Thermodynamic Characteristics Of Adsorption Research Articles

The characteristics of adsorption Cr(VI) by iron-modified and iron-doped phosphorus-based biochar biochar

ABSTRACT In this study, we evaluated the effect of the modification of biochar on the adsorption of Cr(VI) under weakly acidic conditions. Sesame straw biochar (BC) was modified by treatment with ferric chloride to produce iron-modified biochar (FBC) and ferric chloride and chlorapatite to produce iron-doped chlorapatite-modified biochar (FBCP). Analysis by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) showed that the adsorption mechanism of Cr(VI) by FBC and FBCP was reduction, physical adsorption, ion exchange, and functional group complexation. Experiments were performed to evaluate the kinetic, isothermal, and thermodynamic characteristics of adsorption, demonstrating that the adsorption of Cr(VI) by FBC and FBCP was a spontaneous endothermic reaction, consistent with the pseudo-second-order kinetic model and Langmuir model, and the process was dominated by monolayer chemical adsorption. The Langmuir model revealed maximum saturated adsorption capacities for Cr(VI) of 7.907 and 12.625 mg/g by FBC and FBCP, respectively, equating to 4.06 and 6.48 times the maximum saturated adsorption capacity of BC, respectively. Compared with FBC, the phosphate ions in FBCP also co-precipitated with Cr(III), further improving the removal efficiency of pollutants.

Thermodynamic Characteristics and Selectivity of the Liquid-Phase Adsorption of Aromatic Compounds on Hypercrosslinked Polystyrene Networks with Ultimate-High Crosslinking Densities by Data of Liquid Chromatography.

This study delves into the thermodynamics of liquid-phase adsorption on hypercrosslinked polystyrene networks (HPSNs), widely recognized for their distinct structure and properties. Despite the considerable progress in HPSN synthesis and characterization, gaps persist regarding the chromatographic retention mechanism, thermodynamics of adsorption, and their impact on the adsorption selectivity, especially in the case of networks with ultra-high crosslinking densities (up to 500%). Utilizing high-performance liquid chromatography (HPLC), we have explored, for the first time, the thermodynamic intricacies of liquid-phase adsorption onto HPSNs crosslinked in the entire range of the crosslinking degree from 100 to 500%. Our findings reveal the dependences of thermodynamic characteristics and selectivity of adsorption on the crosslinking degree, textural features, and liquid-phase composition in the region of extremely low adsorbent surface coverages (Henry's range). We have detected that, in the case of HPSNs, the dependence of the thermodynamic characteristics of adsorption on the liquid-phase composition is different than for classical HPLC stationary phases. Moreover, we scrutinize the impact of the molecular structure of the studied aromatic compounds on the thermodynamic characteristics and selectivity of the liquid-phase adsorption on HPSNs. Investigating liquid-phase adsorption selectivity, we demonstrate the pivotal role of π-π interactions in separating aromatic compounds on HPSNs. Eventually, we unveil that the thermodynamic characteristics of adsorption peculiarly depend on the crosslinking degree due to the profound impact of the crosslinking on the electronic density in benzene rings in HPSNs, whereas the separation throughput peaks for the polymer with a 500% crosslinking degree, attributed to its exceptionally rigid network structure, moderate swelling and micropore volume, and minimum specific surface area.

Adsorption of Organic Compounds on the Surfaces of Silicas with Grafted Acetoacet Ether Groups Saturated with Transition Metal Ions

A set of physicochemical means is used to study the adsorption properties of surfaces of silicas based on Silochrome C-120 with surface-grafted groups of acetoacetic ester saturated with transition metal ions. Gas chromatography is used to study the effect nickel, cobalt, and copper ethylacetoacetates have on the thermodynamic characteristics of adsorption (TCA) of different classes of organic substances on SiO2. Experimental data on the retention of adsorbates with different donor-acceptor properties (n-alkanes and chloroalkanes, alkenes, aromatic and oxygen-containing substances) are used to calculate differential molar heats of adsorption q¯dif,1 the change in the standard differential molar entropy ΔS¯S1,C and deposits Δq¯dif,1(spec) in the energy of dispersion and specific interactions.

