Freundlich Langmuir Model Research Articles

Molecularly Imprinted Polymeric Nanoparticles as Drug Delivery System for Tenofovir, an Acyclic Nucleoside Phosphonate Antiviral.

A molecularly imprinted polymer of Tenofovir (1), an FDA-approved acyclic nucleoside phosphonate with antiviral activity, was synthesized using a non-covalent approach. A pre-polymerization complex was formed between (1) and DMAEMA and in-house synthetic N1-[(2-methacryloyloxy)ethyl] thymine, with EGDMA as a cross-linker in an MeCN/H2O (9:1, 1:1) mixture as a porogen, giving an imprinting factor (IF) of 5.5 at 2.10-5 mol/L. Binding parameters were determined by the Freundlich-Langmuir model, Qmax and Ka, and well as the particle morphology for MIP and NIP. Finally, the release profiles, for MIP and NIP, were obtained at 25 °C and 37 °C, which is body temperature, in a phosphate buffer saline, pH 7.4, mimicking the blood pH value, to determine the potential sustained release of our polymeric materials.

Removal and Adsorption Mechanisms of Phosphorus, Cd and Pb from Wastewater Conferred by Landfill Leachate Sludge-Derived Biochar

There is a high treatment cost and secondary pollution to the environment due to the high organic content and complex composition in landfill leachate sludge in refuse incineration power plants. Landfill leachate sludge-derived biochar (LLSDB) was prepared via pyrolysis in order to realize its resource utilization and remove pollutants from wastewater. The study focused on the removal of nutrients phosphorus and heavy metals (Cd(II) and Pb(II)) from wastewater through the adsorption process using LLSDB. The investigation also looked into the kinetics and thermodynamics of the adsorption process. It was found that the Freundlich–Temkin–Langmuir model was the best model for describing the initial concentration of total phosphorus, (TP) 0–1.0, 1.0–20, and 20–120 mg/L, respectively, while the Freundlich–Langmuir model was the best model for Cd(II) 100–500 mg/L, Pb(II) 500–5000 mg/L, respectively. Additionally, while the exothermic entropy reduction process for TP (˂1.0 mg/L) was spontaneous, the endothermic entropy increment processes for TP (≥1.0 mg/L), Pb(II) and Cd(II) in wastewater increased with the adsorption temperature. It was inferred for the adsorption mechanism of LLSDB that the adsorption of low concentrations of TP, Cd(II) and Pb(II) from wastewater was mainly physical adsorption, following a linear distribution, while that of high concentrations was mainly chemical adsorption because of a series of chemical reactions; TP, Cd(II) and Pb(II) from wastewater were nicely adsorbed and removed by LLSDB600, which was an incredibly superior strategy for controlling waste with waste.

Comparison of the adsorption capacity and mechanisms of mixed heavy metals in wastewater by sheep manure biochar and Robinia pseudoacacia biochar.

Under various pyrolysis temperatures, the characteristics and heavy metal adsorption capabilities of biochar obtained from sheep manure (SMB) and Robinia pseudoacacia (RPB) were studied. The results indicated that SMB had higher yields, pH values, and ash contents than RPB. SMB3 and RPB3 have more oxygen-containing functional groups, whereas SMB8 and RPB8 have higher aromaticity and polarity. The maximum adsorption capacities of SMB for Pb2+ (20.2 mg·g-1), Cu2+ (13.9 mg·g-1), Cd2+ (3.2 mg·g-1), and total heavy metals (37.3 mg·g-1) were obtained by SMB3. However, the maximum adsorption capacities of RPB for Pb2+ (7.4 mg·g-1) and Cu2+ (10.5 mg·g-1) were obtained by RPB8. Furthermore, SMB and RPB had relatively higher adsorption capacities for Pb2+ and Cu2+ than for Cd2+. The pseudo-second-order model and the Freundlich Langmuir model provided a good fit to the adsorption kinetics and isotherms, indicating that chemical adsorption was dominant in the heavy metal adsorption by SMB and RPB. According to the contribution of various mechanisms, ion exchange and mineral precipitation were the primary mechanisms responsible for RPB8, while functional group complexation was the dominant mechanism for SMB3. This study provided important information on the comprehensive recycling utilization of SMB and RPB and promoted sustainable development.

