Modified Langmuir Isotherm Model Research Articles

Novel Nanocomposite of Carbonized Chitosan-Zinc Oxide-Magnetite for Adsorption of Toxic Elements from Aqueous Solutions.

Herein, a novel nanocomposite (carbonized chitosan-zinc oxide-magnetite, CCZF) was developed to effectively remove toxic elements in water remediation. Combining the high adsorption capacities of chitosan with the magnetic properties of magnetite and the chemical stability of zinc oxide, the combination of these unique properties makes it an efficient and versatile material that offers a sustainable solution for water purification. The (CCZF) nanocomposite was synthesized through the coprecipitation method and characterized using various techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) analysis, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and zeta potential analysis. The results showed impressive maximum adsorption capacities of 891.34 mg/g for Ni2+, 1269.35 mg/g for Co2+, and 1502.67 mg/g for Cu2+, fitting well with a modified Langmuir isotherm model. The adsorption process was spontaneous and endothermic, characterized by low positive enthalpy (ΔH) values ranging from 10.95 to 34.9 kJ/mol, indicative of the physical adsorption mechanism. Additionally, the nanocomposite demonstrated good reusability over multiple adsorption and desorption cycles. This research highlights the potential of the (CCZF) nanocomposite as a highly efficient, reusable adsorbent for the removal of toxic elements from aqueous solutions, contributing significantly to environmental remediation efforts and pollution control.

Highly fast and efficient coupled Fe/Sn galvanic nanocatalyst with H2O2 Fenton-like process for synergistic reduction–oxidation of nitroaromatic compound

Herein, the reinforced electron transfer ability of nano-galvanic Fe/Sn bimetallic particles deposited on talc for catalytic elimination of 2,4-dinitrotoluene (2,4-DNT) was investigated at different conditions. FESEM, XRD and FTIR characterization confirmed the successful and uniform formation of bimetallic galvanic particles on support. Ultrafast and intensified galvanic cell effects of bimetallic core-shell Fe/Sn nanoparticles enabled the nanocomposite to reach solely to 2,4-DNT removal efficiency of 91 % under the optimized condition. In addition, the synergistic combination of Fe/Sn galvanic nanocatalyst and H2O2 heterogeneous Fenton-like system, which took advantage of bimetallic Fe/Sn particles potential as viable adsorbent-reductant in pollution removal and effective source for generation of hydroxyl radicals, achieved 100 % 2,4-DNT removal within 10 min. The performance of this remediating process was evaluated under different nanocatalyst amount, pH, temperature, contaminant concentration, and H2O2 concentration. The removal process was in agreement with the pseudo-second-order kinetic model and the modified Langmuir isotherm model. Findings elucidated that the removal mechanism involved the electrostatic adsorption, galvanic oxidation–reduction and co-precipitation by nanocomposite, which was intensified by synergistic reaction of the hydroxyl radicals with pollutant. Overall, this study investigated the high potential of the combinational nZVI bimetallic galvanic nanoparticles and Fenton remediating processes, and the findings demonstrated the superior degradation capacity of the process as an innovative remediating approach.

Long-Term Fertilization Contributes to Carbon Saturation in Neutral-To-Alkaline Soils but not in Acidic Soils

ABSTRACT The study investigated the adsorption of dissolved organic carbon (DOC) on Chinese soils from four long-term experiments involving five treatments: (1) no fertilization (control), (2–4) inorganic nitrogen (N), phosphorus (P), and potassium (K) fertilization (N, NP, and NPK), (5) NPK plus manure (NPKM). The results showed that DOC adsorption followed a modified Langmuir isotherm model effectively (R2 = 0.912 ~ 0.991). The maximum adsorption capacity (Q max ) (i.e. saturation deficits) generally increased with increasing soil organic carbon (SOC) due to fertilization in Luvic Phaeozem, Haplic Gypsisols, and Eutric Cambisols. However, it decreased significantly in acidic soils (Haplic Acrisols) from 15.59 g/kg for control, to 13.96, 13.03, 9.30 and 8.02 g/kg for N, NP, NPK and NPKM, respectively. Moreover, long-term fertilization, particularly with organic fertilization (e.g. NPKM), resulted in an increase of carbon (C) saturation by 1.42 g/kg (5.52%) in Luvic Phaeozem, 9.27 g/kg (44.29%) in Haplic Gypsisols, and 3.75 g/kg (27.66%) in Eutric Cambisols; however, there was a slight decrease by 1.70 g/kg (−7.49%) in Haplic Acrisols. Canonical correlation analysis (CCA) revealed that clay content and soil available iron (AFe) might be the crucial factors controlling C deficits, and subsequently, C saturation, along with current SOC. In conclusion, long-term fertilization contributed to C saturation in neutral-to-alkaline soils, but not in acidic soils. Thus, further attention should be paid to the long-term effects of fertilization on C saturation.

