Adsorption of arsenate on Fe-(hydr)oxide

Adsorption using metal oxide materials has been demonstrated to be an effective technique to remove hazardous materials from water, due to its easy operation, low cost, and high efficiency. The high number of oxyanions in aquatic ecosystems causes serious pollution problems. Removal of arsenate (H2AsO4 -), is one of the major concerns, since it is a highly toxic anion for life. Within the metal oxides, the iron oxide is considered as a suitable material for the elimination of oxyanions. The adsorption of H2AsO4 - on Fe-(hydr)oxide is through the formation of inner or outer sphere complexes. In this work, through computational methods, a complete characterization of the adsorbed surface complexes was performed. Three different pH conditions were simulated (acidic, intermediate and basic), and it was found that, the thermodynamic favourability of the different adsorbed complexes was directly related to the pH. Monodentate complex (MM1) was the most thermodynamically favourable complex with an adsorption energy of -96.0kJ/mol under intermediate pH conditions. © Published under licence by IOP Publishing Ltd

Dyes removal from water using low cost absorbents

In this study, the removal capacity of low cost adsorbents during the adsorption of Methylene Blue (MB) and Congo Red (CR) at different concentrations (50 and 100mg•L-1) was evaluated. These adsorbents were produced from wood wastes (cedar and teak) by chemical activation (ZnCl2). Both studied materials, Activated Cedar (AC) and activated teak (AT) showed a good fit of their experimental data to the pseudo second order kinetic model and Langmuir isotherms. The maximum adsorption capacities for AC were 2000.0 and 444.4mg•g-1 for MB and CR, respectively, while for AT, maximum adsorption capacities of 1052.6 and 86.4mg•g-1 were found for MB and CR, respectively. © Published under licence by IOP Publishing Ltd

Density functional theory studies of the adsorption of Cr (VI) on Fe-(hydr) oxide: Gibbs free energies and pH effect

Adsorption of chromium (VI) on iron oxides is a potential removal method from industrial wastewater. Cr (VI) is a toxic specie for human health due to its easy mobility in the environment. Currently, US EPA drinking water standards establish a maximum Cr level of 100 ?g/L. Since the adsorption process occurs in the solid/liquid interface, pH is one of the main factors that affect this process and it is a very important parameter to study. Understanding the adsorption process and the molecular geometries of complexes, is essential to predict the environmental transport of Cr (VI) and to develop appropriate models for the remediation of Cr (VI). Therefore, in this work, we describe the adsorption of Cr (VI) onto Fe-hydr (oxides) through computational methods. A complete characterization of the adsorbed surface complexes was performed, and three different pH conditions were simulated (acidic, intermediate and basic). It was found that, the thermodynamic favourability of the different adsorbed complexes was directly related to the pH. Bidentate complex (BB) was the most thermodynamically favourable complex with an adsorption energy of -143.3 kJ/mol under acidic pH conditions. © Published under licence by IOP Publishing Ltd

Chloride adsorption on Fe- and Al-(hydr)oxide: estimation of Gibbs free energies

In this study, we used chemical quantum methods to analysis the adsorption of chloride on Al and Fe-(hydr)oxide clusters. Inner and outer sphere complexes were the generating complexes during the adsorption process on variably charged Al- and Fe-(hydr)oxide clusters. For the chloride adsorption on Al-(hydr)oxide, the outer sphere complexes—H-bonded—were favored for all clusters, while the adsorption modes as inner sphere complexes—BB or MM—were not favored. It was found, that the H-bonded complex on neutral clusters was the most thermodynamically favored with an adsorption energy of − 63.4 kJ/mol. For iron clusters, thermodynamic favorability was observed for both outer (− 70.5 kJ/mol) and inner monodentate (− 65.8 kJ/mol) sphere complexes. These theoretical results indicated that the thermodynamic favorability of chloride adsorption on Fe and Al-(hydr)oxide was directly related to positive surface charge. © 2018 Springer Science+Business Media, LLC, part of Springer Natur

Adsorbent materials obtained from palm waste and its potential use for contaminants removal from aqueous solutions

This work reports the production of an adsorbent material obtained by H3PO4 chemical activation of oil palm waste (fiber). The experiments were carried out to explore methylene blue uptake by this adsorbent. The influence of initial dye concentration and adsorbent dosage was investigated. The adsorption equilibrium data of methylene blue onto the adsorbent material were best fitted to the Langmuir model. The maximum adsorption capacity monolayer was of 20.85 mg g-1, which showed to be high compared to other adsorbent materials reported in the literature. Adsorption of methylene blue onto adsorbent material followed pseudo-second order model. The structural and chemical characterization of the adsorbent material was carried out by using various analytical techniques. FTIR showed the formation of oxygenated functional groups on the surface, which are very important for adsorption applications because they act as active sites capable of interacting with dye molecules. © 2019 Published under licence by IOP Publishing Ltd

Removal of dyes from aqueous solutions by adsorbent prepared from coffee residues

This study reports the production of an adsorbent material derived from extracted coffee residues using phosphoric acid and zinc chloride as activating agents. The structural features of the materials were characterized using different analytical techniques. The BET surface areas were found between 3.81 m2.g-1 y 176.27 m2.g-1, while the FTIR analysis showed the formation of oxygenated functional groups, which are active in the adsorption process. These materials were evaluated as adsorbents for the removal of methylene blue from aqueous solution. Batch adsorption tests were performed at room temperature and the effects of contact time and, initial dye concentration was investigated. The equilibrium adsorption results were complied with Langmuir isotherm model and its maximum monolayer adsorption capacity was 15.92 mg.g-1. Adsorption kinetics studies indicated that the pseudo second order model yielded the best fit for the kinetic data. This typical dependence of methylene blue uptake on kinetic studies indicated the adsorption process to be both chemisorption and diffusion controlled. The experimental data obtained in the present study indicate that coffee residues are suitable candidates for use as adsorbents in the removal of cationic dyes. © 2019 Published under licence by IOP Publishing Ltd