Mobility of organotin pesticides: azocyclotin and cyhexatin in clayey and sandy soils from the Northern Paraná state—Brazil

Azocyclotin and cyhexatin are pesticides commonly used in mite control. However, these organotin compounds (OTC) are highly harmful to the aquatic ecosystem and supposedly mobile in the soil. In addition to not existing defined rules of use, few studies have been carried out on organotins’ behavior and environmental control. Liquid chromatography has been pointed out for the OTC quantitation because of gas chromatography’s thermal stability and derivatization limitations. Hence, a new high-performance liquid chromatography method with photodiode array detection was developed for quality assurance and quality control and environmental performance assessment purposes. Hysteresis index (HI) and mobilization factor were determined from sorption/desorption in sandy and clayey soils to assess mobility and environmental risk. Mobilization was observed for the two compounds by applying the dual-mode Freundlich–Langmuir model to the isotherms. Azocyclotin showed greater mobility, 23% and 19%, and HI of − 0.15 and 7.8 \(\times \) 10\(^{-4}\) for clayey and sandy soil samples, respectively. Although cyhexatin was practically immobile for both soil samples, it can be mobilized as an azocyclotin metabolite, increasing the environmental impact and risk for agricultural uses.

Hydration mechanisms of scheelite from adsorption isotherms and ab initio molecular dynamics simulations

Apart from its interesting optical properties, scheelite is one of the main tungsten-bearing minerals, widely processed by the froth flotation method. A precise and comprehensive description of the hydration state of scheelite is required to achieve satisfactory flotation performance. The hydration mechanisms of scheelite have been poorly studied, using only theoretical methods. Manometric gas sorption experiments were combined with ab initio molecular dynamics simulations, including correction for dispersive interactions. The isosteric enthalpy of adsorption was used as the value to link experimental and theoretical results, since it can be determined by both methods. We have found that water adsorbs more favorably in its molecular form, with two adsorbed water molecules per calcium atom on the (001) surface, and with three adsorbed water molecules for two calcium atoms on the (112) surface. The very first water molecules adsorb with an isosteric enthalpy of adsorption of–80 kJ·mol−1 on the (001) surface, and of –117 kJ·mol−1 on the (112) surface, at 300 K. This is in very good agreement with the value of −90 kJ·mol−1 calculated using the Clausius-Clapeyron approach on three experimental isotherms, accurately fitted with a dual-site Freundlich-Langmuir model.

Crayfish shell biochar modified with magnesium chloride and its effect on lead removal in aqueous solution.

In this study, crayfish shell was pyrolyzed at 600°C to obtain an unmodified biochar (CS600). MgCl2 was used as a modifier to pretreat crayfish shell to produce a modified biochar (CS600-MgCl2) under the same pyrolysis conditions. The two biochars were characterized for physicochemical properties and evaluated for lead (Pb2+) sorption ability to determine the modification mechanism. Mono-element batch adsorption experiments were conducted to compare the sorption performances of CS600 and CS600-MgCl2 to Pb2+ in aqueous solutions. All the experiments were carried out at pH of 7. According to the Freundlich-Langmuir model, CS600-MgCl2 had a higher adsorption capacity (152.3mg/g) than CS600 (134.3mg/g). FTIR, SEM, XRD, BET, and ICP analyses were applied to inform the interpretation of the mechanism. CS600 was calcium-rich and mainly removed Pb2+ through the ion exchange mechanism by replacing Ca2+ in the biochar. The increased Pb2+ adsorption capacity of CS600-MgCl2 was mainly due to the enlarged specific surface area and the formation of Mg3(OH)5Cl·4H2O on the modified biochar. Findings of this study suggest that both CS600 and CS600-MgCl2 can be used to remove heavy metal ions from wastewater and MgCl2 can improve the sorption performance of biochar.