Effect of Aging on Adsorption of Tetracycline by Microplastics and the Mechanisms

As new pollutants, microplastics (MPs) can adsorb antibiotics in the water environment and migrate together as carriers. However, microplastics will age continuously in the environment, and their adsorption capacity and adsorption mechanism will change accordingly. With polyethylene (PE) and polystyrene (PS) as the target MPs, which were irradiated by ultraviolet (UV-254), the changes in the physical and chemical properties of MPs before and after aging, such as the color, surface morphology, and functional groups, were compared, and their effects on the adsorption of tetracycline (TC) as well as the related mechanism were explored. The results showed that the pseudo-second-order model could better fit the adsorption process, the adsorption equilibrium was reached within 24 hours, the adsorption capacity of aged MPs for TC was significantly higher than that of original MPs, and the adsorption capacity of PS was higher than that of PE. Langmuir and Freundlich isothermal adsorption equations could both describe the adsorption isothermal test data, and the adsorption of TC on MPs was a spontaneous and endothermic physical adsorption process, whereas aging had no obvious effect on the adsorption thermodynamic characteristics of MPs. With the increase in pH value, the adsorption capacity first increased and then decreased. The maximum adsorption capacity of MPs before and after aging was reached at pH=5. UV aging increased the specific surface area of MPs, generating oxygen-containing functional groups such as -C＝O, -OH, and O＝C＝O, changing the physical and chemical properties of MPs, and thus changing the adsorption mechanism of MPs for TC. Compared with the original PE MPs, in addition to hydrophobic distribution, van der Waals forces, and electrostatic interactions, pore filling was also an important adsorption mechanism of aged PE. The main adsorption mechanisms of original PS microplastics were hydrophobic distribution, van der Waals forces, electrostatic interaction, and π-π interaction, whereas there was hydrogen bonding for aged PS.

Effects of Pore Structure of Different Rank Coals on Methane Adsorption Heat

Adsorption thermodynamic characteristics are an important part of the methane adsorption mechanism, and are useful for understanding the energy transmission mechanism of coalbed methane (CBM) migration in coal reservoirs. To study the effect of coal pore characteristics on methane adsorption heat, five different types of rank coals were used for low-pressure nitrogen, low-pressure carbon dioxide, and methane adsorption experiments. Pore structure and adsorption parameters, including maximum adsorption capacity and adsorption heat, were obtained for five coal samples, and their relationships were investigated. The results show that the low-pressure nitrogen adsorption method can measure pores within 1.7–300 nm, while the low-pressure carbon dioxide adsorption method can measure micropores within 0.38–1.14 nm. For the five coal samples, comprehensive pore structure parameters were obtained by combining the results of the low-pressure nitrogen and carbon dioxide adsorption experiments. The comprehensive results show that micropores contribute the most to the specific surface area of anthracite, lean coal, fat coal, and lignite, while mesopores contribute the most to the specific surface area of coking coal. Mesopores contribute the most to the pore volume of the five coal samples. The maximum adsorption capacity has a significant positive correlation with the specific surface area and pore volume of micropores less than 2 nm, indicating that methane is mainly adsorbed on the surface of micropores, and can also fill the micropores. The adsorption heat has a significant positive correlation with the specific surface area and pore volume of micropores within 0.38–0.76 nm, indicating that micropores in this range play a major role in determining the methane adsorption heat.

