Sorption Of Acid Research Articles

Sorption of flavonoids and aromatic acids on hypercrosslinked polystyrene in systems with addition of imidazolium ionic liquids

In this work the effect of the addition of five imidazolium ionic liquids (ILs) to the water-acetonitrile eluents on the sorption of aromatic acids and flavonoids on hypercrosslinked polystyrene (HPS) was evaluated by reversed-phase HPLC (RP HPLC). It was found that both the nature of the cation and the nature of the anion of the used IL influence the retention of the studied compounds. The retention of aromatic acids and flavonoids in the systems without and with the addition of trifluoroacetic acid (TFA) to the eluent was investigated. It was shown that the addition of TFA to the water-acetonitrile eluent changes the mechanism of action of imidazolium ILs on the retention of sorbates on HPS. In particular, the sequence of elution of ferulic acid, salicylic acid and caffeic acid in the systems with addition of ILs to the mobile phase on HPS varies depending on the pH of the medium (depend of the addition of TFA). The Snyder-Soczewiński and Soczewiński–Wachtmeister models were used to evaluate the influence of water-acetonitrile eluent composition on the retention of studied compounds. The angular coefficients of the corresponding models were calculated.

Modeling and optimization of adsorption behavior of lactic acid onto zirconium-based metal-organic framework: response surface methodology (RSM)

ABSTRACT Lactic acid is readily generated in bacterial fermentations; however, a significant amount of processing and expenses are required for the purification of lactic acid in the fermentation broth. In this work, the sorption of lactic acid from a simulated broth has been studied by utilizing zirconium-based metal-organic framework (Zr-UiO-66 MOF) that acts as a prominent adsorbent due to its specific geometries and functional groups. The morphological, and structural properties of the prepared MOF are investigated using different characterization techniques such as Field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) pattern, Fourier transform infrared (FTIR) analysis, and Brunauer-Emmett-Teller (BET) analysis. The characterization results demonstrate the accuracy of the synthesis procedure. In order to achieve an efficient lactic acid separation process, it is essential to determine the optimal operational conditions. To address this, response surface methodology (RSM) was employed to devise an approach for optimizing five crucial process parameters for achieving the optimal response in lactic acid recovery removal. These parameters include initial LA concentration (ranging from 1 to 36 mg.L−1), pH (3–10), temperature (25 to 55 °C), adsorbent mass (0.25 to 1 g), and contact time (10 to 240 min). The RSM analysis revealed that the quadratic model provided the best fit for the experimental data, with a high coefficient of determination (R2). Three validation trials were carried out to determine the precision of the optimization process, leading to a maximum adsorption efficiency of 97.7% being reached under the optimized conditions (initial concentration = 18.5 mg.L−1, pH = 6.5, adsorbent mass = 0.625 g, contact time = 240 min, and temperature = 40 °C).

Microstructural Modification and Sorption Capacity of Green Coffee Beans.

To enhance the pore structure of green coffee beans (GCB) and detect the sorption capacity and extraction characteristics of flavor compounds before roasting, this study employed several methods: hot air drying (HD), freeze-drying (FD), 3-levels short-time heating with puffing (SH1P, SH2P, and SH3P), and 3-levels microwave with puffing (MW45P, MW60P, and MW75P). These methods were applied to GCBs pre-soaked in water for different times. The effects of these treatments on color change, porosity, microstructure, citric acid sorption capacity, and caffeine and chlorogenic acid extraction yield were investigated. Results indicated that, except for GCBs treated with SH1P, SH2P, SH3P, and MW75P, all other modified GCBs showed minimal color change. GCBs treated with MW60P exhibited favorable pore structures. MW60P treatments significantly improved the extraction yield of caffeine and chlorogenic acid. Furthermore, the increased porosity and improved pore size distribution of GCB after MW60P resulted in a significant increase in the sorption of citric acid onto modified GCB. The rate of the sorption reaction followed the pseudo-first-order kinetics. In conclusion, MW60P are effective treatments for enhancing the microstructure of GCB, improving sorption capacity, and improving the extraction yield of flavor compounds.