Ordered Mesoporous Carbons for Adsorption of Paracetamol and Non-Steroidal Anti-Inflammatory Drugs: Ibuprofen and Naproxen from Aqueous Solutions

The adsorption of paracetamol and non-steroidal anti-inflammatory drugs (ibuprofen and naproxen) on ordered mesoporous carbons (OMC) and, for comparison, on commercial activated carbon, were investigated in this work. OMC adsorbents were obtained by the soft-templating method and were characterized by low-temperature nitrogen adsorption and scanning electron microscopy (SEM). The effects of contact time and initial concentration of organic adsorbates on the adsorption were studied. The contact time to reach equilibrium for maximum adsorption was 360 min for all the studied adsorbates. The adsorption mechanism was found to fit pseudo-second-order and intra particle-diffusion models. Freundlich, Langmuir and Langmuir-Freundlich isotherm models were used to analyze equilibrium adsorption data. Based on the obtained experimental data, the adsorption isotherm in the applied concentration range for all the studied adsorbates was well represented by the Freundlich-Langmuir model. The adsorption ability of ordered mesoporous carbon materials was much higher for paracetamol and naproxen in comparison to commercial activated carbon. The removal efficiency for ibuprofen was significantly lower than for other studied pharmaceuticals and comparable for all adsorbents. Theoretical calculations made it possible to obtain optimized chemical structures of (S)-naproxen, ibuprofen, and paracetamol molecules. Knowledge of charge distributions of these adsorbate molecules can be helpful to explain why paracetamol and naproxen can react more strongly with the surface of adsorbents with a large numbers of acidic groups compared to ibuprofen facilitating more efficient adsorption of these pharmaceuticals on ordered mesoporous carbons.

Novel chitosan–ethylene glycol hydrogel for the removal of aqueous perfluorooctanoic acid

It is urgent to explore an effective removal method for perfluorooctanoic acid (PFOA) due to its recalcitrant nature. In this study, a novel chitosan-based hydrogel (CEGH) was prepared with a simple method using chitosan and ethylene glycol through a repeated freezing–thawing procedure. The adsorption of PFOA anions to CEGH agreed well to the Freundlich–Langmuir model with a maximum adsorption capacity as high as 1275.9 mg/g, which is higher than reported values of most adsorbents for PFOA. The adsorption was influenced by experimental conditions. Experimental results showed that the main removal mechanism was the ionic hydrogen bond interaction between carbonyl groups (COO−) of PFOA and protonated amine (NH+) of the CEGH adsorbent. Therefore, CEGH is a very attractive adsorbent that can be used to remove PFOA from water in the future.

Triclosan as model system for the adsorption on recycled adsorbent materials

The adsorption of triclosan as model system was studied to qualify activated carbon sorbents recycled from gas masks (civilian gas mask GP5). The triclosan equilibrium concentration was measured spectrophotometrically, the morphology of the activated carbon characterized by scanning electron microscopy, and the amount of the adsorbed triclosan on the activated carbon quantified by a mass balance method. Experimental isotherms were fitted by Langmuir, Freundlich and Sips adsorption models. It was obtained that the contact time is a crucial sorption parameter that provides information on the optimum adsorption efficiency. It was shown that the maximum efficiency of GP5 (88%) is obtained after 10days of adsorption at a maximal concentration of triclosan and carbon loading 1mg/l. No significant adsorption efficiency differences were measured after 5 and 10days of adsorption. The non-linear Sips isotherm, a combined Freundlich–Langmuir model, provides suitable fitting results. The observed remarkable adsorption capacity of activated carbon (GP5) towards triclosan adsorption (∼85mg/g) makes it a viable solution for wastewater treatment.

Iniferter-mediated grafting of molecularly imprinted polymers on porous silica beads for the enantiomeric resolution of drugs.