Understanding PFOS Adsorption on a Pt Electrode for Electrochemical Sensing Applications

AbstractPer‐ and polyfluroalkyl substances (PFAS) are drawing increasing attention in the research community due to their wide spread applications and their toxicity to animals and humans. Effective early detection method of PFAS chemicals in aqueous environment is important to reduce exposure and mitigate the potential toxic effects. This study focuses on the electrochemical detection of per‐fluoro octane sulfonate (PFOS) with differential pulse voltammetry and electrochemical impedance spectroscopy on a bare platinum electrode. We observe three distinct regions of adsorption behaviors with respect to PFOS concentration from 0–1000 nM, reflecting changes in the modes of adsorption due to different adsorbate‐adsorbate interactions on a bare electrode. The adsorption isotherm constant for PFOS adsorption on a Pt electrode is calculated to be 1.6×1012 cm3 mol−1 from fitting the electrochemical data with a modified Langmuir isotherm model.

Effect of phosphate in medium on cell growth and Cu(II) biosorption by green alga Neochloris oleoabundans

Green alga Neochloris oleoabundans cultivated in medium of varied phosphate (K2HPO4) concentration was investigated as the biosorbent for Cu(II) removal from aqueous solutions. The highest biosorption capacity of 180.19 mg-Cu/g-biomass was achieved with biomass grown in medium containing 300 mg/L K2HPO4, which was 2.4 and 2.3 times of that of the biomasses grown in media containing 100 and 500 mg/L K2HPO4, respectively. The Cu(II) biosorption was fast with equilibrium established within 10 min of contact time and the kinetics was characterized as pseudo-second order. A modified Langmuir isotherm model is proposed to account for the inhibition of Cu(II) biosorption by the cell aggregation induced by Cu(II). Furthermore, it was shown that the Cu(II)-induced cell aggregation could be explored to enhance the sedimentation of biomasses to facilitate biomass recovery after Cu(II) adsorption.

Phosphorus sorption - Desorption behaviors in the sediments cultured with Hydrilla verticillata and Scripus triqueter as revealed by phosphorus fraction and dissolved organic matter

The migration of sediment phosphorus (P) could be affected by the existence of aquatic plants. To explore the effects of aquatic plants on the P sorption-desorption behaviors in the sediments, sediment in Caohai wetland was collected and cultured with the submerged plant (Hydrilla verticillata) and emerged plant (Scripus triqueter). Then the sorption and desorption experiments were performed, and physicochemical properties, P fractions, and dissolved organic matter (DOM) characteristics were evaluated. Results showed that the treated sediments exhibited similar P sorption kinetic process fitted well with the two-compartment first-order model. Nevertheless, H. verticillata cultured sediment could be well described by the modified Langmuir isotherm model, while S. triqueter cultured sediment fitted the modified Freundlich equations well. The obvious changing P fractions in cultured sediments were BD-P and NaOH-SRP during sorption. H. verticillata and S. triqueter displayed different sorption-desorption behaviors by altering BD-P, humification index, fluorescence intensity, and PARAFAC component contents in sediments. Compared to raw sediment, H. verticillata presented higher P sorption and lower P release from sediments by decreasing BD-P and increasing DOM (fulvic acid-like and humic-like components) content, while S. triqueter showed adverse P sorption and release effects by reducing DOM components. The growth of submerged plants was suggested to make a positive influence on the high efficiency of P retention capacity and low release risk.

