (6 nm). Two factors contributing to the enhanced reactivity of nanoscale maghemites were determined. The first is related to a size-dependent structural modification of the surface of particles and the decrease of the occupancy of the tetrahedral site that leaves vacant, highly reactive adsorption sites. In particular, there is a site localized in a six-membered iron octahedral ring. This site is the only one for which an oxidation of As(III) occurs. The second factor relates to the thermodynamics of a decrease of the surface free energy. The high density of As adsorbed at the saturation of the surface can be related to crystal growth.

The role of functionalised multiwalled carbon nanotubes based supercapacitor for arsenic removal and desalination of sea water

“…From the experimental results, it can be seen that Langmuir and Freundlich models fit for both metallic impurities (arsenic and sodium). Maximum adsorption capacity for arsenic was found to be 109.457 mg g is larger than other reported values [29,30]. Freundlich constant n was found to be greater than 1 for both impurities, which is a favourable condition for adsorption.…”

Uptake of Zn2+ and As3+ from Wastewater by Adsorption onto Imine Functionalized Magnetic Nanoparticles

“…Adsorbents dose of 40 mg were agitated with a 20 mL aliquot of Zn(II) and As(III) on a thermostated oven shaker at temperature ranges of 293, 303, 313 and 318 K for 4 h. The solutions were separated magnetically and the concentration of Zn(II) and As(III) in the filtrate determined by using AAS. The experimental adsorption data were fitted into two isotherm models; Langmuir and Freundlich models [30][31][32]. Table 2 shows the equations of the models.…”

Recovery of Phosphate from Mixed Solutions Using Surface Modified Maghemite Nano-Adsorbents

“…γ-Fe 2 O 3 nanoparticles are highly paramagnetic with a magnetic saturation between 70 and 76 emu/g for when the diameter is > 25 nm implying a large response to magnetic fields [13][14][15]. This characteristic is particularly attractive as it affords the possibility of separating the adsorbent/adsorbate complex from solution without the need for clarification or filtration processes [16].…”