A surface-imprinted chiral stationary phase for the enantiomeric resolution of the antidepressant drug, citalopram, is presented in this work. N, N'-diethylaminodithiocarbamoylpropyl(trimethoxy)silane has been used as silane iniferter for the surface functionalization of the solid silica support. A molecularly imprinted polymer thin film, in the nm scale, was then grafted on the silanized silica using itaconic acid as the functional monomer and ethylene glycol dimethacrylate as the cross-linker in the presence of the template S-citalopram. The total monomer amount was calculated to obtain the desired thickness. Non-imprinted stationary phases were prepared similarly in the absence of S-citalopram. Characterization of the materials was carried out by scanning electron microscopy, thermogravimetric analysis, elemental analysis and Fourier transform infrared spectroscopy. Stationary phases have been applied to the chromatographic separation of the target. Conditions for best chromatographic resolution of the enantiomers were optimized, and it was found that a mobile phase consisting of a mixture of formate buffer (40 mM, pH 3) and acetonitrile (30:70 v/v) at 40 °C provided best results. Binding behaviour of the developed material was finally assessed by batch rebinding experiments. The obtained binding isotherm was fitted to different binding models being the Freundlich-Langmuir model, the one that best fitted the experimental data. The developed material has shown high selectivity for the target enantiomer, and the stationary phase could be undoubtedly exploited for chiral separation of the drug.

Biosorption of As(III) and As(V) from aqueous solutions by brown macroalga Colpomenia sinuosa biomass: kinetic and equilibrium studies

In this research, capability of brown macroalga Colpomenia sinuosa for biosorption of arsenic [As(III) and As(V)] from aqueous solutions was investigated in a single-component batch system. Kinetic experiments indicated that As(III) and As(V) biosorption by C. sinuosa was rapid, and that 90–98% of equilibrium capacity of biosorption in 30 min was reached. Biosorption kinetics of As(III) and As(V) by the biomass at different concentrations were well described in terms of pseudo-second-order rate model (R2 > 0.999 and ɛ% < 12.1%). In the pH range of 2–9, the optimum pH values for As(III) and As(V) biosorption were determined to be 6 and 2, respectively. The optimal pH of As(V) biosorption is highly acidic and its provision in operating the process would be difficult. Isotherm experiments were conducted in initial ion concentration range of 2–100 mg/L. The isotherm data were fitted to the Langmuir, Freundlich, Langmuir–Freundlich, and Redlich–Peterson models. Isotherm data of As(III) biosorption were found to be in the best fitness with the Freundlich–Langmuir model (R2 > 0.996 and ɛ% < 4.2%) while the Langmuir model (R2 > 0.995 and ɛ% < 5.6%) described the isotherm data of As(V) biosorption better than the other isotherm models. According to the Langmuir model, the maximum biosorption capacities (qm) of As(III) and As(V) were obtained to be 95.6 and 59.9 mg/g, respectively. This study indicated that C. sinuosa biomass could be used as an efficient biosorbent for removal of As(III) and As(V) from aqueous environments.

Boc- l-tryptophan imprinted polymeric microparticles for bioanalytical applications

Molecularly imprinted polymer (MIP) microparticles with good chromatographic characteristics were synthesized via the suspension polymerization process in a single preparative step. Initially, the effects of process parameters (i.e., porogen concentration, polymerization temperature, types and concentrations of functional monomer and cross-linker) on the particle size distribution and particle morphology were experimentally investigated. Subsequently, various MIP microparticles were synthesized in the presence of an amino acid derivative (i.e., boc- l-tryptophan), acting as template molecule. Batch-wise guest binding experiments were then performed to determine the rebinding capacity of the synthesized MIP microparticles towards the template molecule. Competitive binding experiments were also carried out with boc- d-tryptophan (i.e., the enantiomer of boc- l-tryptophan) to assess the selectivity of the imprinted polymer microparticles towards the two enantiomers. Finally, a quantitative description of the experimentally measured rebinding isotherms was obtained using the well-known Freundlich–Langmuir models. The present results clearly demonstrate the potential application of the synthesized MIP microparticles for bioanalytical separation of peptides and proteins since the amino acid templates employed in this study are the building units of larger biomolecules.

Comparison of three Mexican aluminosilicates for the sorption of cadmium

The sorption of cadmium from aqueous solutions was evaluated in three Mexican aluminosilicates (two zeolites and one clay). The effects of pH and contact time on the sorption process were examined. Cadmium was analyzed by neutron activation analysis in the exchanged aluminosilicates. The sorption of cadmium by aluminosilicates was the same in the pH range from 4 to 8, considering the standard deviation. Kinetic studies were carried out and showed a rapid sorption of cadmium in the first 5 hours but the equilibrium was reached in about 20 hours. The sorption kinetics of cadmium ions was best described by the second-order Ritchie modified model. The experimental results obtained in different concentrations and at room temperature for both zeolites were fitted with classical isotherms of Freundlich, Langmuir and Freundlich-Langmuir models. The sorption pattern followed the Langmuir-Freundlich model.