Kinetics and thermodynamics of methylene blue adsorption on the Fe-oxide nanoparticles embedded in the mesoporous SiO2

Fe-oxide nanoparticles with a diameter of ~10 nm embedded into the porous structure of mesoporous SiO2 particles using temperature regulated chemical vapor deposition and a subsequent annealing process. The kinetics and thermodynamics of MB adsorption on bare SiO2 and Fe-oxide/SiO2 particles were investigated. MB adsorption kinetics of both SiO2 particles can be described by pseudo first order and intra particle diffusion plot. Thermodynamic parameters were calculated based on the modified Langmuir isotherm model. Equilibrium constant and spontaneity of MB adsorption was increased with the presence of Fe-oxide nanoparticles inside the SiO2 pores, which can be ascribed to the more negative values of ΔH of Fe-oxide/SiO2 particles compared to bare SiO2. A higher affinity of Fe-oxide nanoparticles for MB adsorption facilitated the intra particle diffusion of MB molecules at a longer time of MB adsorption and improve the maximum MB adsorption capacities of Fe-oxide/SiO2 compared to bare SiO2. The maximum MB adsorption capacities of bare SiO2 and Fe-oxide/SiO2 particles reduced as the initial pH of MB solution increased, however, Fe-oxide/SiO2 particles always exhibited the higher capacity of MB adsorption than bare SiO2.

Modified natural loofah sponge as an effective heavy metal ion adsorbent: Amidoxime functionalized poly(acrylonitrile-g-loofah)

Natural loofah sponge is a low cost adsorbent, but its adsorption property needs to be improved. A grafted copolymer of poly(acrylonitrile-g-loofah) [poly(AN-g-loofah)] was prepared using cericammonium nitrate (CAN) as initiator. The poly(AN-g-loofah) was further functionalized into a amidoxime-modified poly(AN-g-loofah), which was characterized through FT-IR, X-ray diffraction, and thermogravimetric analysis. The adsorption capacity of amidoxime-modified poly(AN-g-loofah) was investigated under different adsorption conditions. Amidoxime-modified poly(AN-g-loofah) with approximately 70% conversion of the nitrile group could adsorb 51.40mg/g Cu2+, which is more than two times higher than that obtained by previous studies. The modified Langmuir isotherm model and pseudo-second-order model fitted well with the Cu2+ adsorption data. A good adsorption amount of Cu2+ was obtained after five adsorption–deadsorption cycles. Hence, amidoxime-modified poly(AN-g-loofah) could be used as a novel substance for waste water treatment in industrial level.

Simultaneous adsorption of Remazol brilliant blue and Disperse orange dyes on red mud and isotherms for the mixed dye system.

The paper presents the adsorption of Remazol brilliant blue (RBB) and Disperse orange 25 (DO25) dyes from aqueous solution of the mixture of dyes onto concentrated sulphuric acid-treated red mud (ATRM). First-order derivative spectrophotometric method was developed for the analysis of RBB and DO25 in mixed dye aqueous solution to overcome the limitations arising due to interference in the zero-order spectral method. The optimum conditions to maximize RBB adsorption favoured the adsorption of RBB, and those for DO25 favoured DO25 adsorption from the mixed dye aqueous solutions. Presence of a second dye always inhibited the adsorption of a target dye. The uptake and percentage adsorption of each of the dyes onto ATRM from the aqueous solution of the mixture of dyes decreased considerably with increasing concentrations of the other dye showing the antagonistic effect. Monocomponent Langmuir isotherm fitted the mixed dye adsorption equilibrium data better than the monocomponent Freundlich isotherm. However, monocomponent models are suitable for the fixed concentration of the other dye. Modified Langmuir isotherm model adequately predicted the multi-component adsorption equilibrium data for RBB-DO25-ATRM adsorption system with a good accuracy and is more generic from the application point of view.