Adsorption studies of carbon dioxide and anionic dye on green adsorbent

As a consequence of the use of obsolete coal and oil and manufacturing techniques, pollution levels are rising, posing a significant threat to the environment and public health. As a result, nearby is a pressing essential to investigate actual CO2 emission and dye removal controls. Though, the achievement of this approach dependent particular on the use of low-cost adsorbent with high CO2 discrimination and high adsorption bulk. In this study, date seed active carbon (DSAC) for capturing CO2 was made using a two-step technique with KOH as the activation and varied carbonization rates. The properties of surface area on carbonization rate were investigated. The DSAC was subjected to BET, XRD, IR, and SEM examination. The researchers discovered that the micro-porous geometry has a significant impact on the adsorption efficiency of DSAC. The greatest CO2 adsorption of 3.7 mmol/g was attained under optimal circumstances of calcination temperature 700 °C, adsorption temperature 0 °C, and pressure 1 bar. Furthermore, activated carbon with a carbonization temperature of 700 °C has a high selectivity for CO2 over N2, indicating that it has a promising future in CO2 capture applications. Langmuir, Henry, Temkin, Toth, Dubbin, Harkin-Jura, Redlich Peterson, Elovich, and Josene models showed the greatest fit for any empirical sorption process that predicted heterogeneous surface characteristics of DSAC. Factors include beginning pH, catalyst loading, contact time, and temperatures have all been explored in order to determine appropriate adsorption parameters of acid yellow 99 (AY99) from aqueous systems. The isotherm of Langmuir was found to be an excellent match for the experimental data. The pseudo-second-order rate expression was utilized to characterize the dye uptake mechanism. Energy of adsorption activation was also determined to be 14 kJ/mol, suggesting chemisorption as the mode of adsorption. At varying temperatures, thermodynamic limitations such as ΔGo, ΔHo, and ΔSo were established. It was endothermic and unexpected, according to the adsorption thermodynamic characteristics. The findings of the research project are presented in form of chemical activation processes for date seeds produced adsorbents for capturing carbon dioxide and AY99 adsorption.

Experimental and electrical studies of zeolitic imidazolate framework-8 for the adsorption of different dyes

The zeolitic imidazole framework-8 (ZIF-8) was prepared in this study, which is a form of metal organic framework (MOF). ZIF-8 was characterized using powder X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), Brunauer-Emmett-Teller surface area (BET), scanning electron microscopy (SEM) and Energy dispersive X-ray spectroscopy (EDX). The material was used to eliminate Remazol Black 5 (RB5) and Brilliant Green (BG) dyes from aqueous media via chemical adsorption process. Adsorption kinetics, isotherms, dosage effect, initial concentration effect and pH were all investigated. According to the findings of the previous studies, the pseudo-second-order kinetics model and the Langmuir isotherm match our experimental adsorption data. Thermodynamic adsorption characteristics such as enthalpy, entropy, and Gibb's free energy were calculated. The sorption process was taking place spontaneously and it was endothermic in nature with high disorder of solid–liquid interface. ZIF-8′s AC and DC properties were investigated, and it revealed typical semiconductor activity.

Adsorption characteristics of modified rice straw biochar for Zn and in-situ remediation of Zn contaminated soil

Remediation of heavy metal pollution in farmland soil is very important to protect human health and ecological security, and biochar has a certain adsorption and fixation effect on soil heavy metals. In this paper, three kinds of biochar (unmodified biochar, acid modified biochar and biochar from pyrolysis of alkali modified rice straw, abbreviated as RBC, HRBC and KRBC, respectively) were prepared from rice straw, the surface morphology characteristics of RBC, HRBC and KRBC were characterized with SEM scanning, BET specific surface area measurement and porosity measurement and the adsorption characteristics of Zn in/on the three kinds of biochar and the in-situ immobilization effect for the soil Zn were investigated through the laboratory simulation. The results showed that KRBC had larger specific surface area, richer porosity, more oxygen-containing functional groups on the surface, as well as higher aromaticity and carbonization degree than that of RBC and HRBC; the adsorption kinetic characteristics of Zn in RBC, HRBC and KRBC were fitted well with the quasi second-order kinetic model and the adsorption thermodynamic characteristics of Zn in RBC, HRBC and KRBC could be described well with both the models of Langmuir and Freundlich, the maximum adsorption capacity of Zn was the order of KRBC>RBC>HRBC; KRBC had the strongest immobilization ability for Zn in soil, which was related to the strongest ability of KRBC to improve soil pH and soil organic carbon. Therefore, biochar from pyrolysis of alkali modified rice straw (KRBC) was being of the significant immobilization remediation effect on soil Zn pollution. This study can provide theoretical and technical support basis for remediation of Zn contaminated soil. • KRBC had larger specific surface area, richer porosity, more oxygen-containing functional groups on the surface, as well as higher aromaticity and carbonization degree. • KRBC has the largest adsorption capacity for Zn than that of RBC and HRBC. • KRBC had the stronger immobilization ability for Zn in soil, and stronger ability to improve soil pH and soil organic carbon.

