Effect of the Surface Charge on the Adsorption Capacity of Chromium(VI) of Iron Oxide Magnetic Nanoparticles Prepared by Microwave-Assisted Synthesis

Abstract

Solid phase extraction using magnetic nanoparticles has represented a leap forward in terms of the improvement of water quality, preventing the contamination of industrial effluents from discharge in a more efficient and affordable way. In the present work, superparamagnetic iron oxide nanoparticles (MNP) with different surface charges are tested as nanosorbents for the removal of chromium(VI) in aqueous solution. Uniform magnetic nanoparticles (~12 nm) were synthesized by a microwave polyol-mediated method, and tetraethyl orthosilicate (TEOS) and (3-aminopropyl) triethoxysilane (APTES) were grafted onto their surface, providing a variation in the surface charge. The adsorptive process of chromium was evaluated as a function of the pH, the initial concentration of chromium and contact time. Kinetic studies were best described by a pseudo-second order model in all cases. TEOS@MNP barely removed the chromium from the media, while non-grafted particles and APTES@TEOS@MNP followed the Langmuir model, with maximum adsorption capacities of 15 and 35 mgCr/g, respectively. The chromium adsorption capacities abruptly increased when the surface became positively charged as the species coexisting at the experimental pH are negatively charged. Furthermore, these particles have proven to be highly efficient in water remediation due their 100% reusability after more than six consecutive adsorption/desorption cycles.

Coupling of kenaf Biochar and Magnetic BiFeO3 onto Cross-Linked Chitosan for Enhancing Separation Performance and Cr(VI) Ions Removal Efficiency

“…The Vibrating Sample Magnetometer (VSM) of CKB in Figure 3e shows that the saturation magnetization (M s ), coercivity (H c ) and retentivity (M r ) of the composite are 0.37 emu/g, 160 O e , and 0.067 emu/g, respectively. Near-zero retentivity and minor value of coercivity indicates the superparamagnetic property of CKB [35,36]. The inset in Figure 3e confirms that it can achieve solid-liquid separation quickly after adsorption via a magnet.…”

“…The Freundlich model accounts for a non-ideal adsorption on a heterogeneous surface concerning physical and chemical interactions between adsorbates and adsorbents [51]. Temkin isotherm equation is based on the assumption that the heat of adsorption is linearly decreased with the coverage of molecules because of the repulsions between adsorbates and adsorbates [36,52]. The experimental data were greatly fitted with Langmuir model as the correlation coefficient (R 2 ) values ranging from 0.923 to 0.945, suggesting that monolayer coverage may occur in the adsorption process.…”

Removal of Cu(II) from Aqueous Solutions Using Amine-Doped Polyacrylonitrile Fibers

“…The Langmuir model was derived to describe adsorption on homogeneous adsorbent surfaces, where each adsorptive site could be occupied only once. Mathematically, the Langmuir model can be described as follows [16]:…”

“…where q m (mg/g) is the maximum sorption capacity of the metal ions on the adsorbent, and K L (L/mg) is the Langmuir adsorption equilibrium constant. The Freundlich model is used to describe the adsorption of an absorbate on heterogeneous adsorbent surfaces, and its mathematical expression could be written as follows [16]:…”

Magnetophoretic Harvesting of Nannochloropsis oculata Using Iron Oxide Immobilized Beads

“…Magnetic nanomaterial iron oxides (Fe 3 O 4 ) are widely used as a reusable adsorbent/flocculant for wastewater treatment [14,15]. Especially ferrous ions (Fe 2+ ) of Fe 3 O 4 , which can be used as Fenton catalysts when under an acidic environment [16].…”