Predicting heavy metals' adsorption edges and adsorption isotherms on MnO2 with the parameters determined from Langmuir kinetics

Although surface complexation models have been widely used to describe the adsorption of heavy metals, few studies have verified the feasibility of modeling the adsorption kinetics, edge, and isotherm data with one pH-independent parameter. A close inspection of the derivation process of Langmuir isotherm revealed that the equilibrium constant derived from the Langmuir kinetic model, KS-kinetic, is theoretically equivalent to the adsorption constant in Langmuir isotherm, KS-Langmuir. The modified Langmuir kinetic model (MLK model) and modified Langmuir isotherm model (MLI model) incorporating pH factor were developed. The MLK model was employed to simulate the adsorption kinetics of Cu(II), Co(II), Cd(II), Zn(II) and Ni(II) on MnO2 at pH3.2 or 3.3 to get the values of KS-kinetic. The adsorption edges of heavy metals could be modeled with the modified metal partitioning model (MMP model), and the values of KS-Langmuir were obtained. The values of KS-kinetic and KS-Langmuir are very close to each other, validating that the constants obtained by these two methods are basically the same. The MMP model with KS-kinetic constants could predict the adsorption edges of heavy metals on MnO2 very well at different adsorbent/adsorbate concentrations. Moreover, the adsorption isotherms of heavy metals on MnO2 at various pH levels could be predicted reasonably well by the MLI model with the KS-kinetic constants.

Improving the sensitivity of carbon nanotube sensors by benzene functionalization

The detection of dissociated gas species, generated either by plasma or partial discharge, is of great interest because the dissociated species can alter inherent potential of a gas: for example, the insulating characteristics of SF 6. Here we report that the sensitivity of carbon nanotubes (CNTs) about dissociated species of SF 6 substantially increases by functionalizing with benzene. The sensors were prepared by the dielectrophoretic deposion of CNTs on microelectrodes. The target analytes were chemisorbed on the benzene-functionalized CNTs, and the sensors also could be regenerated by annealing at around 400 °C. The sensor response was analytically described by the modified Langmuir isotherm model. Through the density functional theory calculations, we identified that SOF 3 was particularly influential on the electronic structure of the benzene-functionalized CNTs whereas SOF 1, SOF 2, SO 2F 2, and HF showed negligible effects. The proposed functionalization methodology provides insight into how to increase sensitivity of carbon nanotube sensors for the detection of dissociated SF 6 species.

Effect of Soil Reduction on Phosphorus Sorption of an Organic‐Rich Silt Loam

Phosphorus flux from agricultural landscapes to surface waters may cause eutrophication. In the northeastern United States, P transport largely depends on P sorption of soils in variable source areas or in land treatment systems. Soil redox fluctuation commonly occurs in these areas. Nevertheless, the effect of soil redox on P sorption has been variable in the literature. This study investigated P sorption of an organic‐rich northeastern glaciated silt loam (Langford) under air‐dried, field‐wet, and reduced conditions using batch P sorption experiments. Additionally, the influence of farm wastewater on soil P sorption was studied. Major results indicated that soil reduction increased the maximum amount of P that can be sorbed (Smax) and decreased the aqueous P concentration at which P sorption and desorption are equal (EPC0), both determined from a modified Langmuir isotherm model. The slightly reduced field‐wet soils had no significant difference in Smax due to limited soil reduction. Using the diluted wastewater as the sorption solution matrices instead of 0.01 mol L−1 KCl solution, the soils generally exhibited greater Smax and lower EPC0 except for the EPC0 of a reduced surface soil, implying more complex P sorption in the field. Identified P sorption mechanisms include phosphate precipitation, ligand exchange with organic matter, and adsorption onto Fe hydroxides. Transformation of Fe compounds during soil reduction is primarily responsible for the changes in soil P sorption.

Modeling Arsenite Adsorption on Rusting Metallic Iron

Experimental data on As(III) adsorption by rusted zero valent iron (ZVI) could be modeled using a simple Langmuir isotherm model. However, the adsorption equilibrium was observed to shift with time, as continued rusting produced additional sites on the rusted ZVI surface for potential arsenic adsorption. A modified Langmuir isotherm model was formulated taking into consideration the temporal variation in the site concentration for potential arsenic adsorption on the rusted ZVI surface. This model simulated the long-term experimental data on As(III) adsorption quite well. The model was further refined by apportioning the arsenic adsorbed on the rusted ZVI surface into labile and irreversibly adsorbed fractions. Finally, the developed model was used to simulate the performance of an adsorption column. The simulation results indicate that an adsorption column of length 0.4 m and diameter 0.056 m, i.e., containing 0.001 m3 of rusted ZVI weighing 4.76 kg, and operated at an empty bed contact time of 12 min, c...