Rebuttal to Correspondence on "Effects of Temperature and DC Electric Fields on Perfluorooctanoic Acid Sorption Kinetics to Activated Carbon".

Rebuttal to Correspondence on "Effects of Temperature and DC Electric Fields on Perfluorooctanoic Acid Sorption Kinetics to Activated Carbon".

Correspondence on "Effects of Temperature and DC Electric Fields on Perfluorooctanoic Acid Sorption Kinetics to Activated Carbon".

Correspondence on "Effects of Temperature and DC Electric Fields on Perfluorooctanoic Acid Sorption Kinetics to Activated Carbon".

Sorption of PFOS onto polystyrene microplastics potentiates synergistic toxic effects during zebrafish embryogenesis and neurodevelopment

Microplastics (MPs) have become an emerging anthropogenic pollutant, and their ability to sorb contaminants potentially enhances the threats to the ecosystem. Only a few studies are available to understand the combined effects of microplastics and other pollutants. The present study investigated the sorption of perfluorooctane sulfonic acid (PFOS) onto polystyrene microplastics (PS-MPs) at varying concentrations, using molecular dynamics simulation (MDS) to preliminarily explore the adsorption behavior. The MDS results revealed negative interaction energies between PFOS and PS-MPs, underscoring PS-MPs' role as a potential adsorbent for PFOS in an aqueous solution. Thereafter, zebrafish embryos were employed to explore the toxic effects of combined exposure to PS-MPs and PFOS. Fluorescence and Scanning Electron Microscopy (SEM) suggested PS-MP accumulation individually and in combination with PFOS on the embryonic chorion membrane. As a result, the exposed group showed increased inner pore size of the chorionic membrane and accelerated heartbeat, indicating hypoxic conditions and hindered gaseous exchange. PS-MPs aggravated the toxicity of PFOS during larval development manifested by delayed hatching rate, increased mortality, and malformation rate. Additionally, increased ROS accumulation and altered antioxidant enzymatic status were observed in all the exposed groups suggesting perturbation of the redox state. Additionally, co-exposure of zebrafish larvae to PS-MPs and PFOS resulted in an abrupt behavioral response, which decreased AChE activity and altered neurotransmitter levels. Taken together, our results emphasize that PS-MPs can act as a potential vector for PFOS, exerting synergistic toxic effects in the aquatic environment, and hence their health risks cannot be ignored.

Quantifying the sediment sorption of organic ultraviolet filter chemicals using solvophobic theory

Hydrophobic organic chemicals (HOCs) that enter the aquatic environment often negatively impact organisms, endangering aquatic biodiversity. Understanding sediment sorption equilibria for these chemicals can properly direct mitigation efforts. In addition, many HOCs of environmental concern lack sufficient environmental fate data to adequately assess their risk to ecosystems and humans. In this study, a sorption method addressing solvophobic effects was used to quantify the sorption of an HOC of current environmental concern, OD-PABA (padimate O, 2-ethylhexyl-4-(dimethylamino)benzoate), to a variety of sediments. OD-PABA is an organic ultraviolet filter chemical used in commercial sun protection products; it has been shown to exhibit cytotoxic effects and is known to photochemically transform under natural sunlight conditions. Given its commercial use, it enters the aquatic environment via recreational use and wastewater treatment plant effluent. OD-PABA is strongly hydrophobic; to mitigate the adsorption of OD-PABA to the container walls during sorption experiments, a precise concentration of methanol was used to avoid solvophobic effects. This sorption method was used to determine the sorption capacities for OD-PABA of four sediment samples, each with unique geochemical characteristics. Sediment-water distribution coefficients (Kd) were quantified and were normalized to various sediment characteristics to assess the main driving force(s) for sorption of OD-PABA. Organic carbon content was found to be a main driving force, with organic carbon-normalized distribution coefficients (log Koc) ranging from 4.4 to 4.6 for sediments with total organic carbon (TOC) > 10%); the clay fraction was also found to be important, especially for sediments with low TOC. The sorption of para-aminobenzoic acid (PABA), a water-soluble analog of OD-PABA was also investigated to assess the experimental approach, yielding a log Koc of 2.1 for the sediment with the greatest TOC.

