Arsenic(V) sorption reaction with nanostructured hydrous iron(III)-zirconium(IV) bimetal mixed oxide (NHIZO) was investigated experimentally with varying parameters, viz., the effects of pH, contact time, and isotherm equilibrium at (303 ( 1.6) K. The optimum pH estimated ranged between 5.0 and 7.0. The kinetic and equilibrium data (pH 7.0 ( 0.2) described the pseudosecond order and the Langmuir isotherm equations well, respectively. The Langmuir monolayer capacity estimated was (9.3582 ( 0.3116) mg • g -1 . Thermodynamics analysis of the data of isotherm equilibrium suggested the endothermic and spontaneous nature of the sorption reaction, and the latter took place with the increase of entropy (∆S 0 ) +96.6087 J • mol -1 • K -1 ). The estimation of sorption energy (E ) 12.4700 kJ • mol -1 ) from the Dubinin-Radushkevich (D-R) isotherm analysis had suggested chemisorption of arsenic(V) on NHIZO.

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The sorption behaviors of M(II) (M = Cu, Cd) were investigated from their aqueous solution by magnetic Mn-doped Fe(III) oxide nanoparticle implanted graphene (GMIO) at varying pH, contact times, and concentrations. Kinetically, the pseudo-second-order equation governed the overall sorption process at optimized pH (5.1 ± 0.1). Redlich− Peterson (R−P) (0.97 < R 2 < 1.00, 0.84 < g < 1.00) and Langmuir (0.96 < R 2 < 1.00) isotherms described sorption equilibriums better than Freundlich (0.86 < R 2 < 0.96). Monolayer sorption capacity values of GMIO for M(II) increased (88 mg•g −1 to 127 mg•g −1 for Cd; 130 mg•g −1 to 144 mg•g −1 for Cu) with increasing temperature from 288 K to 333 K. Negative ΔG 0 values indicated spontaneous sorption nature despite positive ΔH 0 values owing to an entropy increase (positive ΔS 0 ) at the solid−liquid interface. Relatively less regeneration (∼70%) of M II −GMIO by 0.1 M HCl possibly stemmed the chemisorption of metal ions, and this is well-corroborated by the nature of Stern−Volmer plot of fluorescence quenching data with reaction time.

Agglomerated nanoparticles [(40 to 50) nm] of synthetic iron(III) + chromium(III) mixed oxide (NHICO) were investigated for the equilibrium and thermodynamics of arsenic(III) removal, respectively, at pH 7.0 (( 0.2) and temperature (T ( 1.6) ) (288 and 303) K from solutions with background ions that coexist in groundwater. Langmuir and Redlich-Peterson isotherm models described the equilibrium data better than Freundlich model. The Langmuir capacity (θ 0 • 10 2 , mmol • kg -1 ) values estimated, 10.404 and 10.686 in the absence of ions at studied temperatures, were higher than that in the presence of ions (except for HCO 3 -) at background. The enthalpy (∆H 0 ) and entropy (∆S 0 ) changes were positive, indicating endothermic reactions driven by entropy increase at the solid-liquid interface. Negative values of free energy change (∆G 0 ) indicated that the reactions were spontaneous, which increased with increasing temperature on reactions. The treatment of groundwater (arsenic concentration: 1.347 µmol • dm -3 ) by the NHICO packed fixed-bed column (height: 6.0 cm, i.d.: 1.0 cm, bed volume: 4.71 cm 3 ) yielded 4.7 dm 3 (∼1000 BV) of water with an arsenic concentration of e 0.133 µmol • dm -3 . The used bed was regenerated up to a level 90 (( 1.5) % of its initial capacity with 0.350 dm 3 of optimized 0.25 M NaOH solution.

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