Thermodynamics of Adsorption on Nanoporous Silicas with Grafted Methylsiloxane and Wettability

Thermodynamic characteristics of adsorption of different classes of organic compounds on nanoporous silicas with chemically grafted methylsiloxane have been determined by gas chromatography. It was shown that an increase in the concentration of grafted groups from 1.5 to 1.7 nm–2 leads to an increase in the Henry’s constants and heats of adsorption and, as a rule, to a decrease in the standard entropies of adsorption. With respect to arenes, the polarity of the samples is practically the same as that of the liquid phase OV-1. The set of gas chromatographic and static data on vapor adsorption, taking into account the values ​​of the contact angles of wetting with water and hexadecane for similar monolayers fixed on silicon wafers, allows us to conclude that the degree of lyophobization of the surface of the methylsiloxane layers is significantly higher than that of the hexadecyl layers, but inferior to that of the polyfluoroalkyl layers.

Adsorption and Chromatographic Characteristics of Graphitized Carbon Black, Modified by Adenine with Respect to a Series of Organic Compounds

Graphitized carbon black, modified by 0.95% adenine, is selected as the main object of study. The thermodynamic characteristics of adsorption of a series of organic compounds on modified carbon black is investigated by inverse gas chromatography. Analysis of the resulting data shows that the additivity of molar changes in the internal energy of adsorption is violated in the considered sample, in a homologous series of n-alkanes and other compounds. In contrast to a series of adsorbents studied earlier, there is no violation of additivity for pairs, but there is for at least three members of the homologous series, testifying to the presence of cavities or voids with different sizes in the supramolecular structure of adenine. The sizes of the molecules for which the violation of additivity is observed allow us to estimate the sizes of the cavities in the supramolecular structure of adenine as 5.5–6 to 9–9.5 A. It was also found that modification by adenine increases the polarity of the surface. The use of adenine at Viedma ripening conditions provides the modified adsorbent the chiral recognition capability.

Adsorption of caffeic acid on chitosan powder

Adsorption of caffeic acid (CA) on chitosan (CH) powder from aqueous solution has been investigated to obtain insoluble CA–CH complex powders having different amount of CA. The pseudo-second kinetic model and the Langmuir, Freundlich and Dubinin–Radushkevich adsorption models were used to describe the kinetic and equilibrium adsorption of CA on CH. With the increase of adsorption temperature, the rate of adsorption increased while the amount of adsorbed CA decreased. The Langmuir adsorption model predicted that adsorption of CA takes place on the ionized amino groups of CH. However, with the increase of adsorption temperature the ion-exchange between carboxylic groups of CA and amino groups of CH became moderately difficult. The thermodynamic characteristics of adsorption have been evaluated. CA–CH complex formation was confirmed by FT-IR spectroscopy. With increasing amount of adsorbed CA the CA–CH powder was becoming more hydrophobic. 2,2′-Azinobis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS) assay confirmed that CA retained the antioxidant activity when immobilized on chitosan power.

Получение и исследование адсорбентов на основе ультрадисперсного диоксида кремния и β-циклодекстрина

Получены поверхностно-слойные адсорбенты путем нанесения наночастиц диоксида кремнияи наночастиц диоксида кремния, модифицированных незамещенным β-циклодекстрином, на инертный кремнеземный носитель. Определены геометрические параметры полученных адсорбентов. Методом газо-адсорбционной хроматографии изучены адсорбционные свойства полученных образцов поотношению к парам органических соединений различной природы, в том числе энантиомерам, и рассчитаны термодинамические характеристики адсорбции для исследованных соединений. Предложенвариант строения наночастиц, модифицированных циклодекстрином