Conceptualizing Controlling Factors for PFAS Salting Out in Groundwater Discharge Zones Along Sandy Beaches.

Understanding fate and transport processes for per- and poly-fluoroalkyl substances (PFAS) is critical for managing impacted sites. "PFAS Salting Out" in groundwater, defined herein, is an understudied process where PFAS in fresh groundwater mixes with saline groundwater near marine shorelines, which increases sorption of PFAS to aquifer solids. While sorption reduces PFAS mass discharge to marine surface water, the fraction that sorbs to beach sediments may be mobilized under future salinity changes. The objective of this study was to conceptually explore the potential for PFAS Salting Out in sandy beach environments and to perform a preliminary broad-scale characterization of sandy shoreline areas in the continental U.S. While no site-specific PFAS data were collected, our conceptual approach involved developing a multivariate regression model that assessed how tidal amplitude and freshwater submarine groundwater discharge affect the mixing of fresh and saline groundwater in sandy coastal aquifers. We then applied this model to 143 U.S. shoreline areas with sandy beaches (21% of total beaches in the USA), indirectly mapping potential salinity increases in shallow freshwater PFAS plumes as low (<10 ppt), medium (10-20 ppt), or high (>20 ppt) along groundwater flow paths before reaching the ocean. Higher potential salinity increases were observed in West Coast bays and the North Atlantic coastline, due to the combination of moderate to large tides and large fresh groundwater discharge rates, while lower increases occurred along the Gulf of Mexico and the southern Florida Atlantic coast. The salinity increases were used to estimate potential perfluorooctane sulfonic acid (PFOS) sorption in groundwater due to salting out processes. Low-category shorelines may see a 1- to 2.5-fold increase in sorption of PFOS, medium-category a 2.0- to 6.4-fold increase, and high-category a 3.8- to 25-fold increase in PFOS sorption. The analysis presented provides a first critical step in developing a large-scale approach to classify the PFAS Salting Out potential along shorelines and the limitations of the approach adopted highlights important areas for further research.

Volatile compounds of Croatian cheese in a lamb skin sack prepared from a mixture of goat's and cow's milk

Volatile aroma compounds are one of the main parameters in consumer choice and acceptance of cheese. The traditional way of making cheese, still preserved in Croatia, is the anaerobic ripening of curds in a lamb or goat sack. Cheeses produced in such a way have a specific aroma. The objective of this study was to determine the volatile compounds of Croatian cheese in a lamb skin sack prepared from a mixture of goat's and cow's milk and relate them with the aroma of this traditional cheese. The cheese extracts were obtained by headspace solid-phase microextraction (HS-SPME) and ultrasonic solvent extraction (USE) and analysed by gas chromatography-mass spectrometry (GCMS). HS-SPME was performed at different temperatures (40, 50 and 60°C) using 2 fibres, divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fibre and carboxen/ polydimethylsiloxane (CAR/PDMS) fibre. Increasing the extraction temperature resulted in higher sorption of fatty acids on both fibres. A total of 28 volatile compounds were identified in the cheese samples including 13 acids, 10 esters, 2 alcohols, 2 hydrocarbons and 1 ketone. Results revealed that fatty acids were the predominant group of volatile compounds in all samples. In samples obtained by HS-SPME, the most abundant were hexanoic, octanoic, butanoic, acetic and decanoic acid while (Z)-octadec-9-enoic, hexadecanoic, decanoic and tetradecanoic acid were the most abundant in the sample obtained by USE.