Adsorption isotherms of a molecular imprinted polymer prepared in the presence of a polymerisable template: Indirect evidence of the formation of template clusters in the binding site

The current opinion about molecular imprinted polymers (MIPs) is that their molecular recognition properties are due to the presence of nanocavities formed during a polymerization process developed in the presence of a template molecule. According to this principle, the shape of these nanocavities is complementary to that of the template and non-covalent interactions are established between the binding site and a single template molecule. Nevertheless, there are some experimental indications that the real molecular recognition mechanism involves clusters of template molecules being packed into the binding site. Recently, it has been proposed that template molecules covalently linked to the binding site can act as nucleation points, enhancing the formation of these molecular clusters. We have tested this hypothesis by studying the adsorption isotherms of polymers prepared by imprinting them with 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). Three different polymers were considered: P0, prepared without the template, P1, whose template was represented by 2,4,5-T molecules, and P2, whose template was 1/3 constituted by the polymerisable 2-(2,4,5-trichlorophenoxyacetoxy)-ethylmethacrylate (2,4,5-TEMA) and 2/3 by 2,4,5-T. The polymers were prepared by thermoinduced polymerization of template mixtures, 4-vinylpyridine and ethylene dimethacrylate. The crushed polymers were packed into HPLC columns and frontal chromatographic runs were performed by eluting the columns with a mobile phase containing variable amounts of 2,4,5-T. The experimental adsorption isotherms were fitted by using several isotherm models, and the Freundlich–Langmuir model was found to give the best fitting in terms of F-test. All the models considered showed a significant difference between the affinity constant values measured for the polymer P1 and P2, with a higher value for the polymer P2 (for Freundlich–Langmuir model: polymer P1, k=(2.00±0.43)×10 4 M −1; polymer P2, k=(1.93±0.0535)×10 5 M −1; ratio P2/P1, 9.65±2.09). Such experimental results support the hypothesis that a polymer prepared with a limited amount of template covalently attached to the binding site shows an increased affinity for the template itself.

Protein Interaction with Immobilized Metal Ion Affinity Ligands under High Ionic Strength Conditions

An investigation into the adsorption behavior under batch equilibrium binding conditions of hen egg white lysozyme (HEWL) with the immobilized metal ion affinity chromatographic adsorbent, Cu2+–IDA Sepharose CL-4B, in the presence of high concentrations of NaCl or KCl has been undertaken. When the concentration of NaCl or KCl in the adsorption buffer was ≤0.2M, the adsorption data correlated with predictions based on the Langmuir model. However, when the salt concentration was ≥0.5M, the adsorption data appeared to follow the Freundlich–Langmuir model under these higher ionic strength conditions. Under elevated ionic strength conditions, the protein–ligand interactions were shown to involve positive cooperativity by Scatchard plot analysis of the experimental data. The number,n, of interacting protein molecules increased with the salt concentration, while the apparent dissociation constantKdunder these high ionic strength conditions was less dependent on the type of salt present in the adsorption buffer. These studies reveal that the binding of Cu2+–IDA Sepharose CL-4B to HEWL acceptor molecules under conditions of high ionic strength is characteristic of general heterogeneous interactions, whereby the immobilized metal ion affinity chromatography (IMAC) ligands bind to a protein acceptor undergoing isodesmic indefinite self-association and multisite attachment. As a consequence, these results on the adsorption behavior of HEWL have important general implications for the preparative use of immobilized metal ion affinity adsorbents in packed and expanded bed systems, particularly with regard to the resolution and productivity of the separation for the target protein. In addition, the results from these studies are relevant to investigations involving analytical affinity chromatographic or biosensor assessment of the interaction of proteins with immobilized IMAC ligands when high ionic strength equilibration feedstocks or conditions are employed.