Showing papers on "Langmuir published in 2020"

Development of synthetic zeolites from bio-slag for cesium adsorption: Kinetic, isotherm and thermodynamic studies

Abstract: This study reported a novel synthetic zeolite based adsorbent developed from the municipal wastewater sludge molten slag (bio-slag) through the hydrothermal modification process for removal of cesium (Cs) from simulated wastewater. The artificial zeolites were produced from the raw bio-slag which was identified by the several physicochemical experimental procedures such as the surface area analysis (the BET technique), the FESEM, the XRF and the XRD. The Cs adsorption process of modified bio-slag was exmined by the linear pseudo-first order, pseudo-second order and intra-particles diffusion models whilst the second order kinetic model confirmed a better agreement with the correlation coefficient, R2 = 0.999-1.000 for 20-400 mg/L Cs solution. The Langmuir, Freundlich and the Temkin isotherm model were investigated using the adsorption isotherm data. A satisfactory correlation coefficient value (R2= >0.980) proved that the isotherm parameters were perfectly fitted to the Langmuir and Freundlich model and the highest Cs adsorption ability of modified bio-slag were 51.02, 51.02 and 49.51 mg/g at 288, 298 and 308 K, respectively. The better agreement of adsorption data with the second order kinetic model and the Langmuir model proved the adsorption mechanism was controlled by the chemical reaction (ion-exchange). Thermodynamic studies under the different temperatures proved that the adsorption reaction was endothermic ( Δ H =20.53 kJ/mol) and Δ S = 0.021 kJ/mol/K) and non-spontaneous ( Δ G > 0 ). Moreover, the modified bio-slag effectively removed Cs even in the co-existence of Na+ and K+ as competitive ions at their wide range of concentrations (upto 300 mM) although the higher concentration slightly affected the Cs adsorption.

A mechanistic approach of chromium (VI) adsorption onto manganese oxides and boehmite

Abstract: The concentration of chromium (VI) in the soil is an important environmental concern due to its mobility and acute toxicity. Due to its toxicity, removal of this species is very important. The mobility of Cr(VI) is highly governed by its adsorption onto the mineral surfaces. Manganese oxides are naturally-occurring scavengers and have a significant influence on the distribution, and transport of chromate species. Thus, to understand the fate of chromate species and its removal process, it is important to study chromium (VI) adsorption. In this study, birnessite (δ-MnO2), pyrolusite (β-MnO2), hausmannite (Mn3O4), manganite (γ-MnOOH), boehmite (γ-AlOOH), and Mn-Al binary oxide was used as adsorbents to adsorb Cr(VI) over a range of solution pH and initial Cr(VI) concentrations. A combined approach using the Langmuir and Freundlich models, proton stoichiometry and surface complexation model (SCM) have been used to describe the probable Cr(VI) adsorption process. Birnessite was the most potent adsorbent at low pH. The Langmuir model could describe the equilibrium isotherm data well, suggesting a uniform surface nature. Proton stoichiometry indicated that Cr(VI) adsorption involved more than one type of reaction. The findings confirm that Cr(VI) species bind to functional groups by the inner- and outer-sphere chromate complexes, with the extent of binding dependent on solution pH. The study presented herein can be applied to soils with a variety of surface properties, pH, and Cr (VI) concentrations. The study further advances our understanding of the interaction between Cr(VI) and minerals at the solid-water interface.

Thermodynamics and Adsorption Study of the Corrosion Inhibition of Mild Steel by Euphorbia heterophylla L. Extract in 1.5 M HCl

Abstract: This work investigates the thermodynamics parameters and adsorption mechanism of Euphorbia heterophylla L. extract as a corrosion inhibitor for mild steel in 1.5 ​M HCl. The gravimetric method was used to determine the inhibition efficiency and corrosion rate. Relevant thermodynamic equations were employed to determine the activation energy, enthalpy change and entropy change. The adsorption isotherms were used to evaluate the Gibbs free energy change. Observation from the results of the study showed that the activation energy of an inhibited process was higher when compared with the uninhibited process. Also, the enthalpy change was positive and less than 100 ​KJ/mol threshold. The adsorption study showed that the data fit into the Langmuir, Flory-Huggins, El-Awary’s and Temkin isotherms but Flory-Hugins gave the best fit. The Gibb’s free energy change of adsorption was negative and less than the −20 ​KJ/mol threshold. As concluded from the results, the adsorption of Euphorbia heterophylla L. on mild steel in 1.5 ​M HCl medium is feasible, spontaneous and it occurred by physical adsorption according to Flory-Hugins isotherm model.

Cationic Dye Removal Using Novel Magnetic/Activated Charcoal/β-Cyclodextrin/Alginate Polymer Nanocomposite.

Abstract: New magnetic iron oxide (Fe3O4)/activated charcoal (AC)/β-cyclodextrin (CD)/sodium alginate (Alg) polymer nanocomposite materials were prepared by direct mixing of the polymer matrix with the nanofillers. The obtained materials were utilized as nano-adsorbents for the elimination of methylene blue (MB), a hazardous water-soluble cationic dye, from aqueous solutions, and showed excellent regeneration capacity. The formation of the nanocomposites was followed by high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectrometry (EDX), Fourier-transform infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM), X-ray diffraction (XRD) and adsorption of N2 at -196 °C. The rate of adsorption was investigated varying several factors, namely contact time, pH, amount of adsorbent and MB concentration on the adsorption process. Studies dealing with equilibrium and kinetics were carried out in batch conditions. The obtained results indicated that the removal rate of MB was 99.53% in 90 min. Langmuir's isotherm fitted better to the equilibrium data of MB. Fe3O4/AC/CD/Alg polymer beads shows amazing adsorption capacities in the elimination of cationic dyes (2.079 mg/g for polymer gel beads and 10.63 mg g-1 for dry powder beads), in comparison to other adsorbent materials. The obtained adsorbent is spherical with hydrophobic cross-linked surface properties that enable an easy recovery without any significant weight loss of in the adsorbent used.

Green preparation of activated carbon from pomegranate peel coated with zero-valent iron nanoparticles (nZVI) and isotherm and kinetic studies of amoxicillin removal in water

Abstract: In present research, the activated carbon was prepared by a green approach from pomegranate peel coated with zero-valent iron nanoparticles (AC-nZVI) and developed as adsorbent for the removal of amoxicillin from aqueous solution. The physicochemical properties of the AC-nZVI were investigated using XRD, FTIR, and FESEM techniques. The optimal values of the parameters for the best efficiency (97.9%) were amoxicillin concentration of 10 mg/L, adsorbent dose of 1.5 g/L, time of 30 min, and pH of 5, respectively. The adsorption equilibrium and kinetic data were fitted with the Langmuir monolayer isotherm model (qmax 40.282 mg/g, R2 0. 0.999) and pseudo-first order kinetics (R2 0.961). The reusability of the adsorbent also revealed that the adsorption efficiency decreased from 83.54 to 50.79% after five consecutive repetitions. Overall, taking into account the excellent efficiency, availability, environmental friendliness, and good regeneration, AC-nZVI can be introduced as a promising absorbent for amoxicillin from aquatic environments.