Activation of sawdust biochar with water and wastewater treatment residuals for sorption of perfluorooctanesulfonic acid in water

Recent research has found biochar to be a cost-effective adsorbent for removal of perfluoroalkyl substances in water. To promote cleaner production and sustainable waste management, this study explored the potential to produce activated biochars by co-pyrolyzing sawdust with iron-rich biosolids and polyaluminum sludge. The maximum capacity to adsorb perfluorooctanesulfonic acid (PFOS) reached 27.2 mg g−1 with biosolids-activated biochar and 19.2 mg g−1 with aluminum sludge-activated biochar, compared to 6.2 mg g−1 with sawdust biochar. The increased adsorption capacities were attributed to electrostatic interactions between the anionic PFOS and metal functionalities on the biochar surface. In contrast, hydrophobic interaction was the dominant adsorption mechanism of sawdust biochar. The presence of dissolved organic matter at 5–50 mg L−1 was found to inhibit adsorption of PFOS in water, while pH as low as 3.0 and sodium chloride concentrations up to 100 mM enhanced removal of PFOS by all the three adsorbents. In batch adsorption tests at environmentally relevant PFOS dosages and adsorbent dosage of 0.25 g L−1, the biosolids-sawdust biochar and Al sludge-sawdust biochar removed 71.4% and 66.9% of PFOS from drinking water and 77.9% and 87.9% of PFOS from filtrate of sludge digestate, respectively. The biosolids-sawdust biochar additionally removed Fe, although the Al sludge-sawdust biochar released Al into the alkaline drinking water and filtrate. Overall, this study proved co-pyrolyzing sawdust and Fe-rich biosolids to be an effective approach to activate sawdust biochar for enhanced removal of PFOS while recycling wastewater treatment residuals and sawdust.

Effects of Temperature and DC Electric Fields on Perfluorooctanoic Acid Sorption Kinetics to Activated Carbon.

Sorption to activated carbon is a common approach to reducing environmental risks of waterborne perfluorooctanoic acid (PFOA), while effective and flexible approaches to PFOA sorption are needed. Variations in temperature or the use of electrokinetic phenomena (electroosmosis and electromigration) in the presence of external DC electric fields have been shown to alter the contaminant sorption of contaminants. Their role in PFOA sorption, however, remains unclear. Here, we investigated the joint effects of DC electric fields and the temperature on the sorption of PFOA on activated carbon. Temperature-dependent batch and column sorption experiments were performed in the presence and absence of DC fields, and the results were evaluated by using different kinetic sorption models. We found an emerging interplay of DC and temperature on PFOA sorption, which was linked via the liquid viscosity (η) of the electrolyte. For instance, the combined presence of a DC field and low temperature increased the PFOA loading up to 38% in 48 h relative to DC-free controls. We further developed a model that allowed us to predict temperature- and DC field strength-dependent electrokinetic benefits on the drivers of PFOA sorption kinetics (i.e., intraparticle diffusivity and the film mass transfer coefficient). Our insights may give rise to future DC- and temperature-driven applications for PFOA sorption, for instance, in response to fluctuating PFOA concentrations in contaminated water streams.

Sorption of picolinic acid by Cu(II)-containing sulfocationite KU-2-8

Objectives. To study the equilibrium distribution of components between KU-2-8 sulfocationite and an aqueous solution containing picolinic acid and Cu(II); to show the possibility of immobilization of cations of picolinic acid and Cu2+ in sulfonic cation exchanger KU-2-8; to calculate the component compositions of the equilibrium solution, in order to obtain the required ionic composition of the KU-2-8 sulfonic cation exchanger according to the selectivity coefficients of binary ion exchange, and the constants of formation of such complexes in water.Methods. The concentrations of the individual components in multicomponent solutions were calculated using the HySS 2009 program (Hyperquad Simulaton and Speciation). The calculation of the equilibrium ionic compositions of KU-2-8 sulfocationite was performed using the selectivity coefficients of binary ion exchanges and the formation constants of complexes of picolinic acid with Cu2+ and H+ cations. Experimental study of the equilibrium distribution of components between aqueous solutions of picolinic acid, copper nitrate, and KU-2-8 sulfocationite was carried out by means of the dynamic method at a temperature of 298 K. Fourier-transform infrared spectroscopy and electron paramagnetic resonance spectroscopy were used, in order to determine the ionic forms of the components contained in the sulfocationite.Results. It was shown that the equilibrium solution contains H+ protons, Cu2+ cations, LH picolinic acid molecules, protonated picolinic acid cations [H2L]+, deprotonated picolinic acid anions L-, Cu2+ complexes with the deprotonated picolinic acid anion [CuL]+, and Cu2+ complexes with two anions of deprotonated picolinic acid [CuL2]. The concentration of H+, Cu2+, and [H2L]+ cations in the solution significantly exceeds the concentration of other components at pH values from 0 to 0.5. The content of [CuL]+ cations and neutral complexes [CuL2] increases significantly in the solution, while the [H2L]+ cations disappear at pH greater than 1. It was experimentally established that the concentrations of picolinic acid and copper in the polymer phase are many times higher than the concentrations of these components in an aqueous solution. The partition coefficients are about 24 and 210 for picolinic acid and Cu(II), respectively. The calculated dependencies of the concentrations of Cu2+, [H2L]+, H+, [CuL]+ cations in the polymer vs pH of an equilibrium solution containing picolinic acid were obtained. The experimental data on the concentrations of all cations in the ion exchanger is in the intervals of the calculated compositions within the limits of measurement errors.Conclusions. KU-2-8 sulfocationite is proposed as a container for obtaining drugs based on picolinic acid and Cu2+ cations. It was shown that the selectivity coefficients of binary ion exchanges and the formation constants of [H2L]+, [CuL]+ complexes can be used to precalculate the ionic compositions of the equilibrium solution, in order to obtain the required compositions of the sulfocationite.

