Removal of arsenate using graphene oxide-iron modified clinoptilolite-based composites: adsorption kinetic and column study

In this study, graphene oxide (GO), iron modified clinoptilolite (FeZ), and composites of GO-FeZ (GOFeZA and GOFeZB) were synthesized and characterized using SEM, EDS, XRF, FTIR, and pHpzc. The arsenate uptake on composites of GOFeZA and GOFeZB was examined by both kinetic and column studies. The adsorption capacity increases with the increase of the initial arsenate concentration at equilibrium for both composites. At the initial arsenate concentration of 450 μg/L, the arsenate adsorption on GOFeZA and GOFeZB was 557.86 and 554.64 μg/g, respectively. Arsenate adsorption on both composites showed good compatibility with the pseudo second order kinetic model. The adsorption process was explained by the surface complexation or ion exchange and electrostatic attraction between GOFeZA or GOFeZB and arsenate ions in the aqueous solution due to the relatively low equilibrium time and fairly rapid adsorption of arsenate at the beginning of the process. The adsorption mechanism was confirmed by characterization studies performed after arsenate was loaded onto the composites. The fixed-bed column experiments showed that the increasing the flow rate of the arsenate solution through the column resulted in a decrease in empty bed contact time, breakthrough time, and volume of treated water. As a result of the continuous operation column study with regenerated GOFeZA, it was demonstrated that the regenerated GOFeZA has lower breakthrough time and volume of treated water compared to fresh GOFeZA.

Surface chemistry of bovine serum albumin with hematite nanoparticles and its effect on arsenate adsorption

Environmental contextHematite nanoparticles are efficient adsorbents for proteins and pollutants in environmental and biological systems. Hematite and the protein bovine serum albumin (BSA) were used as models to investigate the surface chemistry and competitive role of BSA in arsenate adsorption. Results show that surface BSA inhibits arsenate adsorption, potentially altering its mobility and bioavailability. AbstractThe surface chemistry of metal oxide nanomaterials controls their health impacts and fate in environmental and biological systems. These systems contain proteins capable of binding to nanoparticles, which forms a protein corona that modifies the surface properties of the nanoparticles and reactivity towards pollutants. Using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, we investigate the adsorption of bovine serum albumin (BSA) and quantify the competitive effect of BSA on the adsorption kinetics of arsenate, AsV, to hematite nanoparticles. Experiments were conducted in the flow mode at pH 7. BSA was first adsorbed on hematite, then AsV was allowed to flow over the BSA/hematite thin film. Adsorption kinetic and thermodynamic parameters were calculated using a modified Langmuir adsorption model for both BSA and AsV. The adsorption thermodynamic model showed that BSA binds through two active sites with a binding energy of –41 kJ mol−1, which corresponds to the spontaneous formation of chemisorbed and physisorbed species. When AsV flowed over the BSA/hematite film, only 11 % of surface BSA was desorbed by AsV. This result highlights the inhibitory effect of BSA for AsV adsorption. Structural analysis of BSA revealed changes to the local conformational geometry upon adsorption to and desorption from hematite nanoparticles. Molecular docking simulations showed that the binding free energy of a modelled hematite nanoparticle towards the BSA surface is –6.8 kcal mol−1 (−28.5 kJ mol−1) owing to the formation of various bonds, which agrees with the adsorption kinetics modelling. Overall, surface BSA inhibits arsenate adsorption and therefore increases its mobility and bioavailability.

Arsenate Adsorption on Fly Ash, Chitosan and Their Composites and Its Relations with Surface, Charge and Pore Properties of the Sorbents

One of the ways to recycle millions of tons of fly ash and chitin wastes produced yearly is their utilization as low-cost sorbents, mainly for heavy metal cations and organic substances. To improve their sorption efficiency, fly ashes have been thermally activated or modified by chitosan. We aimed to deeply characterize the physicochemical properties of such sorbents to reveal the usefulness of modification procedures and their effect on As(V) adsorption. Using low temperature nitrogen adsorption, scanning electron microscopy, mercury intrusion porosimetry, potentiometric titration and adsorption isotherms of As(V) anions, surface, pore, charge and anion adsorption parameters of fly ash activated at various temperatures, chitosan, and fly ash modified by chitosan were determined. Arsenate adsorption equilibrium (Langmuir model), kinetics (pseudo-second order model) and thermodynamics on the obtained materials were studied. Neither temperature activation nor chitosan modifications of fly ash were necessary and profitable for improving physicochemical properties and As(V) adsorption efficiency of fly ash. Practically, the physicochemical parameters of the sorbents were not related to their anion adsorption parameters.