Protein Interactions in Hydrophobic Charge Induction Chromatography (HCIC)

A quantitative understanding of how proteins interact with hydrophobic charge induction chromatographic resins is provided. Selectivity on this mode of chromatography for monoclonal antibodies as compared to other model proteins is probed by means of a linear retention vs pH plot. The pH-dependent adsorption behavior on this mode of chromatography for a hydrophobic, charged solute is described by taking into account the equilibrium between a hydrophobic, charged solute and an ionizable, heterocyclic ligand. By analogy, an equation that is seen to adequately describe macromolecular retention under linear conditions over a range of pH is developed. A preparative, nonlinear isotherm that can capture both pH and salt concentration dependency for proteins is proposed by using an exponentially modified Langmuir isotherm model. This model is seen to successfully simulate adsorption isotherms for a variety of proteins over a range of pHs and mobile phase salt concentrations. Finally, the widely differing retention characteristics of two monoclonal antibodies are used to derive two different strategies for improving separations on this mode of chromatography. A better understanding of protein binding to this class of resins is seen as an important step to future exploitation of this mode of chromatography for industrial scale purification of proteins.

Phosphorus adsorption on natural sediments: Modeling and effects of pH and sediment composition

The classic Langmuir isotherm equation was modified to describe phosphorus (P) adsorption on P-polluted sediments. The P adsorption characteristics of six sediment samples from Chinese Taihu Lake were studied by short-term isotherm batch experiments and related to sediment composition. The maximum P adsorption capacities (PAC) and P-binding energy constant (k) were obtained by nonlinearly fitting sorption data using the modified Langmuir isotherm model. Native adsorbed exchangeable phosphorus (NAP), the zero equilibrium P concentration value (EPC 0), and partitioning coefficients ( K p) were subsequently calculated by corresponding formulae. K p and PAC were linearly related to the contents of active Fe and Al in sediments by least squares regression analyses ( R 2 ≈ 0.9 for both). The effect of pH in a wide range on adsorption process was investigated and H 2PO 4 − was presumed to be the preferential sorption species in overall sorption process. The fact that the amount of P sorbed and zeta potential of sediment particles have no necessary relationship reveals that a strong contribution to the P binding still comes from a ligand-exchange process on the Me–OH 2 + and Me–OH sites rather than electrostatic attraction. In addition, the influence of oxidation–reduction potential (ORP) was investigated and discussed and the dual nature of sediments as a pool or source of P in natural waters was evaluated in site T1–T4.

Acid‐activated spent bleaching earth as a sorbent for chromium (VI) in aqueous solution

Spent bleaching earth, an industrial waste produced after the bleaching of crude palm oil, was investigated for its potential in removing Cr(VI) from aqueous solution. The earth was treated with different amounts of sulfuric acid and under different activation temperatures. Results show that the optimum treatment process involved 10% sulfuric acid at 350° C. The effects of contact time, pH, initial concentration, sorbent dosage, temperature, sorption isotherms and the presence of other anions on its sorption capacity were studied. Isotherm data could be fitted into a modified Langmuir isotherm model implying monolayer coverage of Cr(VI) on acid activated spent bleaching earth. The maximum sorption capacity derived from the Langmuir isotherm was 21.2 mg g‐1. This value was compared with those of some other low cost sorbents. Studies of anion effect on the uptake of Cr(VI) on acid activated spent bleaching earth provided the following order of suppression: EDTA >PO4 3‐>SSO4 2‐ >NO3>Cl‐.

Natural Organic Matter Sorption by Kaolinite: Modified Langmuir Isotherm

This technical note describes the use of the modified Langmuir isotherm (MLI) model recently introduced by Gu and coworkers to describe the adsorption and desorption of natural organic matter (NOM) onto Kaolinite. The MLI was able to describe the adsorption of two different NOM samples with the use of three adjustable parameters. A commercial humic acid adsorbed to a much larger extent than a NOM sample collected from a swamp. The hysteresis coefficient was used to describe adsorption-desorption reversibility. Both samples had similar hysteresis coefficients. Such affinity parameters, however, determined from adsorption and desorption experiments, varied significantly. This study concludes that the new MLI model is better than the traditionally used Langmuir isotherm in describing adsorption-desorption of NOM to Kaolinite and desorption parameters may be considered to describe dissolved organic carbon concentrations in subsurface environments.