Selective sorption of hippuric acid and 4-methylhippuric acid by polyethylene glycol modified ZIF based molecular imprinted polymer

A novel solid phase extraction (SPE) adsorbent, polyethylene glycol (PEG) immobilized zirconium ion-modified zeolite-imidazole framework (ZIF) molecular-imprinted polymer (ZIF@PEG@Zr@MIPs), was developed for detecting hippuric acid (HA) and 4-methylhippuric acid (4-MHA) in human urine using HPLC-UV. Zirconium ions (Zr4+) anchored on the porous ZIF act as binding sites, facilitating coordination and electrostatic interaction with HA and 4-MHA carboxyl groups. Dopamine (DA) imprinting introduces additional sites, enabling π-π conjugation and hydrogen bonding with HA and 4-MHA, enhancing specific adsorption. The adsorbent, using HA as a template, demonstrated adsorption capacities of 37.98 mg g−1 for HA and 32.99 mg g−1 for 4-MHA. Imprinted factors (IF) were 2.68 for HA and 2.17 for 4-MHA, with a limit of detection (LOD) of 0.015 mg L−1 for HA and 0.011 mg L−1 for 4-MHA. The SPE-HPLC-UV method achieved 84.8–96.2% recovery and 0.3–2.2% relative standard deviation (RSD), illustrating its potential in health monitoring and environmental safety.

Degradation and sorption of the herbicide pelargonic acid in subsoils below railway tracks compared to a range of topsoils

BackgroundPelargonic acid is a non-selective herbicide derived from natural sources with a range of potential applications in areas where synthetic herbicides may be less acceptable. One such use area is weed control on railway tracks. To assess the potential leaching of pelargonic acid to groundwater for this specific use, we conducted degradation and sorption studies with soils from railway tracks and, for comparison, with a range of topsoils.ResultsDegradation of pelargonic acid was very rapid in subsoils from railway tracks with half-lives (DT50) of < 1 day (geom. mean DT50, 5.8 h), and even faster in the selected agricultural topsoils (1.5 h). The starting concentration had a strong influence with much slower degradation at higher spike levels. Adsorption to the railway soils (alkaline soils with low organic matter content) was expectedly weak (Freundlich adsorption coefficients KF of 0.06–0.31 mL/g) and clearly stronger in the topsoils (0.2–40 mL/g). Organic carbon normalized adsorption coefficients (KFoc) ranged from 11 to 371 mL/g (all soils) and were pH dependent, consistent with the behaviour of weak acids. Computer modelling using the software PELMO and a set of scenarios for herbicide use on railway tracks developed for the authorisation in Germany yielded predicted environmental concentrations in groundwater of < 0.001 µg/L when parameterised with the adsorption and degradation endpoints from subsoils.ConclusionsThe leaching potential of pelargonic acid may be considered low even in application scenarios with sandy soils with low organic matter content such as those found below railway tracks.