Adsorption and Chromatographic Separation of Thiophene Derivatives on Graphitized Thermal Carbon Black

The thermodynamic characteristics of adsorption (TCA) of thiophene and its derivatives are determined under the conditions of equilibrium gas adsorption chromatography (GAC) on columns with graphitized thermal carbon black (GTCB) of Carbopack C HT grade. It is shown that the TCA values ​​ depend largely on the number and nature of the substituents in the main structural fragment. It is found that the surface of the GTCB is characterized by low structural selectivity for positional isomers in the series of thiophene derivatives. The effect of polar retention of an adsorbate on graphite from the gas phase due to additional intermolecular specific interactions of polar groups of the adsorbate with an easily polarizable surface of the base face of graphite is established and studied. Conclusions are reached on the applicability of the two-dimensional ideal gas model for describing the mobility of strongly polar molecules of thiophene derivatives on surfaces of graphite, and on the considerable limitations of this model when applied to the adsorption of thiophene molecules, along with its methyl and halogen derivatives.

The Influence of Water–Acetonitrile Solvent Composition on Thermodynamic Characteristics of Adsorption of Aromatic Heterocycles on Octadecyl-Bonded Silica Gels

The thermodynamics of adsorption of some substituted 1,3,4-oxadiazoles and 1,2,4,5-tetrazines from water–acetonitrile solutions with acetonitrile volume fraction varying within a range of 0.35–0.90 on chemically modified Luna C18 and Discovery C18 silica gels has been studied within a temperature range of 313.15–333.15 K. The thermodynamic characteristics of the adsorption of these compounds on Luna C18 and Discovery C18 silica gels have been determined as depending on solution composition. In the case of Discovery C18, the character of the dependences of different thermodynamic characteristics of the adsorption on liquid phase composition is similar to that of the corresponding dependences previously observed for modified Ascentis®Phenyl silica gel. A similarity has also been found for the dependences of the thermodynamic characteristics of the adsorption on Luna C18 and modified Diasfer-110-C18 silica gel studied previously. The mechanism of the liquid-phase adsorption of 1,3,4-oxadiazoles and 1,2,4,5-tetrazines on Luna C18 is changed within a range of acetonitrile volume fractions of 0.60–0.75, as it is in the case of Diasfer-110-C18. At acetonitrile volume fractions of higher than 0.75, the studied heterocycles are adsorbed on Luna C18 surface dynamically modified with acetonitrile without a direct interaction with the grafted layer of the chemically modified silica gel. At the same time, the mechanism of their adsorption on Discovery C18 remains unchanged while acetonitrile concentration is increased in the liquid phase.

Adsorption Equilibria in the Nanopores of Silicas with Grafted Bromopropyl Groups

The dependence of the thermodynamic characteristics of adsorption of various classes of organic compounds on the chemical nature of the silica surface modified with 3-bromopropyltrichlorosilane to form a monolayer coating (Br-2 sample), a grafted polymer type layer (Br-5 sample), and additionally silanized layer (Br-5* sample) was studied by gas chromatography. The dispersion interactions on bromosilicas were more active than on the starting support or the NH2 sample with a grafted aminopropyl layer of the polymer type. The role of specific interactions generally decreases in the series Br-2 > Br-5 > Br-5* > NH2. An analysis of the obtained data indicates that the retention mechanism on silicas with bromopropyl groups is determined by the penetration of adsorbed molecules into the grafted layer. In contrast, the aminopropyl polymer layer has a more rigid structure with limited conformational mobility of the grafted aminopropyl groups, the adsorption retention mechanism dominating in this case.