Experimental and theoretical studies of the interactions of alanine onto surfaces of olivine and montmorillonite: relevance in astrobiology

Abstract Amino acids have been detected in some meteorites and are readily synthesized in prebiotic experiments. These molecules may have been precursors of oligomers and polymers in the early Earth. These reactions were likely to happen in the protected confined spaces on the porous surface of olivine and in the interlayer nanospace of montmorillonite. This study describes experimental and theoretical research on the sorption of l-alanine onto surfaces of silicate minerals, olivine and montmorillonite. Kinetics of the sorption of this amino acid at different pH media was performed. This sorption has been also studied at atomic scale by means of quantum mechanical calculations finding that this sorption is energetically favourable. These results strongly support the premise that minerals could have actively participated in prebiotic reactions.

Sorption behavior of three aromatic acids (benzoic acid, 1-naphthoic acid and 9-anthroic acid) on biochar: Cosolvent effect in different liquid phases

Influence of the cosolvent on the sorption of organic acids on biochar has not been well understood. For this purpose, the sorption (log Km, L kg−1) of three aromatic acids (benzoic acid (BA, pKa = 4.20), 1-naphthoic acid (1-NAPA, pKa = 3.70), and 9-anthroic acid (9-ANTA, pKa = 3.65) was evaluated as a function of methanol volume fraction (fc = 0.0, 0.25, and 0.5), liquid pH (2.5 and 7.0), ionic composition (CaCl2 and KCl) and ionic strength (0.005 M, 0.5 M, and 1 M CaCl2). A giant Miscanthus-derived biochar (ZPC of 2.86) was used as the sorbent. For all solutes, the sorption coefficients (log Km) measured at pH 2.5 (i.e., pH < pKa) tended to decrease with increasing fc, as expected from the cosolvency model, while the result obtained at pH 7.0 was not fully explained by the same model. The log Km of 1-NAPA in the CaCl2 system was always greater than in the KCl system (p < 0.05) and the impact became pronounced at high pH (>pKa) with increasing fc. Increasing the Ca2+ concentration at fc = 0.0 (from 0.005 M to 1 M) enhanced the value by 0.32 log unit of Km. These phenomena indicate a significant role of dissolved Ca2+ in the liquid phase, most likely due to the formation of cation bridges between aromatic carboxylates and the biochar surface (i.e., [R-COO--Ca2+]-{Biochar−}). A decrease in the dielectric constant of the methanol mixture could fortify the formation of this bridge. Regardless of the degree of cosolvency power (σ), as the number of aromatic rings of solutes increases, Km decreases in the order BA > 1-NAPA > 9-ANTA, where fc = 0.0. In conclusion, the sorption potential of biochar can be significantly weakened by increasing pH and fc, and in the absence of a divalent cation.

Promotion of phosphate release from humic acid-iron hydroxide coprecipitates in the presence of citric acid

Phosphate (P) resources are expected to be depleted within a century. Therefore, promoting balanced phosphorus fertilizer use and understanding phosphorus dynamics in soils containing iron (III), organic acids, and iron (III)-organic molecule particulates is crucial. This study investigated the sorption of citric acid onto humic acid-iron hydr(o)xide coprecipitate (HAFHCP) and the reciprocal effects of citric acid and P sorption on HAFHCP with different C/Fe ratios. The results showed that the maximum sorption capacity (MSC) of citric acid on HAFHCP decreased with increasing C/Fe ratios in the HAFHCP. The P sorption on HAFHCP pre-sorbed with citric acids (denoted as C–P) decreased by 50% compared with that of the MSC on FH. However, citric acids could only reduce P sorption by 20% when P was pre-sorbed on HAFHCP (denoted as P–C). The results suggested that upon the formation of HAFHCP, citric acids might increase P availability, especially in the C–P system. Although citric acids initially inhibited P sorption on HAFHCP in the P–C system, P sorption increased with prolonged reaction time. The exposures of new sorption sites upon dissolution of Fe from HAFHCP by citric acids or/and the formations of Fe bridge between P and organic domains of HAFHCP might contribute to these results. Additionally, a number of large HAFHCP aggregates became smaller while sorbing P due to the increasing electric repulsion on the surfaces of FH, enabling the subsequent dissolutions of more Fe by citric acids from HAFHCP in the P–C system. By integrating these innovative and sustainable strategies, the recycling and reuse of P can be optimized, thereby minimizing the reliance on synthetic fertilizers and mitigating environmental impacts. This approach fosters the efficient utilization of phosphorus resources, improves soil fertility, and enhances the overall resilience of agricultural systems and ecosystems.