Adsorption thermodynamic characteristics of Chlorella vulgaris with organic polymer adsorbent cationic starch: Effect of temperature on adsorption capacity and rate

Aiming at optimizing the adsorption process of Chlorella vulgaris and cationic starch, the adsorption thermodynamic characteristics were evaluated. Different from inorganic calcium salt adsorbent, the adsorption nature of organic polymer cationic starch is exothermic (ΔH° < 0) and spontaneous (ΔG° < 0). Besides, the adsorption capacity and rate can be well described by Langmiur isotherm and pseudo second kinetic models. As results of exothermic nature and great driving force of lower temperature, the adsorption capacity and rate declined with the rising temperature. The maximal values of them were obtained at 278.15 K, which were 9148.14 mg microalgae (g cationic starch)−1 and 8.74 × 10−6 mg g−1 min−1. Additionally, with insufficient adsorbent, the highest adsorption efficiency (96.37%) was achieved at 278.15 K for stirring 150 min. For 288.15, 298.15, 308.15 and 318.15 K, the adsorption efficiency decreased to 93.77%, 86.75%, 83.32% and 81.57% and the time consumed were at least 40 min longer.

Factors influencing the gas adsorption thermodynamic characteristics of low-rank coal

Low-temperature nitrogen and isothermal adsorption experiments were conducted on six typical low-rank coal samples from the Fukang mining area, Xinjiang, PR China. Using different temperatures, the effects of the coal’s pore structure on gas adsorption and other thermodynamic characteristics were analyzed. The Clausius–Clapeyron equation was used to calculate the isosteric heat of adsorption, and the standard adsorption equilibrium constant was derived to calculate the adsorption free-energy and entropy. The relationships between pore structure characteristics and gas adsorption thermodynamic parameters were investigated. The results showed that the adsorption free-energy and enthalpy of the coal samples decreased with an increase in temperature. Adsorption heat and adsorption entropy were affected by an increase in pore volume and specific surface area. The specific surface area and transition pore volume exhibited quadratic relationships with the free-energy and total pore volume, whereas the mesopore volume exhibited a positive linear relationship with the adsorption free-energy. No prominent relationships among average pore diameter, adsorption heat, adsorption free-energy, and adsorption entropy were observed. No correlation was identified between micropore volume and adsorption free-energy. Fractal dimension was linearly and positively related to the adsorption heat and entropy but had no effect on the free-energy.

Thermodynamic characteristics of adsorption of organic compounds on the surface of a polystyrene sorbent Dowex V503

Thermodynamic characteristics of adsorption of organic compounds on the surface of a polystyrene sorbent Dowex V503

Thermodynamic characteristics of the adsorption of organic molecules on modified МCM-41 adsorbents

The adsorption of a number of organic molecules on samples of МCM-41 adsorbent modified with dichloromethylphenylsilane and subsequently treated with sulfuric acid (MDCS) and N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride (MNM) is studied. Specific retention volumes equal to the Henry constant are determined by means of inverse gas chromatography at infinite dilution. The thermodynamic characteristics of adsorption, the dispersive and specific components of the Helmholtz energy of adsorption, and the increment of the methyl group to the heat of adsorption are calculated. It is shown that the grafting of aminosilane and phenylsilane groups enhances the forces of dispersion and reduces specific interactions. A greater drop in polarity is observed for MDCS than for MNM, due to the stronger polarity of amoinosilane; the enthalpy factor makes the main contribution to the adsorption of organic compounds on the investigated adsorbents. It is found that the MNM sample is capable of the irreversible adsorption of alcohols.

Adsorption of organic molecules on the highly ordered MCM-41 sorbent modified by different amounts of melamine

Thermodynamic characteristics of adsorption of organic molecules on the ordered organosilylated composite MCM-41 with grafted trimethylsilyl groups (MMet) and modified by melamine deposited on the surface were studied by inverse gas chromatography. Mole changes in the internal energy and entropy of adsorption, the dispersion and specific components of the value proportional to the Helmholtz absorption energy, and the contribution of the methyl group to the heat of adsorption were calculated from the specific retention volumes. The change in the retention volumes was established to be determined by the dispersion component of the Helmholtz energy of adsorption, whereas the energy of specific interactions remains almost unchanged. After the adsorbent surface was coated by the second and third melamine layers, the changes in −ΔU and −ΔS for adsorption of the members of the homologous series of n-alkanes are so small that lie within admissible measurement inaccuracies. This phenomenon can be explained by the regularities of alkane adsorption in slit-like pores of the supramolecular structure of melamine.