Influence of temperature on non-exchange sorption of aromatic amino acids by anion exchanger AV-17-8

The equilibrium in thearomatic amino acid (tryptophan, phenylalanine, tyrosine and histidine) – anion exchanger AV-17-8 (Cl-) systems at different temperatures was investigated In order to identify the influence of both increased and decreased temperatures on the sorption equilibrium the temperature range was 277-343 K was studied. Sorption isotherms were obtained at 277, 293, and 343 K. The thermodynamic description of sorption systems was carried out using an approach based on the idea that the sorption process is stoichiometric. The integral and differential energy characteristics and the compensation effect between the enthalpy and entropy components for the studied sorption systems were calculated. A change in temperature led to a change in the physicochemical properties of the studied sorbates and sorbent. In the temperature range 277-243 K, the solvent content in the sorbent phase remained unchanged. A low solvent content at a temperature of 333 K and an increase in its amount at 343 K were experimentally established. It should be considered that at different temperatures the ionization constants of functional groups and the regions of existence of ionic forms of amino acids change, but the sorption mechanism does not change, since the recharging of amino acids did not occur. It was established that the process is exothermic for tryptophan and phenylalanine. With increasing temperature, the amount of sorbed substance decreased. The absorption energy was low due to the significant compensatory effect of enthalpy and entropy factors, the differential Gibbs energy was practically independent of temperature due to the stabilizing effect of hydrophobic forces in the sorbent phase. For the poorly soluble amino acid tyrosine, when the temperature increased from 277 to 293 K, a slight increase in sorption was observed, and with a further increase, a decrease to trace amounts was revealed. In the temperature range of 277-293 K, the sorption process was characterized by the formation of a supersaturated solution in the sorbent phase and was endothermic. The sorption of hydrophilic histidine increased with increasing temperature, which correlates with the solvent content in the sorbent phase, including low content at 333 K. The process of histidine sorption is endothermic, characterized by a strong dependence of the differential Gibbs energy on temperature and the absence of a compensation effect between the enthalpic and entropic components.

Sorption of Picolinic Acid and Iron(III) by Sulfocationite Dowex 50

Sorption of Picolinic Acid and Iron(III) by Sulfocationite Dowex 50

Investigation of Adsorption Isotherm Models for Interaction of P(AAm-ClAETA) and Carminic Acid, and Theoretical Approaches

In this study, the adsorption isotherm models for the sorption of carminic acid on P(AAm-ClAETA) hydrogels are explained by experimental and theoretical studies. The crosslinked hydrogels with ethylene glycol dimethacrylate were prepared by radical addition reaction of acrylamide (AAm) and 2-(acryloyloxy)ethyl trimethylammonium chloride (ClAETA) monomers in an aqueous solution. The spectral and morphological analyses of P(AAm-ClAETA) hydrogels were performed by FTIR/ATR and SEM, respectively. The adsorbed amounts of carminic acid on P(AAm-ClAETA) hydrogels were evaluated by Giles, Langmuir, and Freundlich adsorption isotherm models. Langmuir parameters were calculated for the adsorption of the dye on the hydrogels according to the L-type Giles isotherm. In addition, it was determined that its adsorption was appropriate from the RL values calculated for 500 mg L-1 carminic acid concentration. In addition, molecular electrostatic potential (MEP) mapping was performed to predict the reactive sites of P(AAm-ClAETA) hydrogels and carminic acid. The results showed that the theoretical and experimental data of the hydrogels were in agreement with each other. As a result, it can be said that P(AAm-ClAETA) hydrogels are suitable for the removal of anionic dyes such as carminic acid from aqueous solutions.